Maintain current

[stevo11]

ty for the info

[ridelong]

Ok, I need some help
I built this thing, everything was working perfect. I was able to adjust it to 20 amps, then the amperage just started droping for no reason. The max I can get now is about 16 amps. I checked the generator and it is still capable of pulling 40 amps.
What happened?

Keith,

What power source are you using? Could the voltage be dropping?

Measure the source voltage and the voltage delivered to the gen. If they are very close to the same, the pwm is running full on , and the pwm can't regulate. This could be because the gen impedence has increased for some reason.

I noticed that when the gen impedence decreases (electrolyte heats up), the circuit will actually back the current down a little, but not drastically

[stevo11]

third attemp with failure... I hook the pwm to a battery charger at 12vdc with a car light attached in place of a cell. at 10 amps the lamp is barely orange not even glowing, when i turn the pot nothing happens. at 50 amps the lamp is only a little bit more orange but still not glowing, when i turn the pot nothing happens. I will post some detail pitcture of both sides of the pwm tomorrow. maybe someone will see the problem.



Stevo

[Keith's Garage]

Ok, now I have a new problem. When I finally got the PWM installed on a vehicle, the heat from the FET got so high that the solder started to melt. And now the PWM wont regulate the amperage.
First, how are you guys keeping the heat down
Second, what do you think burnt up?

[donnylynn]

I assume you mean the solder on the FET. If you got hot enough to melt the solder, then you probably burned up the FET. Was it mounted to a heat sink? What is the part number of the FET?

[ridelong]

Keith's Garage,

Make sure you have the correct schematic!

My first pencil drawing had a mistake on it. I have since fixed the pencil drawing, but the guy who drew it with a layout program never fixed his.

The mistake WILL MAKE THE FET OVERHEAT and probably toasted the fet. The fet will get only mildly warm at 14 amps with the listed heatsink and no fan if the circuit is operating correctly.

Here is the correct schematic:

www.mikecramer.com/images/ifeedpwm.jpg

[stevo11]

I dont know if it matters but my pwm regulatesthe amps at 3.3 wether its on 10 amp or 50 amp. i just can not adjust it up or down.

Can anyone post detail pics of there pwm both sides?

Stevo

[stevo11]

I am posting how the layout of the pcb board with the components placed in specific areas. I am not an EE so i just named most of the stuff R. one of my questions is are R9 and R4 in the proper positions. I also conected all the unused pins in LM339 and brought them to a ground. Does the pot need to be wired in any way in particular? TY for all the support for a nub.



Stevo

[sp1r0]

I am posting how the layout of the pcb board with the components placed in specific areas. I am not an EE so i just named most of the stuff R. one of my questions is are R9 and R4 in the proper positions. I also conected all the unused pins in LM339 and brought them to a ground. Does the pot need to be wired in any way in particular? TY for all the support for a nub.



Stevo

not bad for a n00b, not bad at all. I double and triple checked your layout, everything is correct, except you have no power going to your lm339. Here's what it should look like...

Just to be clear here, your PCB layout is on top of the pcb, that is, you should mount and solder the parts right on the etched (top) part of the board according to your pcb layout. If you wanted to mount the parts on top of the board and solder underneath, like most hobbyists do, you will have to mirror the image.

[sp1r0]

Actually if you want to get technical, ridelong says to ground all unused inputs of the lm339, just good practice, creates less noise in the circuit. Good luck. I hope it works for you!

Note: Do not connect the outputs to ground or you may damage the lm339!
P.S., I've not built this circuit yet, just going from ridelong's latest schematic and stevo11's pcb layout.