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Battery Bank Disconnect Switch for large off-grid system

AmpLee

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So my system design is a bit unconventional since I'm building it around 40KW of used LTO modules that came from used EVs. Each of the 36 modules will be paralleled into two separate Square D QO load centers, each with a dedicated 2 pole breaker. I'm using two load centers because each will hold only 20 spaces for the 2 pole breakers and I'll need 36 spaces total for all the batteries. Because of this, I will be joining 4/0 wires coming from each load center onto a common busbar before sending the single 4/0 wire into my Sol-Ark 12k inverter.

I'm looking for a way to isolate one half of the battery bank (18 modules connected to a single load center) with a disconnect switch. The other half of the battery bank/load center would also get a disconnect switch. Because the LTO modules I'm using cycle between 48-60V I'm having a hard time finding a DC disconnect that can support 60V and 300+A. Any recommendations?

I'm also curious that without a disconnect switch, if I were to turn off the breakers in one load center would there be any potential problems if I'm still drawing electricity from the other load center?
 
So you are using 2 different battery chemistries? One set of battery banks is a different capacity then the other?

Square D QO load centers are for AC voltage not DC....

Batteries should be an input to the Sol-Ark and on the AC output side you connect your Square D QO load centers to supply AC to your house.

Guess I am confused and trying to help.....good luck
 
So you are using 2 different battery chemistries? One set of battery banks is a different capacity then the other?

Square D QO load centers are for AC voltage not DC....

Batteries should be an input to the Sol-Ark and on the AC output side you connect your Square D QO load centers to supply AC to your house.

Guess I am confused and trying to help.....good luck

Square D breakers are also rated for DC.


https://www.se.com/us/en/product-subcategory/50370-dc-rated-circuit-breakers/
 
So my system design is a bit unconventional since I'm building it around 40KW of used LTO modules that came from used EVs. Each of the 36 modules will be paralleled into two separate Square D QO load centers, each with a dedicated 2 pole breaker. I'm using two load centers because each will hold only 20 spaces for the 2 pole breakers and I'll need 36 spaces total for all the batteries. Because of this, I will be joining 4/0 wires coming from each load center onto a common busbar before sending the single 4/0 wire into my Sol-Ark 12k inverter.

I'm looking for a way to isolate one half of the battery bank (18 modules connected to a single load center) with a disconnect switch. The other half of the battery bank/load center would also get a disconnect switch. Because the LTO modules I'm using cycle between 48-60V I'm having a hard time finding a DC disconnect that can support 60V and 300+A. Any recommendations?

I'm also curious that without a disconnect switch, if I were to turn off the breakers in one load center would there be any potential problems if I'm still drawing electricity from the other load center?

Hello!
I have purchased the same Toshiba SCIB modules, I had read all your posts and conversations on the forum but I still cannot understand are you going to use BMS or not. What is formula of your system: 12S36P?
I am confused with my project, and I still cannot decide do I need to split all modules and run cells in parallel and then make them in series, or leave them in series and connect then in parallel. My system is "48V" - I will run 24S
Any advice?
Thanks!
 
I am confused with my project, and I still cannot decide do I need to split all modules and run cells in parallel and then make them in series, or leave them in series and connect then in parallel. My system is "48V" - I will run 24S

My plan for my leaf modules is 48v packs (14s) each with their own BMS. Each of those packs will connect to a main 48v buss (they will be in parallel) I anticipate haveing 4(ish) done this way.
 
I haven't seen a breaker that is rated for DC and AC. Must be some kind of special order.
 
So you are using 2 different battery chemistries? One set of battery banks is a different capacity then the other?

Square D QO load centers are for AC voltage not DC....

Batteries should be an input to the Sol-Ark and on the AC output side you connect your Square D QO load centers to supply AC to your house.

Guess I am confused and trying to help.....good luck
Not true, the system he appears to be using is identical to mine. All the Square D 250AMP box is used for is a buss bar and fuse holder for up to 20 batteries by using the Square D DC Double pole breakers.
 
So my system design is a bit unconventional since I'm building it around 40KW of used LTO modules that came from used EVs. Each of the 36 modules will be paralleled into two separate Square D QO load centers, each with a dedicated 2 pole breaker. I'm using two load centers because each will hold only 20 spaces for the 2 pole breakers and I'll need 36 spaces total for all the batteries. Because of this, I will be joining 4/0 wires coming from each load center onto a common busbar before sending the single 4/0 wire into my Sol-Ark 12k inverter.

I'm looking for a way to isolate one half of the battery bank (18 modules connected to a single load center) with a disconnect switch. The other half of the battery bank/load center would also get a disconnect switch. Because the LTO modules I'm using cycle between 48-60V I'm having a hard time finding a DC disconnect that can support 60V and 300+A. Any recommendations?

I'm also curious that without a disconnect switch, if I were to turn off the breakers in one load center would there be any potential problems if I'm still drawing electricity from the other load center?
First, why do you need a switch for either side? All you have to do to eliminate your problem, is turn off the 18 breakers in the box. No reason to spend several hundred dollars ea on two more switches. If you want a switch check online at ZORO. For hundreds of dollars they can get you anything.
 
The Square-D breakers (of a certain range) are UL listed for 48 (or was that 50VDC.) "Square-D Certified" for 125VDC if both legs interrupted by a 2-pole breaker. In other words, they assure you that one pole of the breaker can interrupt 62.5VDC. Those also have interrupt rating of a particular kA, something in the 4kA to 10kA range as I recall.

The short circuit interrupt current is probably fine for one of your batteries driving into a short. Maybe not if one battery is shorted and all the others dump into it.

You've got quantity 36 of 60V max batteries, and 40 slot breaker panel (that accepts 20, 2-pole breakers.)
Hmmm....

Looking for a 300A switch? Per pole? Need to be clear on how many amps total you're trying to carry. You can get a split-phase load center with 225A bus. There is a 3-phase same size, need to double check what amperage.
 
He is only using 18 batteries per box with double pole breakers. Not 36!
 
18 ... 36 yes, I got that.
But then I hinted (nudge, wink) that if 2 poles could interrupt 125VDC, one pole could most certainly interrupt 62.5VDC, and it kind of looks like a 40-slot QO panel could then handle as many as 40 batteries, and 450A total. Might need something else for un-fused combining of all the negative cables, though, because only one neutral available for 225A
 
Hello!
I have purchased the same Toshiba SCIB modules, I had read all your posts and conversations on the forum but I still cannot understand are you going to use BMS or not. What is formula of your system: 12S36P?
I am confused with my project, and I still cannot decide do I need to split all modules and run cells in parallel and then make them in series, or leave them in series and connect then in parallel. My system is "48V" - I will run 24S
Any advice?
Thanks!
His formula, because he has a 48V system is 24S 36P. You probably figured it out by now but if you haven't, I would be happy to post a picture of one of my battery bank racks showing how to do it.
 
18 ... 36 yes, I got that.
But then I hinted (nudge, wink) that if 2 poles could interrupt 125VDC, one pole could most certainly interrupt 62.5VDC, and it kind of looks like a 40-slot QO panel could then handle as many as 40 batteries, and 450A total. Might need something else for un-fused combining of all the negative cables, though, because only one neutral available for 225A
Because you are using double pole breakers, your positive and negative wires are connected to the breaker in mirror images on each side so the bars are acting as a positive and negative through each side. You don't use the ground in the box for anything other than your ground rod. You couldn't use a single breaker for this application.
 
Because you are using double pole breakers, your positive and negative wires are connected to the breaker in mirror images on each side so the bars are acting as a positive and negative through each side. You don't use the ground in the box for anything other than your ground rod. You couldn't use a single breaker for this application.
And just why (ignoring codes or precisely what is "Square-D Certified" for the moment) couldn't I combine battery negatives on neutral bar (possibly also a second neutral bar for the current), and connect each battery positive to one leg of a double-pole breaker? And then run a cable from each busbar to the load, tying them together there?

Single pole breakers would probably be fine, but I say one leg of a double-pole breaker because those are the ones with "125VDC for 2 poles" certification.

In other words, don't put breaker in both positive and negative leads of battery because it isn't 125VDC, just use for positive because it is only 60 VDC?

Not saying this actually works, mind you! Just asking, "Why?", because that's what I've done since childhood (to the annoyance of others), and sometimes it leads to better understanding.
 
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The Square-D breakers (of a certain range) are UL listed for 48 (or was that 50VDC.) "Square-D Certified" for 125VDC if both legs interrupted by a 2-pole breaker. In other words, they assure you that one pole of the breaker can interrupt 62.5VDC. Those also have interrupt rating of a particular kA, something in the 4kA to 10kA range as I recall.

The short circuit interrupt current is probably fine for one of your batteries driving into a short. Maybe not if one battery is shorted and all the others dump into it.

You've got quantity 36 of 60V max batteries, and 40 slot breaker panel (that accepts 20, 2-pole breakers.)
Hmmm....

Looking for a 300A switch? Per pole? Need to be clear on how many amps total you're trying to carry. You can get a split-phase load center with 225A bus. There is a 3-phase same size, need to double check what amperage.
Here's what I am using: Square D QO142L225G breaker box, Square D QO 220 20AMP Double Pole breakers (certified for DC applications). I am back feeding each battery through the breakers and panels fused separately in each panel by a T-300AMP Fuse then both positive 4-0 cables to a common buss bar and then to my Sol-Ark 12k. I am using 10AWG THNN-TWNN 19 Strand copper wire of equal lengths between my batteries and breakers. Go to YouTube and look for Ben's Solar and Battery. He is a solar installer and certified electrician in Vermont. He has the same system that I copied. Maybe, after watching his two videos on his system, you will have a better understanding of how it works. He will state the maximum amount of current you can use in this system safely. His system was updated recently to a Sol-Ark 12k. He is on-grid where I am off-grid and he is using lithium batteries in his battery bank, where I am using LTO batteries. Other than that, everything else is identical in both of our systems. Because single pole breakers are limited to a maximum of 48V I can't use them with batteries rated 64.8V. I have my batteries set at 60V Nominal and 48V Minimal for my most effecient use of my batteries. Hope this helps you get a better understanding of how and why this system works and, yes, it will pass code.
 
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