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[Amps] NTC thermistors as soft start

To: amps@contesting.com
Subject: [Amps] NTC thermistors as soft start
From: Conrad PA5Y <g0ruz@g0ruz.com>
Date: Thu, 28 Jan 2016 14:22:12 +0100
List-post: <amps@contesting.com">mailto:amps@contesting.com>
I have just acquired a GS35B PSU. It is 3 phase and the schematics show 3 x NTC 
thermistors in series with each primary. I presume that these are some kind of 
soft start. I am not familiar with these devices but they make me 
uncomfortable, I have always used a series resistor that is shunted by a relay 
after a few seconds in the past. I do not have the model number of the devices 
used as I will need to open the PSU to find out what they are but I assume that 
they are similar to this device. 

http://www.ametherm.com/datasheetspdf/MS325R020.pdf

The resistance varies depending on the load current and they get hot in order 
to operate, this really puts me off. They have quite a long time constant so I 
am uneasy about them altogether. 

Should I be concerned and replacing them with a soft start for each phase? 

Apart from that the PSU is very nicely made and will provide up to 1.6A@ 3600V. 

Regards 

Conrad PA5Y 
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