# Protecting motor from overspeed damage?



## e_canuck (May 8, 2008)

Hi RKM.

I do not know about the Zilla. They have somekind of optionnal rpm thing doing on. I do not think it is for RPM limitation.

The Curtis does not. If it does, please somebody tell me.

I am still accumulating toys and inspecting cars with cancer and broken windshield.

I will want my daughter to drive it eventually. So I am in the same boat.

First line of defense, I am thinking of reinstating the original tachometer.

Then get, build, steal a frequency Meter. There are plenty enough on Ebay but I have sofar not found one with an alarm or somekind of preset value.

The initial plan is that when the motor RPM will reach that value, as set by me, the contactor will open. Killing the power to the motor.

Followed by, and I am still working that one, activation of a brake on the motor's tail shaft.

I know, I know. There are a lot of problems with that. At first sight.

I am thinking of a modified disk brake, the kind you see on some mountain bikes.
And an actuator to apply the brakes.

The whole thing waste energy, but save the motor.
The motor cutting out and braking will be a learning thing for the driver. If you are anoyed enough, you will avoid it.
The brake would rub a bit. But it has to be ajustable, we are talking about bike technology here.

And sometime S*** appens. I like the idea of somthing monitoring me.

Hope that help or stirr something ou there,

DP


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## judebert (Apr 16, 2008)

The thing you need -- and me too -- is an RPM Limiter. In other circles, it is frequently referred to as a Speed Switch. They can cost more than $100, but they're protecting a $1500+ motor! Definitely worth it.


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## e_canuck (May 8, 2008)

Hi judebert.

Do you know of a ready made system? Or can you expand on that?

DP


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## piotrsko (Dec 9, 2007)

couple of simple thoughts here: mechanical like adapting the advance system from an old distributor so that when the weights fly outwards they activate a switch for a kill button, or a a capaciitive PI filter on the input of an 741 op amp tapped from some part of the motor input


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## elevatorguy (Jul 26, 2007)

I have been giving this some thought as well as I won't be the only driver.
I plan on using a photo sensor or magnetic sensor to get pulses from the motor to drive a tachometer (leftover from ICE race days) that has a shift lamp. I will use the output from the shift light to drive a cutoff or throttle reduction setup to limit the motor. It is simple and adjustable, and I don't have to design too much. 
I wanted a tach on the motor anyway so this kills two birds with one stone.
I suppose I could go one step further and add the braking setup


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## mopargarage (Jul 2, 2008)

RKM said:


> I've read that an unloaded motor can/will overspeed and self destruct very very quickly.
> 
> Will some controllers protect against this happening (Zilla or Curtis)? I'd like for anybody to be able to drive my car when it is converted, without fear of accidentally blowing up the motor.
> 
> ...


If you are inclined/able to build your own, this chip (LM2907) can be wired as a speed switch. http://www.national.com/an/AN/AN-162.pdf


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## bblocher (Jul 30, 2008)

I have an example on my blog of building an rpm sensor for my motor. This can be used very easily with a BASIC stamp to monitor your RPMs and then you can disable the contactors and/or controller with the microcontroller. You can also then use this to send whatever digital pulse is required by your RPM gauge (if you have one or want to add one).


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## Astronomer (Aug 7, 2008)

If you plan to eliminate the clutch, as I do, then the biggest opportunity for the motor to free-wheel is between gears.

One thing I've considered doing is putting switches on the transmission that close a circuit only when the transmission is in gear (like the switch used to activate the reverse lights, but for all gears). That circuit would then be incorporated into the traction electronics so that when the transmission is in neutral, the motor will not get any power.

Although this won't limit RPMs when the car is in gear (which is still a danger), it will at least prevent someone else from blowing your motor (and grinding your transmission to dust) because he can't remember to take his foot off the accelerator between gears.

This certainly doesn't eliminate the need for an RPM limiter, but it will allow others to drive your EV more effectively and safely with minimal instruction, and without having to completely understand the mechanical theory of 
synchros, rotor mass and moment of inertia, or sinusoidal henways.

And for you racers out there, a neutral-kill-switch like this could allow for faster clutchless shifting, since you no longer need to choreograph your accelerator pedal machinations with your manual gear-shifting. Just keep the accelerator floored as you upshift, and your shifting speed will be limited only by the activity of the synchros.

Not that I would do that, mind you.


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## judebert (Apr 16, 2008)

@e_canuk: Yes, there are prebuilt systems available, as long as you've got a signal to provide them. I found several by Googling. I just haven't purchased one yet. I'm living on borrowed time.


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## bblocher (Jul 30, 2008)

Astronomer said:


> If you plan to eliminate the clutch, as I do, then the biggest opportunity for the motor to free-wheel is between gears.
> 
> One thing I've considered doing is putting switches on the transmission that close a circuit only when the transmission is in gear (like the switch used to activate the reverse lights, but for all gears). That circuit would then be incorporated into the traction electronics so that when the transmission is in neutral, the motor will not get any power.


That's a pretty cool idea. I don't know enough about transmissions to get in there and start adding sensors. The only problem I can see with the design is that in order to down shift won't you need to slightly rev the motor? I guess the syncros will eventually get it up to speed but seems it would be such a huge delay.


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## Wattmotion (Sep 10, 2008)

I have a friend that is using a K&W ENGINEERING _TD-100_ Tachometer Drive/Rev Limiter that he swears by as the best. It fails safe, has a pick up sensor to read keyways, fan blades, what ever and an output to a tach meter. I am told they no long make this unit and I would love to get my hands on one to reverse engineer and build for myself, or at least a similar circuit.


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## RKM (Jun 9, 2008)

I read that the DCP Raptor 600 amp controller featured a built in motor rev limiter. This information is from DriveEV.com. I understand that this controller is no longer being made.

I would have thought that this would be a standard feature for all controllers. An rpm input and programable max rpm should be simple enough.

Is someone here able to come up with a plug and play package for those of us without an EE degree?

Thanks for all the input.

Rob


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## OHM (Jun 30, 2008)

This is the biggest problem for us in Australia, controllers are not easily to deal with faults here. If your Ev stops you are out of luck for either a few weeks or more. I suppose it doesnt matter where you are its always a problem with DC systems.

Ive seen the electric 24 volt brakes on the back of many motors used for industry and wondering if its possible to somehow use them for this issue?


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## O'Zeeke (Mar 9, 2008)

bblocher said:


> I have an example on my blog of building an rpm sensor for my motor. This can be used very easily with a BASIC stamp to monitor your RPMs and then you can disable the contactors and/or controller with the microcontroller. You can also then use this to send whatever digital pulse is required by your RPM gauge (if you have one or want to add one).


Thanks Brian, thats a great car. Like you, trashing a good running ICE was the hardest part for me but done for very good reasons. I look forward to seeing your progress.


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## cupp747 (Aug 23, 2008)

_my raptor controller has a built in speed control that receives signal from zolex mag signal on front of motor. my tach gets its signal from the ac signal on the altenator that i use as regen braking._
_my previous research showed ignition boxes for ice using the tach shift light signal and zolex pick-up would work . zolex has 4 signals per rev. _
_using an altenator that has output that can be switched on with bat input (main 12 v )can be activated on overspeed as the contactor is shut off for motor controller._
_this stops motor overspeed when disconnected from drivetrain._
_unless your regen is large enough it wont help in wrong gear down hill or system shuts down when batteries are fully charged. like when you live on on a hill and you are still half asleep in the morning._
_I also have safety switch activated by unused clutch pedal. uses cam over fixture clamp and truck starter contacts._


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## RKM (Jun 9, 2008)

e_canuck said:


> Hi RKM.
> 
> I do not know about the Zilla. They have somekind of optionnal rpm thing doing on. I do not think it is for RPM limitation.
> 
> ...


 
E_Canuck

I like the idea for a signal to open the contactor at a preset rpm. I would have hoped this function would have been incorporated into the design of the controller. Do you think an active brake would be necessary. I would hope that once current stops, the motor would freewheel to a stop. It shouldn't continue to overspeed to destruction should it? Maybe I'm missing something.

I have a daughter who will be a new driver this coming year. I'm hoping that she will be able to be the first in Manitoba, perhaps Canada to take her driver's test in an EV conversion!

Rob


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## bblocher (Jul 30, 2008)

RKM said:


> E_Canuck
> I like the idea for a signal to open the contactor at a preset rpm. I would have hoped this function would have been incorporated into the design of the controller. Do you think an active brake would be necessary. I would hope that once current stops, the motor would freewheel to a stop. It shouldn't continue to overspeed to destruction should it? Maybe I'm missing something.


I've been tossing the phyics of this around in my head well before this post and I'd have to agree. Once you stop applying an outside force it can't continue to accelerate. However, the delay in your reading/calculation of the RPM of the motor and the time to cut the power could be significant. You would want to make sure you are sampling the RPM as fast as possible (if you're using some type of microcontroller idea) so you can react quickly. If it was a mechanical solution then the RPM cutoff will not be exact each time. So the real question is how many seconds or even fractions of a second does it take to do damage once you reached the redline of the motor. Just to play it safe I will probably set my FB1-4001 to something like 6500-7000 cutoff (I think I read somewhere 7500 is max?, anybody know for sure?). I've seen some performance graphs just above 8k but since the efficiency point of this motor is 4,500 I don't see much point in having a limiter too significantly high anyway since the performance and efficiency starts dropping off quickly at those points.



RKM said:


> E_Canuck
> I have a daughter who will be a new driver this coming year. I'm hoping that she will be able to be the first in Manitoba, perhaps Canada to take her driver's test in an EV conversion!
> 
> Rob


That would be really cool!


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## e_canuck (May 8, 2008)

RKM said:


> Do you think an active brake would be necessary. I would hope that once current stops, the motor would freewheel to a stop. It shouldn't continue to overspeed to destruction should it? Maybe I'm missing something.
> 
> Rob


Normally once the power is off the motor as to slow down. But if the motor is in gear and you are going downlhill, even with no power the gears will accelerate the motor. That's why I would like to have an "engine brake". Wastefull of coasting energy but I think worth considering.

DP


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## RKM (Jun 9, 2008)

bblocher said:


> I've been tossing the phyics of this around in my head well before this post and I'd have to agree. Once you stop applying an outside force it can't continue to accelerate. However, the delay in your reading/calculation of the RPM of the motor and the time to cut the power could be significant. You would want to make sure you are sampling the RPM as fast as possible (if you're using some type of microcontroller idea) so you can react quickly. If it was a mechanical solution then the RPM cutoff will not be exact each time. So the real question is how many seconds or even fractions of a second does it take to do damage once you reached the redline of the motor. Just to play it safe I will probably set my FB1-4001 to something like 6500-7000 cutoff (I think I read somewhere 7500 is max?, anybody know for sure?). I've seen some performance graphs just above 8k but since the efficiency point of this motor is 4,500 I don't see much point in having a limiter too significantly high anyway since the performance and efficiency starts dropping off quickly at those points.
> 
> Brian,
> 
> ...


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## bblocher (Jul 30, 2008)

e_canuck said:


> Normally once the power is off the motor as to slow down. But if the motor is in gear and you are going downlhill, even with no power the gears will accelerate the motor. That's why I would like to have an "engine brake". Wastefull of coasting energy but I think worth considering.
> 
> DP


Yeah I forgot about that side of things. It's really not that easy to take into account all levels of crappy drivers. Now I can see what auto manufactures have to go through.

You can use the motor as the break by shorting across the terminals with resistance. However, I don't think the bigger series wound like it much. Some of the controllers ,I think Kelley is one, have this built but really not sure which motors it is ok to use it with.


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## RKM (Jun 9, 2008)

e_canuck said:


> Normally once the power is off the motor as to slow down. But if the motor is in gear and you are going downlhill, even with no power the gears will accelerate the motor. That's why I would like to have an "engine brake". Wastefull of coasting energy but I think worth considering.
> 
> DP


DP,

I take your point. I've heard about hills, but have never seen one here in Manitoba. So long as the driver is aware of the hazard of this situation, the car brakes can be applied or the stick could be popped into neutral.

I'd speculate that it would take a massive single caliper and disc to effectively slow a vehicle on a steep hill. The caliper would need to be well anchored and the torque through the motor shaft may well be excessive and cause damage. I don't mean to be critical and may be way off wrt the forces involved. These are my thoughts.

Rob


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## bblocher (Jul 30, 2008)

RKM said:


> Your conversion is most impressive, Brian. Did it hurt just a bit to abort the wonderful engine in your S2000?
> 
> Rob


I love that car, but was actually ready to sell it and find some much more economical. I spend $200-$300 a month on gas, it varies as the gas prices change. So I was debating putting money down on an Aptera, the next gen Prius...something. Then I started thinking of how much cheaper it would be to just convert my car. It wasn't easy to start but once I got going on the project the better I felt. It's been a blast looking for weight to shave off, reversing engineering the electronics of the car to figure out how I can integrate components, etc. One of the hardest things is not tearing it apart, it's waiting to drive it converted!


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## Wattmotion (Sep 10, 2008)

bblocher said:


> I've been tossing the phyics of this around in my head well before this post and I'd have to agree. Once you stop applying an outside force it can't continue to accelerate. However, the delay in your reading/calculation of the RPM of the motor and the time to cut the power could be significant. You would want to make sure you are sampling the RPM as fast as possible (if you're using some type of microcontroller idea) so you can react quickly. If it was a mechanical solution then the RPM cutoff will not be exact each time. So the real question is how many seconds or even fractions of a second does it take to do damage once you reached the redline of the motor. Just to play it safe I will probably set my FB1-4001 to something like 6500-7000 cutoff (I think I read somewhere 7500 is max?, anybody know for sure?). I've seen some performance graphs just above 8k but since the efficiency point of this motor is 4,500 I don't see much point in having a limiter too significantly high anyway since the performance and efficiency starts dropping off quickly at those points.
> That would be really cool!


Brian, 
I see you mentioned programming a Basic Stamp to provide a speed cutout. I am looking at using an on board industrial computer (PLC) with a high speed input to do the same. It would protect the motor from overspeed by dropping the drive enable. But like other have said, if the motor is still in gear running down a hill, not much you can do. We have flat land here and I am worried about a family member racing the motor into pieces. I will probably flash a screen on the dash to disenage the tranmission if it detects high revs and the drive is disabled. You idea of a basic stamp could incorporate all of those ideas in one unit.


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## bblocher (Jul 30, 2008)

Wattmotion said:


> Brian,
> I see you mentioned programming a Basic Stamp to provide a speed cutout. I am looking at using an on board industrial computer (PLC) with a high speed input to do the same. It would protect the motor from overspeed by dropping the drive enable. But like other have said, if the motor is still in gear running down a hill, not much you can do. We have flat land here and I am worried about a family member racing the motor into pieces. I will probably flash a screen on the dash to disenage the tranmission if it detects high revs and the drive is disabled. You idea of a basic stamp could incorporate all of those ideas in one unit.


Yeah microcontrollers can be really powerful for these types of applications. Even if somebody decided to build some type of mechnical engine break the microcontroller could be used to engage that system as well.

For those interested I got this kit when I started messing with them. http://www.parallax.com/Store/Micro...ortField/0/Level/a/ProductID/297/Default.aspx
It's really great for prototyping ideas before you build a circuit. Parallax has a ton of other great things and most of the electronics items you've seen in my blog were purchased from them. Most often they will even give you code to show how to integrate an item you buy from them with one of their micro controllers. The BASIC Stamp is by far the easiest one to use, but not the most powerful. I may move to the Javalin controller for the final project because it's capable of doing many things at the same time (parallel processing). So for example I can be reading my RPM signals and reacting to those at the exact same time I'm monitoring battery voltages, amps and other little tasks without taking away processing time from critical tasks. The Javalin is a much more advanced chip though so it's not the place to begin learning.


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## elevatorguy (Jul 26, 2007)

Some type of hysteresis will be needed in your control circuit or your main contactor will pop in and out if the driver leaves a foot on the accelerator.
Probably not good for the contactor or controller, cycling at full power


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## bblocher (Jul 30, 2008)

elevatorguy said:


> Some type of hysteresis will be needed in your control circuit or your main contactor will pop in and out if the driver leaves a foot on the accelerator.
> Probably not good for the contactor or controller, cycling at full power


Yes good point, my S2000 used to do something which actually was really dangerous but would work well for electric motors.

Once you hit 9,000 RPMs the rev limiter would kick it but would stay engaged until the car went down considerably. I can't remember exactly but it was somewhere between 5-7k RPM. For this engine in first and second gear it was like grabbing the ebrake and would throw you into the dash and if you were turning at all...you're done. I wipped out once really good from that stupid thing.

Anyways, the electric motor not having all that resistance will be fine and then you could safely enable the motor again at some configured value (say 5,000 rpms, more or less if you like).


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## Wattmotion (Sep 10, 2008)

I would write the program to enable an external relay if a high rev was detected dropping the drive enable and after a slight delay, the contactor would open to lessen arcing. After the motor revs. dropped to a very low level, say 2000 RPM the drive could be turned back on. What ever scheme you wish the computer to protect the drive could be programmed into the unit. In fact as you approach a dangerous RPM, the unit would flash a warning at you to decrease RPM or drive will be disabled.


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## mark1030 (Jul 28, 2008)

I haven't really researched this yet, but my first instinct is you guys are over-complicating the solution. I did a google search for 'centrifugal switch' and one of the first places I tried had a product that would probably work, especially if you have a backside shaft on your motor. Check out http://www.baumerhuebner.com/drehzahlschalter.html?&L=1. With a little bit of research you might find a product that's the right price and availability to disengage the throttle or contactor when your motor hit a certain RPM. I'm trying to use an AC motor so this is an academic exercise for me, but it might give you some ideas.


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## Tom Thomson (Jun 11, 2008)

Has anyone personally ever blown a motor or seen it happen? I'm not convinced that it's a problem.
tommyt


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## elevatorguy (Jul 26, 2007)

Tom Thomson said:


> Has anyone personally ever blown a motor or seen it happen? I'm not convinced that it's a problem.
> tommyt


Check Jim Husted site for pictures, they will fly apart. I for one would rather put some type of limiting and never use it than take the chance of destroying a expensive motor.
One characteristic of a series wound motor is that it will increase speed without a load until something fails. If I was the only driver I would not be concerned, but if you take your car in for tires or some service and the unaware person hits the accelerator out of gear it could be all over. 
My motor documentation addresses the rpm limits of the motor, so there must be a reason to limit the rpm.
Since I won't be the only driver, I am going to make it almost foolproof


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## judebert (Apr 16, 2008)

Tom Thomson said:


> Has anyone personally ever blown a motor or seen it happen? I'm not convinced that it's a problem.
> tommyt


Yup. Although Jim Husted was more than fair (practically over-accommodating), it's still an expensive repair.

For lack of a nail...


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## Tom Thomson (Jun 11, 2008)

Jerry
What kind of motor do you have? My D&D came with no userdoc whatever.
tommyt


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## elevatorguy (Jul 26, 2007)

Tom Thomson said:


> Jerry
> What kind of motor do you have? My D&D came with no userdoc whatever.
> tommyt


I bought the Warp 9 motor. 
To paraphrase, they stated the commutators withstood testing to 8000, can take 5000 for short intervals but recommend 3500 as a safe rpm.


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## OHM (Jun 30, 2008)

judebert said:


> Yup. Although Jim Husted was more than fair (practically over-accommodating), it's still an expensive repair.
> 
> For lack of a nail...


In most cases its not a repair but replacement.

Even DC motor controllers with over-speed or rev limiters are prone to this dilemma. When they fail the motor will go up in revs till something goes or if you are lucky enough to shut down power. 
A documented case was lucky enough that in gear going up a big hill noticed the his controller with inbuilt rev limiter start smelling and cook but had enough time to hit the power off.

I dont see anyone wanting to be worried about shutting down power every second on a non-direct drive setup. Id rather focus on my driving and enjoy the experience than be worried about going to the main switch. Also breakdowns dont encourage EV signups.

Imagine it happens while reversing or slowing down at an intersection.
Even if your multitasking skills kick in while watching pedestrians and everything around you, you will still be left stranded if unlucky in front of a non PRO-EV audience.

The embarrassment will pass but the potential damage to EV reputation wont. Why risk it when a couple of bucks more you could have peace of mind?


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## elevatorguy (Jul 26, 2007)

I am going to use both a rev limiter and a disconnect 
I hope I never use either


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## judebert (Apr 16, 2008)

OHM said:


> In most cases its not a repair but replacement.


Absolutely! That's why it's so expensive. My "repair" involved a complete replacement of the commutator and rotor, with a rewrap and bake of the stator coils.

I was desperately wishing I had spent the extra couple of hundred for a rev limiter.

OHM, it sounds like you're saying we need something besides a rev limiter, either standalone or built-in to the controller. Were you thinking of something specific?


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## OHM (Jun 30, 2008)

judebert said:


> OHM, it sounds like you're saying we need something besides a rev limiter, either standalone or built-in to the controller.


No just stand alone I think in case controller gives up the ghost and it cant control that inbuilt function (if its an inbuilt function).

I would like to see from the experts if a separate ECU would be better for controllers of the future. Heating seems to be an issue with the all in one
box and Toyota tackled this by packaging the ECU separately which also runs all the other bits eg gauges, rev limiter, lights and the rest.


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