# Motor Over-Speed Control??



## Yabert (Feb 7, 2010)

It's a real risk.... that happen to me last week: http://www.diyelectriccar.com/forums/showthread.php/smart-fortwo-ev-high-power-version-51472p14.html


The Soliton controller can limit the motor rpm. You will need to install a prox sensor.


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## PeterH (Mar 20, 2009)

Wow... thanks for the reply and the link to your thread... sorry to hear about that disaster but I really appreciate the warning!


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## MalcolmB (Jun 10, 2008)

The Soliton has a tachometer input and you can set the max motor rpm, so you all you need is a suitable sensor.

Reading about Yabert's accident persuaded me to find a solution for my own twin motor setup. I'm just collecting the parts for a pair of rpm switches based around the LM2917 chip, which is a frequency to voltage converter. There are a few different variants of the same chip, but the one I plan to try is the LM2917N-8. It takes an AC input from a cheap magnetic pickup and produces an output of 50mA when the frequency reaches the set level. This level is determined by a capacitor/resistor pair. There are plenty of example circuits in the data sheet.

The pickup will be triggered by a six-tooth gear that I'm fitting to the motor tail shaft.

Couple of things I'm not clear about yet:
Will a simple magnetic pickup suffer too much interference in close proximity to an electric motor?

What's the best way of using the output from the chip? I was thinking of using it to close a relay that would put a resistor in parallel with the throttle, to limit the max. motor voltage to around 12V. (This is with an Alltrax controller, which produces a fairly linear voltage output).


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## PeterH (Mar 20, 2009)

Fortunately I'm at least 2 months away from trying to power anything up so I have time to deal with this issue.

I just downloaded an updated version of the Soliton Jr. manual and I'm re-reading the manual. I should have mentioned that I have purchased the Evnetics throttle for this build.

My current problem is just how to get a tach sensor on my Kostov motor. I don't have a tail end shaft to use. The tail end of the motor is covered by a large cooling fan. I pulled the fan to examine the end and the motor shaft is recessed in the motor end plate. The drive end of the motor will be buried in the adapter and coupler so I don't see any way to include a tach pickup sensor there. I really want a tach on this motor so I can use it with the Soliton Jr. software to help prevent any over speed condition.

Pete


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## Woodsmith (Jun 5, 2008)

Jimdear2 was suggesting to me that I could use a conventional aftermarket tacho with programmable shift light.
The activation of the shift light would interupt the controller and kill power to the motor.

I have yet to look into the easiest ways to cheaply and simply adapt one of those to work on a motor though.
I am thinking of a hall effect pick up but not sure how that would connect to the distributor pickup on the tacho.


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## Ektus (Feb 15, 2011)

PeterH: You could always place a sensor near the flywheel, using the gear there to actuate the sensor. You would have to check the tooth count and resulting frequency and use an appropriate sensor (fast enough) and probably a simple divider to get the frequency down to what your controller needs.



Regards
Ektus.


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## PeterH (Mar 20, 2009)

Placing a pickup of some sort inside the bell housing might turn out to be my only option. However, I've had the starter gear removed and the flywheel cut down a bit to lessen its weight.

My supplier just told me that he has a solution and is just waiting for some part. So I may not be in that bad of shape for a tach input as I thought.

I'll post the final result of this effort so that this thread eventually offers some sort of conclusion. 

Peter H.


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## piotrsko (Dec 9, 2007)

you didn't mention how new on the Kostov. mine has an optional sensor, perhaps Plamenator can get you an equivalent set-up. Otherwise just carefully tap the outer edge of the flywheel for a # 10 or less screw in 2 places equally spaced, choose screw to fit. on the other side, paint a pulley 1/2 white and use a optical sensor. if you are into hacking, take apart an old optical mouse and make a notch wheel to taste. Pertronics makes a universal hall effect ignition sensor to replace points in 70's era cars that will drive about 40 watts.

I can go on, but you ought to see a pattern here.


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## PeterH (Mar 20, 2009)

My Kostov is new... only got it last month. I'm hoping my supplier is waiting for the optional sensor you mentioned. How does it attach to your motor?


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## Qer (May 7, 2008)

MalcolmB said:


> What's the best way of using the output from the chip? I was thinking of using it to close a relay that would put a resistor in parallel with the throttle, to limit the max. motor voltage to around 12V. (This is with an Alltrax controller, which produces a fairly linear voltage output).


Why give the motor any power at all if you have an overspeed situation? If I were you I'd just cut power completely since the motor is running outside it's useful (and safe) parameters.


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## MalcolmB (Jun 10, 2008)

Thanks Qer, that makes sense for most applications. Mine's a little different though as I'm using two motors with independent drive to each front wheel. One scenario is that one of the drive chains could break. I would still have drive through one wheel, so it could be useful from a safety point of view to have enough speed to limp off the road.


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