Boat running 24v system with 12v for lighting and pumps.

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jon111 asked Dec 4, '18

Boat running 24v system with 12v for lighting and pumps.

Hi,

For reference, the boat is 54ft x 10ft, standard wide beam. I've just built it, so it's a start from scratch with everything.

I'm contemplating running a 24v forklift battery bank, with a 24/5000 Multiplus, then having a 24v - 12v DC-DC converter to run all my DC domestic on board, which will be lighting, shower pump, water pump and bilge pump.

The reason for wanting 12v on board is ease of buying lights etc, 24v is not so readily available. I am also being majorly persuaded to go 12v by a boater friend, who says 12v is the most efficient way of having light. I understand the larger size cable costs for voltage drop, I'm ok with this.

The reason I want a 24v battery bank and Multiplus is because I will have 2.94kw of solar panels on the roof (12 x 245w) and I'm told having this at 24v will be much better. This is why I'm split between the 2 systems.

I guess my question is, will this system work for me? I plan to be off grid so I want to get this right.

I'm new to all this so I'm very much learning as I go.

Thanks in advance for any advice.

Jon

Orion DC-DC Converters not smart solar

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Answer 1 · 2018-12-04T19:25:08Z

markus answered · Dec 04, 2018 at 07:25 PM

You have built your own boat? Great!

Your explanations are conclusive, I would not say lighting by 12V is most efficient, but the easiest and maybe cheapest solution in your case.

Have a good ride!

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markus ♦♦ commented · Dec 04, 2018 at 07:29 PM

I would consider, using a 24V bilge pump. They do not cost much more and if your DC-DC converter fails...

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jon111 markus ♦♦ commented · Dec 04, 2018 at 08:50 PM

Ok Thanks Markus. Would I be looking at an isolated or non-isolated converter? Thanks

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markus ♦♦ jon111 commented · Dec 04, 2018 at 09:14 PM

That depends on your type of installation.

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jon111 markus ♦♦ commented · Dec 04, 2018 at 09:27 PM

So my understanding of the DC side would be from 24v battery bank > DC -DC Converter > Circuit breaker/Switch panel, which will feed all the appliances.

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markus ♦♦ jon111 commented · Dec 04, 2018 at 09:32 PM

Do you use 24 and 12 volt common ground as minus? Thats what the difference is for.

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jon111 markus ♦♦ commented · Dec 04, 2018 at 09:43 PM

yes I think I would.

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Answer 2 · 2018-12-04T21:44:07Z

wkirby answered · Dec 04, 2018 at 09:44 PM

I'll jump in if I may and confirm that the DC-DC option for stepping down to 12V would be the better option. In fact I do this very thing in my system.
24V halves your current for the big things like MultiPlus where at 5KVA, it's over 400A on a 12V system, which is terrifying! Fuses will need to be massive. 24V bings this down to a more sensible 200A. Circuit breakers are more easily available in range.
Any given MPPT solar charger can handle twice as much PV power on a 24V system compared to a 12V one.

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Answer 3 · 2018-12-04T21:51:46Z

Peter Polz answered · Dec 04, 2018 at 09:51 PM

In case of anyway planing a DCDC .. why you are not thinking about 48V for MP and MPPT?

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jon111 commented · Dec 04, 2018 at 10:18 PM

I hadn't really thought about that until you've just said. So I could go with a 48v system and just step down to 12v for domestic power inside through a 48v-12v DC-DC converter. Would this make more sense over 24v?

The only difference to consider I guess is a bigger battery bank to get 48v, but I have made a pretty big engine room which would easily accommodate this.

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mvader (Victron Energy) ♦♦ jon111 commented · Dec 04, 2018 at 10:42 PM

Just my 2cts: note that when using an 48V battery bank, it won’t be bigger in size or heavier than its 24v equivalent in energy.

It will be equal.

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markus ♦♦ jon111 commented · Dec 04, 2018 at 10:29 PM

For marine application, I would keep in mind that there are many useful 24V devices available that could be used directly without use of a DC step down. Just thinking of anchor winch, Nav., Radar, radio set, etc.

Also keep in mind, that you engines alternator (if you have) might be 24V.

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jon111 markus ♦♦ commented · Dec 04, 2018 at 10:42 PM

Yes this is true Markus. My engine is 12v but I was going to add a 24v alternator to it for the batteries. If I went with 48v, using the engine for back up charge wouldn't work.

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markus ♦♦ jon111 commented · Dec 05, 2018 at 02:00 PM

So your starter is operating at 12V? I would consider, changing the starter to 24V too.

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Answer 4 · 2018-12-05T03:35:16Z

JohnC answered · Dec 05, 2018 at 03:35 AM

Hi Jon. All good advice here, but there's another approach you could consider too.

I incorporated twin 12V engine systems, lights, instruments and pumps into a single 12V 'hub' using leftover batts from a 48V 'house' storage replacement. It ended up quite massive, like 1350Ah @12V. But does help take the load off my house batts. Not seagoing critical, so suits me.

Charged with just a 230ac/12dc workshop charger on a $5 powerpoint timer set for absorption/float times. (I would have bought a blue one but I had it lying about.)

Prior to that I had a blue Orion 48>12 converter. It's redundant now, up my sleeve..

With 2.94kW of pv, you're beyond 12V usefulness, and even at the higher end of the 24V range. But a pretty good match for a 100A mppt.

I went with an Easysolar 5000, the included 'switchboard' won me there.

Congratulations on your build too. Good work, and good luck with the finishing touches. You do know blue is a 'lucky' colour?.. :)

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