relay for offroad lights?

Most folks use one relay per light.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Jet wrote:

I have a set of 150 watt 385,000 candle power KC offroad lights on my jeep and I melted a 30 amp relay. it was a $6 relay I bought at the auto parts store that the guy insisted would work. so what you guys are using? also my brother in-law has 4 of same lights on his off roader and is also having problems finding a relay that works on the 4 lights. any suggestions? thanks carmine

Could have been bad connections at the relay. Where did the relay melt... at the terminals? As DougW says 12.5 amps each but that is pushing the limit of a $6 relay. And to Bill's point, if you have less than 12 volts at the relay, the current goes up and then you approach the "30 amp rating" of the relay. You could use a starter solenoid.

-- JimG

80' CJ-7 258 CID 35" BFG MT on 15x10 Centerlines D44 Rear, Dana 30 Front. SOA 4.56 Gears, LockRight F&R Dana 300 w/4:1 & Currie twin sticks Warn X8000i w/ dual batteries

Or try MCM Newark at

I'd go for something like a 25 Amp relay at 12 volts for that and think seriously about mercury wetted contacts.

With the added advantage you never lose both.

Bosch makes some heavy duty ones, but PITA to use as they are socketed.

Good point, Lon, on the Bosch relays. They are socketed, but you can buy the socket prewired, so all you have to do is cut and splice. In my opinion, there is a reason that the major manufacturers use Bosch relays. There are dozens on any given car, and they generally last the life of the vehicle.

Jerry

I just plug in connectors without sockets. I get 6 or more of them for free from every european car I see heading for the scrap yard. BMW's Bosch relays have the terminals in the same configuration, but are wired differently, but have the schematic on the case.

And I definitely forgot to mention that they are readily available at any junkyard, having been used since at least the mid-70s on Porsche, VW, etc. Often a nice rack of them is available in the engine compartment.

The one for the fan on an old Porsche or VW is easily strong enough, but I never observed any difference in rating marked on that one compared to the fuel pump relay or such. Just be sure the schematic markings are still there, and you can get the socket out of the panel on the old early 70's fuel injected porsche, vw, etc if you want it in the event the relay has to be changed.

If you go MCM Newark or a local electronics distributor, stick to metal cased relays, not the cheap plastic ones. A continuous duty high current relay is best, and mercury wetted altho politically incorrect, does cut the contact resistance enough to avoid heating.

I had 2 fuses on the lights about 4 inches away from the battery. i had a 25 amp on the light side and a 3 amp on the switch side the 25 amp fuse was blown but it didn't blow until the relay was burt to a crisp. I guess their

30 amp rating was a little off. I will try running 2 relays. all the wires that I used was supplied by k.c. in the kit with the lights. the original k.c. relay in the kit looked identical to the one I put in there the only reason I changed it is because one of the terminals corroded off.

the kc relay lasted 2 years

thanks carmine

"...because one of the terminals corroded off." -- there's your problem. It wasn't that the relay melted because you were pulling too much current through it, it was that the terminals you connected to it were rusty. A connection that isn't bright and clean will have resistance, resistance causes heat, heat encourages more corrosion. The _connection_ got hot and the heat melted the plastic base of the relay. If you reuse those connectors it will fail again. Cut the wires back until you have bright copper, put on new terminals and pack them with bulb grease before you reconnect them.

NEVER EVER use 'automotive' grade connectors on **anything** that has large current draw .... they will ALWAYS corrode and eventually give high resistance, etc. then fail !!!!!!! When the **crappy** automotive connectors develop high resistance due to corrosion, etc. the current draw goes UP when the voltage goes DOWN due to the resistance, when the current goes UP the plastic componentry softens, etc.

BETTER is to use pre-tinned 'marine grade' crimp connectors and marine grade pre-tinned wire. .... use on EVERYTHING, dont use the crappy automotive grade crimp connectors if you dont want to replace every damn year because of oxidation/corrosion.

Use mar> "...because one of the terminals corroded off." -- there's your problem.

Good article on corrosion/oxidation proof wiring techniques:

ENJOY !!!!!

I use a starter relay from an old 60's car to do my 2 KC 385,000 CP lights. I saw this setup on an old bronco that a freind of mine bought back in high school, and it was a hell of an idea. When I flip the light switch I hear a the clunk of the relay designed to channel hundreds of amps and my lights come on. When I turn it off another click. I've had this setup for 6 years with no problems on my CJ. Only thing strang is when someone is looking under the hood and says "WTF you've got to started solenoids!!" I can take a picture of the setup if your interested. It is pretty easy to setup.

I prefer a constant-duty solenoid over a starter solenoid. Starter solenoids can "pop" when they get hot from constant use and then you're in the same boat as with a cheap relay - no power.

Constant duty solenoids are commonly used for running a charging wire to a trailer or camper battery (only "on" when ignition is on so you won't draw down your starting battery), which I think is a good feature for high-draw offroad lights. They are a few dollars more than a starter solenoid, but worth it. Available at any good auto parts counter, NAPA, trailer supply stores, etc.

Robert Bills KG6LMV Orange County CA

Well, the quick math says that one 150W bulb at 12V will draw 12.5A. If your brother has 4 lamps at 12.5A each, then he is drawing 50A through a 30A relay. My guess is this will melt.