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Old 01-05-2020, 06:59 PM   #1
bgalla
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Default charge battery via alternator lug

This is a 31 ford stock except for a 12V system with a single wire output Alternator. Can I charge the battery (witch is hard to access) with out harming the diodes by connecting one lead of the charger to the alternator lug and the other to ground? See any problems with that? Negative ground. Thanks
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Old 01-05-2020, 07:11 PM   #2
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Default Re: charge battery via alternator lug

Yes, you can do that, if it is a low amp charger (up to 10 amps). You are correct, it is a very easy place to connect to. You can also connect to either of the little wing nuts on the front of the terminal box (on the firewall).

You can also connect the charger clip to the big post on the starter switch where the battery cable connects to the switch. That cable can take all the amps you want to throw at it. But be careful with the clip around the starter switch or it will short out as you connect to the post.

Double check the polarity of the charger alligator clips, compared to the battery install. Don't get it backwards. Stock wiring was positive ground, but your 12 volt car may now be negative ground.
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Last edited by Jim/GA; 01-06-2020 at 06:48 PM.
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Old 01-06-2020, 02:31 PM   #3
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Default Re: charge battery via alternator lug

Amen!
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Old 01-06-2020, 05:27 PM   #4
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Default Re: charge battery via alternator lug

You can see the positive post on my remote battery terminals. About $20 a pair at Speedway plus cables. Easy to use jumper cables and trickle chargers
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Old 01-10-2020, 11:47 AM   #5
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Default Re: charge battery via alternator lug

A little delayed, but thanks all for the reassurance and suggestions. Bruce
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Old 01-10-2020, 12:09 PM   #6
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Default Re: charge battery via alternator lug

Interesting wheel cover.
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Old 01-10-2020, 01:24 PM   #7
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Default Re: charge battery via alternator lug

This is awesome, I did not know this was a thing. So I can charge my 6V-pos. ground battery (3A charger) by connecting the red lead to ground and the black lead to that nut on the starter switch? No manual disconnecting of anything required?
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Old 01-10-2020, 01:35 PM   #8
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Default Re: charge battery via alternator lug

"that nut on the starter switch" is a direct connection to the battery negative terminal unless there's a disconnect switch in between.
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Old 01-10-2020, 02:06 PM   #9
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Default Re: charge battery via alternator lug

I realize that, I mainly wanted to confirm that there's no risk of damage to the electrical components by leaving the normal circuit in place. Previously, if I wanted to charge the battery, I would open the access port in the floorboard, disconnect the ground cable, and connect my charging leads. It would be nice not to have to do that.
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Old 01-11-2020, 09:37 AM   #10
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Default Re: charge battery via alternator lug

Quote:
Originally Posted by alexiskai View Post
I realize that, I mainly wanted to confirm that there's no risk of damage to the electrical components by leaving the normal circuit in place. Previously, if I wanted to charge the battery, I would open the access port in the floorboard, disconnect the ground cable, and connect my charging leads. It would be nice not to have to do that.
No need to disconnect battery to charge it. The best way to charge any battery is with a trickle charger. 2 amps or less. Leave it on for 24+ hours. Much better for the battery than fast charging. Also, if you have an electronic voltage regulator a fast charger can damage it.
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Old 01-11-2020, 10:15 AM   #11
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Default Re: charge battery via alternator lug

That post on the alternator is where the output comes through after it passes through the diode bridge in the alternator. The diodes are generally pretty tough and can hold fast against a back current flow. The bridge is what rectifies the AC current to DC for charging plus it acts like a cut out for back voltage or current. If you connect anywhere on the bus then you are also connecting to all points previously mentioned since they all share the bus circuit. Ground is ground and can be connected to anywhere on the vehicle that is bonded with the frame. A dedicated ground location should be bare metal and be protected with something like silicon grease to keep it from corrosive effects. The starter switch is likely the best place to access the bus circuit and it should be protected against corrosion as well.

If folks have a regular lead acid battery, it should be checked on a regular schedule for electrolyte levels up to par. Take good care of the battery and it will take good care of you.
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