Relays and Switches

Hi all,

might be a daft question, but I am wiring a bank of Carlin switches, for various bits.

is there a level where a relay should be used to activate from the switch vs when not to use a relay?

second question, is it ok to feed the switches used to activate the relays using a single cable - only need to fuse the one cable then.

thanks in advance

JoelC said:

Hi all,

might be a daft question, but I am wiring a bank of Carlin switches, for various bits.

is there a level where a relay should be used to activate from the switch vs when not to use a relay?

second question, is it ok to feed the switches used to activate the relays using a single cable - only need to fuse the one cable then.

thanks in advance

Click to expand...

If you intend to use standard 12V automotive relays, then as a general answer, yes one main feed wire can be used. Be aware that the feed wire isn’t infinite and won’t power thousands of relays, but will quite happily supply 10-20 @ 20-30mA each. A simple way to work out what each relay will draw is to measure the resistance of the coil, and work current back using V=I*R.

As for the first part of your post, a general rule (not trying to be funny here) is if you need to ask the question, then use a relay. I say that because several factors need to be taken into account, load type, inrush current (start up current for motors etc). Land Rover wiring isn’t known for being over spec’d, so try to use a relay. It saves possibly setting fire to the vehicle. On the other hand, be more specific with the application, and people can advise.

I often use fused relays, this allows you to add more protection on the high current side without a lot of extra wiring. Think about what you need to run if the fuse on the realy supply blows. If you run it all off one fuse you may loose too many things and don't share the fuse with anything that could be prolematic like a heater fan, heated rear window or wipers.