16s 48v wiring, whats up with his layout?

Stewfish

Solar Enthusiast
Am I missing something for the layout of 16s 48v?

I did a Google search for 48 volt wiring and came across this lithium solar video and I'm kind of confused why he has the bus bars making a square at 14:59 in the video and why the bus bars are jumping all over the place. Why not just snake it from each + to each - with the batteries flipped + to -?


Another wierd layout at 8:47 of this video


I'm doing the Batrium K9 and I'm just double checking my plan of attack, bc his layout threw me off.

Here is a quick diagram I just made. I have always snaked cables/bus bars like a golfcart layout which resembles more of a "snake" than bus bars.
16267504678236964882137431973891.jpg
 
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podilamaya

Solar Enthusiast
both battery systems in the picture have multiple batteries in parallel before make them serial. eg xP16S and what you planning to do is 16SxP

This document may help you to understand.
 

Hedges

Photon Sorcerer
I think his is 2p16s
Your sketch is 16s2p

Key distinction is 2p16s uses one 16s BMS, while 16s2p uses two 16s BMS (which gives redundancy and double the current handling)
 

Stewfish

Solar Enthusiast
I think his is 2p16s
Your sketch is 16s2p

Key distinction is 2p16s uses one 16s BMS, while 16s2p uses two 16s BMS (which gives redundancy and double the current handling)
What the difference?

The K9 runs 16s and then the two K9s run to the watchmon core to manage everything.

I found this in a forum search it shows 2p16s. Why not just parallel the two 16s batteries if the k9 is managing it?

Screenshot_20210719-204011.png
 

Stewfish

Solar Enthusiast
I already have the batteries in boxes like the 16s block in that picture bc I wasn't sure if I could find a 32s bms or some way to setup 32 cells e.g 16s2p so I was going to parallel two inverters and the 16s batteries would go to each inverter. For now I want to hook up both batteries to one inverter until I get another 24 solar panels put up.

So the larger block layout in that picture is a Jerry rig for 16s?
 
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podilamaya

Solar Enthusiast
Batrium supports monitoring multiple cells using the K9 modules, but many of the BMS in the market don't. Many of these battery layouts are designed for generic 16s BMS systems, which can only monitor 16 batteries in parallel.
 

Stewfish

Solar Enthusiast
In theory the square will keep the end cells in better balance. May not matter in practice.

All in series will be perfect balance every time.
Wouldn't my two K9 BMSs manage all that? The watchmon core manages both K9 to do 16s for both batteries at once
 

Stewfish

Solar Enthusiast
I think his is 2p16s
Your sketch is 16s2p

Key distinction is 2p16s uses one 16s BMS, while 16s2p uses two 16s BMS (which gives redundancy and double the current handling)
What I starting to think is that the larger block is a way to do BMS with the 16s BMS limitation. So a "Jerry rig" type setup.

I wonder how the charge and discharge of the two batteries in parallel will work. Won't they alway be trying to balance out like my RV batteries. I have 4/0 wire with tinned lugs between the two batteries bc I had left over welding wire from the main wire to the inverter and it wasn't much more than smaller guages when I bought the 4/0 10' red and 10' black pack, not sure why, maybe they had too many of those kits or its a common welding leng so cheaper.
 

time2roll

Solar Addict
Wouldn't my two K9 BMSs manage all that? The watchmon core manages both K9 to do 16s for both batteries at once
Yes of course. All your cells are in series. Even if your two batteries were slightly out of balance it would be at the battery level and all the cells would stay balanced.
 

Stewfish

Solar Enthusiast
Well I'm going to stick with my layout and batrium also shows the same layout on the support page for the K9
Screenshot_20210719-211540.png
 

Hedges

Photon Sorcerer
What the difference?

The K9 runs 16s and then the two K9s run to the watchmon core to manage everything.

I found this in a forum search it shows 2p16s. Why not just parallel the two 16s batteries if the k9 is managing it?

BMS has to be able to measure the voltage across every cell.
With 16s, that takes 17 wires. Same for 2p16s, because each pair of cells is wired in parallel.
For 16s2p, usually there are two BMS each with 17 wires. Maybe this BMS can monitor two strings of cells, in which case it will have 34 wires.
Sounds like "K9" has 17 wires to a 16s battery, and two K9 take care of two batteries? That would work too.

What I starting to think is that the larger block is a way to do BMS with the 16s BMS limitation. So a "Jerry rig" type setup.

I wonder how the charge and discharge of the two batteries in parallel will work. Won't they alway be trying to balance out like my RV batteries. I have 4/0 wire with tinned lugs between the two batteries bc I had left over welding wire from the main wire to the inverter and it wasn't much more than smaller guages when I bought the 4/0 10' red and 10' black pack, not sure why, maybe they had too many of those kits or its a common welding leng so cheaper.

Current draw (or charge) will split according to resistance of wires, busbars, cells. Make them perfectly symmetric, and stay somewhat below 2x the current rating of one because it won't be perfectly matched.

With 2p16s, if one cell had poor contact it's mate would carry almost all the current. It would show up only as greater voltage deviation, higher IR. With 16s2p, one poor contact should show dramatic voltage deviation and BMS disconnect.

Because LiFePO4 has so much lower internal resistance than LA, flatter discharge curve, it won't balance as well. In the extreme, one could take all the current until it hits knee of curve then stop and wait for the other to take all the current and catch up. Measure it with clamp ammeter if it isn't reported independently for your two 16s batteries, and look for outliers in cell voltages during testing. Want to catch any high resistance and fix them.
 

Sanwizard

Solar Addict
I already have the batteries in boxes like the 16s block in that picture bc I wasn't sure if I could find a 32s bms or some way to setup 32 cells e.g 16s2p so I was going to parallel two inverters and the 16s batteries would go to each inverter. For now I want to hook up both batteries to one inverter until I get another 24 solar panels put up.

So the larger block layout in that picture is a Jerry rig for 16s?
I think you need to share batteries if putting inverters in Parallel to handle the AC load. Unless one will be a completely seperate backup for you.
 

Hedges

Photon Sorcerer
I think you need to share batteries if putting inverters in Parallel to handle the AC load. Unless one will be a completely seperate backup for you.

The inverter I use has a master which knows SoC and directs charging by the others, so shared battery.

With 2 inverters and 2 batteries, I'd use a 3-hole or 4-hole busbar with the batteries on outer holes and inverters on inner hole. Or vice versa.
Current flow would be like one battery per inverter, but strapped together so always at same voltage.
 

Stewfish

Solar Enthusiast
It would show up only as greater voltage deviation, higher IR.
Each Batrium K9 watches each 16 cells and shows you which are low or high on the screen. You can the swap out/fix things. It was the only way to monitor and manage 32 cells not just 16. With more K9s the Batrium core will do up to 6 batteries 16s each.
 
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