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Someone want to check me on my plan?

Rednecktek

Rednecktek

Solar Wizard
Joined
Sep 8, 2021
Messages
5,510
Location
On a boat usually.
So I know it's a "Bad Thing" to parallel more than 4 batteries, but what about paralleling paralleled batteries? This is my current thought given my budget, the amount of shelf space I have for batteries, and the desire to cut all loads on the batteries that I can when I leave for 6 months.

I know the MPPT controller will draw a little, I'm just hoping it's less than what all the panels can provide.

My goal is to maximize my run hours and keep it 12v because there are already a LOT of little things on the system that are already 12v and it just doesn't make sense to step up to a 24v or 48v and then have to rectify it back down to 12v.

So, here's a krappy MSPaint drawing of my idea. I'm planning on upsizing the inverter now (since I haven't bought that yet) so I don't have to buy a bigger one in the future (or at least any time soon) and will still be overkill for my needs of about 500w max load. Granted, I haven't re-done my power audit yet and I don't remember how much load is on the 12v, but what my napkin math tells me is that the 12v bus only tops out at about 35a with everything first firing up and then drops to about 15a once the heaters are fired up.

I'm going to put a disconnect in the 12v line between the bus blocks and the inverter/fuse block so I can kill all the loads without killing the charger.

Does this make sense or am I missing something?

Thanks guys!
 

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Oh, I should probably list out the parts:

What I Have:
4x 120Ah FLA batteries <1yr old
60a MPPT SCC
100a Knife Blade Disconnect
Fuse Blocks
2x 100w Poly panels

What I need to get:
2x batteries
200a Fuse
2000w Inverter
200a Disconnect
2x Bus Blocks - 4 Lug, 200a rated
Pallet of Panels (got a few projects going)
 
I'm not sure where this idea that its bad to parallel more than 4 batteries comes from.
Battleborn has a whole box filled with parallel cells and it's regarded as one of the best on the market.

Yes I understand the argument about internal resistance and all that but voltage drop in a given battery relative to the others in the parallel system will help encourage current bias towards the more fully charged battery. I believe will has a video on this and it's a bit more apparent (read; more gooder) in lead batteries due to the steeper discharge curve.

If you're worried about balance, make sure each battery has the same length leads as the others and call it an day. This means your drawing as it sits now is less than ideal, but it seems you plan to use bus bars anyways?

Ideally, each battery would connect to a set of bus bars so that they're not significantly increasing in wiring length away from the point of use.

As with anything I say I could be wrong so please wait for someone else to either confirm, or using cunningham's law come tell me I'm wrong as loudly as they can.
 
Rednecktek said:
So I know it's a "Bad Thing" to parallel more than 4 batteries, but what about paralleling paralleled batteries? This is my current thought given my budget, the amount of shelf space I have for batteries, and the desire to cut all loads on the batteries that I can when I leave for 6 months.

I know the MPPT controller will draw a little, I'm just hoping it's less than what all the panels can provide.

My goal is to maximize my run hours and keep it 12v because there are already a LOT of little things on the system that are already 12v and it just doesn't make sense to step up to a 24v or 48v and then have to rectify it back down to 12v.

So, here's a krappy MSPaint drawing of my idea. I'm planning on upsizing the inverter now (since I haven't bought that yet) so I don't have to buy a bigger one in the future (or at least any time soon) and will still be overkill for my needs of about 500w max load. Granted, I haven't re-done my power audit yet and I don't remember how much load is on the 12v, but what my napkin math tells me is that the 12v bus only tops out at about 35a with everything first firing up and then drops to about 15a once the heaters are fired up.

I'm going to put a disconnect in the 12v line between the bus blocks and the inverter/fuse block so I can kill all the loads without killing the charger.

Does this make sense or am I missing something?

Thanks guys!
Click to expand...
an active balancer might be a good idea to manage that many parallel batteries.
 
Oh and fair warning, I believe that particular one is designed for a 24v system where it has a couple 12v strings of parallel batteries but that link is more of a demonstration than a specific suggestion.
 
I almost suggested this in my first post but thought against it because it's largely not a concern for your setup.

The simple fact is that as one battery draws down, so does its voltage, and this causes the parallel system to naturally draw from the higher voltage/more full battery.

Will did a video on this at some point with lithium batteries and the effect should be more pronounced with lead acid.


Just set yours up with equal length cables and see how it works before worrying about active balancing of batteries, in my opinion.

The catch is you want to ensure all of them are fully charged before hooking them up to one another to avoid large currents between them.
 
If you REALLY want to investigate this, it becomes more complex with multiple batteries beyond just two, but here's an inexpensive model to start 'researching' the technology.

I don't know anything about this specific model and am not recommending it but just pointing it out for example.

Their wiring "diagram" is bad and confusing as well here.

Affordable Electric Vehicle Batteries & Components from Electric Car Parts Company

Electric Car Parts Company is your one-stop-shop for affordable electric vehicle parts and components including batteries. Shop our selection and order now!
www.electriccarpartscompany.com
 
Wow that sounds like a LOT of wire by the time I've got 6 batteries in there. I do like those bus bars though, but I'm working on a budget and have limited space to play with and I still need to have room for the fuses and shunt and inverter and all.

So I can do a 3-way connection OK without totally overbalancing the batteries?
 
Oh, I'm no stranger to crimping large cables, you should see what our cranes and generators out here on the ships use. However, the cost of all that copper would be INSANE which is why I'm considering scaling down the 12v system to 2 batteries and doing a 24 or 48v AIO system next to it. I still get both the 12v AND the 120v busses and if something on one system dies, the other is there still so I have redundancy.
 
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