Li-ion battery balancing

I recently purchased a Li ion battery pack and charger.

The supplier's website advises the battery charger conducts 'balancing'.

I understand that the basic premise is for the battery charger allows the individual cells to charge equally so one cell doesn't cop it can catch fire.

But... without access to the individual cells- how does it actually do this?

The charger has two red leds and the fan running when its charging, and a red and a green + fan stops when it has stopped charging and is 'balancing'.

How do it know its doing anything other than just charging it and then stopping (signaled by fan turn off and light changes?)

Assuming it's a complete battery and not lipos. The balancing isn't done by the charger. It's done by the circuit board attached to the cell-pack inside the battery casing.

The most common method uses bleed resisistors that open when the cells get close to their maximum voltage to drain them down to the same level.

Imagine a row of tanks of water, all with a little hole at the same height near the top, so that the water dribbles out until it drains down to the correct level if you overfill it

The balancing takes place after the green light comes on , this is when the charger is in cv mode . Its a rubish system as you have no idea as to when the cells are balanced and charging have truly finished. The best thing to do is leave the charger on when the green light comes on for at least a extra 30-60 minutes to give the cells a little bit of a chance to balance it the charger turns green then after a while then red again then is is a indectation that there are 1 or more cells that are a very long way out of balance and there for can take many hours to balance

The battery is bottle cage mount pack from em3ev

http://em3ev.com/store/index.php?route=product/product&path=35&product_id=160

I was leaving it on to balance from an hour or so after charging is finished.. its just I have been reading about how to prolong the life of a li ion battery, and the suggestion was to only use it to 90% of its capacity. If that's the case, the charger would never enter the balancing mode as it only does it when charging is complete. Given the battery is being charged and drained daily.... its definitely going to have a short life being charged 100% every day.

I think amberwolf has misunderstood. I'm asking these questions because I have been reading other threads - they are just either on slightly different topics and don't apply or they counter information I've read from other sources. Ill keep reading regardless., hence the name 'Lurkin'

I'm trying to figure this out because im interested in shifting to a laptop style of charger (fanless and silent) and I need to figure out how to tell if it is balancing or at least capable of it at least.

Lurkin said:

The battery is bottle cage mount pack from em3ev

http://em3ev.com/store/index.php?route=product/product&path=35&product_id=160

I was leaving it on to balance from an hour or so after charging is finished.. its just I have been reading about how to prolong the life of a li ion battery, and the suggestion was to only use it to 90% of its capacity. If that's the case, the charger would never enter the balancing mode as it only does it when charging is complete. Given the battery is being charged and drained daily.... its definitely going to have a short life being charged 100% every day.

I think amberwolf has misunderstood. I'm asking these questions because I have been reading other threads - they are just either on slightly different topics and don't apply or they counter information I've read from other sources. Ill keep reading regardless., hence the name 'Lurkin'

I'm trying to figure this out because im interested in shifting to a laptop style of charger (fanless and silent) and I need to figure out how to tell if it is balancing or at least capable of it at least.

Click to expand...

The balance mode and at what point it starts is all down to the bms in the battery and , if you only wanted to charge to 90% and have the cells balance then you will need to change the bms and the charger voltage but you dont know that the battery may already only be charged to 90% and balanced.. you will need to open the battery and measure at what point the cells balance and what is the charge voltage of you charger. I dont think you can use a laptop PSU to use as a charger for a number of reasons.

Lurkin said:

The battery is bottle cage mount pack from em3ev

http://em3ev.com/store/index.php?route=product/product&path=35&product_id=160

I was leaving it on to balance from an hour or so after charging is finished.. its just I have been reading about how to prolong the life of a li ion battery, and the suggestion was to only use it to 90% of its capacity. If that's the case, the charger would never enter the balancing mode as it only does it when charging is complete. Given the battery is being charged and drained daily.... its definitely going to have a short life being charged 100% every day.

I'm trying to figure this out because im interested in shifting to a laptop style of charger (fanless and silent) and I need to figure out how to tell if it is balancing or at least capable of it at least.

Click to expand...

You've got it figured out pretty well. It's a bit of a dilemma.

I always charge my batteries to the maximum, and I haven't worn one out yet. The main reason for my lack of problems is that after two years, there's always better batteries coming out. We used to dream of batteries like you've got, but now they're a reality. In another two years, the batteries we dream of today will be real, so I'll be changing again, no doubt.

Laptop style chargers can be used, so long as the voltage and current are appropriate and it is capable of allowing the cv cycle ( welcome to correct me here).

I think I will be able to test the limitations of the battery given I am using it to commute 80kms per day, requiring daily charging.

I am also investigating whether a lifepo4 or lipo battery would have been a better choice. Lifepo4 is often written about on here as the safer charging option but is contrasted based on cost against lipo. This argument is irrelevant in my case as both are well cheaper than using the car. I may just stick with li ion for ease but it seems silly not to question further if I am repurchasing charging infrastructure.

Lurkin said:

Laptop style chargers can be used, so long as the voltage and current are appropriate and it is capable of allowing the cv cycle ( welcome to correct me here).

I think I will be able to test the limitations of the battery given I am using it to commute 80kms per day, requiring daily charging.

I am also investigating whether a lifepo4 or lipo battery would have been a better choice. Lifepo4 is often written about on here as the safer charging option but is contrasted based on cost against lipo. This argument is irrelevant in my case as both are well cheaper than using the car. I may just stick with li ion for ease but it seems silly not to question further if I am repurchasing charging infrastructure.

Click to expand...

if the laptop psu has current limiting and the correct output voltage then yes they can be used..

the small Ac adapters used to charge laptop batteries do not work on these big lifepo4 packs. your charger voltage has to match the voltage of the balancing network which is usually 3.60V/cell for lifepo4 and 4.20V/cell for lipo and lithium ion chemistry.

some chargers will turn off totally when they reach final voltage and they will not push the balancing current needed to balance the pack. you need to know which you have.

The current charger is 42v and 2.5a - so I would be looking for something similar.

I think rather than source locally I may considering making another purchase from em3ev. Paul has advised he has some of these chargers on offer. I will confirm with him that it conducts the balancing cycle appropriately before purchasing. Still not sure if I'm content as it offers no more protection against fire. I was intending to use it to charge the battery in the office, but the current charger is too noisy and appears its a bit of a risk.

it's a self fulfilling prophecy to an extent - if I charge it in the office it has to be quiet. However, the air temp is very comfortable due to decent air conditioning. Fire risk is now unacceptable. Move out to the warehouse area - no air conditioning. Temp frequently gets up to 40+ degrees on a hot day. Consequently, the charger will be trying to cool itself with hot air. similarly, the battery is also surrounded by hot air. Then apply charge and heat everything up...... Less to burn (around it) but increases the chance of overheating.

I am rehousing the original charger from its cheapo tiny case into an old, gutted computer case to allow for larger fans (large fan, less rpm to achieve same airflow) and will house the battery in the bottom whilst charging to (kind of) provide a steel box round it while its charging but still allow decent airflow to the charging circuit. The original cheapo box arrangement is incredibly noisy and doesn't offer much fire protection. I have tried replacing the cheapo fan with a decent Sunon Maglev, but the noise is about the same - due to the airpressure and obstruction in the tiny case.

I think I will make this and use it in the warehouse area. Further, may also install a cut off circuit (as well as an additional fan circuit) so the power is cut upon either the temp increasing to an unacceptable level in the box and upon the detection of smoke... I think this will be the most durable, safe, long term solution.

you should be able to confirm the balancing current yourself if you have a wattmeter or have an ammeter in your DVM. i think the chargers he sells use a latching output that cuts off.

I don't have a dvm.

But a cycle analyst is on the shopping list. Assuming this would be able to tell me this information, and log it.

Lurkin said:

I don't have a dvm.

But a cycle analyst is on the shopping list. Assuming this would be able to tell me this information, and log it.

Click to expand...

I don't believe that a Cycle analyst will help for that. You just need a simple $12 inline wattmeter to measure your charging current.

Regarding your comments about LiFePO4. Your present battery is good quality, a lot lighter, a lot neater and easier to install than any equivalent LiFePO4 battery. Four years ago, LiFePO4 would have been a good choice, but things have moved on now.

d8veh said:

I don't believe that a Cycle analyst will help for that.

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Sure it will. Mine does that on every charge cycle on CrazyBike2, and others have theirs setup that way too.

How do you do that? Could you provide a schematic?

A wattmeter is good at the time, but insufficient if it's not being monitored. Hence the idea of using a Cycle Analyst - to provide logging as well. I haven't fully investigated how to incorporate it as I don't charge the battery on the bike - may require two, one for the bike, one for the charger.

d8veh said:

How do you do that? Could you provide a schematic?

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Since I use the CA with the external shunt, it's hooked up the same way you'd hook up any wattmeter between battery and controller, plus a second controller-side connection for the charger to go into (like a y-cable).

Though you can also just unplug the controller from the CA's shunt and plug the charger in instead. I used to do that but now my controllers and stuff are all hardwired in, no connectors, to remove corrosion/oxidation/loose-plug worries.


If you use a DP type CA that uses the controller's shunt, then you would need to add a charger plug wire inside the controller. The positive just goes to the battery positive. The negative goes to the FET side of the shunt (not the battery side).

d8veh said:

How do you do that? Could you provide a schematic?

Click to expand...

Since I use the CA with the external shunt, it's hooked up the same way you'd hook up any wattmeter between battery and controller, plus a second controller-side connection for the charger to go into (like a y-cable).

Though you can also just unplug the controller from the CA's shunt and plug the charger in instead. I used to do that but now my controllers and stuff are all hardwired in, no connectors, to remove corrosion/oxidation/loose-plug worries.


If you use a DP type CA that uses the controller's shunt, then you would need to add a charger plug wire inside the controller. The positive just goes to the battery positive. The negative goes to the FET side of the shunt (not the battery side).

amberwolf said:

Since I use the CA with the external shunt, it's hooked up the same way you'd hook up any wattmeter between battery and controller, plus a second controller-side connection for the charger to go into (like a y-cable).

Click to expand...

Some (if not many) chargers won't give the green light like that because you would be effectively powering the controller with the charger. The controller takes upwards of 4W when on standby. Anybody trying that should disconnect the controller first when charging, which seems to defeat the object of having a Y-connection. It's the same with the DP version attaching charge cables direct to the controller. I wouldn't recommend that.

All things considered, I think it would be much safer and easier for the average guy to get a $12 wattmeter and leave it permanently connected to the charger. Sure, if you plan your installation, you can put switches in the appropriate places, but that just brings more complication.

None of the 3 or 4 chargers I've used this way so far have that problem (even if I forget to turn off the lighting DC-DC which draws way more than the pair of controllers).

Doesn't mean some won't, but these are typical cheap chargers, AFAIK. KingPan/KingPower, Modary, HiPower, I forget the other one.

But it doesnt' really matter--if you have a wattmeter or CA, all you need do is check the Ah in vs the Ah used (in the case of the CA, it'll be near zero on the main Ah used field when done). When the total is a little more Ah back in than taken out, it's probably fully charged.

If you're not sure, just note the idle current on the CA or wattmeter before hooking up the charger, and hwen it has dropped down to about that, vs when it's doing balancing if you have a BMS, then it's done charging if the Ah also tallies up.

That's all the green light usually says, anyway, is that the current dropped below some level. (it doesn't even mean that it's done charging, since the BMS could still be balancing and just not drawing any current, so a green light is deceptive, while the wattmeter / CA readout is a little more definitive unless you have a really badly out of balance pack).




Also, if you have a keyswitch that turns off power to the "ignition" wire on the controller, that will take out almsot all the current draw from it. Some have these built in (crystalyte, grin) already.

i think he only needs to determine if the charger actually does have a balancing current.

those chargers that he sells do not go into balance mode CV at the end of charge. they shut totally off when they reach final voltage. i call it latching output. i think i said that already.

he just needs to demonstrate that to himself so i asked him to use the ammeter in his DVM.

something he cannot do it appears. so no way to know if the charger does produce the balancing current at CV.

Noob question, I want to create my own 18650 battery pack. Probably 10s3p and I am not planning to install BMS. I want to use simple charger, probably similar to this http://m.aliexpress.com/item/422328869.html
Will all of cells be charged at full capacity/voltage when charger stop charging?

that depends on how balanced and matched the cells are.

If:

--you get a charger that has the correct final voltage for the number of cells in series for the "full" voltage of the chemistry you choose

and

--all of your cells are always perfectly balanced and all have exactly the same capacity, internal resistance, etc.,

then, yes.

But if any of your cells are not balanced, due to imperfections, age, etc., then no, it won't do what you want, becuase some cells will be overcharged while others are undercharged.

You would need to manually monitor voltages on each group in the pack to ensure this doesn't happen, if you don't have a BMS.


That said, I dont' have a BMS *or* monitor the voltages on my EIG NMC 20Ah pack. I do check it every so often, and in it's most recent checkup found a weak cell that has been replaced from spares.


But if I built an 18650 pack of such small capacity as a 3P, I would probably be doing one or the other or both, at least for the first several or many cycles, and periodically thru it's life.

Does anyone know if this Cycle Analyst is the appropriate module to buy? (to do what is being described above?)

http://www.emax-ebikes.com.au/store/p22/GRIN_TECHNOLOGIES_-_Cycle_Analyst_Version_3_-_DPS.html

Intended for use with a Bafang 250w mid drive as described