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

[()blivion]

Hummmm.... Looks like the first resistor in that BOM is now back order. Might want to change that to something else if you want to get all your parts shipped right away.

 

[ronv]

The FETs I have are IRF4905's. I think they are 200 watts, but if your doing 12 volts max naybe not to bad.
I think I have about a tubes worth so we can figure out how many you need.
I think the BOM should update on your end as well as mine so you can just enter the number in the e-mail and it should be there.

 

[jocanon]

ronv, when you get a chance can you post the schematic again? I think we changed one of the resistors (to make it go to 60amps). Also, I am like 99.99% sure I already know the answer to this question...but this version can be run on 12v and 24v without a switch, correct?

edit: I see now, the only one that changed was R3 went to 68.1...that's also the one that's out of stock...I will see if I can find one that's in stock.

 

[()blivion]

this version can be run on 12v and 24v without a switch, correct?

Yes, it is a constant current design. This means that it will make it's self conduct more and more until the sense resistor output voltage matches the control voltage. So, no matter what the DUT is outputting voltage wise, the dummy load will draw whatever current you set it to.

 

[ronv]

$#%&*!

How can they have 12000 of 1 and 0 of another? Oh well.

Yes no switch needed as long as you have the separate 12 volt regulated supply for the op amps.

I updated the BOM and here is the latest schematic.

Remember.... No smoking.

 

[jocanon]

you beat me too it...I was going to ask if this one would work:
https://www.mouser.com/ProductDetai...=sGAEpiMZZMu61qfTUdNhG/DQawzJ6c7Ppn1fzrSBjd8=

I see that's what you updated the BOM to, so I take it that it does They appear to be the exact same resistor.

 

[jocanon]

Alright, any last minute tweaks? Otherwise I am clicking "buy".

 

[()blivion]

Remember.... No smoking.

Bomb? lol. Every time some one walks into my work space I get odd looks. Because, if there are wires and components scattered on your table, OF COURSE your OBVIOUSLY making improvised explosive devices to blow up the government with. I mean... what the hell else could you be doing?

I'm thinking of getting a bunch of crap to really scare people that walk in my house unannounced. Maybe some steal pipes and caps, some clocks, and a map of the US, and a bunch of red thumbtacks to put in the map, some news paper clippings of the current running politicians.

You know.... Normal every day electronics stuff.

Alright, any last minute tweaks? Otherwise I am clicking "buy".

None here.

 

[jocanon]

Order placed.

 

[jocanon]

()blivion, ronv, or anyone that knows, how complicated would it be to make it so that when I first plug in the PSU the fan goes on for a brief moment then goes back to the normal temperature controlled operation? If it is very simple I think it would be good to do, just so the user knows that it is on...if it is complicated then I don't even want to go there, I'll just leave it the way it is.

 

[()blivion]

In my temp controlled fan circuit, you can put a capacitor between the gate of the FET and the +12v line. 100uF is on full for about 1.5 seconds with my exact circuit and the pot in it's lowest setting and the NTC thermistor at it's coldest. Your mileage may vary.

 

[jocanon]

Awesome, thank ()blivion.

 

[()blivion]

NP.

I'm curious, when you get some time. Could you send me some pictures of your pipe, fittings, hose, and all that. I'm most interested in how your going to flatten your pipe and how big it is. Mine was quite small. Something like 1/4 or 1/2 inch copper propane line. Is this about the same as what you have? Also, what do you have for soldering and other tools and such? It would be nice to know exactly what you have to work with. If you do any kind of hobby RC flying, then I imagine you also do some building, and thus prolly have a shop of sorts. And you decided to take on this project, so you must have some kind of tools, I'm just wondering what.

You have to proceed in different directions depending on what your looking at if you want to end up at the same destination... you know what I mean?

 

[jocanon]

Like this?

 

[()blivion]

Yes

(more text in message so it is over the minimum length allowed -/)

 

[jocanon]

I went a little larger on the pipe, it's 3/4". I got a large C clap to bend it. I already did a little test bend to make sure it is strong enough. My soldering station is 60 watts. I got the torch to solder the copper pipe fittings.

 

[jocanon]

For conformal coating, I have some regular old polyurethane wood finish laying around. Could I get away with using the polyurethane (in pic), or should I spring for something more like this (in link):

https://www.galco.com/buy/Techspray/2103-12S

 

[()blivion]

I went a little larger on the pipe, it's 3/4". I got a large C clap to bend it. I already did a little test bend to make sure it is strong enough. My soldering station is 60 watts. I got the torch to solder the copper pipe fittings.

Good set up, your iron is better than my similar sized one. You may not want to use the torch for soldering the FET's to the pipe though. Ideally, you would use a large >100 Watt iron for doing things like stained glass work and such. It is going to take a lot of heat, but too much will destroy the FET's. You may be able to get away with using the torch if your good. It's not going to be easy though. You really can't heat the FET's for long. The data sheet will say how long and how hot the max is.

The pipe looks survivable. If it's too thin for how big around it is, it will end up buckling before it flattens out. I'm also thinking you may want to add some thing metal to the inside of the tube, something like the metal round scouring pads. This would be to give the metal more internal surface area and a better thermal interface with your water. But with as long as your pipe is, this will probably be unnecessary. If you do do this though, pack enough in to just start to slow the water, no more, no less. Too much and you risk forming a block if things shift around. Too little and there won't be enough pad and pressure to keep the pads in good thermal contact with the pipe, defeating the purpose.

For conformal coating, I have some regular old polyurethane wood finish laying around. Could I get away with using the polyurethane (in pic), or should I spring for something more like this (in link):

I have no idea how that stuff finishes, though it isn't critical. I'd say use what you got. It just needs to make a durable plastic coating over all your parts to keep water off. You're going to have to use your best judgment on whether that stuff will accomplish the goal or not.

 

[jocanon]

I was thinking I would use the torch just for soldering the iron fittings, but I was going to use the iron for the FET's. If it's not hot enough, I wonder if I could just tin the copper pipe using the torch and then solder the FET's onto it afterward with the iron?

Edit:
In order to get more area I was going to make a loop with the copper pipe. I would have the water enter one side of the loop and drain out the other. I was thinking I could put FET's on both sides of the loop to spread them out to help with cooling.

 

[()blivion]

I was thinking I would use the torch just for soldering the iron fittings, but I was going to use the iron for the FET's. If it's not hot enough, I wonder if I could just tin the copper pipe using the torch and then solder the FET's onto it afterward with the iron?

Your iron will not solder that pipe and FET's. The torch will, but it can easily over shoot the optimal temperature, which as I said can ruin your FET's. It can also oxidize your solder/pipe faster creating a barrier that will make things harder. Ton's of flux will help with the oxidizing problem. You're options are (1) get a larger iron. (2) Use the torch carefully with lot's of flux, possibly while measuring temperature. With the torch, you're going to need to put the pipes down on something fire proof, as well as heat insulating. With a heavy iron, the fire proof bit is largely unnecessary. I used the wood top of my bench with out problems. I could do it with a torch, but I have been soldering for 15~20 years. And I'm not saying I would enjoy it.

Edit:
In order to get more area I was going to make a loop with the copper pipe. I would have the water enter one side of the loop and drain out the other. I was thinking I could put FET's on both sides of the loop to spread them out to help with cooling.

Your way of getting area is fine. As I said, your exact construction methods depend entirely on what you have at your disposal.