The BMS, good or bad?

[Tench]

How many times have we had people post on here that their over the counter battery or turn key bike wont function because they left it alone for a short period. Or the battery voltage is too low, Or the mileage from a charge is not what it used to be. There seems to be a massive lack of info given to people who buy these bikes so they then unknowingly kill the battery through not being made aware of how the system works. They are lead to believe it is plug and play, along way from the reality!
These are the people who need a BMS yet it would appear the only people who actually benefit are the ones who have some knowledge, use them correctly and keep an eye on things. The BMS for everyday folk is a pack killer, probably responsible for doing a lot more harm than good.

Can the manufacturers do anything about this, Surely the BMS should be switched so storage does not create a problem, or goes into a sleep mode.
Charging procedure also seems to be unclear, taking a pack off the charger as soon as the green light shows itself is often not sufficient for the good of the pack.

It just seems to me that the people who most need a BMS system are the ones who would actually be better off without one! With charger HVC and controller LVC being more reliable than the BMS for most people.

A solution I can think of would be to mount the BMS inside the charger, the charge lead connecting to the bike would have more wires in it. the pack would be charged exactly the same. The power limiting function the battery mounted BMS's perform could be handled by the controller, most controllers can do this already. So just what is the benefit if any of having a pack mounted BMS?

Cell level LVC, the controller can only monitor whole pack voltage as far as LVC is concerned. So lets say a BMS is in the charger, it works! the pack is happy and balanced ish, the controller lvc is set to a safe limit to keep even the lowest cell away from danger land. What else is needed?

I think the answer is the charger, if the integral BMS/charger, lets call it a Balance charger! had the intelligence of a cell log, hardly an expensive addition, then it could display the min and max cell voltages when the charger was connected, so the very first time you come to charge a pack after any 1 cell has started to under perform or failed the charger would alert you. And lets face it, there is no need to be alerted any sooner, a cell going low for the first time is about as soon as it gets!!

Now this to me seems far better than a bms, often by the time a BMS tells you something is wrong part of the pack has cancer which has often spread beyond the originally affected cell.

So it would seem to me to be in the industries interest to rethink the whole BMS situation as those who have been let down by the BMS, often in a very costly way, are mostly dipping their first toe into the EV world. It is not a very good start, many may never touch an EV again!! Once Bitten!!
The completely under thought primitive systems currently employed to safe guard the cells is doing more damage than good to not only the cells themselves but also the growth of the EV industry.

Rant Over,, fire away!

 

[cal3thousand]

Agreed.

I also see that BMS in their current configuration are made to be cheap. They don't include a DC-DC step down so that the BMS can draw from the whole pack, instead drawing from a subgroup of cells. That's the major problem of the "BMS for the masses", as it kills cells within a pack.

 

[dnmun]

all bullshit. they do not consume much power at all. even the ping which is the watt hog doesn't drain the first four cells down until it sits for months and months.

if you don't understand how a BMS works or have never worked on one or analyzed how they work you should not make pronouncements about them which are wrong and mislead others into believing you know what you are talking about.

 

[amberwolf]

I think that the major thing that would help is clear instructions with each pack that explain it's usage and storage requirements in n00b terms.

That alone would prevent more problems than anything else.

I don't really think that BMSs kill many packs at all. I suppose if someone doesn't know how anything works, and drains the pack to LVC then sticks the bike in a closet for a long time unused, without first recharging it, then a BMS might drain a cell or cells down below safe recharging levels.



I suppose some things like that could be improved by a "smart" BMS that would
A) run off the pack as a whole instead of a few cells (as some still do) and
B) completely cut off it's power usage once a cell drops below some certain point and
C) is powered by the incoming charger voltage after that point, so that it will still recharge normally.

Also, better QC (in some cases, ANY QC!) on the cells, pack construction, and BMS manufacture would help.


I don't think most of the problems are actually caused by the BMS itself, but by people not understanding how things work and why they stop working--most of them can be explained very simply well enough to get people to understand, and thus help their expectations meet reality, and their usage meet ability of their pack to do what they want.

The next most major problem is the QC of the various parts, which if they were actually done right in the first place would probably work better / last longer by a lot, compared to now, for hte average product out there.

After that, design changes like those listed above, in how the BMS actually works, would probably do most of the rest.


But some people expect miracles of operation with zero maintenance or understanding on their part, and not even a really simple set of tools like hammer and nail work like that. :lol:


(I've known a number of poeple that didn't even know they had to change the oil in their cars, or add water to the radiator or battery, or that it even HAD a battery, etc. And I've known a couple of poeple that ran out of gas on their first car and didn't knwo why it suddenly stalled out on a hill, until someone else asked them when they last put gas in it--they didn't even think to check that, cuz it ran fine on the flat, but didn't when the gas all sloshed to the back when on the hill).

 

[Tench]

all bullshit. they do not consume much power at all. even the ping which is the watt hog doesn't drain the first four cells down until it sits for months and months.

if you don't understand how a BMS works or have never worked on one or analyzed how they work you should not make pronouncements about them which are wrong and mislead others into believing you know what you are talking about.

If you lived in the uk or other parts of the world where many people don't ride for months and months over winter then find their bike is dead come the spring you would understand. An isolated battery would be fine over this period.

Your reaction was expected.

 

[Tench]

I don't think most of the problems are actually caused by the BMS itself, but by people not understanding how things work and why they stop working--most of them can be explained very simply well enough to get people to understand, and thus help their expectations meet reality, and their usage meet ability of their pack to do what they want.

Exactly my point, these things are made for the masses yet are not Noob friendly.

People know their car has a battery, it is fitted under the bonnet and may require them to think about it once every 5 years, this is their expectation of an ebike battery. And this needs to become the reality.

The present system requires maintainence knowledge yet is aimed at the first time user.

 

[Tench]

I suppose some things like that could be improved by a "smart" BMS that would
A) run off the pack as a whole instead of a few cells (as some still do) and
B) completely cut off it's power usage once a cell drops below some certain point and
C) is powered by the incoming charger voltage after that point, so that it will still recharge normally.

Also, better QC (in some cases, ANY QC!) on the cells, pack construction, and BMS manufacture would help.


I don't think most of the problems are actually caused by the BMS itself, but by people not understanding how things work and why they stop working--most of them can be explained very simply well enough to get people to understand, and thus help their expectations meet reality, and their usage meet ability of their pack to do what they want.

The next most major problem is the QC of the various parts, which if they were actually done right in the first place would probably work better / last longer by a lot, compared to now, for hte average product out there.

After that, design changes like those listed above, in how the BMS actually works, would probably do most of the rest.


But some people expect miracles of operation with zero maintenance or understanding on their part, and not even a really simple set of tools like hammer and nail work like that. :lol:

Amberwolf, your "B" idea above is really good and would save a lot of the cells that are drained to 0v, if once a cell is noticed to be at or just dropped below lvc then the bms shuts it self and the pack down completely, re-awakened by the charger next time it is plugged in. That is a great idea!

Modern day standards have taught people to expect maintenance free as the norm.

 

[cal3thousand]

There are many solutions on this forum to mitigate all these various issues, but still no single acceptable solution to be considered as the 'best practice'.

Will it take someone on this board to create?

 

[dnmun]

can anyone honestly say they have had this problem or is this just made up stuff? the ping signalab with the opto transistors is the only one i have ever known to drain the source current cells down. otherwise this is just bullshit about how they use too much power. 20uA is not too much power.

and mr smarty pants twench, you can act like you are better than me because you can insult me for free here but there is not any evidence this is a problem other than just specualtion.

 

[Tench]

can anyone honestly say they have had this problem or is this just made up stuff? the ping signalab with the opto transistors is the only one i have ever known to drain the source current cells down. otherwise this is just bullshit about how they use too much power. 20uA is not too much power.

and mr smarty pants twench, you can act like you are better than me because you can insult me for free here but there is not any evidence this is a problem other than just specualtion.

I have had this problem. I have owned 3 batteries all bought with inbuilt BMS from different sources, all of them needed opening up for maintenance within the first year. That's 100% of the batteries with BMS that I have owned. The few packs I have built from Hk lipo with no bms fitted have been no trouble what so ever.

Dimnun, typos seem to be your thing, I think you should use your immense understanding of these systems in a positive way, for the benefit of EV's. I don't have your electronic knowledge, I do know the currently available systems are far from ideal, when it comes to fit and forget, the BMS as we know it is not good enough.

 

[AussieJester]

Have read many posts over the years about BMS causing issues, they weren't given the name Battery Murdering System for nothing... Personally, I monitor my pack myself when charging, the occasional balance with the Hyperion my cells have remained nearly perfectly balanced for the time I have had then (~12months)

KiM

 

[999zip999]

Everyone wants a 800usd. Battery for 350usd. You cheap sakes.

 

[oatnet]

A solution I can think of would be to mount the BMS inside the charger, the charge lead connecting to the bike would have more wires in it. the pack would be charged exactly the same. The power limiting function the battery mounted BMS's perform could be handled by the controller, most controllers can do this already. So just what is the benefit if any of having a pack mounted BMS?

I am with you Tench. After many BMS issues in 2007, I swore off them. The money I have saved on BMS far outweighs the cost of cells I have trashed being stupid, so skipping the BMS is a net cost savings. What you describe is, effectively, single cell charging/SSC. I do that with banks of voltphreaks wall-wart chargers or banks of Dc-Dc converters, each cell gets its own charger putting out 3.65v. The "Flintstone chargers" from 2007 were a box with (12) chargers bult onto 2 motherboards, and 13 wires going to a connector on the pack. There are a few monster threads here on the topic.

Some people SSC their packs every day, I bulk charge daily with higher amps, and periodically balance charge with SSC.

-JD

 

[999zip999]

Oatnet where a good place for voltpheaks lifepo4 3.65v isolated single cell chargers. Couldn't find them. Plus a 4.2v model ?
Hope everthing is fine I can see the smoke from up here. Best wishes.

 

[John in CR]

I'm a better BMS than any cheap BMS, and I'd much rather buy more battery than invest in a quality BMS. It works because I don't deep discharge. For those who insist on using their full pack capacity or can't remember to recharge, then a BMS is a must. If building an ebike for someone else a BMS is a must, because they don't listen even to very explicit and repeated instructions about battery care.

 

[999zip999]

JohnCR has been known to have a special right battety hand can detect battery heat, voltage and I.R.
Don't know what his left hand does.

 

[999zip999]

Don't run a bms, but have 17ah. I would run a bms on a 12ah pack or a friend.