Which is less problematic: Six 12v batteries in parallel, or use a Switch to switch between two isolated battery banks of three batteries in parallel?

[crayfish21]

I'm planning my electrical system for a van. I'm not running high wattage appliances and I'll only be using about 1-3kwh per day, but I'll often be away from grid for 6+ days and my solar won't be enough to fully recharge batteries. Ultimately I need to have ~14kwh of capacity. Here are two possible 12v system battery bank set-ups.

• Option 1: Buy three SOK 12v 206ah LiFePO4 batteries now, and then when I can afford it in 6-12 months, buy three more batteries, for a total of six batteries wired together in one of the Victron Unlimited parallel wiring set-ups.

• Option 2: When I'm able to buy the additional three batteries, rather than wiring them in with the other three, use this switch to create two completely separate, isolated battery banks in the van. Only one bank would charge/discharge at a time. Periodically I'd use shore power to recharge each bank separately, one after the other. I don't know if this usage is even possible with this switch or if I'd have to physically disconnect wires every time instead? But if this could work, I'd seemingly avoid the balancing issues people report when wiring more than 3 batteries in parallel or adding newer batteries to older banks.

I understand that the ideal option is to go to 24v or 48v (although that would make alternator charging difficult and require converting a lot of things to 12v). Theoretically, if I could afford four 200ah 12v batteries to start, I could wire them in 2p2s for 24v, and then get the additional two and wire the bank 3p2s. The batteries need to be in a row of six, however, and not sure if that would make it very difficult to wire 3p2s? (I've also looked at 24v 200ah batteries, but cannot find a configuration of 3 that would fit in in the space I have available (LxWxH) 51" x 12" x 16" and I'm looking to avoid DIY batteries.)

So assuming 24v/48v is out, which of the above 12v options is the least bad?

If option 2 can work, any guidance on how I wire the positives and negatives coming off the two different banks so they are actually isolated with the switch and will be safe?

Thanks!

 

[x98myers7]

simpler is always better in my experience.

have you considered putting out more solar on ground mounts to increase production? you also get the benefit of being able to place them perfectly for highest production. would be pretty easy to assemble a 2x200w briefcase from rigid panels.

 

[Rocketman]

Here are my thoughts…
1. Add more solar - the portables are an excellent idea!
2. Start with what you can do - three or four batteries. Then if you really need more add the additional batteries into one large bank. While not ideal - the lithium’s last so long than mixing slightly older batteries should not cause issues.

I would hook each battery up to a battery buss bar using exactly the same (overall) length of cables. Make your buss bar large enough now to handle any future expansion and make the future battery cables now.

 

[73powerstroke]

Adding more solar or better panels would be my first choice. Can't fill a cup with water if you got no water. Keep it simple.
All the batteries in the world don't do you any good if your solar can't properly charge them

 

[crayfish21]

Thanks @x98myers7 @Rocketman and @73powerstroke

I'll have 600w of solar on roof, and while I could potentially put additional solar on the ground, I'd still like to be prepared in situations when sky is cloudy for an extended period and I'm relying almost entirely on my battery system for 6-7 days. I plan on returning to shore power periodically to recharge what solar can't recharge.

@Rocketman Is a buss bar effectively like exposed wire? If yes, what is the recommended way to cover it to keep it safe?

​

 

[73powerstroke]

Thanks @x98myers7 @Rocketman and @73powerstroke

I'll have 600w of solar on roof, and while I could potentially put additional solar on the ground, I'd still like to be prepared in situations when sky is cloudy for an extended period and I'm relying almost entirely on my battery system for 6-7 days. I plan on returning to shore power periodically to recharge what solar can't recharge.

@Rocketman Is a buss bar effectively like exposed wire? If yes, what is the recommended way to cover it to keep it safe?

​

They sell a buss bar that has a cover

 

[rhino]

For example: https://www.bepmarine.com/en/Products/Connectors-and-Insulators/Pro-Installer-Bus-Bars

 

[x98myers7]

IMO go with the biggest bank you can wire without complication.

and... normally i wouldn't recommend it... but, being an RV owner myself.... have you considered a small 2kw gas inverter genset for the rare case when you might run out of juice? they're pretty much purpose built for this scenario.

 

[Rocketman]

Rino linked one above.

If I had room (and money) I would put in a Victron Power-in and add the Mega -Fuses- (there is a YouTube for that). I think that makes a nice clean system and it covers them well. Four batteries now - if you add more - just add another.

Lynx Power In - Victron Energy

Connect batteries to the Lynx DC distribution system with the Lynx Power In, a modular DC busbar. Find a dealer nearby.

www.victronenergy.com

 

[Aly_Oops]

I was about to suggest that, as that what I am planning to add to my Lynx Shunt, Lynx Distributer and Multiplus. (For project Cougar) I also would get the bolts and nuts so you can fused each bank. In fact, I just order it now. We just got SOK 206 marine/bluetooth and plan is to get a few more. Welding/battery 2/0 cable is more than sufficient.

You can then create a set of 2 x 206 batteries. With proper parameter setting, you will not have a big problem with balancing. I suspect SOK has a batch of bms that have issue with balancing, but they have newer version coming out. Currently they balance during charging, but once they hit 13.4 the balancing seems to drift. However, the capacity seems to be there.

Each time you parallel, your charging and discharging will double. If you have same equipment as mine, you can then setup DVCC, where it will share temperature, voltage and set max charge current, limit charge voltage for what is best for your configuration. Communication with devices is the gold here.

I have a honda 2000 generator, so if needed, I can charge up the batteries. If you can find a small unit that can be turn on/off with Victron, then that get to be very nice. Regarding Solar panels, if lying flat then you need a whole bunch, but if it can be setup for tilting, then you only need one or more, depending on wattage needs. Why overload roof of RV or vehical. A small quiet generator is cheaper and more efficient.

I believe the 2023 Dodge Airstream vans went that route. Keep in mind, those switches are rated for under 300amp for 48 vdc and less for 12vdc. I notice lots of people are exceeding the rating of those switches. I wonder if one could fabricate replacing the fuses with individual breakers/switchs. Nay probably not, lol.

Doing this in steps/batches is the way to go. Start with enough to have a working system, then add as needed. Avoid upgrading from the beginning. It surprises me how so many don't use Lynx distributer. It is a lot cleaner, tidy and safer looking and if they add up all the pieces they needed to go that route, price would be approaching even, if not cheaper, depending on purchases prices.

This info may be too late, but never know, someone may now be thinking of similair project. Hope it help them.

If doing a residence, then yes 48vdc is better way, but for average RV, truck, car then 12vdc is more than okay. You will be using less wire, so wire cost not as strong argument. Set it up as a UPS system with battery backup to feed your unit system.

 

[time2roll]

3x 206 is actually a good amount of power depending on the loads. If needed I would just go direct to 6 in parallel.
Get the fuses right.... that is a lot of amps.

Easy to get a battery switch with A, B, A+B, off. Just need to manually avoid selecting A+B if one set is full and the other is empty.

 

[Aly_Oops]

I would need the 3 x 206 and disconnect switches is for working on it and disc/conec situations. I be using lynx power in and each bank will be fused. My victron system, Lynx shunt, distributor, multiplus, will handle all current/voltage/temp monitoring. Also, they give me more space than 6 battery units. I have 3 x 100 which I use for other projects.

 

[TacomaJoe]

I'm not sure of the advantage of Option 2. If your solar makes 3Kw a day, it doesn't matter if it puts 1Kw into 3 batteries each, or 500W into each of 6 batteries. Unless you have a mobile option to remove one bank and give it a charge somewhere else, I don't see any advantage.

 

[Aly_Oops]

I am hoping not to use too many panels, as sun options are not too good in the north. The most wattage I would have is 1200, but only want to use 400 watt but with tilt capability. Larger battery banks is required, unless you depend on generators, shore power, etc. (Cougar Project only, other have different criteria)

Regarding parallel 100 or 206 amp SOK batteries. No difference. The 100 has 4 cells and the 206 has 4 cells but larger capacity. If they are using the same BMS on both (I believe that is the case, then balancing would be very slow in comparison to 100 amp SOK.). Also show why the charge and discharge is not that great with one 206 amp SOK Battery. Once buyers are aware of SOK 206, this will slow in sales, unless they replace the BMS on it, I am guessing.