james-yardley avatar image
james-yardley asked

How to charge a 48V system from a 12V vehicle alternator

Hey everyone, First post on here!

We're just in the middle of setting up our Victron system and want to use a 48v system (due to cable sizing and efficiency) in our overlander which has a 12v alternator.

My question is, can the Victron batteries be charged in parallel (i.e each batter individually charged) but drawn from in series?

If so are there Victron products or suggestions on the best way to achieve this setup, there will at some point also be some solar power introduced too, so if that could be kept in mind it would be great!

Any advice/suggestions gratefully appreciated!


battery charging
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7 Answers
JohnC avatar image
JohnC answered ·

Hi @James Yardley And welcome.

Not saying this can't be done, but you'd find it quite onerous to do. Eg. You couldn't use the same charger, as each batt (presuming 12V's) has a different 'earth', so need isolated outputs. Then there's balancing them.. too hard.

This is quite an unusual request, so unusual that Victron don't have a product to do this 12 > 48 thing.

Usually road-going applications like the biggest of trucks would use 24V. Do you really need 48V? Maybe you foresee an off-the-shelf Li batt pack?

At 24V, Victron have this new little gem:

Your future solar charger might impinge on your decision too. There's a big range at 24V, the 48V-capable ones mostly at the high power end.

Sorry to deviate, but need to ask this stuff..

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kai avatar image kai ♦ commented ·

I kind of agree, 12->48v would be unusual. You essentially need an extra 3 chargers if using the 4x converter route.

I'm assuming if you're using 48V its thirsty loads which implies high charging current, and there the 12v becomes a bottleneck.

Not sure about the battery chemistry you're looking at and what you're planning on doing (powering a big winch?), but one option could be to add a 48v alternator (ones used for buses/emergency vehicles), with either an internal or external regulator for charging; need to confirm if you have suitable mounting point and belt for it.

edit: replacing the 12v alternator would mean touching the 12v loads, so that's definitely in the too hard basket.

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james-yardley avatar image james-yardley kai ♦ commented ·

Hey thanks for the reply...

Ha Second alternator, That's what I figured tonight.

The 48v System has come about because of a specific need for a 2kw heating element, I've wound thee element now and encased ready for a 48v system. The problem is 2kw on 12v just draws an obscene amount of current and the wiring involved is ridiculous.

There's definitely room for a 48v alternator, plus a lot easier to go from 48v to 12v should I decide to add a 'charge starter battery' facility.

Thanks for advice all.

Oh and FYI the 2Kw loading is for quite short durations 10mins max. - the battery bank is LifePo4

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james-yardley avatar image james-yardley commented ·

Hmmm, Thought that may be the case....

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jd-travelers avatar image jd-travelers commented ·
I had a 48V motorhome a few years ago and I am building a new camper with a 48V system. 48V systems are becoming more popular amongst RVers. I am looking for an Orion solution for 12V to 48V alternator charging as a backup charging source. That way I can ditch the generator.
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Fuso avatar image
Fuso answered ·

Hi James, did you find s solution yet ? I plan to do similar. I am currently using an auxiliary 12v 120a alternator but plan to replace it with a 24v 120amp alternator and run a 48v house battery. A 48v Alternator would be an easier solution but are not commonly available yet and very expensive. @ James Yardley

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jwfrary avatar image
jwfrary answered ·


A packaged 48v alternator exists, it’s called integral. And made in the uk by triskel marine.

If your going that route you may find it easier to fit the one 48v alt and step down to 12 for the vehicle loads.

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Nickus de Vos avatar image
Nickus de Vos answered ·

Hi there, as already said rather consider going 24V, yes this will result in higher current draw, but it gives you a lot more options in terms of off the shelf equipment. You will be able to charge a 24V battery from your 12V alternator and you'll also be able to use the smaller Victron MPPT chargers if you go that route.

Converting from 24V back to 12V for your consumers like lights, phone charges etc. will also be a lot easier in the end.

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johnk avatar image
johnk answered ·

I've been trying to figure out a solution to this as well, but it seems the best answer is to try to avoid a 48v system. I've been unable to find a cost effective stand alone DC to DC converter that can be adjusted to the needed output voltage.

(I'd like to be able to use a 48v system as I'd like to be able to use a 48v DC generator. The 24v ones that are available aren't as good, and the 12v ones are even worse.)

The best I could find are things like this 20A converter, or this 10A converter, but I'm not sure if either would be great for, or adjustable to work with, a 48v LiFePo4 battery bank. (A bunch more here.)

Other thoughts turned to a terribly inefficient setup of dedicated 12v -> 110v AC inverter + AC -> 48v charger, with relay to cutoff the 12v supply to the inverter when the alternator isn't running -- but that's more reminiscent of a Rube Goldberg machine.

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bathnm avatar image bathnm commented ·
Do a search for Safiery and Scotty. A great solution for 48v system charged from stock 12v alternator. It can do 3Kw, and there are other models which are smaller.
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johnk avatar image johnk bathnm commented ·

Thanks. I did look at their products, but I wouldn't really put their converts in the "cost effective" category for my project. $3.5k could add a good amount of battery capacity.

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shaneyake avatar image
shaneyake answered ·

The easiest solution is to get 2x Victron Orion-Tr isolated 12/24-15.
You can put the two 24V outputs in series to get 48V and charge your battery from that.
Will be limited to 720W of charge power but that isn't too bad.

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48v-on-56north avatar image 48v-on-56north commented ·
My thoughts exactly. 200V isolation barrier, so careful schematic and wiring with twin volt free contact to turn on and off. Have you actually tried this or is it an educated guess. I am faced with same challenge for Electric sail boat application wanting two way transfer between 12V service/instrumentation battery and 48V traction battery
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shaneyake avatar image shaneyake 48v-on-56north commented ·
I have done this with DC-DC converters from Meanwell and it has worked really well. Similar specs to the victron DC-DC just much higher standby current so would not recommend using them.

The only thing I would be worried about is the Remote On/Off but it looks like it is referenced to the input so should be fine.

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sk8erboy avatar image sk8erboy commented ·
Hi, I've just seen this response, and I'm looking to do something similar (currently trying to decide between 24v and 48v).

Is this a Victron recommended configuration for the Victron Orion-Tr 12/24 series?

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ian-norton avatar image
ian-norton answered ·

Looks like there's a new product in Q3 2023 from Sterling Power.

Would be nice if there was a Victron option :)


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