# Motor Runaway/Overrev stopper systems - How To



## Jimdear2 (Oct 12, 2008)

This is a subject that really needs to be covered.

The motor and controller builders (except Zilla to my limited knowledge) have kind of left this out of the standard features (what few there are) of their products.

We are left with no real positive solution.

What I would like to see here is real both real world operating systems with schematics and suggestions and some brainstorming. 

Please preface each resposnse with real or proposed system.

I'll start off with a discription of a real working system for my pulling tractor and later I'll post a few proposed systems that use the EV existing tach or even one for those without tachometers.


REAL,




My current system consists of:
A 5 inch racing tachomter with settable shift light, $50.00 new off Ebay
A proximity sensor. $11.00
A homemade four pulse reluctor for the proximity sensor N/C
A home made adapter board with relay with a NC and NO contact installed (I'll explain the purpose of the adapter board later) $15.00 to $40.00 depending on scrounging abilities
Necessary metal strap, hardware, wire and connectors $5.00
Also used
A suitable main High Voltage contactor. Mine is an Albright SD200 combination contactor disconnect
A D&D motor
A Altrax 7245 controller
A brief description of operation
An absloute maximum RPM is programed into the Tachometer shift light perminant memory.
My four pulse per motor rpm reluctor mimics the signal of a V8 ICE so the tach cylinder selector is set to V8

During normal operation the normally closed (NC) contacts of the relay carries the Key On current to the main contactor.
The runaway relay operating coil circuit is connected to the tachometer shift light output
The runaway relay coil circuit is also set to seal (latch) in the the normally open (NO) position once the runaway relay is activated.
When the motor attempts to runaway or overrev the tachometer shift light circuit is activated and triggers the coil of the runaway relay.
This opens the NC contact (causing the main contactor to open) and closes the NO contacts.
These NO contacts now power the runaway relay coil and seal (latch) it in this position until the Key On power is removed to reset the system.
This particular setup is going to positivly shutdown power to the controller because of the type of use (Tractor pulling). Later I will build a second system that will allow separation of runaway and overrev.

The relay adapter board:
Different tachometers use different voltages to activate the shift light. This board allows use of this system with tach light output voltages from 2 volts to 14 or so volts.

There have been some minor changes (Prox switch and relay adapter board) since I last updated my wiring diagram but the function is the same.


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## DIYguy (Sep 18, 2008)

Real;
As mentioned on another thread, I had an over rev limit designed into my Electrocraft controller. It is set-able in firmware. An inductive proximity sensor is used to generate two pulses per motor rotation.

Proposed;
There is some discussion elsewhere of the inability to control over rev when not driven by the controller...such as coasting in too low of a gear. It would be very possible to have a centrifugally (sp?) actuated motor brake. Just as centrifugal clutches are made to engage at specific RPM, the brake would be a different application of the same technology. I think it would be very straight fwd to make/adapt. One negative may be giving up your aux shaft if you have another use for it... or having one in the first place.

just a thought......


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## Jimdear2 (Oct 12, 2008)

DIYguy said:


> Real;
> As mentioned on another thread, I had an over rev limit designed into my Electrocraft controller. It is set-able in firmware. An inductive proximity sensor is used to generate two pulses per motor rotation.


How are / what are you using to supply the RPM signal to the controller.



DIYguy said:


> Proposed;
> There is some discussion elsewhere of the inability to control over rev when not driven by the controller...such as coasting in too low of a gear. It would be very possible to have a centrifugally (sp?) actuated motor brake. Just as centrifugal clutches are made to engage at specific RPM, the brake would be a different application of the same technology. I think it would be very straight fwd to make/adapt. One negative may be giving up your aux shaft if you have another use for it... or having one in the first place.
> 
> just a thought......


Wow 
This is much simpler then the disc brake, hydraulic pump/motor and rpm switching and control I was thinking of proposing. you could pretty much adapt an existing clutch unit ny mounting the hub with shoes and springs to the tailshaft (if you have one) and the shell to a torque arm attached to the frame or motor mounts. I think I would want to fan cool it though.

Proposal for a hill brake
DIYguy's proposal above suggested this idea. 

Attach a self actuating electric trailer brake backing plate to the motor shell and/or motor mounting and the drum to the tail shaft (again if you have one) use a variable pot or even a standard trailer brake contoller to power the actuation magnet.

These are ideas that could also be simply engineered into existing motors with very little cost.

*Motor Builders ATTENTION;*
I think anyone living in a hilly area using series motor would want one. Put together a package.


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## DIYguy (Sep 18, 2008)

Jimdear2 said:


> How are / what are you using to supply the RPM signal to the controller.
> Im using an industrial inductive proximity sensor. It works on 10 - 30 vdc. It much more robust than a reed switch. I have some pics in my thread. I actually shot a video testing it...but it was too big to upload,... i have to try again.
> 
> 
> ...


I was just thinking of attaching the shell of the clutch to the motor case.

My motor actually had a brake on the aux shaft and I was thinking of using it for a parking brake/rev limiter. 
I decided to put regen on though, and mounted an electric clutch. This clutch is mounted on the motor and the pully remains still unless engaged by the electromagnet. This will drive a rewired, high output alternator. This unit will be more than enough to slow the motor. The fellow I have been talking with who did this, said it will skid the rear wheels when in second gear at higher rpm. I plan to use a momentary button on the stick shift (considered brake pedal switch...decided against it). I could also drive this circuit with the over rev protect if I wanted... to acheive a similar effect more "automatically".
I'll even get a bit of energy back!


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## Jimdear2 (Oct 12, 2008)

DIYguy said:


> I was just thinking of attaching the shell of the clutch to the motor case.
> 
> My motor actually had a brake on the aux shaft and I was thinking of using it for a parking brake/rev limiter.
> I decided to put regen on though, and mounted an electric clutch. This clutch is mounted on the motor and the pully remains still unless engaged by the electromagnet. This will drive a rewired, high output alternator. This unit will be more than enough to slow the motor. The fellow I have been talking with who did this, said it will skid the rear wheels when in second gear at higher rpm. I plan to use a momentary button on the stick shift (considered brake pedal switch...decided against it). I could also drive this circuit with the over rev protect if I wanted... to acheive a similar effect more "automatically".
> I'll even get a bit of energy back!


I went to the same Prox Switch set up that you did, except mounted at the other end of the motor. No tail shaft but the shaft was drilled and tapped for the Hall Sender magnet. I gave up on the expensive Hall sender shown in my diagram when I think I damaged it. the Prox Switch is cheaper and easier to set up.

I've seen that brake on hi-lo pump motors. I think maybe it is used to stop the motor fast to reverse the motor to reverse the fluid flow. Probably cheaper then valving. Also on drive motors, must be the only brake for the hi-lo 

Is the field of your alternator going to be adjustible. 

Reason I ask is I was talking to a brake systems engineer at a meeting recently and he said the the prototype systems they are testing use a variable field to set the level of the regen brakeing effect. They set it light effect for highway and medium to heavy for in town. Regen braking comes in gradually after you release the throttle. I didn't have time to ask what they did when the batteries were at 100% SOC. They are working on intigrating regen seamlessly into the overall brakeing picture.

Just some ideas for you and others going for regen to think about


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## DIYguy (Sep 18, 2008)

Jimdear2 said:


> I went to the same Prox Switch set up that you did, except mounted at the other end of the motor. No tail shaft but the shaft was drilled and tapped for the Hall Sender magnet. I gave up on the expensive Hall sender shown in my diagram when I think I damaged it. the Prox Switch is cheaper and easier to set up.
> I originally had my prox mounted on the aux shaft end. I moved it mainly because of the electric clutch. I could have made it work but I think it would have been a bit hokey. The pic I posted here, is actually on the drive end. see below, you can see the mount bracket. The collar that the screws are set into sits just behind my taper lock and serves dual purpose as it takes up all of the unused shaft length. I have also heard the the electric clutch wreaks havock with the hall effect sensors.... I don't think the prox would be a prob...but it was an easy decision.
> 
> I thought Hall sender switches were very inexpensive??? The inductive prox I used is actually kind of pricey. What brand type is yours?
> ...


just learned something else....need at least 10 character answers....and it doesn't see the ones embedded in the quote...


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## Jimdear2 (Oct 12, 2008)

DIYguy said:


> just learned something else....need at least 10 character answers....and it doesn't see the ones embedded in the quote...


A suggestion. to break up a quote box into multiple statement and answers do the following. Use the "begin quote" statement 
_left square bracket _*the word *_quote equal sign right square bracket_ *no spaces*


> to begin a quote box and


 _left square bracket slash_ *the word* _quote right square bracket_ *no spaces* 
to end a quote box then insert your text then begin another quote box with


> the begin quote statement again to start capture the next block of quote and end it again with the end quote statement


Again add your text.

Continue until you are done with your answers.

Hope this helps


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## Coley (Jul 26, 2007)

A trailer self energizing brake would only be good for one direction of the motor. So if you only park facing up hill or down, it would work, one direction, but not both.


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## m38mike (Dec 27, 2008)

What I would like to see is essentially a programable relay switch. It would be placed inline between the 12v on/off power switch and the high voltage relay. It would take input from a magnetic pickup, like those used for magnetic tachs to determine motor rpm. It should be adjustable for 1-4 pulses per revolution. That would make it work with many different types of sensors/magnets combinations. It should be programable/adjustable for different rpms in 100 or 500 rpm increments. 

Upon reaching the target rpm the relay would open, shutting off power to the high-voltage relay, thus shutting off power to the controller and motor. It should be reset by turning off the 12v power and turning it back on.

This would not apply any break to the motor, but would cut off the power. I wonder what would happen with the power generated by the motor as it winds down to zero.


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## Jimdear2 (Oct 12, 2008)

m38mike said:


> What I would like to see is essentially a programable relay switch. It would be placed inline between the 12v on/off power switch and the high voltage relay. It would take input from a magnetic pickup, like those used for magnetic tachs to determine motor rpm. It should be adjustable for 1-4 pulses per revolution. That would make it work with many different types of sensors/magnets combinations. It should be programable/adjustable for different rpms in 100 or 500 rpm increments.
> 
> Upon reaching the target rpm the relay would open, shutting off power to the high-voltage relay, thus shutting off power to the controller and motor. It should be reset by turning off the 12v power and turning it back on.
> 
> This would not apply any break to the motor, but would cut off the power. I wonder what would happen with the power generated by the motor as it winds down to zero.


 
m38mike,

Look these over;

http://www.jegs.com/webapp/wcs/stor...ch&Ntx=mode+matchpartial&Dx=mode+matchpartial

these can be controlled by the Prox switch (see DIYguy's switch above) and if you subsitute this for the tach shift light signal (see my diagram) to operate the relay the way I have it wired it will work just like I discribe.

The MSD type switch require a plug in module for rpm limit then when the motor exceeds that limit it would trip the relay. Wired the way it is shown in my diagram to control the main contactor works. I've tried it. This would be a set it forget it setup.

Talk to Westach they may have a tach (even in 2 inch) with a setable shift light. I know I've seen them in 3 1/2 inch tachs.


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## OBeer-WAN-Kenobi (May 28, 2010)

Thanks for pointing me towards this thread Jim.

I've been thinking about two simple ideas I'd like to try first before moving on to these more complex solutions.

The first thing I'm going to try is a sinple centrifugal switch which I'll calibrate for the proper RPM. They're extremely cheap and shoulld be fairly reliable since they are used on motors all the time, albiet for a different purpose.

The second simple idea is just to put some cent.force actuated weights (ballanced of course) that are calibrated to an RPM and do nothing more than extend out to add load at the proper RPM. This seems to be the most fool proof to me. Add load and it won't run away.

On another note, does it matter that un my current project I'm running my moter at rated RPM and voltage? I mean, if it runs away, how much will it actually run? Is there a way to figure out what RPM a motor is actually capable of in a lost load situation? Especially one with an internal fan.


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## major (Apr 4, 2008)

OBeer-WAN-Kenobi said:


> On another note, does it matter that un my current project I'm running my moter at rated RPM and voltage? I mean, if it runs away, how much will it actually run? Is there a way to figure out what RPM a motor is actually capable of in a lost load situation? Especially one with an internal fan.


Hi Obeer,

It was the Prestolite MGT type motor, right? It is a series wound motor. You may run it at rated voltage (36V), but that does not mean it will run at rated speed. Unless you have a fixed load which never varies and that load is exactly "rated", then the RPM will be dictated by the load. More load, less RPM. Less load, higher RPM. And at no load, RPM tries to go to infinity. True, there is always internal load on the armature like the brush friction and windage including the fan. But this load will not prevent overspeed when the external load goes to zero and rated voltage is applied. Now "overspeed" may not explode the motor, but it might. It is very likely even if the motor held together, there would be distortion to the commutator which could be non repairable.

The safe thing to do is to plan for the worst. And if the motor loses load and power is not cut immediately, expect 33 copper bullets flying out of there at high speed. That is why race rules require a scatter shield or flak jacket around DC commutator motors.

major


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## OBeer-WAN-Kenobi (May 28, 2010)

Thanks major,
That's what I needed. On another note, I just checked both my hydraulic motor and the ICE. Both run CW when looking from the top. Whoo hoo!


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