2-Volt Batteries

[Chance]

While doing research into larger battery banks for a motorhome, I ran across 2-Volt batteries from a few major manufacturers.

Has anyone used them or even thought about installing 2-Volt batteries in lieu of 6- or 12-Volt deep-cycle batteries?

There have been a few threads discussing interest in large-capacity battery banks for motorhomes, and while the topic of 6-Volt versus 12-Volt batteries comes up occasionally, I don't recall 2-Volt batteries being discussed; or ever coming up.

Any thoughts on pros and cons of 6 X 2-Volt batteries wired in series?

[JamieGeek]

Like this guy:
https://www.solar-electric.com/trl111ah2dec.html
I can see cost being a factor ($353 x 6 yikes) and space required (says on that page that the 2-volt "fits in the space" of a 6 volt thus you'd need more space).

You're basically just getting the same number of cells: whether you're buying X amp hours of 12V batteries, 6V batteries, or 2V batteries its still just X amp hours (if you get them all rated at the same discharge rate).

I would think the advantage of 2V batteries would be easier replacement when a cell dies since each battery is a cell you are only replacing a single cell instead of multiples (e.g. if only 1 cell goes bad it is more cost effective to replace only that cell).

[Chance]

Originally Posted by JamieGeek

Like this guy:
https://www.solar-electric.com/trl111ah2dec.html
I can see cost being a factor ($353 x 6 yikes) and space required (says on that page that the 2-volt "fits in the space" of a 6 volt thus you'd need more space).

You're basically just getting the same number of cells: whether you're buying X amp hours of 12V batteries, 6V batteries, or 2V batteries its still just X amp hours (if you get them all rated at the same discharge rate).

I would think the advantage of 2V batteries would be easier replacement when a cell dies since each battery is a cell you are only replacing a single cell instead of multiples (e.g. if only 1 cell goes bad it is more cost effective to replace only that cell).

Jamie, that particular battery example is quite a bit larger than I was evaluating (comparing). Six of those would yield 1,110 Amp-hours at 12-Volts, which is the equivalent of about 12 standard-size batteries -- hence why cost is much higher than you'd expect.

The main advantages I see are two (no pun intended): You'd buy 6 batteries of whatever size you want/need, then wire them in pure series. Because of that, wiring is simple and location wouldn't be critical. Since they'd be in series all batteries get same current no matter where they get placed or how long/short the cables are.

The other main advantage I was considering is the lower weight of each battery compared to using fewer but larger 12-Volt batteries; otherwise you get into too many 6-volt batteries (on very large systems) or fewer 12-volt batteries that are each too heavy or requiring too many parallel strings.

I'm not sure I follow your number of cells comment. As I understand it (which isn't in much depth), each battery is essentially one large 2-Volt cell, so there would be a total of 6 cells. By comparison, 8 X 6-Volt batteries would have 24 cells, as would 4 X 12-Volt batteries.



For what it's worth, I started looking for around 680 Amp-hours at 12-Volts (design goal). At this lower end of battery-bank size it's also possible to use 6 X 6-Volt, 8 X 6-Volt or 3 X 12-Volt (large 8D batteries). Comparing costs of AGM from Lifeline each option was close in price and total weight.

http://bdbatteries.com/marinebatteries.php

[Chance]

P.S. -- Sourcing seems like it could be a huge "con". If a battery suddenly fails during a trip, where do you get a replacement?

[scrubjaysnest]

The 2 volt cells are typically used in solar power homes or off grid cabins.

[TyCreek]

Individual cells for fully managed Lithium packs makes logical sense to me. But with lead acid Individual cells just externally connected in either series or parallel or both, the only positive I can think of right off is the ability to rotate cell lineup every so often. Personally I'd rather buy just one battery solution designed specifically to output the specifications I want. Battery size/form factor availability can sure limit choices with many projects.

[Chance]

Originally Posted by scrubjaysnest

The 2 volt cells are typically used in solar power homes or off grid cabins.

Yeah, and apparently large luxury yachts too. What 2-Volt batteries appear to offer most is being able to create very large-capacity systems without having dozens of batteries, particularly at lower system voltages, which would lead to many parallel strings. As RV battery-bank capacity get larger, it may make sense to look at 2-Volt batteries also (assuming lithium doesn't replace lead batteries first).

[Chance]

Originally Posted by TyCreek

Individual cells for fully managed Lithium packs makes logical sense to me. But with lead acid Individual cells just externally connected in either series or parallel or both, the only positive I can think of right off is the ability to rotate cell lineup every so often. Personally I'd rather buy just one battery solution designed specifically to output the specifications I want. Battery size/form factor availability can sure limit choices with many projects.

If you needed 500 to 1,000 pounds of lead batteries to store required energy, how would you split it up to make each battery "component" manageable in size and weight?

I think fewer numbers of larger cells is typically considered superior for deep cycle applications. That's one of the advantages of 6-Volt batteries over 12-Volt batteries. Using 2-Volt for larger systems just takes it another step in that direction. Or does it?

[TyCreek]

I see the advantage of 6V over 12V simply as price per usable AHr capacity for X amount of probable life in a form factor that is readily available. Getting the same type of individual cell capacity of a GC but in a single 12V package has always been quite a bit more expensive option in my battery power solutions for projects.

Basically the idea of using 2V individual cells boils down to what impact those external connections might make. My rule of thumb in every series configuration I've done is that the connection between cells in series must be identical and that would be difficult if the cells had to be in different locations. I wouldn't recommend a long distance between GC batteries either ... if you must store in multiple locations I'd recommend each location to have same capacity and final voltage so they connect in parallel.

[Chance]

Originally Posted by TyCreek

I see the advantage of 6V over 12V simply as price per usable AHr capacity for X amount of probable life in a form factor that is readily available. Getting the same type of individual cell capacity of a GC but in a single 12V package has always been quite a bit more expensive option in my battery power solutions for projects.

Basically the idea of using 2V individual cells boils down to what impact those external connections might make. My rule of thumb in every series configuration I've done is that the connection between cells in series must be identical and that would be difficult if the cells had to be in different locations. I wouldn't recommend a long distance between GC batteries either ... if you must store in multiple locations I'd recommend each location to have same capacity and final voltage so they connect in parallel.

I can't follow what you seem to be implying -- sorry if I'm not reading it correctly.

I'm talking about building the equivalent of a single 12-Volt battery out of 6 cells connected in series. All 12-Volt lead acid batteries have 6 cells connected in series. When we connect two 6-Volt batteries in series we also end up with a total of the same 6 cells connected in series, right? In that case most connections are built into battery and one is external.

When you only have two 6-Volt batteries in series, why is the interconnecting cable length critical? Granted you want to keep all cables as short as possible, but why would that particular cable make a difference compared to ground or positive cables?

I'm also confused by your reference to connecting in parallel. The main goal here is to eliminate parallel connections regardless of battery bank size. Instead of many batteries in a combination of series and parallel, we'd only have 6 cells (each of very large size) just like if it was one very large 12-Volt battery. The only real difference is that the 5 connections between the 6 cells are external instead of internal.

[TyCreek]

I get what you're thinking about with the large capacity cells and assuming the cells are a near enough match it is my preferred way to build a DC supply when a packaged option just isn't best.

Single cell options are great when you can connect them with buss bars or nice cable stubs designed to minimize impact or role in the charge/discharge behavior. I suggest any plan to separate those cells by distance will disrupt "balance". How much sort of depends but my bet is you'd be unhappy in the end.

I also suggest that a remote location as a simple parallel interconnect, would be my choice and bet for long term success. Certainly open to an argument to sway me otherwise

In reference to 6V in series ... or as an example ... Think about optimal long term use providing usable 12V, the series jumper wire between them must be as optimal as the internal interconnects. Since that's not likely, the use of GC batteries for 12V is a technical compromise where the low cost outweighs the negative impact. For this topic, look up interconnect recommendations.

[Chance]

Originally Posted by TyCreek

....cut... I suggest any plan to separate those cells by distance will disrupt "balance". How much sort of depends but my bet is you'd be unhappy in the end.

...cut....

Thanks for feedback -- it's appreciated.

I'll have to research your concern regarding "balance". My assumption was that as long as you have a single string made up of 6 identical 2-Volt cells, that electrical current would always be the same through all cells regardless of how long or short the cables would be -- not that you'd make then longer than necessary. I'm not presently sure why cells would get out of balance any more than cells of a 12-Volt battery.


More recently I've seen that the future will be 48-Volt DC, so I'm more likely to end up with 4 X 12-Volt batteries or 8 X 6-Volt batteries -- all also in series. The principle of connecting batteries purely in series still remains the same -- and with similar concerns.

Thanks again.

[TyCreek]

What sticks in my head for higher voltages is that you can get more power (watts) with smaller wires due to less current needed (watt = amp x volt).

This concept was a huge factor when I was building electric bicycles using a hub motor where wire size was limited by the space in the axel. Splicing in thicker wires helped however, increasing the voltage of the battery supply was the biggest gain in performance and reduction in the heat generated by those small wires.

From an RV or off-grid perspective cables sized to carry current (amps) could get crazy big for power hungry use. So really there's no choice but to increase voltage. To increase voltage we connect cells in series making the battle of cell variance factors increase. Balance of individual cells or cell groups is what leads us to circuit controlled array storage systems (BMS is one of the acronyms).