# Overspeed, motor run away



## major (Apr 4, 2008)

DONEAL said:


> What is the cause of the motor (Over speed) run away?


Hi DONEAL,

The most common causes of motor overspeed are running down hill or towing when in too low of gear, down shifting at too high a mph or applying a high voltage to an unloaded series motor.




> Do you not use a contactor?


Well, you always have the contactor there. But in normal driving, one should have a RPM sensor on the motor which is fed back to the motor controller thru the appropriate circuit which will shut down the motor controller when the RPM limit is reached. This will only save the motor in driving conditions, like spending too long in first gear or missing a gear when shifting and pushing down the throttle while in neutral. It will not protect against downhill or towing overspeed. You could put on some type of alarm to warn you in those events.




> In the event of a run away doesnt the contactors disengage


Unlikely, unless you have designed it and wired it that way. Most use the controller, not contactors to shut down the motor power when you reach max RPM. The contactor should be used if there is a malfunction in the motor controller and it cannot be turned off normally.

Hope that helps,

major


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## dtbaker (Jan 5, 2008)

DONEAL said:


> Do you think I still need another type of disconnect?
> In the event of a run away doesnt the contactors disengage?


exactly.... although unlikely, it seems that contactors can and do occasionally weld themselves closed; in that case you really want to have a MANUAL circuit breaker or manually triggered Anderson Disconnect to physically break the circuit.

As far as I can tell the overspeed thing is generally from lack of shifting, downshifting at too high a speed, or overspeed down a hill. High voltage at no load might happen if you are pulling up a hill and the transmission adaptor/clutch fails and motors spins free for a couple seconds before you notice.


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## DONEAL (Sep 10, 2008)

Thanks, I have the Anderson disconnects, but no way to operate it from the cab. This will be something I will need to work on. I’m also working on a tachometer sensor for the tail shaft of the motor. I’m about 90% complete on my s-10 conversion. I have to purchase the batteries yet and build the battery box for them.
Do you know anything about the following post? I can’t post a reply on this page to ask bill.
 I have the same controller and can’t find anything in the literature that came with it about a ceramic resistor
<begin copy/paste>
*[EVDL] Curtis Precharge Resistor* 
​I have been using a 820 ohm 25 watt rectangular ceramic resistor with my Curtis 1231 for the past three years without any problems, cross my fingers on both hands and toes on both feet  now that I said it.
Menlo Park III,
Bill


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## chamilun (Jun 17, 2008)

your two contactor setup is safer from overspeed. if taking your foot off the pedal is not effective, you can turn the key off. many people are using one contactor, which is a bit less safe.


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## dtbaker (Jan 5, 2008)

DONEAL said:


> Thanks, I have the Anderson disconnects, but no way to operate it from the cab.


people typically use a choke cable with pull from inside cab.... I haven't seen any details on bracket for Anderson, but there are probably some floating around.


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## elevatorguy (Jul 26, 2007)

DONEAL said:


> Thanks, I have the Anderson disconnects, but no way to operate it from the cab. This will be something I will need to work on. I’m also working on a tachometer sensor for the tail shaft of the motor. I’m about 90% complete on my s-10 conversion. I have to purchase the batteries yet and build the battery box for them.
> Do you know anything about the following post? I can’t post a reply on this page to ask bill.
> I have the same controller and can’t find anything in the literature that came with it about a ceramic resistor
> <begin copy/paste>
> ...


I believe Bill is refering to the precharge resistor that would go across the main contactor contacts, maybe one on each of yours, not sure how you are wiring your vehicle. It can be ceramic or a sand filled resistor.
There are handles that bolt to the Anderson connectors that you would attach a cable to and bolt the other half to a fixed bracket.


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## e_canuck (May 8, 2008)

chamilun said:


> your two contactor setup is safer from overspeed. if taking your foot off the pedal is not effective, you can turn the key off. many people are using one contactor, which is a bit less safe.


Hi.

Do not forget that turning the key off while driving can cause the steering wheel to lock. A dangerous thing.

DP


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## chamilun (Jun 17, 2008)

that would be if you turn the key all the way off. turning to 'acc' position would disengage the contactor (unless both have failed, which would be very strange indeed) and leave the steering well fine.

i assume you have a one contactor setup?


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