It's true that the resistance of inrush current limiters varies with
the load, but the time constant is long, 30 seconds or longer, for the
resistance to return to the initial cold value. They work fine for HV
power supplies in CW or SSB applications, and in AM modulstors.
73,
Jim w8zr
Sent from my iPhone
> On Feb 2, 2016, at 8:19 AM, Conrad PA5Y <g0ruz@g0ruz.com> wrote:
>
> Yes for the heater transformer I will leave them in but for the HV supply I
> am uncomfortable with them. The resistance varies with load so how can this
> be good for anode supply regulation? The parts for a GM3SEK style soft start
> using Omron GL7 25 amp relays arrived from Farnell Electronics this morning.
> I will shunt the thermistors after 1 second or so.
>
> Regards Conrad PA5Y
>
>> On 29 January 2016 10:35:58 CET, Branko <branko.cehner@guest.arnes.si> wrote:
>> Hi,
>>
>> I think NTC's are the simpliest solution for providing soft start. I
>> use
>> them in the tube heating power supplay on the secondary of transformer
>> as
>> the heating current is 3 to 4 A. For higher heating current it is wise
>> to
>> put them on the primary side of heater transformer
>>
>> Yes they getting hot, but they provide current limiting to the heater
>> filnament of the tube which is well advised for QRO tubes.
>>
>> Best regards, Branko, S52V
>>
>> -----Original Message-----
>> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Conrad
>> PA5Y
>> Sent: Thursday, January 28, 2016 2:22 PM
>> To: amps@contesting.com
>> Subject: [Amps] NTC thermistors as soft start
>>
>> 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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>> Amps@contesting.com
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