Charging at 15.8V - what's wrong?

[Boble]

Electrical gurus, need your help:

Symptoms:
* Charging at idle: 11.8 V
* Charging when rev'ing her up: 15-16 V
* The other day the engine stopped in a traffic light in front of a fire truck with full sirens (my daughter driving the beetle was NOT very happy... ).
Battery was flat. Managed to push it to start. When driving, the generator light came on, lighting all the time. After recharging the battery over night the generator light was still on all the time.
Doing some fixing today, the generator light is now working as normal (goes off after start), car runs well. However, as mentioned above, I get a reading of 15.8 V when rev'ing the engine.

Is this normal? Worried about overcharging the battery.

The car:
* 1972 Superbeetle, 1600 DP
* Generator-type with regulator under the back seat.

Thanks for help!

[Harleyelf]

Regulator is the first suspect. What voltage do you read across the generator at 2000 rpm? 11.8 at idle is low unless you idle at 700rpm or less.

I'd put an alternator in and scrap the old regulator. Easy to do and the motor does not have to come out. Intake manifold slides off to left to expose fan backing plate screws.

[Boble]

[EVfun]

I would just change the regulator. The generators don't put much out at idle, but the regulator shouldn't let them over 15 volts. After a few miles driving even idle should show over 12 volts at the battery, and with the engine at 2000 rpm you should be over 13.6 volts.

If you have a big sound system, or a lot of other added accessories, then you should consider an alternator upgrade. If you electrical system is basically stock then the stock generator system should prove fine.

Before swapping out the regulator I would redo the connections at the generator, the connections at the regulator, and make sure the transaxle to frame ground strap is in place (that missing or broken usually causes a slow starter too.) If you happen to have a regulator with a removable cover they can often be adjusted back into spec.
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[Boble]

Thanks for good advise.

I take it that 16 V is above the limit and something is wrong...(?). Changing the regulator makes sense.

[Danwvw]

Yes the old regulators are usually bad. If running a generator get the new bosch solid state regulator. They are much better 113 903 803E and Rock Auto has others.
The thing to do though since the battery was dead is to check it's electrolyte, it may just be low. But probably needs a new regulator too.
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1960 Beetle And 1679cc DP W-100 & Dual Zeniths!

[Bob Brugge]

Racing alternators put out 16v. Did the alt/gen ever put out the right voltage? Or is this a new unit?

[Luft kühl]

Check (measure) the ground connection between the generator case and the regulator. If you are unsure, temporarily run a jumper wire between the two
and recheck the charging voltage.

The regulator uses this ground as a reference point to determine when to start and stop charging the battery.

[Boble]

[Boble]

Fixed. Changed the regulator. Now it charges 12.8 V on idle and 13.9 to 14.0 V on 2000-3000 rpm steady.

Thanks for input, guys.

[SBD]

If you haven't already done it, it would be a good idea to check the fluid level in your battery now that you have things figured out.
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"Just $99 down and $64 a month for 36 months buys you a brand new Volkswagen Beetle!"

[EVfun]