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Old 01-03-2020, 03:45 PM   #1
cederholm
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Default Headlight amperage

Hi guys,

I'm converting to 12v and would like to add a fuse to the headlights. Does anyone know the amperage of these?

https://www.snydersantiqueauto.com/P...earchByKeyword

Thank you,
Carl

...And Happy New Year!
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Old 01-03-2020, 05:02 PM   #2
Ak Sourdough
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Default Re: Headlight amperage

A fuse is a bad idea. What you need is a self resetting circuit breaker, or you will eventually be in the dark fumbling around looking for a fuse so you can get home before daylight. All factory headlight switches (well, I can't speak for computerized cars) since the 50's at least, have a circuit breaker built into the switch.



As far as amperage capacity, I can't answer that. The fuse/breaker is there to protect the wire, so if you determine the wire size a simple internet search for wire ampacity should get you the information you need.
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Old 01-03-2020, 06:29 PM   #3
nick c
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Default Re: Headlight amperage

On my big 29 AA, I have 12v, modern ign. sw., acc. off, on, start. The dim and the brites both pull 14.5A each, I put a switch to tie both on at the same time, 17.5A. I have a 30A blade fuse that feeds the ign switch, then a relay, then to a lite switch.
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Old 01-04-2020, 09:34 AM   #4
cederholm
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Default Re: Headlight amperage

Thanks Sourdough, I agree and meant circuit breaker. What you say about the fuse size being determined by the wires size, is also correct, but the wire size is determined by the amperage draw. ... a little chicken/egg I think.

Best,
Carl

Quote:
Originally Posted by Ak Sourdough View Post
As far as amperage capacity, I can't answer that. The fuse/breaker is there to protect the wire, so if you determine the wire size a simple internet search for wire ampacity should get you the information you need.
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Old 01-04-2020, 09:35 AM   #5
cederholm
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Default Re: Headlight amperage

Perfect! Thanks Nick

~ Carl

Quote:
Originally Posted by nick c View Post
On my big 29 AA, I have 12v, modern ign. sw., acc. off, on, start. The dim and the brites both pull 14.5A each, I put a switch to tie both on at the same time, 17.5A. I have a 30A blade fuse that feeds the ign switch, then a relay, then to a lite switch.
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Old 01-04-2020, 10:47 AM   #6
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Default Re: Headlight amperage

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Originally Posted by cederholm View Post
Thanks Sourdough, I agree and meant circuit breaker. What you say about the fuse size being determined by the wires size, is also correct, but the wire size is determined by the amperage draw. ... a little chicken/egg I think.

Best,
Carl
You're right, chicken/egg. Wire size is determined by current draw. Most A wiring is 16 AWG; ampacity of 16 gauge wire is 10 amps. Wires from generator to lighting switch and through ammeter to battery should be 12 gauge (20 amps).

At 6V, incandescent bulbs draw:
50CP 36W = 5A
32CP 24W = 4A
21CP 18W = 3A

12V bulbs draw half the current of 6V.
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Old 01-04-2020, 11:57 AM   #7
Jim Brierley
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Default Re: Headlight amperage

12v. doesn't pull as many amps as 6v. so doesn't require as large a wire. That said, don't use too small wire size, cheap insurance.
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Old 01-04-2020, 12:44 PM   #8
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Default Re: Headlight amperage

I'm thinking if you have a ammeter in the circuit put the head lights on and the draw on the meter will tell you the amps.
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Old 01-04-2020, 04:06 PM   #9
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Default Re: Headlight amperage

What globes are you using? Over here, globes are described not by some seemingly arbitrary number but by their voltage and wattage. Eg, 12v 45w. To know how many amps that globe draws, simply divide the wattage by the volts. (3.75) For the fuse, go a little more and you should be good. So you are not going to be left blind at the worst possible moment by a blown fuse (they will ALWAYS blow at the worst moment), maybe you should consider fusing each side separately.
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Old 01-05-2020, 10:37 AM   #10
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Default Re: Headlight amperage

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Originally Posted by rocket1 View Post
I'm thinking if you have a ammeter in the circuit put the head lights on and the draw on the meter will tell you the amps.
Headlights + taillights. With your foot on the brake, you'll read those too.
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Old 01-05-2020, 06:13 PM   #11
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Default Re: Headlight amperage

When I turned the key to ON, I was also feeding to the coil and electric fuel pump, the hi beam and lo beam are both 5A each. Sorry, my mistake.
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Old 01-05-2020, 07:21 PM   #12
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What globes are you using? Over here, globes are described not by some seemingly arbitrary number but by their voltage and wattage. Eg, 12v 45w. To know how many amps that globe draws, simply divide the wattage by the volts. (3.75) For the fuse, go a little more and you should be good. So you are not going to be left blind at the worst possible moment by a blown fuse (they will ALWAYS blow at the worst moment), maybe you should consider fusing each side separately.

Hi Syncro, Model A globes are rated in CP (Candle Power) which is a measure of Illumination. Example 50 CP. It is an older method of categorizing globe performance/brightness. There is no way to use CP in the use of Ohms law parameters.
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Old 01-06-2020, 12:22 AM   #13
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Default Re: Headlight amperage

The only real way is to put an ACCURATE ammeter in the circuit and test it. Fuse or breaker at double running amperage. The ammeter in the car is not accurate. Car needs to be started and at running RPM so voltage is up and stable.
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Old 01-06-2020, 11:29 AM   #14
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Default Re: Headlight amperage

FWIW, according to an old catalogue I have, the 12 volt incandescent bulbs shown in the link on post #1 draw aproximately 2.25 amps on the 32CP side and aproximately 3 amps on the 50CP side.
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Old 01-06-2020, 01:02 PM   #15
cederholm
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Default Re: Headlight amperage

Thanks all, very helpful info!
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Old 01-06-2020, 02:14 PM   #16
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Default Re: Headlight amperage

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Thanks all, very helpful info!
you can obtain a circuit breaker that pushes in to same gap as a fuse , some are self resetting when they cool off and others are Manuel reset.
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Old 01-06-2020, 04:30 PM   #17
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Default Re: Headlight amperage

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Originally Posted by 30 Closed Cab PU View Post
Hi Syncro, Model A globes are rated in CP (Candle Power) which is a measure of Illumination. Example 50 CP. It is an older method of categorizing globe performance/brightness. There is no way to use CP in the use of Ohms law parameters.
Weird!
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Old 01-07-2020, 11:47 AM   #18
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others are Manuel reset
It seems like there's never a Manuel around when you need one.
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