DDM - Thanks for the info. Sounds like my understanding of a battery charge C rating is backwards. I thought the 0.2C meant the maximum amperage you should charge. The Lifeline info you reference indicates that it is the minimum - at least for their AGMs. I would think other manufactured AGMs would follow the same guidance. Did I interpret that correctly?
Within reason, the acceptance current of a lead/acid battery is self regulating.
With a lower initial current of say .2C, the voltage will rise slowly to the regulator set point, then hold there and current will slowly taper towards zero as the battery reaches full charge.
With a higher initial current of say 1C, the voltage will rise more quickly to the regulator set point, then hold there and current will again slowly taper as the battery reaches full charge.
It sounds like your max possible current will be well less than 1C, so I don't think you have any issues at all.
It seems that your alternator set point is 13.4V which is fine. It won't charge as quickly vs if controlled by an eternal multi-stage regulator, but it also wont overcharge on longer runs.
To me, the only question is why your 90A alternator is only putting out 60A. Possibilities are:
- You have other DC loads of 30A such that the alternator it putting out 90A, but you are only measuring 60A into the batteries. That would be correct operation and not a problem.
- At 1000 rpm, 60A is all the alternator can produce. That too would be normal operation, and could be confirmed by increasing rpm to see if output increases.
- As alternators get hot, their output declines. This too is normal, but I can't say whether 60A is the expected consequence. Also, starting from a cold alternator, I would expect the output to rise for a few minutes, then come down as the alternator heats up, and you didn't report anything like that.
- A more sophisticated internal regulator will monitor temperature and limit output accordingly. Like above, if this were happening I would expect to see an initial higher output as the alternator is heating up.
- Alternator ratings are best-case numbers. Running cool, running at full rpm, and running for an extended period of time. All those things are pretty much never true at the same time.
Bottom line, I think 60A is just fine, and you don't have any problem.