Inrush protection failures.

[Peter Daniel]

I eventually decided on two CL-70 in series (just to be safe ) It's no wonder your fuses blew, I'm using 8A on my A75. Your use of a relay seems like a good idea, especially if you have to switch the amp right after you switched it off. The circuit you using is from Elector magazine?

 

[macka]

Peter,

Yes that relay design was from EleKtor, it is quite easy to implement and has proven very reliable.

The circuit is so simple I hand drew the pcb using an Etch resistant pen, I then mounted the PCB (3x3 inches)next the the transformer in an aluminium channel which forms part of my chassis to make it safe and out of harms way (being 240vac).

I our mains is 240 volt and I still few fuses without the thermistor, I imaging 120vac with 2 x current surge would be a major issue.

I will post a few pics soon.

regards

macka

 

[Peter Daniel]

I tried this circuit, but my relay is 120ohm, 12V (really nice 30 A contacts). So the series resistors had to be in 1K ohm range and I had real problem with achieving longer delay time. Even with 3,000uF the time was only about 2-3 sec, otherwise the voltage drop on resistor was too high to get 12V on relay.

 

[macka]

Peter,

I would suggest a 24 volt mini relay rated at say 5 amp, they are reasonably cheap, my NEC relay was only $3.60.

You parrellel the contacts if current was an issue, but remember the thermistor as already dealt with the surge and there would be little switch current as you are shunting a resistance of less than 1 ohm.

Alternatively, you could string 2 12 volt zeners like the BOSOZ supply and reference the 12 volt relay from the 2nd zener, that should increase the delay?

regards

macka

 

[stani772577]

Macka

Have you still got the schematics and the PCB layout for that soft-start cicuit from Elektor? I had the whole article, but lost half of the pages and can not find them anywhere. If you have them can you please post them to me, I'll supply you with my e-mail address.

Kind Regards

Stan

 

[Peter Daniel]

Here it is: http://mitglied.lycos.de/Promitheus/delay_circuit_for_toroids.htm

 

[stani772577]

Thanks for the reply Peter, but I tried to open that link several times in the last 3 - 4 days and all I received was a response from the server:
ERROR
The requested URL could not be retrieved

--------------------------------------------------------------------------------

While trying to retrieve the URL: http://mitglied.lycos.de/Promitheus/delay_circuit_for_toroids.htm

The following error was encountered:

Connection Failed
The system returned:

(110) Connection timed out
The remote host or network may be down. Please try the request again.

That's why I tried to find some alternative sources.

Regards

Stan

 

[Peter Daniel]

I can open it.

 

[Peter Daniel]

And here's the rest:

List of parts:

R1, R2 470K 0.25W 1% mf
R3 220R 0.25W 1% mf
R4, R5, R6, R7 10R 5W
C1 330n 250V (for direct mains connection)
C2, C3 470uF 40V electr.
B1 B250C1500
Re1 24V (250V-8A contact)
F1 Depends on the amp

 

[stani772577]

Thank you very much Peter,
you saved me a lot of time and running around.

Thanks again

Stan

 

[panos29]

Delay

I do not mean to complicate things even further byt, there is another circuit from elektor magazine that using the same topology, accomplish the task of using a very small turn on switch!
I use this in my aleph's 680KVA (+200,000uf)toroid for some years now with absolutely no failures, as well as in my 3KVA transformer in a tubed linear rf amplifier.
The subject is covered on:
http://www.diyaudio.com/forums/showthread.php?threadid=3321&perpage=15&pagenumber=2

Sincerely,

Panos

 

[stani772577]

I just found an old article from Elektor (9/97) with a soft start protection circuit, which I think is better thn the one here. Unfortunately the file size is larger than the limit here, so if anyone is interested send me e-mail to:

stan_nesta@yahoo.com.au

and I wil "post" it to you.

Regards

Stan

 

[stani772577]

Looks like the addrsess did not appear properly:

stan_nesta @yahoo.com.au

that is: stan_nesta

Regards

Stan