Ykick
1 GW
Most of this posted in another thread https://endless-sphere.com/forums/viewtopic.php?f=14&t=82228 but I don’t wanna derail that fella’s topic and maybe those interested might not see it over there?
Anyway, the deal is with my RC Lipo commuter pack I feel better using cell level charge protection. As the years tick by I’ve come to realize discharge protection isn’t nearly as critical as charge protection. Basic pattern of fully attended discharge use outdoors seems to be much less risk of serious damage and deadly injury.
Here’s what I’ve taken to using for 16S RC Lipo ebike pack charge only BMS -
http://www.ebay.com/itm/201434924156?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
It’s too early to declare a win but 4qty for $10 and they appear to play nicely together in series. I’m currently trying to determine how much parasitic drain while sitting? Also, still unsure if they draw power evenly from all cells? Or, is it the CellLog 8 problem of a couple cells powering the circuit and over long periods of time will drag the pack out of balance?
Got ‘em plugged into 4qty 4S Turnigy hardcase (16S, 60-67V) in the appropriate cell order and charge 2-5A through dedicated charge port using stock JST balance wiring/connectors. JST extensions soldered to the pads.
For discharge, I plug a cheap lighted volt meter into the battery charge port and if/when that goes OFF, I then know about a potential cell voltage problem even though power is not disrupted going to the bike. It shouldn’t be too hard to rig slightly more elaborate warning lights/buzzer that simply plugs into the battery charge port?
Basically, it’s cell voltage warning only during discharge and reliance on controller LVC but it's a reasonably well protected charge and none of that stupid-ass bleed balance resistor heat and shorted switching transistor nonsense. And @ $2.50ea plus a few similarly priced JST extension harnesses it's not an expensive solution. No mods to the battery packs either.
These boards have been terminating charge around 4.15-4.18V/cell. But keep in mind, I’ve only logged and compared a couple different channels so far. Other channels might be higher or even lower but I do like this cutoff range for the charger I’m using where the cells settle to about 4.1V once the charger turns off. If I ever want to maximize full SOC it’s simple matter to charge through the discharge port and bypass BMS boards.
If/when cells do ever go out of balance, I go in with a USB power bank along with a cell phone BMS or some other Lipoly 1S USB charger and merely bring up a low cell. Knowing when there’s a low SOC cell problem is most of the battle.
As the lawn power tool companies have apparently realized, discharge is the least of a battery pack fire hazard concern in these applications. Much like an ebike, lawn tools are used outdoors so smoke isn’t so much an issue while finding a reasonably non-flammable spot (middle of a paved road if nothing else) to dump it and get away isn’t too difficult. Plus, fire during discharge is much more likely to occur during lower SOC so there’s also less energy to dissipate and it's almost always an attended situation.
Charging however is a much more sinister/dangerous thing. Often happens indoors, unattended and cells are more likely to have their maximum or above full capacity available to dissipate into a building and/or enclosure. Living area, garage space, etc.
Anyway, the deal is with my RC Lipo commuter pack I feel better using cell level charge protection. As the years tick by I’ve come to realize discharge protection isn’t nearly as critical as charge protection. Basic pattern of fully attended discharge use outdoors seems to be much less risk of serious damage and deadly injury.
Here’s what I’ve taken to using for 16S RC Lipo ebike pack charge only BMS -
http://www.ebay.com/itm/201434924156?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
It’s too early to declare a win but 4qty for $10 and they appear to play nicely together in series. I’m currently trying to determine how much parasitic drain while sitting? Also, still unsure if they draw power evenly from all cells? Or, is it the CellLog 8 problem of a couple cells powering the circuit and over long periods of time will drag the pack out of balance?
Got ‘em plugged into 4qty 4S Turnigy hardcase (16S, 60-67V) in the appropriate cell order and charge 2-5A through dedicated charge port using stock JST balance wiring/connectors. JST extensions soldered to the pads.
For discharge, I plug a cheap lighted volt meter into the battery charge port and if/when that goes OFF, I then know about a potential cell voltage problem even though power is not disrupted going to the bike. It shouldn’t be too hard to rig slightly more elaborate warning lights/buzzer that simply plugs into the battery charge port?
Basically, it’s cell voltage warning only during discharge and reliance on controller LVC but it's a reasonably well protected charge and none of that stupid-ass bleed balance resistor heat and shorted switching transistor nonsense. And @ $2.50ea plus a few similarly priced JST extension harnesses it's not an expensive solution. No mods to the battery packs either.
These boards have been terminating charge around 4.15-4.18V/cell. But keep in mind, I’ve only logged and compared a couple different channels so far. Other channels might be higher or even lower but I do like this cutoff range for the charger I’m using where the cells settle to about 4.1V once the charger turns off. If I ever want to maximize full SOC it’s simple matter to charge through the discharge port and bypass BMS boards.
If/when cells do ever go out of balance, I go in with a USB power bank along with a cell phone BMS or some other Lipoly 1S USB charger and merely bring up a low cell. Knowing when there’s a low SOC cell problem is most of the battle.
As the lawn power tool companies have apparently realized, discharge is the least of a battery pack fire hazard concern in these applications. Much like an ebike, lawn tools are used outdoors so smoke isn’t so much an issue while finding a reasonably non-flammable spot (middle of a paved road if nothing else) to dump it and get away isn’t too difficult. Plus, fire during discharge is much more likely to occur during lower SOC so there’s also less energy to dissipate and it's almost always an attended situation.
Charging however is a much more sinister/dangerous thing. Often happens indoors, unattended and cells are more likely to have their maximum or above full capacity available to dissipate into a building and/or enclosure. Living area, garage space, etc.
