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Nobadays
Member
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# Posted: 9 Jul 2024 14:25
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Hopefully catch Steve before he "retires!"
At the time I got my Chins lifepo4 batteries they didn't offer 48v units so I have 4 x 24v - 2s2p. They have been in service over 3 years and they are great! (We discussed on another thread that I do need to Disconnect them and test to see if the voltages are the same.)
My question is; Should all positives and negatives be connected. (I'm guessing better balancing? )
The reason I ask is the LiTime manual shows this being done when series/paralleling their batteries. They are also showing negatives and positives going to a busbar prior to the inverter/charge controller. All my negatives go to a busbar but the positives go to a breaker box- which is really a glorified/controllable busbar.
Picture attached
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ICC
Member
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# Posted: 9 Jul 2024 15:02
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I parallel connect everything through buss bars. One of the reasons that is my preferred method is that allows me to remove any one of those paralleled batteries with no disturbance to any of the other interconnected batteries. Buss bars also likely make the parallel battery balancing work better. No proof but that is what I believe. I don't think it can hurt. Just be careful when working with all those connections. Use insulated wrenches.
When I used 6-volt golf cart batteries I had two strings of series connected batteries to have 24 volts and paralleled each string to buss bars. Now I have a single 24-volt SOK battery, still connected to the buss bars because the buss bars are there and it is easiest.
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travellerw
Member
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# Posted: 9 Jul 2024 15:07
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That image would be the "proper" way to do it. Its all about the lowest resistance between the cells to achieve non-active balancing. You can't control the connections within the batteries themselves, but you can control the interlinks.
More copper = More better!
BUT, like everything its a trade off. You could spend 1000s on low oxy copper bars as interconnects and I doubt you could measure the performance gain over 1ga copper cable at 24V.
Personally, I think its more important to do a yearly rotate of the batteries themselves. This is up for debate if still required for lithium with an active BMS, but I would still do it. Its a 1/2 hour of work and gives you the opportunity to clean all the connections and reapply anti corrosion.
As to the busbar. In the image, those busbars are there to provide an equal resistive path to either batteries. In an ideal world, the cables to each of the batteries would be the same gauge and length. The outgoing connection would also be connected between the 2 cables coming from the batteries on the busbar (an equal distance between the 2).
That is really "old school" FLA type design. In reality any modern lithium battery with a BMS would not require that level of precision.
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Nobadays
Member
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# Posted: 10 Jul 2024 12:35
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Thanks guys! Mine do go to busbars... the positive through breakers first so I can turn off each set of batteries. From the breaker box then to the inverter. Negatives direct to busbars then to the inverter.
I guess I was wondering if all batteries should be tied together... ( -/-, +/+) but further thought says no. The reason is it would then make it impossible to isolate one set from the other. My breakers on each set would become useless.
Seems the best idea is that which Steve suggested before, being disconnect and test to make sure voltages are all the same. If not I can top balance them.
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Steve_S
Member
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# Posted: 10 Jul 2024 12:47
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The cleanest & simplest solution is 99% of the time the best answer.
I gave up on using unplated copper busbars a while back. My preference is for Nickel Plated first, tinned second. But I spend the wee extra for Nickle plated lugs & terminals so I never have to worry about corrosion or other.
It may not seem like it but do keep in mind with those packs fully charged there i a LOT of potential in them and you CAN Vapourize metal if not cautious. Be careful with your tools !
I'll be around in Lurk Mode and respond when appropriate. I actually prefer answering folks here than on DIYS now as that's gotten a tad too Randy and I won't argue with YT Educated dorks who love to bork peoples stuff for fun.
I'll be regularly peeking in as usual...
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gcrank1
Member
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# Posted: 10 Jul 2024 15:09
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SO glad to hear that Steve, I (we) value you highly 
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travellerw
Member
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# Posted: 10 Jul 2024 16:07
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Quoting: Nobadays I guess I was wondering if all batteries should be tied together... ( -/-, +/+) but further thought says no. The reason is it would then make it impossible to isolate one set from the other. My breakers on each set would become useless.
I know the breakers are convenient, but I lean the same way as Steve. Simple. I stay away from breakers and instead use fuses (as close to the batteries as possible).
Yup, it means I have to actually disconnect cables to isolate, but again its something I only do about once a year (even on my old LFePO4 bank with a rudimentary home built BMS). In the 4 years we used that bank, the cells never went out of balance.
I do use a brand name high quality disconnect switch between the batteries and devices (solar controllers, Inverter, ect). As well as between the solar arrays and the controllers. Well, at least on customers installs. I'm a little more "risky" on my stuff now that I'm not on a boat. I'm currently using some Amazon off brand battery switches.
Anyway.. If its working for you and your cells aren't going out of balance, then I wouldn't change it. Maybe just monitor your breakers in case of a high resistance failure (breakers will get hot).
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Steve_S
Member
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# Posted: 10 Jul 2024 18:33
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Just as a clarification with regards to my setup (which has evolved over time).
- Every Battery Pack has its own 200A DC Breaker.
(there will now be 7x280AH all in parallel for a total of 1960AH / 49.15kWh stored energy.
- Each Battery Pack is connected to the Common DC Bus which uses a 1000A 8 Post Busbar set with covers. Nickel Plated Pure Orange Copper).
- Each (+) wire is connected to that busbar through a 200A MRBF ( I am 24V - MRBF is fine up to 36V)
- Each Battery Cable to Busbar is 42-3/4" long "exactly" with Nickle Plated Terminals.
- Each Wire is KALAS 1/0 Flexwhip which uses UltraFine Pure Segmented copper stands and capable of 400A < 25'.
COMMON Bus to SCC/Inverter (within Midnite E-Panel with 250A Master Breaker) is connected via Royal Excelene 4/0 Premium welding wire.
My DC Breakers are Polarized DC Breakers from Midnite Solar. (Master 250A not polarized)
My Fuses (MRBF's) are BlueSea (LittleFuse).
AC Boxes & Breakers are all Square D.
2 Solar Arrays:
1) Midnite Classic 200 with 2080W in 4S2P layout.
2) Midnite Classic 150 with 2370W in 2s3p Layout.
*1 Using Canadian Solar 260W Poly Panels. Provides 79A charge.
*2 Using Q-Cell 395W Panels (great in shade/cloud) provides 94A Charge
NB: QCELL Panels far outperform others in Shade & Cloud due to the segment design. It is REALLY worth paying the few extra cents to ensure better generation through most weather conditions. And it REALLY IS CENTS DIFFERENCE in the grand scheme of things. I do not have Bi-Facials.
And YES, I am still using that amazing Samlex EVO-4024 Inverter ! What a terrific beast with very low overhead (18W idling without powersave on).
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