Controlling Aquarium Air Pump Output

[Clifford Heath]

On 31/03/16 12:42, ~misfit~ wrote:

Once upon a time on usenet Clifford Heath wrote:
If you used a fixed mains transformer with, say, a 30-0-30V winding,
you could wire the 60v in antiphase from the active to step down to
180v from 240. That might be the cheapest way to reduce output, even
though it's not easily adjustable.
Interesting. I hadn't even considered that such a thing is possible. LOL,
n00b alert!!!

The nice thing is that the resultant current rating is the rating
of the secondary. So if it was a 60VA transformer, you can get
one amp at 180v, or 180VA from it. A small transformer scavenged
from a discarded audio amp would do just fine - they often have
main secondary windings between +-20 and +-30 (bigger for more
powerful amplifiers, of course). As I said, the cheapest solution,
though not easily adjustable (unless you have extra windings or
taps).

Neither type is guaranteed to produce balanced AC - you might get
more +ve than -ve or vice versa. That's bad for an iron-cored
inductor because it can easily cause core saturation and high
currents that will melt your windings.
This model (assuming that mine is the same as the one Clive reviewed - and
I'll check that as soon as I get it) has a clever diode bridge arrangement
and "it doesn't go unstable" especially at lower settings and keeps the
output symetrical.

Right - it's an SCR circuit in a bridge rectifier, instead of a
triac circuit that has, effectively, separate +ve and -ve triggers
(actually inside one diac, but not guaranteed symmetrical).

He says transformers and motors don't like non-symetrical
AC and get hot.
He says "the advantage of this is that if you're controlling inductive loads
like transformers or motors you're not going to go into a dodgy situation
where you end up with a slightly non-symetrical wave form. Most standard
incuction motors and transformers hate if the sine wave is being half-wave
triggered or not quite symetrical it creates a bit of heat in the
transformer...."

Which confirms what I said about saturation from a DC component.

I just don't know if the sudden on/off of the phase control will
cause dramas. Trailing edge definitely will. Leading edge will
cause audio hum and RFI problems if it's not well damped, but
might work ok. Check your stereo, radio and TV with the pump on
and off, at different power settings.

I thought this might be easier as I have some 7.5W, 0 - 5l/min air pumps
that are adjustable. They have a pot (variable resistor?) and a small PCB.
The PCB has two resistors, one a 1/4 watt and a big one (22 long x 7mm
diameter), a small diode, two 0.1uF capacitors, a trimpot and a Z0102
transistor. I'd use one of these pumps but they're noisy compared with the
big 30l/min pump.

Almost certainly a simple DC rectifier (half wave) followed by
a voltage or current regulator - wasteful of energy and will
only work with a universal or DC motor - not your pump which
absolutely needs AC.

At this point, I'm at the limit of my knowledge. I would trust
Phil A's opinion here. Phil? Tell me what I got wrong please...
I can't find Phils answer in this thread.

I can't either . But I think we have the answers you need.

You might be able to help me. I want an oil-free air compressor
(so probably diaphragm) of about 200W and capable of 1Bar output,
perhaps 20litres/minute. Highly resistant to corrosion, because
it will operate in direct proximity to sea water, which means
probably stainless steel. Low voltage, either 12-24V preferably.
Any thoughts?

Clifford Heath.

 

[~misfit~]

Once upon a time on usenet Clifford Heath wrote:

On 30/03/16 11:42, ~misfit~ wrote:
Once upon a time on usenet Clifford Heath wrote:
On 29/03/16 16:53, ~misfit~ wrote:
Once upon a time on usenet Clifford Heath wrote:
Does the armature have any centering spring around which it
oscillates? If so, then Jason is right and it is resonant at
somewhere near the mains frequency. Changing the frequency will
reduce the efficiency.
Please see my reply to Jason. No spring as such, the centering
after pulses is due to 'rubber' diaphragm suspension. Well I guess
they *are* actually acting as springs in this device but I doubt
they'd have a similar sort of resonant frequency as say a steel
spring.

Yup, not much resonance involved then. The "push" energy goes into
one cylinder and the "pull" energy the other; very little into any
energy storage (spring and mass).

Yes, but the resonance is not very high-Q. The goal is to convert
the energy into compressed air, after all. Changing the frequency
if the Q is low will just reduce efficiency, but not
catastrophically.

That's a bit beyond me... Or not if by 'Q' you mean resonant
frequancy of the armature assembly?

Q is a ratio of the amount of energy circulating (stored in the
moving spring & mass in this case) divided by the amount of energy
extracted in each cycle. So if it's putting out 25 watts at 50
cycles per second, each cycle puts out half a joule. If the
spring/mass oscillation stores (say) 10 joules, the Q is 20
(=10/0.5). But your pump sounds like it has a Q of less than 1. Not
resonant.
Probably operates exactly at mains frequency, and will probably
work at a lower frequency, producing less air volume. Just don't
feed it DC or the magnets will saturate and probably melt wires.
You really need an AC current source, enough to produce the correct
stroke at your desired power output.

Thanks for the reply and explination.
So ideally a variac then - which I'd assumed and which I don't have.

No, ideally, frequency reduction, at the right current.

Ok. I can see how that would be best. However from what little I know that's
a complicated procedure requiring (relatively) expensive equipment - and
that's just to output square wave.

A variac will work, but will reduce efficiency, because it works by
reducing the stroke length. A certain volume of air in each stroke is
wasted opening and closing valves, and that doesn't become less as the
stroke length reduces, so you lose some efficiency. Probably not
enough to matter much though.

Yep. There's 'fixed overhead', a small amount of air needed for valve
opening/closure. It's not a lot as a fraction of volume at mains voltage but
I see that it would become a larger fraction as the voltage dropped.

If you used a fixed mains transformer with, say, a 30-0-30V winding,
you could wire the 60v in antiphase from the active to step down to
180v from 240. That might be the cheapest way to reduce output, even
though it's not easily adjustable.

Interesting. I hadn't even considered that such a thing is possible. LOL,
n00b alert!!!

Do you know if the device that I've ordered will hurt my pump?

It might. I'm not an expert on dimmers, but most don't like inductive
loads. There are leading-edge and trailing-edge dimmers. The trailing
edge dimmer turns off part-way through the half-cycle. With an
inductive load, that will produce massive voltage spikes that will
blow up the dimmer and possibly other things in the vicinity.
The leading-edge dimmers turn on part-way through the half-cycle,
which won't produce a voltage spike.

Going by the youtube video that Clive did these are leading edge 'dimmers'
(Clive calls them 'power regulators' and says they seem to be industrial
control equipment.)

Neither type is guaranteed to produce balanced AC - you might get
more +ve than -ve or vice versa. That's bad for an iron-cored
inductor because it can easily cause core saturation and high
currents that will melt your windings.

This model (assuming that mine is the same as the one Clive reviewed - and
I'll check that as soon as I get it) has a clever diode bridge arrangement
and "it doesn't go unstable" especially at lower settings and keeps the
output symetrical. He says transformers and motors don't like non-symetrical
AC and get hot.

He says "the advantage of this is that if you're controlling inductive loads
like transformers or motors you're not going to go into a dodgy situation
where you end up with a slightly non-symetrical wave form. Most standard
incuction motors and transformers hate if the sine wave is being half-wave
triggered or not quite symetrical it creates a bit of heat in the
transformer...."

This is why, after watching the video
https://www.youtube.com/watch?v=_4PwYm_7HKg I thought that it might be good
for controlling my air pump. (It's also why I included a link to the video
in my first post.)

I asked him in the comments if it would do the job I want it for (after I'd
started tis thread) and he said I'd be better to restrict the air output
(but I don't think he knows about rubber diaphram air pumps, the only air
pump he's reviewed has a close-tolerance ceramic-coated piston.) He also
said that the air pump "wouldn't be a high enough load for a dimmer" but he
might be thinking it's a little 5W thing.

I thought this might be easier as I have some 7.5W, 0 - 5l/min air pumps
that are adjustable. They have a pot (variable resistor?) and a small PCB.
The PCB has two resistors, one a 1/4 watt and a big one (22 long x 7mm
diameter), a small diode, two 0.1uF capacitors, a trimpot and a Z0102
transistor. I'd use one of these pumps but they're noisy compared with the
big 30l/min pump.

At this point, I'm at the limit of my knowledge. I would trust
Phil A's opinion here. Phil? Tell me what I got wrong please...

I can't find Phils answer in this thread.

I have smaller airpumps. However most domestic models work by having
the permanent magnet on the end of an arm (which is usually pivoting
on an energy-wasting rubber bush)

Wastage depends on the quality of the rubber. Good silicon rubber
wouldn't waste much - but this type is resonant (the rubber is the
spring).

All I know is that there's quite a bit of damping of the arm movement cause
by the rubber pivot bush and that 'arm' type reciprocating air pumps tend to
give (usually quite a bit) less than 1litre/min per watt whereas the
double-ended type start at over a litre/min per watt and go up to more than
twice that. They're also a lot more expensive but are much more reliable.

Cheers,
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[~misfit~]

Once upon a time on usenet Computer Nerd Kev wrote:

Once upon a time on usenet Jasen Betts wrote:
On 2016-03-27, ~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

probably reducing the input voltage will do what you want. so a
series dropper of some sort, or a step-down transformer. you could
try a fan speed controller, or to test this out a 100w lamp.

I don't have any of the above.

Actually I may be able to dig out a 60 or 75 watt incandescant light
bulb from the back of the cupboard - I only use LED lamps in the
house now, swapped out the CFLs a while back. What would the effect
of wiring an incandescant bulb in parallel to the pump be? I
mentioned I'm new to electrical theory yes?

That'll drop the input voltage to the pump. You look at the light
bulb as a resistor and use the voltage developed across it (Ohms law)
to subtract from the voltage otherwise applied to the pump. But for
heaven's sake wire it in _series_, not parallel.

Yep, my bad - I meant series. Parallel wouldn't do anything.

The controller you've bought is also a form of voltage control, but
as it works by switching the input waveform rather than droping the
voltage over a resistance, other considerations (inductive spikes,
completion of compressor stroke) arise.

Yep, hence my questions here.

As has been noted, frequency control rather than voltage control may
be the better option.

Indeed.

Does anyone know of a cheap, purchasable device
that would achieve this?

I would like to know the answer to this.

Thanks for the reply.
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[Computer Nerd Kev]

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

Once upon a time on usenet Clifford Heath wrote:
On 30/03/16 11:42, ~misfit~ wrote:

Thanks for the reply and explination.
So ideally a variac then - which I'd assumed and which I don't have.

No, ideally, frequency reduction, at the right current.

Ok. I can see how that would be best. However from what little I know that's
a complicated procedure requiring (relatively) expensive equipment - and
that's just to output square wave.

In theory it wouldn't be any more complicated electronically than the
controller you've bought. It would just require detecting the zero-crossing
of the AC waveform, then using a logic circuit or microcontroller to turn
off the output for every cycle after a certain interval. Eg. every 2nd, 3rd,
4th... cycle.

The zero-crossing detection and SCR switching circuit are (hopefully) common
with your controller. The difference that will complicate things is that I'd
guess many of your controller's functions are performed by one of the various
Phase Control ICs available, whereas with a frequency controller the main
functions may have to be designed and built separately, unless a suitable IC
is available.

The Audio amp and power transformer method I would consider to be more of a
test set-up than a permanent solution. If nothing else, it won't be power
efficient. However a PC could be used to produce the sine wave, in order to
save building a custom oscillator to feed the amp.

--
__ __
#_ < |\| |< _#

 

[Jasen Betts]

On 2016-03-31, ~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

As has been noted, frequency control rather than voltage control may
be the better option.

Indeed.

Does anyone know of a cheap, purchasable device
that would achieve this?

I would like to know the answer to this.

A variable frequency drive
$80 delivered on aliexpress for one with a case,
$55 for a used one - needs a case
both are marked 220V so may not be reliable on Aussie 240V

much cheaper to buy a new pump.

http://www.aliexpress.com/item/2015-Hot-Sale-New-3W-Super-Silent-Adjustable-Aquarium-Air-Pump-Fish-Tank-Oxygen-Air-Pump/32580955417.html?spm=2114.01010208.3.19.7YaLLZ&ws_ab_test=searchweb201556_1,searchweb201602_4_10036_10035_301_10034_507_10032_10020_10017_10005_10006_10021_10022_401_10018_10019,searchweb201603_9&btsid=08c5dc1d-e491-4371-b006-d9db91461c28

just needs a new plug fitted.

--
\_(ツ)_

 

[Jasen Betts]

On 2016-03-30, Clifford Heath <no.spam@please.net> wrote:

On 31/03/16 12:42, ~misfit~ wrote:

This model (assuming that mine is the same as the one Clive reviewed - and
I'll check that as soon as I get it) has a clever diode bridge arrangement
and "it doesn't go unstable" especially at lower settings and keeps the
output symetrical.

Right - it's an SCR circuit in a bridge rectifier, instead of a
triac circuit that has, effectively, separate +ve and -ve triggers
(actually inside one diac, but not guaranteed symmetrical).

Nah, it's not. it's a triac circuit, the bridge rectifier (used for
current steering, not rectification) only passes the timing currents.

--
\_(ツ)_

 

[Jasen Betts]

On 2016-03-31, Computer Nerd Kev <not@telling.you.invalid> wrote:

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Clifford Heath wrote:
On 30/03/16 11:42, ~misfit~ wrote:

Thanks for the reply and explination.
So ideally a variac then - which I'd assumed and which I don't have.

No, ideally, frequency reduction, at the right current.

Ok. I can see how that would be best. However from what little I know that's
a complicated procedure requiring (relatively) expensive equipment - and
that's just to output square wave.

In theory it wouldn't be any more complicated electronically than the
controller you've bought. It would just require detecting the zero-crossing
of the AC waveform, then using a logic circuit or microcontroller to turn
off the output for every cycle after a certain interval. Eg. every 2nd, 3rd,
4th... cycle.

a ring generator (telephone ring voltage generator) might be just the thing
might not be cheap though

or perhaps a curcuit that passes every third half-cycle

_ _ _ _ _ _
/ \ / \ / \ / \ / \ / \
_/ \_/ \_/ \_/ \_/ \_/ \

_ _
_/ \______ ______/ \_____ ______
\_/ \_/

_ _ _ _
___ / \___/ \ ___ / \___/ \
_/ \_/ \_/ \_/ \


--
\_(ツ)_

 

[Xeno]

On 1/04/2016 3:38 PM, Jasen Betts wrote:

On 2016-03-31, ~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

As has been noted, frequency control rather than voltage control may
be the better option.

Indeed.

Does anyone know of a cheap, purchasable device
that would achieve this?

I would like to know the answer to this.

A variable frequency drive
$80 delivered on aliexpress for one with a case,
$55 for a used one - needs a case
both are marked 220V so may not be reliable on Aussie 240V

You might need to update your thinking on this score.

http://tinyurl.com/dybf5rv

In 2000, Australia converted to 230 V as the nominal standard with a
tolerance of +10%/−6%.,[10] this superseding the old 240 V standard,
AS2926-1987.[11] As in the UK, 240 V is within the allowable limits and
"240 volt" is a synonym for mains in Australian and British English.

much cheaper to buy a new pump.

http://www.aliexpress.com/item/2015-Hot-Sale-New-3W-Super-Silent-Adjustable-Aquarium-Air-Pump-Fish-Tank-Oxygen-Air-Pump/32580955417.html?spm=2114.01010208.3.19.7YaLLZ&ws_ab_test=searchweb201556_1,searchweb201602_4_10036_10035_301_10034_507_10032_10020_10017_10005_10006_10021_10022_401_10018_10019,searchweb201603_9&btsid=08c5dc1d-e491-4371-b006-d9db91461c28

just needs a new plug fitted.

--

Xeno

 

[Computer Nerd Kev]

Jasen Betts <jasen@xnet.co.nz> wrote:

On 2016-03-31, Computer Nerd Kev <not@telling.you.invalid> wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Clifford Heath wrote:
On 30/03/16 11:42, ~misfit~ wrote:

Thanks for the reply and explination.
So ideally a variac then - which I'd assumed and which I don't have.

No, ideally, frequency reduction, at the right current.

Ok. I can see how that would be best. However from what little I know that's
a complicated procedure requiring (relatively) expensive equipment - and
that's just to output square wave.

In theory it wouldn't be any more complicated electronically than the
controller you've bought. It would just require detecting the zero-crossing
of the AC waveform, then using a logic circuit or microcontroller to turn
off the output for every cycle after a certain interval. Eg. every 2nd, 3rd,
4th... cycle.


a ring generator (telephone ring voltage generator) might be just the thing
might not be cheap though

One problem is that I doubt those devices would be designed to switch at
the zero-crossing of the AC waveform, and doing otherwise is likely to
cause inductive spikes and their associated problems.

or perhaps a curcuit that passes every third half-cycle

_ _ _ _ _ _
/ \ / \ / \ / \ / \ / \
_/ \_/ \_/ \_/ \_/ \_/ \

_ _
_/ \______ ______/ \_____ ______
\_/ \_/

_ _ _ _
___ / \___/ \ ___ / \___/ \
_/ \_/ \_/ \_/ \

I'm having trouble imagining how cutting half-cycles would be any
easier to implement. Nice ASCII waveforms though.

--
__ __
#_ < |\| |< _#

 

[Jasen Betts]

On 2016-04-01, Computer Nerd Kev <not@telling.you.invalid> wrote:

Jasen Betts <jasen@xnet.co.nz> wrote:
On 2016-03-31, Computer Nerd Kev <not@telling.you.invalid> wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Clifford Heath wrote:
On 30/03/16 11:42, ~misfit~ wrote:

Thanks for the reply and explination.
So ideally a variac then - which I'd assumed and which I don't have.

No, ideally, frequency reduction, at the right current.

Ok. I can see how that would be best. However from what little I know that's
a complicated procedure requiring (relatively) expensive equipment - and
that's just to output square wave.

In theory it wouldn't be any more complicated electronically than the
controller you've bought. It would just require detecting the zero-crossing
of the AC waveform, then using a logic circuit or microcontroller to turn
off the output for every cycle after a certain interval. Eg. every 2nd, 3rd,
4th... cycle.


a ring generator (telephone ring voltage generator) might be just the thing
might not be cheap though

One problem is that I doubt those devices would be designed to switch at
the zero-crossing of the AC waveform, and doing otherwise is likely to
cause inductive spikes and their associated problems.

They generate about 90V AC at 16.67Hz seems about right to run a pump at
1/3 power.

or perhaps a curcuit that passes every third half-cycle

_ _ _ _ _ _
/ \ / \ / \ / \ / \ / \
_/ \_/ \_/ \_/ \_/ \_/ \

_ _
_/ \______ ______/ \_____ ______
\_/ \_/

_ _ _ _
___ / \___/ \ ___ / \___/ \
_/ \_/ \_/ \_/ \

I'm having trouble imagining how cutting half-cycles would be any
easier to implement. Nice ASCII waveforms though.

A triac with the right drive, not sure what the crcuit to do that is
though.


--
\_(ツ)_

 

[Computer Nerd Kev]

Jasen Betts <jasen@xnet.co.nz> wrote:

On 2016-04-01, Computer Nerd Kev <not@telling.you.invalid> wrote:
Jasen Betts <jasen@xnet.co.nz> wrote:
On 2016-03-31, Computer Nerd Kev <not@telling.you.invalid> wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Clifford Heath wrote:
On 30/03/16 11:42, ~misfit~ wrote:

Thanks for the reply and explination.
So ideally a variac then - which I'd assumed and which I don't have.

No, ideally, frequency reduction, at the right current.

Ok. I can see how that would be best. However from what little I know that's
a complicated procedure requiring (relatively) expensive equipment - and
that's just to output square wave.

In theory it wouldn't be any more complicated electronically than the
controller you've bought. It would just require detecting the zero-crossing
of the AC waveform, then using a logic circuit or microcontroller to turn
off the output for every cycle after a certain interval. Eg. every 2nd, 3rd,
4th... cycle.


a ring generator (telephone ring voltage generator) might be just the thing
might not be cheap though

One problem is that I doubt those devices would be designed to switch at
the zero-crossing of the AC waveform, and doing otherwise is likely to
cause inductive spikes and their associated problems.

They generate about 90V AC at 16.67Hz seems about right to run a pump at
1/3 power.

Oh I see, I was thinking on the wrong track. Yeah, if it can survive
the unusual load conditions it might just work. No doubt somebody
sold one on Ebay once.

or perhaps a curcuit that passes every third half-cycle

_ _ _ _ _ _
/ \ / \ / \ / \ / \ / \
_/ \_/ \_/ \_/ \_/ \_/ \

_ _
_/ \______ ______/ \_____ ______
\_/ \_/

_ _ _ _
___ / \___/ \ ___ / \___/ \
_/ \_/ \_/ \_/ \

I'm having trouble imagining how cutting half-cycles would be any
easier to implement. Nice ASCII waveforms though.

A triac with the right drive, not sure what the crcuit to do that is
though.

Yes, though a Triac could also be used to cut a whole cycle:

_ _ _
__/ \ ______/ \ ______/ \ ____
\_/ \_/ \_/

A basic implementation for fixed 1/2 division of the supply
frequency may be as follows:

|ZERO CROSSING| |FLIP| | SCR |
| |---|FLOP|---| |
| DETECTOR | | /2 | |(TRIAC)|

The Flip Flop divides the signal from the Zero Crossing
Detector (which produces a pulse on every 0V transition
of the mains waveform) by two. This signal activates
the SCR (which powers the compressor) for one of every
two mains cycles.

Mains Waveform to Zero-Crossing Detector:
_ _ _ _ _ _
*/ \* X/ \X */ \* X/ \X */ \* X/ \X
_/ \_/ \_/ \_/ \_/ \_/ \
"*" & "X" Indicates pulse from Zero Crossing Detector
"*" = SCR Triggered
"X" = SCR Disabled

SCR Output Waveform to Compressor:

_ _ _
__/ \ ______/ \ ______/ \ ____
\_/ \_/ \_/

A variable division of the Zero-Crossing signal would
be desireable to allow further reduction of the supply
frequency if required. A counter which disables the SCR
for just one cycle after a certain count of zero-crossings
may be used instead of the divide-by-two Flip-Flop for
frequency reduction less severe than 1/2 division.

Oops, out of time. I'll have to hope all that made sense,
no time for a final check!

--
__ __
#_ < |\| |< _#

 

[~misfit~]

Once upon a time on usenet Clifford Heath wrote:

On 31/03/16 12:42, ~misfit~ wrote:
Once upon a time on usenet Clifford Heath wrote:
If you used a fixed mains transformer with, say, a 30-0-30V winding,
you could wire the 60v in antiphase from the active to step down to
180v from 240. That might be the cheapest way to reduce output, even
though it's not easily adjustable.
Interesting. I hadn't even considered that such a thing is possible.
LOL, n00b alert!!!

The nice thing is that the resultant current rating is the rating
of the secondary. So if it was a 60VA transformer, you can get
one amp at 180v, or 180VA from it. A small transformer scavenged
from a discarded audio amp would do just fine - they often have
main secondary windings between +-20 and +-30 (bigger for more
powerful amplifiers, of course). As I said, the cheapest solution,
though not easily adjustable (unless you have extra windings or
taps).

Yep, I can see how it would work now. However while possibly being cheap
(I've got a few amps kicking around) it's not exactly elegant.

Neither type is guaranteed to produce balanced AC - you might get
more +ve than -ve or vice versa. That's bad for an iron-cored
inductor because it can easily cause core saturation and high
currents that will melt your windings.
This model (assuming that mine is the same as the one Clive reviewed
- and I'll check that as soon as I get it) has a clever diode bridge
arrangement and "it doesn't go unstable" especially at lower
settings and keeps the output symetrical.

Right - it's an SCR circuit in a bridge rectifier, instead of a
triac circuit that has, effectively, separate +ve and -ve triggers
(actually inside one diac, but not guaranteed symmetrical).

As Jasen says it's a diac-triggered triac system. The bridge rectifier is
used instead of discrete diodes to discharge any partial charge in the
triggering capacitor when the phase changes to make it operate more smoothly
at lower settings rather than have charge build up from seperate peaks and
result in an unstable, non-symetrical waveform output.

Or something - I'm trying to learn as I go.

I got the unit I ordered a few days ago and opened it up to check it wasn't
going to let any smoke out when connected. It's indentical to the one Clive
strips down (except mine doesn't have the un-soldermasked power tracks and
legs of the triac left on to beef up power connections). However the
labeling is wrong going by Clives schematic. What Clive calls input is
labeled output, both on mine and his units so I asked him but no reply to
that one yet. Worrying as I haven't studied further to see if they can be
swapped.

Then reading down the comments I saw this;
"I have the same device, but it came with a 100 ohm in the snubber. If you
want to do inductive loads, best swap in & output, so the fuse is on the
output. Otherwise a fuse break will almost definitely damage the triac.
Also, mod it like this for better inductive control
http://flowcon.us/td/neondimmer/ ?"

So I guess the fact that they're labeled differently to Clives schematic
doesn't matter - or (whisper it) Clive's wrong.

He says transformers and motors don't like non-symetrical
AC and get hot.
He says "the advantage of this is that if you're controlling
inductive loads like transformers or motors you're not going to go
into a dodgy situation where you end up with a slightly
non-symetrical wave form. Most standard incuction motors and
transformers hate if the sine wave is being half-wave triggered or
not quite symetrical it creates a bit of heat in the transformer...."

Which confirms what I said about saturation from a DC component.

I just don't know if the sudden on/off of the phase control will
cause dramas. Trailing edge definitely will. Leading edge will
cause audio hum and RFI problems if it's not well damped, but
might work ok. Check your stereo, radio and TV with the pump on
and off, at different power settings.

I still haven't applied mains AC to my device yet. Life can be demanding
like that. However I don't use radios and my TV is digital (and only used
for a maximum of 20minutes day for news headlines and weather). I could
always add a large choke, I have a bunch of bits salvaged from old PC PSUs.

I thought this might be easier as I have some 7.5W, 0 - 5l/min air
pumps that are adjustable. They have a pot (variable resistor?) and
a small PCB. The PCB has two resistors, one a 1/4 watt and a big
one (22 long x 7mm diameter), a small diode, two 0.1uF capacitors, a
trimpot and a Z0102 transistor. I'd use one of these pumps but
they're noisy compared with the big 30l/min pump.

Almost certainly a simple DC rectifier (half wave) followed by
a voltage or current regulator - wasteful of energy and will
only work with a universal or DC motor - not your pump which
absolutely needs AC.

It can't be because that airpump is also an AC 'vibrator' pump (and indeed
there is an indentical model without the output control) They're called
Optima (and Maxima) and were sold by Rolf C Hagen aquarium products. However
they're 'arm' type as opposed to the better, quieter but more expensive
'armature suspended between two diapragms' type.

It was seeing this rather simple circuitry, the only difference between the
two models, that got me going down this path originally.

At this point, I'm at the limit of my knowledge. I would trust
Phil A's opinion here. Phil? Tell me what I got wrong please...
I can't find Phils answer in this thread.

I can't either . But I think we have the answers you need.

You might be able to help me. I want an oil-free air compressor
(so probably diaphragm) of about 200W and capable of 1Bar output,
perhaps 20litres/minute. Highly resistant to corrosion, because
it will operate in direct proximity to sea water, which means
probably stainless steel. Low voltage, either 12-24V preferably.
Any thoughts?

Sorry nothing comes to mind and I've pondered on this for a few days now.
The only thing I could think of was perhaps a water pump and venturi set up
going into a separating tank to get your pressurised air? Not very elegant
but then again not my field.

Cheers,
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[~misfit~]

Once upon a time on usenet Computer Nerd Kev wrote:

Jasen Betts <jasen@xnet.co.nz> wrote:
On 2016-04-01, Computer Nerd Kev <not@telling.you.invalid> wrote:
Jasen Betts <jasen@xnet.co.nz> wrote:
On 2016-03-31, Computer Nerd Kev <not@telling.you.invalid> wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Clifford Heath wrote:
On 30/03/16 11:42, ~misfit~ wrote:

Thanks for the reply and explination.
So ideally a variac then - which I'd assumed and which I don't
have.

No, ideally, frequency reduction, at the right current.

Ok. I can see how that would be best. However from what little I
know that's a complicated procedure requiring (relatively)
expensive equipment - and that's just to output square wave.

In theory it wouldn't be any more complicated electronically than
the controller you've bought. It would just require detecting the
zero-crossing of the AC waveform, then using a logic circuit or
microcontroller to turn off the output for every cycle after a
certain interval. Eg. every 2nd, 3rd, 4th... cycle.


a ring generator (telephone ring voltage generator) might be just
the thing might not be cheap though

One problem is that I doubt those devices would be designed to
switch at the zero-crossing of the AC waveform, and doing otherwise
is likely to cause inductive spikes and their associated problems.

They generate about 90V AC at 16.67Hz seems about right to run a
pump at 1/3 power.

Oh I see, I was thinking on the wrong track. Yeah, if it can survive
the unusual load conditions it might just work. No doubt somebody
sold one on Ebay once.

or perhaps a curcuit that passes every third half-cycle

_ _ _ _ _ _
/ \ / \ / \ / \ / \ / \
_/ \_/ \_/ \_/ \_/ \_/ \

_ _
_/ \______ ______/ \_____ ______
\_/ \_/

_ _ _ _
___ / \___/ \ ___ / \___/ \
_/ \_/ \_/ \_/ \

I'm having trouble imagining how cutting half-cycles would be any
easier to implement. Nice ASCII waveforms though.

A triac with the right drive, not sure what the crcuit to do that is
though.

Yes, though a Triac could also be used to cut a whole cycle:

_ _ _
__/ \ ______/ \ ______/ \ ____
\_/ \_/ \_/

A basic implementation for fixed 1/2 division of the supply
frequency may be as follows:

ZERO CROSSING| |FLIP| | SCR |
|---|FLOP|---| |
DETECTOR | | /2 | |(TRIAC)|

The Flip Flop divides the signal from the Zero Crossing
Detector (which produces a pulse on every 0V transition
of the mains waveform) by two. This signal activates
the SCR (which powers the compressor) for one of every
two mains cycles.

Mains Waveform to Zero-Crossing Detector:
_ _ _ _ _ _
*/ \* X/ \X */ \* X/ \X */ \* X/ \X
_/ \_/ \_/ \_/ \_/ \_/ \
"*" & "X" Indicates pulse from Zero Crossing Detector
"*" = SCR Triggered
"X" = SCR Disabled

SCR Output Waveform to Compressor:

_ _ _
__/ \ ______/ \ ______/ \ ____
\_/ \_/ \_/

A variable division of the Zero-Crossing signal would
be desireable to allow further reduction of the supply
frequency if required. A counter which disables the SCR
for just one cycle after a certain count of zero-crossings
may be used instead of the divide-by-two Flip-Flop for
frequency reduction less severe than 1/2 division.

Oops, out of time. I'll have to hope all that made sense,
no time for a final check!

That's interesting but way beyond my skills to design / build. All I need is
to find a supplier.
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[~misfit~]

Once upon a time on usenet Jasen Betts wrote:

On 2016-03-31, ~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

As has been noted, frequency control rather than voltage control may
be the better option.

Indeed.

Does anyone know of a cheap, purchasable device
that would achieve this?

I would like to know the answer to this.

A variable frequency drive
$80 delivered on aliexpress for one with a case,

I just searched and the cheapest was US$90 delivered. It's a shame there
isn't something smaller and cheaper - the one I found does 1 to 400Hz and is
rated at 400w. I only need perhaps 5 to 50Hz and maybe 50w (my pump is rated
25w).

$55 for a used one - needs a case
both are marked 220V so may not be reliable on Aussie 240V

much cheaper to buy a new pump.

http://www.aliexpress.com/item/2015-Hot-Sale-New-3W-Super-Silent-Adjustable-Aquarium-Air-Pump-Fish-Tank-Oxygen-Air-Pump/32580955417.html?spm=2114.01010208.3.19.7YaLLZ&ws_ab_test=searchweb201556_1,searchweb201602_4_10036_10035_301_10034_507_10032_10020_10017_10005_10006_10021_10022_401_10018_10019,searchweb201603_9&btsid=08c5dc1d-e491-4371-b006-d9db91461c28

just needs a new plug fitted.

Yeah, thanks but I wasn't asking advice on aquarum air pumps.

I have a couple decades in the aquarium industry under my belt, half of that
as a consultant on large private and public aquatic systems. I have maybe 20
airpumps of varying sizes and the little 'domestic models' are noisy and
unreliable in the longer term. I've always belived in, wherever possible
using kit that's way over-rated for the requirement and then using it at a
lower duty cycle so that it lasts a long time.

That said this is looking to be too problematic, requiring far more of my
limited time than I'd hoped so I might go through my collection of smaller
pumps and find the least-noisy one that will supply the ~5l/min that I need
and hope that it lasts. It's a shame to mothball this really quiet and
efficient 30l/min unit though. I was hoping to be able to leave it in place
and just ramp up the output again if required.

I'm sure that I'll find another use for the 'power controller' that I bought
hoping it would do the job. It wasn't hugely expensive, I just ate lightly
for a few days and saved enough money to pay for it.

Cheers,
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[Computer Nerd Kev]

Computer Nerd Kev <not@telling.you.invalid> wrote:

Once upon a time on usenet Jasen Betts wrote:
On 2016-03-27, ~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

probably reducing the input voltage will do what you want. so a series
dropper of some sort, or a step-down transformer. you could try a fan
speed controller, or to test this out a 100w lamp.

I don't have any of the above.

Actually I may be able to dig out a 60 or 75 watt incandescant light bulb
from the back of the cupboard - I only use LED lamps in the house now,
swapped out the CFLs a while back. What would the effect of wiring an
incandescant bulb in parallel to the pump be? I mentioned I'm new to
electrical theory yes?

That'll drop the input voltage to the pump. You look at the light bulb as
a resistor and use the voltage developed across it (Ohms law) to subtract
from the voltage otherwise applied to the pump. But for heaven's sake wire
it in _series_, not parallel.

The controller you've bought is also a form of voltage control, but as it
works by switching the input waveform rather than droping the voltage over
a resistance, other considerations (inductive spikes, completion of
compressor stroke) arise.

I recently discovered there are some fairly cheap high power wire-wound
potentiometers ("rheostat" is the name to use when searching for them)
on Ebay.

This 1K 25W version should be OK for reducing your 50W pump to half power:
http://www.ebay.com.au/itm/331645073377/

Of course the unused power will simply go as heat (no doubt these get rather
hot at 25W), but it might do what you want. On the other hand, the pump
might not function well mechanically at the lower voltage, but as I've
already said, I don't know much about that side of the equation.

Maybe these are how the speed controls on your cheap pumps work?


I'm personally thinking of buying a couple of 20R 50W types to connect in
parallel inside a box and make a 100W 0-10R "Watt-Box" (AKA a variable
load for testing electronics). I'm not sure how to connect the shafts of
the two pots together though, so they can be turned as one. Plastic gears
would probably melt, and making small metal gears is a bit above my
machining skill. I might give it a go some day.

--
__ __
#_ < |\| |< _#

 

[~misfit~]

Once upon a time on usenet Computer Nerd Kev wrote:

Computer Nerd Kev <not@telling.you.invalid> wrote:
Once upon a time on usenet Jasen Betts wrote:
On 2016-03-27, ~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

probably reducing the input voltage will do what you want. so a
series dropper of some sort, or a step-down transformer. you
could try a fan speed controller, or to test this out a 100w lamp.

I don't have any of the above.

Actually I may be able to dig out a 60 or 75 watt incandescant
light bulb from the back of the cupboard - I only use LED lamps in
the house now, swapped out the CFLs a while back. What would the
effect of wiring an incandescant bulb in parallel to the pump be? I
mentioned I'm new to electrical theory yes?

That'll drop the input voltage to the pump. You look at the light
bulb as a resistor and use the voltage developed across it (Ohms
law) to subtract from the voltage otherwise applied to the pump. But
for heaven's sake wire it in _series_, not parallel.

The controller you've bought is also a form of voltage control, but
as it works by switching the input waveform rather than droping the
voltage over a resistance, other considerations (inductive spikes,
completion of compressor stroke) arise.

I recently discovered there are some fairly cheap high power
wire-wound potentiometers ("rheostat" is the name to use when
searching for them)
on Ebay.

This 1K 25W version should be OK for reducing your 50W pump to half
power: http://www.ebay.com.au/itm/331645073377/

I mentioned that I'm still learning electronics yes? For my application what
effect does the resistance have in this instance? I've seen these devices
rated from 5 ohms to 1K and still don't quite get that part of it.

(Sorry to appear dense, I have a learning disability. My parents dragged me
around a bit as a schoolchild and because I was obese, foreign and put ahead
a couple of years I got bullied something fierce. End result is an anxiety
disorder that persists to this day. I get headeaches from thinking and the
more I concentrate on something the worse my headache gets. So the only way
for me to learn is in small bites, trick my subconscious into believing that
I'm not actually learning. It's a real Catch-22 because I've never been
happy if I'm not learning new stuff.)

Of course the unused power will simply go as heat (no doubt these get
rather hot at 25W), but it might do what you want. On the other hand,
the pump might not function well mechanically at the lower voltage,
but as I've already said, I don't know much about that side of the
equation.

Maybe these are how the speed controls on your cheap pumps work?

Quite possibly. Likely with just a carbon track too(?) as they pumps are
only 7.5W at full power and there's a rather beefy resistor in circuit.

I'm personally thinking of buying a couple of 20R 50W types to
connect in parallel inside a box and make a 100W 0-10R "Watt-Box"
(AKA a variable
load for testing electronics). I'm not sure how to connect the shafts
of the two pots together though, so they can be turned as one.
Plastic gears would probably melt, and making small metal gears is a
bit above my machining skill. I might give it a go some day.

Interesting. A while back I was into 1970/80s stereo gear and wanted a
variac so that, with things that hadn't been plugged in for ages I could
slowly bring up the voltage and perhaps 'reform' capacitors to a certain
extent. However due to circumstances my hobbies need to be.... cheap, and a
variac was out of reach of my budget. (I hadn't discovered the benefits of
ordering from China direct back then.)

Would the device you're envisioning serve to do what I wanted to do with old
stereo gear? I still have a few intersting untested components.

Cheers,
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[Computer Nerd Kev]

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

Once upon a time on usenet Computer Nerd Kev wrote:
Computer Nerd Kev <not@telling.you.invalid> wrote:
Once upon a time on usenet Jasen Betts wrote:
On 2016-03-27, ~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

probably reducing the input voltage will do what you want. so a
series dropper of some sort, or a step-down transformer. you
could try a fan speed controller, or to test this out a 100w lamp.

I don't have any of the above.

Actually I may be able to dig out a 60 or 75 watt incandescant
light bulb from the back of the cupboard - I only use LED lamps in
the house now, swapped out the CFLs a while back. What would the
effect of wiring an incandescant bulb in parallel to the pump be? I
mentioned I'm new to electrical theory yes?

That'll drop the input voltage to the pump. You look at the light
bulb as a resistor and use the voltage developed across it (Ohms
law) to subtract from the voltage otherwise applied to the pump. But
for heaven's sake wire it in _series_, not parallel.

The controller you've bought is also a form of voltage control, but
as it works by switching the input waveform rather than droping the
voltage over a resistance, other considerations (inductive spikes,
completion of compressor stroke) arise.

I recently discovered there are some fairly cheap high power
wire-wound potentiometers ("rheostat" is the name to use when
searching for them)
on Ebay.

This 1K 25W version should be OK for reducing your 50W pump to half
power: http://www.ebay.com.au/itm/331645073377/

I mentioned that I'm still learning electronics yes? For my application what
effect does the resistance have in this instance? I've seen these devices
rated from 5 ohms to 1K and still don't quite get that part of it.

As you've probably noticed, I went through and worked through the full maths
of it all. That might be a bit much for you, so I'll start off with just a
basic verbal explanation. A resistor in series with a motor (which itself
can be considered just another resistor), uses some of the power going to
the motor to heat itself. At the same time, it gets in the way of the
power going through the circuit, so less power flows in total as well.
Both of these effects increase as the resistance increases, so 5 Ohms
does little to decrease the power that gets to your motor, but 1000
Ohms (1K) decreases it significantly.

This is all proportional to the resistance of the motor though. If the
motor resistance was 5 Ohms (which could well happen with a motor
designed to run on low voltage DC power), then just another 5 Ohms in
series would be enough to significantly reduce the power getting to the
pump.

However your pump runs on 240V and, as is shown below, has a resistance
of somewhere around 1200 Ohms. An extra 5 Ohms would make very little
difference to the power going to this pump, but an extra 1000 Ohms
in series would definately make an impact on the pump's power.

Here's the full maths of it all:
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
You want to reduce the Voltage going to the pump. The pump is 50 Watt, and:
Power (Watts) = Voltage x Current (Amps).
So, as the pump is running on 240V (or 230, 220, someone probably gets
250, let's just assume 240 for now):

Current = 50W / 240V = 0.2A

Mr Ohm reckoned "V(Voltage) = I(Current, Amps) x R(Resistance, Ohms)", so:
R = V / I
R = 240V / 0.2A = 1200R

The other way that equation can be rearranged is of course:
I = V / R
And sure enough,
I = 240V / 1200R = 0.2A

But, if we make R bigger by putting our 1K potentiometer in series at its
maximum resistance:

I = 240V / 2200R = 0.11A

Which means the total power now being used is:
Watts = 240V x 0.11A = 26.4W

Now when current flows through a resistance, a voltage differance is created
as the energy used up. With the pump plugged in normally, the voltage
difference is 240V because there is 240V at the + connection and 0V at the
- connection. Now though, we have two devices using the power, and although
we know that in total the voltage difference must still be 240V, we can also
work out how that voltage drop is distributed over the two components.

For the 1K Potentiometer:
V = I x R, so:
Voltage = 0.11A x 1000R = 110V

For the pump:

Voltage = 0.11A x 1200R = 132V

You may notice that these numbers have just boosted your mains voltage up
to 242V . That's because I rounded up the current, just pretend the
total is 240V.

The power turned into heat by the Resistor is therefore:

Power = 0.11A x 110V = 12.1W

And the power turned into motion and, as is the way of physics, more
heat, by the Pump is:

Power = 0.11A x 132V = 14.52W

So you've now got yourself a pump (hopefully) running on 14.52W, a
potentiometer running at 12.1W, and a total of 26.62W sacrificed to the
fish gods.

If you set the pot to half (500R, 0.5K), then the power to the pump
would be:

Current = 240V / 1700R = 0.141A
Voltage = 0.141A x 1200R(pump resistance) = 169.412V
Power = 0.141A x 169.412V = 23.89W

And over the potentiometer would be:

Voltage = 0.141A x 500R = 70.5V
Power = 0.141A x 70.5 = 9.94W


With the pot at 100R, the pump would get 41.07W, and of course at 0R,
we're back to 50W again.

(Sorry to appear dense, I have a learning disability. My parents dragged me
around a bit as a schoolchild and because I was obese, foreign and put ahead
a couple of years I got bullied something fierce. End result is an anxiety
disorder that persists to this day. I get headeaches from thinking and the
more I concentrate on something the worse my headache gets. So the only way
for me to learn is in small bites, trick my subconscious into believing that
I'm not actually learning. It's a real Catch-22 because I've never been
happy if I'm not learning new stuff.)

Of course the unused power will simply go as heat (no doubt these get
rather hot at 25W), but it might do what you want. On the other hand,
the pump might not function well mechanically at the lower voltage,
but as I've already said, I don't know much about that side of the
equation.

Maybe these are how the speed controls on your cheap pumps work?

Quite possibly. Likely with just a carbon track too(?) as they pumps are
only 7.5W at full power and there's a rather beefy resistor in circuit.

Normally wire-wound potentiometers are used where numerous Watts are
dissipated by the potenetiometer, but maybe they managed to get away
with a special type of carbon pot. The series resistor might be to
adapt the motor to 240V instead of 110V, wasting power in the
process.

I'm personally thinking of buying a couple of 20R 50W types to
connect in parallel inside a box and make a 100W 0-10R "Watt-Box"
(AKA a variable
load for testing electronics). I'm not sure how to connect the shafts
of the two pots together though, so they can be turned as one.
Plastic gears would probably melt, and making small metal gears is a
bit above my machining skill. I might give it a go some day.

Interesting. A while back I was into 1970/80s stereo gear and wanted a
variac so that, with things that hadn't been plugged in for ages I could
slowly bring up the voltage and perhaps 'reform' capacitors to a certain
extent. However due to circumstances my hobbies need to be.... cheap, and a
variac was out of reach of my budget. (I hadn't discovered the benefits of
ordering from China direct back then.)

Would the device you're envisioning serve to do what I wanted to do with old
stereo gear? I still have a few intersting untested components.

Hmm, I hadn't thought of that. It should work OK for the purpose you
describe, as long as you make sure not to go over the Wattage limit of
the potentiometer/s.

Things like Variacs can sometimes be found cheaply at "HamFests", where ham
radio enthusiasts sell their junk. I don't know if there are many held in
NZ though.

--
__ __
#_ < |\| |< _#

 

[~misfit~]

Once upon a time on usenet Computer Nerd Kev wrote:

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
Computer Nerd Kev <not@telling.you.invalid> wrote:
Once upon a time on usenet Jasen Betts wrote:
On 2016-03-27, ~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

probably reducing the input voltage will do what you want. so a
series dropper of some sort, or a step-down transformer. you
could try a fan speed controller, or to test this out a 100w
lamp.

I don't have any of the above.

Actually I may be able to dig out a 60 or 75 watt incandescant
light bulb from the back of the cupboard - I only use LED lamps in
the house now, swapped out the CFLs a while back. What would the
effect of wiring an incandescant bulb in parallel to the pump be?
I mentioned I'm new to electrical theory yes?

That'll drop the input voltage to the pump. You look at the light
bulb as a resistor and use the voltage developed across it (Ohms
law) to subtract from the voltage otherwise applied to the pump.
But for heaven's sake wire it in _series_, not parallel.

The controller you've bought is also a form of voltage control, but
as it works by switching the input waveform rather than droping the
voltage over a resistance, other considerations (inductive spikes,
completion of compressor stroke) arise.

I recently discovered there are some fairly cheap high power
wire-wound potentiometers ("rheostat" is the name to use when
searching for them)
on Ebay.

This 1K 25W version should be OK for reducing your 50W pump to half
power: http://www.ebay.com.au/itm/331645073377/

I mentioned that I'm still learning electronics yes? For my
application what effect does the resistance have in this instance?
I've seen these devices rated from 5 ohms to 1K and still don't
quite get that part of it.

As you've probably noticed, I went through and worked through the
full maths of it all. That might be a bit much for you, so I'll start
off with just a basic verbal explanation. A resistor in series with a
motor (which itself can be considered just another resistor), uses
some of the power going to the motor to heat itself. At the same
time, it gets in the way of the
power going through the circuit, so less power flows in total as well.
Both of these effects increase as the resistance increases, so 5 Ohms
does little to decrease the power that gets to your motor, but 1000
Ohms (1K) decreases it significantly.

This is all proportional to the resistance of the motor though. If the
motor resistance was 5 Ohms (which could well happen with a motor
designed to run on low voltage DC power), then just another 5 Ohms in
series would be enough to significantly reduce the power getting to
the pump.

However your pump runs on 240V and, as is shown below, has a
resistance
of somewhere around 1200 Ohms. An extra 5 Ohms would make very little
difference to the power going to this pump, but an extra 1000 Ohms
in series would definately make an impact on the pump's power.

Here's the full maths of it all:
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
You want to reduce the Voltage going to the pump. The pump is 50
Watt, and: Power (Watts) = Voltage x Current (Amps).
So, as the pump is running on 240V (or 230, 220, someone probably gets
250, let's just assume 240 for now):

Current = 50W / 240V = 0.2A

Mr Ohm reckoned "V(Voltage) = I(Current, Amps) x R(Resistance,
Ohms)", so: R = V / I
R = 240V / 0.2A = 1200R

The other way that equation can be rearranged is of course:
I = V / R
And sure enough,
I = 240V / 1200R = 0.2A

But, if we make R bigger by putting our 1K potentiometer in series at
its maximum resistance:

I = 240V / 2200R = 0.11A

Which means the total power now being used is:
Watts = 240V x 0.11A = 26.4W

Now when current flows through a resistance, a voltage differance is
created as the energy used up. With the pump plugged in normally, the
voltage difference is 240V because there is 240V at the + connection
and 0V at the - connection. Now though, we have two devices using the
power, and although we know that in total the voltage difference must
still be 240V, we can also work out how that voltage drop is
distributed over the two components.

For the 1K Potentiometer:
V = I x R, so:
Voltage = 0.11A x 1000R = 110V

For the pump:

Voltage = 0.11A x 1200R = 132V

You may notice that these numbers have just boosted your mains
voltage up to 242V . That's because I rounded up the current, just
pretend the total is 240V.

The power turned into heat by the Resistor is therefore:

Power = 0.11A x 110V = 12.1W

And the power turned into motion and, as is the way of physics, more
heat, by the Pump is:

Power = 0.11A x 132V = 14.52W

So you've now got yourself a pump (hopefully) running on 14.52W, a
potentiometer running at 12.1W, and a total of 26.62W sacrificed to
the fish gods.

If you set the pot to half (500R, 0.5K), then the power to the pump
would be:

Current = 240V / 1700R = 0.141A
Voltage = 0.141A x 1200R(pump resistance) = 169.412V
Power = 0.141A x 169.412V = 23.89W

And over the potentiometer would be:

Voltage = 0.141A x 500R = 70.5V
Power = 0.141A x 70.5 = 9.94W


With the pot at 100R, the pump would get 41.07W, and of course at 0R,
we're back to 50W again.


(Sorry to appear dense, I have a learning disability. My parents
dragged me around a bit as a schoolchild and because I was obese,
foreign and put ahead a couple of years I got bullied something
fierce. End result is an anxiety disorder that persists to this day.
I get headeaches from thinking and the more I concentrate on
something the worse my headache gets. So the only way for me to
learn is in small bites, trick my subconscious into believing that
I'm not actually learning. It's a real Catch-22 because I've never
been happy if I'm not learning new stuff.)

Of course the unused power will simply go as heat (no doubt these
get rather hot at 25W), but it might do what you want. On the other
hand, the pump might not function well mechanically at the lower
voltage, but as I've already said, I don't know much about that
side of the equation.

Maybe these are how the speed controls on your cheap pumps work?

Quite possibly. Likely with just a carbon track too(?) as they pumps
are only 7.5W at full power and there's a rather beefy resistor in
circuit.

Normally wire-wound potentiometers are used where numerous Watts are
dissipated by the potenetiometer, but maybe they managed to get away
with a special type of carbon pot. The series resistor might be to
adapt the motor to 240V instead of 110V, wasting power in the
process.

I'm personally thinking of buying a couple of 20R 50W types to
connect in parallel inside a box and make a 100W 0-10R "Watt-Box"
(AKA a variable
load for testing electronics). I'm not sure how to connect the
shafts of the two pots together though, so they can be turned as
one. Plastic gears would probably melt, and making small metal
gears is a bit above my machining skill. I might give it a go some
day.

Interesting. A while back I was into 1970/80s stereo gear and wanted
a variac so that, with things that hadn't been plugged in for ages I
could slowly bring up the voltage and perhaps 'reform' capacitors
to a certain extent. However due to circumstances my hobbies need to
be.... cheap, and a variac was out of reach of my budget. (I hadn't
discovered the benefits of ordering from China direct back then.)

Would the device you're envisioning serve to do what I wanted to do
with old stereo gear? I still have a few intersting untested
components.

Hmm, I hadn't thought of that. It should work OK for the purpose you
describe, as long as you make sure not to go over the Wattage limit of
the potentiometer/s.

Things like Variacs can sometimes be found cheaply at "HamFests",
where ham radio enthusiasts sell their junk. I don't know if there
are many held in NZ though.

Thanks for taking the time. I'm working on getting my head around it.

(I know it's basic stuff but as I said, learning issues... I appreciate you
applying Ohm's Law to this situation for me to check out.)
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[Computer Nerd Kev]

I haven't quite been able to get all this out of my head,
and as a result I've come up with a few things to add
regarding this method of power control (always sending
complete mains cycles to the load):

Most notable would be that, while looking through one
of my electronics books, I stumbled across the real name
for this form of power control. It's called "Burst Fire",
as it generally describes a method whereby busts of
mains cycles are provided to the load over a period
determined by the quantity of power reduction required.
It is most commonly used to control large electric
heating elements, where the Phase Control method may
cause excessive noise on the mains supply.

There are Burst Fire power control ICs available, two
that I have found are below:

http://www.elektronik.sk/datasheet/U217B.pdf
http://www.elektronik.sk/datasheet/TEA1024.pdf

The first pages of those datasheets show circuits to
perform the required task.

There are Burst Fire power controllers available as
pre-built modules, but I couldn't find any cheap
Chinese ones during my breif searching (they may be
listed under another name, or even included amongst
listings with Phase Control types). These are the
two cheapest models at RS:

United Automation, ZVS-16DV, Thyristor Power Controller
Assembly, 3.7kW, 16A, 58 x 55 x 36mm
- $99.06 AU ($108.97 NZ):
http://nz.rs-online.com/web/p/thyristor-power-controller-assemblies/2143979/

United Automation, PR1-DIN-2.5KW, Thyristor Power
Controller Assembly, 2.5kW, 11A, 94 x 75 x 83mm
- $99.30 AU ($109.23 NZ)
http://nz.rs-online.com/web/p/thyristor-power-controller-assemblies/0493077/

Both about the same price at around $100, and both
far over spec'ed for your application (though all
such controllers are likely to be, due to the
technology and their intended application as
heater controllers).

As a final note, here are my other circuit ideas
(they will likely exceed your design ability, but
I feel like putting them on the record):

Use a 4527 BCD Rate Multiplier IC clocked from a
mains Zero-Crossing Detector circuit, and with
it's output buffered and used to control a TRIAC
switching the mains waveform. This allows the
number of mains cycles sent to the load over a
time period of ten cycles to be varied from 0-9
using a rotary switch with BCD outputs. The main
advantage of this circuit would be that I wouldn't
have to buy anything if I built it myself.

Use a CA3059 TRIAC Control IC and a 555 timer
configured as an oscillator with a frequency
variable using a potentiometer, or multi-pole
switch. The 555 output enables the CA3059 to
turn on the TRIAC at the next mains crossing
point after it goes high, and to turn the TRIAC
off at the crossing-point after it goes low.
In this way, it works like one of the dedicated
Burst-Fire ICs above, sending "bursts" of mains
to the load. Actually... I could avoid buying
anything for this too, if I replaced the CA3059
with some discrete circuitry to provide the same
functions. Probably no more complicated than
the previous option.

--
__ __
#_ < |\| |< _#

 

[~misfit~]

Once upon a time on usenet Computer Nerd Kev wrote:

I haven't quite been able to get all this out of my head,
and as a result I've come up with a few things to add
regarding this method of power control (always sending
complete mains cycles to the load):

Most notable would be that, while looking through one
of my electronics books, I stumbled across the real name
for this form of power control. It's called "Burst Fire",
as it generally describes a method whereby busts of
mains cycles are provided to the load over a period
determined by the quantity of power reduction required.
It is most commonly used to control large electric
heating elements, where the Phase Control method may
cause excessive noise on the mains supply.

There are Burst Fire power control ICs available, two
that I have found are below:

http://www.elektronik.sk/datasheet/U217B.pdf
http://www.elektronik.sk/datasheet/TEA1024.pdf

The first pages of those datasheets show circuits to
perform the required task.

There are Burst Fire power controllers available as
pre-built modules, but I couldn't find any cheap
Chinese ones during my breif searching (they may be
listed under another name, or even included amongst
listings with Phase Control types). These are the
two cheapest models at RS:

United Automation, ZVS-16DV, Thyristor Power Controller
Assembly, 3.7kW, 16A, 58 x 55 x 36mm
- $99.06 AU ($108.97 NZ):
http://nz.rs-online.com/web/p/thyristor-power-controller-assemblies/2143979/

United Automation, PR1-DIN-2.5KW, Thyristor Power
Controller Assembly, 2.5kW, 11A, 94 x 75 x 83mm
- $99.30 AU ($109.23 NZ)
http://nz.rs-online.com/web/p/thyristor-power-controller-assemblies/0493077/

Both about the same price at around $100, and both
far over spec'ed for your application (though all
such controllers are likely to be, due to the
technology and their intended application as
heater controllers).

As a final note, here are my other circuit ideas
(they will likely exceed your design ability, but
I feel like putting them on the record):

Use a 4527 BCD Rate Multiplier IC clocked from a
mains Zero-Crossing Detector circuit, and with
it's output buffered and used to control a TRIAC
switching the mains waveform. This allows the
number of mains cycles sent to the load over a
time period of ten cycles to be varied from 0-9
using a rotary switch with BCD outputs. The main
advantage of this circuit would be that I wouldn't
have to buy anything if I built it myself.

Use a CA3059 TRIAC Control IC and a 555 timer
configured as an oscillator with a frequency
variable using a potentiometer, or multi-pole
switch. The 555 output enables the CA3059 to
turn on the TRIAC at the next mains crossing
point after it goes high, and to turn the TRIAC
off at the crossing-point after it goes low.
In this way, it works like one of the dedicated
Burst-Fire ICs above, sending "bursts" of mains
to the load. Actually... I could avoid buying
anything for this too, if I replaced the CA3059
with some discrete circuitry to provide the same
functions. Probably no more complicated than
the previous option.

Thanks Kev, interesting stuff. I've put the project on the back burner for
now (and the SCR unit in a 'box of bits').

Cheers.
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)