How to wire up a Relay

Ian Anderson · Post by **Ian Anderson** » Sun Feb 22, 2009 5:28 pm

On the dash vents of the GT40 I fitted 2 electrical fan heaters / blowers
They are rated at 168 watts each (See here http://www.cbsonline.co.uk/electric-dem ... -309-p.asp)

I had them coupled up to a single toggle switch but strangely enough the switches don't last with the current draw (sbout 28 amps by my calculation)

So I bought a fused relay rateda at 30 amps - but have never wired one of these before so could someone please assist.

I have on the relay 4 pins
They are marked 30, 85 , 86 , 87 (to me it would be more helpful if it said mains, earth, switch and heater element!

So is this a standard relay numbering ? or is it try it and see but make sure you have a fire extinguisher near by? (Oh and a can ot the Lucas wire fixer for when the smoke escapes?)

Cheers
Ian

bodger · Post by **bodger** » Sun Feb 22, 2009 5:32 pm

http://www.weendoggy.com/images/relay_wiring.jpg

or

http://www.ado13.com/techs/relay.htm

Ian Anderson · Post by **Ian Anderson** » Sun Feb 22, 2009 5:42 pm

Many thanks - those diagrams make sense now!

Is it permissable to wire up the feed to the main / fused fircuit and to the toggle switch or does the toggle switch circuit needto be fused too? If so at what sort of amp rating

cheers

Ian

Eliot · Post by **Eliot** » Sun Feb 22, 2009 8:24 pm

Ian Anderson wrote:Many thanks - those diagrams make sense now!

Is it permissable to wire up the feed to the main / fused fircuit and to the toggle switch or does the toggle switch circuit needto be fused too? If so at what sort of amp rating

cheers

Ian

I dont fuse the low current side, as I'm usually drawing that from a fused circuit anyway.

Ian Anderson · Post by **Ian Anderson** » Tue Feb 24, 2009 4:21 pm

So I can connect this up!

Do I do 1 relay with a 30 amp fuse that runs the 2 heaters
or
Do I do 2 relays (activated by a single switch) and each of them with a 15 amp fuse and then each relay runs 1 heater unit?

What is correct?

Ian

tetlow · Post by **tetlow** » Wed Feb 25, 2009 8:18 am

I would go for the two relays Ian.

That would mean if one fan has a problem the other will still work.

Dave

ian.stewart · Post by **ian.stewart** » Wed Feb 25, 2009 11:29 am

better stil see if you can geta higher rated relay, 28a is getting near to the max of the relay rating,

stevieturbo · Post by **stevieturbo** » Wed Feb 25, 2009 10:25 pm

A lot of OE relays are rated at 40A

Running 2 totally seperate circuits could make sense though.

Ian Anderson · Post by **Ian Anderson** » Thu Feb 26, 2009 7:57 am

OK

So I have one non fused circuit through a switch to activate 2 relays
Each relay in turn powers one heater elemement / fan
As each element is rated at 168w I'd down grade the fuse to 15 amps in each relay unit. (I presume 15 amp is available in blade fuses)

All this to get around burning out a simple toggle switch?
No wonder the electronic industry makes loadsa dosh!

Ian

Eliot · Post by **Eliot** » Thu Feb 26, 2009 7:26 pm

I run two relays for my two cooling fans, because they chug alot of power on startup and you have redundancy if something goes wrong.