Hello. So I'm preparing to commence my battery bank build which will be comprised with 2x 2p16s batteries (LifePO4 3.2v 280Ah cells) to commence with and I will probably add a third 2p16s down the road, hopefully in a few months time. Each battery will have its own BMS and T Class fuse. My question is this...do I need a DC breaker for each battery or would a single large DC breaker which all the batteries connect to suffice?
Do I Need Breakers for Each Battery
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sunshine_eggo
Happy Breffast!
More likely that you need an actual fuse for each battery. if you don't have a fuse for each battery, you run the risk of one battery feeding into another at high current, e.g., battery 1 has a cell failure, and it's voltage drops. The parallel battery 2 will dump current into it.
timselectric
If I can do it, you can do it.
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It depends on how you might want to isolate in the future. I have a breaker for each battery. So that I can take them offline individually.
Zwy
Solar Wizard
Each battery in my bank has a Class T fuse before the busbar.
timselectric
If I can do it, you can do it.
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timselectric
If I can do it, you can do it.
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It's really just a convenience thing.
Do what you think will be helpful in the future.
Do what you think will be helpful in the future.
sunshine_eggo
Happy Breffast!
If you use a breaker, it's going to need to have the same AIC rating of a class T fuse - possibly higher.
Zwy
Solar Wizard
In my system, at this point I do not have a reason to have a breaker for each battery in the bank.
Batrium BMS with ABB shunt trip breaker for the whole bank.
Installing a 3 pole double throw so I can bypass the inverters if I need to take the system down for repairs or the Batrium sensed a fault and tripped the ABB breaker and I want to restore power while looking for the fault.
For 3 batteries, it would cost about $105 each to install a Midnite Solar breaker for a total of $315 plus a possible enclosure depending on the construction of his bank. At $0.315 cents per Kwh, that's 1000 Kwh. Doesn't make much sense financially to add the breakers if one can simply shut down the system, remove the T fuse for one battery and turn system back on.
sunshine_eggo
Happy Breffast!
sunshine_eggo
Happy Breffast!
wmgeorge
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More likely that you need an actual fuse for each battery. if you don't have a fuse for each battery, you run the risk of one battery feeding into another at high current, e.g., battery 1 has a cell failure, and it's voltage drops. The parallel battery 2 will dump current into it.
What are the odds of that happening and the result? Can you quote a source when that happened and how often. Is it in the NEC?
What are the odds of that happening and the result? Can you quote a source when that happened and how often. Is it in the NEC?
sunshine_eggo
Happy Breffast!
I've personally had it happen with FLA and NiMH. The NiMH hit thermal runaway and melted the shrink wrap. IR gun reported 280°F. I haven't had it happen with Lithium, but I have dozens of failed Lithium cells. Do you believe these cells can't internally short and drop to near 0V? What do you think will happen if you have two parallel batteries, one with 3.2V lower voltage than the other?
It's likely that you just haven't been around here long enough, but having fuses for individual LFP batteries is common practice on this forum.
wmgeorge
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Well I am 79 years old and been in electrical since 1962 first licensed in 1970 and retired as a Master specializing in controls in 2007 after teaching for 12 years. Not seen references to what your talking about here? And Who are you besides being a Waffle maker?
Samsonite801
Solar Wizard
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If you don't have a fuse/breaker on each battery, then the main fuse would have to be sized to protect the smallest cable in the system, and even then, I would not feel comfortable (as others stated) with having a shorted cell or something on one pack trying to pull down on the rest of the packs, it's nice to have a battery able to break off of the pack.
And simply for maintenance purposes, I prefer to have breakers on the batteries, so I can turn an individual battery off (break it out of the bank easily) to do maintenance or troubleshooting, and then have the Class-T fuses on the main DC bus, one for each inverter.
Just remember that fuses / breakers are supposed to protect the cables / power paths, in case the highest current situation occurs, there can't be any fire hazard or meltdown.
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Zwy
Solar Wizard
I have an ABB S5N with shunt trip I purchased used off ebay. Similar to the one Lithium Solar used only mine has the cable terminals instead of lugs and it also contains auxiliary switches which could be used to shutdown PV using a relay.
You will need a 48V to 24V transformer for the shunt trip. I'm not a fan of pulling off 1/2 of a battery.
Zwy
Solar Wizard
He certainly isn't the average Iowa native......
I know because I have lived in Iowa my entire life.
Curmudgeon possibly?
Anyway to Sir WmGeorge, the reason for fusing each battery in a bank with LFP cells is if there is a problem with a cell such as a short (and yes, lead acid will short a cell too but just drains the other battery), the amount of electrons that will move from one or two good LFP batteries will be quite tremendous. The same as sticking a wrench across the positive and negative terminals of a LFP battery. Lead acid had high internal resistance and the cells that haven't failed will limit some of the discharge from the other batteries. With the LFP chemistry, the internal resistance is very low, thus the movement of the electrons will be quite accelerated. It's the same reason you don't charge LFP directly from an alternator, the alternator will burn up due to the battery low internal resistance thus leading to full output of the alternator.
wmgeorge
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Well I can find Nothing in the current 2020 NEC about fusing individual batteries. Regardless of being posted on Here or not. If its not in this edition of the Code then its not required nor needed. IF it was a common danger then the Code would have it listed.
Please list the fires that have been posted on Here.
Yes my experience goes back to my USAF air craft days, never did I see a fuse between any batteries! Even those early NiCad ones.
Please list the fires that have been posted on Here.
Yes my experience goes back to my USAF air craft days, never did I see a fuse between any batteries! Even those early NiCad ones.
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sunshine_eggo
Happy Breffast!
Zwy
Solar Wizard
Reasonable on ebay
You and me both. I already have 48-12V converter to power the WiFi access point and Mini-PC running the Batrium Toolkit. What's another for 24V?
DDR-60L-24 MEAN WELL | Jameco Electronics
MEAN WELL DDR-60L-24 DC-DC Converter, DIN Rail. Products in stock and ready to ship. Quotes, samples and datasheets available at Jameco Electronics.
I used this one.
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