Very hot rectifier

[Archangel]

Consider the fact the average electric blanket is around 25 watts . . .

[AvionicsMaster1]

Rambling a bit here but just some thoughts.

Well, your location says UK so I'm assuming 220 VAC 50 HZ. The datasheet only specs a 60 Hz curve but I doubt that is the source of your heat.

If I understand you correctly, your powering this rectifier by 12VAC input to the rectifier. I'm also assuming the output has twice the input frequency so it should be 100 Hz before capacitor smoothing. If the bridge rectifier is good you should have a doubling of the frequency. You could check that to make sure the rectifier is good.

I'd think anything metal would be a good enough heatsink for your current load. A small chunk of metal with a little transfer compound on it should work. I'm curious if that will do it.

[Charlie]

Rambling a bit here but just some thoughts.

Well, your location says UK so I'm assuming 220 VAC 50 HZ. The datasheet only specs a 60 Hz curve but I doubt that is the source of your heat.

If I understand you correctly, your powering this rectifier by 12VAC input to the rectifier. I'm also assuming the output has twice the input frequency so it should be 100 Hz before capacitor smoothing. If the bridge rectifier is good you should have a doubling of the frequency. You could check that to make sure the rectifier is good.

I'd think anything metal would be a good enough heatsink for your current load. A small chunk of metal with a little transfer compound on it should work. I'm curious if that will do it.

I'm not sure why you mention frequency. It has absolutely nothing to do with the problem. If the circuit (no schematic shared) is a full wave bridge rectifier, then at any point in time 2 of the 4 diodes will be conducting.(except for the very small time the AC is within 0.9V of 0V).
From the data sheet, at 5A the forward volt drop will be 0.9V.
2 elements are conducting, so 5A x (0.9 * 2) = 9 Watts being dissipated in a 1/2 cubic inch of material = very toasty. Hence the giant hole in the middle of the device for a #8 screw to bolt it tightly to a heat sink. How big of a heat sink? Work out the thermal impedance to ambient air. How do you do that? Click on the link in my previous post.

[AvionicsMaster1]

OK. Sorry for the ramble. Link appreciated.

[The Master]

Charlie:
Thanks for the datasheet. It looks a bit complicated though I might just have to join them to the biggest chunk of metal I can find. A fan might help too.

It does make sense that power devices will get hot and I wasn't expecting them to be completely cold but I just didn't expect this extreme heat from such a small percentage of it's capability. I've also used some of these same rectifiers in an audio circuit powering 30W speakers without them getting the slightest bit warm. Speakers don't draw constant though.


amgen:
The LEDs do use PWM which helps but they have the potential to be turned on full for long periods of time so that's my test condition.


Archangel:
I've never had an electric blanket but I do own a few smoke machines that are designed to heat up and are rated at 700-800W each and they don't seem that much hotter.


AvionicsMaster1
That's correct. 12VAC 50Hz into the rectifier and 100Hz out of it. I have 14 rectifiers running and they are all identical. I'd be really unlucky if all 14 were faulty.


Thanks everyone for your help. It's clear now that this temperature is normal and the largest heatsink I can fit in (and maybe fan) are needed.

I've attached a picture (from before the ABS melted) in case anyone is curious about the project