Adapter fails to power DC motor

[Terry Pinnell]

Michael Kellett <mk@mkesc.co.uk> wrote:

On 03/03/2020 12:17, Terry Pinnell wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.

Terry, East Grinstead, UK

Are you quite sure that the motor stall current is only 4A with full
working voltage applied ? This is quite different from stalling the
motor and measuring the current (which will likely be limited by the
power supply.) I would expect the rated voltage stall current of the
motor to be at least 10x the full load working current.

MK

As described earlier, it's an old 2.4V ex-screwdriver motor, and I don't
know its rated stall current. FWIW the last time I took a meter to it
and deliberately stalled it think I saw about 4.5A from the batteries.

I have just noticed a data sheet link for the adapter/wart on the
Farnell page I referenced and in that PDF
https://www.dropbox.com/s/2shohl2zekvpe62/2871891.pdf?dl=0
I see
"Over Current Protection: >3.6A with auto-recovery function".

Does that imply that said recovery function is not working in this case?

 

[Terry Pinnell]

jlarkin@highlandsniptechnology.com wrote:

On Tue, 03 Mar 2020 16:48:57 +0000, Terry Pinnell
me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.

Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK

If there was no load on the big cap, the supply would eventually
charge it. But the start current of the motor could collapse
everything when it was connected. A supercap might work. Or a better
power supply.

Thanks, understood. I have a few of these on order to play with:
https://www.ebay.co.uk/itm/Cylinder-Farad-Capacitor-2-7V-500F-Electrical-Component-Super-Capacitor-Black/163826403836?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

 

as a test,
connect the motor then get it started by spinning it by hand.
does that work?

m

 

[Terry Pinnell]

DemonicTubes <tlackie@gmail.com> wrote:

On Tuesday, March 3, 2020 at 12:17:29 PM UTC-7, Rick C wrote:
On Tuesday, March 3, 2020 at 1:11:09 PM UTC-5, DemonicTubes wrote:
On Tuesday, March 3, 2020 at 9:53:11 AM UTC-7, Terry Pinnell wrote:
Terry Pinnell <me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.

Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK

Meant to add: while fiddling with this, tapping wires at various
intervals, there was just *one* instance when the motor *did* start
running at what appeared full speed. Spent another few minutes trying in
vain to reproduce that.

You could always try putting an NTC resistor in series as an inrush current limiter. Cheap, easy, probably works...why not?

Doesn't even need the temperature coefficient. The NiMH batteries power the motor at '3.8 to 4.1 V". This supply runs at 5 volts and he has not said anything about reducing that voltage that I saw. They guy is not very precise in his description of the circuit though. I don't know what he means by "ex-screwdriver 2.4 motor". Is that 2.4 volts? 2.4 amps? Maybe 2.4 revision???

Anyway, a quarter ohm or maybe a bit more resistance should be added between the motor input and the PSU output. That would drop the volt at full power. Or maybe use a smaller resistor (~0.1 ohm) and a diode drop. Or maybe two diode drops, one silicon and one Schottky plus optionally a tenth ohm resistor.

I'm not at all surprised he is getting an overload driving a 4 volt motor from a 5 volt supply.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

Certainly a normal resistor would most likely work. The reason I suggested an NTC ('thermistor' as they are commonly known) is to avoid wasting power. They are readily available and dirt cheap...of course if you don't have one on hand and need to get it working now, yeah just throw a low value resistor on there and go for it.

I'm sure you know all this, but this is for OP's benefit.

Those NTC thermistors are often called 'inrush current limiters'. They start out at a few ohms, but quickly drop to almost nothing after a moment of current flow.

Thanks a bunch, that fixed it!

With a series resistance of two 0.5 R in parallel, plus some
croc-to-crocs and other wires, it starts at once. With no load quickly
settled at 2.7A and 3.9V. I couldn't quite stall it but got close, when
those became 5.1A and 2.0V.

That was with an identical but little used motor, but I'm fairly
confident the installed motor will behave in similar fashion.

Terry, East Grinstead, UK

 

[Terry Pinnell]

George Herold <ggherold@gmail.com> wrote:

On Tuesday, March 3, 2020 at 1:11:09 PM UTC-5, DemonicTubes wrote:
On Tuesday, March 3, 2020 at 9:53:11 AM UTC-7, Terry Pinnell wrote:
Terry Pinnell <me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.

Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK

Meant to add: while fiddling with this, tapping wires at various
intervals, there was just *one* instance when the motor *did* start
running at what appeared full speed. Spent another few minutes trying in
vain to reproduce that.

You could always try putting an NTC resistor in series as an inrush current limiter. Cheap, easy, probably works...why not?

Oh! So this is a hack and the best bet will be a bigger power supply.
but as long as the DC motor isn't starved for torque, then you just need
to limit the current some.. so how about a series resistor, ~0.1 ohms?

George H.

Thanks George. That fix from you and DemonicTubes gets the seegar! See
also my more detailed reply a minute ago.

Terry, East Grinstead, UK

 

[Rick C]

On Wednesday, March 4, 2020 at 10:58:27 AM UTC-5, Terry Pinnell wrote:

DemonicTubes <tlackie@gmail.com> wrote:

On Tuesday, March 3, 2020 at 2:14:00 PM UTC-7, Rick C wrote:
On Tuesday, March 3, 2020 at 3:40:56 PM UTC-5, DemonicTubes wrote:
On Tuesday, March 3, 2020 at 12:17:29 PM UTC-7, Rick C wrote:
On Tuesday, March 3, 2020 at 1:11:09 PM UTC-5, DemonicTubes wrote:
On Tuesday, March 3, 2020 at 9:53:11 AM UTC-7, Terry Pinnell wrote:
Terry Pinnell <me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.

Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK

Meant to add: while fiddling with this, tapping wires at various
intervals, there was just *one* instance when the motor *did* start
running at what appeared full speed. Spent another few minutes trying in
vain to reproduce that.

You could always try putting an NTC resistor in series as an inrush current limiter. Cheap, easy, probably works...why not?

Doesn't even need the temperature coefficient. The NiMH batteries power the motor at '3.8 to 4.1 V". This supply runs at 5 volts and he has not said anything about reducing that voltage that I saw. They guy is not very precise in his description of the circuit though. I don't know what he means by "ex-screwdriver 2.4 motor". Is that 2.4 volts? 2.4 amps? Maybe 2.4 revision???

Anyway, a quarter ohm or maybe a bit more resistance should be added between the motor input and the PSU output. That would drop the volt at full power. Or maybe use a smaller resistor (~0.1 ohm) and a diode drop. Or maybe two diode drops, one silicon and one Schottky plus optionally a tenth ohm resistor.

I'm not at all surprised he is getting an overload driving a 4 volt motor from a 5 volt supply.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

Certainly a normal resistor would most likely work. The reason I suggested an NTC ('thermistor' as they are commonly known) is to avoid wasting power. They are readily available and dirt cheap...of course if you don't have one on hand and need to get it working now, yeah just throw a low value resistor on there and go for it.

I'm sure you know all this, but this is for OP's benefit.

Those NTC thermistors are often called 'inrush current limiters'. They start out at a few ohms, but quickly drop to almost nothing after a moment of current flow.

Trouble is he needs to waste power anyway. He is mismatching a 5 volt supply to a 3.8-4.0 volt motor. So the NTC will only set him up for a future motor failure.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

Ah. Sorry, it wasn't clear to me that it is a 4 V motor. If that is the case, a proper supply is a better solution.

It's not, it's a 2.4 V ex-screwdriver motor, originally powered by two
1.2 V NiCads.

For the last 16 years, as I mentioned, it's been powered by three Nimh
batteries (C-type, not AA, another typo, sorry), "...delivering a
voltage of about 3.8 to 4.1 V...". A lower voltage of 2.5 V or so from
two such batteries delivers insufficient current to open and close the
quite heavy curtains. It's running well at present, closing smoothly in
just over 2 secs:
https://www.dropbox.com/s/b96xyihr4ustgjq/Curtains-1.mp4?raw=1
but I'd rather like battery independence.

You state two batteries provided insufficient current so you upped the number of cells which provided more voltage. Do you see the problem with that?

NiMH cells have a higher internal resistance than do NiCd or Li-ion cells of similar size. So when trying to open the curtain with two NiMH cells you were losing voltage in the series resistance and so the delivered power was too low. By adding a third cell the voltage increased to where it should have been and were able to get sufficient power to open the curtain.

Now your cells are showing their age and no longer hold a charge long enough to power the curtain with the original charging current. So you pick a power supply to directly drive the motor, but at more than twice the rated voltage. So the peak current is far higher than either required or allowed by the PSU and it doesn't work.

No, a couple of series diodes are not going to work. You need a power supply that puts out the correct voltage at the correct current. To charge a battery power source at 2.4 volts seems problematic since you don't want to use a proper system to do this. I think I would go with a capacitor/super capacitor based system. They can be charged at a higher rate for quick recharge and are resistant to overcharging as long as your power source doesn't drive them to an excessive voltage. In fact, there is a capacitive doubler/halfing circuit you could use to charge caps to 2.5 volts from your existing 5 volt supply. It is a simple circuit and would only require some FETs and a 555 timer chip.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

 

[George Herold]

On Wednesday, March 4, 2020 at 12:45:12 PM UTC-5, Terry Pinnell wrote:

George Herold <ggherold@gmail.com> wrote:

On Tuesday, March 3, 2020 at 1:11:09 PM UTC-5, DemonicTubes wrote:
On Tuesday, March 3, 2020 at 9:53:11 AM UTC-7, Terry Pinnell wrote:
Terry Pinnell <me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.

Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK

Meant to add: while fiddling with this, tapping wires at various
intervals, there was just *one* instance when the motor *did* start
running at what appeared full speed. Spent another few minutes trying in
vain to reproduce that.

You could always try putting an NTC resistor in series as an inrush current limiter. Cheap, easy, probably works...why not?

Oh! So this is a hack and the best bet will be a bigger power supply.
but as long as the DC motor isn't starved for torque, then you just need
to limit the current some.. so how about a series resistor, ~0.1 ohms?

George H.

Thanks George. That fix from you and DemonicTubes gets the seegar! See
also my more detailed reply a minute ago.

Terry, East Grinstead, UK

Excellent. thanks for the update.
George H.

 

[Jasen Betts]

On 2020-03-04, Terry Pinnell <me@somewhere.invalid> wrote:

Michael Kellett <mk@mkesc.co.uk> wrote:

As described earlier, it's an old 2.4V ex-screwdriver motor, and I don't
know its rated stall current. FWIW the last time I took a meter to it
and deliberately stalled it think I saw about 4.5A from the batteries.

You can use Ohm's law to determine stall current.
At 5V it'll be more than twice what it was at 2.4V

I have just noticed a data sheet link for the adapter/wart on the
Farnell page I referenced and in that PDF
https://www.dropbox.com/s/2shohl2zekvpe62/2871891.pdf?dl=0
I see
"Over Current Protection: >3.6A with auto-recovery function".

Does that imply that said recovery function is not working in this case?

From your description it sounded like it was working as designed: the
5V comes back when the load is removed.


--
Jasen.

 

[John S]

On 3/4/2020 10:03 AM, Terry Pinnell wrote:

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

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.

overcurrent... a fairly common problem when tyrying to run motors off
switching powersupplies.

adding large capacitors may help.

I have a couple of supercapacitors on order (from China, so maybe I'll
be waiting a long time) but as you see from my earlier post a 100,000uF
electrolytic didn't fix it.

100,000uF is .1F. If you use two of those supercaps in series, you'll
have 250F. That would be 2500 times more than the 100,000uF you tried. A
considerable difference.

However, equalizing the voltage across the series arrangement remains a
problem for you.

 

On Wednesday, 4 March 2020 15:58:27 UTC, Terry Pinnell wrote:

DemonicTubes <tlackie@gmail.com> wrote:

On Tuesday, March 3, 2020 at 2:14:00 PM UTC-7, Rick C wrote:
On Tuesday, March 3, 2020 at 3:40:56 PM UTC-5, DemonicTubes wrote:
On Tuesday, March 3, 2020 at 12:17:29 PM UTC-7, Rick C wrote:
On Tuesday, March 3, 2020 at 1:11:09 PM UTC-5, DemonicTubes wrote:
On Tuesday, March 3, 2020 at 9:53:11 AM UTC-7, Terry Pinnell wrote:
Terry Pinnell <me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.

Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK

Meant to add: while fiddling with this, tapping wires at various
intervals, there was just *one* instance when the motor *did* start
running at what appeared full speed. Spent another few minutes trying in
vain to reproduce that.

You could always try putting an NTC resistor in series as an inrush current limiter. Cheap, easy, probably works...why not?

Doesn't even need the temperature coefficient. The NiMH batteries power the motor at '3.8 to 4.1 V". This supply runs at 5 volts and he has not said anything about reducing that voltage that I saw. They guy is not very precise in his description of the circuit though. I don't know what he means by "ex-screwdriver 2.4 motor". Is that 2.4 volts? 2.4 amps? Maybe 2.4 revision???

Anyway, a quarter ohm or maybe a bit more resistance should be added between the motor input and the PSU output. That would drop the volt at full power. Or maybe use a smaller resistor (~0.1 ohm) and a diode drop. Or maybe two diode drops, one silicon and one Schottky plus optionally a tenth ohm resistor.

I'm not at all surprised he is getting an overload driving a 4 volt motor from a 5 volt supply.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

Certainly a normal resistor would most likely work. The reason I suggested an NTC ('thermistor' as they are commonly known) is to avoid wasting power. They are readily available and dirt cheap...of course if you don't have one on hand and need to get it working now, yeah just throw a low value resistor on there and go for it.

I'm sure you know all this, but this is for OP's benefit.

Those NTC thermistors are often called 'inrush current limiters'. They start out at a few ohms, but quickly drop to almost nothing after a moment of current flow.

Trouble is he needs to waste power anyway. He is mismatching a 5 volt supply to a 3.8-4.0 volt motor. So the NTC will only set him up for a future motor failure.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

Ah. Sorry, it wasn't clear to me that it is a 4 V motor. If that is the case, a proper supply is a better solution.

It's not, it's a 2.4 V ex-screwdriver motor, originally powered by two
1.2 V NiCads.

For the last 16 years, as I mentioned, it's been powered by three Nimh
batteries (C-type, not AA, another typo, sorry), "...delivering a
voltage of about 3.8 to 4.1 V...". A lower voltage of 2.5 V or so from
two such batteries delivers insufficient current to open and close the
quite heavy curtains. It's running well at present, closing smoothly in
just over 2 secs:
https://www.dropbox.com/s/b96xyihr4ustgjq/Curtains-1.mp4?raw=1
but I'd rather like battery independence.

Long ago I learnt that mains power was far more reliable than any battery. The ability to manually open & close will also be far more rleiable than any battery.

I've not measured anything but suspect the motor is likely drawing way above 4A for tiny fractions of time. A 2.4v screwdriver motor that self limited to 4A on 5v wouldn't be a lot of use.


NT

 

[Michael Terrell]

On Thursday, March 5, 2020 at 9:06:20 PM UTC-5, NT wrote:

Long ago I learnt that mains power was far more reliable than any battery. The ability to manually open & close will also be far more rleiable than any battery.

I've not measured anything but suspect the motor is likely drawing way above 4A for tiny fractions of time. A 2.4v screwdriver motor that self limited to 4A on 5v wouldn't be a lot of use.

Yes. That motor is an inductive load that takes more than the measured stall current to start.

 

[Jeroen Belleman]

Michael Terrell wrote:

On Thursday, March 5, 2020 at 9:06:20 PM UTC-5, NT wrote:

Long ago I learnt that mains power was far more reliable than any
battery. The ability to manually open & close will also be far more
rleiable than any battery.

I've not measured anything but suspect the motor is likely drawing way
above 4A for tiny fractions of time. A 2.4v screwdriver motor that
self limited to 4A on 5v wouldn't be a lot of use.

Yes. That motor is an inductive load that takes more than the measured
stall current to start.

I see DC motors as a big lossy *capacitive* load. Think about
it: Initially, it draws a large starting current, which then
progressively drops to more modest values when the motor
comes up to speed and develops a back-EMF. The EMF persists
when you disconnect, dropping exponentially as the loss
consumes the stored energy until the motor is stopped.

Jeroen Belleman

 

[Michael Terrell]

On Friday, March 6, 2020 at 2:36:11 AM UTC-5, Jeroen Belleman wrote:

Michael Terrell wrote:
On Thursday, March 5, 2020 at 9:06:20 PM UTC-5, NT wrote:

Long ago I learnt that mains power was far more reliable than any
battery. The ability to manually open & close will also be far more
rleiable than any battery.

I've not measured anything but suspect the motor is likely drawing way
above 4A for tiny fractions of time. A 2.4v screwdriver motor that
self limited to 4A on 5v wouldn't be a lot of use.

Yes. That motor is an inductive load that takes more than the measured
stall current to start.

I see DC motors as a big lossy *capacitive* load. Think about
it: Initially, it draws a large starting current, which then
progressively drops to more modest values when the motor
comes up to speed and develops a back-EMF. The EMF persists
when you disconnect, dropping exponentially as the loss
consumes the stored energy until the motor is stopped.

I've never seen a wire wound, Permanent Magnet capacitor.

 

[Jeroen Belleman]

Michael Terrell wrote:

On Friday, March 6, 2020 at 2:36:11 AM UTC-5, Jeroen Belleman wrote:
Michael Terrell wrote:
On Thursday, March 5, 2020 at 9:06:20 PM UTC-5, NT wrote:

Long ago I learnt that mains power was far more reliable than any
battery. The ability to manually open & close will also be far more
rleiable than any battery.

I've not measured anything but suspect the motor is likely drawing way
above 4A for tiny fractions of time. A 2.4v screwdriver motor that
self limited to 4A on 5v wouldn't be a lot of use.
Yes. That motor is an inductive load that takes more than the measured
stall current to start.
I see DC motors as a big lossy *capacitive* load. Think about
it: Initially, it draws a large starting current, which then
progressively drops to more modest values when the motor
comes up to speed and develops a back-EMF. The EMF persists
when you disconnect, dropping exponentially as the loss
consumes the stored energy until the motor is stopped.


I've never seen a wire wound, Permanent Magnet capacitor.

I suppose you can enlighten us with a reasoned discussion
on the apparent impedance of permanent magnet DC motors?

Jeroen Belleman

 

[Michael Terrell]

On Friday, March 6, 2020 at 5:36:36 AM UTC-5, Jeroen Belleman wrote:

Michael Terrell wrote:
On Friday, March 6, 2020 at 2:36:11 AM UTC-5, Jeroen Belleman wrote:
Michael Terrell wrote:
On Thursday, March 5, 2020 at 9:06:20 PM UTC-5, NT wrote:

Long ago I learnt that mains power was far more reliable than any
battery. The ability to manually open & close will also be far more
rleiable than any battery.

I've not measured anything but suspect the motor is likely drawing way
above 4A for tiny fractions of time. A 2.4v screwdriver motor that
self limited to 4A on 5v wouldn't be a lot of use.
Yes. That motor is an inductive load that takes more than the measured
stall current to start.
I see DC motors as a big lossy *capacitive* load. Think about
it: Initially, it draws a large starting current, which then
progressively drops to more modest values when the motor
comes up to speed and develops a back-EMF. The EMF persists
when you disconnect, dropping exponentially as the loss
consumes the stored energy until the motor is stopped.


I've never seen a wire wound, Permanent Magnet capacitor.

I suppose you can enlighten us with a reasoned discussion
on the apparent impedance of permanent magnet DC motors?

i shouldn't have to. You have to overcome the inductance to build the required magnetic field. Once the motor starts to turn, the commutator converts the DC input into a crude, chopped AC field that is required for the motor to continue to turn.

Now try to explain your capacitor theory.

 

[Jeroen Belleman]

Michael Terrell wrote:

On Friday, March 6, 2020 at 5:36:36 AM UTC-5, Jeroen Belleman wrote:
Michael Terrell wrote:
On Friday, March 6, 2020 at 2:36:11 AM UTC-5, Jeroen Belleman wrote:

Michael Terrell wrote:
On Thursday, March 5, 2020 at 9:06:20 PM UTC-5, NT wrote:

Long ago I learnt that mains power was far more reliable than
any battery. The ability to manually open & close will also be
far more rleiable than any battery.

I've not measured anything but suspect the motor is likely
drawing way above 4A for tiny fractions of time. A 2.4v
screwdriver motor that self limited to 4A on 5v wouldn't be a
lot of use.
Yes. That motor is an inductive load that takes more than the
measured stall current to start.
I see DC motors as a big lossy *capacitive* load. Think about it:
Initially, it draws a large starting current, which then
progressively drops to more modest values when the motor comes up
to speed and develops a back-EMF. The EMF persists when you
disconnect, dropping exponentially as the loss consumes the stored
energy until the motor is stopped.

I've never seen a wire wound, Permanent Magnet capacitor.
I suppose you can enlighten us with a reasoned discussion on the
apparent impedance of permanent magnet DC motors?



i shouldn't have to. You have to overcome the inductance to build the
required magnetic field. Once the motor starts to turn, the commutator
converts the DC input into a crude, chopped AC field that is required
for the motor to continue to turn.

Now try to explain your capacitor theory.

I already did, see above. You should read it. Now, I'll admit
that a DC motor isn't a pure capacitance. The equivalent
circuit might be a parallel RC in series with an inductance.
The capacitor models the back EMF and the energy stored in the
rotating mass. The resistor models the work that needs to
expended to keep the thing rotating. And yes, the inductance
models the rotor coil with its iron yoke. My point is that
this latter component isn't dominant, except maybe on single-
digit milli-second time scales or shorter.

Finer detail would add still more components. My model still
ignores rotor winding and commutator resistance, variable
reluctance effects, iron losses and magnetic saturation, to
name a few.

It's the parallel RC that largely dominates the impedance,
except at 'high' frequency. The meaning of 'high' depends on
the inertia of the motor and its load.

So again, even though a DC motor has coils, its dominant
impedance is a parallel RC. The often heard claim that
it's inductive is false.

Jeroen Belleman

 

[Phil Hobbs]

On 2020-03-06 05:13, Michael Terrell wrote:

On Friday, March 6, 2020 at 2:36:11 AM UTC-5, Jeroen Belleman wrote:
Michael Terrell wrote:
On Thursday, March 5, 2020 at 9:06:20 PM UTC-5, NT wrote:

Long ago I learnt that mains power was far more reliable than any
battery. The ability to manually open & close will also be far more
rleiable than any battery.

I've not measured anything but suspect the motor is likely drawing way
above 4A for tiny fractions of time. A 2.4v screwdriver motor that
self limited to 4A on 5v wouldn't be a lot of use.

Yes. That motor is an inductive load that takes more than the measured
stall current to start.

I see DC motors as a big lossy *capacitive* load. Think about
it: Initially, it draws a large starting current, which then
progressively drops to more modest values when the motor
comes up to speed and develops a back-EMF. The EMF persists
when you disconnect, dropping exponentially as the loss
consumes the stored energy until the motor is stopped.


I've never seen a wire wound, Permanent Magnet capacitor.

PM motors do look like very large capacitors at low frequency.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Jeroen Belleman]

George Herold wrote:

On Friday, March 6, 2020 at 8:04:09 AM UTC-5, Jeroen Belleman wrote:
[Snip!]

So again, even though a DC motor has coils, its dominant
impedance is a parallel RC. The often heard claim that
it's inductive is false.

Jeroen Belleman

That makes sense. So the 'capacitance' is the energy you have to
put into spinning up the rotor?

George H.

Yep! From the motor terminals, it looks like a large leaky
capacitor.

Jeroen Belleman

 

[George Herold]

On Friday, March 6, 2020 at 8:04:09 AM UTC-5, Jeroen Belleman wrote:

Michael Terrell wrote:
On Friday, March 6, 2020 at 5:36:36 AM UTC-5, Jeroen Belleman wrote:
Michael Terrell wrote:
On Friday, March 6, 2020 at 2:36:11 AM UTC-5, Jeroen Belleman wrote:

Michael Terrell wrote:
On Thursday, March 5, 2020 at 9:06:20 PM UTC-5, NT wrote:

Long ago I learnt that mains power was far more reliable than
any battery. The ability to manually open & close will also be
far more rleiable than any battery.

I've not measured anything but suspect the motor is likely
drawing way above 4A for tiny fractions of time. A 2.4v
screwdriver motor that self limited to 4A on 5v wouldn't be a
lot of use.
Yes. That motor is an inductive load that takes more than the
measured stall current to start.
I see DC motors as a big lossy *capacitive* load. Think about it:
Initially, it draws a large starting current, which then
progressively drops to more modest values when the motor comes up
to speed and develops a back-EMF. The EMF persists when you
disconnect, dropping exponentially as the loss consumes the stored
energy until the motor is stopped.

I've never seen a wire wound, Permanent Magnet capacitor.
I suppose you can enlighten us with a reasoned discussion on the
apparent impedance of permanent magnet DC motors?



i shouldn't have to. You have to overcome the inductance to build the
required magnetic field. Once the motor starts to turn, the commutator
converts the DC input into a crude, chopped AC field that is required
for the motor to continue to turn.

Now try to explain your capacitor theory.

I already did, see above. You should read it. Now, I'll admit
that a DC motor isn't a pure capacitance. The equivalent
circuit might be a parallel RC in series with an inductance.
The capacitor models the back EMF and the energy stored in the
rotating mass. The resistor models the work that needs to
expended to keep the thing rotating. And yes, the inductance
models the rotor coil with its iron yoke. My point is that
this latter component isn't dominant, except maybe on single-
digit milli-second time scales or shorter.

Finer detail would add still more components. My model still
ignores rotor winding and commutator resistance, variable
reluctance effects, iron losses and magnetic saturation, to
name a few.

It's the parallel RC that largely dominates the impedance,
except at 'high' frequency. The meaning of 'high' depends on
the inertia of the motor and its load.

So again, even though a DC motor has coils, its dominant
impedance is a parallel RC. The often heard claim that
it's inductive is false.

Jeroen Belleman

That makes sense. So the 'capacitance' is the energy you have to
put into spinning up the rotor?

George H.

 

On Fri, 06 Mar 2020 16:41:41 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:

George Herold wrote:
On Friday, March 6, 2020 at 8:04:09 AM UTC-5, Jeroen Belleman wrote:
[Snip!]

So again, even though a DC motor has coils, its dominant
impedance is a parallel RC. The often heard claim that
it's inductive is false.

Jeroen Belleman

That makes sense. So the 'capacitance' is the energy you have to
put into spinning up the rotor?

George H.

Yep! From the motor terminals, it looks like a large leaky
capacitor.

Jeroen Belleman

Really big energy storage applications use what are essentially DC
motor-generators instead of capacitors for storage. High-field
magnets, electromagnetic aircraft launchers, things like that.



--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"