question

mikewh avatar image

input 12 v lead acid starter battery output 24 v electric motor lithium battery

Looking for a dc to dc charger to charge my 280 ah 24 v / 6800wh lifepo4 electric trolling motor drive battery from my 200 ah 12 v starter battery. (50 Amp 12V alternator on main engine)

Can you give me an advice what kind of dc to dc charger would suit my needs ?

something like a orion tr smart 12/24-15a (360w) isolated dc-dc charger should work ?

Lithium BatteryOrion DC-DC Converters not smartcharge controller compatibilitylead-acid
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4 Answers
Paul B avatar image
Paul B answered ·

not much around that goes from 12 volt to 24 volts DC

with out going into details, as to why , but the below is the easiest way

Buy a small 12 volt inverter, say a 220v AC 500 watt unit and a small 220volt to 24 volt battery charger (Less than 500w not over 15 amps) and you can then do what you are after.


the smaller the inverter then the smaller the battery charger needs to be

or you may already have a charger at home so use that, but remember that if the battery charger is 30 amp then you will need a 12v 700 watt inverter to match the chargers output size

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mikewh avatar image
mikewh answered ·

My boat has a 225hp main motor that I will use to go fast and I could use it to charge the electric trolling motor batteries when on a long trip. I will use the electric trolling motor for trolling (actually trolling for fish with 12 rods) . I will try the inverter method . mains charger Victron Energy Blue Smart IP67 24V 12a should work ?

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justmurph avatar image
justmurph answered ·

The orion tr smart 12/24-15a will do exactly what you want. The Orion TR smart can be set to throttle back if the alternator on the supply side isn’t keeping up (i.e. if your engine is idling). It also has engine running detection, so it will turn on and off automatically. I use one of these in my boat and it’s a great unit. I wouldn’t use the Orion TR high power version, as that will pull more than your alternator can put out and lacks the smart features.

I have no idea why anyone would use an inverter and a battery charger to do this.

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mikewh avatar image
mikewh answered ·

It would be nice to be able to set the charging voltage to 27.6v or maybe even down to 26.8v (and then once a month charge to 28.8v to re balance. it sure would be nice if the microprocessor of the charger could do this automatically . I think this could give the longest life and least hassle .


I need to maintain a speed of 2knots runtime 7 hours minimum (more is better). I'm expecting to use at least 30amps to maintain that speed .


It is really hard to find a suitable charger for a 24v system at least a 30amp charger would be nice.

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The output voltage on the TR Smart is fully configurable, but it won't change itself automatically. You shouldn't need to charge to a high voltage to balance a LiFePo4 battery. The BMS should do that for you.


So you say you want a 30A @ 24V charger, but that's more power than the engines alternator can supply ( 50A max @ 12V). Either you need to have another charge source, or rely on storage in the batteries. Running down the start battery isn't a great idea, so I think using a slightly undersize charger and running down the trolling battery is the way to go.

Running your 6800Wh battery down to 20% will give you almost 7 hours run time @30A, so with the addition of the charger putting in 15A @ 24V it will easily do 10+ hours. That of course relies on your engines alternator actually putting out more than 30A....which it probably won't when idling.

I mean I would like to find a faster and smart shore power charger. tr smart is great to charge from the starter battery/alternator

Copy that. Pheonix Smart IP43 and Phoenix will do 25A. Skyla TG has a 50A option.