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Re: (ET) E 20 - charger hum kinda

Regarding runaway Elec-traks due to stuck contactors:

Wait a sec....
If you have an E20 type tractor, there are two contactors (1F,1R or 2F,2R) that need to be energized in order to move. If you were to jam one and hit the brake, pop the seat, or turn off the key the tractor will stop. End of story.
If one jammed you would find out fast the next time you went into reverse, so it's doubtful you would jam one, then a few days later jam the other one.
If both contactors really jammed on, then you turn off the key. This will drop FR and power to the field. Motor will at best crawl slowly. 1A,2A,3A will also drop, leaving you with a tractor in speed 1 (all resistors in series with the armature)
I can see this being a problem if you have an electric car conversion that consists of one contactor straight to the motor or something stupid like that. But this is an Elec-trak, and they have a lot of points of failure. I think it's safe to say that the Elec-trak doesn't really *want* to run anyway. :-) 

Chris




...Walt
Erie PA

-----Original Message-----
From: elec-trak-bounces cosmos phy tufts edu
[mailto:elec-trak-bounces cosmos phy tufts edu]On Behalf Of matt
Sent: Tuesday, June 06, 2006 8:19 AM
To: elec-trak cosmos phy tufts edu
Subject: Re: (ET) E 20 - charger hum kinda


At 10:54 AM 6/5/06 -0400, you wrote:


In case a contactor sticks and you can't stop the tractor!
When I first started really getting into EVs almost 20 years ago, I heard about a '70s vintage EV hobbyist who decided he had to try out his not-quite- finished conversion before having any kind of emergency disconnect in place. The controller failed and the motor went full on! He was careening down the road, braking with all his might, to no avail.
Fortunately he had a couple of batteries loose on the front floor of the car, and his tools on the seat beside him. He was finally able to stop the car by beating a battery post with a hammer until it broke off. 


Brings to songs to mind, " HOT ROD LINCON, LITTLE NASH RAMBLER"
Matthew P. Magda Jr.

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Elec-trak cosmos phy tufts edu
https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak