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Zero Motorcycles Forum | 2013+ / Re: Zero fx dying power packs
« on: May 21, 2024, 09:50:44 AM »
When pack are deffective ( at the cell module level) it can be:
1 - All cell internal resistance are high = no more usable due to voltage sag too low under load
2 - Magic charge = one or more cell have connection problem in serie ( bad crimp between cells tab) = making voltage sag under load to one or more cells
3 - One or more cell having high internal resistance = voltage sag anyway which also make the BMS to shut down the power prematurely
for 1, your pack is pretty DEAD
for 2: It is possible to open the pack and re-crimp or spotweld the bad cell connection with couple hours labor and patience and care.. but you will have to dig the potting manually without puncturing the cell below. I did it when i reconfigured a ZF2.5 brick into a 51V module for my nefew 's electric ATV. The battery was a situation 1 where all cells were too high internal resistance, but spliting the connection into two seperate groups of 14s in parallel made enough power to get about 2.2kWh out of it and make his mini electric ATV to go 90km
For 3, It is possible to solve the single cell internal resistance problem by paralleling another high C current low capacity cells to it to rematch to the other cells the internal resistance and have all internal resistance the same again. I am making it for a Long brick ZF7.2 that I use as range extender on my 2017 SR. The problem is that the cell group no 17 always charge higher voltage than the rest and always sag lower voltage than the rest under load. My plan is to measure the actual internal resistance of the deffective cell group no 17 and to measure the internal resistance of all other cells and to match the calcualted internal resistance to put in parallel to the problematic cell. I think that this job really worth if it can save a 7.2kwh battery that already fit in a ZERO if it can cost let say 100$ in material and 4-5 hours of work.. maybe more
So what it involve:
- Measure all the cells internal resistance ( 28 total) by applying a load to the pack direct terminal ( before the contactor), using a 500w or 300W light bulb and measure all the cells voltages with and without the load.
- Find the deffective one that have higher internal resistance than the rest
- Calculate the resistance of the cell to parallel to it to make it having the same internal resistance than the rest ( https://www.allaboutcircuits.com/tools/parallel-resistance-calculator/)
- Open the long brick aluminum sheet that is hardly stick to the putting material inside
- Find the location of the deffective cell tabs under the semi transparent potting
- Dig with cutter, exacto and grip carefully until you reach the metal tabs
- Unfold the crimped tab
- Solder connections to it and take care to not transfer too much heat to the tabs... or drill a horizontal hole thru the crimped tab and install wires with terminal and screw
- extend these wires outside the pack,
- Connect a permanent high current ( high C rate) NMC chemistry cells
- Redo the load test with the bulb and make sure the voltage sag of all celsl are now the same. If not adjust the cell capacity or C-rate until getting uniform Internal Resistacne on all the channels
IMPORTANT: YOU MUST HAVE A MINIMUM OF BATTERY DIY SKILL TO MAKE THAT.
I made a video to explain the concept in french but you can use the auto translate as well.
( Dont forget to subscribe to my channel if you like it! there are videos in english and video in Français)
https://youtu.be/5WSYysw-4cM?si=eqSow1lNeui6EjcR
Doc
1 - All cell internal resistance are high = no more usable due to voltage sag too low under load
2 - Magic charge = one or more cell have connection problem in serie ( bad crimp between cells tab) = making voltage sag under load to one or more cells
3 - One or more cell having high internal resistance = voltage sag anyway which also make the BMS to shut down the power prematurely
for 1, your pack is pretty DEAD
for 2: It is possible to open the pack and re-crimp or spotweld the bad cell connection with couple hours labor and patience and care.. but you will have to dig the potting manually without puncturing the cell below. I did it when i reconfigured a ZF2.5 brick into a 51V module for my nefew 's electric ATV. The battery was a situation 1 where all cells were too high internal resistance, but spliting the connection into two seperate groups of 14s in parallel made enough power to get about 2.2kWh out of it and make his mini electric ATV to go 90km
For 3, It is possible to solve the single cell internal resistance problem by paralleling another high C current low capacity cells to it to rematch to the other cells the internal resistance and have all internal resistance the same again. I am making it for a Long brick ZF7.2 that I use as range extender on my 2017 SR. The problem is that the cell group no 17 always charge higher voltage than the rest and always sag lower voltage than the rest under load. My plan is to measure the actual internal resistance of the deffective cell group no 17 and to measure the internal resistance of all other cells and to match the calcualted internal resistance to put in parallel to the problematic cell. I think that this job really worth if it can save a 7.2kwh battery that already fit in a ZERO if it can cost let say 100$ in material and 4-5 hours of work.. maybe more
So what it involve:
- Measure all the cells internal resistance ( 28 total) by applying a load to the pack direct terminal ( before the contactor), using a 500w or 300W light bulb and measure all the cells voltages with and without the load.
- Find the deffective one that have higher internal resistance than the rest
- Calculate the resistance of the cell to parallel to it to make it having the same internal resistance than the rest ( https://www.allaboutcircuits.com/tools/parallel-resistance-calculator/)
- Open the long brick aluminum sheet that is hardly stick to the putting material inside
- Find the location of the deffective cell tabs under the semi transparent potting
- Dig with cutter, exacto and grip carefully until you reach the metal tabs
- Unfold the crimped tab
- Solder connections to it and take care to not transfer too much heat to the tabs... or drill a horizontal hole thru the crimped tab and install wires with terminal and screw
- extend these wires outside the pack,
- Connect a permanent high current ( high C rate) NMC chemistry cells
- Redo the load test with the bulb and make sure the voltage sag of all celsl are now the same. If not adjust the cell capacity or C-rate until getting uniform Internal Resistacne on all the channels
IMPORTANT: YOU MUST HAVE A MINIMUM OF BATTERY DIY SKILL TO MAKE THAT.
I made a video to explain the concept in french but you can use the auto translate as well.
( Dont forget to subscribe to my channel if you like it! there are videos in english and video in Français)
https://youtu.be/5WSYysw-4cM?si=eqSow1lNeui6EjcR
Doc