Driver heat. Why?

[Machinist Joe]

Hello guys. I am powering a 445 with a 1.3A jib drive I bought off a member here. I am using the case pin for the v- supply. The laser works, and it works well, but after about 15 seconds, the driver gets too hot to touch... Why is this? I have tested it with two different drivers. I am powering them from 2 18350s in a guidesman host.

 

[Sigurthr]

Because you're pumping 1.3A through tiny PCB traces, components, and wires? All electronics have less than 100% efficiency, and losses are almost always turned in to either noise or heat (if not both). 2x Li-Ion = 8.4V top voltage x 1.3A (lets assume it is unrealistically efficient, there will actually be more draw from the batteries) = 10.92W of heat the components need to dissipate. IIRC the Easy Bake oven runs off a 10W bulb. Make sense now?

 

[Machinist Joe]

Really? I thought I read somewhere that these didn't really need heatsinking. But too hot to touch after 15 seconds, I didn't think that was normal...

 

[Sigurthr]

I don't know the specifics of the Jib driver, but even a buck driver will need heatsinking at ~11W input.

 

[Machinist Joe]

Well, my thermal adhesive is drying right now. I will get back with the results after its dried. Thanks for your help.

 

[Sigurthr]

Anytime, good luck with the build! Always better to have unnecessary heatsinking than insufficient heatsinking.

 

[Machinist Joe]

Ok, I added some heatsinking, but it is still getting pretty darn hot. Is it supposed to be like this? Does it get hot and stay there or does it keep on getting hotter and hotter?

 

[Sigurthr]

What size heatsink are you using? Is it a host heatsink or lab heatsink or generic electronics heatsink? Define hot (~90F, 100F, >110F)? How long did it take to get hot?

 

[Machinist Joe]

I broke some fins off of a computer heatsink. Its not big, but I would expect its enough. I don't know how hot, too hot to touch, and only about 20 seconds... Maybe I got a freak LD with a really low voltage.

 

[Sigurthr]

It is possible you have an inefficient LD, they certainly do exist. We get spoiled by all of Lazeerer, DTR, RHD, etc seeing all these 2W builds, there are a lot of meh diodes out there. Diode efficiency won't cause your driver to overheat though. I trust the diode is pressed in to a rather large heatsink or in a module inside a rather large heatsink, right?

How big of a fin? Normally a driver's heatsink isn't much bigger than the stick on chipset heatsinks, maybe 1/2" by 1" by 3/32" or so.

Again, I'm not familiar with the Jib driver, but if the laser is lasing fine and the driver's pumping out heat, it could just be an inefficient driver, and will need hefty heatsinking. I pretty much stick to LDO Linears and Flexdrives.