Anybody posted this video here before? A lot of enlightening things about LiFePo4 batterries.
Do you mean that this video does not support Jacks claims ?I see Jack Rickard is claiming this video supports his arguments against using a BMS – I guess he pressed the stop button as soon as he'd heard what he wanted to hear. I'd recommend watching the whole thing, but if you're in a hurry the relevant part is from 65 minutes on.
Took me a couple of cracks to get through it... but REALLY GOOD.... especially the last third that was more about application... Thank you!Anybody posted this video here before? A lot of enlightening things about LiFePo4 batterries.
It all depends on terminology used and how we understand this terminology. He was way too brief on the subject and the audience was too mesmerized to ask the right questionsDo you mean that this video does not support Jacks claims ?
I can pretty much hear Jay saing that it is a waste of money to put single cell management in a battery pack, and that the most cost effective way of doing pack management is String management of well matched cells that has been taken to the same state of charge, that being either top, bottom or middle (if you can find a good way of doing that).
Hi !It all depends on terminology used and how we understand this terminology. He was way too brief on the subject and the audience was too mesmerized to ask the right questions
Here is how I understood it. Single cell management is the ability to remove individual cell from the circuit and/or reroute energy around it, such that single cell failure does not stop the whole pack. This requires power electronics ( like IGBT modules ) for each cell, to be able to route energy around bad/empty cell. Some people proposed such BMS schemes, even on this forum, but for anyone familiar with electronics involved its 100% clear that such solution is not cost effective. I think this is what Jay was referring to, he actually mentioned bypassing a cell.
String management, the way I understood him, is monitoring cell level voltages and taking action upon entire pack, i.e. stopping charge/discharge when any cell goes outside of norm. He actually mentioned cell level monitoring using simple cheap circuits. This type of management is precicely what most affordable BMS systems do. Its a string management, based on cell level monitoring.
Sure, if you have the luxury of hand picking cells based on AH and IR match from a large pile of tested cells, and also size the pack such that you never reach top or bottom, then BMS requirement is reduced. However, us DIY folks don't have such luxury.
I'm expecting some rocks being thrown my way because I am the evil BMS pusher , but I strongly believe there are real benefits in a simple affordable BMS, despite what EVTV crowd is lead to believe by their fearless leader
BTW, the video was awesome, by far the best info about Lithium batteries in a simple easy to understand form, although it probably helps to have some background in electrochemistry.
I also liked how simple in 1-2 sentences he explained how to balance a new pack before first use. There are pages and pages of forum threads here discussing complicated ways of doing the same thing that can be done in few simple steps. Parallel all cells, charge or discharge to get them outside of flat area, let them sit for a while, then connect in series, done, end of story.
Hi Dimitri,Here is how I understood it. Single cell management is the ability to remove individual cell from the circuit and/or reroute energy around it, such that single cell failure does not stop the whole pack. This requires power electronics ( like IGBT modules ) for each cell, to be able to route energy around bad/empty cell.
Yep, that part interested me too, but I don't understand it.What I found really interesting was his suggestion that pulsing would be beneficial to the cells. I wonder if the charge reversal of regen fits into this category or if he meant higher frequency pulses?
First BMS I built was also based on G/F design and I quickly realized that normally open bus is prone to issue you describe and also to wiring failures, etc. This was the main reason I started MiniBMS design from scratch, with normally closed loop being the key feature. NC loop immediately detects "busbar" cell or loose wiring, this is why I laugh when people state loose wiring as the reason they hate/fear BMS.but I don't know if it handles a problems that I have faced with my ThunderSkys.
One of my cells became a busbar. 0v just plain conductor. The BMS would not spot it, because the voltage was to low. I don't know how long I had the cell that way, but it freaked me a little, that and a shunt that went haywire and started bleeding a cell that was in normal voltage.
From that day I have no BMS.
I haven't bottom balanced yet but I plan to do.
I used a ver2.6 of the Goodrum/Fechter BMS, Probably mostly my own fault for not using an ESD safe area when soldering and handling the components.
I believe you, without a doubt. But the professor in this video was talking about himself, burning down a battery with incorrect wiring. Don't know anymore what he did wrong or what happend exactly....I personally observed some scary things people do with their EVs...
It could be interpreted this way, but I think professor Jay was focusing on more important points of pack management. I don't think he even thinks of shunting as a BMS function since in his field of large scale economics pack balancing is done at the factory, not in the car. Shunting represents such small part of overall pack management that its not worth all the attention it seems to get in EV forums. BMS spends 99% of the time managing/monitoring bulk charge and bulk discharge, everything else, including shunting/balancing is just icing on the cake. This is why I believe his references to cell management vs string management refers to removal/bypassing a cell during bulk usage, which is clearly not cost effective. String management is what most people do, when done cheaply and effectively it makes sense. When done expensive and complicated it makes no sense.Hi Dimitri,
It is not completely clear to me, he meant just that. Shunting during charging could also be interpreted in this way.
This is where we have a disconnect. I don't know specifically which wiring or BMS's you refer to, but BMS's that I consider effective have just one wire. 10,000 miles after installation this wire is in the same place where I left it, it didn't go anywhere, it didn't touch anything, it didn't beg for anything. It sits there just like 1000 other wires which exist in every one of 100,000,000 cars on the roads today. The wire argument is just silly. Its the same as saying if I piss in the gas tank my gas car will fail. Simple solution to the problem, stop pissing in the gas tankAnd a BMS with all its wiring in such a critical place, is just the part begging for it.