Electronics > Projects, Designs, and Technical Stuff
DC load using a CPU cooler
eneuro:
--- Quote from: Spikee on September 25, 2014, 10:36:53 am ---I have a top of the line soldering iron with around 240W of capacity (JBC) but the heatpipes of the cpu cooler are to good. After a fuckload of time the temperature only achieves around 60-80 deg C.
--- End quote ---
That is why I'd like to try spot weld mosfets TO220 tap in 3-4 spots to copper heatsink or flat heatpipe.
This should prevent cooling spot area, but of course high energy short pulses needed, so there will be no time to disipate heat.
Just wondering if 30A on spot welder trafo primary 230VAC, so close to 7kW will do the trick, while copper has quite low resistance, but cross section area of those spots will be much lower than transformer a few turns secondary, so maybe? >:D
Anyone tried this?
macboy:
--- Quote from: eneuro on September 27, 2014, 06:09:02 pm ---
--- Quote from: Spikee on September 25, 2014, 10:36:53 am ---I have a top of the line soldering iron with around 240W of capacity (JBC) but the heatpipes of the cpu cooler are to good. After a fuckload of time the temperature only achieves around 60-80 deg C.
--- End quote ---
That is why I'd like to try spot weld mosfets TO220 tap in 3-4 spots to copper heatsink or flat heatpipe.
This should prevent cooling spot area, but of course high energy short pulses needed, so there will be no time to disipate heat.
Just wondering if 30A on spot welder trafo primary 230VAC, so close to 7kW will do the trick, while copper has quite low resistance, but cross section area of those spots will be much lower than transformer a few turns secondary, so maybe? >:D
Anyone tried this?
--- End quote ---
Spot welding will give you a good (and irreversible) mechanical connection to the heatsink, but what about the thermal connection? You will still have air gaps in the imperfections between the device tab and the heatsink. A metal-air-metal thermal interface is very poor. The soldering technique provides a metal-metal-metal (tab-solder-heatsink) thermal interface, which is as close to ideal as you can practically get.
eneuro:
--- Quote from: macboy on September 29, 2014, 02:20:05 pm ---Spot welding will give you a good (and irreversible) mechanical connection to the heatsink, but what about the thermal connection? You will still have air gaps in the imperfections between the device tab and the heatsink.
--- End quote ---
Finally found tips how to spot weld those tabs ;)
How to Spot Weld Copper
--- Quote ---"Spot welding copper requires special electrodes and brazing paste in order to achieve the same sturdy welding job that can be more easily achieved with metals such as steel."
--- End quote ---
Extracted recipe from this link below:
--- Quote ---"Apply brazing paste in between the two points to which you will apply the electrodes of the spot welder."
"Lower the electrodes of your spot welder and pinch the two pieces of copper you will spot weld."
"Activate your spot welder for quick bursts, turning the welder off and removing the electrodes after each burst."
--- End quote ---
This is what I was thinking about and it looks like that Silver Solder Paste could be used for brazing copper like in this video using classic high power heater
I'd like to solder heatsink to tap using powerfull spot welder, while I do not like to put mosfets in high temperature stress when heater is used during assembly, so it is time to try those tricks above and see what happends if high energy short pulses will be apllied to TO220 mosfets taps :-/O
Note: Just checked SSQ-6 Silver Solder specs here http://muggyweld.com/ssq6-silver-solder-paste and it looks like it
--- Quote ---"Melts at 1050° F"
--- End quote ---
which means
1050ºF = 565ºC >:D
Maybe classic solder pase used in SMD assembling will be better for brazing copper to copper , but it is interesting to test spot weld copper to aluminium heatsink using this SSQ-6.
Joenuh:
@Microbug: Did you get a reply from ixys? Because I sent an email with a sample request yesterday and I already got a reply.
Also, are those ranges correct? I assume from the calculations that you are using a 4.096V Vref and a 16bit DAC? Wouldn't that give a lowest range of 62.5uA instead of 6.25uA? Or are you using a gain of 0.1, which would make no sense to me?
That resolution would be really hard to get I think, considering input offset voltage and stuff like that. I'm even in doubt about getting my (accurate) 1mA resolution with a shunt of 0.1 Ohm.
16bit DAC would be the way to go I think or would it be overkill and am I thinking to hard about this?
microbug:
I didn't get a reply from IXYS, I think the email might not have sent. I'll send another!
I'm now using a 12 bit DAC (you can have an external reference, and it's more accurate) with the REF2041, as suggested by timb. There is a mux which controls the range by connecting the appropriate resistor divider. Moe details to come later!
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