RE: Rudman Was Right! (was Dualin'7s Smoked Controllers)

[Rod.Hower@ametek.com]

I don't know how the DCP's operate, hopefully Rich could answer that.
The GE EVT-15 does not allow the bypass contactor to close until 92-94%
IGBT on time
This means you will get a very small if any arc on the contactor and a
small increase
in motor current.
I once wrote software that would pull in the Bypass contactor at 55% on
time.  In this situation
the motor voltage is at approximately 55% of battery (excluding losses), so
when the contactor
closes you get a big surge in current (from about 450A to 750A in my case).
I think the best way to protect your contactor and make it last for a long
time
is to prevent bypass until you have adequate voltage at the motor
terminals.
Your launch won't be as impressive, but you may not be smoking the tires
either.
This is somewhat of a trade off, but why not let the DCP do its job?
Its sounds like it is in current limit and at a very low duty cycle when
the bypass is
pulled in, punishing the contactor.
Rod



Perhaps, but since it is the bypass contactor that is failing
the discussion was focused on how to protect it from being hammered.

At the instant that the contactor closes, if the MOSFETs are
conducting then the contactor sees a much smaller inrush current
than it would otherwise.  If the MOSFETs are again conducting
when the bypass contactor opens, then it breaks a much smaller
current than it would otherwise since the current will have
divided between the resistance of the parallel MOSFETs and
resistance of the contactor.

Cheers,

Roger.

-----Original Message-----
From: owner-ev@listproc.sjsu.edu [mailto:owner-ev@listproc.sjsu.edu] On
Behalf Of Joe Smalley
Sent: August 30, 2001 6:17 PM
To: ev@listproc.sjsu.edu
Subject: Re: Rudman Was Right! (was Dualin'7s Smoked Controllers)


I thought it was when the contactor opened that hammered the MOSFETs.

When the contactor is closed, there is no voltage across the MOSFETs and
no current flowing.

Joe Smalley