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lithium hi amp balancers
I had problems with my 4s20p 110ah  lifepo4 battery pack not getting a full charge due to the BMS always tripping early due to one cell always reaching 3.65 volts while the other 3 cells where at 3.40 volts, this has been going on for 6 months. When the BMS tripped, the solar charge controller would surge (voltage would go over 15 volts) resulting in damaging anything connected to the battery , mainly burning out my swampcooler fans. About 5 of them in the past 6 months.

I installed an overvoltage relay to try and control the surge but it wasn't fast enough to prevent the damage. 

Fast forward to last week finally got a 4s balancer, this unit will balance at a constant 6 amps and (will peak at 10 amps). The balancers on many of the BMS are in the 60 milliamp range which are next to useless for balancing a low ah battery let alone a 110 ah lifepo4. Also these built-in balancers don't start balancing until the cell reaches 3.60 volts (which is nearly full for lifepo4 3.65 is full). At 6 amp balancing you can charge at 24 amps and the balancer will keep up with that rate of charge. For comparison my 14 amp balance charger will drop to less than 1 amp of charge current once the battery starts going out of balance. 

I been testing it all week and like its performance. It is always on and balancing while connected, will balance while charging/discharging. With this balancer I can just let the overvoltage relay set for 14.4 volts disconnect the solar panel when that voltage is reached. 14.6 volts is when the battery is fully charge but setting at that voltage is too risky because it will trip the BMS, 14.4 volts is close enough and a voltage I never reached except when connected to a balance charger. To get that close with a solar controller is a major achievement.  

These balancers is mainly for those with DIY lithium battery packs. It will work on li-ion,lifepo4 and there is no limit (recommended 50 to 1000 ah), you just add more balance modules as needed. They are interconnected and they work by bleeding from the hi-cell and transferring to the low-cell instead of wasting the excess voltage as heat. They do make a high frequency noise while working which is all the time. But you need to be next to them to hear it. If you DIY your own battery pack you won't have any problem installing or using this balancer. You just connect it and it works in the background. Just disconnect it if you wont be using the battery pack, it is always running and using power.  

I paid 80 dollars plus 10 dollar shipping for my 4s balancer. I bought from electriccarpartscompany but also available from overseas sellers. Expensive but worth it if you got a lifepo4 with balance problems.

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The following 1 user says Thank You to jonyjoe303 for this post:
Itripper (02-14-2018)
Links to tech details, docs, sources for your cells and BMS, also for the balancer, other than that vendor please

That's a lot more parallel strings than I'd want, general rule of thumb is 3 max, maybe 4.

I would never let a BMS do active balancing. The most knowledgeable installers disable that feature on even the proprietary packaged systems costing many thousands, often the added complexity causes (a lot) more harm than good.

Assuming this is gentle, sub-C rate House usage, not EV propulsion, get them balanced manually when commissioning, and then just check periodically, with a quality bank many go for 4+ years without them needing manual rebalancing.

Also, if you're following vendor specs for that **very** high definition of "full", you will get only a fraction of the bank's potential longevity.

I would never charge above 3.45Vpc (for 4s packs = 13.8V) in normal daily cycling, and even then only if consumer loads were all set to start discharging immediately.

That only gives up maybe a couple percent AH, still well within their new capacity rating, but at least 3-4x the lifetime.

While not active, keep at low SoC, maybe around 3.05V.
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Here's my "boilerplate" LFP summary, mostly from marine electrics discussion forums involving long-term users and professionals, with special thanks to Maine Sail (see below).

Any and all feedback is welcome, especially if more "canonical" information from the links cited conflict with my summary.

Systems: OceanPlanet (Lithionics), Victron, MasterVolt, Redarc (Oz specific?)

Bare cells: ​Winston/Voltronix, CALB, GBS, A123 & Sinopoly

Best to size your cells for two parallel strings for redundancy, unless you have a separate reserve/backup bank. Don't go past three, or you may see balancing issues that affect long-term longevity, maybe four in a pinch.

Note nearly **every** vendor, also those of ancillary hardware touted as "LFP ready", gives charging voltages **way too high** for longevity.

My (conspiracy) theory is that manufacturers would prefer their cells get burned out in under 10 years.

EV usage is very different from much gentler House bank cycling. Most EV people talking "lithium-ion" mean other chemistries not as safe as LFP, much shorter lifetimes, and with completely different setpoints and behaviors.

My charge settings for LFP: 3.45Vpc, which = 13.8V max for 4S "12V".

The point is to look at the SoC vs Voltage chart, and avoid the "shoulders" at both ends, stay in the smooth parts of the curve.

Either "just stop" charging when voltage is hit, or if you want another couple % SoC capacity, stop when trailing amps **at your spec'd voltage** hits endAmps of .02C, or 2A per 100AH.

Note even at the "low" max charge voltage, letting the charge source continue to "push" even low currents long past the endAmps point is **over-charging, and will** greatly reduce lifecycles.

So if you can't then "just stop", set Float well below resting Full voltage, at say 13.1V, but that is a compromise, and *may* shorten life cycles.

With LFP, you don't need to fill up all the way at all, as far as the cells are concerned. In fact, it is bad for them to sit there more than a few minutes. Therefore only "fill up" if consumer loads are present, ready to start discharging, ideally right away.

Store the bank as cool as possible and at 10-20% SoC, or maybe higher to compensate for self-discharge, if not getting topped up regularly (I would at least monthly).

Letting the batts go "dead flat" = instant **permanent unrecoverable** damage.

Same with charging in below 32°F / 0°C freezing temps.

Persistent high temps also drastically shortens life.

Charging at 1C or even higher is no problem, as long as your wiring is that robust, vendors may spec lower out of legal caution.

Again, going above 14V won't add much AH capacity, but will shorten life cycles dramatically.

And of course, we're talking about gentle "partial C" House bank discharge rates, size appropriately and be careful feeding heavy loads like a winch or windlass.

Following these tips, letting the BMS do active balancing is unnecessary and potentially harmful, just look for LVD / OVD and temp protection. Multiple layers of protection are advised if it is a very expensive bank, so you don't rely on any one device to keep working.

Check cell-level voltage balance say monthly to start, then quarterly, finally every six months if there are no imbalance issues, but only if that seems safe to you.

This thread is long but informative

, make sure to give both Maine Sail and Ocean Planet your close attention.

Also MS' summary notes here

**Everything** at that site is worth reading, very valuable. He also has great articles in Practical Sailor. His new site under development transitioning the pbase content is here, feel free to make a donation to help with those expenses.

Best of luck, and do please report back here!
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these are the cells (brand new) I'm using 80 of them. Configured in 4s10p pack (55ah) then that 55ah pack connected to another identical 4s10p (55ah) pack, is the only way I could fit all batteries into a group 34 battery box. Both packs have balance connectors joining them and should remain in balance. But during charging one cell(series) always drifts out of balance.  

Manufacturer: LFR/Tenergy
Model: LiFePO4 32650-5500/32700PP
Nominal Voltage: 3.2 - 3.3 V
Nominal Capacity: 5500 mAh 5.5Ah
Charging current: 3.3 A Max.
Discharging current: 9.9A continuous  
Operating Temperature:
Charging:    0° to 45°C
Discharging:  -20° to 60°C

Cycle Performance:
>2000 (80% of initial capacity at 0.2C rate, IEC Standard)
2 times more than NiMH  and 10 times more than SLA

Dimensions (DxH): 32.5mm (1.28") x 65.66 mm (2.58")

bms is 30 amp 4s lifepo4. It cost me 5 dollars, but it does the 2 important functions high and low voltage cutoffs very well. But it wont balance, though it has that function. The more expensive bms I looked at also have very low rates of balancing, only suitable for charging at low amps. They wouldnt have worked in my situation. I like to fast charge my lifepo4 at least to what my 240 watt panel puts out. 

balancer specs 4s

The cells you mention in your post are the large giant ones. Those I suspect will remain in balance since there are fewer connection between them. But I did notice the company that sells the balancers, the balancers are demonstrated on those larger cells. 

With the balancers in place, I have been getting the cells up to 3.55 volts, which for me is excellent. Its about 14.2 volts total. Less than a full charge. 
Because of voltage drop I have my controller set to 14.5 volts float, anything less and the controller will be putting out 0 amps. At 14.5 volts the controller puts out less than an 1 amp once the battery reaches 14.1 volts even in full sunlight. That 1 amp will slowly get it up to 14.2 volts. 

The backups are the overvoltage relay which trips at 14.4 volts and the bms which trips at 14.6 volts. So far with the balancers neither has tripped yet. I like to see my battery in perfect balance while charging and so far I got my lifepo4 finally working with my solar system, before I had to adjust the float voltage throughout the day and occasionally disconnect the solar panel.
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(02-14-2018, 09:24 PM)jonyjoe303 Wrote: The cells you mention in your post are the large giant ones.
AKA prismatic cells. IMO the only way to go.

More power to you for using the little cylindrical ones, extreme version of DIY, more trouble than it's worth afaic.

I've seen people do the same with NMC 18650 cells, sometimes even scavenging them from discarded laptop batts.

I guess it's a hobby.

But long as it's LFP the care and charging guidelines should be the same, going that way is certainly not cheaper per AH, so best to try for a nice long lifespan.
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You shouldn’t attempt to use voltage as a measure of state of charge with LFP batteries, you should use active draw/supply measurement. While you can get away with measuring by voltage, possibly for years, you risk balance issues (especially if you’re not actively balancing) and failing to detect damage (either due to degradation in the wiring, physical damage or balance issues.)

Whatever the size and type of your cells, you should be balancing them when charging, always. Active balancing is probably an ideal situation and something reasonably accomplished by any decent BMS.

I think unfortunately a lot of lead acid assumptions are bleeding over into the information being given.

I am not relying on experts here, I have worked with LFP as far back as 2007, when I was using prototype A123 cells. I have taken them to failure a great deal in the harshest environment possible, and charged them similarly.

But even in the relatively gentle environment of an RV, whenever you are dealing with large amounts of power, such as 100 AH, you must balance your charging.

I’m not aware of any limitations on number of batteries in series or parallel, or any scientific reason for such, if you have a BMS properly managing them—- though obviously if you aren’t managing them at all you would want to keep the number of cells that are unmanaged small. (Which makes me think that advice is coming from the same people who are turning off charge management.)

You may be able to build a system that stays in balance for weeks or years, but you have zero expectation that it won’t go drastically out of balance in the next week, and potentially catastrophically so— though with LFP their failure mode is USUALLY less dangerous than lithium ion, the smell is one you won’t soon forget ... and may render your RV uninhabitable.

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OP: would love to see a link to the manufacturer website and or datasheets for that BMS.

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"Whatever the size and type of your cells, you should be balancing them when charging, always. Active balancing is probably an ideal situation and something reasonably accomplished by any decent BMS."

This I agree 100 percent. I think it should be done everytime you charge the battery. Whenever I can I try to charge my lifepo4 with my 14 amp balance charger, but even that charger struggles with its limited ability to bleed the high cells. It can take hours to fully charge it. Many of the BMS that I looked at, they all seem to start balancing when one of the cells reaches 3.60 volts, if you are charging at high amps, that will always trip the high voltage shutoff. BMS should only be use to control the low and hi voltage cutoffs or be used in battery packs that don't drift too much out of balance. 

I build my own li-ion and lifepo4 battery packs, not as a hobby but to actually use it for day to day use. The 110ah lifepo4 I built out performs any of the lead acid batterys I have used. Having the ability to keep the cells in perfect balance allows me to be 100 percent solar no longer relying on the balance charger. 

this where I bought the balancers,  theres links to the user manuals in there website. 

This is a picture of them in use. Normally the top reading on the LCD 3in1 meter would read 3.60 volts, the other 3 cells will be at 3.40 volts. With the balancer connected they all read about the same, and its still charging at 4.04 amps. The balancers themselves so far have never got hot or even warm. 
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You should definitely **check** for imbalance on a regular basis.

But active balancing is IMO too dangerous, especially since it's completely unnecessary

And even with just monitoring for balance, doing so **every charge cycle** is IMO just nuts.

I know dozens of happy users of prismatic House banks, what systems vendors call "DIY" or "bare cell" setups, that regularly check per-cell voltages at rest, **manually**.

Most started out doing so weekly or monthly, then after a year or two switched to quarterly or even twice a year, since they usually find no actual need for balancing at all, often for over many years.

Since most methods are easy to do and not very harmful to longevity as long as not done too often or too high or low a V, while the pack is split you can do so anyway if you like.

Many started out with cell-level hardware, even if just for "live" monitoring, data logging etc, but find more problems caused than solved by that level of complexity, multiple points of failure, so they end up ripping it all out and doing everything at the whole-bank or pack level.

At that point it's possible to get the essential protective BMS functionality

3 current limiting
4 temperature protection

from quality OTS standalone units from known quality mainstream vendors like Samlex, Blue Sea, Victron etc

I agree that there should be more reasonably priced, adjustable non-proprietary, good quality all-in-one BMS projects out there, but I have not yet found one.

Best I've seen along those lines is the costly proprietary packaged systems from Victron and Lithionics, with the per-cell components carefully disabled or removed.
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