Atomic 4 voltage regulation

[EveningTide]

A friend has a Cal 28 with an Atomic 4 motor. The motor is a rebuilt, installed two year ago and the alternator is also rebuilt. The motor was slow cranking and we had to use a shore battery charger for 15 minutes to raise the battery voltage to the point that the motor would start. After it had run 10 minutes I noticed that the battery voltage read 13.4 volts. I checked with my multimeter and got the same reading. Changing the RPM did not affect the voltage at all- it seems the regulator is set at 13.4 volts. This voltage seems about right for float charging but would be way too low if you wanted to fully charge a battery that had been significantly discharged. This boat is used as a day-sailor and there is very little electrical load when sailing so the batteries will rarely get discharged. Could the alternator purposely have been set to float the batteries rather than overcharge them? Is this how they did it back in the Atomic 4 days? Comments, please.

[djmarchand]

Most alternators even today have a simple, single voltage regulator set to supply 13.5 to 14.0 volts. It sounds like your alternator is doing what it is supposed to.

I would hook up the shore power charger to the batteries once in a while to bring them up to fully charged status.

David

[S/V Alchemy]

You need to either swap out the internal regulation or consider external regulation. Then you can charge the batteries at set points you determine.

Of course, if you have the stock 35 amp Motorola or Delco alternators, you're not going to charge anything particularly quickly. I think of the alternator on a direct-drive Atomic 4 as being fit to run nav lights under motor at night, and not a whole lot else.

You can always shorten and "up gauge" your wiring, too, to get maximum pop out of the juice you are making, but I would say if you have charging issues, go to a pair of Group 27s or even Group 31s, upsize to a 55 amp alt, and monitor state of charge with some sort of regulation when 14.2 needs to go to 13.4 or whatever equals "float" on this boat.