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GregH2 23rd August 2010 06:48 AM

Thermistor Selection
Hello all,

I am building an Aleph 3 for use in Australia (240v supply), and am trying to determine the correct thermistor to use for inrush current supression. I assume the lower average current draw from the 240v line makes the standard CL60 unsuitable. Can you guys give some advice on which model to use? A spec sheet can be seen here:

Using the specs from the Aleph 3 service manual, I see that the power consumption is 250w which means an average current draw of just over an amp.

I was thinking the CL130 might be a good candidate for my purposes given its 50 ohm initial resistance and 1.6 amp rating. However, I am not sure if my proposed 200 000uF of capacitance will be too much as I am not sure how to scale down the capacitance on the secondary side of the transformer.

Any advice would be appreciated.



Zen Mod 23rd August 2010 07:29 AM

simple as :

for 120V use one CL60

for 240V use two in series

GregH2 23rd August 2010 08:24 AM


Originally Posted by Zen Mod (
simple as :

for 120V use one CL60

for 240V use two in series

Thanks for your reply.

I would have thought this would be undesirable as in normal use the CL60s will be passing nowhere near their rated current and will hence be fairly resistive. Could you please explain your reasoning?

Zen Mod 23rd August 2010 08:54 AM

lets just say that Papa don't hesitate to use them that way , at least for my knowledge ( as part of soft start and mains voltage selection ) ;

I have few more logical reasons , but they're weaker as facts :rofl:

Melon Head 23rd August 2010 09:14 PM

If you look at any of the firstwatt user manuals it looks like Nelson is happy using one CL60 for 240V mains power.
So CL60 should be fine. As zenmod suggested, use 2 in series if 1 is not enough.
CL70 is another option that other people have used.

Zen Mod 23rd August 2010 10:00 PM

yup - you're right - I was obviously messed with memory :rofl:, and turned it around ;

still - nothing wrong with two CL60 in series , considering that amount of capacitance

GregH2 24th August 2010 11:11 AM

Actually, yes you are all right. The CL60 will only drop a volt or so under normal operation with my Aleph 3 and 240v. For some reason I thought it was a lot more. I'm an idiot.

Zen Mod 24th August 2010 12:01 PM


Originally Posted by swordfishy (
.... I'm an idiot.

welcome to the Club


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