Voltage/Amperage question?

jayvee34

jayvee34

Senior Member
On a 6 volt negative ground alternator that test 6.57 Volts with headlights on
low beam and the Amp meter reads 5 amps +. With the headlights on high beam the voltage is still testing 6.57 volts, but the amp meter is now reading
-1 amp.
Is there a problem with my amp gauge? I don't understand a constant 6.57
volt reading and the amp gauge dropping off as mentioned above.

I can increase the RPM's and the amp needle does not move. (still showing
6.57 volts) I can turn the lights off and amp needle does not move.
I can shut the engine down and restart, the amps needle goes to 30 + amps,
and then slowly decrease to 9 amps and stay there until I turn the lights on, then it is back to as mentioned above.
Any answer or help will be greatly appreciated.:)
 
Last edited:
If your charge rate is always 9 amps without any load then I'd say you have a bad regulator. The needle should move near centered as battery gets charged after the engine start with no load turned on.

If the ammeter is near centered with no load and deflects to discharge under load [ engine not running] then its OK.
 
Patrick L. said:
If your charge rate is always 9 amps without any load then I'd say you have a bad regulator. The needle should move near centered as battery gets charged after the engine start with no load turned on.

If the ammeter is near centered with no load and deflects to discharge under load [ engine not running] then its OK.
Click to expand...

Thanks very much, your answer is most appreciated.:)
John
 
So at 9 amps of charge, the battery voltage stays at 6.57 volts? After starting, it is normal to see a high charge rate, then tapering down, but I would expect the battery voltage to be in the 7 v range. Use a piece of emery cloth, remove and clean all connections incuding the ammeter. Fyi, some ammeters are very inaccurate, if you really want to know use a good quality ammeter right at the battery. A quick check of your wiring is to do a voltage test from the + side of the battery to the output lug of the alternator. The closer to zero voltage drop the better.
 
Short answer, the regulator is failing. As eagle and Anteek29 say, your voltage is too low.

9 amps at 6.57V is probably normal for original wiring, ammeter reads coil current as well as battery. If FSB 11/29 has been applied, then the needle will stay close to center, is it reads only battery charge of 1-2 amps.

With headlights on, the alternator is not providing enough current, low beams it barely keeps up, high beams are discharging the battery.

You can live with this situation by using original 21/21 CP bulbs, but the alternator needs a new regulator inside.
 
Badpuppy said:
9 amps at 6.57V is probably normal for original wiring, ammeter reads coil current as well as battery. If FSB 11/29 has been applied, then the needle will stay close to center, is it reads only battery charge of 1-2 amps.
Click to expand...

Please excuse my lack of enlightenment but what does "If FSB 11/29 has been applied" mean?
 
The GM type conversion 1-wire alternators put out closer to 7.5-volts and sometimes more. The regulator is integral to the alternator. Rebuild kits for 6-volt 10si alternators are available in a kit form.

Reproduction ampere meters leave a lot to be desired. The originals were very good units even though cheaply built. The reproduction ones that I've seen cant be trusted for proper amp indication. I'd trust a good 90+ year old unit over any new ones.
 
rotorwrench said:
Reproduction ampere meters leave a lot to be desired. The originals were very good units even though cheaply built. The reproduction ones that I've seen cant be trusted for proper amp indication. I'd trust a good 90+ year old unit over any new ones.
Click to expand...

I agree but as long as it is indicating + or - is good enough for me.
 
Thanks again everyone, got it going (fixed). Flashed the alternator, got 7.72 Volts,
loaded got 7.55 volts, 30 amps, then backs off to 15amps.
 
Patrick L. said:
You ' flashed ' the alternator ?
Click to expand...

Flashed, meaning excited, sorry about the wrong terminoloy.

Yep, Number one terminal to the case, got the info from Gary @
QuickStart. "Jumper wire connected to the case (grounded), just touch the
other end of the jumper to the # 1 terminal on the alternator. For positive
ground alternator's only.

For negative ground alternator's, Jumper wire from alternator output post
other end just touch the # 1 terminal.
 
jayvee34 said:
Flashed, meaning excited, sorry about the wrong terminology.

Yep, Number one terminal to the case, got the info from Gary @
QuickStart. "Jumper wire connected to the case (grounded), just touch the
other end of the jumper to the # 1 terminal on the alternator. For positive
ground alternator's only.

For negative ground alternator's, Jumper wire from alternator output post
other end just touch the # 1 terminal.
Click to expand...

Jayvee, I think you had it right. You 'flashed' the alternator. When you REV the engine, you 'excite' the alternator. Two different things.
 
How old is the battery? If very old it may need replacement. As others have said, after a few minutes the amperage should go to zero as the battery becomes fully charged. The volt meter should be about 7.2 to 7.5 at that point depending on where the regulator is set at.
 
Ruth said:
Jayvee, I think you had it right. You 'flashed' the alternator. When you REV the engine, you 'excite' the alternator. Two different things.
Click to expand...

Thanks, I thought so too! Just wanted to say what I did so those who answered
my question would know.;)
 
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