View Single Post
Old 06-10-2011, 09:18 PM   #326 (permalink)
Freyguy
EV Builder
 
Freyguy's Avatar
 
Join Date: Nov 2010
Location: Macungie, PA
Posts: 157
Thanks: 15
Thanked 64 Times in 40 Posts
Quote:
Originally Posted by mora View Post
What did I mess up when changing battery capacity to 90Ah and pmile to 13? I get 49 KTE when at 100% SOC, but it lowers faster than odometer is showing. Today I drove a bit over 30km and KTE read 0. Battery amps look correct on the screen and pack voltage is less than 0.1V off. User manual says more aggressive driving lowers MTE/KTE faster than actual miles travelled, but can it be this far off?

Fuel gauge also shows full after certain point (can't remember if it was under 20% SOC or after 0 KTE). It starts lowering from there but looks like its status gets reset somehow.
Mora,
Accuracy of KTE/MTE is dependent on accuracy of the SOC meter. You can enter in your capacity and Peukert exponent as a starting point, but you’ll need to monitor the calculated SOC value compared to actual measured capacity and make adjustments.
I don’t know if you’re using lithium or lead acid, but get the peukert right first.
For my lead acids, I used a peukert of 1.30 based on battery datasheet 100A rate. But SOC was dropping too fast relative to measurements made on the batteries 15 minutes after a long drive (I measured using both “no load” voltage and hydrometer readings).
Readjusting to 1.25 was better, but 1.20 put me spot on.
Once the SOC meter appears right, then charge to 100%, go for a drive to drop it to 60% and note the kilometers driven on odometer. Doubling this gives the kilometers you can drive down to 20% capacity or basically your usable range. This is the value you should set the pmile to generate. Pmile represents % capacity used per mile and is a fixed value.
Driving aggressively will use a higher % capacity per mile and would create an error.
The only way to make this more accurate is to have a speed sensor interfaced to the LCD board. It could then determine % capacity used per mile and change it dynamically to reflect driving habits.

As for SOC resetting down ~ 20%, I haven’t seen it. Granted I haven’t run my batteries that low, but on bench simulations months ago I would run SOC down to 0 repeatedly without issue. I did see the SOC change from power down to power up, but I posted the fix for that. It will be implemented in version 1.4.
  Reply With Quote