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pjared avatar image
pjared asked

24v IP67 - Charging two 12v batteries in series for first time?

I recently purchased two 12v LifePo batteries that I'll connect in series and a 24v 8amp Blue Smart charger for my boat. I was just about to install it all when I read that both batteries should be charged individually first to the same voltage before being connected in series. Is that possible with this 24V charger?

I do own a basic Noco charger that I could use with a multimeter and aim for a common voltage. And while this sounds basic, I fear that I'll charge one to say 13.5v and then charge the other to the same voltage only to come back to the first and find that it settled on 13.3 or something. Advice?

Is the Blue Smart the right charger for this application on my boat or should I have purchased a 12v two-bank charger?

battery charging
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3 Answers
Mike Dorsett avatar image
Mike Dorsett answered ·

a 12v 2 bank charger is designed for charging 2 12V batteries with a common negative, so you do have the right charger. Try to rest the batteries for an hour after charging to make sure that the rest voltage is similar - you need to charge to about 3.4V per cell, or 13.6v. match to +/- 50mV. Also ensure that if you are not monitoring each cell with a BMS, then the center voltage is monitored. Keep the Absorption voltage about 100 - 150mV below the theoretical battery maximum for safety.

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pjared avatar image
pjared answered ·

Thank you, Mike. I will try your suggestions. I can monitor each of my Epoch batteries through their app. While I can see the individual cell voltage, I don't see that I have any influence to affect them individually.

Regardig your last sentence, my batteries suggest 14.4V for bulk, 14.4 for absorption and 13.8 for float. Since these will be in series, should I set the Blue Smart's absorption to roughly 28.77? Thanks

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Justin Cook avatar image
Justin Cook answered ·

I think Mike may have misunderstood your question.

To fully charge each individual battery prior to connection in series as your battery manual no doubt states, you will need a 12v battery charger, and charge each battery separately to the manufacturer recommended settings. This allows the individual batteries' BMS to complete the first balancing cycle and etc.

Thereafter, connect the two batteries in series and charge them with your 24v battery charger.

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