6v vs 12v Batteries

[kazetsukai]

Originally Posted by john61ct

No idea why that would be the case, 800-1200Ah banks are very common in 12V.

I'm not saying they are uncommon. I said beyond 1200W of solar / PV input, or heavy loads, you may want to up the voltage of your battery bank for a few reasons.

Originally Posted by john61ct

Some people have very high amp loads like winches, air compressors for SCUBA, big RO water purifiers, or specialised freezer / aircon systems that need higher voltages for greater efficiencies. . .

Or have big inverters, case in point: I'd kind of like to be able to run the coffee machine at the same time as the microwave. And/or a little convection oven. Maybe I'd like to park on a piece of land with a well on it and run the pump.

I sized my system for an electric residential dryer... Who knows if I'll stick with electric now that I plan to put the dryer in a trailer, but that was the benchmark. I'm not saying it can't be done with 12V, but personally I wouldn't consider it with any level of seriousness. If you anticipate regular loads beyond 2kW you're better off bumping up, in my opinion.

Originally Posted by john61ct

But regular household load devices, not too huge a living space, just sticking to regular KISS 12V is usually the way to go, avoiding wasteful conversion as much as possible.

I agree to keep it as simple as possible, but I'm not convinced that stepping down is actually all that more complex.

I have a 24V DC load center. The added complexity in my system needed to power 12V devices is a little 480W 24V -> 12V step down transformer I place between the 24V fuse panel and a 12V fuse panel. It powers any and all of my 12V loads no problem and it remains stable at 12V regardless of the state of charge of my bank (there are step-downs that specifically target 14.4V, 13.8V, etc and do the same).

Compare this to the alternative: My solar charge controller is a Victron 150V/100A. Wasn't cheap. On a 12V battery bank, it would be current limited to 1200W of usable PV, maximum. @ 24V, 2400W. Part of the reason I'm going up to 48V is that I'm in the middle of putting 3000W on the roof. A 12V system would require three of them, not one. Which case is more complex?

All I need to move to a 48V bank is change my inverter out, replace the 24V->12V step down with a 48V->12V step down and reconfigure the batteries. Nothing on the consumption side cares what voltage my batteries are, and I think its probably better that way.

[john61ct]

I prefer one small SC per panel, to best handle partial shading. Can actually work out cheaper the way Victron pricing goes for the 10-20A units, especially as you say if going to 24V.

I try to avoid AC devices as much as possible, my very long life have never considered owning an electric clothes drier, actually consider it one of the evil aspects of excess 'Murican consumerism. In an off-grid living scenario LOL preposterous!

But hey that's what makes the world interesting, you do you man

[rydawg3000]

Hmm, not to hijack the thread but I feel some others might read this and come to the same conclusion that we have:

I think we have realized that we want to go with 12v AGM or GEL so that our battery bank can be stored inside the back of our bus, at least for now. I haven't been able to find many 6v Sealed Lead Acid batteries with a high enough Ah Capacity (at least 100-200Ah) on my research online besides this Amstron GC2 6v AGM 200Ah https://www.atbatt.com/amstron-ap-gc...iABEgLEi_D_BwE

I am fine with using two 6v batteries in series to give me the 12v bank I need but it does mean a little more money to due to connections and such.
Also, at $209 a piece I'd spend about the same on 2 of those as I would just buying this 1 200Ah AGM ($359) or GEL ($405) from Renogy. That's not counting the cost of cables and connections. I want to start out small as this will only be used to power the 12v side of our bus which pulls very minimal power. We will increase our battery bank once we are ready to install solar.

AGM: https://www.renogy.com/deep-cycle-ag...12-volt-200ah/

Hybrid GEL: https://www.renogy.com/deep-cycle-hy...12-volt-200ah/

1) Are there any reasons (other than perhaps space/weight) why running 2 of the 6v SLA batteries in Series is a better option than just 1 larger 12v AGM or GEL?

2) Are there any better priced 12v AGM or GEL batteries on the market by reliable manufacturers?

Thanks for any input!

[gs1949]

I am also seriously thinking about putting my batteries inside, but I would use FLA 6 volt golf cart batteries and ventilate the box. Sealed batteries are much more expensive and they don't last as long as well-maintained FLA

Obviously the lid would have to be well sealed, but I don't think it would be difficult to design and build something that would allow hydrogen to vent outside. As long as the vent was at the highest point of the battery box, it would be completely safe.

[rydawg3000]

Originally Posted by gs1949

I am also seriously thinking about putting my batteries inside, but I would use FLA 6 volt golf cart batteries and ventilate the box. Sealed batteries are much more expensive and they don't last as long as well-maintained FLA

Obviously the lid would have to be well sealed, but I don't think it would be difficult to design and build something that would allow hydrogen to vent outside. As long as the vent was at the highest point of the battery box, it would be completely safe.

I agree it wouldn't be too hard to design a sealed box of some sort if you had the space. However, I also like the idea of having the access to cables/connections to and from the battery being easier to get to which would be the case if they didn't need to be in a sealed box.
Our battery bank will be stored on a shelf type of unit so building a vented box doesn't work for our application because they will be stored so close to window height. (The cat's litter box station is what has influenced our batteries to be on a "shelf")

Any reason why (if the price comes out to about the same) why one or two large 12volt GEL batteries wouldn't be a better option since the GEL will outlast the FLA, SLA and reportedly AGM too? Seems to be the simpler and more cost efficient down the road.

[gs1949]

Putting batteries on a shelf would make me very concerned about what might happen in a front impact or even an extreme braking situation. But as long as they are very well-secured it should be OK.

[kazetsukai]

My batteries are in the cabin as well, lithium cannot charge while frozen. Climate control was the primary reason, a nice bonus was easy accessibility. The drawbacks are obvious: It uses up floor space.

[gs1949]

I am curious as to the freezing point of a lithium battery. Or does the freezing point change with the level of charge like lead-acid batteries do?

[TheArgobus]

I also have a LiFePo4 bank, although it's a little unconventional (I have forty 3.2V 30amp hour pouches). I am also NOT an expert by any means. My understanding is that the low temp issue with lithium has more to do with charging. Everything I've seen says not to charge my cells in temps below 32F. If the cells themselves are at or below those temps, I've read that it's important to put a light load on them--lights, for example--as the act of discharging them warms them up before connecting a charger/solar controller. As far as simply discharging them, I've read their good down to 20F but this is really up to the manufacturer to design/test them. Big picture: the colder the battery gets, the higher the resistance in its internal structure, which lowers its voltage.



Some guys on here have considered putting a heating mat under their bank and a relay controlled by an Arduino/temp sensor. It's not an issue for me, fortunately, as I'm a fair weather sailor.

[john61ct]

So many disparate topics per one thread. . .

If you really want sealed, you will pay more per Ah per year, no way around that.

And you need precisely regulated charge sources, so easy to murder the bank either under and over charging.

For AGM, the main three makers of decent quality for deep cycling are

Odyssey
Northstar
Lifeline.

Do not order online, call the mfg for a local dealer and pick them up.

For GEL, Sonnenschein or Deka.

That is all. Do not throw your money away shopping in automotive or consumer retail channels.

[chinchl143]

I have four of both of these batteries!

Simple question is it better to run the four 12v in parallel, or the four 6v in series then parallel.

#1 are 6volt Rural King RC (25A): 390.
AH Capacity (20hr) 186
one year old always on float charge.

#2 are 12v B.B. Battery MPL80-12.
78ah @ 10hr rate F.V.
Two years old always on float charge.

Specs are right off each batteries web site. Not sure why #1 is at 20hr and #2 at 10 hr. (Do i dbl or divide does it matter ��).
It just confusing me to all end.

Simple dorm fridg, freezer and LCD 30" tv draw. I have 520 watts of solar. And a 30amp MPPT controller.

[john61ct]

The 20-hour rate 0.05C is going to yield a bigger Ah capacity than 10-hour 0.1C.

See Peukert's Law.

The 6V units, first in parallel get to 370Ah, then series those pairs to get up to 12V.

The 12V paralleled give 300+Ah but likely won't last as long.

You could run both sets in parallel for 650Ah total, but that would be bigger than most require, and very heavy.

Break down your panels, all identical?

[chinchl143]

Thank you John, I'm looking up Peukert's Law today.
Panels are four Kyocera KC130TM with a P Max of 130w in a series parallel configuration.

[john61ct]

Likely to get 130-150 Ah per day in ideal conditions, assuming a good controller.

So keep consumption average lower, depending on the weather.

A large bank capacity just give a bit more days' buffer, unless ICE inputs on demand are available.

A SoC monitor helps you keep track, care for the batts get better longevity.

[chinchl143]

Once again thanks. What do you mean by "ICE inputs on demand are available".

[john61ct]

fossil-fueled power on demand, running AC / DC genset and/or charging off vehicle alternator