Passive cooling PSU mod

Fuzzymuff · 5th December 2009, 05:40 PM

Hi, I've stripped a working PSU, (its spare and old), of its heat-sinks. As far as I can tell, my wiring is okay. I've extended the connections to all the mounted semiconductors and mounted on a huge heat-sink, and just in case the heat-sinks carried a connection from one side of the board to the other, I soldered a bridge wire in where the heat-sink mounting tabs were. I connected a cdrom drive and an old motherboard and plugged it in. Nothing! The CPU fan turns a little then stops. My DMM measured 3 volts on the 12 volt rail then 0 volts.

Does anyone know whats up with this?

Fuzzymuff

microsim444 · 5th December 2009, 06:40 PM

Quote:

Originally Posted by Fuzzymuff

Hi, I've stripped a working PSU, (its spare and old), of its heat-sinks. As far as I can tell, my wiring is okay. I've extended the connections to all the mounted semiconductors and mounted on a huge heat-sink, and just in case the heat-sinks carried a connection from one side of the board to the other, I soldered a bridge wire in where the heat-sink mounting tabs were. I connected a cdrom drive and an old motherboard and plugged it in. Nothing! The CPU fan turns a little then stops. My DMM measured 3 volts on the 12 volt rail then 0 volts.

Does anyone know whats up with this?

Fuzzymuff

I think you need to wrap it in foil, and plug it in

Fuzzymuff · 5th December 2009, 06:52 PM

Hey dude, how you goin? Ha ha, got that site up yet? We'z waitin!

godfrey · 6th December 2009, 12:13 AM

Hi Fuzzymuff

OK, I'll take a stab at this (since no-one else is).
Don't know too much about SMPS but:

1) The semiconductors you've put on the big heatsink probably need to be insulated from it (with mica washers or similar) otherwise those with metal cases or tabs will all be short-circuited through the heatsink.

2) SMPS normally use high-speed switching, so maybe it just can't work with long leads to the switching transistors due to wiring inductance etc.

Good luck - Godfrey

microsim444 · 6th December 2009, 12:50 PM

However, What are you trying to get from that kind of test?

5th December 2009, 05:40 PM	#1
Fuzzymuff diyAudio Member Join Date: Mar 2009	Passive cooling PSU mod Hi, I've stripped a working PSU, (its spare and old), of its heat-sinks. As far as I can tell, my wiring is okay. I've extended the connections to all the mounted semiconductors and mounted on a huge heat-sink, and just in case the heat-sinks carried a connection from one side of the board to the other, I soldered a bridge wire in where the heat-sink mounting tabs were. I connected a cdrom drive and an old motherboard and plugged it in. Nothing! The CPU fan turns a little then stops. My DMM measured 3 volts on the 12 volt rail then 0 volts. Does anyone know whats up with this? Fuzzymuff __________________ Wrap it in foil, and plug it in.

5th December 2009, 06:52 PM	#3
Fuzzymuff diyAudio Member Join Date: Mar 2009	Hey dude, how you goin? Ha ha, got that site up yet? We'z waitin! __________________ Wrap it in foil, and plug it in.

6th December 2009, 12:50 PM	#5
microsim444 Account Disabled Join Date: Oct 2008	Helo However, What are you trying to get from that kind of test?

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6th December 2009, 12:13 AM	#4
godfrey diyAudio Member Join Date: Nov 2009 Location: Cape Town	Hi Fuzzymuff OK, I'll take a stab at this (since no-one else is). Don't know too much about SMPS but: 1) The semiconductors you've put on the big heatsink probably need to be insulated from it (with mica washers or similar) otherwise those with metal cases or tabs will all be short-circuited through the heatsink. 2) SMPS normally use high-speed switching, so maybe it just can't work with long leads to the switching transistors due to wiring inductance etc. Good luck - Godfrey

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