[ausev] need advice on power management doo-hickey

[Chris Robison]

On Tue, 2008-01-22 at 08:24 -0600, MLAB wrote:

> Say there was a device that monitored current in the battery line and 
> when it saw that a small current had been flowing for a couple of hours 
> it would open a contactor and isolate the battery.  Normally, there 
> would be either no current flowing (battery disconnected) or 
> intermittent high current (vehicle in use), so it would recognize if 
> there was a steady leak.

Some good suggestions here about how to fix this problem in a practical
way. 

In a different sense though, (not in the sense of properly shutting down
the DC/DC or leaving it powered only when the vehicle is plugged in), I
think there's an idea for preventing damage to the pack. I think it's
easier to base this on voltages than current patterns. This way you can
use a "stateless inspection" design, not needing to maintain a memory
buffer of recent usage.

As a last line of defense, a proper battery management system should
watch each battery, or each cell in a system where cell voltages are
available, and when any one of them gets below their critical "dead"
voltage or some chosen threshold above that, it should send a signal to
open a contactor, and the battery pack should disconnect from all loads.
This threshold could be different between driving and sitting -- when
driving, you'd probably want it to shut off later, to get the most
distance out of it as you creep home. Just a guess.

I don't know of a battery management system that does this but maybe
there are some. I do know of a few that are being developed; maybe this
will be among their features... :o)

  --chris


> 
> Does anyone know of such a doo-hickey?
>