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Old 26th March 2010, 09:01 AM   #1
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Default How to control the cooling fan ... ?

Hi folks,
donīt know who else could give solid tips when not YOU ...

My problem: I am using a Nemic Lambda SMPS 32 V / 10 A with very pleased
results but the cooling fan works everytime. At lower listening levels its really disturbing. Either it should be cut off or replaced by a temperature regulated cooling fan. But how ... ?

I see two possible reactions of the SMPS when the fan is cut off :
1) the SMPS doesnīt work from the beginning because itīs monitored
2) the SMPS shuts down after a specific temperature

The amp has about 2 x 40 Watts (max. power)

I can upload pictures if someone wants make a look. Any suggestions ... ?
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Old 26th March 2010, 06:37 PM   #2
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I do not know about Nemic Lambda SMPS 32 V / 10 A. But if you want to make your power supply temperature dependent, you can do that by using current source IC... ie LM234... as a temp sensor to drive an opamp then some leftover output transistor to drive a cooling fan. You might want to keep Vs of fan circuit close to fan's rated voltage in case of output transistor failure. Hope this help
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Old 26th March 2010, 10:53 PM   #3
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Being a PIC man I would use a PIC with a thermistor into an A2D convert for temperature sense. I would use a PWM output into a driver transistor.
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Old 26th March 2010, 11:09 PM   #4
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Elliot Sound Products (Sydney Australia) have a diy thermo controlled fan design.

Punch "Elliot Sound Products" into Google and look for Project Number 42.

That might be useful. Cheers Jonathan
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Last edited by Jonathan Bright; 26th March 2010 at 11:17 PM.
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Old 27th March 2010, 02:05 PM   #5
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Thanks much to all. As I am a newbee and need really solid help from experienced diy people I offer you some pics. God damnn - whatīs that. Is this the reason why I am listening to better audio level ??

Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.

Maybe soemone identifies the fan supplier and the shematic of the SMPS. Itīs really
complicated for me, an I donīt want make bad and dangerous things.

Last edited by TheDealer; 27th March 2010 at 02:05 PM. Reason: pics
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Old 30th March 2010, 04:33 AM   #6
star882 is offline star882  United States
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A friend of mine is working on a 12-15v, 35A digitally programmable power supply for a small DC power system. At light load, the fans would use enough power to significantly decrease efficiency. To solve that problem, his current solution is a circuit that only turns on the fans at load. One fan on above about 5A, speed controlled by temperature, both fans on maximum above about 20A. The second fan will also turn on at maximum if the first fan fails to provide a watchdog signal for some redundancy.
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Old 6th April 2010, 04:44 AM   #7
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That fan looks like a 120v fan, you can't really properly slow it down. It looks very noisey, I have one similar.

You might want to make a small low-voltage circuits of sorts and replace that fan with a PC fan,

You can get PC fans with temp probes and speed controls.
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Old 6th April 2010, 05:11 AM   #8
col is offline col  Australia
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I had a similar problem on a Nemic-Lambda 24v 340W SMPS. The fan was 12v still far to noisy. I removed it and placed 2 x12v in series which span slower and was a lot quieter. With heavy loads the thermal cutout used to flip though. You should be able to see the thermal switch next to one of the transistors on the heatsink. Ended up replacing it with a Meanwell which has a thermally regulated fan.

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