MTFCA Forum

Hi Fellas,

So, I accidentally connected my 12v Battery Tender to my 6v T for a day. Now, my ammeter shows no charging, but the lights and starter work just fine. What did I damage - the voltage regulator or the generator? All else seems okay.

Thanks,

John

Possibly just burned up the coil in the amp meter. They normally will work fine on 12 volts but could have been weak. Take the cover off of the generator and cut out and inspect for burning. Disconnect the battery of course first.

Hope this Helps,

Hank

What was the charger hooked up to? if to the battery, then there is no complete circuit to effect the amp gauge, if you had the positive of the charger on the power wire of the generator cut out then that would be running through the amp gauge to charge but I can't see how a tender charge would worry it even at 12v The amps are very low on a tender. It wouldn't even boil your battery and if a good brand of tender would shut down if the battery was full, if the tender didn't shut down then there would be a lot of car and shed fires

Any damage would be to the battery as long as the lights and key was off. Your battery is charged! Others with more technical experience may differ.

If the ammeter is correctly connected, the current from the battery to the ignition or to the lamps goes through the ammeter. When the generator is charging, the current goes back through the ammeter to the battery. So if the wiring is connected to the wrong side of the ammeter, it would go directly from the battery to the lights and not through the ammeter. Having said the above, why did you connect the charger? Was the battery dead or low? When the engine ran before you charged, did the ammeter show a charge? or if the lights were turned on before charging did the ammeter show a discharge? And finally, did you do any changes to the wiring before you charged the battery? This is what I suspect: The current is going through the ammeter, however, the needle is stuck and doesn't show either charge or discharge. If your cutout or voltage regulator is open, you should not run the engine until you ground the output of the generator, or the generator will overheat and burn out. To check the cutout, You check the cutout by first putting a DC voltmeter between the wire terminal where the wire is connected to ground. Do this with the engine not running. If you get 12 volts at that point your wire is connected to the battery (should be through the ammeter). Now touch the lead on the volt meter to the generator side of the cutout. With the engine not running, you should get zero volts. Next start up the engine and if you get 12 volts at the terminal on the generator, the generator is working. If you get a much higher voltage at the generator, the cutout could be bad.
Norm

Redleg wrote: ↑

Thu Oct 22, 2020 6:16 pm

Hi Fellas,
So, I accidentally connected my 12v Battery Tender to my 6v T for a day. Now, my ammeter shows no charging, but the lights and starter work just fine. What did I damage - the voltage regulator or the generator? All else seems okay.
...

Am I reading it correctly, that you charged your 6 volt battery with a 12 colt tender(not charger) for a day?! Applying too much voltage to a battery will cause the electrolyte to overheat, and will damage the battery. Not sure why you needed to charge it in the first place but before you waste your time checking circuitry you should have your battery checked out. Autozone and others do it for free

My battery tenders don't have a voltage selector, they just "know" what voltage battery they are hooked to. I can move them from 12v to 6v and they just work.

If you have a voltage regulator and your amp gauge is showing no charge, it is likely because the battery is fully charged and needs no additional input from the generator/alternator.

When it's running, turn on your lights and see if the gauge remains at zero or shows a modest charge. If so, you're fine, your battery is just topped up and needs nothing at zero load. If it shows a heavy discharge with lights on while running at a fast idle or running down the street, you may need some diagnostic work done.

If the car is wired as an original Model T and you didn’t turn on the ignition or start the engine during the charging process, then you did no damage.

My reasoning is simple if you follow the wiring diagram, as there will be no path for an excess voltage or current to reach the generator (the engine is not running and the cutout contacts will be open) or the coils (the ignition is off).
There is simply no path for voltage or current to reach the generator.
If you turned on the ignition or ran the motor, all bets are off.

Thanks Fellas,

I apparently fried the voltage regulator.

I finally got some garage time today and confirmed no charge showing on the ammeter with the engine at speed on magneto and lights off. I then swapped out the VR with a spare and, voila, the ammeter shows charging at speed. Ammeter functions normally, reflecting the draw of the lights when on. All else appears unharmed.

Thank you to all of you who posted - I learn something from every one.

John

If the regulator was one of Fun Projects, contact John Regan as he might be able to test & repair it.