Alternator/Regulator Behavior

[CShelton]

Hello all, I'm currently working through updating the electrical stuff on my new to me A4 powered Cat27 and I seem to have a problem with the alternator charging the battery.

I have the stock 35amp Motorola and when checking the output voltage from the Alternator with a voltmeter, I get a reading of about 4.5 volts for the first few minutes, then it might jump up to around 14.5 volts.

Do these alternators take a few minutes to "warm up" before they start putting out charging voltage?

Is charging voltage RPM dependent or should my alternator be able to charge a battery while on a low idle?

I've searched the forums and I can't seem to find an answer to these questions, please advise, thanks!

[jhwelch]

My alternator has an external regulator now, but I seem to remember that
before I installed it I'd have to run the motor up to a medium speed
to get the alternator to kick in. I've seen this on other alternators; a
friend was really puzzled why his alternator tested out okay in the
shop but wasn't working on his boat (with the motor idling).

So try bumping the engine up to a higher speed. Once the alternator
kicks in drop the engine speed down.

-jonathan

[rigspelt]

I have the stock 35amp Motorola and when checking the output voltage from the Alternator with a voltmeter, I get a reading of about 4.5 volts for the first few minutes, then it might jump up to around 14.5 volts.
Some alternators only start producing output above a threshold RPM, but I thought the stock 35 amp alternator only produced about 13 and a half volts. Perhaps consider getting the alternator bench checked at an alternator shop? Perhaps its regulator is aging?

[s/v Dearbhail]

I read somewhere here in the forums about the older alternators needing to have the field "charged" , it's a small red wire running from the + terminal of the coil. I did read in several of theose forums that some alternators without that wire require the ngine to be revved up, the field energizes and the alternator produces like it's supposed to.

Hope that helps. My old alternator had that red wire.

[sastanley]

I don't really see this 'feature' as a bad thing. I don't necessarily want my alternator kicking in right away on a cold engine, even if it is the little 35amp guy. Needing to kick the throttle up above idle after you've let the engine warm up for a minute seems OK to me. It can be a little unnerving though when you are looking at the ammeter and it happily sits there at '0' with the engine running though..always makes my heart skip a beat!

[CShelton]

Thanks for the help and suggestions everyone, it seems that it was an RPM dependant situation. I can actually feel the motor "shudder" momentarily when the alternator kicks in, after that, it's working hard.

My idle may be a little low though, I don't have a tach so I don't know how low it is exactly but the alternator only puts out 12.5 volts when she's set idling.