Ok, but going to the next level...
BMS systems can't monitor individual cells in a parallel level, right? They can monitor the voltage of the paralleled set - and MAYBE (at least in theory - though I doubt they do in practice) they could possibly monitor the temperature of the individual cells in the parallel group. But if you have 2 or more cells connected in parallel, they can't and don't monitor the individual cells - right?
If one of the cells in a parallel group becomes weaker than the rest, there isn't a decent way to detect that. Right?
John
On Tuesday, October 2, 2018, 2:39:05 PM CDT, 'james@deny.org' james@deny.org [electricboats] <electricboats@yahoogroups.com> wrote:
It was a good read, and there opening statement mirrored my advise exactly:
"Whenever possible, using a single string of lithium cells is usually the preferred configuration for a lithium ion battery pack as it is the lowest cost and simplest. However, sometimes it may be necessary to use multiple strings of cells. Here are a few reasons that parallel strings may be necessary:
1. Redundancy (only for specific applications)
2. Hot swap capability (UPS applications, telcom, scalable systems, etc.)
3. When you must use a particular type of cell which is only available in a module with several cells in a string with no means of directly paralleling the cells.
Important Note: Due to the risks of parallel strings, additional external safety systems must be used in conjunction with the BMS when the Orion BMS or Orion Jr. BMS are used with parallel strings. Electrical engineering is required to use the Orion BMS or Orion Jr. BMS with parallel strings, and this work must be performed by an electrical engineer who is trained in working with and understands the risks of paralleled lithium ion batteries. Do not attempt to use parallel strings without proper training."
This is there opening statement and hardly counts as "talk positively" but like they and I have said, sometimes you don't have a choice to use a series string, and paralleling is an unavoidable evil. But is almost always the lesser choice.
Since you are in a situation where you need to use parallel strings, do so. But go in knowing it is the less optimal choice.
On Oct 2, 2018, at 7:25 AM, clh5_98@yahoo.com [electricboats] <electricboats@yahoogroups.com> wrote:
James,
Here is a link to the Orion BMS White Paper where I read about paralleling cells. They talk positvely about paralleling at the cell level, but site many issues and complexity when paralleling strings. https://www.orionbms.com/manuals/pdf/parallel_strings.pdf
Chris
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