Mosfet Transistor N-channel Getting Hot, What Should I Do?

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rs14smith

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I'm currently building a solar tracker and have MOSFETs (IRF510) in my circuit, and everything works the way I want it to, however, two of my MOSFETs are getting extremly hot after the gate gets the signal to start turning the motor a certain way.

I have 4 MOSFETs total, so 2 get the signal, and the other 2 provide enough current to power my motor, but I wont go into detail unless you guys need it.

My main question is, do MOSFETs normally get hot, and if so, what can I do to help it not overheat, as I've basically fried 2 already? I think too much current or something is going through them when they switch on.

Thanks!
 
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Your FETs may not be turning on enough causing them to drop too much voltage and thus generate heat. Post a schematic of your circuit.
 
I was thinking of using a resistor to stop so much current flowing into the MOSFET but I don't think I'll have enough current to power the motor then. Are there other FETs similar to mine that I can purchase that can handle more current/voltage?

Here is the schematic: https://i48.tinypic.com/mr8lu9.jpg (image stretched the page so there is the direct link)
 
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The IRF510 has an on resistance of 0.6Ω @Id=2A when the gate voltage is 10V. Not a very good FET as modern FETs go. The circuit you posted can apply at most about 5V to the gate. No wonder it is getting hot.
 
MikeMl said:
The IRF510 has an on resistance of 0.6Ω @Id=2A when the gate voltage is 10V. Not a very good FET as modern FETs go. The circuit you posted can apply at most about 5V to the gate. No wonder it is getting hot.
Click to expand...

Hmm, so what do you suggest I do, just get a FET that allows more current to flow or?

Like my OP AMP doesn't put out enough current to make my motor run, so that's why I had to use FETs to help supply enough current. When looking at my digital multimeter, when my power supply is at 7v, my FET is pushing out almost 2A, but only 709mV.
 
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MikeMl said:
Are the FETs mounted on a heatsink? If so how big?
Click to expand...

Nope, and that's something else I was wondering about as I'm still a little new to FETs.
Do you think that would fix the problem I'm having, and if so, where do you purchase heat sinks for the type of FETs I'm using?

Thanks for the help so far!
 
If you raised the voltage to around 18V on pin 4 of the LM324 and left the 7V on the drain of Q1 & Q2 there would be enough gate voltage. But the shoot through current issue would remain. Shoot through current will happen because the OpAmp outputs take time to go from 0V to 16V and back again. That means that there will be a "short time" (pun intended) when both Q1 and Q4 are on at the same time. Same goes for Q2 and Q3.
EDIT: Q3 & Q4 are drawn with their source and drain terminal backwards.
 
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Measure the Drain to Source Voltage, multiply by the current. 0.7V*2A is 1.4W, which if not mounted on a heatsink, will make the FET too hot to touch. You need a large slab (6"x6") of aluminum to mount all four transistors. Could be smaller if it were finned. You will need the special mica insulator, Teflon bushing, spring washer to mount the TO220 to the aluminum heatsink (DigiKey "TO220 mounting kit").
 
Just get a better FET. The one you have now is crap. A better FET will likely not even need a heatsink.

Also raising the voltage would help. 7V is a little low, 10V would be better.
 
speakerguy79 said:
Just get a better FET. The one you have now is crap. A better FET will likely not even need a heatsink.

Also raising the voltage would help. 7V is a little low, 10V would be better.
Click to expand...

Yeah, regarding the 7V, the reason I have it set to that now is because if I raise it higher, I risk frying those 2 front MOSFETs again because too much current is going through them.

But I agree, getting a better FET probably is better, but sorry, could you recommend me one, as RadioShack only seems to have the one there in the schematic, so I'm wondering if I were to order one online, what exactly am I looking for to know if it's better or not?
 
Check your circuit! As drawn it won't work no matter which FET you use. Q3's and Q4's Drain/Source terminals are backwards and their body diodes will short the current from Q1 and Q2 to ground!
 
Hmm what about one like this: Jameco Electronics ICs & Semiconductors: INTERNATIONAL RECTIFIER: IRFZ44NPBF

It says it's max is 55V and 49A. lol I'll never go over that.
However, for my circuit to work correctly, will I have to make other changes because I'm using a FET that allows more Volts and Amps, like, will I have to push more voltage into the Gate for the FET to work correctly? Or is it as easy as just taking the others out and putting the one in the link in?

Thanks
 
kchriste said:
Check your circuit! As drawn it won't work no matter which FET you use. Q3's and Q4's Drain/Source terminals are backwards and their body diodes will short the current from Q1 and Q2 to ground!
Click to expand...

Hmmm maybe that's why I'm having this heat issue? lol I'll try that and see what happens.
 
Another thing. For Q1 and Q2. You are getting body effect over there, try to ger P-Channel mosfets to do that job.
 
Alright, I've made those changes to what I believe you all were saying was wrong, however, it's still putting out a crap load of Amps, and a small amount of volts, so why does the direction matter if you get the same results? I'm sure there is a reason.

https://i45.tinypic.com/fyj0nc.jpg
 
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Young man:

1st. We are not saying anything wrong.
2nd. To use an ammeter, you use it in SERIES, not in PARALLEL.
3rd. Direction DOES matter. Current flows from DRAIN to SOURCE. If you wire it wrong way = SHORT CIRCUIT, because you forward bias the FET's internal protection diode.
 
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