Do any BMS's balance at 4.1V instead of 4.2V?

Is it possible to adjust an existing BMS family to balance at 4.1V per P-group?

I have seen lots of credible data recently that indicates if a battery is only charged to 4.1V per cell, the life of the pack can be significantly improved. It has been suggested in discussions that a pack can be charged to 4.1V per cell on a daily basis, and then I can give my pack a full 100% 4.2V balance charge every couple of weeks, if I am concerned with cell balance.

Any way to end up with balance-charged pack all the time while always going to only 4.1V? (by any strategy you might think up?)

I haven't seen any other than Adaptto that can do that off the shelf. The typical Chinese style BMS uses Seiko chips or similar for the balancing shunts. They CAN be made for 4.1v, but this would seem to require a custom order, which is usually 2,000 units minimum.

A simpler strategy would be to simply charge the pack to 4.1v most of the time and only do an occasional balancing charge to 4.2V. The degradation is a function of voltage, temperature and time spent at those conditions. If you did a 4.2v balancing charge and immediately used the pack enough to get it down to 4.1v, the degradation would be minimal.

Most packs I have that were made with new, unabused cells keep their balance for a very long time.

I wanted the same thing. I ended up using a standard 4.2V BMS combined with a Battery Satiator which can be set to stop charging at any voltage you please. It cost me an extra $200 over the price of a more standard charger, but if I can double the life of my $800.00 battery, then well worth it.

-Jim

Before settling on lipo and a balance charger, I searched for something with a programmable cell voltage as I wanted to set them at 4.05/cell. They exist but can be a bit pricey. I couldn't find an affordable (non-programmable) one that did less than 4.2 (or more) volts per cell.

Thank you all for the responses, I appreciate the time that each one of you took to post here...

As many of you may know, I occasionally write for electricbike.com. A recent article I produced that was a synopsis of a lecture given freely by Dr Jeff Dahn, who I had the pleasure of emailing with, as a result. He is currently under a contractual agreement with Tesla, but that 2013 lecture is still available to the general public, and he was as openly helpful as he was able to be. This isn't about promoting or denigrating (insert favorite vendor here), or about the cell manufacturer (Samsung, Panasonic, LG, etc). This is information that affects every lithium battery that any customer has.

The big take-away from that research was:

Buy the biggest battery you can afford, and that will fit.

Spec a cell with a C-rate that will allow a pack that size to provide your desired amps without getting physically hot.

Never charge to 4.2V per cell unless you will be riding immediately.

Your standard charge after every ride should be to 4.1V per cell (90%), or even 4.05V (80%, if possible).

Regardless of the state of charge, getting it hot by parking in a garage in Arizona in the summer is bad (120F degrees).

Long term storage (winter?) of any lithium battery should be done at low voltage and cooler temps (3.3V per cell is good, and room temp or even a refrigerator is good)

If you charge to 4.2V every day, its bad...if you get the pack hot during charge or discharge its bad, if you store it over the winter at 4.2V per cell its very bad.

So...the question came up about making sure to balance the pack. The problem is that...if you charge to a full pack voltage of 4.2V per 13S "48V" pack = 54.6V using a dumb non-balancing 54.6V charger...then some of the cells can arrive at 4.1V per cell, while others arrive at 4.3V per cell (due to variable internal resistances in manufacturing). In that situation, the very few 4.3V cells will die early, leading to the pack sagging badly, or throwing an error code. (actual voltages exaggerated for example).

This is why it is vital to balance the pack. However, if you only charge to 4.1V per cell, then our theoretical 13S X 4.1V "48V" pack will be 53.3V...And, "if unbalanced yet", some of the cells might be at 4.0V, and others will be at 4.2V...for an "average" of 4.1V per cell. This is the important distinction that means none of the cells ever reach 4.25 or 4.30V...

As stated by others above, you can do a full balance charge on your pack on occasion, but...how often is the minimum to be safe? Once every ten charges might be acceptable, even once a week could be OK (for a daily ebike rider), by doing it just before a ride to minimize the time the pack sits at 4.2V

Regardless of the manufacturer or vendor, this can double the life of an expensive lithium battery pack, and that is worth talking about.

Firstly, no cell should ever get to 4.3v because no lithium pack should ever be charged without balancing. Ever.

Otherwise, yep, those of us with electric cars have been operating under these guidelines for years. High voltage and heat kills lithium batteries. Leafs use 4.15 volts as an absolute maximum voltage. Tesla's encourage 80% charging unless absolutely needed. Nissan learned the hard way that heat kills packs. It took them 4 years to adequately cool their batteries in order to prevent rapid capacity loss.

-Jim

If you had a quick and easy way to check the balance, you would know when you needed to do it. With new, good quality cells, I would expect to not need balancing for 20 cycles or more. By measuring, you could get a good idea for what is really needed. I've heard guys claim some packs stayed balanced for over 100 cycles. As the pack ages, it becomes more likely to go out of balance. My old abused A123 pack needed balancing on every cycle.

CellLogs are handy if you have a connector for them.

I have a random ali-expresses 18S BMS that surprised me by starting to balance at 4.1V.

My understanding is that good quality cells have now improved to the point where charging/resting voltage doesn't affect their life much. The main factor is time-at-temperature, whether that's from a high ambient, or internal heat from charging/discharging.

fechter said:

I haven't seen any other than Adaptto that can do that off the shelf. The typical Chinese style BMS uses Seiko chips or similar for the balancing shunts. They CAN be made for 4.1v, but this would seem to require a custom order, which is usually 2,000 units minimum.

A simpler strategy would be to simply charge the pack to 4.1v most of the time and only do an occasional balancing charge to 4.2V. The degradation is a function of voltage, temperature and time spent at those conditions. If you did a 4.2v balancing charge and immediately used the pack enough to get it down to 4.1v, the degradation would be minimal.

Most packs I have that were made with new, unabused cells keep their balance for a very long time.

Click to expand...

Could probably just hit up mouser or whatever and order some 4.1v Seiko IC's. Some of these use little SOT-23-5 packages that are pretty tiny but not hard to solder if you've done them a few times.

But are voltage and capacity at the same level at 4.1v for each and every cell as oppose to 4.2v as far as capacity. Is the volume of charge equal at lower voltage.

Punx0r said:

I have a random ali-expresses 18S BMS that surprised me by starting to balance at 4.1V.

My understanding is that good quality cells have now improved to the point where charging/resting voltage doesn't affect their life much. The main factor is time-at-temperature, whether that's from a high ambient, or internal heat from charging/discharging.

Click to expand...

I agree with this.

I think that a lot of lithium ion rules about charging are from older studies on older cells. From dealing with newer lipo, I found that they don't suffer or self-deteriorate fast at all.

What has really surprised me was a cell phone battery.,

I had a battery that was a couple of years old and had a reasonable amount of cycles on it. I expected it to have lost a lot of capacity. I bought a new battery and compared the capacity in both and there was almost no loss in capacity.

I also accidently overcharged a couple of 18650 cell to something like 4.3 volts, or about 500 MAH extra capacity. I have been checking the cell carefully for signs of capacity loss and it has not shown any difference in the year, still perfectly balanced with the rest of the cells over many cycles.

This makes me believe that even slightly over charging is not all that bad.

Offroader said:

I also accidently overcharged a couple of 18650 cell to something like 4.3 volts, or about 500 MAH extra capacity. I have been checking the cell carefully for signs of capacity loss and it has not shown any difference in the year, still perfectly balanced with the rest of the cells over many cycles.

Click to expand...

Is this how LiHV works? Some random cells in the batch can take a higher voltage without issue and so they report them as higher capacity/higher voltage.

On the other end of the scale, in large battery packs (such as electric cars) you have to design around the lowest common denominator. So charging to 4.1V etc. means you never stress out the weakest cells of the pack over the course of it's life. Which would in turn force the other cells to work harder.

If that is the case then you can either charge lower and ensure good battery life cycles, or go for full voltage/capacity and monitor your cells for weak links, until you prove empirically that you have a good pack.

999zip999 said:

But are voltage and capacity at the same level at 4.1v for each and every cell as oppose to 4.2v as far as capacity. Is the volume of charge equal at lower voltage.

Click to expand...

I would assume that as the rate of change of voltage on a discharge graph is further from vertical, they would be more likely to be at different capacities at this point. However, they will be similar throughout discharge, and it gives no indication as to how well they drop off at heavily discharged. It's still best to have a cutoff set to avoid any cell being able to be fully discharged at all. Either by BMS or LVC.


To get the thread back on topic, is anyone aware of customisable BMSs? It might be better to use a RC battery hobbycharger (that you could set to 4.1V/cell) to manage the balancing while charging, but I don't know if this would work with a BMS fitted.

In lieu of such a BMS being readily available I use a 3010b and only charge to 4.05v.

I will try again if all cells are at 4.1v. Ok. Even if all cells are at 4.1v they may not be balance as far as capacity. So you may be losing ah on the bottom (lvc) and losing ah on top (hvc).

That is a very interesting question.

I know that on a given MOQ, some supplier of BMS can program these the way you want for teh voltage range you want.. such as bestech when they indicate (adjsutable)

My choice for the adaptto is for MANY reasons including that fact that the adaptto BMS can be programmed at the desired voltage (balance volt, cut volt, critical volt.. etc)

what spinningmagnets mentionned is pure GOLD and everyone should know that. I spend over the years , hours repeating that to the people since i know lithium ion cells...

In fact my chevy volt charge the NMC cells to 4.05V max... that should be considered as a good exemple as teh Volt battery have SOLID reputations for durability and power

Just look at this vid where they put out 440hp at the wheel with these battery:


Tesla Motor in Lotus Evora makes 440whp on Dyno
https://www.youtube.com/watch?v=fKCMyHic2fU
[youtube]fKCMyHic2fU[/youtube]

Doc

Bestech make programmable BMSes and do single unit sales for reasonable prices. At least, that's what I read on this board. (I have not used them, but they were recommended to me in another thread)

http://www.bestechpower.com/communicationbms/

I have also seen some Aliexpress BMSes that let you choose 4.1v vs 4.2 - I suspect more to support older Li-Ion cells than to preserve LiPo's life. Again, I have not purchased any.

Basically, these days, I use BMSes as removeable cell balancers, rather than set and forget devices. I set my bulk charger to charge to 4.1v per cell, but since I only use about 20% of my capacity a day, most days, and about 80% once a month, I've never needed to balance. I take it out once a quarter to check, but 0.02v is the biggest variation I've had so far.

By the way, to those who have overcharged their packs and haven't suffered any capacity loss, capacity loss is not really the mark of LiPo degradation. Power loss is. I had a set of LiPos that were 3 years old and about 500-600 cycles and 85% of capacity. But where sag on full throttle was about 2v new, it was closer to 10v at that age. I could hit LVC from full by going full throttle uo a hill.

More telling regarding whether you damaged the packs by overcharge is whether DCIR went up after the overcharge.

Well worth the money to use a programable bms with display.
The two types I use work on any cell count up to 24s and voltage can be set from 1.5 to 5v.
Balance start voltage anywhere you want.
Bluetooth programming on one.
Under $300.
Use the same one on 2.3v, 3.2, or 3.7v chemistries.

That sounds very good, would you please tell us what the model numbers are?

https://endless-sphere.com/forums/viewtopic.php?f=31&t=85357

spinningmagnets said:

That sounds very good, would you please tell us what the model numbers are?

Click to expand...

BMS-24 and BMS-24T

I can say more in the for sale section. I liked these so much that I became the USA distributor.
Here is a screen shot of the bluetooth model. Mostly Chinese, no support, no defaults, for techies only.
In the process of installing in my Gem truck using 2016 Volt 44s module.
The new Volt has 630ma smd pico fuses on bms leads. The 1.2 amp balance current pops them.
I'm going to see if current can be adjusted with new fw.

What canbe the difference in charging 18650 cell at 4.0v on different cell groups ? Meaning I'm asking asking at what voltage do 18650 cells driff ? Which would be different in voltage and as in voltage range of lifepo4 as to lipo for is a flatter and hvoltage to understand capacity as it relates to voltage. But 18650 has sharper voltage drop to capacity in numbers. As this is part of balance Capacity.
Are at lower voltages your only concern and not capacity of volume of the cells

Satiator.
Charges my 24, 36, 48, and 52v batteries at 80 and 90%, with occasional 100% to balance. Even at the cost its cheaper than changing BMS. Or being a trial user for bestech.

A few are showing up, but not quite what we want.
http://www.greenbikekit.com/bms-pcm/smart-programmable-lithium-bms.html

spinningmagnets said:

Is it possible to adjust an existing BMS family to balance at 4.1V per P-group?

Click to expand...

The title question is different from the first question in your post. To the title question, do any BMS's balance at 4.1V? Yes of course and many have provided examples here. On our LiGo batteries the BMS balances whenever the cells are over 3.8V if there is a voltage discrepancy between them. Also, it does NOT balance when the pack is charging, (or discharging for that matter), it only balances when the battery is sitting idle. That way if there are differences in cell internal resistance (as can happen if there is a temperature gradient in the pack), you won't be balancing cells as a result of the varying cell terminal voltages under load. It will only balance based on the open circuit voltage.

To your first question, is it possible to "adjust" an existing BMS to balance at 4.1V. That of course depends very much on the circuitry and chipset used to make the BMS board. If it's made up of discrete fixed value BMS IC's (usually inexpensive 4s or 5s chips put in series for 10s-14s ebike voltages) then no, if they do bleeding at all it will be triggered by the cell being above a fixed reference voltage. You would have to replace the chip that is on them. But if it's a BMS that has a more advanced analog front end, like some of the BMS IC's from 02Micro and TI etc., then usually you have full control over the conditions when balancing occurs and if you have access to the BMS paramters or the firmware on the micro which is controller the BMS, then you should have no problem modifying it to balance at 4.1V or any voltage for that matter.

I have seen lots of credible data recently

Click to expand...

Just recently? This as common lithium battery knowledge goes back many years. However I would concur with what others have said here that the effects (especially of storage at higher voltage) seem to be overstated with current cells. It's like by the time the info suddenly gets mainstream just around the time that the technology has moved past that. There are people who've had 18650 cells in storage for a couple years all sitting at 4.2V/cell and don't see any adverse effect on a capacity discharge test. So this whole claim here

spinningmagnets said:

if you store it over the winter at 4.2V per cell its very bad

Click to expand...

May need to have its emphasis revisited. If only it didn't take years to perform these tests we might see more people doing at-home experiments.

Any way to end up with balance-charged pack all the time while always going to only 4.1V? (by any strategy you might think up?)

Click to expand...

Yes, buy a battery with a BMS that is smart about when and how it does balancing, and/or get a battery made with such good cell matching and consistency that it doesn't require any active balancing in the first place. Sometimes the only reason a battery goes out of balance is because of the BMS in the first place, and avoid BMS circuits that do that (unbalance cells) like the plague.

spinningmagnets said:

if you charge to a full pack voltage of 4.2V per 13S "48V" pack = 54.6V using a dumb non-balancing 54.6V charger...then some of the cells can arrive at 4.1V per cell, while others arrive at 4.3V per cell (due to variable internal resistances in manufacturing).

Click to expand...

This statement in brackets is incorrect. Varying cell internal resistance will not cause a pack to go out of balance, it's varying leakage currents that do that. If the only difference between the cells is that they have varying internal resistance, then the voltage's will spread a little bit while under full charge current but by the time the charger is at the CV portion they will all taper off to exactly 4.2V / cell.

A little out of the realm here, but, still within the thread.

I have a nearly new Leaf Battery that I am having a bit of a problem with very slow sales. Seems that people are convinced that a BMS of some sort is needed for these loose modules. I am thinking golf car installs. I like the idea of balancing while the cells are NOT being charged or discharged, as most people are in gated communities where my son works, so they are gone for months at a time.

He constantly has to scrape concrete floors and epoxy over the cleaned area from Lead batteries.

So, for someone who doesn't understand code but could probably install and occasionally check on clients golf cars, what is the recommended BMS for a 7 module, 52/53V leaf battery? I will get my son onto this thread, so he can digest what is being discussed.

Thanks for all the input. It should clear up some of the untrue information being spread around the E-revolution.

Thanks for all the responses, this has cleared up a lot for me.