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Power for Headlight Relay #1311432
Tue May 21 2019 07:55 PM
Tue May 21 2019 07:55 PM
P
Phak1  Offline OP
Wrench Fetcher
Joined: Feb 2019
Posts: 72
Upstate NY
After posting a question about headlight relays, I was looking for a good power source for the relays and came across another post that linked to a website. This site suggested using the alternator as a power source and also a good place to pick up a ground. That makes sense to me as its near the headlight terminal block. I would think, by using the alternator, the draw from the headlights would show on the ammeter.

Is there is a downside to utilizing this convenient location?


Last edited by Phak1; Tue May 21 2019 08:11 PM.
Re: Power for Headlight Relay [Re: Phak1] #1311448
Tue May 21 2019 10:50 PM
Tue May 21 2019 10:50 PM
H
Hotrod Lincoln  Offline
Boltergeist
Joined: Feb 2004
Posts: 18,559
Dellrose, TN
Any source of battery voltage with a heavy conductor available is sufficient to power the headlight relays, and if the current draw is showing on the ammeter, that means the charging system isn't working. The charging system, whether it's a generator or an alternator, is going to supply all the electrical demand- - - -ignition, lights, heater blower, electric wipers. etc. before the battery gets any charge. Whether a specific current draw shows up on the ammeter is pretty immaterial one way or another.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Power for Headlight Relay [Re: Phak1] #1311495
Wed May 22 2019 01:46 PM
Wed May 22 2019 01:46 PM
P
Phak1  Offline OP
Wrench Fetcher
Joined: Feb 2019
Posts: 72
Upstate NY
Jerry,
I’m confused. Please correct me if I am wrong, but if I draw current from the starter terminal for the headlights, the ammeter could be showing a positive charge while in reality the total current draw could be more than the alternator is putting out, slowly draining the battery before I knew there was an issue with the alternator.

I know that the real answer is to install a voltmeter, but in the meantime I was hoping to be able to rely on the ammeter.


1952 Chevrolet 3100 w/59’ 235
Re: Power for Headlight Relay [Re: Phak1] #1311498
Wed May 22 2019 02:09 PM
Wed May 22 2019 02:09 PM
H
Hotrod Lincoln  Offline
Boltergeist
Joined: Feb 2004
Posts: 18,559
Dellrose, TN
If your alternator can't keep up with the current draw of a set of headlights, you need a different alternator. You're correct, technically. In real-life terms, you're nitpicking. The only situation I can imagine where there might be a problem would be if you've got a bad diode in the rectifier, which reduces the alternator output to less than 1/3 of its rated capacity- - - -typically, 10 amps or less. That situation allows the alternator to develop normal voltage, and it will keep a battery charged as long as there's minimum current draw, but it can't handle multiple loads such as headlights, A/C, sound system, etc. If you want to monitor total charging system performance, you would need a voltmeter, an ammeter, and some way to keep a constant check on the specific gravity of the battery acid, plus a few years' worth of experience interpreting those readings.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Power for Headlight Relay [Re: Phak1] #1311503
Wed May 22 2019 02:31 PM
Wed May 22 2019 02:31 PM
B
beltfed  Offline
Shop Shark
Joined: May 2005
Posts: 1,570
Knoxville, TN
I agree with Jerry. Tapping headlight power at alternator will not show up on amp meter, it’s ‘upstream’ of the amp meter. That is if the alternator is outputting correctly. However, total current draw with lights on, no matter where you tap off for power, remains the same. As Jerry says, your wire to and from your connection point has to be able to handle the load.

Last edited by beltfed; Wed May 22 2019 02:44 PM.

Six volt guy living in a twelve volt world
Re: Power for Headlight Relay [Re: Phak1] #1311505
Wed May 22 2019 02:54 PM
Wed May 22 2019 02:54 PM
H
Hotrod Lincoln  Offline
Boltergeist
Joined: Feb 2004
Posts: 18,559
Dellrose, TN
If the ammeter is wired correctly, the alternator output will be reflected in the charge/discharge indication, and tapping the relay power wire off the back of the alternator would be OK. It's just a bit less complicated, wire routing-wise, to connect at the battery cable/starter junction. Either method will get the job done, and in practical terms, there won't be a noticeable difference in performance.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Power for Headlight Relay [Re: Phak1] #1311563
Thu May 23 2019 12:38 AM
Thu May 23 2019 12:38 AM
P
Phak1  Offline OP
Wrench Fetcher
Joined: Feb 2019
Posts: 72
Upstate NY
Thanks for the info. You guys are great.


1952 Chevrolet 3100 w/59’ 235
Re: Power for Headlight Relay [Re: Phak1] #1312343
Wed May 29 2019 06:09 PM
Wed May 29 2019 06:09 PM
P
Phak1  Offline OP
Wrench Fetcher
Joined: Feb 2019
Posts: 72
Upstate NY
I just finished installing my headlight relays that I bought on eBay as suggested by Jerry (4) 60 amp relays with pigtails for $13). I did tap power and a ground from the Alternator and I decided not to hide the relays for a few reasons. First I didn’t like the idea of the relays being exposed to the rain they would receive in front of the radiator core and figured they would be better protected on the inner fender. Second, I wanted to keep the pigtails as short as possible without adding another splice, and finally, I plan on doing a full frame restoration after I work out all of my mechanical issues to include a new harness complete with a fuse box.

The existing 6014 bulbs are much brighter and I feel allot better not exposing my brand new $50 headlight switch to the higher amperage, not to mention eliminating the high amperage under the dash. I added an inline 40 amp fuse at the alternator. Safer and brighter, all good!

Thanks all for your input helping me tackle this job!

Attached Files

1952 Chevrolet 3100 w/59’ 235

Moderated by  Rusty Rod 

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