[jddcircuit]

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.

I must have misunderstood what he meant by that.

Jeff

[dougingraham]

Originally Posted by jddcircuit

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.

I must have misunderstood what he meant by that.

Jeff

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]

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

[favguy]

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]

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]

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]

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]

Originally Posted by jddcircuit

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]

Originally Posted by JRP3

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]

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.