The Stovebolt Site Forums The Shop Area The Electrical Bay Halogen bulbs

I'm considering changing my headlights to the halogen conversions with the common H4 bulbs. Does anybody know how many amps these bulbs draw? I'm concerned about the load on the generator and headlight switch. Dave

Year of truck?

1949 12 volt truck

The generator can handle the load without a problem. Use relays to take the load off the headlight switch and the dimmer switch. It's a very easy conversion.
Jerry

Thanks Jerry. Will do

I switched to reflector headlights with H4 bulbs on my 51 1 Ton. I also converted it to 12 volts. So the main beams are nominally 60 watts drawing about 5 amps each. Your original wiring and switches will handle this easily. My headlights look identical to sealed beams but the performance is like a much more modern vehicle, perhaps in the 80s. I believe I purchased them from Octane lighting and there were no modifications required for a good fit.

Thanks for the reply truckernix

I did a Hella housing, Sylvania H-4 bulb, dual relay headlight conversion last year. I had previously converted the original generator over to an early 60s GM style externally regulated alternator back in the early 80s, probably 37 amps or so, maybe less. The headlight conversion was a really really good improvement. That being said, it was too much for the low amp alternator which was not able to keep up. Swapped to a Tough Stuff 100 amp alternator and electronic external regulator (was not looking to mess with the wiring but the mechanical regulator will not work with that kind of draw, keeps cycling on and off. The heavy duty electronic external regulator does not suffer that issue). That did the trick.

I am not electrically savvy - is a 100 amp alternator needed for those H-4 bulbs (60W, 12v, 5amp draw each)?

Or, is the 100 amp needed for other 12v volt devices/accessories?

I'm confused now also.

On a simple swap to halogen lights, I do not think an alternator upgrade would be needed. But if your total amp draw load for lights and a bunch of other stuff exceeded the capacity of the original alternator, then the battery would slowly draw down. Think of it as filling and emptying a bucket at the same time. If the emptying flowrate exceeds the filling flowrate, then the bucket will eventually be empty.
I doubt that a lightly modded stovebolt electrical system would need a 100 amp alternator, but if someone stuffed a monster amp sound system in the back, that would be another story, and maybe the alternator would need to be upgraded (or turn off the tunes to allow the alternator to recharge the battery, then turn them back on.)

I can only tell you what my experience was. Accessories consist of a tach, an electric temp gauge, three light bulbs one each for the tach, the temp gauge and an oil gauge, electric chokes for the carbs, and a retro sound radio, no amps. There are no other added electrical draws, no AC, no electric windows, seats, nothing. Before the Halogen swap, no problems with the low amp alternator keeping up--over 30 years --same style charging system and the alternator had been rebuilt within the year by a professional rebuilder and a new battery installed. After the conversion, drained the battery fairly quickly when the lights were on. Two to three of hours cruising around and then would hardly start. Swapped over to the 100 amp alternator (probably a little over kill) and that solved the charging issue. So I cant say about anyone else's experience with an H4 Halogen conversion except to say that my low powered early 60s style alternator would not keep up but that an upgraded 100 amp does keep the battery from discharging when the lights are on.

The H4 style bulbs made for on road use are a 60 watt unit and thus draw 5 amps each. You can buy H4 style bulbs of higher wattage which are illegal to use on the road. They are marketed as "off road " bulbs.

So 5 amps each for the bulbs For a total draw of 10 amps on just the headlights alone. So with a typical 25 amp generator, leaves 15 amps for ignition, turn signal, tail and brake lights, relays, horn, dash lights, fuel gauge, heater/defroster, radio/stereo, cigar lighter, interior lights, license light, idiot lights, clock and losses through the switches and wires. Worse I guess if you are adding basic stuff like tach, additional guages, other small accessories, you can see how it all adds up and might exceed the 15amps left after the halogens are added.

There is no doubt that the electrical usage adds up.

You might even strain your 37 amp alternator.

The question I asked was regarding a 100 am alternator: asking what other devices might exceed the 37 amp alternator you now have.

I did strain the 37 amp alternator, lol. Ran the battery down one night. Could not get it started in a parking lot after a cruise night. Just don’t have the patience for that any more, lol, So I probably went overboard with the 100amp. I did later add an electric fuel pump and pleanty of capacity if I ever decide to add ac, although not likely.

Just for grins I checked the 1946 Truck Data Book. The original rating for the generators back then was 35 amps. Two Halogen bulbs would consume 4 amps (total) less than the original T-3 bulbs, which drew 7 amps each operated at high beam.
I was curious because I want to use the Halogen bulbs on Sparky and have already added electric wipers, turn signals with emergency flashers, LED tail lights and a cigarette lighter for use as a GPS or cell phone charging port. In the process now of tracking down the power usage for some of these. But, it looks so far like the power draw buget will be within the 35 amps available. This will be a 12volt system with the generator modified to 12volt.

FWIW...the explanation provided in the Electrical section of the Tech Tips link at the top of the Stovebolt Banner above, is excellent at explaining the basics of amps vs Watts vs voltage.

46Sparky,
where did the figure of 4 amps total for two halogen headlights come from?

12 volts X 4 amps = 36 watts. Actual voltage will be more like 14 with the engine running, so 3 amps of current draw at 14 volts would produce 42 watts. Each halogen bulb would draw somewhere between 3 and 4 AMPS to produce its rated wattage. I run a pair of 55 watt halogen driving lights on my Honda Gold Wing, and the original equipment charging system keeps the battery up with no problem. I have no idea what amperage capacity that one is. WATTS = VOLTS X AMPS. A 55-65 amp alternator will produce all the current the average electrical system will ever need unless a 4 jillion watt sound system and/or a bunch of lowrider electro-hydraulic pumps are being powered.
Jerry

[quote=truckernix]46Sparky,
where did the figure of 4 amps total for two halogen headlights come from?[/quote

The halogen bulbs draw 5 amps each vs the 7 amps each for the original T-3 lamps. So, two halogen lamps will draw 10 amps vs 14 amps for two T-3 lamps. Net savings is 4 amps.

Sparky,
sorry I read that wrong. I believe the H4 bulbs that I use are 60 watts on low beam. At a nominal voltage of 12 volts that would be 5 amps. In any case they are much better then the original sealed beams, especially the 6 volt ones.

I went back and reread my initial post and now see how poorly worded it was, sorry. Others were likely confused as well. That’s what happens when gramps stays up too late, especially after having played with the grandkids all day.
Cheers,