Re: (ET) crash

["David Roden (Akron OH USA)" <roden ald net>]

On 8 Jun 2002 at 21:39, Neil Dennis wrote:

> The only safety is a neutral
> start (clutch must be depressed0 in the start circuit. 

The clutch is the safety feature, such as it is.  I guess they figure that 
should the contactor weld or otherwise stick on, you can always disengage 
the clutch to stop the tractor.  I can just imagine the scene:  "What are 
you doing still sitting on the tractor with the motor running?"  "The 
contactor's welded.  I'm waiting for the battery to go dead."

There's a legend in the on-road EV world about one of the old-timers.  
Unfotunately I've long since forgotten who it was.

In any case, it seems he was testing a new conversion, and hadn't 
installed 
very many of the civilized niceties yet.  His batteries were just sitting 
on 
the floorboards of the car, and -- note well -- he had no main contactor 
and 
no safety shutoff.

For whatever reason, the controller failed full-on (may have been one of 
the 
SCR controllers) and the car dug in, full-speed-ahead.  He knew he could 
push in the clutch, but that would mean overspeeding the motor and 
destroying it.  

Fortunately he had his toolbox in the car.  He grabbed a hammer and, still 
half-watching the road, bashed on a battery post until he broke it off.

Truth or myth?  I don't know, but it makes a pretty good cautionary tale.  
In an EV, you want a positive-acting emergency disconnect capable of 
interrupting the full fault current of the vehicle.


David Roden - Akron, Ohio, USA
1991 Solectria Force 144vac
1991 Ford Escort Green/EV 128vdc
1970 GE Elec-trak E15 36vdc
1974 Avco New Idea 36vdc
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