LifePO4 batteries for use with Midnite Classic 150?

[createthis]

I had a 48 volt 100 AH set of them. I liked them mechanically, but performance lacked due to very high internal resistance of the cells and higher than expected capacity loss. Mechanically I liked the covers and 4-point bussbars. But for the 23% higher price than CALB's was very disappointing performance. So got rid of them and replaced them with Leaf cells.

The 12V 100AH GBS battery I bought was $700 shipped to my door. I live on the East Coast. It looked like shipping for the CALB was going to be more. This was the only for sale page I could find for CALBs: http://www.electriccarpartscompany.c...ails_p_38.html and they talk about pallets and lift gates. I just didn't want to deal with it.

I was aware of the greater internal resistance of the GBS cells before I made the purchase, though I admit I don't fully understand how it will affect my system in practice yet. Worst case, I buy a CALB set later. No big deal. I'll probably end up with lots of different batteries before my curiosity is sated.

[inetdog]

I don't see how you could take karrak's quote to mean anything other than the capacity of the cell. He very clearly said "if the cells [...] they will not [...] their capacity". Therefore I still don't see how his quote is inaccurate.

I was not referring to any specific quote, such as karrak's. I was referring to the overall discussion, in particular your posts and SK's posts going back and forth.
The text of yours that I quoted was probably not the best example for that purpose.

[createthis]

Big problem with this approach is that if the cells are balanced at the bottom end they will not be balanced at the top end unless their capacity is the same you are in real danger of overcharging some cells and damaging them.

You and SK are going back and forth on this one because you are using the same words with different meanings. The quote above can be made accurate by simply substituting SOC for capacity.

If capacity means how many AH can be withdrawn from a cell starting at its current state and going to a stopping point which is determined on a per cell basis, then SK is correct that in a bottom balanced bank all cells will always be at equal capacity. But at no point but the bottom will they be at the same SOC, measured on a per cell basis.

If by capacity you mean the total AH capacity of a cell, not a bank, as determined on a per cell basis, then no amount of balancing will produce a bank with equal cell capacities.

I don't see how you could take karrak's quote to mean anything other than the capacity of the cell. He very clearly said "if the cells [...] they will not [...] their capacity". Therefore I still don't see how his quote is inaccurate.

[createthis]

Maybe he is happy to wait the 33 hours and use a power supply that he already has rather than pay a couple of hundred dollars for something that would do it quicker but might only be used once. Anyway if you charge then in series first, then in parallel it cuts down the time to probably around half that time.

That was my logic, yeah, but I ended up buying a PowerLab 8 v2 to aid in automatically pulling the battery voltage down to 2.5V. Didn't feel like babysitting it, and I figure I'll probably make more battery systems in the future, so why the hell not?

[Willy T]

What happens if the coulomb efficiency of the individual cells is not the same and the battery goes out of balance at the bottom end over time. Not all cells will reach 2.5 volts under these conditions



The weakest cell in the battery will always dictate the capacity of the battery, doesn't matter whether you top balance or bottom balance. With top balance, when charging all the cells will get to 3.6volts at the same time and you can use overall battery voltage to stop charging, when discharging the weakest will get to 2.5 volts first and you will have to the use individual cell voltage to shut down the load. With bottom balance, when charging the weakest cell will reach 3.6 volts first and you will need individual cell voltage to shut down the charger, when discharging all cells will reach 2.5 volts at the same time and you can use overall battery voltage to disconnect the load. If the battery goes out of balance individual cell voltage monitoring at both the high and low level is needed to protect the battery.

The maximum Ah capacity of the battery is equal to the Ah capacity of the weakest cell. If you bottom balance you can measure the number of Ah going into the battery while charging until the weakest cell reaches 3.6 volts, that is the Ah capacity of your battery. For top balancing you can measure the number of Ah being drawn from the battery while discharging until the weakest cell reaches 2.5 volts, that is th Ah capacity of your battery

Karrak, thanks for posting this Information, it's great to get concise and accurate facts about LiFepo4. Your the one consistent poster with the longest experience using them on a PV offgrid system.

[Sunking]

when charging the weakest cell will reach 3.6 volts first and you will need individual cell voltage to shut down the charger, when discharging all cells will reach 2.5 volts at the same time and you can use overall battery voltage to disconnect the load.

Nope and that is the part you do not understand. You never take the weakest cell to 3.6 volts. Proves you have not read one thing over the year since you arrived. If you do you will unbalance the pack. Lithium batteries do not go out of balance. The only metric that throws them out of balance is difference in leakage current which takes months to accumulate.

However I do agree you need to use top balance because you do not know the technology and how it works. It is not for consumers like yourself who need to rely automation to protect your batteries.Bottom balance is very simple and requires very little automation. Manufactures do not like or approve because it does not make them money if they cannot sell you a BMS.

Karrak you came here for one purpose and one purpose only. To harass me. You even conspired on another forum to bring others here to help you. You found one poor soul. At least he had enough common sense to give up and leave.

[karrak]

In Bottom Balanced system at 2.5 volts, all cells will have the exact same capacity of 0 AH per cell, and all SOC voltages of 2.5 volts per cell. Both Capacity and SOC are equal at the Bottom in a Bottom Balanced System. Thus you have no need to monitor cell voltages to protect over discharge. Setting the Inverter to 10.5 volts or greater does that for you.

What happens if the coulomb efficiency of the individual cells is not the same and the battery goes out of balance at the bottom end over time. Not all cells will reach 2.5 volts under these conditions

In a Top Balanced system all cells are charged to 100% SOC and capacity AH is not equal and unknown. Only SOC is known, not AH capacity .No two cells are equal in AH capacity and Chi-Com cells AH capacity tolerance is sloppy -3%/+15%. So a 4S pack weak cell can be as low as 97 AH, and the highest of 115 AH. The 4S pack capacity is dictated by the weakest cell in the string just like links in a chain. In this example is 97 AH would be maximum AH capacity. The 115 Ah cells can eat the 97 AH cell if discharged down to the PACK 20%SOC voltage of 12 volts. In a Top Balanced system you must have cell monitors with a LVC circuit to operate if any cell reaches 2.5 volts which wil be the weak 97 AH cell. The other three cells stil have capacity left in them to drive the discharge cell to reverse polarity. Game over.

The weakest cell in the battery will always dictate the capacity of the battery, doesn't matter whether you top balance or bottom balance. With top balance, when charging all the cells will get to 3.6volts at the same time and you can use overall battery voltage to stop charging, when discharging the weakest will get to 2.5 volts first and you will have to the use individual cell voltage to shut down the load. With bottom balance, when charging the weakest cell will reach 3.6 volts first and you will need individual cell voltage to shut down the charger, when discharging all cells will reach 2.5 volts at the same time and you can use overall battery voltage to disconnect the load. If the battery goes out of balance individual cell voltage monitoring at both the high and low level is needed to protect the battery.

The maximum Ah capacity of the battery is equal to the Ah capacity of the weakest cell. If you bottom balance you can measure the number of Ah going into the battery while charging until the weakest cell reaches 3.6 volts, that is the Ah capacity of your battery. For top balancing you can measure the number of Ah being drawn from the battery while discharging until the weakest cell reaches 2.5 volts, that is th Ah capacity of your battery

[karrak]

If you use your hobby charger and decide to Top Balance, it is going to be a very slow process and you will not be able to detect when they are fully charged with a 6-amp charger with all 4 cells in parallel. At 400 AH you hold 3.6 volts until charge current Tapers to 3% of C. 3% of C on a 400 AH battery is 12 amps. See the problem? Only way to Top Balance with your Hobby Charger is one cell at a time and terminate when charge current tapers down to 3 amps. Either way will take a couple of days with 4 cells. See a problem with that?

Where did the magic figure of 3% come from. As long as the charge current is larger than 'leakage current' of the cells they will charge to full and reach 3.6 volts

[karrak]

If this poor guys wires his cell in parallel will make a 400 AH pack. Assuming 50% SOC just how long does it take to charge them with 6 amps? 200 AH / 6 amps = 33 hours. Hell of a lot better waiting days for the Balance Chargers to Top Balance in series. While he is waiting he can paint a wall, and then watch paint dry to keep him entertained.

Maybe he is happy to wait the 33 hours and use a power supply that he already has rather than pay a couple of hundred dollars for something that would do it quicker but might only be used once. Anyway if you charge then in series first, then in parallel it cuts down the time to probably around half that time.

[PNjunction]

1. If you build a battery bank out of random off the dealer's shelf cells, all the same brand and model and hopefully same or similar manufacturing date, how likely is it that the cells will be reasonably (within the capacity of the BMS to handle) balanced as to SOC when you get them?

They usually arrive sitting around 3.2v, but that means nothing really from a capacity standpoint. You could purchase four 100ah cells, but lo and behold, they mistakenly slip in a 60ah cell. Yet all four are sitting at 3.2v upon arrival.

Instead of buying random, you deal with a distributor that will ship cells ideally from a sequential set. Some contain bar-codes or other identifiers. Upon request, some even come with test sheets showing both capacity and IR all along the charge/discharge curve - if you want to go that far. Most pre-made packs, or batteries from reputable dealers aren't just cobbled together from a random shelf-pull, unless one is going cheap.

2. Same question but a group of cells ordered new from the factory or from a large internet dealer as a single order? Better or worse than the first situation?

New from the factory usually means China - and sometimes that poses problems for some. US or other country distributors may have stock in your continent/country/state.

GBS can be found in many places, but the main distributor in the US is Elitepowersolutions.

CALB in the US is mainly in Pomona, Ca. CALB USA Inc.

Some EV places carry all the major brands, like Evolve Electrics, EV Source, EV West etc. Others may find LFP at batteryspace, or GWL/Power in Europe. So you can deal direct with the mainland, with a trusted nearby main distributor, EV outlets, and even battery specialist places like batteryspace. Find one you can trust.

3. Same question but this time you buy a preassembled battery pack with an integrated BMS?

Sure! Many do. Remember that most of the time the main customer is EV users, who may put together higher-voltage / multiple bank systems, rather than us simplistic guys putting together simple 4S / 8S / 12S systems for an energy-storage application.

Where between those two extremes do the boards continue to make sense? Clearly not for typical solar PV where charge/float time is limited, and especially if you deliberately never bring the bank to 100% SOC where the cell bypass function kicks in.

Vampire boards are too risky, and prone to failure causing the problem they are meant to cure! In addition, they have their own accuracy specs, which can deviate over time, so you really ARENT balanced at all. Just making voltmeters line up. Meanwhile ....

The point being that we have a tendency to overcomplicate the issue with endless top/bottom balancing talk. Most users just go underground now with shared experiences as the topic is an endless rehash over and over.

Charge each cell individually to 3.6V, falling to .05C. If you haven't purchased hacker trash, you'll be close in both capacity and internal resistance. Close is good enough in our application. You'll never need to charge to this level again. This is an initial charge.

Normal charging - 3.4 to 3.45v per cell. Absorb current can fall to almost nothing at 3.4 without harm as you'll never fully charge it and leave it that way without use at some point.

Stop when any cell gets to 2.7v under load. This is fine in our application. Stop sooner if you like. Heck, even your typical 10.7 to 11.2v lead-acid lvd will stop you from destroying the bank completely, although at that point, I'd recharge *slowly* to get back to at least 3.1v and then don't do that again on a regular basis.

My suggestion is to just get a sample small 4S bank, and test it. Then you'll see where you can ignore about 2/3rds of all forum talk based on your own desires and experience.

Make it simple or complex - it's up to you.

[PNjunction]

PN I think you would agree the CALB's are the best of the Chi-Coms. Would you not agree with that?

In our application, which is a realtively low-current energy-storage application, and not a "power" application like an EV, I think the differences are minimal. EV's - certainly I'd use the higher-end calb's.

That being said The CALB's are less expensive and twice the warranty/cycle life of GBS and Winston. Knowing that which one would you buy?

That's great if one can get that deal. Not that you'll get any great performance advantage in our low-current application, but sure no problem with Calb.

Today i have Leaf cells in the cart operating at 96ish volts. Mucho Better performance. Very low voltage sag when accelerating, and very little capacity loss for their age. Me and a couple of friends down here bought a set of Leaf Batteries from a salvage yard.

Some EV guys are going that route. Different chemistry, different charge / maintenance procedures.

[Sunking]

What he said wasn't ignorant. It was accurate.

No sir it is not

Top balance means capacities are off at the top and over charging is a risk.

That part is half correct, At the top, all cells are at maximum capacity, but capacity is not equal. The only thing that is equal at the top is SOC voltage of 3.6 volts. Both over charge and over discharge are is highly likely without a BMS.

Bottom balancing means capacities are off at the bottom and over discharge is a risk. It's really a personal preference thing.

None of this statement is correct and leading you to the wrong conclusions. When you BB all cells both AH capacity and SOC voltages are equal in all cells. Capacity = 0 AH, and SOC Voltage = 2.5 volts. Over discharge risk is minimized to almost impossible. Like Top Balance, over charge is possible with BB system if you try to push the weak cell to high. The magic of BB systems is capacity is equal in all cells at all SOC levels. You stop charging when the weak cell reaches 80 to 90% SOC. So in the proceeding example if the weak cell is 97 AH and you charge the weak cell to 90% capacity, all cells have 87.3 AH. The weak cell will have ever so slightly higher voltage than all others when charged up. But the voltage difference is very small roughly .05 volts or less. The weak cell should be up around 3.41 to 3.43 volts at rest, and the others around 3.36 3.38 volts so in a 4S pack totals roughly 13.5 volts.

[Sunking]

You and SK are going back and forth on this one because you are using the same words with different meanings. The quote above can be made accurate by simply substituting SOC for capacity.

If capacity means how many AH can be withdrawn from a cell starting at its current state and going to a stopping point which is determined on a per cell basis, then SK is correct that in a bottom balanced bank all cells will always be at equal capacity. But at no point but the bottom will they be at the same SOC, measured on a per cell basis.

If by capacity you mean the total AH capacity of a cell, not a bank, as determined on a per cell basis, then no amount of balancing will produce a bank with equal cell capacities. Capacity defined that way cannot be changed except by partially destroying the better cells. Using this definition of the word, balancing does not equalize capacity, it equalizes SOC (Post #62). The point at which the SOCs match must be specified (either top or bottom) since cells of different individual capacity cannot stay balanced through charge or discharge if you pass the same current through all of them.

Correct sir.

In Bottom Balanced system at 2.5 volts, all cells will have the exact same capacity of 0 AH per cell, and all SOC voltages of 2.5 volts per cell. Both Capacity and SOC are equal at the Bottom in a Bottom Balanced System. Thus you have no need to monitor cell voltages to protect over discharge. Setting the Inverter to 10.5 volts or greater does that for you.

In a Top Balanced system all cells are charged to 100% SOC and capacity AH is not equal and unknown. Only SOC is known, not AH capacity .No two cells are equal in AH capacity and Chi-Com cells AH capacity tolerance is sloppy -3%/+15%. So a 4S pack weak cell can be as low as 97 AH, and the highest of 115 AH. The 4S pack capacity is dictated by the weakest cell in the string just like links in a chain. In this example is 97 AH would be maximum AH capacity. The 115 Ah cells can eat the 97 AH cell if discharged down to the PACK 20%SOC voltage of 12 volts. In a Top Balanced system you must have cell monitors with a LVC circuit to operate if any cell reaches 2.5 volts which wil be the weak 97 AH cell. The other three cells stil have capacity left in them to drive the discharge cell to reverse polarity. Game over.

Having said that BB systems should only be attempted by experienced users who fully understand the technology. All commercial systems use Top Balance for liability reasons and added profit.

[inetdog]

What he said wasn't ignorant. It was accurate.

Top balance means capacities are off at the top and over charging is a risk. Bottom balancing means capacities are off at the bottom and over discharge is a risk. It's really a personal preference thing.

I feel like this thread is those two guys in Frozen arguing bark side up or bark side down.

You and SK are going back and forth on this one because you are using the same words with different meanings. The quote above can be made accurate by simply substituting SOC for capacity.

If capacity means how many AH can be withdrawn from a cell starting at its current state and going to a stopping point which is determined on a per cell basis, then SK is correct that in a bottom balanced bank all cells will always be at equal capacity. But at no point but the bottom will they be at the same SOC, measured on a per cell basis.

If by capacity you mean the total AH capacity of a cell, not a bank, as determined on a per cell basis, then no amount of balancing will produce a bank with equal cell capacities. Capacity defined that way cannot be changed except by partially destroying the better cells. Using this definition of the word, balancing does not equalize capacity, it equalizes SOC (Post #62). The point at which the SOCs match must be specified (either top or bottom) since cells of different individual capacity cannot stay balanced through charge or discharge if you pass the same current through all of them.

And then there is a hint of a third definition of capacity being used by createthis, which has something to do with how much farther you can charge a given cell before reaching 100% SOC./

Seems simple enough, but easy to provoke disagreement and talking past one another when you do not share the same definitions of the words you use.
If you actually read your posts and SK's posts you may realize that you are both describing the same physical reality even though you seem to be disagreeing.

[Sunking]

Balancing lifepo4 is simple matter and if you have the right equipment it's effortless. All this babble about top and bottom balancing is ridiculous and really shows how little some know about how to use the technology properly.

You have to perform a Initial aka Gross balance when you receive them, and either pick Top or Bottom. No way around it no matter what country you are from. After that just stay away from the knees using CC/CV, no BMS required.