question

alen avatar image
alen asked

Don't know which charger to choose

Excuse me, there are two batteries on my boat, A is STARTER BATTERY (70AH), B is LITHIUM (80AH), I installed Orion-Tr DC-DC Converters (12V) in the middle to isolate the two batteries, the engine is directly connected A charging, when A battery voltage is sufficient during driving, B battery will be charged through DC-DC.

I want to use a charger to charge battery A when the ship is towed back to shore, and then charge battery B through DC-DC. I don't know which charger and how much current charger can be selected for this configuration to avoid overheating?

*****Please forgive my english*******

charger
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@alen

The charger you choose should be based on the max charge current your batteries can take according to the manufacturer.

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3 Answers
basil katakuzinos avatar image
basil katakuzinos answered ·

If most of your use is on your house battery it may be worth charging that directly and skipping the starter battery but charging the starter battery is an option, I would go for something rated at least above the DC-DC charging capacity of your existing charger so that it can keep up. The blue smart IP22 is generally a good bet, and its nice and mobile so if you want to charge your house battery directly moving it is not hard

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alen avatar image
alen answered ·
Ok~ I will study IP22, thanks
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kevgermany avatar image
kevgermany answered ·

To keep things simple, I'd simply charge the the starter battery. But too much is unclear. Are you using the boat when it's back to shore (e.g. as liveaboard). Is electrical equipment still running even if you're not living on board.

If the answer to these questions is no, then you're looking at covering self discharge of the batteries, very low for lithium, higher for lead acid. You need a charger that will provide low power, but be intelligent enough to monitor and maintain a float voltage on the lead acid. Cheap car 12V chargers don't do that. You need an intelligent charger.

The other issue here is that the lithium charger may need to be able to charge when the lead acid is at float voltage, possibly even storage voltage. This will depend on your expected load on lithium while the boat is moored. Also how long between periods of use. So if lithium has zero load and you're going to use the boat once a month, probably not an issue, but if there's load (fridge,) and the boat will be unused for months, it needs to charge.

So... Look at loads. Including the orion. Time out of use. Get a smart charger that can cover the load and maintain float without overcharging. Tweak the Orion to kick in at slightly lower than float voltage.

If the boat will be in the water and you're charging from AC, fit a galvanic isolator as well.

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