DIY Battery Backup - Sizing the system

[AixRmz]

Hi there, a bit of newb on this sort of thing... Nice to meet y'all!
(posted this in r/SolarDIY but I figure I could try picking your brains... : )
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I would really like your input regarding sizing the amps in my system... are the busbars, t-fuse, circuit breaker, and shunt correctly sized? Does the order I placed them seem ok? Thanks!!!
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The hardware:
2 x 48v 100ah Eco-Worthy Server rack batteries
2 x 48v 330ah Eeel DIY battery box kits
32 x EVE MB31s 330ah
2 x 600a bus bars https://signaturesolar.com/600a-12-stud-busbars-red-black-kit/?searchid=1286563
1 x 400a Soutbend T-fuse https://www.amazon.com/gp/product/B0DHYD9W5Q/ref=sw_img_1?smid=A3VQTEFXHZ70BS&th=1
1 x 300a T tocas 300 Circuit Breaker https://www.amazon.com/gp/product/B06Y3T3YND/ref=ox_sc_saved_title_3?smid=ALHXFZX1L0DAX&psc=1
1 x 500a Victron Smartshunt
1 x EG4 12000xp
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My biggest concern are the t-fuse (I don't know how fast they really are, I believe, fast-fast... so 300a might not do it, so using 400a). The circuit breaker... It's right now the best option I see, I saw some 400a DC breakers by Dihool, but not sure how realiable is that brand. Also, not really familiar with T Tocas haha so would like to hear your recommendations on a better solution...
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I already own the batteries, the inverter, and the shunt. Everything else I'm ordering this week. Also, on wiring... that's a whole other conversation, maybe I'll do a post just on that... but thinking 2/0 to the bus bars and 1/0 from the busbars and up. https://www.currentconnected.com/product/bc-inverter-cables-0awg/ and https://www.currentconnected.com/product/copper-battery-cables-i-00-awg/
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Thank you so much for your input!

 

[sunshine_eggo]

12000/51.2/.85 = 276A

Size your conductors for that current. To use a 400A fuse, you need to have wire rated for 400/1.25 = 320A

Class-T fuses are sized 1.25X the conductor rating, and they are tolerant of typical surge currents from motors, etc. If you choose something besides class T, you want to confirm it's AIC rating is at least 20,000A.

T Tocas is not a bad brand. It appears to be between your super cheap versions and your bluesea, etc., brands. They claim UL ratings. I use one between my MPPT and my battery.

Welcome to the adventure!

 

[AixRmz]

12000/51.2/.85 = 276A

Size your conductors for that current. To use a 400A fuse, you need to have wire rated for 400/1.25 = 320A

Class-T fuses are sized 1.25X the conductor rating, and they are tolerant of typical surge currents from motors, etc. If you choose something besides class T, you want to confirm it's AIC rating is at least 20,000A.

T Tocas is not a bad brand. It appears to be between your super cheap versions and your bluesea, etc., brands. They claim UL ratings. I use one between my MPPT and my battery.

Welcome to the adventure!

This was super useful! Thank you for your input. I've resized the conductors and fail-safes will post an update tomorrow.

 

[Backyard]

Im not sure a single T class fuse after the busbar is a good idea. For one, 860AH of lithium at 50+ volts will surge a lot of current during a short and a single fuse might not be enough. Even at 20k AIC. Unless your individual batteries are separately fused, I don't know too much about the Eco-Worthy or Eeel batteries, you might want to put fuses on each battery. Think about where the current will flow if one of those batteries shorts out. Follow the current path and see where the problem is with your current design

2nd. If you had a short on any of the cables running to the busbar from the batteries, that fuse won't do anything. Best to have your fuse(s) as close to the battery as possible

You can also use smaller amp rated fuses since you would be dividing up the current each fuse needs to handle

The breaker can be installed after the busbar. This is normally best used as an overload protection and leave the T class fuses to short circuits

As mentioned above. Fuses and breakers should be sized based on your wire current carrying capacity or smaller. It's not good practice to oversize your OCPD. If you do, you should be very knowledgeable if what you are doing and the risks involved

For the breaker. I personally like to use double pole and break both the positive and negative sides. This increases the voltage capabilities or more correctly, the ability for the breaker to extinguish the arc during a fault condition

 

[AixRmz]

Im not sure a single T class fuse after the busbar is a good idea. For one, 860AH of lithium at 50+ volts will surge a lot of current during a short and a single fuse might not be enough. Even at 20k AIC. Unless your individual batteries are separately fused, I don't know too much about the Eco-Worthy or Eeel batteries, you might want to put fuses on each battery. Think about where the current will flow if one of those batteries shorts out. Follow the current path and see where the problem is with your current design

2nd. If you had a short on any of the cables running to the busbar from the batteries, that fuse won't do anything. Best to have your fuse(s) as close to the battery as possible

You can also use smaller amp rated fuses since you would be dividing up the current each fuse needs to handle

The breaker can be installed after the busbar. This is normally best used as an overload protection and leave the T class fuses to short circuits

As mentioned above. Fuses and breakers should be sized based on your wire current carrying capacity or smaller. It's not good practice to oversize your OCPD. If you do, you should be very knowledgeable if what you are doing and the risks involved

For the breaker. I personally like to use double pole and break both the positive and negative sides. This increases the voltage capabilities or more correctly, the ability for the breaker to extinguish the arc during a fault condition

That's a great point. I'm using MBRF terminal fuses at the + battery terminals. Think that's a good idea? 100a for the 100ah batteries and 150a for the 330ah batteries, meeting their spec for max discharge (which I'll never use, unless there's a short like you said).

Do you suggest I move the t-fuse closer to the inverter than currently located (as per the crude drawing attached) near the bus-bars?

I see your point on the breaker... do you have a recommendation on a double pole breaker? website or amazon link? : )

 

[AixRmz]

This was super useful! Thank you for your input. I've resized the conductors and fail-safes will post an update tomorrow.

12000/51.2/.85 = 276A

Size your conductors for that current. To use a 400A fuse, you need to have wire rated for 400/1.25 = 320A

Class-T fuses are sized 1.25X the conductor rating, and they are tolerant of typical surge currents from motors, etc. If you choose something besides class T, you want to confirm it's AIC rating is at least 20,000A.

T Tocas is not a bad brand. It appears to be between your super cheap versions and your bluesea, etc., brands. They claim UL ratings. I use one between my MPPT and my battery.

Welcome to the adventure!

Here we go... fuses, breaker, busbar, conductor gauges all sized "correctly" I think. Care to take a look and point out concerns? : )

 

[Backyard]

That's a great point. I'm using MBRF terminal fuses at the + battery terminals. Think that's a good idea? 100a for the 100ah batteries and 150a for the 330ah batteries, meeting their spec for max discharge (which I'll never use, unless there's a short like you said).

Do you suggest I move the t-fuse closer to the inverter than currently located (as per the crude drawing attached) near the bus-bars?

I see your point on the breaker... do you have a recommendation on a double pole breaker? website or amazon link? : )

An MBRF on each battery might be ok. Would have to do the AIC calculations to know for sure.

As for the ratings. I don't think you'll have different amperages coming from each battery. So you aren't going to be doing much with different sized fuses on each sized battery. Lets say you have an overload of 400+ amps. That will be over the 100 amp fuses on the 100AH packs. So those will go first. Then all the current will shift over to the 330AH packs. 400+ amps will overload the two 150A fuses. So those will go next. Basically, whatever will cause the 100A to blow will also cause the 150A fuses to blow. Might as well keep them all 100A.

Midnight makes a handful of double pole breakers

Category Products - MidNite Solar's

MidNite Solar Category Products.

www.midnitesolar.com