Friday, June 20, 2008

New Batteries and Charger

Earlier this spring I swapped out two group 31 lead-acid batteries for an AGM 8D and an AGM group 24. Scamper's DC system is wired so that one battery is dedicated to starting and one battery is dedicated to the house. Not a bad setup but, since they're dedicated to different jobs, both batteries don't need to be identical.

What I had was essentially 100 amp-hours for the house and 100 amp-hours for starting. Scamper doesn't use all that much power - no fridge, no water system, all LED lighting - but 100 AH is pretty low if you want to anchor or sail for several days without running the engine.

Further, a group 31 battery can supply around 700 cold cranking amps (CCA) but Yanmar specifies that the 3GM only needs 200 CCA max. So there was a lot of excess capacity in the start battery.

The two group 31s weighed a total of about 145 pounds. The AGM 8D and group 24 together weigh about 205 pounds. So for 60 pounds I was able to more than double the AH capacity of the house bank - 100 to 245 AH.

In order go gain space for the 8D I needed to not use a battery box. AGMs can be fastened down without a box since they can't leak. You just have to insulate the terminals. I really like the idea that the batteries can't spill in a knockdown.

All in all it was a great upgrade. The hardest part was lowering the 150 pound 8D down the companionway. I used a tackle from the boom.

In order to keep all this electrical storage full I needed to replace the old Guest 10 amp charger. I went with a Xantrex Truecharge 20 amp model. The 40 amp model would have been a little better specification for the size of the house battery but the 20 amp model fit the space better, didn't require me to add active ventilation to the space, and was a bit cheaper. Accessories for the 20 amp model are a little cheaper too and I got the remote panel pictured above.

It is nice to be able to see what the charger is doing but the AGM setting on the device uses a lower range of voltages for bulk and maintenance charges. This puts the voltage indication on the remote panel at the very lowest end of its range so it's not as much fun as it could be.

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