headlight relays

[crooked1/2dozen]

Good Day:

I'm sure it's in the archives, but I couldn't find the search function.

What amperage relay is required for headlights?

I've got some 20A and 30A, will the 20A be OK or should I use the 30A?

1964 Valiant.

TIA

Dan

 

[momoparman]

Based on a car with 2 head lights you are drawing 10.83 amps
Typical headlamp is 55watt low and 65 watt high beam load.

65watts/12volts = 10.83 amps

20 should work on a car with two headlights.
30 for a 4 lamp car based on same info.

Mop

 

[cudajim]

Based on a car with 2 head lights you are drawing 10.83 amps
Typical headlamp is 55watt low and 65 watt high beam load.

65watts/12volts = 10.83 amps

20 should work on a car with two headlights.
30 for a 4 lamp car based on same info.

Mop

Your math does not sound right to me. If E=IR (ohms law) and W=IR then 10.83 amps x 12 volts = 129.96 Watts. If your real wattage is 65 then you're only pulling 5.41 amps. You also should base all your calculations on 14 volts, not 12.
I would recommend using at least a 20 amp relay for either headlight and possibly a higher rating if using halogens depending on the wattage given from the manufacturer.

 

[67Dart273]

Check what headlamps you will be using.

 

[momoparman]

Your math does not sound right to me. If E=IR (ohms law) and W=IR then 10.83 amps x 12 volts = 129.96 Watts. If your real wattage is 65 then you're only pulling 5.41 amps. You also should base all your calculations on 14 volts, not 12.
I would recommend using at least a 20 amp relay for either headlight and possibly a higher rating if using halogens depending on the wattage given from the manufacturer.

Sorry I forgot to show my calculation as multiply 65watts by 2headlights. CRAP thats a 0% on the test.](*,)

 

[67Dart273]

Well the thing is you should use 14V instead of 12 something. That is what the system runs at.

 

[slantsixdan]

Go read this page and here, too. I use 30A relays, one for both low beams and one for both high beams. Make sure you use first-quality name-brand relays (Bosch, Tyco, Omron, P&B), not no-name Chinese garbage. And run good, fat wire—14-gauge minimum, preferably 12ga) for all three wires to each headlamp: low beam feed, high beam feed, and ground. Run your grounds all the way to a good, proper ground, too; battery negative or alternator housing. Sheetmetal grounds aren't good enough.

 

[momoparman]

Well the thing is you should use 14V instead of 12 something. That is what the system runs at.

Yes I suppose your right....however 12 volts is an example that is close enough to work. Based on stock style headlamps high beam load. Two relays required.

130/14 = 9.28
9.28 x 1.5 (chosen continuous load factor) = 13.9
13.9 up to next highest size is 20
20-amp relay will work fine and be more than adequate to handle a continuous load.
30-amp is even better and would be considered a heavy duty application.

This should clear things up:toothy7:

 

[momoparman]

Ditto on the ground. Bring a dedicated ground with you and terminate on battery if possible.

 

[cudajim]

I have to disagree that sheetmetal grounds aren't good enough. They're just headlights, not a critical opamp or other electronic component. I guess if you live in the rust-belt you might consider redundant grounds but I've never had a problem with bad grounds going to the sheetmetal.

 

[slantsixdan]

Disagree all you like; fact is filament bulb light output changes exponentially with voltage input. Small voltage drop means large light loss. It's dumb to have your headlamps dimmer than they could be just because you can't be bothered to run proper grounds (or to understand why sheetmetal grounds aren't good enough).

 

[67Dart273]

"Sheet metal grounds." It depends on what the sheet metal "is" and how the ground is done. Consider this

These cars are all welded unibody construction. So except for a few loose pieces like trunk lid, hood, doors and front fenders, and a few other parts, it's all one big welded piece of ..............sheet metal.

Consider the second. many of us use trunk mount batteries. I don't think many of us run a complete separate ground conductor up to the engine. We bond the battery main ground to......sheet metal. And we bond the engine block to ........sheet metal. This is good enough to crank any engine we want to toss in the works.

I don't advocate sheet metal SCREWS, nor haphazard rusty/ corroded connections. but if connections are properly made, "sheet metal" --if it's part of the main unibody AND if the battery is PROPERLY bonded to the engine block and the .......sheet metal as it SHOULD BE, then your voltage drop, at least on the ground leg, just went away.

 

[slantsixdan]

Agreed on all points, but on most daily-driven cars, this particular "as it should be" usually…ain't. Go put a brick on the brake pedal and read the voltage drop across the battery negative terminal and the grounded shell of the brake light bulb. Headlights are closer to the battery? Sure, and they're also higher-current devices.

This is really kind of a silly argument.

 

[67Dart273]

..............this is really kind of a silly argument....................

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[clhyer]

Dan,
Hope you continue to read this thread as I have a related question for you. I just purchased a wiring kit from Ron Francis. I am working on a '72 Duster, two headlights. I told them I was installing the GE H6024NH Nighthawks and ordered this relay:
http://www.ronfrancis.com/prodinfo.asp?number=HR-56

I was told that with these bulbs I wouldn't need the relay and therefore didn't get it. What's your take on this? I would much rather have it and be safe than not have it and need a new switch xx months down the road.
Thanks,
C

 

[hemitheus]

Go read this page and here, too. I use 30A relays, one for both low beams and one for both high beams. Make sure you use first-quality name-brand relays (Bosch, Tyco, Omron, P&B), not no-name Chinese garbage. And run good, fat wire—14-gauge minimum, preferably 12ga) for all three wires to each headlamp: low beam feed, high beam feed, and ground. Run your grounds all the way to a good, proper ground, too; battery negative or alternator housing. Sheetmetal grounds aren't good enough.

\6dan is right here. I have rewired many cars, the one thing I like to do is to run a very heavy gauge wire (usually a segment of battery cable) from the negative battery post to a shielded fender mounted terminal post. I use this post to ground all heavy current items. headlights, relays, audio.....

Think of it as taking the freeway home from a road trip versus the back roads.

you WILL get low performance out of body grounded items.

 

[slantsixdan]

I told them I was installing the GE H6024NH Nighthawks and ordered this relay: http://www.ronfrancis.com/prodinfo.asp?number=HR-56

Sacred poo (i.e., holy sheet!), Ron Francis gets most of fifty bucks for that pathetic handful of wire and no-name relay? What a joke. My opinion of Ron Francis continues to drop.

I was told that with these bulbs I wouldn't need the relay and therefore didn't get it.

You certainly don't need that relay. It would do about 1/3 of the job; it would take the workload off the headlamp switch but would leave the factory's too-thin feed and inadequate ground wires. But RF is wrong, you definitely need headlamp relays (real ones done up properly as in the two links I posted above), even with headlamps of standard wattage like the H6024NH, if you are to get full power to the lamps and see properly at night.

 

[clhyer]

Thanks Dan!:thumrigh:
C

 

[cudajim]

I'm still not agreeing with the whole ground thing for an everyday driver. I have the battery up front and grounded locally to the sheet-metal and then within 2 feet is the ground for the headlights. I'm also running relays for the headlights. They're nice and bright so I don't feel there is a need for redundant grounds. While theoretically I may have a millivolt drop I really don't care. I don't want to bugger up the look of the car just for nonsense.

 

[crooked1/2dozen]

Thanks for all replies. I was going to just wire in to use the last few feet of factory wires on each headlight but I'll use my scavenged headlight plugs with fresh heavy guage wire. For now I'll use a 20A relay I have for the lows with a 30A for the highs, all circuits fused, with dedicated heavy gauge wire to battery ground, or equivalent. Test voltage drop after install. Oh, and SSD, where in Canada (or Calgary to be specific), can I get Nighthawks for my car????


TIA

Dan, from Toronto (in Calgary now), with a slant six....but not THAT SSD