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Advice on 24v vs 48v for expedition motorhome

jonnyo

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Nov 23, 2019
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i m building a expedition motorhome. will have some 12v light and simple item. The main draw will be a Midea 10 000btu AC, induction cooking, fridge, hot water heater, etc. not everything will work at the same time of course.

I ordered 16X 280ah cells that should arrive soon. I m wondering if i better build 2X 24v battery with each there BMS (overkill) vs going with a 48v battery with 1 bms (overkill). I was going to order a growatt 3000w all in one to power everything in the truck. Any reason to go with 24v vs 48v?
 
In my opinion, I would always go straight to the 48v unless there was a specific 24v device you needed to operate, like a 24v diesel heater or something. Going straight to 48v lowers current further, and allows future expansion (parallel stacking) if needed.

That's just me though, there may be others here who have their reasons for liking 24v... But my general rule for RVs is, use 12v up to the max watts of around 3000w (where we max out on 4/0 cable), but if you need more than that, just jump straight to 48v (unless you have specific 24v device you need to feed).

The only other caveat to that, might be that since you will need to run a higher PV input voltage to stay above a 51.2v battery bank voltage, so means more panels in series, and I know I've heard of some people who travel a lot, may stop at parks with partial shading, so they rather run more panels in parallel and not series, so they'd have less trouble keeping good charging when sunlight gets choppy (because series will kill the whole string when even one panel gets blocked).
 
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I'm a big fan of 24v systems myself because of physics. When you say to yourself "Self, this is great but I'm murdering my batteries, I should buy more!" and then you have to figure out where to STICK those batteries, well a 24v battery setup takes about half the space of a 48v battery.

Plus the panel voltage thing. 30v is easier to acquire than 60v on panels.

Having said that, if space isn't really an issue, go for the 48v setup and save the copper costs!
 
One other thing to consider is that the fuses and distribution for lower amps for 48v can be tricky. Eg Mega fuses for 48v are not available down below 100amp (although a recent thread found newly released littelfuse at 60amp for 48v).

This can be a problem for space in an RV.

The things that need lower amp fuses are solar charge controllers (eg 40amp) and 48-12 converters (eg 30amp or lower).

I ended up using din mounted DC breakers (Midnite), which are good because also a disconnect, but take up additional space (I ended up with a victron lynx busbar and a DIN rail box).

As large as they are If I was starting my build again I’d look at the Midnite MPV12 combiner box, and put both 48v DC And 120v AC breakers in there. Has the busbars (inc ground). Extra space at the bottom for shunt and mega fuse holder for inverter (din rail breakers above 63amp are expensive and large).

One other issue to consider: it is difficult to charge 48v batteries from a 12v alternator. As far as I can see it’s either 12-24 then 24-48, with plenty of loses or it’s a 12-120v AC inverter than an AC charger. Any other suggestions?
 
Since this is a from-scratch build, a 48 volt system may be appropriate. However, the components available at that voltage start to decrease, compared to 12 and 24 volt. There are a lot of components that are rated up to 48 volt but not beyond that. A LiFePO4 battery bank will spend it's entire life above 48 volts.

You likely have no high amp 12 volt devices, so a relatively inexpensive 48v-12v converter will do for those 12 volt devices like lights and pumps.
 
Since this is a from-scratch build, a 48 volt system may be appropriate. However, the components available at that voltage start to decrease, compared to 12 and 24 volt. There are a lot of components that are rated up to 48 volt but not beyond that. A LiFePO4 battery bank will spend it's entire life above 48 volts.

You likely have no high amp 12 volt devices, so a relatively inexpensive 48v-12v converter will do for those 12 volt devices like lights and pumps.
Any ideas for 12v to 48v charging from the alternator?
 
Victron doesn't make a 12v-48v converter for that scenario.

For getting 12v, Victron does make a 48v-12v converter, up to 30 amps.


Victron's high amp converter only goes up to 24v.
 
Any ideas for 12v to 48v charging from the alternator?

I've observed some people here in this forum, and in the RV communities referring to this unit, which I've never tried myself, but seems like it might be something to look into...

 
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