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Re: (ET) Hybrid Electrak?

On 1/15/2011 10:35 AM, Banks, Michael J. wrote:

I was under the impression, that using the tractor while charging was a
bad thing.

That depends on the charger.  There are a couple of circumstances where 
using a charger on a running EV could cause damage.

	- The noise from the charger could damage control electronics or simply 
cause it to be confused.  The battery does act as a nice filter for 
lower frequency disturbances though.
	- The charger cannot react quickly to load changes(0).  EVs will 
produce rapid load changes.  The worst case is probably going from full 
torque to zero torque(1). All of a sudden the voltage will rise as the 
current is diverted to the battery.  This could damage the control, the 
charger or the battery if not limited.  A near fully charged battery 
will be more of a problem in this case.

        - It would also play havoc with any charger's end of charge 
determination.


However given a good clean DC source with a good fixed maximum voltage 
with a fast response there is no reason to expect a problem. A PM motor 
rotating at a fixed (or strictly limited maximum) speed is almost ideal 
for this.

Robert


0 - This is part of the reason that you'll often see chargers say the 
charger must be off before disconnecting the battery, they cannot react 
to the sudden load change quickly enough.

1 - Even worse is on an EV with regen when you go from full torque in 
one direction to full torque in the other.  Imagine the following 
scenario.  Vehicle takes 200A from the bus in full acceleration, battery 
provides 100, charger provides 100.  The vehicle then switches to full 
regen returning 200A to the bus.  The battery has now one from sourcing 
100A to sinking 300A (100A charger, 200A regen).  Now regen and accel 
currents will not often be this symmetric but it should be obvious that 
dramatic changes in current at the battery are possible complicating the 
charger's needed response.

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