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

[jocanon]

Oh, I hooked up the pot wrong. I'll fix it and see what I get on pin 3

 

[jocanon]

Ok pin 3 is adjustable between 0 and .8

 

[ronv]

Cool, so see if tou can find a 10 ohm resistor to repace the .13. Once you have done that you should be able to adjust the FET side of the 10 ohm resistor between 0 and .8 as well. And you are home free.
jocanon, I'm sorry but I have to go. Will be back in a few hours, but I think you are ok now.

 

[jocanon]

Cool thx...found the resistor... Will test and let you know.

 

[jocanon]

It's working! Thanks guys! Not done yet, but we got the main part of it working. I am going to work on it some more tomorrow hopefully. We are getting very busy at work right now ramping up to the 9-15 extended corp tax return filing deadline, but this is also a priority for me as I need to start selling off some inventory that is just cluttering up my basement right now, so I will have to find some time to work on this. Thanks again ronv & ()blivion!

So to sum up, my problem was that I didn't have the grounds of the smaller and larger supplies connected. Also, I had the pot wired incorrectly. Once I fixed those two things it worked. I still need to test it out up to 5.5+ amps per FET with the .13 ohm resistor and heat sink, but with the 10 ohm resistor the load is adjustable between 0 and about .08 amps.

 

[()blivion]

Good to hear you got a test unit working. It ALWAYS takes some playing with and rearranging at first, just stick with it when it happens. And when you have tough problems, let us know just like you did. The battle is not over just yet, you have longer to go still and will more than likely break some parts on the way, it's virtually inevitable with high power projects. Just know that you will be joining the club.

 

[jocanon]

Thanks ()blivion. Yeah, I know there's still a ways to go, but it sure is nice to at least get past that first hurdle.

 

[ronv]

1 watt down 1200 to go!

 

[jocanon]

1 watt down 1200 to go!

Lol yes.

 

[()blivion]

So... you still alive jocanon? I would hate for you ta have electrocuted yourself or something....

 

[jocanon]

Still alive and well it's been a crazy week at work, but I did manage to squeeze a couple hours in last night on the project. I got the copper pipe cut and planned out how I am going to install it, I also did some work on the case by putting a piece of wood in it which I will be able to mount the PCB to.

 

[ronv]

Gotta get Romney's taxes done.

 

[jocanon]

right, right

 

[jocanon]

I've been reading about grouding and wondering if I should connect my metal case to ground? Would that prevent any potential electrocution if some wire got shorted out to the metal case? I have to admit, I am a little confused by this. I was thinking I wanted to keep the case insulated from every part of the electical wiring, including the ground wire, but now I am wondering if I got it wrong and I should actually connect the case to ground.

 

[()blivion]

Not 100% sure what the best thing to do would be. I have found ground to be more of a health hazard to me than it is a safety feature. Electricity needs a complete circuit to conduct, and grounded cases make for a nice other half of that circuit when you happen touch a live wire. It's just one more wire that can kill you IMHO. The worst times I have been shocked were to ground, so I learned to disconnect it when servicing stuff. They also don't have breakers on ground, neither does neutral. So if neutral is not tied to ground... but somehow has voltage potential to ground, *POOF*... fire. Safer to use a plastic case and no ground, but then I'm just ranting at the state of system now.

All things being equal, I'm not an expert on "To ground or not to ground?" I would ignore my ranting and raving and ground the case of the project to earth ground if you can. Best practice I'm told.

IF YOU DIE, NOT MY FAULT. BUT I WILL BE VERY SORRY

 

[jocanon]

I think I actually understand your rantings, to be honest, I had the same thought about the whole "complete circuit to conduct...". I did want a plastic non-conductive case as well, but went with the larger one instead. On the upside, one thing I have notices is the metal computer case has a decent conformal coating already on it because when I checked with my meter, the outside of the case is non-conductive.

 

[ronv]

The low voltage stuff (24 volts) won't shock you cause the voltage is to low, bur the 110 volts comming is will, so the case is usuall grounded to earth ground (green wire) so that if the line voltage is shorted to the case the breaker blows.

The thing you need to watch out for is getting a ring or a watch across the big 24 volt supply. You can get a nasty burn from the heat generated,

 

[jocanon]

...The thing you need to watch out for is getting a ring or a watch across the big 24 volt supply. You can get a nasty burn from the heat generated,

Are you referring to like if I were to short out the electrical connections inside the load bank, i.e. on the PCB where the 24v is flowing, with a ring or watch or anything metal? I guess I am just trying to understand, you don't mean that there is any risk of this on once the project is complete and the case is screwed shut, right? Unless of course I were to short the leads of the DUT.

 

[ronv]

Right. The risk is from the big supply. Imagine your ring in place of the .13 ohm resistor that burned.

 

[jocanon]

right, I could see how that might hurt a little