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

[ronv]

Hope all is well. Parts are in the mail.

 

[jocanon]

How much current will the logic circuitry draw? I wonder if I will be able to power 2 12v fans with the smaller power supply that goes up to 1 amp. The fans draw .21 amps each max.

 

[ronv]

The logic won't take much (.01 A without the alarm) but the start up current on the fans will often be 4 or 5 times their running current. The supply may tolerate the short term overload.

 

[jocanon]

I may end up trying to power the fans from the logic supply then because I got the 24v fans in the mail yesterday and appearently my PSU is too high a voltage rating for them since the PSU is really more like 25 volts. The fans won't work. I can put a resistor in series and they will come on, but then it runs slower on 12v and I don't really want to have to use a switch to bypass the resistor when on 12v. I think I can find a good 12v 80mm fan.

 

[ronv]

Hmm. Seems strange they won't run on 25 volts.

 

[jocanon]

Yeah, it does seem strange, they just sputter for about 2 seconds then don't do anything at all.

 

[()blivion]

You can put several normal 1A diodes in line with the fans. Each one will drop the voltage the fans see by 0.6~0.8 volts. You'll need quite a lot to drop it far enough. Could also be line noise on the PSU though, caused by running them at such a low load condition. If you have something 24v that can draw ~2 amps, you may want to hook that up to the PSU to load it some, then hook up the fans and see if that fixes it. A good 12v lamp or two might work well.

 

[jocanon]

What if I just order another ac adapter that is 24v? I found one for only $6. I have enough room in the pc box to put a power strip that I can plug everything into. That way the fans will run consistently no matter why PSU I am testing, 12v or 24v, and I can put a household outlet on the outside of the box to plug the PSU into and put an on/off switch on the outside of the box as well that controls the power strip so I can turn everything on at the same time.

 

[ronv]

It needs to be a regulated supply. Can you post a link?
It will need some other changes for the reference voltage, LED and alarm as well.
My bet is () is right and your big supply just needs some load to stay on, but can't be sure.
How about 110 volt ac fans?

 

[jocanon]

I tried it with a load on it, not much of one though, and it did the same thing. Here's the link:

**broken link removed**

 

[jocanon]

I already purchased the 24v supply in the above link, so if there is a way to make it work great, if not, I'm only out $6.75.

 

[ronv]

Since you already have the 12 volt supply how about using the 24 volt one just to run the fans. Then you don't need to change any parts in the original design.

 

[jocanon]

Yep, that's what I was thinking. I wanted to use the 24v for the fans only. I don't want to change any parts in the original design. Do you think that 24v ac dc adapter will work for the fans only?

 

[ronv]

Should work fine.

 

[jocanon]

What is the best way to insulate the copper pipe from the metal case? I was looking at fish paper. I was also consider just building some sort of plywood frame around it, that might be cheaper. The only thing that concerns me is the heat. But since we are setting it up to shut down at 88 degrees Celsius, I don't think that is hot enough to set the wood on fire. Maybe I will just go with thin plywood.

 

[()blivion]

I would.....

(1) make it solid so nothing will move. One of the most important rules of building things to last is to secure every thing properly.
And
(2) cover the whole finished working project with conformal coating/varnish when we are done. This will stop most shorts from happening by it's self.

 

[jocanon]

Sounds good. So the alone will be enough? I guess that seems reasonable if it is solid it will most likely not touch the metal case anyway, and in the event it does the conformal coating will add some protection.

 

[jocanon]

I can put the coating on really thick...multiple coats. I have an air compressor to spray it on, left over from when I built a baby crib years ago.

 

[ronv]

They make plastic pipe clamps. That might be the ticket. Maybe Home Depot?

https://www.pexuniverse.com/store/category/plastic-pipe-clamps

They may relax a bit when they get hot so you still need to make sure they can't slip.

 

[jocanon]

Lol, when I first saw those I thought they $10.95 for 1! Yeah, that's $10.95 for 100. I think those will work, if I can't find them in lesser quantities I can just get 100 of them. I am thinking I will secure the copper pipe to the sides of the case with these. As far as the PCB I can build a little table for it out of plywood which I will screw down to the CD/DVD tray in the computer case. Then I will add little blocks of wood in the corners of the plywood table to mount the PCB too so it will be raised up a little from the plywood table to give room for the electircal components. Does this sound like a good idea?