Considerations for the NON 12v solar systems = 24v - 48v

[Captain Morgan]

I started off with the "simplicity" of a 12v system plan. Then I considered some of the benefits of a 24v and a 48v system, such as wire gauge etc.

When it comes to controllers you just buy one that's rated for the voltages from your solar wiring configuration and a "WTF do I care what the input voltage is if the controller can handle it?"

One can wire the batteries in series/parallel and have a 24v system, or go 48v . . . but then you need a DC-DC for the 12v stuff in your rig. OK FINE that isn't a big expense and the money you saved on smaller supply cables is more than the DC-DC costs.

However on a 24v or a 48v setup you can't charge the batteries directly from the alternator or the in-house generator setup. I will probably never have shore power to use or count on. So there's even more design consideration madness.

I have a Grayhawk 29MV and I mean to put as much frickin solar on that roof as possible and if there's 1' wasted space, I'll add a wind turbine. I'm talking solar saturation, I'm not up there to work on my tan.

I've been looking at making a 4x100Ah bank with the Fortune 100Ah Lithium Battery LiFePO4 to start with and maybe add on to next year.

Who here went 24v and what's your experience with charging from alternate sources?


Same as above with a 48v system, what did you end up using?


Thanks in advance.





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[morleyz]

Originally Posted by Captain Morgan

I've been looking at making a 4x100Ah bank with the Fortune 100Ah Lithium Battery LiFePO4 to start with and maybe add on to next year.

No experience with alternative voltages, but 4 of those batteries is only 12V and 100Ah total. Maybe I misunderstood, but are you planning 8 or 16 batteries to get you to 24V or 48V?

You want my opinion? You're over thinking it. If you want to max out your solar, series-parallel your panels to the max volts/amps your controller can handle (wire appropriately) and build the biggest 12V battery bank you can afford. 100Ah is nothing if you're never going to use shore power and your alternator is basically a trickle charge to the house batteries, especially if you're not motoring down the road.

The complexity you add will outweigh the wiring costs and minor efficiency downgrade. The batteries, panels and controller are your biggest expenses. 50 feet of wire isn't going to shift your budget. Also, every non-12V battery controller I have seen is massive and usually meant for mounting on a wall in a room. Space is going to be a consideration at some point between battery bank and controller (and how to wire them where you have space).

[norty1]

Weight may also enter into it. Someone must be working on smaller, more efficient batteries.

[Captain Morgan]

When I say 400Ah I mean 400AH, which is 16 of the modules. 4x4 in series / parallel, depending. Everything else is just a given and obvious. I can afford whatever I want to.

I'm good on space and weight, that wasn't the question here.

Please allow me to rephrase the ask:

what's your experience with charging from alternate sources? (since I said no shore power I'm inferring a generator or alternator step-up etc)

Same as above with a 48v system, what did you end up using? (no solar days and no alternative method means you're foobarred, "motoring down the road" won't help)

See the potential downside here? Is there anyone that has the real world experience to speak to the questions?




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[morleyz]

Originally Posted by Captain Morgan

See the potential downside here? Is there anyone that has the real world experience to speak to the questions?

I can only see downside actually. Where is the advantage? Any advantage you think you get by increasing the voltage you lose during step down to power the 12V coach. Yes, 48V allows you to drop the current so you can have smaller wires and go over longer distance with less loss, but unless everything in your rig is converted to natively support the different voltage, you're actually going to consume more DC power because of the conversion overhead. Just do the math:

W = V * A

Say your fridge draws 100W. At 12V you pull 8.3A off your battery bank. At 24V you pull 4.2A (awesome, 50% savings) BUT you now have to reconfigure your battery bank which cuts your total capacity in half and now you have to step down to 12V to actually power the fridge, lights, etc. which comes with an inherent power leak (which will be release in heat that you have to deal with). At 24V, your 16 cell battery bank is only worth 200Ah. At 48V, 100Ah.

The reason there are no real world people doing this is because it doesn't make sense unless you convert EVERYTHING in the rig and then it still probably doesn't make sense. Until you're dealing with much larger power draws, there isn't going to be an advantage. Is it worth the hassle to save 1Ah by doing a full conversion to 24V? Maybe if you're designing a golf car or the next Tesla, but at the consumption rates of RV appliances, you're going to see essentially the same power capacity at all voltages, and if you're off-grid, that's really all that matters. You'll be light years ahead staying at 12V and just adding more battery capacity if you want to power your rig longer while off-grid.

[Captain Morgan]

OK NOW we're talkin. There's plenty of "experts" on various forums, RV forums and so on that advise people "you should go with the 24 or 48v system because...." and they have some banter about why it makes sense to them.

Frankly I don't see the logic in saving money on lessor diameter cables to the CC if I have to re-spend it on multiple other compensations.

I bought 25' of 2/0 welding cables for my rigs just for the winching and ran through the frame rails. So a 15' run of 3 or 4 is no big deal if I can get it snaked down to where it needs to be. I sweat the lugs myself etc so I know it's done well.

But it doesn't hurt to throw this out there to the experts and ask why they do what they do. Except this is a forum and you know how experts can get. And where are they now?

What I have drafted is a system that uses 2 panels in series and 5 or 6 sets of them in parallel depending on available roof space. This combined voltage should be fine for a CC that's rated for it, and I could use 24v panels on the roof going to the CC and still have a 12v system. The current plan (no pun) is to put the 4x12v banks in parallel and buy a 100A CC. This has always been the most simple and straight forward plan AFAIK.

Thanks for the exacting reply.


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[LazyLightning]

So...how'd it work out?..did you need a PV combiner for the panel pairs? What does your current system look like comparatively?