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Old 01-18-2012, 06:27 PM   #77 (permalink)
IamIan
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Quote:
Originally Posted by MetroMPG View Post
Correct me if I'm wrong, but isn't maximum regen current half of maximum assist? (I thought I'd read 50 A vs. 100 A.)
Yes.
At OEM resistance levels... which are not static by the way ... the Batteries resistance changes under different conditions ... even brand new the batteries resistance changes with different SoC ... even brand new they change at different temperatures ... even brand new discharging resistance is not = to charging resistance.... etc... so there is a range the system is designed to tolerate.

If your pack or cells have higher resistance it applies to any current flow ... in any direction ... the OEM BCM is expecting certain things ... and what it is expecting is already designed for the 50Amps of Regen and 100Amps of Assist... if you have high enough resistance you will eventually be out of that BCM expected range just as much at 50Amps of regenerative braking as you would be at 100Amps of Assist... because the BCM is programed to expect certain things for 50Amps and or 100Amps.

If for example your battery resistance were say ~20% higher Ohms than brand new ...
  • That means at any Level of Assist Amps the terminal voltage will read ~20% lower ( V=IR ) than what would be expected from the lower resistance brand new battery ... it will have a larger voltage sag / drop due to the higher resistance under the same load.
  • At the same time the same batteries at the same ~20% higher Ohms than brand new would also have ~20% higher Voltage at any given amount of regenerative braking amps ( V=IR ) the higher resistance will create a larger voltage rise from the same amount of charging current.

The way around it is to take advantage of the resistance range built into the BCM to take into account the variation of the resistance under different conditions , even with brand new battery ... so if for higher battery resistance purposes you need to reduce your peak Assist amps by 10% down to ~90Amps you should also equally reduce your peak regen Amps by the same 10% amount down to ~45Amps... etc... as far as resistance goes ... duration or frequency of Assist or Regen is less important than the Peak Current Flow amount of Amps.
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