Adding Lithium Battery to Racing Sailboat

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barilkobart asked Jun 21, '21

Adding Lithium Battery to Racing Sailboat

We have a MUMM 36 racing sailboat, with some pooched AGM batteries.
We have ordered two Lithium batteries:
One small for starting (dedicated)
One 100Ah for house

House runs basically run the electronics, cabin lights, and nav lights.

We typically do long distance overnight races, charging every 8-12 hours with a 55 amp standard alternator.

To charge the Lithium when underway, I have purchase a 12/12-30 DC-DC Charger from Victron.

Hopefully you can read this diagram!

The only thing not on the diagram are 60amp fuses at the positive battery posts.

There are 3 existing single pole battery switches that isolate the start and house batteries.
We never operate these switches when underway.

Should the Smart TR charger be cabled directly to the batteries, or on the other side of the isolation switches so it is closer to the alternator?

NOTE: also installing a Smart Shunt, but it is back ordered with our supplier.

Thanks

Bart
Toronto, Canada

Lithium Battery

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Mike Dorsett answered · Jun 21, 2021 at 07:52 PM

Your diagram did not upload. However: The TR charger should be wired to the non battery side of the isolation switches. Also, I would be dubious as to using a lithium battery as a starter battery - the cranking amps would be way too high for a 'small battery'. Depending on your engine, initial cranking amps will be 1000 - 700Amps, and not many lithium batteries could support this!! I would use a small lead acid battery for starting, and keep this float charged from the house bank. I had a cruising yacht for 11 years with this set up. We changed the engine alternator to 55A 24V to charge the house bank, and float charged the starter and radio batteries.

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Answer 1 · 2021-06-21T22:44:24Z

barilkobart answered · Jun 21, 2021 at 10:44 PM

Thanks

Agreed on the placement of the charger.

The small lithium starting battery is 8 ah 430 CCA.

We have been using a 400 CCA AGM starting battery for the past 4 years without issue.
Same battery as in my 1991 Miata.
The Yanmar 2GM20 does not draw a lot of power on startup.

zamboni-charging-system.jpg (47.3 KiB)

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Answer 2 · 2021-06-21T22:52:07Z

Mike Dorsett answered · Jun 21, 2021 at 10:52 PM

From your diagram above, I would move the input to the charger to the alternator output (other side of starter isolator), and the output form the charger to the load side of the house bank isolator. If your starting amps are within the CCA rating of your startter battery, that's ok too. Some people would not have thought of that.

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