2001-03 Prius battery experiment
#1
2001-03 Prius battery experiment
Hi
With insights from the "Prius_Technical_Group" group, I'm working on reconditioning individual cell assemblies for NHW11 batteries. For example, the cell assembly in the photo has an ending capacity of 3.2 Ahr, enough to match the cells in a used pack that has suffered one or more failed cell assemblies:
The automated battery conditioner first discharges the cell assembly to 1 VDC. It then charges it up and records the capacity. Three full cycles appear to give consistent results. NiMH charging generates gas so the battery must be clamped to prevent the sides from bowing out and destroying the cell. The VOM has a capacitance tester and the 13.3 nF is the clamp load, no additional pressure from the cell under test.
The batteries have interlocking 'cups' and 'dimples' and using just a flat board would lead to local, mechanical stress on the sides. So a pair of plastic shims cover each side providing strain relief for these raised surfaces. One board has a capacitive, load sensor to detect excessive gas pressure:
This approach takes usable cell assemblies from a salvage battery or one with bad modules (preferred) and reconditions the working cells. Someone with a failed battery pack can get replacement cell assemblies, ~$30-40 each, and replace just failed cell units. This won't be a 'new' battery pack but a reworked pack, good enough to keep the Prius rolling for a lot less than the $2,300 of a whole battery pack.
Questions? Comments? Concerns?
Bob Wilson
With insights from the "Prius_Technical_Group" group, I'm working on reconditioning individual cell assemblies for NHW11 batteries. For example, the cell assembly in the photo has an ending capacity of 3.2 Ahr, enough to match the cells in a used pack that has suffered one or more failed cell assemblies:
The automated battery conditioner first discharges the cell assembly to 1 VDC. It then charges it up and records the capacity. Three full cycles appear to give consistent results. NiMH charging generates gas so the battery must be clamped to prevent the sides from bowing out and destroying the cell. The VOM has a capacitance tester and the 13.3 nF is the clamp load, no additional pressure from the cell under test.
The batteries have interlocking 'cups' and 'dimples' and using just a flat board would lead to local, mechanical stress on the sides. So a pair of plastic shims cover each side providing strain relief for these raised surfaces. One board has a capacitive, load sensor to detect excessive gas pressure:
This approach takes usable cell assemblies from a salvage battery or one with bad modules (preferred) and reconditions the working cells. Someone with a failed battery pack can get replacement cell assemblies, ~$30-40 each, and replace just failed cell units. This won't be a 'new' battery pack but a reworked pack, good enough to keep the Prius rolling for a lot less than the $2,300 of a whole battery pack.
Questions? Comments? Concerns?
Bob Wilson
Last edited by bwilson4web; 01-04-2008 at 01:06 PM.
#2
Re: 2001-03 Prius battery experiment
Wow. Excellent research. I think this thread will become popular in the near future as the original Prius batteries approach their useful lifetime.
A few questions:
* If I remember correctly, NIMH batteries release this gas as they approach their max charge. Could you add circuitry that monitors the battery temperature (via thermistor) and reduces charging current as the temperature increases to prevent gas buildup?
* Also, I remember that NIMH battery cells (for consumer use) have a catalyst in them that removes the gas pressure and produces heat as a byproduct which greatly reduces battery damage in the event of overcharging. Do the Prius NIMH cells have this catalyst?
* How hot do the cells get during the reconditioning?
A few questions:
* If I remember correctly, NIMH batteries release this gas as they approach their max charge. Could you add circuitry that monitors the battery temperature (via thermistor) and reduces charging current as the temperature increases to prevent gas buildup?
* Also, I remember that NIMH battery cells (for consumer use) have a catalyst in them that removes the gas pressure and produces heat as a byproduct which greatly reduces battery damage in the event of overcharging. Do the Prius NIMH cells have this catalyst?
* How hot do the cells get during the reconditioning?
#3
Re: 2001-03 Prius battery experiment
Why are the manufactures not using this method to repair HHW11 packs. Is it too labour intenssive or not condusive to making money? Thanks for the research, Bob. H
#4
Re: 2001-03 Prius battery experiment
. . .
A few questions:
* If I remember correctly, NIMH batteries release this gas as they approach their max charge. Could you add circuitry that monitors the battery temperature (via thermistor) and reduces charging current as the temperature increases to prevent gas buildup?
A few questions:
* If I remember correctly, NIMH batteries release this gas as they approach their max charge. Could you add circuitry that monitors the battery temperature (via thermistor) and reduces charging current as the temperature increases to prevent gas buildup?
. . .
* Also, I remember that NIMH battery cells (for consumer use) have a catalyst in them that removes the gas pressure and produces heat as a byproduct which greatly reduces battery damage in the event of overcharging. Do the Prius NIMH cells have this catalyst?
* How hot do the cells get during the reconditioning?
* Also, I remember that NIMH battery cells (for consumer use) have a catalyst in them that removes the gas pressure and produces heat as a byproduct which greatly reduces battery damage in the event of overcharging. Do the Prius NIMH cells have this catalyst?
* How hot do the cells get during the reconditioning?
I checked the battery and it had a full charge so I shipped it and let the customer know all they had to do was discharge the battery to the same level as the adjacent cells and go to town. I offered to replace it if there was a problem and mentioned the sides bowed out. However, he didn't see the bowed out sides, which tells me the catalyst worked.
I now have a charging setup with a load cell that I can use to determine if gas has been generated. If so, I'll keep the cell clamped down until the pressure subsides. As long as the sides don't flex, they should handle the stress easily.
Bob Wilson
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