hydrogen avatar image
hydrogen asked

Battery Bank Voltage Recommendation (12V vs 24V)

I am considering a 24V Multiplus with 12V batteries in series or 24V batteries in parallel, or even a 48V Quattro setup and looking for battery voltage recommendations.

This would be a LiFePO4 based bank.

A 24V battery setup would make a 24V system simple and provide for smaller 'sets' of batteries run in series for a 48V system (should I go with 48V now or upgrade to it in the future).

A 12V battery setup provides a secondary, 'fallback' option of using AGM batteries in some future scenario if I ever had a failure across the LiFePO4 bank and LiFePO4 was hard to come by or cost prohibitive.

What I don't care for with having too many 12V in a series is dealing with the need for all packs in series set to be 'matched' and if one goes bad, replacing it pulls the entire set out of 'spec' to some degree.

I am considering Battle Born 12V and 24V batteries, but open to hearing opinons here.

Thank you!

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3 Answers
wkirby avatar image
wkirby answered ·

Higher Voltage is always better. Lower current means lower cost cabling and smaller dimension DC components in general.
48V is what I'd recommend. There are a wider range of 48V commercial batteries available.
As you are considering future upgrades then this is another reason for 48V since the higher power levels are more easily accommodated on the DC side.
You need to decide your battery Voltage early on. Once you buy in to 12V for example then it's expensive to move to a different system Voltage as your existing MultiPlus would be unusable. I have made this mistake myself in the past......

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shaneyake avatar image shaneyake commented ·
I agree with wkirby, higher voltage is always better. Not always possible in van/small systems but I would go 48V if your PV array can run at around 100V or higher. 48V tends to work out cheaper as you need lees MPPTS for the same power, cabling is smaller etc.
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hydrogen avatar image hydrogen shaneyake commented ·

@shaneyake You just brought up something I was going to ask in a separate question, but will ask here instead.

If I understand correctly, the PV array must produce at minimum Vbatt+5V for Victron MPPTs to power-up, then Vbatt+1V thereafter.

But in your experience, what % of a PV panel's Voc can they typically produce at minimum when there is daylight, but not directly overhead? Or partial shade over a panel (that has diodes).

As I would like to consider 48V for the system, 2 x 24V panels per series (with additional pairs in parallel) may not be sufficient Voltage, correct? I have limited space for panels and they will not be in a permanent install (e.g. on the roof). For the time being this is for emergency scenarios. I can probably fit 6, maybe 8, but tops 10 total 200-300W panels.

Thank you!

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shaneyake avatar image shaneyake hydrogen commented ·
I just quickly looked at a few of my sites. If VOC is 47V, VMP is 39.1V, system runs around 37V per panel.

These are 410W panels. So I would say the panels should run pretty close to Vmp. For a 48V system I would aim for 80V+ but you can run lower.

Another thing I want you to make sure you are thinking about is a

MPPT150/35 running at 12V can only do 490W

Same MPPT at 24V can do 980W.

Same MPPT at 48V can do 1820W.

This is the case for all victron MPPTs.

Are you in the US? There are a lot of rack mount or wall mount 48V batteries on the market these days.

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hydrogen avatar image hydrogen shaneyake commented ·
Thank you again for your response. Yes, in the US. If you have any references to 48V batteries, I would appreciate it. The only LiFePO4 48V pack I've seen yet is made by Renogy for their Lycan system, but can be used for others, I presume.
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shaneyake avatar image shaneyake hydrogen commented ·

There are quite a few options, and it seems like one ones every day.

Simpliphi probably have the best name right now, however their CAN bus system doesn't support Victron yet for battery coms.

As you said Renogy has the 48V smart battery, coms also doesn't work but I think very over priced.

Signature Solar has the EG4 and EG4 Pro batteries.
I haven't tried to get coms working with Victron but might be possible with community project. The best price out of all the packs.

SOK Server rack battery

I also haven't seen anything about CAN bus compatibility but I think it should be possible.

Big Battery has a few options like the Rhino.
No coms at all but does have it own app.

Then there is always kinda DIY.
Signature solar sells a 8cell kit and 2 of those in serise with an Orion bms works really well with Victron, with native CAN support. Bms is like $800 ready to go. this is $1000 for 2 which is 5.24kwh

This is just a few.
How import is coms between battery and Victron GX? It isn't needed but is a very nice to have. If the coms works correctly it will look most battery parimaters to VRM, like MIN/MAX cell voltage, BMS Max voltage, BMS Max charge current, BMS Max dischare current, BMS SOC, BMS pack state of health. BMS tempture. Really helpful it in watching the batteries over time.
The next thing is that it puts the BMS in control of the charge proccess, this means if there is any problems, like high cell voltage it will slow down the charge so the bms has time to rebalance that cell before the BMS has to shut the pack off. You also don't need to install a smart shunt or BMV becasue you can get SOC data from BMS. All the systems I install have CAN bus coms, unfortually right now in the US it is really hard to find batteries that are fully supported. I have ended up building our own packs this far. All my international installations I use FreedomWon or Plyontech packs both not available in the US.

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Trevor Bird avatar image
Trevor Bird answered ·

It depends upon what power level you are considering. Anything up to 5kVA I would go for 24 volt batteries in parallel. I would try to avoid putting batteries in series to acheive the correct voltage (like 2 x 12 volt to acheive 24 volt) as they may get out of balance. If this happens and the BMS becomes very active it seems to cause unusual consequences. If you need to consider cable size a good referecne is the Victron Wiring Unlimited booklet.

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Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

In my opinion it also depends on what kind of system you are planning.

In a caravan or boat I would recommend 12V or 24V to easily use the alternator to recharge while the engine is running.

In a house I would recommend 48V.

To your PV question: The open circuit voltage is rising very quickly even in low light conditions. A "24V panel" has typically 36-40Voc, so you have 72-80Voc with two in series. That's enough to start the MPPT. But there are also panels available with higher Voc.

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