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

[jocanon]

What would be nice would be to have two thermistors, one on each PSU, but still have the fans tied together such that they always operate at the same speed but take that speed from the thermistor that is the hottest at any given moment in time. That would be nice, but cost/time to make such a circuit would probably outweigh the benefit, unless it is a very easy thing to do.

 

[ronv]

Here is an amplifier. I used the LM358 cause I know you have some. It will only go to withing 1.5 volts of the positive supply so the maximum is 10.5 volts at about 50C. We can order one that is called rail to rail that will go all the way to 12 volts, but this will check things out.
So when you are testing it it should go from about 3.8 volts at room temperature to 10.5 volts when hot.

 

[ronv]

Each supply needs its own because 1 supply ground is 12 volts higher than the other one since they are in series.

 

[jocanon]

Ah, yes that it is true.

 

[jocanon]

R1 is the 10k thermistor, right?

 

[ronv]

R4 is the themistor.

 

[jocanon]

Nice, this circuit is solid! Works great I was so stoked it worked (and that I was able to read the schematic and put it together correctly ), that I forgot to write down the max voltage it got up to on pin 4...I think it was 11.27, whatever it was it got up to that and then stayed there, it was 11.something, at 47 amps. I am running it at 12 amps now and it seems to have stabilized at 7.21v on pin 4. I love it! It doesn't even waste any extra heat so I won't need to heat sink anything and no need to splice fan wires or make a 555 timer circuit and we still get the protection if the fan goes out that the PSU will shut down to save itself, nice work! OK maybe that is enough exlamantion points for one night . Now I just need to decide where for sure to put the thermistor. I think I am going to put it on the heat sink where I have always had it, it seems to work well there. That's where it is now.

 

[ronv]

Yes, this is a good solution. I like the fact there is no modification to the supply. Good job.

I would just make sure it is fully on at 47 amps.

 

[jocanon]

Oh, and interestingly, I still do get the ramp up in fan speed when I increase current even with this circuit going through the PSU's built in fan speed control pin, but it is very very slight, like you have to really pay attention to even know it's there.

 

[jocanon]

Yes, this is a good solution. I like the fact there is no modification to the supply. Good job.

Thanks, I really like that fact too, but you are the one that made the circuit, so good job to you and many thanks as well.

 

[ronv]

Keep in touch and post some pictures when you get the whole thing together.

Good job on Romney's taxes by the way. Just that one little deduction problem.

 

[jocanon]

Regarding Romney, thanks, I am an advocate for my client .

I will be posting pictures soon. I am going to start up a website soon as well. It will be www.solidhobby.com where I will be selling these (I will also be selling them on eBay, Amazon, RC Groups classifieds...). My website isn't up yet, that's the next project . So far I have my logo designed but that's about it. I am proud to say I designed it myself, I didn't pay anyone to design my logo. I have other things in the works but selling the PSUs is going to be the main thing for now, my other ideas require a little more capital. My goal is to raise money selling the PSUs to fund more projects in the future. I will keep you posted.

Do you have a good part recommendation for the rail to rail op-amp, or will any one do?

 

[jocanon]

I think we are almost done, but I still have a few questions. Here they are:

1. Need to find a good rail to rail op-amp to use instead of the LM358.
2. If I need to adjust the temperature range what part of the circuit should I tweak?
3. If I need to adjust the voltage on the op-amp output at room temperature which part of the circuit should I tweak?

 

[ronv]

1. Need to find a good rail to rail op-amp to use instead of the LM358.

They are a little hard to find that will run off 24 volts or more, but you can use the LT1636 from Digikey

2. If I need to adjust the temperature range what part of the circuit should I tweak?

R3 will adjust the range. A larger value will make the range smaller

3. If I need to adjust the voltage on the op-amp output at room temperature which part of the circuit should I tweak?

Easiest way would be to make R1 and R2 a pot with te wiper (center) to the op amp.

PS

If you are getting 11.27 out of the current op amp you won't benifit much for the extra $2 for the RtoR.

 

[jocanon]

Awesome, thanks ronv...btw, I put a plug in for you, ()blivion and electro tech here:

https://www.rcgroups.com/forums/showthread.php?t=1581061&page=42

 

[jocanon]

They are a little hard to find that will run off 24 volts or more, but you can use the LT1636 from Digikey.

You are probably right, because you usually are, but are you sure it needs to be 24v on the second supply in the series? I ask because when I check with my volt meter from the ground on the second supply to +Vcc on the second supply I only get 12 volts (the difference between the two). The only time I get a reading of 24v is if I take the reading from ground of the lower supply and +Vcc of the upper. But the temp control circuit will be connecting to ground of the upper and Vcc of the upper, not ground of the lower supply and Vcc of the upper.

 

[ronv]

Thanks Jer,

Your absolutely right, I'm still stuck back in the old one. Each of these guys lives in it own world with its own ground. That opens it up a little. One that I have used is the TS924 - good at 16 volts as I recall.

Your much to young to be bald, but if you want to practice you could make some little pc boards to sell to the guys at RC group. Small quantities are a bit expensive but you could put a lot of them on 1 fair sized board to get the price down.

I've used PC Express, it's a free download and you can get quotes easy.

 

[jocanon]

Yeah, that is what I am probably going to do. I want to sell the entire PSU with the circuit installed, but for those that already have the PSU I will offer them just the temperature control circuit on a PCB and put up short instructions on how to fit it on youtube most likely or just printed on paper.

So, I probably could control both fans off one circuit, question is do I want to? I think it would be fairly safe to do so. If I control both fans off one circuit I will only be getting temperature readings off the one supply, but I do not believe there is a very tight range that the fan speed has to operate, in other words, as long as the fan speed is fairly close to the speed it needs to be based on temperature I think it will be fine. I don't think it will matter if the two PSUs are slightly different temperatures. The only thing that does concern me a bit is that it's possible to put leads on the ground of the upper PSU's ground and Vcc and the lower at the same time such that you could get two 12 volt supplies or one 24 volt supply out of the same set up and somebody that has it set up this way could potentially only use the 12 volts from the upper and not the lower. Then if I have the thermister on the lower it will not speed up the fan when the upper heats up...so maybe it I should just have one for each unit. Possibly in the ones I sell I could have one for both and just not put a lead on the ground of the upper, if they want 12v they would have to connect to the lower. Any thoughts/opinions?

 

[jocanon]

...I've used PC Express, it's a free download and you can get quotes easy.

That's a good idea. I didn't think about that, I was just thinking of doing a homebrew job on a PCB, but a pc board woud probably be smaller and cleaner. I will have to look into price.

 

[ronv]

No, you can't use one for both. Each supply uses it's own ground as a reference point. So if you use supply 1 as the reference for the circuit the ground on supply 2 is 12 volts higher. It works ok with 2 circuits because each circuit uses the ground from the supply it is attached to.
So for the single scheme to work the minimum voltage for the first supply would be 4.65 but it would need to be 16.65 for the second supply since its ground is already at 12 volts. Not a very good explanation, but maybe it will help. Think of 2 batteries in series with the ground reference at the bottom (and the ground of the voltmeter)