# Did Jack say he needs a BMS?



## dougingraham (Jul 26, 2011)

jddcircuit said:


> On EVTV yesterday I thought I heard Jack Rickard say he could have used a BMS on his Escalade project since he believes he damaged one of his cells by overdischarging.
> 
> I was very surprised to hear this coming from him since he has criticized so many others that have tried to protect themselves from this type of situation.
> 
> ...


Yeah, I heard it too but there are any number of things he could have meant by the comment. So when he updates his blog ask him what he meant.


----------



## JRP3 (Mar 7, 2008)

He did say in the video that the cell that died seemed to be weak to begin with.


----------



## favguy (May 2, 2008)

I thought I heard him mention that he was looking for a suitable BMS product for his online store. I have to assume he is referring to a monitoring system only as his stance on management is well known!


----------



## Ziggythewiz (May 16, 2010)

He's said it a number of times, because he keeps destroying batteries through neglect. I think he just needs a better attention span/common sense. If the one cell was always acting weaker than the others, just monitor it. 

I think having part of your pack (or a single cell) weaker than the rest is actually a benefit. You monitor the weak link and charge before it's an issue, no need to monitor the rest.

Also, keep in mind there 2 kinds of BMS, Monitoring and Management, sometimes called passive and active. I think Jack is interested in a passive system that can turn stuff off to prevent damage, rather than the active type that can overheat while shunting and cause damage.


----------



## JRP3 (Mar 7, 2008)

I'd call a BMS that can stop charging an active BMS. Monitoring only means just displaying information without taking action. Certainly a shunting BMS is a higher level of an active BMS.


----------



## jddcircuit (Mar 18, 2010)

Having cells within a stack of varying capacities seems inevitable to me at some point of the stacks life. Sometimes sooner than later as Jack is demonstrating. Knowing when to stop charging or stop driving as to not over stress or damage cells prematurely is the objective. 

Management can not really happen without being able to first measure or estimate some state or condition about the cells or stack. The trick seems to be determining the least expensive and most benign method of acquiring and tracking pertinent cell or stack information. I find this monitoring an interesting design challenge when you take the fault resolution down to the cell level of a high voltage stack.

It would be refreshing to me if that is what Jack is referring to.

Jeff


----------



## JRP3 (Mar 7, 2008)

jddcircuit said:


> Having cells within a stack of varying capacities seems inevitable to me at some point of the stacks life.


It's there from day one, you never get a pack of cells all exactly the same. However they should be close enough to not make a meaningful difference in daily use as long as you don't push your pack to the extremes, (which you shouldn't do anyway.) A cell that is out of range from the pack is a bad cell and needs to be replaced. A BMS might help you limp it along for a while but that cell is going to limit your range and will probably fail prematurely anyway.


----------



## Ziggythewiz (May 16, 2010)

JRP3 said:


> they should be close enough to not make a meaningful difference in daily use as long as you don't push your pack to the extremes, (which you shouldn't do anyway.) A cell that is out of range from the pack is a bad cell and needs to be replaced.


Bad can be anything from 5% less capacity than the others to 100% less. I don't recall what Jack was doing when the cell died, however he has driven a car to a halt on purpose before to prove how great bottom balancing is. If you stop discharing when the pack average is at 70-80% DOD they barely even need to be balanced at all.


----------



## JRP3 (Mar 7, 2008)

I'm in my third year of a bottom balanced no BMS pack, including 3 deep discharge events, one where the car stopped moving, with no issues so far. I'm also running CALB cells which seem to be more reliable than the TS/Winston, or at least they have better QC.


----------



## GizmoEV (Nov 28, 2009)

Ziggythewiz said:


> I don't recall what Jack was doing when the cell died, however he has driven a car to a halt on purpose before to prove how great bottom balancing is.


Didn't he say it took out his charger because the cell went open circuit? Maybe I'm miss remembering it.


----------



## JRP3 (Mar 7, 2008)

Yes, he said the cell "opened up while we were charging and took out the Manzanita."


----------



## Coulomb (Apr 22, 2009)

JRP3 said:


> Yes, he said the cell "opened up while we were charging and took out the Manzanita."


Took out as in damaged it? How does an open circuit cell damage a charger? Surely the charger just sees the current go to zero, and terminates the charge soon after.

The cell and its battery monitor / management system (if installed) has to deal with full charge voltage less rested pack voltage across the cell, which is a design challenge. But the charger I would not expect to be stressed at all.

[ Edit: maybe if it doesn't open circuit cleanly, it might open and close milliseconds apart for a while, which might cause current or voltage spikes that the charger isn't designed for. But it still seems like a stretch to me. ]


----------



## Ziggythewiz (May 16, 2010)

I'm guessing it sees the open cell and thinks, hey! 0 voltage! This thing needs some serious charging!

And then it tries to dish out the juice.


----------



## Coulomb (Apr 22, 2009)

Ziggythewiz said:


> I'm guessing it sees the open cell and thinks, hey! 0 voltage!


But the charger won't see zero volts, it will see a pack that is whatever voltage the charger is presently putting out, and won't take any current. An open circuit, in fact.

So maybe it will periodically stop charging, and measure the resting voltage; that will be zero volts. So then it "tries to dish out the juice", which means it will go to its CV setting, and no current will flow. It's not like it's going to try to go to infinite voltage to try to make some current flow.


----------



## JRP3 (Mar 7, 2008)

I don't remember the technical explanation but the Manzanita chargers cannot be turned on with no load, if they are they die. I guess the same thing happens if load is removed during charging.


----------



## PStechPaul (May 1, 2012)

If there is inductance in the output, an open circuit (actually probably seen as a capacitance) might cause an inductive spike or even a resonant circuit where high voltages may be produced. Once it starts to break down components, things could go south in a hurry. But that would indicate a poor design or a component failure to start with. A battery charger should be able to tolerate anything from an open circuit to a short circuit, as well as some inductance and capacitance.

I just looked at the charger information at http://www.manzanitamicro.com/downloads/category/15-chargers, and it seems that they can be used for anything from 12V to 450V output. So if they have an internal bus of 180 or 360 VDC, they must use some sort of buck/boost topology which involves an inductor and a high frequency PWM. But the "potential" is there for the full high voltage to be applied to the battery pack until the regulation kicks in. Apparently you can adjust the output over this wide range to match your battery pack, and there is always the chance that the voltage or current settings were incorrect. And a true current mode regulator will use all of its DC bus voltage in an attempt to get the charge current needed. The specs say it starts in current mode and then switches to voltage mode, so unless it also has a voltage limiter it would apply up to 450 V to the pack with an open cell. And that might be bad...


----------



## palmer_md (Jul 22, 2011)

There is a clear warning right in their manual....page 8....



> NOTICE! DO NOT unplug the gray SB-50 Anderson connectors (DC line) from
> your charger while it is charging! If the battery pack is disconnected while the
> charger is putting out power the charger can be damaged. Failure to heed these
> warnings may result in significant internal damage to the charger which is not
> covered under your warranty!


http://www.google.com/url?sa=t&rct=...xNS9Bg&usg=AFQjCNFdFcA1JYTQHdfU4-M_yTyjL6EG9Q


----------



## JRP3 (Mar 7, 2008)

From the Manzanita manual:



> NOTICE! DO NOT unplug the gray SB-50 Anderson connectors (DC line) from
> your charger while it is charging! If the battery pack is disconnected while the
> charger is putting out power the charger can be damaged. Failure to heed these
> warnings may result in significant internal damage to the charger which is not
> covered under your warranty!


----------



## JRP3 (Mar 7, 2008)

Beat me to it  As I remember there is a mod you can have them do to the charger if you know you don't need the max voltage possible. If there is a lower max voltage limit hard wired I guess things won't blow up if you open circuit it.


----------



## tomofreno (Mar 3, 2009)

JRP3 said:


> Beat me to it  As I remember there is a mod you can have them do to the charger if you know you don't need the max voltage possible. If there is a lower max voltage limit hard wired I guess things won't blow up if you open circuit it.


 Yes, that's correct, I don't remember the details though. 
Edit: How would a bms have helped? You would then have full pack voltage across the shunt circuit. In the minibms this would blow the fuse and open the circuit, leaving you where you are with no bms. If the shunt is unfused, you may well set the board on fire. Greg of Greg's Garage in the UK speculated that a cell going high resistance during charging is what caused the fire that consumed his car a few years back. The Manzanita's sensitivity to an open circuit load is a safety feature!


----------



## JRP3 (Mar 7, 2008)

I think Jack meant a BMS during the discharge event that damaged the cell would have stopped the discharge process before that cell went too low, which might have kept the cell alive longer and not led to the open circuit event. Of course the cell was suspect before the deep discharge and they had it marked as questionable, so it probably was going to fail prematurely anyway.


----------



## jddcircuit (Mar 18, 2010)

What I got from Jack's experience was that a method of monitoring, logging, and interpreting cell behavior has value beyond detecting a bad cell. Jack claims to have marked the cell as suspect because it didn't feel right which is very cool. However, it might be difficult to transfer the "doesn't feel right" talent to the masses or other DIYers.

The symptoms of the bad cell or the amount of over stress that the cell experienced will remain unknown. It is this data that may offer early detection and possible fault avoidance. The electronics needed to gather this information can be considered an expensive luxury at the moment but would be nice if it wasn't.

With experimental early life vehicles that are being used to develop a method or process to share with others to follow, the data logging would have a much greater informative value than it might if it is a one off solely for personal use.

Jeff


----------



## CroDriver (Jan 8, 2009)

Ziggythewiz said:


> Also, keep in mind there 2 kinds of BMS, Monitoring and Management, sometimes called passive and active. I think Jack is interested in a passive system that can turn stuff off to prevent damage, rather than the active type that can overheat while shunting and cause damage.


We call a passive BMS a shunt type BMS, while an active BMS recycles the balancing energy (transfers energy from a high cell to a/multiple low cell).

Professionals (OEMs) don't even think about the posibility of a battery-pack with no BMS at all or just a monitoring system...


----------



## JRP3 (Mar 7, 2008)

That's because you have the unfortunate burden of releasing your cars to the general public


----------



## DavidDymaxion (Dec 1, 2008)

Did the early Peugeot and Chysler NiCd vehicles have BMSs? What about the NiMh hybrids? (Honest questions, I don't know.)

The lead acid charging system in a conventional ICE car doesn't have any BMS -- but lead is a cheap and a robust chemistry. If Li became cheap enough I wonder if they might forego BMSs then?


CroDriver said:


> We call a passive BMS a shunt type BMS, while an active BMS recycles the balancing energy (transfers energy from a high cell to a/multiple low cell).
> 
> Professionals (OEMs) don't even think about the posibility of a battery-pack with no BMS at all or just a monitoring system...


----------



## PStechPaul (May 1, 2012)

As I understand it, NiMH batteries have a much different characteristic to determine charge level and end of charge. Here are a couple of links:

http://www.cvel.clemson.edu/auto/systems/battery_management.html
http://www.powerstream.com/NiMH.htm
http://www.powerstream.com/li.htm
http://www.powerstream.com/tech.html (lots of good information)

But in essence, a NiMH battery, when fully charged, simply dissipates any excess energy as heat, which can be readily mesured and used to determine EOC. They are not damaged by charge rates under C/10. LiPo types are more sensitive to overcharging but are more easily monitored for cell voltage, which is a reliable indicator of charge level.

One method that is discussed in the above links is to stop charging for brief moments of time so the open circuit voltages can be read.

The powerstream site has a wealth of information about SLA batteries, but they are notably tolerant of moderate overcharging and the voltages for float charging and maximum levels for outgassing are very strongly temperature dependent:
http://www.powerstream.com/SLA.htm


----------



## JRP3 (Mar 7, 2008)

There are ways to balance lithium chemistry without external electronics. 3M makes a redox additive for lithium cells that comes into play around 3.9V, the reversible reaction takes the excess energy and prevents cell voltage from going higher. However I don't know of any cell using it so there must be some issue. Additionally, some lithium chemistry has a similar effect built in where the internal resistance increases during a full charge and excess charge is bled off as heat. I think NMC chemistry may do this.
Also of course there are my CALB prismatic cells which have been running for around 2.5 years with no BMS other than occasional checks with a DVM


----------



## jddcircuit (Mar 18, 2010)

I don't see the main problem as to how to balance cells as much as it is getting insight into the possible performance variation that may exist in any cell population. Does one cell drift more than the others or does it have significantly different behavior under load than the normal population. If everything is happening in the background without monitoring then the evidence or conditions that lead up to the failure point are lost. If a balance mechanism chemical or electrical exists then does it know how often it has to engage or how much energy is has to redistribute indicating an out of normal condition.

I have a group of 50 CALB cells out of the box. Two of these cells swelled up just sitting on the shelf. A hand full of them show significantly different resting voltage than the rest. I could mark them as suspect and blindly put them into the car and wait for them to fail. I could spend time on the bench fully characterizing them in relation to the rest. Or I could put them into a car with monitoring and data logging and use the car as the test bench. Using the car as the test bench makes sense to me if it can be done cost effectively and without masking or altering the cell behavior.

I appreciate the case where someone has 3 years and no failure yet. This is encouraging. How much cell variation is tolerable or expected is a question that will continue especially as supplies change.


----------



## Coulomb (Apr 22, 2009)

jddcircuit said:


> ... getting insight into the possible performance variation that may exist in any cell population.


Good thoughts.



> I have a group of 50 CALB cells out of the box. Two of these cells swelled up just sitting on the shelf. A hand full of them show significantly different resting voltage than the rest. ...
> 
> I appreciate the case where someone has 3 years and no failure yet.


Yes, I was wondering whether you have a "right" to feel unlucky that you have probably 4 oddballs out of 50, while others have no problems over 3 years. But I wonder if many of the latter are those with smaller packs, like 35 cells. I'm thinking if you have 35 cells, you might more often get away without close monitoring than if you have 228 cells. This could be an advantage of the extra low voltage pack (literally, except when charging). Although having a reduced probability of needing monitoring isn't the same as not needing monitoring.

The cells we use are mass produced in China, and I don't think that they get a huge amount of testing before delivery. In fact if they did, I suspect we wouldn't be able to afford them. So in a group of 35 to 228 cells, you possibly would be wise to expect some to exhibit odd behavior. As you say, with monitoring, you get a handle on what is going on, and hopefully can avoid the expense and inconvenience of towing by either replacing a bad cell, or doing some work on it on the bench.

Having said that, I sure hope that if our battery monitoring system identifies a bad cell or one needing attention, that it won't identify one of the ones buried in the middle of our tightly packed sports car.


----------



## JRP3 (Mar 7, 2008)

Ideally you'd do some cell testing before putting them into your car. My first year I had all my cells easily accessible in my trunk so I did use the car as a test bed, and I did have a Cell log 8 that I moved around to check groups of cells under load and charge to get an idea of their behavior. I then put my weakest cells in easily accessible locations in case they might need attention.
I think cell monitoring is a good idea, I just haven't found a solution I really like.


----------



## jddcircuit (Mar 18, 2010)

Coulomb,
Do you have a thread where I can get an update on your BMS progress? I hope things are coming together.

I don't debate the need of monitoring or management. It is obvious that we don't need cell level monitoring in all cases as many demonstrate by not doing it. I am also not overly concerned about the inconvenience factor of the failure occurrence but that is a real issue is some cases and it would suck.

The main reason for me to implement a monitoring system is to gather more information about battery behavior in the field to share with the effort. I see it purely as a test bench on wheels at the present time and not so much as critical operational component. However operating margins will be a moving target as technology changes. Hopefully they will move towards the forgiving side which we will be able to confirm or deny with our monitoring methods.

The data will speak for itself and the more of it shared the better. The only way to say the data is of little or no value is after we have collected and analyzed it over time.

Regards
Jeff


----------



## jddcircuit (Mar 18, 2010)

JRP3 said:


> Ideally you'd do some cell testing before putting them into your car. My first year I had all my cells easily accessible in my trunk so I did use the car as a test bed, and I did have a Cell log 8 that I moved around to check groups of cells under load and charge to get an idea of their behavior. I then put my weakest cells in easily accessible locations in case they might need attention.
> I think cell monitoring is a good idea, I just haven't found a solution I really like.


You are doing it right IMO.

I haven't found a solution I really like either but I am giving a shot at developing one.


----------



## MN Driver (Sep 29, 2009)

"I'm thinking if you have 35 cells, you might more often get away without close monitoring than if you have 228 cells."

Is there anyone running a DIY project with a string of 228 cells in series? Not even sure if there is a controller on the market that handles ~800 volts(228s LiFePO4 on the charger set to a max of 3.5v). I'll be running 100 cells and know others running a similar number but there's little out there available that handles more than this unless it is an OEM solution or otherwise unobtainable. Running a higher number of cells in series allows you to remove a cell, jumper around it and not lose as much capacity as say 33 larger Ah cells with the same total capacity where a cell is lost. Say a 100 mile car(for simplicity), the difference is between losing 1 mile or 3.


----------



## m38mike (Dec 27, 2008)

I've got one volt meter dedicated to monitoring one cell out of the pack to see what it's doing. I've been thinking that I might move the pickup leads from one cell to another cell once a week to see how each cell is performing. I've got 46 cells in my pack. So after almost one year I will have monitored each cell for one week. When I started using the pack I had each cell balanced to 1/100th of a volt. It'll be interesting to see how they all perform. And to see if this method of monitoring helps me find cells that aren't performing well.


----------



## Ziggythewiz (May 16, 2010)

Are your leads clamp-on or screw-on? I wouldn't want to mess with the terminals frequently. While an annual checkup sounds good, I don't think that will find a bad cell before there's other indicators.

If possible you could hook up two DVMs rated for half your pack voltage or greater to each half and watch that for a few days. If you see greater variance on one half you split that side etc. until you identify the gimp(s).


----------



## McRat (Jul 10, 2012)

I know nothing about electronics, but ...

Couldn't you use an LED (+resistor) on each cell, then a splitter resistor to target a given voltage, say 2.7 volts. All cells will be lit that are over 2.7v (use a big resistor, and there will be little draw, it takes almost nothing to run an LED.

When a cell hits 2.7 earlier than the rest by a good amount, then replace just that cell? You could put the LED's anywhere, and even have an "on-off" switch for them. Every once and a while draw your batteries down to whatever target you use to check them.

Cost for this is under $10. Less if you already wire and some LED's floating around, and some resistors.


----------



## PStechPaul (May 1, 2012)

I came up with an idea similar to yours. See:
http://www.diyelectriccar.com/forums/showthread.php/type-bms-75822.html

If the cells are easily visible, LEDs on each cell might make sense. Otherwise you need to run wires, which is a hassle and could cause a problem if there is a short. The BMS ICs are pretty reasonable at about $1/cell, and have the advantage of using a daisy-chain system for communication with a remote indicator/controller, and they also have drivers for active load and charge balancing.

I do think it would be worthwhile to build a simple low-power voltage monitor into each cell (or pack) to give a visual indication of charge if they are used as a backup system or stored on a shelf as spares.


----------



## m38mike (Dec 27, 2008)

Ziggythewiz said:


> Are your leads clamp-on or screw-on? I wouldn't want to mess with the terminals frequently. While an annual checkup sounds good, I don't think that will find a bad cell before there's other indicators.
> 
> If possible you could hook up two DVMs rated for half your pack voltage or greater to each half and watch that for a few days. If you see greater variance on one half you split that side etc. until you identify the gimp(s).


 
My leads have clamps to make them easy to move without unbolting the cell contacts. You're right, one checkup a year is a bit long to wait. The way my pack is stored, it wouldn't be hard to move the contacts each day, so I could check a different cell every day. Or I could get a helper, and perhaps once a month I would run through every cell with the leads while my helper watched the gauge and called out numbers. I'm thinking the once-a-month plan is easier and more productive in finding cells that aren't up to speed.


----------



## JRP3 (Mar 7, 2008)

Get a Cell log 8 and move it around, it's much easier and faster for occasional checks. Don't leave it hooked up to any one group of cells much longer than another since it can create an imbalance over time. I think it only draws power from the first 7 cells, there is a mod to make it draw from all 8, but I just check 7 cells or less at a time.


----------

