Re: (ET) Alltrax Death

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dave maize Wrote
>Has anyone checked out the new Technical Note 010 at the Alltrax 
>website? It talks quite a bit about fuses, contactors, diodes and 
>pre-charged resistors -Dave

I assume that's pre-charge resistors ;)

I just had another thought.  This is a failure mode I've seen (well second
hand) on another vehicle.

If the battery lead inductance is sufficiently high the battery current
will remain constant for a period of time.  If the load that was taking the
current disappears then the only place for that current to go is the power
caps in the controller.  Those caps are a relatively large sink but not
when compared to a high motor load so the voltage would rise fairly
quickly(1).  If the controller is operating I expect anything over about
55V is likely to be problematic.

That's close to what Walter was referring to, just different on the 
details.

The case I know of was fairly severe, the B+ and B- cables were routed on
opposite sides of the vehicle and around a chunk of metal in the process. 
The fix? - run B+/B- in close parallel.

Robert

1 - The reason those caps are there is partly because the battery lead
inductance means the battery can't change current quickly enough to respond
to the MOSFET switching speed.  The caps provide a local charge reservoir
to buck out that inductance, the battery then provides the average current
needed with excess charging the caps when the FETs are off and extra needed
coming from the caps when the FETs are on.


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