Voltage and suggestions for new camper build?

[John Frum]

I think this is the part where I am getting stuck. Does the internal layout of the battery matter to me at that point? If they have the same spec on capacity and number of uses, then what difference does it make? They appear to have the same warranty.

At least for the 24 and 48 volt batteries(I didn't look at the 12 volt model) they will have the same number of identical cells in them.
The 24 volt cells are internally 2 separate batteries and the 48 volt cells are 1 battery.
That means 20 separate batteries at 24 volts
and 10 separate batteries at 48 volts.

All the current paths need to be as close as possible in resistance for the batteries to share the load equitably.
The complexity doubles for the 24 volt solution.

 

[John Frum]

You should contact the manufacture.
For a potential $15000.00USD order I bet they will give you excellent pre-sales support.

 

[Richard9th]

Ok, will do, thanks.

 

[ianganderton]

Can you help me quantify that?
Naively, it seems like it's only a few percentage different?

People keep saying that though, and I believe you!
I recognize I must be misunderstanding someplace, I'm just trying to understand where.

Maybe the max efficiency is similar, but non-max efficiency (which isn't listed) is different?


View attachment 70121

Doubling the voltage halves the current (Amps). Current is where most inefficiencies lie. Inefficiencies are lost as heat. The wires heat up.

Doubling the voltage and halving the current means you can use much thinner cables to connect things together. These are much easier gauges to work with

 

[Short_Shot]

Doubling the voltage halves the current (Amps). Current is where most inefficiencies lie. Inefficiencies are lost as heat. The wires heat up.

Doubling the voltage and halving the current means you can use much thinner cables to connect things together. These are much easier gauges to work with

Yes.

But the difference is largely irrelevant up to a certain degree. I personally believe OP is attempting a moonshot here. There are lots of examples of people running full time AC and induction cooktops with vastly less battery the same or less solar.

You also will need a step down for 12v devices which, depending on the load needed, can entirely negate any cost savings from thinner wires and further introduce inefficiencies which negate the advantage of the higher voltage.

Most people don't need to run a cooktop for a few hours a day for example, but rather a fraction of an hour, and even a little bit of insulation in a 'small camper' is sufficient to cut WAY back on the AC power usage with an inverter mini split.

 

[Rocketman]

With such a large battery- go with 24v or 48v. I wish I was able to setup my MotorHome for either of those.

 

[John Frum]

Here is some math to illustrate the scale and proportion.

5000 ac watts / .85 conversion factor / 48 volts low cutoff = 122.549019608 service amps
122.549019608 service amps / .8 fuse headroom = 153.18627451 fault amps
battery module current = 122.549019608 / 10 = ~12 amps
inverter wire = 2 awg wire and 200 amp fuse
battery wires = 12 awg and 20 amp fuse

5000 ac watts / .85 conversion factor / 24 volts low cutoff = 245.098039216 service amps
245.098039216 service amps / .8 fuse headroom = 306.37254902 fault amps
battery module current = 245.098039216 / 10 = ~24 amps
inverter wire = 4/0 awg wire and 400 amp fuse
battery wires = 8 awg and 50 amp fuse

5000 ac watts / .85 conversion factor / 12 volts low cutoff = 490.196078432 service amps
490.196078432 service amps / .8 fuse headroom = 612.74509804 fault amps
battery module current = 490.196078432 / 10 = ~48 amps
inverter wire = 2x 4/0 awg wire each with 400 amp fuse
battery wires = 6 awg and 100 amp fuse

Summary, 12 volts is nuts, 24 volts is at the bleeding edge, 48 volts is a piece of cake.

 

[time2roll]

To get back to this question though - I apologize for the ask, but can anyone help me understand this better?
I've watched Will's video on this subject, and a few other Youtube videos.

The differences I can see are
* Wires are bigger for lower voltages
Since I'll only be running the wires a very short distance from the battery rack to the inverter, I'm not sure how much this matters?
It would cost a bit more, and be a bit stiffer to run, but other than that it seems to be a one-off install issue.

* Higher voltage systems have larger capacity single-unit gear (such as inverters, solar controllers, etc).
I want to test to verify, but I think my loads will mostly work within the size available for 12, 24 or 48v.
Both my solar load and inverter draw seem like they'd work with any size.
If I did need higher capacity with a lower voltage, I could add parallel systems.
That is a concern for an inverter due to the size, but mppt controllers are pretty small.

* Higher voltage systems are higher efficiency
This seems true, but only by 1-2%? If so, that doesn't seem to be a big deal in either direction.

* Higher voltage needs a step-down converter to run 12v loads.
I don't plan to have these anyway, but even if I did, getting a converter is cheap and easy.

* Lower voltage is a bit safer to work with
Staying below 30v appears to be safer than 48, since 48 can cause more harmful shocks.
12v seems marginally safer than 24, but not materially.

Since most people are suggesting higher voltage, it seems like the way to go, but I'm not sure I understand why.
I'm sure I'm missing it, but it doesn't really seem like the voltage matters all that much one way or the other?

OK so yes wire size is a big deal when powering a 5000VA + surge inverter. Looking at possibly 500 to 700 amps requiring larger than 4/0 wire or parallel cables at the 12v level. 24 volt system cuts you down to 250 - 350 amps and is doable with single 4/0 maybe even 2/0. 48v puts you down to 125 - 175 amps for about #2 wire. Not just the wire but fuses, bus bar, switches, connectors all have to be monster at 12v. all connections are extra critical at 500+ amps. Some equipment could limit what you do or have to double up such as the solar controller. Yes 24v might be best if you do not want to get into voltages close to 60 in a nominal 48v system.

 

[circus]

Have you any idea how much this will cost?

 

[mwk1000]

FWIW this may help. I have my camper running on the 24v EG4 lifepower battery 200ah with a Growatt 3K inverter , the MOST it will power is 2400 watts ( theoretically before the BMS kicks in to shut it off ) at that wattage it is drawing 100 amps and that is the MAX the battery is designed for -- and you will certainly need the largest recommended size wire to carry that safely. The same 2400 watts @ 48V is 50 amps and the wire current size needs are 1/2 So consider what AMP's you will be expecting to pull from your batteries and size appropriately. I saw a fella running a new inverter mini-splt at 500 watts in his camper ( silent ).... I have an old 1600 watt carrier AC that will run off my setup (soft start modified ) but I can kill it if I use a hair dryer , or have the fridge and micro run at the same time etc etc. exceeding my 100 amp limit .. All in all it's not a big deal we can go for days without shore power in comfort. ( Ie. I have a nice big FAN pulling a crazy 65 watts ).

I used a victron 24v->12v converter right off the battery to the original battery terminals it is the new Trailer battery for water pump/Slide out lights etc... easy.