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

["Roger Stockton" <rstockton@delta-q.com>]

Hi Rich,

OK, I'll quit poking fun at your Albrights ;^>

If, as you state, the FETs are full-on the whole time the bypass
is closed, then it shouldn't be getting very hammered by the
rupture event, although as Joe Smalley points out, the FET's might
take a beating should you ever open the bypass while it is carrying
really high current...

It seems that only two things will limit the rate at which the
controllers ramp up to full current, one is motor inductance/back EMF,
the other is the controller software forcing the current limit to
slowly rise fro a low value to its full rating.  If limited by the
motor(s), then the FETs might be full on when the bypass closes, but
if the current is being limited by the motor then you wouldn't see
any significant increase at the instant the bypass closes and the
contactor won't be hammered by the make event.  If the controllers
are controlling the current ramp up, then the FETs are not full-on,
but are switching in current limit (albeit lower than the max rated
limit), so the contactor gets hammered when it closes. 

Otherwise, I'm still confused by your description of what is going
on when the bypass closes.  Each DCP is rated to current limit at
1200 battery amps, but you are seeing a peak of 1350A total with
them, and say that the current with them is even less once they
current limit??? In theory, once they ramp up to full output I
would have expected you to see near 2400A of total battery current
until the motors are spinning fast enough for the controllers to
come out of current limit.

'Course, if you can only get 1460A with a bypass, then that suggests
that is all the current you can force through the motors once your
pack sags under load, so the controllers would presumably be limited
to the same ~1500A instead of their full 2400A potential, but why
shouldn't they be able to force it through the motors upto just about
the same RPM as the bypass since the only advantage of the bypass
should be a somewhat lower voltage drop between the pack and motors
than the FETs achieve?

Madman has written in the past about his frustration with trying to
get Goldie's single 1200A controller to actually suck the full 1200A
from his single string of YTs, and while I don't know how close he has
got to that magic number I'm pretty sure he is doing considerably better
than the 675A peak [per controller] you're seeing... sure would be
interesting to hear his comments on this!

Cheers,

Roger.


-----Original Message-----
From: owner-ev@listproc.sjsu.edu [mailto:owner-ev@listproc.sjsu.edu] On
Behalf Of RichSJ@aol.com
Sent: August 31, 2001 10:51 AM
To: ev@listproc.sjsu.edu
Subject: RE: Rudman Was Right! (was Dualin'7s Smoked Controllers)

[snip]

The MOSFETs are switched on through the entire PWM cycle with no current

limit because there is little or no current flowing through them and my
foot 
is to the floor and the battery pack is still connected. The controller
is in 
parallel with the bypass and being commanded to provide maximum voltage
and 
current, but is actually doing little. The low resistance path is
through the 
bypass.

[snip]

By the time the bypass switches in the controller may not be in current
limit 
yet. It takes some time for the controller to ramp up to full throttle.
It 
may actually be at the point where each controller is trying to provide 
1200A. 

[snip]

On controllers alone, I see 1350 amps peak for the two controllers
together. 
On bypass I see a peak of 1460 amps at launch. Not a huge difference.
The 
huge difference is immediately after launch when the controllers current

limit and the bypass contactor doesn't.  As I said previously, I will 
probably run a delay before switching in the bypass. I think having some
back 
emf built up before switching will be easier on the contactor and my
tires.

BFN,

Rich Brown
San Jose, CA
Dualin'7      144V, 3200lbs and 14.990 in the 1/4 mile