inrush current

[doktor]

Anyone familiar with inrush current limiters. They seem to work much like a thermistor, changing resistance as it heats. Just curious if anyone has used them in audio power supplies? If so how do I choose the right one?

[doktor]

http://www.ametherm.com/Inrush_Curre...iters_pcim.htm
There is lots of info at the above link. Still would like to know if anyone else has used these though

[aandy]

I have used thousands of them in power amplifiers.
thay when used corectly are very good.
what size of amp is it for tx VA ?

[anatech]

Hi doktor,
The most familiar ones to me are made of a resistor with relay contacts across it to short it out after a short time (2 sec ish).

This has been talked about a lot in various threads.

-Chris

[aandy]

old hat and unreliable and out of date

[AndrewT]

Hi Aandy,
which is old hat and out of date?

Doktor,
Relay bypassed power resistors on the mains primary side of the transformer give good soft start characteristics. 300mS delay is appropriate

Relay bypassed Thermistor on the secondary side to slow charge the smoothing caps give the amp/caps an easier time. 2S to 10S delay is appropriate.

Thermistors on their own have too many downsides for my audio type uses.

One of the Thermistor's biggest failings is poor performance with repeated re-starts due to mains supply failure.

[aandy]

relay resistor is the oldest hat
you are correct with the power switch on/off.
but in practice customers donot do the on off on off ect
i have used all off these methods an over all i have had less problems with ntc's
however i am working on smps at the moment an relayed ntc is my current implimentation.
andy

[aandy]

Andy
what size of amps are you making?

[anatech]

Hi Aandy,

old hat and unreliable and out of date

I'm sorry Aandy, but I completely disagree with you on all counts. I am rather stunned by your answer really.

There are more problems with your NTC implementation by far. It remains in series with your AC line and will vary it's resistance depending on current flow. A relay to short that mess out is a good idea, by what is wrong with a properly sized resistor instead? I'm sure that may have been where you experienced your earlier problems.

When done properly, a resistor shorted out as Andrew has described will not create hot parts. There is an added plus in that the relay can be made to drop out under fault conditions, causing the resistor to overheat and go open. Many other things hot and smoking at this point so we might as well limit the damage. Keeps the fuse jockeys from destroying the gear. Seen more than my share of those clowns.

-Chris

Edit: The size of the amplifier has no bearing on the method. You could do this on a 2 wpc amplifier (but why would you?).

[aandy]

Hi Chris
how many amplifiers have you built?
where do you think the inrush comes from?
andy