Help with PSU (Temp control fan, load bank, & PWM circuit)

[jocanon]

The voltage is 9.3v on the fan plug when the fans are running at full speed.

I forgot one other thing, when I originally had the temp controll circuit in the fan plug instead of the 12v rail, it made a strange high pitch noise when the fans were slowing down. I can't remember how slow they had to start going to make that noise, maybe if it was below 5.33 volts I could just keep them there and use that plug power. There is definitely a benefit to being able to just splice into that plug and not needing the 555 timer, I will not be able to let the fans stall going that route. There is a fan speed control pin (pin 4) that MAY be able to let me adjust the voltage above 9.3v, I don't really know how to use it though. Everyone using these either has the fans slowed to standby speed, 4.6v or at 9.3v, nobody that I have ever heard of has tried to speed te fans up above the default 9.3v.

 

[jocanon]

Maybe the key is figuring out how to use the existing fan speed control pin and incorporate a temperature sensor into it. I would need some help with that though because its a bit if a mystery to me. Here is all I know about it...if you short it to ground (pin 4 is the fan control pin and pin 8 is ground) then it slows the fan to 4.6v, standby speed. So there should be a way to make a variable resistance circuit based on temperature that goes between pins 4 and 8, right? Then I would need no 555 timer and the fans would never stall.

Edit:

If I use the pins to control the fan speed, resistance between pins 6 & 8 would have to INCREASE as temperature rises which is opposite from what we have been doing, right now the resistance in the thermistor goes down as temp goes up, but this would need to be the opposite as shorting pins 6 & 8 decreases fan speed, putting resistance between these pins would increase fan speed. As a reference point, someone in the rc forum said putting a 12k resistor between 6 & 8 made the fan go about half speed.

 

[jocanon]

Post 568 in below link has a description of what each pin does:

https://www.rcgroups.com/forums/showthread.php?t=1581061&page=38#post22479278

 

[ronv]

That would for sure be the cleanest way to do it.

Only one thing bothers me:

4 ............ 3 .......................... Fan speed, ground for minimum speed. (For variable speed use ~4.6v to Vcc.)

If ground is minimu speed I'm not sure what 4.6 volts does unless anything under 4.6 is minimum speed.

I'm assuming Vcc is 12 volts, but it could be one of the other voltages or an internal supply.

So a couple of things to carefully try.

If the pin is grounded will the supply still start up?

Can you measure the voltage on pin 4 when the fan is at full speed. This should give us a minimum and maximum voltage for the pin.
We can probably go from there.

 

[jocanon]

I can answer the first one, if the pin is grounded then yes, the supply does start up with 12.5v.

How should I take the measurment voltage on pin 4, would it be touching pin 4 with one lead of volt meter and the other lead of volt meter to ground when pin 4 is not shorted to ground (so the fan is on full)?

I am not really sure what he means by "For variable speed use ~4.6v to Vcc" either. I do know from my previous measurements that the voltage going through the fan when pin 4 is shorted to ground is 4.6v. So maybe he is jsut saying that the fan can be adjusted between 4.6v and 12v. If it's important I can always jump over to the other forum and ask him for clearification, but I think we already knew that it could be adjusted between these amounts.

 

[ronv]

I must have missed your earlier posts. But is sounds like we need to shoot for the 4.6 to 9.3. Easy enough. The only unanswerd question is will the supply start with the pin grounded?

 

[jocanon]

...The only unanswerd question is will the supply start with the pin grounded?

I think we were posting at the same time again, yes the supply does start with the pin shorted to ground.

 

[ronv]

Yes, same time. Anyway I think we are home free.

Yes you can measure with ground of the voltmeter on the ground of the supply and the red on pin 4.

Are you where you can do a couple more experiments? This will either be really easy or just a little harder.

If you have a selection of resistors you can try several between pin 4 and ground. Start with say about 100k and then cut the value in half (or whatever you have handy). With each resistor measure the voltage at pin 4 and across the fan.

 

[jocanon]

I am at my day job right now (doing tax returns in between reading posts...) I can check that tonight when I get home first thing.

 

[ronv]

OK... Just so we are on the same page. My guess is that there is a resistor in the PSU that pulls pin 4 up to +12. The question is what size resistor do we need to make it go down to 4.6 volts. If the resistor is very large we an put the thermistor to +12 and a 47K resistor from the themistor to ground. As the themistor heats up the voltage will go higher making the fan run faster. But, if the resistor is small we will have to use an op amp to "make" it go to 4.6 volts when cold. By changinf the resitors we can get an idea of the size of the internal resistor.

 

[jocanon]

Sounds good. I will get right on it when I get home in about 2 and a half hours from now.

 

[jocanon]

...My guess is that there is a resistor in the PSU that pulls pin 4 up to +12...

Can you elaborate a little on this for me, the newbie here, I thought a resistor decreases current/voltage, but you are saying a resistor to pull up to +12v, are you saying the internal resistor is actually causing the voltage on pin 4 to increase?

Edit:

I see:

https://en.wikipedia.org/wiki/Pull-up_resistor

 

[ronv]

Yes, similar to the picture. So with no input the fan runs fast, with it grounded it runs slow.
I may be a couple of hours later than you getting back.

 

[jocanon]

I may be a couple of hours later than you getting back.

Not a problem at all...thanks for the help!

 

[jocanon]

OK, here we go:

Key: resistor value/voltage from pin 4 to ground/voltage running across fan

•no resistor/11.6/9.6 (this reading is slightly different than before, but I trust this one more because I checked and rechecked it)

•pin 4 fully shorted to ground/0/4.65 (this reading is slightly different than before, but I trust this one more because I checked and rechecked it)

•100K/10.5/8.9

•68K/10.06/8.59

•47K/9.52/8.2

•22K/7.93/7.12

•10K/5.79/5.56

•2.2/2.6mv/4.66

Note that the fan does even go faster, if I touch pin 4 with my finger the speed goes up faster than 9.6v but I don't think we need to speed it up faster than that. Most people use these with pin 4 open or shorted to ground, like I mentioned before, I have never heard of anyone speeding the fan up beyond 9.6v. If you think about it, the PSU will not be used to its full capacity for a very long time, if it ever even is at all because the way lipo chargers work is they start out at at a lot of current then taper off to nil as the batteries approach full charge. I charged 6 lipos in parallel and it only drew about 35amps at 24v at the peak (which I know is a lot, but not the max that the PSU is capable of with its rated max at 47 amps).

 

[ronv]

To cool.
Let me see if I can find a thermistor to match that curve. If not we will need to build an amplifier for the one you have.

 

[jocanon]

Awesome, thanks ronv!

 

[ronv]

I think we need an amp, but still easier than all that other "stuff". Back in a few with a schematic.

 

[jocanon]

Sounds good.

 

[jocanon]

Will it still work to use one amp and thermistor for two fans on 24v, or will they each need their own?