Another spotlight question

[Ace Piker]

Aaaaaargh! I am confused . Got round to wiring up my 130w spotlamps and thought I'd got everything I need when I happened across this in a thread.......
http://www.exploroz.com/Vehicle/Acce...vingLights.asp

I worked out that a 30a relay would do but they reckon a 70a is better. Can anyone tell me what's best?
Cheers
Martin

[Chillitt]

just to slightly broaden this thread, i have a pair of lights with a dip and a main beam, can i run them with a relay for each dip and main, then switch the earth?

[BUSHWHACKER]

Aaaaaargh! I am confused . Got round to wiring up my 130w spotlamps and thought I'd got everything I need when I happened across this in a thread.......
http://www.exploroz.com/Vehicle/Acce...vingLights.asp

I worked out that a 30a relay would do but they reckon a 70a is better. Can anyone tell me what's best?
Cheers
Martin

30a will work just fine.

[paul jones]

Aaaaaargh! I am confused . Got round to wiring up my 130w spotlamps and thought I'd got everything I need when I happened across this in a thread.......
http://www.exploroz.com/Vehicle/Acce...vingLights.asp

I worked out that a 30a relay would do but they reckon a 70a is better. Can anyone tell me what's best?
Cheers
Martin

hi as vince said 30amp will be ok irun 4 130w lamps through 1 30amp relay no problem

[MattF]

You're running approximately 44A of lighting through a 30A relay.

[Ace Piker]

Only 2 spots, are you sure that's 44a, I worked it out to 21.8?

[BUSHWHACKER]

You're running approximately 44A of lighting through a 30A relay.

They ain't gonna be one all the time are they?

[Ace Piker]

260w divided by 12v = 21.666667a

[MattF]

Sorry. I was reading Paul's post and assumed you were running four as well.
With two spotlamps, a 30A relay is fine. Paul's however, is vastly underrated.

[BUSHWHACKER]

My four rooflights are 55W each, running through two 30A relays, (one for each pair) no problems one year later.

[MattF]

just to slightly broaden this thread, i have a pair of lights with a dip and a main beam, can i run them with a relay for each dip and main, then switch the earth?

You can switch any part of the circuit. Positive is always used as the basis of any design due to nothing more than historic reasons, but you can switch any part of the circuit which takes your fancy. With electronics, convential current flow was assumed to be positive to negative, which is why positive is still the accepted starting point. It's merely a case of the theory was used for so long that it is still the norm to work to.

[Ace Piker]

Sorry. I was reading Paul's post and assumed you were running four as well.
With two spotlamps, a 30A relay is fine. Paul's however, is vastly underrated.

No worries, just checking I wasn't being blonde. However being a 3rd Gen driver I can change that quite easily!!!

[MattF]

My four rooflights are 55W each, running through two 30A relays, (one for each pair) no problems one year later.

That's 'cos you're running less than 10A through each relay. Your relays ain't even breaking a sweat.

You can run more through a relay than they are rated for, as Paul is doing, but it will bite you in the arse at some point. The contact materials are only rated for that maximum quoted current. After that, the points will start arcing badly leading to pitting or weld themselves together.

[BUSHWHACKER]

hehehe!! just trying to get this thread up to 37 pages!

[MattF]

No worries, just checking I wasn't being blonde. However being a 3rd Gen driver I can change that quite easily!!!

You're safe. Overrating as suggested on that link you posted could lead to as many problems as underrating. The ones you are using at the moment are fine. If you tried using 70A relays as they suggested, the relays probably wouldn't last too long either. Severe overrating can lead to the flipside of the coin where the contacts oxidise due to lack of required current flow, which would in turn mean non functioning contacts, so stick with the 30A's. Rule of thumb where current or voltage ratings are concerned are that going to the closest size above what you require, or possibly one rating further up the scale, are acceptable. If you underrate, you WILL have problems. If you overrate above the one size larger rule, again, you will more than likely have problems at some point. The maximum rating, therefore, of relay which would be usable in your scenario, for the sake of reliability would be a 50A relay, but you don't need that extra current capacity.