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Electrical "Shoot through"

Number of messages: 11

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duodeluxe
New Hampshire, United States

We have an AC powered, transistorized truck that has an intermittent electrical shoot through. The truck will go into high speed in the forward direction and the only way to stop it is to disconnect the battery. Putting the truck in neutral or reverse won't stop it and braking it will only slow it down. It seems that something is shorting out the system causing full battery voltage to go directly to the drive motors. This is extremely intermittent problem. The truck went 9 months without it happening and then occured twice in 4 hours.

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gitrucks@adelphia.net

Posted 29 Jul 2008 10:12 PM

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FLTdotCOdotUK
Tyne & Wear, United Kingdom

Truck info?

Posted 1 Aug 2008 05:07 AM

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kevin_k
dumfriesshire, United Kingdom

no matter what the truck is . get it parked up before somebody gets hurt. please

Posted 1 Aug 2008 05:16 AM

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duodeluxe
New Hampshire, United States

It is a Still R20 and has bes been taken out of service.

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gitrucks@adelphia.net

Posted 1 Aug 2008 06:54 AM

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justinm
New York, United States

did you see the fault occur in front of you?
and do you have the laptop software?

-------------------------
New York, New York its a heluva town ..you know that The Bronx is up ..and im Brooklyn down

Posted 1 Aug 2008 12:50 AM

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edward_t
North Carolina, United States

and it seems to me, it would be considerably difficult for an A/C truck to wind up with "shoot through" causing full battery voltage like a DC truck (ala PMT) since the motors work considerably differently. I would greatly doubt the controller failure, and more expect this to be a problem between the operator presence pedal and the steering hand crank.
I would also doubt that "applying the brakes does not stop it only slows it down" unless you have found at least part of the problem; a (stuck/broken/shorted) brake switch.

Posted 1 Aug 2008 08:50 PM

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justinm
New York, United States

might be a bad controller
if you apply reverse input the the encoders are reading forward motion, to continue without shutting down defies programmed logic

but i wouldnt condemn it without looking at it on a laptop (since, most likely, its a few thousand dollars to replace )

-------------------------
New York, New York its a heluva town ..you know that The Bronx is up ..and im Brooklyn down

Posted 1 Aug 2008 09:44 PM

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justinm
New York, United States

double post

-------------------------
New York, New York its a heluva town ..you know that The Bronx is up ..and im Brooklyn down

Modified 1 Aug 2008 09:45 PM
by poster.

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elektrodrive
West Midlands, United Kingdom

From what you have stated that it shoots off, i would say whatever the fault, there must be a problem in the controller, as the fail safe circuit is not working. If a fault is detected in most modern controllers, it should either drop out the contactors or prevent the system from working. So it sounds like you have 2 faults one being the fault which is triggering the truck to shoot off and the other being the fail safe circuit not working. That can do some serious damage to someone get it looked at asap.

Posted 2 Aug 2008 03:24 AM

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FLTdotCOdotUK
Tyne & Wear, United Kingdom

Edward, I've actually seen this happen, just this week in fact, but on a BT reach truck, RRB14 - full AC, that was the reason I was asking for truck info.

The driver flew into some racking and he reported that the truck "just took off".

Tested it, checked error log book etc, etc, no fault found, truck running fine other than the fact that the electromagnetic brake would disengage as soon as you turned the key on, even before the K10 contactor closed, which I know people out there are gonna tell me is impossible and to be honest I wouldn't believe it if I hadn't seen it happen myself!

Then, and this is the really weird part, while it was on the jack, no seat switch made, no dead man pedal pressed and without even selecting direction the truck ran flat out when you pressed the brake pedal??!!!

Anyhow, to cut a long story short, yeh, yeh, to late I hear, the four small wires from the encoder bearing had become trapped and the blue and white wires were shorting together behind the drive motor terminal block.

Turns out they had a new terminal eye put on one of the cables a few weeks ago and the engineer who re-ended the cable must of trapped the encoder wiring behind the terminal block. Stuck a new encoder bearing on the motor and hey presto, job's a good 'un. I assume the short was asking the chopper board for full frequency but I still can't explain the fact that it ran without any safety features engaged or direction selected?

Design fault on the wiring harness?

Who knows?

No wiring diagram to check if there was a common rail between the encoder wires and all the safety features so I didn't take it any further.

Obviously not much help with your problem but it is food for thought I suppose, weird things that seem to defy all logic and common sense can and usually do happen.

Good luck.

Posted 2 Aug 2008 03:46 AM

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justinm
New York, United States

if the software detects a major failure or i/o discrepancy it should open the line contactor

some call it when a machine defies its own logic as the "ghost in the machine" or its attempt to exhibit free will lol
cant wait till these thing have their own AI
matrix here we come

yeah FT thats pretty nuts
you would think the control would pick up and encoder reading error at key on with no inputs from the control

bad design i guess?

-------------------------
New York, New York its a heluva town ..you know that The Bronx is up ..and im Brooklyn down

Modified 3 Aug 2008 06:27 AM
by poster.

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