Relay for soft start

robomatique · 6th December 2007, 11:45 AM

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?

Thanks!
Robert

fernando_g · 6th December 2007, 05:24 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:
http://www.littelfuse.com/data/en/Da...ts/312_318.pdf

robomatique · 6th December 2007, 06:34 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!

Robert

paulb · 6th December 2007, 06:38 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.

6th December 2007, 11:45 AM	#1
robomatique diyAudio Member Join Date: Dec 2004 Location: London & Sweden	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? Thanks! Robert

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6th December 2007, 05:24 PM	#2
fernando_g diyAudio Member Join Date: Nov 2007	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: http://www.littelfuse.com/data/en/Da...ts/312_318.pdf

6th December 2007, 06:34 PM	#3
robomatique diyAudio Member Join Date: Dec 2004 Location: London & Sweden	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! Robert

6th December 2007, 06:38 PM	#4
paulb diyAudio Member Join Date: Jun 2001 Location: Calgary	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.