Thermistor Location for F5 power supply

calvinhpk · 21st August 2009, 08:32 AM

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?

max426 · 21st August 2009, 11:50 AM

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

nsklavos · 21st August 2009, 02:55 PM

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.

glaieuldeboua · 21st August 2009, 09:11 PM

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

Am I right on this one???

Renron · 22nd August 2009, 01:31 AM

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

calvinhpk · 22nd August 2009, 03:41 AM

thanks for the reply, understood

toufu · 23rd August 2009, 11:15 PM

Quote:

Originally Posted by max426

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...

njgale · 19th May 2010, 08:52 PM

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)

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

mymindinside · 19th May 2010, 09:27 PM

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

njgale · 19th May 2010, 10:05 PM

link's broken, hopefully this works

21st August 2009, 08:32 AM	#1
calvinhpk diyAudio Member Join Date: Oct 2004 Location: Kuala Lumpur	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?

21st August 2009, 09:11 PM	#4
glaieuldeboua diyAudio Member Join Date: Nov 2005	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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21st August 2009, 02:55 PM	#3
nsklavos diyAudio Member Join Date: Feb 2007 Location: California	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.

22nd August 2009, 03:41 AM	#6
calvinhpk diyAudio Member Join Date: Oct 2004 Location: Kuala Lumpur	thanks for the reply, understood

19th May 2010, 08:52 PM	#8
njgale diyAudio Member Join Date: Feb 2009 Location: Reading	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) 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

19th May 2010, 09:27 PM	#9
mymindinside diyAudio Member Join Date: Jun 2007 Location: Mumbai/Delhi - India	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

19th May 2010, 10:05 PM	#10
njgale diyAudio Member Join Date: Feb 2009 Location: Reading	link's broken, hopefully this works

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