[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Nicad Battery Failures



Question for experienced Satellite builders:

Given a LEO with short eclipses, and a design depth of discharge of less
than 20%, what is the probability of a failure mode with any cells
being a short? 

My 30 years of experinece with old Nicads here on the ground is with
the shorted and reversed cells from long sitting unused and uncharged.
THus, shorted cells are a certainty. But on orbit with a guaranteed
90 minute charge/dischage cycle and small depth of discharge, will we
ever get to shorted cells if we manage our loads?

It seems to me that failure to a high impedance state is more likely in
this case.

The ISSUE is that we have dual redundant solar and batteries.  If I diode
isolate both batteries to feed from both sets of panels then the worst
case failure would be one battery stack failing to a lower terminal
voltage and therefore preventing the other battery from getting a charging
voltage...  

On the ground in typical forget-to-charge scenarios, I am certain this
failure will occur.  But within the constant sun cycles on orbit, is this
failure mode 3 sigma less likely?

Thanks, Bob


----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home