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robomatique 6th December 2007 12:45 PM

Relay for soft start
I know this simple question might have been covered, but I just can't find a simple answer.

I am building a 5 channel UCD180 amp with total 100000uF and a 1000VA toroidal

Q1: What size of the relay should I go for in the soft start (when the soft start is bypassed by the relay, how much current does it have to be able to draw)?

Q2: What fuse size should I go for?


fernando_g 6th December 2007 06:24 PM

1000 VA/ 216V should give you 4.63 amp. I chose 216 volt because that would be 240V - 10%

But always keep a safety margin...go for a 10 amp relay.

For fuses, check the devices I2t curves, see a particular example:

robomatique 6th December 2007 07:34 PM

Thanks for great and quick answer!

That was all I wanted to know... until now...

If I have a DPDT relay being able to handle 5A, can I use both of the poles in parallell to get 10A (can a 5A DPDT relay handle 5A per pole)?

THanks again!


paulb 6th December 2007 07:38 PM

Generally no. Contacts don't share current very well. One opens or closes first. But you could try it if you have one. If you're buying, go for 10A.

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