Re: Rudman Was Right!Bypass control. Launch with SCR?

[jcmassey@netspace.net.au]

At 07:09 AM 31/08/01 -0700, you wrote:
>> 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.
>>
>
>Except contactors don't close instantaneously. If the controller isn't in
>full on mode (100%) then, assuming a 15khz switching rate, the FET is only
>on for less than 0.000066 seconds each time.
>I'm pretty sure the contactors takes longer than that to close.

How about having a large SCR in the bypass system? Instead of just the
bypass contactor, if a large SCR were placed across the bypass contactor,
the contactor would then not have to 'make' pack voltage at full current.
ie: Close the secondary contactors, when the light goes green, trigger the
SCR for instant - on, and then the bypass contactor closes to short the
SCR. This way the bypass contactor is only closing with less that a volt
(whatever the SCR forward voltage is at 1000A+). 

The shorting of the SCR should turn it off (unless the voltage drop across
the contactor is high). Otherwise the secondary contactors would need to
drop out to turn the SCR off.

Feel free to flame me, I don't know if this will make a difference (perhaps
1/100 sec - get a 15.005 down to 14.995?)

This is all a tad academic for me, since I'll not be racing with what I'm
building.

James Massey