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I m at a design stage where im looking at my instrument cluster and deciding where and how best to attach my volt meter display and ammeter display.

The space taken up by the tachometer would fit both of these instruments nicely, but do I need it?

Do I really need it?
I have seen some opinions on the use of it as a way of detecting an over speed on the motor but does the instrument provide any more crucial information than would the instruments i want to replace it with?

Hope to hear peoples input,

Thanks

Roy
 

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I m at a design stage where im looking at my instrument cluster and deciding where and how best to attach my volt meter display and ammeter display.

The space taken up by the tachometer would fit both of these instruments nicely, but do I need it?

Do I really need it?
I have seen some opinions on the use of it as a way of detecting an over speed on the motor but does the instrument provide any more crucial information than would the instruments i want to replace it with?

Hope to hear peoples input,

Thanks

Roy

I used a pillar-mount holding 3 gauges (volts, amps, battery SOC).... mostly because I didn't want to mess around under the dash. I do not HAVE a tach, but would recommend doing the math to calculate your 'redlines' for each gear, and mark them on the speedo.

http://envirokarma.org/ev/13.Instruments.shtml

I was considering using the location of the gas and water temp gauges, but really really really don't like taking apart dashboards...
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Knowing your RPM's is real important but many don't know. Below is why you should know the limits of your motor and keep it within those limits.

Pete : )

This is what happens when a motor pukes it's guts from over reving : (
 

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Poor, poor motor... :(

So would a Tachometer or a heat sensor be more useful for an over-revving engine? Does most of the damage come from the heat(and weakening of the components due to temp) or the actual shearing force-which usually comes first?
 

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I think knowing the rpm in an EV is essential, it allows you to get your gearing right and keep the RPM band correct for either power or economy as needed, you also get to find the "sweet" spots on the RPM band to minimise your current use thus maximising your range, and you can keep the motor from exceeding it's max. design speed. Remember, you'll get no noise from the motor like in an ICE to guage the approximate RPM by ear!!

So keep the Tach, you'll be glad you did, you'll find somewhere convenient to put the other meters!

Paul
 
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It is also very important that, no matter the voltage, motor rpm do not exceed 5000-5300 (has been increased a bit in the newer models).
Calculate your vehicles max speed at 5000-5300rpm and do not exceed it.
This is from a company that builds electric motors!

Pete : )
 

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This is from a company that builds electric motors!

Pete : )
Pete,

I got similar warning info from my motor builder, but no suggestions on how to prevent it.

I'm going to start a new thread under Technical Discussions for people to list their runaway/overrev prevention sysyems. I have two I will list, we will see what the results are.
 
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Well one way is to keep your foot off that accelerator pedal or use a tach or know your gearing and rpms and speed in each gear and do not exceed or build into the controller a way to limit rpm at the high side but that still needs a tach or pickup installed so the computer can see the information. I'd rather see the information and just do it my self saving myself complex computer issues. It can be done. Just if you do not have a tach you need to know your final drive ratio and the ratio of your gears and tires so you know how fast you are going in any gear at any speed so you do not exceed your motors rpm rating. The reason is that if you do exceed that rating your motor will puke. If you do some upgrades to your motor like kevlar banding so you can increase your rpm's then you are in no mans land as to the actual limits the banding has helped. If you are willing to sacrifice a motor to science and want to band a motor and run it until it pukes and record the rpm results from banding we would all love to know. Or you might just ask Jim Husted or John Wayland about that. Maybe some others will pipe in on this subject.

Pete : )
 

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Well one way is to keep your foot off that accelerator pedal or use a tach or know your gearing and rpms and speed in each gear and do not exceed or build into the controller a way to limit rpm at the high side but that still needs a tach or pickup installed so the computer can see the information. I'd rather see the information and just do it my self saving myself complex computer issues. It can be done. Just if you do not have a tach you need to know your final drive ratio and the ratio of your gears and tires so you know how fast you are going in any gear at any speed so you do not exceed your motors rpm rating. The reason is that if you do exceed that rating your motor will puke. If you do some upgrades to your motor like kevlar banding so you can increase your rpm's then you are in no mans land as to the actual limits the banding has helped. If you are willing to sacrifice a motor to science and want to band a motor and run it until it pukes and record the rpm results from banding we would all love to know. Or you might just ask Jim Husted or John Wayland about that. Maybe some others will pipe in on this subject.

Pete : )
Pete,

I agree that keeping YOUR foot out of the pedal is fine when YOU are driving your EV.

But what happens when you put that friend in the drivers seat and they forget. What happens when your coupler breaks (I know it's not supposed to but things happen) while you are accelerating hard. What happens when you hit that slippery spot.

Something that will protect you in those situations where you have no control is worth a few bucks in parts and a bit of time.

Actually I think that the manufacturers and resellers should have addressed this a long time ago. But then maybe blown motors are a profit center for them.
 

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But what happens when you put that friend in the drivers seat and they forget. What happens when your coupler breaks (I know it's not supposed to but things happen) while you are accelerating hard. What happens when you hit that slippery spot.

Until electric motors come with a tach sensor built internally, the 'average' DIY conversion doesn't really have any way to build in over-rev governor to the controller. Anybody can break a motor (gas or electric) by putting it in neutral and flooring it until it flys apart....

I don't see any advange to installing an expensive Hall sensor to display exact motor rpm over putting a sticker on the speedo showing 'redline' in each gear if you don't also have a simple way of using the tach feedback to shut down the controller.
 

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Kelly controllers have the ability to set max RPM in the software, at least on the DC controllers. Shame they dont sell controllers big enough for the big series motors. I'd like to see other controller manufacturers taking heat and RPM protection into account.

Any reason why motor voltage cant be monitored and used to shut off controller if it exceeds the voltage required from max safe RPM's? I'd settle for a big red light on the dashboard!

On the subject of Kevlar, Cedric Lynch uses banding on his new AgniMotor (95 series). He seems happy that his motor is safe to 6000rpm now (I believe up from 4000rpm).
 

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Until electric motors come with a tach sensor built internally, the 'average' DIY conversion doesn't really have any way to build in over-rev governor to the controller. Anybody can break a motor (gas or electric) by putting it in neutral and flooring it until it flys apart.....
As I said previously Motor manufacturers need to address this. A tach/RPM sensor should be included into all motors. Controller designers need to incorperate this into new design controllers.

I don't see any advange to installing an expensive Hall sensor to display exact motor rpm over putting a sticker on the speedo showing 'redline' in each gear if you don't also have a simple way of using the tach feedback to shut down the controller.
You may not. Others might

I know for a fact that others who have replaced motors wish there had been something.

The crude system I'm using as described in the new thread I started in the Technical Discussions page cost me under a $100.00 including a 5 inch Tachometer.

Cheap insurance for a $1500.00 + motor.
 

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Any reason why motor voltage cant be monitored and used to shut off controller if it exceeds the voltage required from max safe RPM's?

overspeed COULD occur at very low voltages if there is no load.... I don't see how you could correlate rpm to voltage reliably.

AND>>>> even if there was a feedback loop from tach to controller, it still would NOT protect you against a stupid downshift or leaving the vehicle in low gear going down a steep hill. This could result in overspeed with NO voltage.

So, once again, a visual 'redline' is about all you can do.....
 

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overspeed COULD occur at very low voltages if there is no load.... I don't see how you could correlate rpm to voltage reliably.

AND>>>> even if there was a feedback loop from tach to controller, it still would NOT protect you against a stupid downshift or leaving the vehicle in low gear going down a steep hill. This could result in overspeed with NO voltage.

So, once again, a visual 'redline' is about all you can do.....
An rpm sensor would protect against most of the failures we commonly see in EV's (namely overrevving under power with or without load).
The main difference between knowing when youve reached the limit between ICE and electric is the noise. An audial signal when max RPM is reached (load screaming "in pain" sound, just like an ICE makes!) would do the trick in all events (even downshifting too far).

Is it really possible to have the motor running fast with a low voltage? I know little about series motors, but in the case of a DC motor the voltage potental will be high accross the motor whether or not the controller is powered when the motor is turning fast..
 

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I asked Darius (Electrocraft) to incorporate a motor RPM limit into my controller. I have the option for either voltage limit or RPM limt. (voltage is approximately equal to rpm). I decided to have my controller set to limit motor rpm to 5000. If 5000 RPM is reached, the controller cuts power and needs to see either hi pot switch or a low rpm (cant recall) before it restores scaled signal again. Mine is set in firmware, not as flexible as some (perhaps better?)...but I am happy with that. My motor has steel banding and some think it will take 6000 rpm... after some discussion and research, I decided on 5000. I can have it changed if I decide.

Cheers.
 

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An rpm sensor would protect against most of the failures we commonly see in EV's (namely overrevving under power with or without load).

Not true at all...
Lets say you go up a steep hill in second gear and let the car coast down the hill on the other side. whoops, you are now going down the hill at 65 mph still in 2nd gear. No voltage, no load, and BANG the motor blows apart.
 

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Which is why I suggest a buzzer or warning light (to replace the scream of an overrevved petrol engine)..

Hopefully none of us will lend our vehicles to someone daft enough to ignore a buzzer!

You don't HAVE to fit it DTBaker, it's just a suggestion for people who want to improve the protection circuitry on their vehicles;)
 

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To suggest that having the ability to limit motor rpm in some scenarios is of no value just because you cannot limit it in all scenarios, is simply not accurate. Lets be realistic.
 

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I recall someone here who blew a motor by just towing the EV in gear.

Until I misplaced my nylon shaft collar with my rare earth magnet, I planned on installing the shaft collar on my motor's rear shaft with a reed switch detecting the RPMs in order to get the stock tach working again sorta like another EVer did with his (see photo below).

Plan B was to send the signal to a racing tach with a shift light that can be set to a pre-selected shift point rpm that would light a warning light on the dash. At the pre-selected over-rev setting, the 12V signal would automatically drop out the primary contactor killing power to the motor.

Although this is a mechanical reed switch which could eventually wear out, the same concept can be done with a magnetic one relatively easy.

Photo courtesy of Keith Mercill

 
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