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How hot should a relay get? - Page 2 - Interior/Exterior/Lights/Glass/Alarms/ICE/HVAC - The Lotus Forums Jump to content
peteyg

How hot should a relay get?

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Suggest pulling the power to two of the lights on the circuit. So the relay is only powering two lights and not four. See what happens then. If the relay doesn't get as warm/hot you know that powering four lights through one relay is too much. You need a bigger amp relay or separate the circuits. Have you simply swapped the relays out like for like to see if you might have a faulty pair?.

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Are they old relays?

I'd suggest pulling all the lamps and turn it on, see if it still gets hot.

The contact in a relay are just that, contacts, not supposed to have resistance so shouldn't dissipate any power/get hot.

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I'll give those suggestions a go. They're brand new and yes I have swapped them with the same results.

Thanks for the help guys. Hope we get to the bottom of this!

Pete

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Ok. Just unplugged all the lights and the relays get very slightly warm but barely noticeable.

Each bank of lamps is wired in series. Is this how they're supposed to be or should there be one feed going into each lamp?

Pete

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I hope they're in parallel...if you wire 4 lamps in series you'll only get 3 volts across each lamp!!

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Maybe I'm getting my terminology mixed up. One light pod, two lamps. The wires from the plug on one lamp feed into the plug of the second lamp which then goes to the power source.

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Don't see a problem with that. I really think you need to up grade to higher amp relays. Just for a giggle, try it with powering just two lights through the one relay and see how warm/hot it gets.

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Unplug the lights at the bulbs themselves. Turn on the lights. The relays should come on but the bulbs won't naturally. Leave like this and see if the relays activate and heat up. If they do then the problem is with the relays not the main circuit itself.

Graeme

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Plugged in 40A relays at the weekend. They get warm but not hot like the 30A ones. The main lead from the fusebox I put in starts to warm up as well as some of the other power/earths between the relays and the lights but not to the point of being too hot. There's obviously something still not quite. Cables shouldn't be warming up at all should they?

Pete

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If the relays are getting that hot then it's a very good sign of a poor connection somewhere.

What is generating the heat is the supply to the coil effectively being switched on/off/on etc and coils don't like this sort of treatment...

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Disagree.

Hot wires are an indication of the wiring taking too much power or has a higher than expected resistacne. The wiring should not be getting hot, neither should the relays.

Can you get to the relay socket terminals - is the wiring nice and bright and clean or is it corroded?

Might be that the wiring is corroded inside the insualtion. I've had it before with old Porsche wiring but that was in the engine bay.

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Hi Rich,

All brand new stuff so contacts shouldn't be the issue. I cleaned up the earth connections too.

Pete

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Anything hot is dissapating power therefore it is not working correctly or is underspecced.

relays and wiring should not get hot routinely. It might in some cases beirfly but it is not a long term prospect as the insulation will degrade and eventually fail.

Just re-read the whole lot and you have just replaced it all.... What size wire did you use? What was the rating?

It also might be worth checking the rating on all the bulbs as it melted the previous wiring already (Which is adequate in all the other cars!)

I have used overspecced bulbs in my old Elise and they were something like 80/100W dip/main which is an awful lot more than 55/65w you normally get and you can get 100/120W bulbs. But they melt bulb holders and wiring...!

Standard:

55W x 2 at 12V draws 9A

65w x 2 at 12V draws 11A

Modded:

100w x 2 at 12v draws 17A

120W x 4 at 12V draws 40A

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I agree totally with Rich, you should check that the gauge of wire you used is suitable for handling current up to 40A at 12v, the cable should be at least 4mm cross sectional area. If the copper in the wire you have used is not thick enough, it will have too much resistance and get warm. Also the connections need to be clean and well terminated. If you have used a relay that is not rated highly enough the contacts will also get warm, if the contacts arc when making/breaking they will become worse with use and at worsed case will start to 'carbon-up' and burn. Measure the voltage at the lamp with a volt meter, what reading do you get ? If you have a healthy voltage at the battery but a lot less at the lamp there's a huge clue - bad wiring and connections will cause a voltage drop, increase current and disipate heat.

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