Hi,
Im completely new to the forum, and worst yet completely new to electronic circuits so I have a massive learning curve, So I apologies in advance and will say don't be gentle with me.
I wanted to understand how we could better manage large... really large packs of lithium Ion batteries.
Im not building an ebike, or a diy powerwall but have taken an interest in what those guys are doing, and have to say it scares me, and I wanted to know if there was a better way to do it.
Background.. wrong, right or the ugly.
Most "DIY/Makers" playing with lithium ion batteries and building packs (they old 7s100p) are relying on the nature of LiOn to "Self" balance when in series, and fuses (fusing each cell) as there safe guards, with BMS providing either/or or both balancing, over and under charge protection.
I can list a who bunch of reasons why this is scary.
- This doesn't take into account the small difference in chemistry between batteries
- defects within the batteries
- batteries in series can still become unbalanced, and can result in over charging or under charging
- only offers protection to over current, circuit shorts
- provides no isolation at a cell level
- provides no thermal protection (for example ensuring the right charging conditions, or isolation from thermal runway)
- fuses only don't prevent thermal runaway (side note its funning most reference tesla style packs and the same protection "fuses" but completely overlook the radiator in the pack which would be dissipate heat in an attempt to prevent venting via flames in some failure scenarios but also provide heat in low temperature charging scenarios)
So it got me interested in my childhood interest in electronic circuits, some 30 years ago, and I started to wonder .
So I actually want to build a battery pack that was 14s10p (42v-58v 52v nominal) @ 20AH how would I go about doing it (factoring in all the safe guidelines for LiOn".
as I looked into it, found that most that there really isn't a lot for managing large packs, with most IC designed around 4~ish cells, 1s..2s..3s..4s, there are two options for 12 and 14 cells but they are really expensive options when building large packs, I also found that most protection IC charge to 4.2 (instead of 80% 4.15) and discharge to 2.7 (instead of the 3-3.5v that some popular cell brands support/recommend)
I was thinking that it needs to include
- SOC
- Temperature
- Passive balancing
- Voltage/Heat per cell (or at least every few cells)
- the ability to isolate per cell
- hold timers for charge and discharge (the idea of charging and discharging a LiOn battery at the same time doesn't seem like a sensible one to me)
- minimal power drain (maybe sleep between sampling)
so what is a cost effective way that people would manage this?
something like MAX17015 or bq2405xon the pack to monitor/fuel gauge the overall SoC
fast/large/accurate ADC to monitor each individual cell voltage and temperature (instead of more expensive MC33771)
resistance protectors ( like Cyntec protectors)
what components would people recommend I look at.
Im completely new to the forum, and worst yet completely new to electronic circuits so I have a massive learning curve, So I apologies in advance and will say don't be gentle with me.
I wanted to understand how we could better manage large... really large packs of lithium Ion batteries.
Im not building an ebike, or a diy powerwall but have taken an interest in what those guys are doing, and have to say it scares me, and I wanted to know if there was a better way to do it.
Background.. wrong, right or the ugly.
Most "DIY/Makers" playing with lithium ion batteries and building packs (they old 7s100p) are relying on the nature of LiOn to "Self" balance when in series, and fuses (fusing each cell) as there safe guards, with BMS providing either/or or both balancing, over and under charge protection.
I can list a who bunch of reasons why this is scary.
- This doesn't take into account the small difference in chemistry between batteries
- defects within the batteries
- batteries in series can still become unbalanced, and can result in over charging or under charging
- only offers protection to over current, circuit shorts
- provides no isolation at a cell level
- provides no thermal protection (for example ensuring the right charging conditions, or isolation from thermal runway)
- fuses only don't prevent thermal runaway (side note its funning most reference tesla style packs and the same protection "fuses" but completely overlook the radiator in the pack which would be dissipate heat in an attempt to prevent venting via flames in some failure scenarios but also provide heat in low temperature charging scenarios)
So it got me interested in my childhood interest in electronic circuits, some 30 years ago, and I started to wonder .
So I actually want to build a battery pack that was 14s10p (42v-58v 52v nominal) @ 20AH how would I go about doing it (factoring in all the safe guidelines for LiOn".
as I looked into it, found that most that there really isn't a lot for managing large packs, with most IC designed around 4~ish cells, 1s..2s..3s..4s, there are two options for 12 and 14 cells but they are really expensive options when building large packs, I also found that most protection IC charge to 4.2 (instead of 80% 4.15) and discharge to 2.7 (instead of the 3-3.5v that some popular cell brands support/recommend)
I was thinking that it needs to include
- SOC
- Temperature
- Passive balancing
- Voltage/Heat per cell (or at least every few cells)
- the ability to isolate per cell
- hold timers for charge and discharge (the idea of charging and discharging a LiOn battery at the same time doesn't seem like a sensible one to me)
- minimal power drain (maybe sleep between sampling)
so what is a cost effective way that people would manage this?
something like MAX17015 or bq2405xon the pack to monitor/fuel gauge the overall SoC
fast/large/accurate ADC to monitor each individual cell voltage and temperature (instead of more expensive MC33771)
resistance protectors ( like Cyntec protectors)
what components would people recommend I look at.