Charger recommendation

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Michael Connolly asked Feb 17, '19

Charger recommendation

The need...

On a boat we have a power snorkel (think diving using an air tube with an air pump floating overhead) and looking to change the AGM batteries over to a Lithium battery. However, naturally, it’s not that simple.

We have an Enerdrive LiFePo setup charges by a Phoenix when on shore power and a 100/30 mppt smartsolar plus alternators while at sea. Don’t want to include the 240v/Inverter in the charging setup as it chews power on standby and the batteries run down when the boat is not in use.

So the simple part of the requested recommendation is for a lithium friendly charger to run off the 12 DC circuit tocharge the new Lifepo4.

The second more complex issue is that because the power snorkel is not used that often the battery sits idle for weeks, months some times. I would like to store the battery at around 50% if charge and it would be brilliant if someone could recommend a way of charging to 50% !!! Weird huh!! But I think you know why!

Anyway, that’s the two part request.

Thanks in advance

Mick

Lithium Battery charger

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Answer 1 · 2019-02-24T05:47:11Z

Paul B answered · Feb 24, 2019 at 05:47 AM

if you have solar then leaving the inverter on while away should not be a issue and as such you could then use a lithium charger to charge to the level you require.

but then leaving a lithium set at say 50-70% for a few months or more, then the unit would not require any charging and thus why do you want a charger as they dont loose that much charge over a year if just left standing.

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Answer 2 · 2019-02-27T18:53:10Z

redwood answered · Feb 27, 2019 at 06:53 PM

One thing comes to my mind. With agm batteries the voltage may get low but the air pump will stay running. With lithium the bms may at any time shut down the power.

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Answer 3 · 2019-03-01T07:48:05Z

kai answered · Mar 01, 2019 at 07:48 AM

LiFePo have a flat SOC curve, so targeting a particular SOC% in the midband will require hardware smarts (a coulomb counter on the charge/load path, integrated with the charger. And you may need to recalibrate from time to time). Easier to just target a (lower) float voltage.

For reference, BMS will also consume power. If you leave the battery connected to the BMS w/o a charging source for a long enough period you risk draining the battery to death unless the BMS cuts itself out of the loop.

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