Thread: Do I need a new alternator?

Originally Posted by naradataranto

Thanks for the help but riddle me this. When the battery is drained and I set off on a trip to charge it again the volt meter does not read a charge at all untill a half hour or so of motoring. After that the charge increases gradually and as the battery gains more charge the charge light on the volt meter rise untill the battery will charge at around 14 volts once almost full.
Despite this it will only charge at full volts when the revs are at around 2700rpm. Also the battery never seems to get to full charge stops at around 80-90% full never 100%.
This is my second battery in the system and is a vada 95amp hour. I want to get it right as the battery alone is around $800.00 and I want to make sure its working likea dream.

What do you mean by the volt meter not showing charge? What is the range of the meter?

Some pics required

My question is " How flat is the second battery?"

It is quite normal for a second (AGM 90AH) battery to charge at say 13.4-6 volts when reasonably flat even in my case with a dedicated 85amp alternator. This increases slowly to say 13.8-9 which is about when the battery is 90% charged. Full charge may take another couple of hours in my case when the charge rate is reading 14.1-2 on a 30c day.

With a 60 amp alternator and aircon running there is not much left over for the second battery and these times may elongate to 4 hours or so to reach 90% and may longer than a day's driving for 100% or 14.1 volt charge rate.

I found this situation when in NT and my second alternator died and I bridged to my main 85 amp. It took more than a day for the combined charge rate to reach 14.1 with the main battery effectively starting at 12.4 or so and the second at 11.6-8. No isolator fitted.

So your situation sound pretty normal with a 60amp alternator if the second battery has say run a fridge overnight. It will probably rarely get to 100% charge.
Regards Philip A