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Old 11th May 2011, 10:58 PM   #1
WSJ is offline WSJ  United States
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Default 12V to ±32V 180W SMPS

I bough two 180W, 12V to ±32V Power Supply Boards listed on eBay. One for $29 with shipping.
One powered up OK with no load, but the other one smoked as soon as I applied 12 V to the input terminals. The 12 V power supply was set to 2 amps current limit and the input voltage dropped to 4 V. The TL494 was very hot, so I need to get it out and check the drivers and FET’s. I charged the output caps to check for shorts, 3,300uF @ 35 V. I could send it back to Hong Kong for $10 postage, but that wouldn’t be any fun.

180W DC12V to DC±32V Boost Power Supply Board Kit 1PC | eBay
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Old 11th May 2011, 11:16 PM   #2
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I have one of those too. The output isn't regulated and it's closer to +/-36V when in a running vehicle.

Sorry, no clue where to start to help you out.
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Old 12th May 2011, 12:25 AM   #3
ppia600 is offline ppia600  United States
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Did you have the transistors sinked, could they have overheated quickly or maybe they were just bad already. Either way, there aren't many parts to replace if you have to. :lol: Amazing what you can buy on fleabay.
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Old 12th May 2011, 12:32 AM   #4
WSJ is offline WSJ  United States
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Quote:
Originally Posted by ppia600 View Post
Did you have the transistors sinked, could they have overheated quickly or maybe they were just bad already. Either way, there aren't many parts to replace if you have to. :lol: Amazing what you can buy on fleabay.
No load and no heat sink, the first one worked fine and nothing got hot.
I pulled the TL494 and the 12 V current is now 6 mA. I pulled primary windings and replaced them with 12 V lights. I will bias each FET pair on one at a time. I have an old board with a TL494, but no new ones.

Last edited by WSJ; 12th May 2011 at 12:34 AM. Reason: Added heat sink info.
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Old 12th May 2011, 01:17 AM   #5
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Confirm that you have ~5v DC on the gate pads of the FETs. Also confirm that the gate resistors are within tolerance.
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Old 12th May 2011, 01:30 AM   #6
WSJ is offline WSJ  United States
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Quote:
Originally Posted by Perry Babin View Post
Confirm that you have ~5v DC on the gate pads of the FETs. Also confirm that the gate resistors are within tolerance.
I pulled 2 FET's and 1 PNP on one side, all three are bad. The other side witches the lamp OK without the TL494 installed. I will get a socket installed and a TL494.
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Old 12th May 2011, 01:41 AM   #7
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You can rule out overheating as the culprit. I've had mine running a small load 24 hours a day for over 6 months now without a heatsink. I'm only pulling a few watts from it, but the FETs aren't even warm.
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Old 12th May 2011, 06:48 AM   #8
luka is offline luka  Slovenia
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always with this kinda kits, measure if there is short on the input right out of the box, check if everything is soldered on ok and if nothing has broken off... current limited supply is always good
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Old 13th May 2011, 06:25 PM   #9
WSJ is offline WSJ  United States
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I received the parts to repair board #2, with new FET’s, TL494, PNP driver and diode it’s working. When I applied a load to board #1, I found it also had a problem, see pic for CE short of the PNP driver. This means neither board was tested at the factory with a load.


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Old 13th May 2011, 07:14 PM   #10
luka is offline luka  Slovenia
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low cost = low testing, which would mean that you should be happy it even powered up once
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