Is there such a thing as too many breakers?

Hello I have been collecting Li-Ion cells for a while planing to build some sort of power storage system. Recently I have upped my collection rate and am now looking at putting the cells into a pack. I have decided to go with a 24v 7s battery design, and I have chosen to use the DiyBMS4 by Stuart. At first this will be wired to a grid tie inverter to provide backup power to my home lab, but when I buy my own home I am going to expand this system into a whole home backup / home solar storage system. But I have a few questions I need some help with before I go ham building packs. First a little background on the problem.

A while back I was looking online at batteries that I could salvage and bought a few Kwh of hover board batteries planing to harvest the cells and adding them to my collection. Turns out they were not 18650 cells but pouch cells. It was my fault, if I read the description I would have seen that these were not the cells I was looking for. Oh well, I can find some use for them. A little while latter I picked up some SPIM08HP cells, this time knowing full well they were pouch cells. So my question is, can I use these two types of pouch cells and the 18650's in a a power wall application? I do not plan on mixing the cell form factors, so I would have several 7s batteries hooked in parallel, each with its own set of BMS boards.

Another question I have is related to the wiring fusing and breaking. Below I have two figures. Figure one I have one fuse on the negative side and one shunt trip breaker on the positive side. If any one of the batteries drops into a fault condition, under or over voltage, the whole system would shut down. The second figure has each separate battery pack with its own shunt trip breaker and fuse. Each pack can be turned off individually if it shows a fault condition. Both systems would be expandable as I built more batteries

Figure one would be the more economical solution since shunt trip breakers that can handle 100+ amps cost hundreds of dollars, and each of the battery packs I am planning to build can easily output that much amperage. Figure two would allow me to isolate each battery if I needed to service, replace, or add a battery. What would be better figure one, two or is there a better figure three that I should explore?

Am I missing any crucial parts to my setup? I welcome any parts recommendations when it comes to shunt trips, fuses, breakers, etc that are good to use.

Rock on!
Kevin

There are various discussions on shunt trips and circuit breakers. Here's a current one -https://secondlifestorage.com/showthread.php?tid=8517&highlight=Shunt+Trip- that might be of help.

A lot of us with larger powerwalls use "ABB SACE" (you can search on this)as cost effective 200, 300, 400a overall battery shunts as in this thread -https://secondlifestorage.com/showthread.php?tid=8877&highlight=ABB+SACE

Personally, I use fuse wire on each cell, then 400a shunt-trip on overall battery to a control box. The control box has circuit breakers on each incoming charge controllers (to break the connection 'charge' current') and breakers on the outgoing power to the inverters. There are circuit breakers on the incoming PV side of the charge controllers. The inverter output has circuit breakers - and then this feeds into a subpanel which has US standard 220/110v circuit breakers.

Have fun!

You could do a regular breaker for each 7s pack for easy pack isolation & extra safety.
General consensus for a small to medium system would probably be one overall shunt trip controlled by the BMS at the combined battery positive for whole system shutdown.
Large systems like daromer is running might have more sections to it.
Charge controllers & loads (inverter, DC systems, etc) connect on the other side of the shunt trip from the battery positive (ie so both charging & discharging is disconnected for a battery issue (cell high/low) or high current).

Any wiring on the mains 240/220/110 side if the inverter should be per local electrical standards.

Based on your initial images, I would go with either fuses for each string, or breakers for each string. I wouldn't use both. And generally fusing/breakers go on the Positive side. Not that it's better, but that it's just more consistent with everything else (like inverters and such).

As mentioned by OffGrid and Redpacket, fuse each cell in each pack. Use a breaker between strings and shunt, and put everything else after the shunt trip. If you have multiple strings, it'd be a good idea to have some kind of physical disconnect (other than a bolt) to shutdown a string independently of the others. Even the older style blade switches would be sufficient for that purpose. And might actually look pretty neat if set up with lots of strings going through them and they are lined up along the wall.

When doing the cell level fusing do you fuse both sides or is it OK to fuse one side of the cell?

Redpacket said:

You could do a regular breaker for each 7s pack for easy pack isolation & extra safety.

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Question about the breakers, can I parallel breakers? Example, using two 50 amp breakers in parallel to get 100 amp breaking capacity. I have been looking at potential power draw, and if I do the math 3000W @ 24V Nominal would require a 125 amp power draw, And if I wanted to do 6000w it would be 250 amp power draw. The highest I have found for a DC breaker ( that is not an ABB or Schnider MCCB's ) is 63 amps.

Korishan said:

Even the older style blade switches would be sufficient for that purpose. And might actually look pretty neat if set up with lots of strings going through them and they are lined up along the wall.

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I agree this would look rad, the ones that I am finding on amazon look to cheap and flimsy to look cool though. I will have to look around some more

nighthawk28 said:

When doing the cell level fusing do you fuse both sides or is it OK to fuse one side of the cell?

Redpacket said:

You could do a regular breaker for each 7s pack for easy pack isolation & extra safety.

Click to expand...

Question about the breakers, can I parallel breakers? Example, using two 50 amp breakers in parallel to get 100 amp breaking capacity. I have been looking at potential power draw, and if I do the math 3000W @ 24V Nominal would require a 125 amp power draw, And if I wanted to do 6000w it would be 250 amp power draw. The highest I have found for a DC breaker ( that is not an ABB or Schnider MCCB's ) is 63 amps.

Korishan said:

Even the older style blade switches would be sufficient for that purpose. And might actually look pretty neat if set up with lots of strings going through them and they are lined up along the wall.

Click to expand...

I agree this would look rad, the ones that I am finding on amazon look to cheap and flimsy to look cool though. I will have to look around some more

Click to expand...

I wouldn't try to'parallel breakers'.

I use "MidNite Solar - 250 Amp 125Vdc DC Panel Mount Breaker MNEDC 250 A"breakers from my 48v battery bank --> 12,000w AIMS inverters -https://www.ebay.com/itm/MidNite-So...868727?hash=item3d55c35137:g:RY0AAOSwj1haV~r6

Using breakers in parallel is not a good idea. Get the right rated one.

https://www.eaton.com/content/dam/eaton/products/low-voltage-power-distribution-controls-systems/switchgear/low-voltage-switchgear-documents/paralleling-lv-power-breakers-ia01301020en.pdf said:

For systems that require continuous current ratings higher than the standard product capabilities, there are two additional solutions to consider:
1. Cooling fans can be added to the circuit breaker cell, allowing increased current through the breaker.
2. Double wide breakers can be used. Forced-air cooling using additional fans is a relatively standard way of addressing higher continuous current requirements. With that said, the art of building switch gear assemblies is increasingly refined; todays smaller, lighter circuit breakers and modern design practices make it easier and more economical to connect two circuit breakers together in parallel as one breaker product. These are often called double wide breakers.
...
Connecting circuit breakers in a parallel arrangement also provides for higher continuous ratings. Eaton has opted to connect the breakers via a common pole shaft. So the two breakers are combined to make one common breaker. In the industry these breakers are often called double wide (DW) breakers. This name is used to describe two breaker current paths combined together within one breaker frame.They share integral trip units and a common mechanism. These breakers can be configured AABBCC or ABCABC. AA is an identification reference to phase A1 and phase A2 connected together in the cassette. So they act as one phase together.

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You can parallel breakers, and it is a common practice. However, you want to bridge the triggering mechanism so that both will throw at the same time. Most single breakers have a hole in the switch handle. A 16 penny nail is usually used to bridge these together. You can also use threaded rod, or some other form rigid metal that is stiff enough to trigger the second breaker.

But, make sure you are absolute positive that you use the correct type of breaker. DC for the DC side, AC for the AC side. Don't use AC for the DC side as it may cause a fire under heavy load triggering.