# another reason why cell level monitoring is a good thing to have



## Lordwacky (Jan 28, 2009)

Hello all,

I got my Elithion BMS setup the other day and ran my car around the block a couple of times while montoring the battery performance on my laptop. I immediately saw on the read out the one my cells was reporting significantly higher voltage sag and higher impedance then the rest of the cells in the pack.

I then started to charge my pack and saw that the same cell was reporting a significantly higher voltage and higher impedance then the rest of the cells.

The Elithion told me which cell it was so there was no hunting, I knew exactly which battery box to remove and which cell in the box was being funky.

I took the bus bar off the cell and saw that some of the Locktite that I use on the battery bolt had oozed out got between the bus bar and battery terminal causing high contact impedance.

Without the BMS I would have had a hard time even knowing about this issue. 

This is exactly why I purchased my BMS. 
My question is, how do the anti BMS people find these issues in thier packs before they cause damage? 

Disclaimer: This post should not be considered as an endorsment of the Elithion BMS system. It should be considered ,however, an endorsment for cell level monitoring.


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## madderscience (Jun 28, 2008)

I just had a very similar experience. I've "only" got flooded lead acid and I have a homebuilt monitoring system that watches each 6V battery. My batteries are only about a year old, and after getting the 2nd generation of my system installed which is a substantial improvement over the 1st generation, I immediately noticed that battery number 15 (out of 21) was substantially lower under load than the others. 

This was very annoying since the batteries are barely a year old and should still be in their prime. However, after thinking about it for a while I realized that due to the way I hooked up my monitoring devices there are sections of battery cable in the circuit so excessive resistance on the cables would cause a low reading under load. This seemed very plausible since I was seeing voltage sag on that battery when the car was hot off the charger, not the same way weak batteries behave.

Sure enough, one of the cables on the "bad" battery was moderately warm while all the others were cool to the touch. I caught it before any damage was done. It is an easy fix, and I didn't have to do anything to know something was wrong other than glance at the bargraph display.


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## JRP3 (Mar 7, 2008)

When first testing my car I checked the temperature of each terminal after a run. I also put a Celllog 8 on the cells to graph how they performed. After testing I removed it. I also didn't use loctite.


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## frodus (Apr 12, 2008)

Yeah. People can argue about balancing all they want. I could care less because we've got ways to charge cells out of balance. The big thing is Monitoring, and protecting the pack (HVC and LVC and overtemp). 

We put together a pack fresh off the boat, and there were a few cells out of balance, but we knew which ones so we charged them up a bit before we started the elithion balance (otherwise it would've taken a LONG time). It worked great.

The thing I like about this one, in particular, is that I can log through the serial port on a tablet or something. I've got a little 800mhz 10" tablet PC (old) that'll work just fine for logging as I'm getting up to speed and debugging my pack.


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## Lordwacky (Jan 28, 2009)

JRP3 said:


> When first testing my car I checked the temperature of each terminal after a run. I also put a Celllog 8 on the cells to graph how they performed.


All my battery banks are enclosed in boxes, two of of which are virtualy impossible to access when the car is assembled. Manual monitoring of each battery would be extremely impratical in my case.



JRP3 said:


> After testing I removed it. I also didn't use loctite.


So how do you detect if one of your battery connections come lose over time? 

And if I were to do this a again, I would put a drop or two of locktite directly into the battery terminal then place bolt in as opposed to putting the locktite on the bolt and then installing it into the terminal.


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## EVfun (Mar 14, 2010)

I have never used Locktite on battery bolts. I always use split lock washers.


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## JRP3 (Mar 7, 2008)

Lordwacky said:


> All my battery banks are enclosed in boxes, two of of which are virtualy impossible to access when the car is assembled. Manual monitoring of each battery would be extremely impratical in my case.


Mine are in open racks, and accessible. In your situation I might run some wires to a convenient location to check cells.



> So how do you detect if one of your battery connections come lose over time?


I check them periodically, haven't found a loose terminal yet. I used NO OX ID on the threads, which prevents galling and allows proper torquing, and used lock washers. 
I can see the benefits of monitoring individual cells, I just haven't found it to be necessary in my situation.


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## ElectriCar (Jun 15, 2008)

Lordwacky said:


> ...one my cells was reporting significantly higher voltage sag and higher impedance then the rest of the cells in the pack.
> 
> I then started to charge my pack and saw that the same cell was reporting a significantly higher voltage and higher impedance then the rest of the cells.
> 
> *My question is, how do the anti BMS people find these issues in thier packs before they cause damage?*


I use the volt meter version in this thread which I posted notes about it and photos. If you get a high resistance connection, the voltage across that connection will increase with an increase in current. Also if you lose a cell you'll see that as well.


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## peggus (Feb 18, 2008)

When I want to know what is going on with my pack I fire up my laptop and connect to the car over bluetooth, and there's the cell voltages, current and temperatures in all their gory detail.

Some day I'll configure my linux server to automatically record each charge session when the car is in range. That would however require digging around in the server and I haven't touched it in 5 years, the darn thing is too reliable.


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## DIYguy (Sep 18, 2008)

peggus said:


> When I want to know what is going on with my pack I fire up my laptop and connect to the car over bluetooth, and there's the cell voltages, current and temperatures in all their gory detail.
> 
> Some day I'll configure my linux server to automatically record each charge session when the car is in range. That would however require digging around in the server and I haven't touched it in 5 years, the darn thing is too reliable.


OK, now I'm envious...


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## ElectriCar (Jun 15, 2008)

peggus said:


> When I want to know what is going on with my pack I fire up my laptop and connect to the car over bluetooth, and there's the cell voltages, current and temperatures in all their gory detail.
> 
> Some day I'll configure my linux server to automatically record each charge session when the car is in range. That would however require digging around in the server and I haven't touched it in 5 years, the darn thing is too reliable.


Now that's just sick!


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## frodus (Apr 12, 2008)

Sweet deal Peggus! Would like to hear more about it.

Do you have a program that runs to read that, or do you just log via the serial stream?

I've got a WiPort from Lantronix I plan on using for the time being before we move to a can-> bluetooth setup for the Curtis AC and Elithion system.


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## jhuebner (Apr 30, 2010)

Heres my experience: Bought 56 Sinopoly 60Ah cells in march to replies the AGMs in my Ligier.
Since I had not decided on which BMS to use, I decided to do the first tests without it.
I installed all the cells, fired up the charger (CC/[email protected]) and checked the cells every now and then with a DMM. When most cells had reached 3.39V I stopped charging.
Due to a lack of material not all cells were bundled in packs. The next day I noticed that one cell had swollen considerably. It must have seen over voltage between my DMM measuring cycles. I disconnected it. 55 cells to go. During the next couple of days I noticed that one cell was around 0.1V ahead of all others when charging and would reach the knee surprisingly fast. I resorted to charging the pack until that one cell had reached 3.9V.
After a couple of cycles the controllers under-voltage protection virtually stopped the car. I discovered all cells depleted to 2.5V except the one mentioned earlier. I disconnected it. 54 cells to go.

Meanwhile I have installed my homebrew BMS so I will not loose any more cells to over voltage.

I know I could have taken more precautions. But then the cells are mounted underneath the passenger and driver seat. No good place to reach with the DMM.

So
a) Lithium cells are extremely sensitive to over(dis)charging compared to lead (no shit...)
b) Cells don't ship equally charged
c) not monitoring seems risky


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## Ziggythewiz (May 16, 2010)

jhuebner said:


> I know I could have taken more precautions. But then the cells are mounted underneath the passenger and driver seat. No good place to reach with the DMM.


Did you do any balancing prior to installation?


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## DIYguy (Sep 18, 2008)

jhuebner said:


> Heres my experience: Bought 56 Sinopoly 60Ah cells in march to replies the AGMs in my Ligier.
> Since I had not decided on which BMS to use, I decided to do the first tests without it.
> I installed all the cells, fired up the charger (CC/[email protected]) and checked the cells every now and then with a DMM. When most cells had reached 3.39V I stopped charging.
> Due to a lack of material not all cells were bundled in packs. The next day I noticed that one cell had swollen considerably. It must have seen over voltage between my DMM measuring cycles. I disconnected it. 55 cells to go. During the next couple of days I noticed that one cell was around 0.1V ahead of all others when charging and would reach the knee surprisingly fast. I resorted to charging the pack until that one cell had reached 3.9V.
> ...


First thing that comes to mind is an old saying.... "stupid is as stupid does". Sorry man. . . but c'mon....


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## JRP3 (Mar 7, 2008)

Yeah, this seems like the "hope and pray" method. To run without a BMS you need to know the relative capacity of your cells, you have to bottom or top balance them first, and you have to stick within the parameters of your pack. None of that seemed to happen in this case.


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## tomofreno (Mar 3, 2009)

jhuebner said:


> Heres my experience: Bought 56 Sinopoly 60Ah cells in march to replies the AGMs in my Ligier.
> Since I had not decided on which BMS to use, I decided to do the first tests without it.
> I installed all the cells, fired up the charger (CC/[email protected]) and checked the cells every now and then with a DMM. When most cells had reached 3.39V I stopped charging.
> Due to a lack of material not all cells were bundled in packs. The next day I noticed that one cell had swollen considerably. It must have seen over voltage between my DMM measuring cycles. I disconnected it. 55 cells to go. During the next couple of days I noticed that one cell was around 0.1V ahead of all others when charging and would reach the knee surprisingly fast. I resorted to charging the pack until that one cell had reached 3.9V.
> ...


 Sorry to hear it. Yes, you should have top or bottom balanced them first as others said, but probably thought you could get away without it and without a bms for a short while if you just used a small amount of their capacity. Seems reasonable, unless one or more are too different in SOC as in your case, and you don't know exactly where they all are in SOC. You should still top balance them, as the bms won't be able to do it if they differ by a few Ah in SOC since the shunt current is so low (assuming you have a typical shunting bms). When you first start using LiFePO4 cells, you really don't appreciate just how fast they go from showing almost no change in voltage with charge or discharge, to changing very quickly near the ends. Thanks for sharing the information. Good lesson for others.


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## jhuebner (Apr 30, 2010)

DIYguy said:


> First thing that comes to mind is an old saying.... "stupid is as stupid does". Sorry man. . . but c'mon....


Hey, take it easy. If you want people to share their stupid mistakes, don't bash on them when they do. I've learned my 120€ (at least) lesson and I'm not blaming anyone but myself.

No I did not do any balancing prior to the first charge because I was too impatient to get on the road.

I own another pack for the R4 which is top-balanced with a lab supply.



> Thanks for sharing the information. Good lesson for others.


welcome


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## DIYguy (Sep 18, 2008)

jhuebner said:


> Hey, take it easy. If you want people to share their stupid mistakes, don't bash on them when they do. I've learned my 120€ (at least) lesson and I'm not blaming anyone but myself.
> 
> No I did not do any balancing prior to the first charge because I was too impatient to get on the road.
> 
> ...


yes, I know. . sorry, don't mean to bash you toooooo much. 

That said, the thread is about BMS (monitoring not management) as if you need it to prevent what happened to you. My real point for the readership is that is not really what was needed here. There is plenty of knowledge now about what is needed . . . sounds like even you knew what to do . . and didn't do it... ????


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## jhuebner (Apr 30, 2010)

DIYguy said:


> yes, I know. . sorry, don't mean to bash you toooooo much.
> 
> That said, the thread is about BMS (monitoring not management) as if you need it to prevent what happened to you. My real point for the readership is that is not really what was needed here. There is plenty of knowledge now about what is needed . . . sounds like even you knew what to do . . and didn't do it... ????


I get it. Not quite the right thread then 
Ok, to prevent what happened to my cells you don't need per cell voltage measurement. Just HVC/LVC. And it also helps to fight ones impatience  (which made me skip the balancing step)


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## EVfun (Mar 14, 2010)

You need at the minimum some type of HVC on the first charge. That could be you standing around with a DMM reading the voltage of each cell every few minutes. Once you get balanced you should be able to walk away when charging.

I added some cells to my pack. The extra cells are the same age and manufacturer, all from a single purchase. They have about 1 less year of use as I started with a 32 cell pack and then added 6 cells to make it a 38 cell pack (I bought a total of 42 cells.) The cells I added do drift upward in voltage at the end of charge. I can set the pack to 3.5 vpc (133 volts for 38 cells) but after a few months they are not all around 3.5 volts. I end up with most of the cells around 3.45 volts and 6 around 3.75 volts. I knock about 0.3 amp hour out of those 6 cells and the cells go back to finishing around 3.50 volts each (+ 0.06, - 0.03). A few months later they the problem is back and I repeat. It has been 3 times now, the first time the 6 cells drifted up to about 3.9 volts each. I have considered putting the EVworks BMS back on the pack but not hooking up the BMS monitoring loop, just using them as shunt regs so I don't have to do it manually. The problem is, if you have shunt regs you need to charge to that point where all the shunt regs are ON. Cell level regulators represent a load that is not equal for every cell. The EVworks BMS varies by less than one tenth of a milliamp between units. That adds up over a year (almost 8800 hours per year.) So that is the downside.

Perhaps Dimitri wants to make some shut reg only modules set to about 3.55 volts. The parasitic load would be lower without a optical isolator to keep on all the time. The voltage set point would be more in line with what works well based on user observations.


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