Each of those rack batteries has a breaker, so they're fine (even if I'm biased towards Class-T fuses for this, but I digress).
Do I Need Breakers for Each Battery
- Thread starter Henderson
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OzSolar
Whatever you did, that's what you planned.
For a few 12v and 24v low power systems I've used a Square D QO load center for my DC loads. Once or twice I used it as a DC load center and battery combiner box. Never 48v though and only on lead acid.
Many years ago I had been told and subsequently found supporting documentation that they are rated for up to 50V DC but not 48v nominal systems. I just now looked for that and found the below from Schneider themselves stating they can used in up to 125VDC applications! Whoa!! Of course this would not replace a Class T fuse on each battery but still it's got my wheels turning.
The QO single Phase Main Lug Load Centers are SQUARE D CERTIFIED for use on 125 V DC systems. The load centers listed ARE NOT MARKED for use on this voltage system, however are suitable for the application. The positive (+) conductor should be connected to one phase lug, while the negative (-) conductor should be connected to the other phase lug. USE QO 2-POLE BRANCH BREAKERS ONLY. QO branch breakers, 10-70 ampere, are also SQUARE D CERTIFIED for use on 125V dc systems. Short circuit current rating is limited to 4,000 amperes (10-30 ampere) or 10,000 amperes (35-70 ampere) when used on 125V dc.
Many years ago I had been told and subsequently found supporting documentation that they are rated for up to 50V DC but not 48v nominal systems. I just now looked for that and found the below from Schneider themselves stating they can used in up to 125VDC applications! Whoa!! Of course this would not replace a Class T fuse on each battery but still it's got my wheels turning.
The QO single Phase Main Lug Load Centers are SQUARE D CERTIFIED for use on 125 V DC systems. The load centers listed ARE NOT MARKED for use on this voltage system, however are suitable for the application. The positive (+) conductor should be connected to one phase lug, while the negative (-) conductor should be connected to the other phase lug. USE QO 2-POLE BRANCH BREAKERS ONLY. QO branch breakers, 10-70 ampere, are also SQUARE D CERTIFIED for use on 125V dc systems. Short circuit current rating is limited to 4,000 amperes (10-30 ampere) or 10,000 amperes (35-70 ampere) when used on 125V dc.
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sunshine_eggo
Happy Breffast!
I've found some breakers that meet 20,000 AIC, but yea... Class-T
Ya, I understand that. But from the discussion here in this thread I was under the impression that was for shutoff and a fuse is still needed (or at least desirable).
It's not strictly needed, the breaker (should be) properly rated. As I mentioned a post or two ago, I prefer class T fuses over a breaker for this, but that's not absolutely needed. If you have fuses, adding breakers just adds a simple way to turn a battery off.
As a retired master electrician, you should be aware the NEC is a minimum standard, and any electrician that builds to the exact requirements of the NEC performs shoddy work indeed. As every one of my code instructors have told me repeatedly.
Well, is always wise to take every precaution when working around power sources, any power source can have a dark side, ever dropped a wrench on a battery, accidentally or by any other means at your disposal? Is amazing how metal can melt in seconds! I have, a few times, in over 50 years of work in the electronics and communications field. Is not pretty, so breakers are not required but I do have few of those, and I think I have a few more I need to put somewhere. Safety First and Always folks! Is better than nothing for sure. If you got the money go for it!
Zwy
Solar Wizard
NEC is still playing catch up mode as the technology is moving faster than it's bureaucratic process. This is well known.
While not required by NEC, there still is a thing called best practices. Over time, best practices can become a standard as it proven to be safe and reliable and may increase longevity of a system. As a retired electrician, you have seen as NEC evolved over the years and how best practices become codified. Take EGC's, grounding, Ufer's, bonding and now even running a bare buried ground conductor in a trench. All evolved over time as failures occurred, or someone figured out how to build a better mousetrap.
You're missing the point, this is about best practices and how they should be adopted and practiced.
Again you need to look at the chemistry involved here. NiCad isn't LFP and certainly doesn't accept or discharge the same as LFP. The chemistry and the anodes are what makes a Li Ion battery flammable and even explosive. Understanding the characteristics of the chemistry involved will lead one to make decisions based upon best practices that over time will probably become a standard. We here on the DIY forum are pioneers in this area, none of the recommendations provided should be taken lightly. Many discussions are involved that points on both sides are debated and researched before a final conclusion is reached.
While you may disagree with the best practice of fusing each battery in a bank, the discussions here in this forum have reached the conclusion the best practice is to fuse a battery and to use a Class T fuse for this purpose. Not ANL, MEGA or other types. The reason is the arc temperature can easily be an ignition source with hot metal being thrown. Whether you agree with assessment is actually immaterial simply because the conclusion was reached to use the Class T under best practices by the various members of this forum.
Keep in mind the current NEC code forbids using lithium chemistry batteries that are not UL listed… odds are good that UL listing likely includes protection.
wiseacre
Solar Addict
Oh fudge
I was thinking of using a Victron Lynx Distributor (with Mega fuses) to fuse 4 batteries in parallel
I've had a long, close relationship with Murphy's Law so don't want to find out what an arc would do in that pretty blue box
So much for "cheap" and easy, looks like 4 Class Ts before a Lynx Power is "Best Practice"
John Frum
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What voltage are the batteries?
wiseacre
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chess-equality
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Let's say I have a 4p 24v bank and each battery has a 100A BMS, but I only have less than 1kw load now and in the very near future, the recommendation is still to fuse each battery?
Yes, it has little to do with your expected load. Suppose one of the batteries develops a short. If you don't fuse the pack, you now have three batteries pumping their energy into that short. It might not be a dead short - imagine a 100A fuse per battery, and one of them develops a fault/BMS issue, causing the other three of them to pump 80A into it. Without the fuse, your BMS on the three might not even consider this a fault, and the 100A fuse on them won't blow. However, the 100A fuse on the faulty battery will since there is 240A going through it.
Yellow alert….shields up…back us out of here ensign….
OK, now you have me second guessing my plan which is in progress.. I have 3 pairs of Battle Born 100ah Batts (6). Each pair is series to 24v .. each pair feed to a dedicated 300 amp class T fuse on the positive cable about a foot away through 4/0 cable. 3 fuses total. Each cable leaves it’s fuse and goes to a 350 amp blue seas large disconnect switch (about a foot away ( a red off- on type ) 3 switch’s total . Each switch turns off each 2 battery string.
The cables leave the switch and go to the positive battery buss (blue seas 600 amp) and are in “parallel” .
Three strings total (24 v).
A main 4/0 cable then leads from that buss to another Class T 300 amp fuse a foot away before it goes to the main positive distribution buss bar. Then it feeds out to different devices . The cable feeding the multiplus from th3 pos distribution bar has a dedicated 350 amp blue seas off/ on switch too.
The negative side is a exact mirror of the positive side except it has no switches or fuses but does go through a Victron 712 shunt/ monitor Gizmo ..All cables in the system are 4/0 except a couple of 2 and 4 gauge going to lower amp devices.
Every positive wire in the system has fusing as just as described above or a bussman MRCB switch in the proper amp rating used for less critical spots. Every device has a dedicated fuse and disconnect .
1) As each string has its own fuse ,if one of my batts shorted within a series string ( two batts per string) would I be ok .? ( the individual switch’s are there to remove from the circuit if need be.)
2). If one of the 3 string shorted , and was paralleled with the other two strings at the battery buss am I ok.?
I think I’m doing OK , but if I’m not , now is the time change the plans as the cutting of wires starts this week.
Is that enough info to readily judge if the parallel batts are reasonably protected.??? How about the series strings of two.??
Thank You,
Jim
timselectric
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1) yes
2) yes
Because you have protected each battery. (Two batteries put in series, is now one battery)
Hurray again… thanks….
Each string needs a disconnect (at a minimum) per code if you are building it up. If it is self-contained UL listed equipmentthen the NEC does not apply (until you make field connections).
A fuse is not a disconnect, it is an overcurrent protective device. Typically a fuse is going to require a disconnect upstream by code (and practicality), but many people take chances at 48V.
The biggest reason to use a circuit breaker in my mind is so that you can disconnect a module and service it while the rest of the system remains online. A fuse provides (some level of) protection, but not that functional means of disconnect.
Does it matter which side of the battery you fuse? + or -
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