Looking for a good BMS for 16 cell lifepo4

I am trying to find a good BMS, which is hard because most of them seems to be crap. I have been running one of my 16s lifepo4 packs bottom balanced without a BMS now for a while which works fine, except for charging termination. No matter the voltage set, one or more of the cells will start climbing in voltage and overcharge if I don't manually stop the charging in good time before the amperage drops to zero.

So, I am looking for a BMS with a overcharge protection voltage that is not too high, like 3.6v. It should balance at around 3.5v and most importantly, be able to balance/discharge more than one cell at a time. I could buy a programmable bms like the "tiny bms" but they are quite expensive.

Are there any good, yet moderately priced BMS's out there?

to be honest i have had much more life from battery useing an rc style charger and a diy lvc lots of bms are junk only time i would use one is if i had one of the awesome new bluetooth ones

So what kind of lifepo4 (brand or link ? ) and what you using it with. Plus what charger you using ? Scary to see a cell racing high. I bulk charge to 3.5v and get 3.48v to 3.56v and don't worry. Since the first triwst of the throttle will fixed that to 3 .39v. I just see any need for 3.6v but almost all bms go to 3.7v or so. That being said I like the signalab from Ping. It does go high 3.65 - 3.8v and bleeds down.

This one is a "no name" 20ah china pack. It is now 4 years old and still holds around 16 amps. I don't think the capacity ever was 20ah though. It is starting to have some voltage sag, but it still does the job on my commuting bike.

The BMS that came with the battery was terrible and discharged some of the cells 2-3 amps during winter storage. So I decided to get rid of the whole thing and add external balancing leads to be able to track cell voltage.

This works a treat except for having to babysit it while charging.

I am currently using a modified PSU for bulk charging which is adjustable both in current and voltage. I have tried turning down the voltage, but as it enters the CV phase and starts dropping the amps, most of the cells will drop a little in voltage while the weakest cells will continue to climb beyond 4V (because it is bottom balanced).

If I had a reliable way of automatically cutting the charging when the current got under a set value, that would fix my problem. But I don't know how to do that. I have my charger set at 6 amps, and when it drops below about 2 amps a couple of cells will start to climb rapidly. That's when I would like it to stop charging.

Those groups of cells are full as 14ah and the others have more capacity to fill at 16ah. Not place for voltage to go but up.
This is a guess, but my guess.

Best to give it a check up. Check all cells groups for voltage and write down and share. Like
1. 3.40v
2. 2.99v
3. 3.69 v


16. Xxx v
Plus charger voltage and battery voltage.

A bms isn't meant to balance a pack it's meant to keep a pack in balance. So before you try to put a BMS on your pack balance your pack then a BMS will help your pack keep in balance. If possible

As Zip said, the current V5.0 Signal Lab BMS that Ping sells does a pretty good job. Unlike the earlier versions (the one that came on your battery?) it powers the BMS from the full battery pack instead of just a few of the cells. However, if storing the battery for an extended period it is still best to either charge the battery on a regular basis or disconnect the BMS by simply unplugging the 16 sense wires, which is what Ping recommends, and the way he ships new batteries.

What I really like about the V5.0 BMS is that you always know when it is fully charged by glancing at the 16 LED's. After the charger is removed, the LED's bleed each of the 16 subs to the same balanced voltage.

It would be nice if the BMS had a little on/off switch for extended storage. I don't know what that would take, but I think Dnmun addressed it when he was active on the forum. There is probably a reference some place if you can find it. I just charge any battery that hasn't been used for a week or so and that way all of my batteries are always ready to go.

999zip999 said:

Those groups of cells are full as 14ah and the others have more capacity to fill at 16ah. Not place for voltage to go but up.
This is a guess, but my guess.

Click to expand...

999zip999 said:

A bms isn't meant to balance a pack it's meant to keep a pack in balance. So before you try to put a BMS on your pack balance your pack then a BMS will help your pack keep in balance. If possible

Click to expand...

I am fully aware of why the problem exists, and I also know how a BMS works. The pack is intentionally bottom balanced so that when it runs out of juice, all the cells will be empty at the same time. That means no need for a low voltage cut, and in theory no need for a battery murdering system. The problem comes at the top of charge when the weak cells will get full before the others do.

Ideally I would like it to stop charging when the weakest cell is full capacity, but that is hard to do without doing it manually. That's why i'm considering going back to a "regular" setup with a BMS. But it has to be a good BMS that doesn't overcharge or drain my cells. I will of course top balance my cells again before connecting a new BMS

Anyways, I think I am going to have a look at the Signal Lab BMS then Although I really like the simplicity of a plain battery with no added electronics except for a fuse.

The points you make seem good, except the idea of bottom balancing doesn't really buy you anything over top balancing. I.e., the available watt hours will be the same whether you start with the cells balanced at the top and stop when one cell reaches its minimum allowed voltage or start with the cells unbalanced and stop when all the cells reach their minimum allowed voltage at (theoretically) the same time.

Even though you may not need the individual cell protection a BMS provides at the bottom, you now have the problem you have described with over charging individual cells at the top.

I think when seemingly smart contributors call a BMS a Battery Murdering Device they are doing a real disservice to the community. If a basic BMS like the Ping V5.0 is used properly along with following correct long term storage suggestions you should get maximum cycles from a LiFeP04 battery. If a member has extensive rc usage and knowledge and decides he can do a better job than the BMS then that is his business and more power to him but the insinuation that using a BMS properly is the wrong way for folks like myself to maintain their batteries is wrong, IMHO. End of rant.