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Needing to use engine alternator vs. generator

1419 Views 7 Replies 6 Participants Last post by  Flint
I have never been "at anchor" longer than a week or two, but am now in the Caribbean where anchoring for a long is the norm. As a result I have not had a "full charge" on my batteries in 6 weeks. This is causing some confusion with the battery monitor and the charging systems.

I am finding that the engines alternator puts in a lot more amps than the generator - more or less double the amps. I hate to run the engine at anchor, I don't need the extra hours of running at idle, but with the generator the amps going in gets to be 20 amps or below quickly and I can be getting 40 or 50 at the same time with the alternator from the engine. They alternator has a separate regulator. Here's the setup:

* 90-100, 135 Amp Balamar alternator on Yanmar 4jh - regulated by a separate Xantrex XAR digital alternator regulator (a multistage regulator).

* Westerbeke 6KW generator, regulated by running through a Xantrex a Freedom 20 charger/inverter/(with a multi stage regulator)

My question is this.... Shouldn't a 6kw generator be able to put in as many or more amps than an engine alternator to charge the batteries? I believe somehow the Xantrex Freedom 20 inverter is "throttling down" the amps from the generator to a lower acceptance level than the separate, free standing alternator that the engine alternator uses. I know I want multi stage charging, but why would the Freedom 20 throttle it down to such a low level? I would much rather run my generator for the same amount of time.

As far as I know there is no way to change the allowed charging rate on the Freedom 20 regulator.

So here I am, in a harbor with a perfectly good generator, charging my batteries using the boats engine. That doesn't seem right.

Any ideas?
1 - 1 of 8 Posts
Of course it depends. In terms of physics and the 2nd law of thermodynamics, running a generator and charger has a lot more places for losses. The path of energy flow has more stuff to go through. Never the less, in terms of your specific equipment the generator is oversized for the task while the ship's engine is grossly oversized for the task.

Optimum equipment design would be for both the engine and the generator/charger to be sized properly to provide the maximum allowable charge rate. If you have flooded cell batteries you might be near to that. If you have gel cell then you could probably do better with a 200 amp charge capability.

If I were you I'd measure the charge rate for both systems and use the system that pumps in energy at the highest rate. Since both systems will have miserable energy efficiency, use the system that gets the job done quickests, Or, buy a solar panel.

1 - 1 of 8 Posts
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