# Learn from my Mistake



## Lordwacky (Jan 28, 2009)

I thought I would post a recent experience I had related to the BMS/battery debate. I want to do this because I want an open dialogue with a real world experience.
I have not posted much about my build on the forum, so for reference of this discussion, I am using 48 SE 180Ahr (delivered late summer 2009) with an Elithion BMS, and manzanita PFC 30, in a MK1 MR2 with Zilla 1K HV. While my compents were purchased in the summer of 2009, my build did not start until late December 2009.
Due to issues that I don’t want to get into I was unable to finish my build prior to me having to attend graduate school overseas. This left my build is an state with the batteries arranged in a series configuration with the Elithion boards in place. Worried at the prospect of my cells having to sit for over a year with the BMS boards in place without being charged I arrange for a highly experienced EV’er to come to my build and prepare the batteries to be charges with the Manzanita and elthion. Unfortunately that arrangement fell through after I left the country and I was stuck. Forced to make a tough decision from half way around the world I asked my father to charge the batteries in series without Elithion control. I was relatively confident that this would work because I had setup the Manzanita before I left to only charge the pack to an average cell voltage of 3.3V/cell and all the cells were closely matched in internal impedance. My father would turn on the charger once a month or so to maintain the charge level of the cells.
I graduated last month and returned to my build, assuming the batteries had been maintained I immediately started working on the elithion to get it setup so all the battery banks were reporting. Once the banks were reporting I noticed the cell level voltages that were being reported from the elithion were far from what I had expected.
I had cell voltages ranging from 3.9V to 0.2V!!! I initially thought that this was an error with the Eltihion. I immediately tore into my pack and started testing with my DMM, I discovered that the Elithion was correct. After testing all my cells I found 1 dead cell cell (0.2V) most of the cells reading 3.6-3.9V and few in the 3.3-3.2 range. 
After trouble shooting the dead cell I discovered the the elithion board that was attached to the cell had been blown (likely due to reverse polarity contact during installation, Human Error ) and it had completely drained the cell dead. Since the cell was dead when the other cells were charged in series the other cells had higher voltages. luckily I don’t think any of the other cells were damaged due to overcharging, but I have not been able to thoroughly test them either. 
Think in this story there is support for both the non BMS argument and pro BMS argument. The argument against the BMS would be, placing the sensors across the cells provides a potential path for draining the cells should a board fail via human error or other cause. While I acknowledge the cause of the dead cell was likely human error in this cause, a failure mode for a BMS to drain cell is a poor design. The board should be designed to be able to tolerate a common installation error like polarity reversal, and the board should fail to an open circuit state, and never fail to a closed circuit state.
The Pro BMS argument is that this is proof that this Cell level monitoring and is critical. In this case a cell died which caused all the other cells to charge to a higher voltage, if I had configured to the level necessary to charge the pack to full more cells would have likely died to overcharging. People will argue that you can measure cell level voltage without a BMS, but I would argue in most cases this is an impractical solution and I severely doubt that the people are doing this every time they charge their packs and It just makes sense to have an automated system monitor this for you. 
This of course doesn’t touch on the balancing issue.
I hope others can learn from my mistake.


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## hbthink (Dec 21, 2010)

I have looked at Elithion data and cannot determine what their parts actually do, there is very little specific data from their website to actually understand the parameters of the devices other than from a very basic functional description. That said the boards appear very simple with only a small Microchip?? PIC device 12f602?? and a few discretes. Failing to short is not a good design and I would hesitate to place these on any cells I cared about. If someone has more information on what the system does or doesn't do or how its designed I would appreciate corrections made to my very simple observations.

Steve


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## NabilAhmad (Feb 26, 2011)

Lordwacky said:


> ... Worried at the prospect of my cells having to sit for over a year with the BMS boards in place without being charged...


Pardon my lack of personal experience - but considering the various comments I've been lurking over about BMS's and LiFePo4's, at 3% monthly discharge at rest, unless your pack was already nearly dead, there would be no need for maintenance during your 12 month absence, would there? From what I've seen, these cells are supposed to be either at full charge or 60% charge from factory (clarify any discrepancy). So you'd have a full year to almost three years of shelf life without any worry. Without a closed circuit, it shouldn't matter that any cell's terminals would or would not be connected to another. While it is more prone to accidental incidents as a complete battery rather than fully isolated cells (picture someone being somewhere they shouldn't be and touching things they shouldn't), there would be no parasitic drain on any given cell if your safety disconnect or maintenance disconnect is open.

I would have to say that your entire situation was architected by an overly worrying gadgeteer who can't trust his battery supplier. Including your probable human error, every part of your problem was directly related to the BMS's existence. I have read elsewhere that one BMS or another has resulted in a parasitic draw that killed cells in weeks of storage. Given that possibility, I would never chance it.

A much better use of the time you spent installing the system would have been to ensure that your cells were all charged to a level that would allow for a 3% per month discharge for your leave of absence without fully discharging.

Yes, I have drunk of the BMS free cool-aid, and this story makes me doubt that the other flavors will be as appealing. And no, I have not yet any personal LiFePo4 experience - just working from observation and reasoning, so any new enlightenment is welcomed.


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## Lordwacky (Jan 28, 2009)

NabilAhmad said:


> Pardon my lack of personal experience - but considering the various comments I've been lurking over about BMS's and LiFePo4's, at 3% monthly discharge at rest, unless your pack was already nearly dead, there would be no need for maintenance during your 12 month absence, would there?


Yeah ok. I understand your point. remember that at this point the batteries had been already sitting for ~ 6 months at my build site, not to mention however long in China, then I was looking at another year of them sitting. I had no idea what thier SOC was when they were delivered nor did I really know what thier self discharge rate was for sure. Also I made the poor choice to leave the pack configured in a series layout with the BMS boards in place. My worry was even in the boards had a very small draw. That small draw extrapolated over a year could have theoreticaly killed the cells. I made the decision to leave the cells in place because I had someone agree to come out get the Elithion configured and manzanita hooked up to charge the cells. I had over $11K invested in my pack, I was worried. 




NabilAhmad said:


> I would have to say that your entire situation was architected by an overly worrying gadgeteer who can't trust his battery supplier.


Yeah thats a fair comment, again I had over 11K invested, which is a highly significant amount of money for me, I was worried about my investment. Also everything I had read at the time suggested that the specs supplied by the chinese manufactors weren't nessisiarly reliable. As far as I knew people were not letting these cells just sit for a long period of time, so I didn't know what to expect.



NabilAhmad said:


> Including your probable human error, every part of your problem was directly related to the BMS's existence. I have read elsewhere that one BMS or another has resulted in a parasitic draw that killed cells in weeks of storage. Given that possibility, I would never chance it.


I disagree. The failed cell was definitly directly due the presence of the BMS. Human error blew the board and the damaged board drained the cell. You can argue that this was because of the BMS. I would argue that this was because of me, or one of the people working with me, made a mistake that resulted in the board failure. You argue that If there were no BMS the cell would not have failed. I can just as well argue that if the BMS were installed properly the cell would not have failed.

The main point I was trying to make was, when the cell failed, the lack of cell level monitoring nearly lead to another failure, because there was a significant risk of over charging the remaining cells. THere are many many ways to kill a cell, a malfunctioning BMS board is only one of those ways. Since there is a possibility for a cell fail whenever for multiple different reasons. if you don't have cell level monitoring to alert you to that failure. Other cells can be damaged due to discharging and/or charging in a series configureation. Monitoring the overal pack voltage simply isn't enough.




NabilAhmad said:


> A much better use of the time you spent installing the system would have been to ensure that your cells were all charged to a level that would allow for a 3% per month discharge for your leave of absence without fully discharging.


Agreed. If I had it to do all over again I would have removed all the batteries, wired them in parallel and charged them with a single cell charger every couple of months.

If I am ever the situation were my EV will not be used for a couple of months, that is what I will do 

I made some bad decisions, no doubt about it, but I want this thread to focus on the mechanics involved and not the poor decisions I made that got me into the situation.



NabilAhmad said:


> Yes, I have drunk of the BMS free cool-aid, and this story makes me doubt that the other flavors will be as appealing. And no, I have not yet any personal LiFePo4 experience - just working from observation and reasoning, so any new enlightenment is welcomed.


Your entitled to you opinion obviously, but I do not share it.

The most potent argument for the anti BMS crowd is the simpler the system the less likely it is fail. This is what I call the Kalashnikova arguement.

The Pro BMS argument is, the less you know about the system and health of each component of the that system the more likely you are to suffer failures.


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## Lordwacky (Jan 28, 2009)

hbthink said:


> I have looked at Elithion data and cannot determine what their parts actually do, there is very little specific data from their website to actually understand the parameters of the devices other than from a very basic functional description. That said the boards appear very simple with only a small Microchip?? PIC device 12f602?? and a few discretes. Failing to short is not a good design and I would hesitate to place these on any cells I cared about. If someone has more information on what the system does or doesn't do or how its designed I would appreciate corrections made to my very simple observations.
> 
> Steve


I would recommend that you go to www.Elithion.com or to http://liionbms.com/ to read up on the the system. http://liionbms.com/ has a good compare and contrast of the current BMS systems.

The Elithion is the most advanced BMS that I know of, it has a long list of capabilities that many other systems do not. Unfortunately, the blown board failure mode is a major flaw in my opinion and I have to say I am not impressed with the build quality of the product.


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## NabilAhmad (Feb 26, 2011)

Lordwacky said:


> The main point I was trying to make was, when the cell failed, the lack of cell level monitoring nearly lead to another failure, because there was a significant risk of over charging the remaining cells. THere are many many ways to kill a cell, a malfunctioning BMS board is only one of those ways. Since there is a possibility for a cell fail whenever for multiple different reasons. if you don't have cell level monitoring to alert you to that failure. Other cells can be damaged due to discharging and/or charging in a series configureation. Monitoring the overal pack voltage simply isn't enough.


To my understanding, there are three ways to for a cell to die. Manufacturing error, abuse/accidental damage, and neglect. My disagreement with your final statement there is that without abuse or neglect, you are left with a cell that was bad at birth in the factory - this is something that no level of management or monitoring can fix. I suspect that with careful and detailed initial observation, one could find the bad apple of the bunch and swap it out. This would leave abuse and neglect. If you can trust the quality of your cells, then an overall pack voltage and a sub-pack comparison will alert you with just as much useful information that the most elaborate system will give you - you have a bad cell in your pack or you don't. The resolution of the information given doesn't change the situation. And a per-cell device has too many additional possible failure vectors for me to see a real value. 



Lordwacky said:


> I made some bad decisions, no doubt about it, but I want this thread to focus on the mechanics involved and not the poor decisions I made that got me into the situation.


I don't mean to distract the purpose you wish this thread to serve either. However, I am of the belief that circumstances can be averted if properly anticipated. You made it clear that you could not fully anticipate your circumstances. I'm not arguing that you could, what I am arguing is that the BMS's inherent complexity got in your way of doing a simple storage preparation that you seemed to have at least some time to have done - that is giving the pack a moderate charge and letting it sit without any parasitic loads possible.



Lordwacky said:


> Your entitled to you opinion obviously, but I do not share it.
> 
> The most potent argument for the anti BMS crowd is the simpler the system the less likely it is fail. This is what I call the Kalashnikova arguement.
> 
> The Pro BMS argument is, the less you know about the system and health of each component of the that system the more likely you are to suffer failures.


I don't believe these two camps of thought you are outlined are exclusive at all - i want both! I agree that generally more information is better than less information, but there is such a thing as going past a point of diminishing returns. That's not to say that the information that the BMS's generate is at all invaluable. Trends are far more insightful than samples.

The real question is wether or not these systems give tangible benefit that has a greater value than the risks of failure introduced through the additional complication. If you have a per-cell probe, that more than doubles the number of possible points of failure. Given any failure rate you wish to assume, you have now doubled it. Also consider the incalculable new possible incidents that can occur - such as the accident that killed your BMS module which in turn killed your cell. 

To top it all off, you are now trusting a more complicated system to be even more error free than the battery pack that you are monitoring for defects in. I find it hard to logically assume that a more complicated system is less likely to have any defects. If there is a false positive in the BMS, then who is at fault? The point of having a more active and meticulous and automated BMS is to not need to worry your heart out. If you aren't worrying, you are less likely to manually verify that all is ok - a manual verification that would lead to a discovery of not only a bad cell but a bad BMS module. Which brings up a question I should have asked earlier: How did you discover that the BMS module was bad? did the system tell you, or was it a manual discovery?

So again I say that no, I mean not to pick apart your situation and wag a finger. I truly value your honest contribution to the continuing debate. I argue that the risk/reward value of a BMS does not escape a series of assumptions. And ironically, the central assumption that the per-cell BMS is needed for is quite simple to test for in much less complicated ways. 

I'd love to have the level of information that a good BMS should give, but without the addition of any possible failure points - and make it double check itself too! And in the name of Lordwacky, make it fail open so that it can't kill a cell!


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## peggus (Feb 18, 2008)

Thanks for sharing your experience, the outcome could have been a lot worse than a murdered cell.

For future reference, when it comes to lithium batteries and storage, just charge them once, remove all loads including BMS, and they'll be good for years of storage.

And when in doubt, ask lots of questions.


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## ElectriCar (Jun 15, 2008)

Lordwacky said:


> ...The Elithion is the most advanced BMS that I know of, it has a long list of capabilities that many other systems do not. Unfortunately, the blown board failure mode is a major flaw in my opinion and I have to say I am not impressed with the build quality of the product.


So even though this is in your opinion the best BMS out there and through it's poor design of not being reverse polarity protected (fixable with a 39cent diode possibly) it destroyed one of your cells yet you still recommend using one. With what I've learned I just can't agree with that. After you see what I'm doing you may change your opinion but if not, that's perfectly understandable. Anyway I've read and debated the merits of BMS use and I'm in the court of BMS free operation. Here's why.

The vast majority of cell failures I've read about happened due to over charging or over discharging. I've only heard of one dying for no reason but MANY due to known reasons. Knowing the causes of failures allows you to work around them. For instance I've installed a maximum voltage relay to pull the plug on my charger should it fail to stop charging at the set voltage. 

I'm also installing a Hart Battery Bridge which will indicate instantly if I lose a cell. While driving it will show other issues developing ie a cell developing a high resistance. 

As far as over discharging, I'm monitoring the charge and discharge Ah, with two separate counters. I'm having a "Low Battery" led illuminate at about 20% SOC while the factory fuel gauge will display battery capacity just as it did with gasoline. At 20% I will set the fuel gauge to just above E so when it hits E I'll still have a little capacity. This will just take a little discipline, no more than driving a petrol fueled vehicle. Likewise if you push it you will walk and I never run out of gas.

On charging, I'm under charging a little as you did which will lengthen their life a little and prevent single cells from reaching the upper knee on the charge curve. Haven't decided on a voltage yet but it's likely to be about 3.4 based on others experience but I will monitor and evaluate then adjust accordingly.

I will have spent more money than some BMS systems but I'll only have 1 wire connected within the pack. Nothing will be "connected" across any individual cells so there's no way possible to drain and thus destroy any cells. 

I may eventually have the monitors shut down a contactor, killing the vehicle if someone insists on driving below 10% SOC setpoint. A BMS can't do that AFAIK. All they can do is shut down at a certain terminal voltage, which is not really useful and will trigger shutdowns or activate limp mode unnecessarily. Terminal voltage is NOT indicative of SOC when under load, ie driving. Heavy acceleration will cause the voltage to drop much more than SOC then recover when you let off the gas pedal. A counter doesn't care or monitor the voltage, only the Ah. That is actually more accurate than a fuel gauge in a normal vehicle and we all depend on that successfully everyday. 

If you can see that I'm not covering some failure types let me know. I just feel my way is inherently safer and more reliable than a BMS as it is minimally intrusive BUT it requires a bit of maintenance as all vehicles do. I'll have to monitor the cell voltages over time to see how much they change due to slight temp and IR variations. Some claim to have driven thousands of miles without a BMS yet their batteries remain closely balanced. I'll see how mine do.


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## dtbaker (Jan 5, 2008)

ElectriCar said:


> .... Some claim to have driven thousands of miles without a BMS yet their batteries remain closely balanced. I'll see how mine do.



me too. 

I sorta figure that the fewer connections and fewer components, the less that can go wrong! I'll check in a month, then 2 then 4 then 6 if all continues to go well....


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## Lordwacky (Jan 28, 2009)

ElectriCar said:


> So even though this is in your opinion the best BMS out there and through it's poor design of not being reverse polarity protected (fixable with a 39cent diode possibly) it destroyed one of your cells yet you still recommend using one. With what I've learned I just can't agree with that.[/


I'm sorry if you are confused my statement with a recommendation for the Elithion. This is what I said:



Lordwacky said:


> I would recommend that you go to www.Elithion.com or to http://liionbms.com/ to read up on the the system.
> 
> The Elithion is the most advanced BMS that I know of, it has a long list of capabilities that many other systems do not. Unfortunately, the blown board failure mode is a major flaw in my opinion and I have to say I am not impressed with the build quality of the product.


At no point in that statement did I recommend purchasing or using an Elithion BMS. The Original post asked about getting more information about the Elithion and I recommended going to the relevent websites. I did not recommend actualy using the BMS.

Also just because I said the Elithion is the most advanced BMS that I know of, DOES NOT mean I would recommend it. In fact I WOULD NOT recommend using the Elithion for multiple reasons:

1) the blown board failure mode, too easy of a mistake to make during installation 
2) the build quality is poor for the price paid
3) the price I paid is far too high in my opinion, it cost me ~ $46-50/ cell when I purchased the system
4) the developer of the system seems to operate under the assumption that anyone using his system is an idiot, and seems to think that all other EV components should have been designed to interface directly with his system regardless of whether they were developed before he developed his system.
5) The developer of the system seems to have little interest in the supporting customers that purchased his hardware through a 3rd party. He charges for tech support and for software upgrades. This punishes the early adopter.

For these reasons and more I DO NOT RECOMMEND the Elithion. There are other, cheaper BMS options out there that do not have these flaws.

at the time I purchased my components, I had two choices, Elithion and VoltBlochers.... I read the specs and promises of the Elithion and I was impressed and purchased it. The product I got has not lived up to my expectations and if I could return it for a refund I would, but I can't, and I don't want to spend the money on another system so, I'm kinda stuck.




ElectriCar said:


> After you see what I'm doing you may change your opinion but if not, that's perfectly understandable. Anyway I've read and debated the merits of BMS use and I'm in the court of BMS free operation.


The System that you have built to Manage your Battery pack seems to be well thought out. I would argue that you yourself have built a basic BMS.

While I now have a Master's degree in a Electrchemical related feild (I didn't when this happend), I do not consider myself expert enough in these specific systems to be able to anticipate every possible way a battery may fail in EV use. I maintain there is a possibility that a battery may fail and the user may not know about it. That battery failure may lead to futher failures if not caught immediately. While I acknowledge that sudden cell failure is unlikely, it is possible, and having a system that can identify that behavior is critical in my opinion. You obviously share this opinion because you built this capability into your pack as well.


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## ElectriCar (Jun 15, 2008)

Ok sorry for the misunderstanding. Here's a link to the Hart device in case you're not familiar with it. http://www.evdl.org/pages/battbridge.html
I'm yet to use it but I think it will turn out to be very helpful. I have to build it as I am still working on my lithium upgrade.


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## EVfun (Mar 14, 2010)

I'd like to see some version of the Lee Hart battery bridge using a comparator chip (used as a window comparator) to drive the LED of an optical isolator. The comparator may need to drive a small MOSFET that in turn drives the isolator to keep current requirements on the power and ground minimal, as I don't know of any 200 volt comparators. The idea of going this route would be to have extremely high impedance on the center tap under any and all conditions. After all, rule *1* of no shunting regulators is don't go unbalancing the pack at all. Just 1 milliamp of current difference between the upper and lower half would result in an annual imbalance of nearly 9 amp hours per year.


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## rfhendrix (Jan 24, 2011)

ElectriCar said:


> Ok sorry for the misunderstanding. Here's a link to the Hart device in case you're not familiar with it. http://www.evdl.org/pages/battbridge.html
> I'm yet to use it but I think it will turn out to be very helpful. I have to build it as I am still working on my lithium upgrade.


Thanks for the link! Simpler is often better. Some say that the devil is in the details, so why have so many details? I am presently leaning toward a setup similar to yours. Thanks for your information.


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## GizmoEV (Nov 28, 2009)

ElectriCar said:


> Ok sorry for the misunderstanding. Here's a link to the Hart device in case you're not familiar with it. http://www.evdl.org/pages/battbridge.html
> I'm yet to use it but I think it will turn out to be very helpful. I have to build it as I am still working on my lithium upgrade.



There is a thread for this with a couple of other circuits Lee Heart sent me. I wanted a meter to show a wider range of things than a single LED on each side of balanced. When built properly the only time the current will be different on each side of the pack is when there is a cell out of range.

http://www.diyelectriccar.com/forums/showthread.php/battery-balance-monitoring-system-54845.html

BTW, Lordwacky, thank you for sharing your experience.


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## tomofreno (Mar 3, 2009)

> I may eventually have the monitors shut down a contactor, killing the vehicle if someone insists on driving below 10% SOC setpoint. A BMS can't do that AFAIK. All they can do is shut down at a certain terminal voltage, which is not really useful and will trigger shutdowns or activate limp mode unnecessarily.


 They typically trigger a small relay when any cell goes below the defined LVC voltage (2.5V for minibms I think, with user adjustable delay). You can use this with a resistive divider to pull the throttle about as low as you like, or it could drive a larger relay to operate a contactor like you have in mind. I think you will do fine with your system since you understand it and will be careful. But I think you are living a bit dangerously at 10 to 20% SOC. The discharge curve is very steep there. Not many Ah left.


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## ElectriCar (Jun 15, 2008)

Yea Tom I have the LED installed for low battery now. The Zeva Plus will drive it and the setpoint is adjustable. Since it is a counter of actual AH I figured 20% would be a good caution point. You know when that low fuel light comes on it gets your attention. It does for me at least.


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