Using a 12V 2A power supply direct and with 3V voltage divid

[Tim Wescott]

On Thu, 26 Feb 2015 17:19:18 -0800, S Keith wrote:

On Thursday, February 26, 2015 at 4:28:35 PM UTC-7, Phil Allison wrote:
S Keith wrote:


Thanks John G. While my ignorance is vast, I know V=IR. I need to
supply 3V, 2mA

** You are being far to literal.

3V at 2mA MEANS with a voltage supply of 3V, the LOAD draws 2mA.


I have a 12V PWM controlled fan.
I don't know anything other than it takes 12V ~1.6A


** That is a very big PWM fan.

High time you supplied a link to the thing.


to run it and a 3V, 2mA signal to activate it.


** PWM fans normally require a PWM signal to control them.

You are contradicting yourself not making sense.


If I could link it for you, I would know more about it. It's the
cooling fan for a Honda Civic Hybrid battery pack.


** Figured it was something weird and automotive.

How do you know it is a PWM fan ??


I "discovered" that I can activate the fan with a multimeter that
puts out a 3V, 2mA current.


** OK - so we FINALLY get to know where your 3V, 2mA nonsense came
from.

The spec sheet for a DMM.

And it does not mean what you assume.


I wish to duplicate this to drive the fan as I thought it would be a
simple solution compared to figuring out how to supply a PWM signal.

** You do not know what is needed.

So neither do we.


.... Phil

Phil,

Since you're clearly not willing to read what I write as evidenced by
your response (I said nothing of any DMM spec sheet), I'm going to
disregard any of your future responses.

I'm not sure what you're getting from your participation in a group
labeled "basics". You remind me of why I stopped using Usenet back in
the day (started in the late 80s).

Simply put, you're an arrogant asshole. I've seen it time and time again
in dozens of groups covering as many topics. Take comfort in your false
sense of superiority. I'm far kinder to those ignorant of my areas of
expertise.

Steve, an essential USENET skill (any-"NET" for that matter) is to just
ignore the trolls. Phil oscillates between being a valuable resource on
audio circuits and an incensed troll. No amount of talk will get him down
from the trees when he's chosen to go there, so you need to just ignore
him. Or bait him on purpose, if it makes you feel better. But trust me
-- many people have tried talking sense to him, and all it does is get him
worked up.

He's:

--> very trustworthy on audio stuff

--> less reliable on regulatory and "that'll burn your house down" stuff

--> not at all reliable when you can tell that there's spittle hitting
the computer screen.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[Ralph Mowery]

"S Keith" <stkeith11@gmail.com> wrote in message
news:f88b0198-af48-4502-9d2a-aa6a8095b8ec@googlegroups.com...
,

I'm trying to understand PWM, and your questions are a bit confusing.
Based on what I've read about how >computer PWM fans work, they "pulse" a
current (around 3-5V and <5ma). When that pulse is active, it applies >12V
to the fan motor. When there is no pulse, there is 0V at the motor. The
voltage of the PWM signal doesn't >vary as part of the fan speed control,
just the duration of the pulse within the cycle.

The pulse occurs at a nominal frequency of 25kHz. For the sake of argument,
if the pulse width duration is 10ms, >and the pulse is active for 7 of
those 10 ms, the fan is at 70% duty cycle (analogous to 70% speed).

..I believe what I have done is inadvertently applied a 100% duty cycle PWM
signal with 3V and 2mA, so I >suspect the fan is running at 100%. I will try
to confirm this over the weekend. Where my logic fails is at the >second
setting of much lower voltage and current. If my understanding of PWM is
accurate, I would expect it to >shut off if the current is too weak rather
than decrease speed.

Am I totally confused?

Thanks,

Steve

I don't know the setup of your motor, but I was thinking that the supply is
the 12 volts and the lead with the 3 volts on it is the speed determing
wire. With a constant voltage on it,it is running full speed as it is a
'pulse' of 100 % . If you fed that wire some pulses then the speed would
change. Just a guess.

When meters are fed pulses they can show many differant voltages depending
on the meter. Most will try and average them. Some will try to show a
true RMS value. Often depends if an analog or digital meter.

 

[Phil Allison]

Shithead Keith wrote:

Indeed, why is he here ?

** Why are YOU here ???

Your idiot Q is way off topic, it's got nothing to do with "basic electronics" and is not answerable.

Only one explanation is possible - you are here to amuse yourself and that means you are TROLLING.

What you don't have the brains to see is the ONLY person currently on this NG who is NOT trolling is me.



..... Phil

 

[Tim Wescott]

On Thu, 26 Feb 2015 06:39:34 -0800, S Keith wrote:

On Wednesday, February 25, 2015 at 10:15:00 PM UTC-7, Phil Allison
wrote:
S Keith wrote:


Thanks John G. While my ignorance is vast, I know V=IR. I need to
supply 3V, 2mA

** You are being far to literal.

3V at 2mA MEANS with a voltage supply of 3V, the LOAD draws 2mA.


I have a 12V PWM controlled fan.
I don't know anything other than it takes 12V ~1.6A


** That is a very big PWM fan.

High time you supplied a link to the thing.


to run it and a 3V, 2mA signal to activate it.


** PWM fans normally require a PWM signal to control them.

You are contradicting yourself not making sense.


... Phil

If I could link it for you, I would know more about it. It's the
cooling fan for a Honda Civic Hybrid battery pack. It's a "squirrel
cage" blower type fan. It blows air into the trunk thereby creating a
vacuum in the sealed case, which then draws cabin air in through the
battery pack and the related electronics.

I "discovered" that I can activate the fan with a multimeter that puts
out a 3V, 2mA current. I wish to duplicate this to drive the fan as I
thought it would be a simple solution compared to figuring out how to
supply a PWM signal.

As has been expressed to you before, nothing can, always and
simultaneously, put out a given voltage at a given current, because the
current at any given voltage (or voltage at any given current) depends on
the load, not the source.

So in the context that you quote it, your "3V, 2mA output" is completely
meaningless. Something else is happening, and I suspect that you want to
know what that is.

I do not know the components involved or their limitations. I only know
the "experimental" input and outcome.

From elsewhere I know that you learned the "3V, 2mA" figure from a meter
data sheet. Here are some observations:

1: That's a data sheet. Data sheets lie on rare occasions, commonly
obfuscate, and are often not written to be easy to understand for
the general public. So you don't want to trust your reading of one
unless it's been a close reading, and you're firm in your knowledge
of the subject.

2: You've been assured that it's physically impossible by more than
one person, the majority of whom have been calm and helpful about
it.

3: A common practice, when one runs into questions on a data sheet, is
to MEASURE. Get another meter (or two), and measure the voltage
on the "3V, 2mA" input, and measure its current, too, if that floats
your boat.

4: Just because it works with 3V (or whatever) on the control input
doesn't mean that it won't suffer long-term damage. Your best bet
would be to measure what's going on at that input when the thing is
in a car, working. If you can get access to a car (even a junker)
and MEASURE, you'll know way better. It could be that the input is
supposed to be 12V, or 5V, or something, and that 3V just barely
turns it on, and leaves it sputtering on and off. It could be that
3V is exactly right -- you don't know.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[amdx]

On 2/27/2015 1:20 PM, S Keith wrote:

Mikek,

I'm trying to understand PWM, and your questions are a bit confusing. Based on what I've read about how computer PWM fans work,

they "pulse" a current (around 3-5V and <5ma). When that pulse is
active, it applies 12V to the fan motor.

When there is no pulse, there is 0V at the motor. The voltage of the
PWM signal doesn't vary as part of the fan speed control,

just the duration of the pulse within the cycle.

The pulse occurs at a nominal frequency of 25kHz. For the sake of argument, if the pulse width duration is 10ms, and the

pulse is active for 7 of those 10 ms, the fan is at 70% duty cycle
(analogous to 70% speed).

I believe what I have done is inadvertently applied a 100% duty cycle PWM signal with 3V and 2mA, so I suspect the fan

is running at 100%. I will try to confirm this over the weekend. Where
my logic fails is at the second setting of much

lower voltage and current. If my understanding of PWM is accurate, I
would expect it to shut off if the current is too weak rather than
decrease speed.

Am I totally confused?

Thanks,

Steve

Hi Steve,
I'm far from an expert, and Google can be your friend.
I don't have any knowledge about computer fan PWM.
That said; The voltage to the motor is a DC pulse and that
can range form 0% to 100% duty cycle (or close). The pulse length is
controlled by an input. Depending on the circuit that input could be 0
to 0.1 volt, 0 to 5 volts, 0 to 10 volts and probably even 4 to 20ma to
adjust the pulse width from 0 to 100% duty cycle.

************************************************
So, the input is a DC level, the output is a pulse whose width is
proportional to the DC level on the input. As I know it.
********************************************************
I was a bit confused by the picture, but it is possible all that
electronic circuit is internal to that.

Mikek


---
This email has been checked for viruses by Avast antivirus software.
http://www.avast.com

 

[ehsjr]

On 2/27/2015 5:51 PM, S Keith wrote:

On Friday, February 27, 2015 at 1:23:41 PM UTC-7, Tim Wescott wrote:
As has been expressed to you before, nothing can, always and
simultaneously, put out a given voltage at a given current, because the
current at any given voltage (or voltage at any given current) depends on
the load, not the source.

I see contradiction in your statement. The VR suggested early in the thread puts out 3V/100mA (max).

There is NO contradiction in Tim's statement.

And the 2950 VR would work fine for you, assuming that the 3V 2mA
figure you measured was accurate. The 100mA current that the VR
is CAPABLE of providing is NOT what it will provide to your load.
At 3 volts, it will provide 2mA to your load - again, assuming
your measurements are correct. With a fixed voltage supply, it
is your load that determines how much current flows.

Add an LED in series with a 100 ohm resistor from the 3V output
of the supply to ground, so that when you switch the supply on
to activate the fan the LED acts as an on/off indicator.

Ed

<snip>

 

[Frnak McKenney]

On Fri, 27 Feb 2015 12:44:05 -0800 (PST), whit3rd <whit3rd@gmail.com> wrote:

On Wednesday, February 25, 2015 at 6:59:28 PM UTC-8, S Keith wrote:

I have a 12V PWM controlled fan. I don't know anything other than it
takes 12V ~1.6A to run it and a 3V, 2mA signal to activate it. I'm
trying to accomplish this. If I supply a higher current, I am
concerned I might damage something.

If the fan is on a fused automotive circuit, and you're bypassing that
power source, you might want to insert a similar fuse in your
'alternate' power connection. As for the 'signal to activate', that
sounds like it might be TTL logic (and that means we cannot be sure
that it sinks 2 mA; it could as easily SOURCE 2 mA, the polarity DOES
matter).

If the fan runs when the signal is at +3V, and does NOT run when the
signal pin is left open, and does NOT run when the signal pin is
grounded, then probably that signal pin has a pulldown resistor and
runs on 3V logic. The "PWM" feature could be implemented by putting a
variable duty cycle onto the signal pin, i.e. constant 3V drive makes
the motor run full speed.

A two-resistor voltage divider, output 3V and impedance about 100 ohms,
would be suitable to arrange this ( +12V<--->360 ohms<--->120
ohms<--->GND). If the 12V source is not regulated, some provision to
prevent overvoltage events on the logic signal pin is recommended.
Automotive +12 power is allowed to have occasional 60V spikes... a fan
doesn't usually care, but logic inputs will.

Is it possible that the OP's "motor" has an inboard transistor/FET?

You all piqued my curiosity, and I had DuckDuckGo do a quick search on
"computer fan 12V pwm speed control circuit". This turned up a circuit
based on the Micrel MIC502 "Fan Management IC" (yup, they have a
"hardware app" for that!):

PWM Fan controller
http://www.bit-tech.net/modding/2001/12/03/pwm_fan_controller/1

What's interesting is that this chip produces (at Vdd=12V) 3.75V PWM
pulses out, intended to drive a transistor controlling a motor. There's
also a "brother" chip, the MIC5021, which does a similar job and assumes
it's driving a MOSFET controlling a motor.

Does this shed any light on the subject?


Frank McKenney
--
...ecause his martyrdom is thus a power to the martyr, modern
people think that any one who makes himself slightly uncomfortable
in public will immediately be uproariously popular. ... The
assumption is that if you show your sincerity (or even your
political ambition) by being a nuisance to yourself as well as to
other people, you will have the strength of the great saints who
passed through the fire.
-- G.K. Chesterton: The Modern Martyr (1908)
--
Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney aatt mindspring ddoott com

 

[S Keith]

Upon taking the fan out of the car, I discovered a few things.

1) Multimeter signal did squat.
2) PWM is +12V potential
3) grounding PWM w/ 0-~5kOhms will cause the fan to run but "pulse" every few seconds, turning itself on and off. >5kOhms = nothing. At the higher resistances, the fan cycles faster and draws less current over a narrow range, probably less than 2kOhms.

So I was totally on the wrong track.

Thanks to everyone for their help.

Steve

 

[amdx]

On 3/1/2015 8:43 AM, S Keith wrote:

Upon taking the fan out of the car, I discovered a few things.

1) Multimeter signal did squat.
2) PWM is +12V potential
3) grounding PWM w/ 0-~5kOhms will cause the fan to run but "pulse" every few seconds, turning itself on and off. >5kOhms = nothing. At the higher resistances, the fan cycles faster and draws less current over a narrow range, probably less than 2kOhms.

So I was totally on the wrong track.

Thanks to everyone for their help.

Steve

Sorry, But I don't know what to make of that, but I don't know that
understand your statements either.

> 1) Multimeter signal did squat.

I don't understand, in car it did cause the motor to spin, out of car
it didn't?

> 2) PWM is +12V potential

Meaning you measured 12V on the positive lead of the motor?
There is a good explanation for that, but I need to know exactly where
you leads were placed for the measurement.
I grabbed the first site I saw, please view the first schematic drawing,
the circuit on the left side. You can see that if you measured from the
positive of the motor to ground, you would get 12V, with motor running
or not.
http://www.precisionmicrodrives.com/application-notes-technical-guides/application-bulletins/ab-001-discrete-driver-circuits-for-vibration-motors

3) grounding PWM w/ 0-~5kOhms will cause the fan to run but "pulse"
every few seconds, turning itself on and off. >5kOhms = nothing. At
the higher resistances, the fan cycles faster and draws less current
over a narrow range, probably less than 2kOhms.

Are you saying you can't get the motor to run at full speed out of the
car?

Hope that helps,
Mikek

 

[amdx]

Hi Keith,
You sounded like you might have been exasperated in your last post,
I know the feeling.
Here's some info about PWM that may help.

Here's a video showing the output wave form.
https://www.youtube.com/watch?v=IESHN5i-OFI

Here's a PWM circuit I have built, I used it to control a motor for
winding a Tesla coil.
It uses a common LM324.

http://www.pcsilencioso.com/cpemma/pwm.html

Then there is the 555 timer ic.
Google will deliver thousands of pages about 555 PWM circuits.

Here's one with some explanation of the 555 to help with the
understanding.

http://www.dprg.org/tutorials/2005-11a/


Mikek

 

[Phil Allison]

Shithead Keith wrote:

Upon taking the fan out of the car, I discovered a few things.

1) Multimeter signal did squat.
2) PWM is +12V potential
3) grounding PWM w/ 0-~5kOhms will cause the fan to run but "pulse" every few seconds, turning itself on and off. >5kOhms = nothing. At the higher resistances, the fan cycles faster and draws less current over a narrow range, probably less than 2kOhms.

So I was totally on the wrong track.

** Alouette, gentille alouette,

Alouette, je te plumerai.




.... Phil