Project ForkenSwift electric car: LED battery gauge

Schematic available here: http://www.evconvert.com/article/led-…

Here’s the full text from the video:

- May 7, 2008
- Testing out an LED battery pack monitor.
- Background: the ForkenSwift runs on used batteries
- Graciously donated by other EV owners.
- (Thanks, Fred!)
- (Thanks, Allan!)
- But there’s a problem with older, mismatched batteries.
- They have different capacities, so they run down at different rates.
- So, just watching the pack voltage with a multimeter isn’t good enough…
- …because it won’t tell you when an INDIVIDUAL battery is out of juice.
- And if you keep running the weakest batteries down too low…
- You’ll soon have a growing pile of dead & damaged batteries.
- Ask me how I know this
- The solution?
- A display that shows the voltage of each battery in the pack at a glance.
- (Eight 6 volt batteries in the ForkenSwift)

[Next subtitles shown while driving, showing the LED gauge in action.]

- Stopped. Accelerating… Changing gears. Accelerating… Changing gears. Accelerating…
- Batteries #1 and #6 (left to right) are weakest. #2 and #4 are strongest.
- Coasting…
- The lowest LED in each column lights up at 5.25 volts.
- Going below 5.25v risks damaging the battery.
- The display shows why the weakest battery in the pack is the limiting factor for range (and power).
- It was made by a clever EV owner in the UK. (Thanks, James!)
- Cool eh?
- The display will make it easier to finally sort through the batteries…
- … identify the duds, and put together an “A pack” and
a “B pack”.
- Nothing like a rolling load tester!

http://www.ForkenSwift.com