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Why are my volt regs so hot?

Simple question:

I am drawing next to nothing from my volt regs and they continue to get hot! I have tried 3 different regulators, a 7805, one with a 3A output and now, one with a 5A output. I have my meter between the battery and the input of the volt reg and I am drawing less than 1/2A ( 440mA to be exact). Even at this level, the heatsink gets too hot to touch.

The current regulator is this one however,  I can't stress enough, I have had the same results with 3 different (brand new) regs.

Is this some kinda ground loop? Maybe the fact that there are 3.3v regulators down the line? I just did a major wiring clean-up and everything is super tidy... I got nuthin' here.

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440mA * 7V = ~3 Watts

While 3 watts is not enough to get something to melt it is probably enough to get it fairly hot especially if not ventilated...

I preffer swichmode even if they are expensive.

I agree with Antonio, because of the voltage drop you are generating about 3W. Your regulators are most likely in TO-220 packages which can handle about 2W maximum at which point you will be at about 150 degrees celcius. Either add a bigger heatsink or go switchmode which will also increase your battery life between recharges.

Heya Chris,

I would try two things, first, do a static test of just the reg to see if it gets hot while not hooked up to anything. I haven't tried hooking up a 5vreg to 12v but I'm a bit surprised that it would get so hot just with 12->5. Sounds like a possible short to me in a way, so I'd double check things.

Second thing I'd try is stepping down in levels, go to a 9v reg, then a 5v reg....or maybe use a switching reg?

12v SLA so really, about 12.5v or so.

Fun reading, this data sheet is... I just read this:

Thermal Design
The AP1086 incorporates an internal thermal shutdown that protects the device when the junction temperature
exceeds the maximum allowable junction temperature. Although this device can operate with junction
temperatures in the range of 150oC, it is recommended that the selected heat sink be chosen such that during
maximum continuous load operation the junction temperature is kept below the temperature.

Do you know what 150C is? It is 302 degrees!! Really?!!? 302 degrees is an acceptable operating temp, it seems. Maybe it IS just the fact that I am burning off 7 volts off of the 12v. Maybe I should just double the heatsink, give this guy some room to breathe and forget about it. Everything seems to be working A-ok, I just don't like hot things. I wish I knew how to do the math on how to figure watts etc. --then I could calculate how hot it SHOULD be. The data sheet has information on that. Hmmm...


What voltage are you feeding the regulator? You know the more voltage it has to drop the more heat it has to dissipate.