Voltage and suggestions for new camper build?

[Richard9th]

I'm setting up a new 50 kWh build for a small camper, and I'm not sure the right voltage to run it at.

I plan to mostly just run everything off of AC via an inverter, rather than using internal DC components.
That makes it pretty easy to buy parts, without having to look for special 12v/24v ones - I can buy regular 110v light bulbs, fridge, inductive cooktop, micro-split, etc.

It looks like I can fit 4 445w solar panels, which look to have an output of vmp of 41, and a voc of 50, and SmartSolar 250 MPPT controller(s).
I think I should be able to use those with a Victron Energy Quattro, with one input connected to an inverter from the vehicle alternator/battery, and one input able to be connected to shore power.

I already have a few various 12v lithium batteries from testing, but my understanding is the advice is generally not to mix them, and to do a system with all similar batteries.

Given that I don't have any 12v loads, it seems like 24v would be the default solution?

The efficiency doesn't seem dramatically different either way, and while running thick wires would add a bit of one-time cost, they're relatively short so the cost is pretty small compared to the batteries and other system costs - They're relatively short, so I don't think there would be be all that much efficiency loss.


I suppose 12v seems like it might be *slightly* safer in case of shocks/etc, and potentially easier to buy things that interface with locally. Would a 12v system work better in partial shade? (That part was somewhat confusing to me)


I know I'm relatively inexperienced - What else should I be considering for this build?

 

[time2roll]

I think the question might be between 24v and 48v. I would not be considering 12v at this level.

What size inverter will be used?

 

[John Frum]

For 50 kwh I suggest 48 volts dc system voltage.
For a system of that scale I totally agree with not having pure dc loads.
Is this a trailer?
Here is some math on the panels...
4 * 445 watts * .9 conversion efficiency = 1602 watts
50000 watt hours / 1602 watts = 31.210986267 hours

I don't see the sense in your proposed storage to generation ratio.

 

[Richard9th]

> I think the question might be between 24v and 48v. I would not be considering 12v at this level.
I may be being overly cautious; I've only done small 12v builds at < 600aH before.
I am nervous about doing something wrong with higher voltage.

> What size inverter will be used?
I'm not 100% on the load for other components - I want to measure them locally to verify their draw, but I was hoping to get away with the 5000VA Quattro, which is available in 12, 24, or 48. If I do end up needing more, I could get two but I worry about the size (The camper only has so much space..)
If I'm reading their spec sheet right, they have 8000 available in 24v, or up to 15000 in 48

 

[Richard9th]

Is this a trailer?
Here is some math on the panels...
4 * 445 watts * .9 conversion efficiency = 1602 watts
50000 watt hours / 1602 watts = 31.210986267 hours

I don't see the sense in your proposed storage to generation ratio.

A small ford transit box truck.

The solar is mostly to help charge it up during the week, without having to install an exterior outlet and worry about plugging it in. I want to leave it for the week, then let me take it out for trips on weekends.

 

[John Frum]

A small ford transit box truck.

The solar is mostly to help charge it up during the week, without having to install an exterior outlet and worry about plugging it in. I want to leave it for the week, then let me take it out for trips on weekends.

That does make sense.
I've not seen anyone try this strategy yet.

 

[John Frum]

50 kilo watt hours of LFP battery is ~700 pounds.

 

[John Frum]

That is a lot of power for a weekend.
Is this going to be concession truck?

 

[Richard9th]

That is a lot of power for a weekend.
Is this going to be concession truck?

I'd like to be able to keep AC running in the summer, and cook while avoiding propane and generators if possible.
A MrCool unit says it can take up to 1500W per hour in the worst conditions, plus a microwave, inductive cooktop, coffee maker, etc.
With the EG4 batteries priced where they are, it isn't cheap, but it's not as bad as it could be.

 

[John Frum]

I'd like to be able to keep AC running in the summer, and cook while avoiding propane and generators if possible.
A MrCool unit says it can take up to 1500W per hour in the worst conditions, plus a microwave, inductive cooktop, coffee maker, etc.
With the EG4 batteries priced where they are, it isn't cheap, but it's not as bad as it could be.

I like those batteries!
1014 pounds plus racking though.
Your idea has given me some ideas.
I wonder what a state of the art mobile recording studio looks like now?

 

[Short_Shot]

If you insulate the thing properly you will be much closer to the minimum output of the air conditioner lol

 

[Richard9th]

I think the question might be between 24v and 48v. I would not be considering 12v at this level.

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?

 

[Hedges]

50 kWh is a lot of storage capacity. But for voltage selection, what matters is wattage drawn.
Induction cooktop would be a heavy user.
5000W, you say? Possible with 24V, preferable 48V.

You've listed < 2kW of PV. Might deliver 10 kWh in a day with sun directly overhead, takes 5 days to fully recharge battery.
How many days do you need to get by without sun?
I'd rather have 10 kWh of battery, maybe just 5 kWh. For size, weight, cost reasons.
5kWh at 1C could power a 5kW induction range for one hour. Recharge in 2.5 hours at 0.4C from PV (on the best day)

Running A/C, you'd like to have PV production exceed average power draw. That is a tall order for a vehicle parked in the sun. I would try to panel 100% of the area from rear bumper to front. The panels you mention might cover most of my full-size (but not crew-cab) pickup. My idea is panels hinged on left and right. They lie flat with one covering the other, or tilt up to meet at a 60 degree angle like a roof. That would fit 2x the panels and produce fairly uniform power all day.

 

[John Frum]

watts = volts * amps

As the voltage doubles the ampacity is halved.
Meaning that you can transmit 2x the power for the same amperage.

Also voltage drop as a percentage halves as voltage doubles.

 

[Richard9th]

50 kWh is a lot of storage capacity. But for voltage selection, what matters is wattage drawn.
Induction cooktop would be a heavy user.
5000W, you say? Possible with 24V, preferable 48V.

I totally might be misunderstanding, but I think the Quattro 5000 looks to be available for 12/24/48.
I recognize the amperage you can draw from it depends on temperature, but I think that if I read the spec right, the unit could accommodate the load. An inductive cooktop is 1200W, plus AC running at full is 1400, so I think even if the inverter were at max temperature, it'd still be in spec.
> Cont. output power at 65°C (W) 3000

You've listed < 2kW of PV. Might deliver 10 kWh in a day with sun directly overhead, takes 5 days to fully recharge battery.
How many days do you need to get by without sun?

Running A/C, you'd like to have PV production exceed average power draw. That is a tall order for a vehicle parked in the sun.

I think I must be doing an rather unusual build - I want to have it sit for 5-10 days next to my house, then take it out for 1-3 days.
Essentially, let it charge up while I'm not using it during the week, then go out camping occasionally.

That's why I want a largish battery - Since batteries are relatively inexpensive and I have the GVWR to spare, it's easy enough to add more battery until the physical space gets in the way.

I think 24v seems straightforward, but maybe the voltage matters more in other build/usage styles than it does it mine?

 

[ianganderton]

If you are using only AC loads then 48V makes most sense. Much more efficient.

 

[Richard9th]

watts = volts * amps

As the voltage doubles the ampacity is halved.
Meaning that you can transmit 2x the power for the same amperage.

Also voltage as a percentage halves as voltage doubles.

Right, that makes sense.
I apologize, I know I'm being terribly obtuse, but I'm trying to understand the practical effect of that.

It seems like as long as I have a sufficiently thick cable to handle the inverter draw, the capacity of the array of batteries doesn't matter, right?
With 10 batteries, they can all be within a few feet of one another.

I'm getting the impression that perhaps I'm over-thinking it, and the voltage won't make a big difference for this build no matter what I use.

 

[Richard9th]

If you are using only AC loads then 48V makes most sense. Much more efficient.

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?

 

[John Frum]

Right, that makes sense.
I apologize, I know I'm being terribly obtuse, but I'm trying to understand the practical effect of that.

It seems like as long as I have a sufficiently thick cable to handle the inverter draw, the capacity of the array of batteries doesn't matter, right?
With 10 batteries, they can all be within a few feet of one another.

I'm getting the impression that perhaps I'm over-thinking it, and the voltage won't make a big difference for this build no matter what I use.

Using the 24 and 48 volt eg4 batteries as an example.

The 24 volt version will be internally 8s2p and the 48 volt version will be 16s1p.

For equivalent capacity the 24 volts system will have double the number of batteries in parallel.
10p for the 48 volt case and 20p for the 48 volt case.
Scaling challenges and efficiencies will be worse at 20p than 10p.

 

[Richard9th]

Using the 24 and 48 volt eg4 batteries as an example.

The 24 volt version will be internally 8s2p and the 48 volt version will be 16s1p.

For equivalent capacity the 24 volts system will have double the number of batteries in parallel.
10p for the 48 volt case and 20p for the 48 volt case.
Scaling challenges and efficiencies will be worse at 20p than 10p.

Thank you for being patient, I think I am close to understanding.

They sell variations of that battery in 12/24/48.

Each of those appear to be the same physical size (18x18x6), weight (100 lbs), and capacity (5 kwh) right?

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.