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Old 21st August 2009, 08:32 AM   #1
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Default Thermistor Location for F5 power supply

Where do you mount the thermistors (both at transformer and at GND)?
Mount them close to heatsink/body of amp or near the transformer?
Any pics of it?
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Old 21st August 2009, 11:50 AM   #2
max426 is offline max426  United States
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This is how i have done it. However I am a rookie at this so I would like to see other comments from experienced builders.
jim
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Old 21st August 2009, 02:55 PM   #3
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The power supply thermistors are not used for temperature sensing but for inrush current suppression. They limit surge current when powering up the amplifier by functioning as a power resistor which drops from a high cold resistance to a low hot resistance when heated by the current flowing through them. They do not need to be close to a source of heat.
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Old 21st August 2009, 09:11 PM   #4
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Default Inrush current

If I am using a soft start circuit, I guess I will not need the Inrush Current Limiter?

Am I right on this one???
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Old 22nd August 2009, 01:31 AM   #5
Renron is offline Renron  United States
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I used this schematic, I wish I could give credit to whom it belongs. (I think it was Papa's from the F3 power supply) I just copied it. You are correct, if you have a different soft start circuit, you do not need the Themistors (in the startup circuitry).

Ron
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Old 22nd August 2009, 03:41 AM   #6
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thanks for the reply, understood
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Old 23rd August 2009, 11:15 PM   #7
toufu is online now toufu  United States
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Quote:
Originally Posted by max426 View Post
This is how i have done it. However I am a rookie at this so I would like to see other comments from experienced builders.
jim
Thanks for that picture, Max, I think I am going to copy your design...
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Old 19th May 2010, 08:52 PM   #8
njgale is offline njgale  England
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Additional question wrt thermistor and 240v transformer.

The PSU pic in the F5 doc that refers to 240v shows a dual 120v primary
(top part of pic)

Click the image to open in full size.

If I only have a single 240v primary, is my alternate position correct (bottom part of pic) or am I going for a Darwin award?

tia for any life saving comments anyone would like to offer, else I guess I'll find out when I power the PSU part up tomorrow ;-)

cheers
Nick
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Old 19th May 2010, 09:27 PM   #9
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This is how i have done it in my F2 clone. However i am concerned that 10 Ohms series resistance does not reduce the inrush current enough. With a 240v supply and 10 Ohms series resistance (ignoring the resistance of the primary winding for now) the inrush current is 24 Amps. i am using a 625VA toroid and when i checked the resistance across the primary winding including the series CL60 thermistor it measured 14 Ohms. Is there a better way to measure the series resistance of the primary winding?
I'd like to hear some experienced voices on this issue... is a single CL60 enough with a 240V supply?

Cheers,
mymindinside
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Old 19th May 2010, 10:05 PM   #10
njgale is offline njgale  England
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link's broken, hopefully this works

Click the image to open in full size.
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