Quote:
Originally Posted by lectruck
Is there any update on the Chargers progress, now that Ben is trying out the Cougar Controller in could come in handy?
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Sorry! I haven't had much time to update progress here. There has been some, but I've been hampered with little time to work on it. Also, I couldn't find an STK500 anywhere! Mouser had a new shipment at the end of April, so I figure I have some time to get this power-section working; Anyway, here's a quick synopsis of progress since my last post.
Apparently the input leads are the source of stray inductance. When I shortened the leads from the blue input caps to the mosfet/diode, the ringing went away and the voltage spike was limited to about 10V.
I then tried charging my EV pack and could only get to about 5A before the mosfet temp rose to 100C (just using a cheap IR thermometer).
I picked up a larger heatsink for $5 at the local surplus shop and got some weird clicking noises from the inductors. Turns out I had to electrically isolate the mosfet from the heatsink in addition to the diode. I had hoped to eliminate a source of thermal resistance...
With the larger heatsink I was able to get up to 15A and the mosfet rose to about 90C for a 65C rise above ambient. I blew up my mosfet driver though, or the gate resistor was too small. My driver was rated to 9A, but one Paul used was rated up to 14 so I ordered a few of those.
I'd like to get up to at least 20A, maybe 25A, and still have the temperature rise be about 60C above ambient. That way, the mosfet temp will stay around 100C on these hot summer days out here in AZ.
I'm sure I can do a better job of thermally attaching the components and figure out a fan arrangement to force more convection. Another option would be paralleling two mosfets to reduce the current through the device. I'm estimating about 57W of total heat generation with 1 mosfet and 44W with 2.
If you had a lower pack voltage and wanted to run strictly off 120V outlets, you could go with the 200V mosfet that Paul used which has lower on-resistance. However, with 240AC rectifying above 300VDC, you'd be close to 200V limit without a high voltage pack.
I could go with a fancier heatsink if i really needed to. I saw some computer CPU heatsink tests showing a fancy $40 heatpump type heatsink move 125W of heat while keeping the CPU to a cool 16C rise above ambient.
So, there's some things to try before the micro comes in at the end of the month. Hopefully it's ready to go by then and I can get right to the task of implementing the microcontroller.
Anyway, there's lotsa options, so I'll keep trying some things