# No throttle switch



## edsammy (Jun 15, 2009)

I was having intermittent lose of power problems on my Jetta EV so I decided to try taking off the microswitch on my potbox and have both of the 2 contactors wired in series close when the key was turned on. The car seemed to run much smoother so I was wondering if it is a hazard to not have the 2nd contactor controlled by the microswitch on the potbox. Any input?

thanks


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## TheSGC (Nov 15, 2007)

edsammy said:


> I was having intermittent lose of power problems on my Jetta EV so I decided to try taking off the microswitch on my potbox and have both of the 2 contactors wired in series close when the key was turned on. The car seemed to run much smoother so I was wondering if it is a hazard to not have the 2nd contactor controlled by the microswitch on the potbox. Any input?
> 
> thanks


There is no hazard in doing that. I only have one contactor, and it's controlled by the Zilla, which gets a signal from my ignition switch. Depending on your controller, having a Dual contactor setup with one controlled by a mircoswitch on the pedal can destroy the controller. I believe the dual contactor setup with microswitch only applies to Curtis controllers, no other controllers. Some controllers, like the Zilla, will see the second contactor shut off as a fault and shut down the controller and give a power failure error.


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## edsammy (Jun 15, 2009)

I have a kelly KDH14500B and a precharge resistor on the second contactor. Is it hazardous to remove the microswitch in the sense that I will lose to ability to shut off the power to the controller by lifting my foot off the pedal in case of an emergency?


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## TheSGC (Nov 15, 2007)

edsammy said:


> I have a kelly KDH14500B and a precharge resistor on the second contactor. Is it hazardous to remove the microswitch in the sense that I will lose to ability to shut off the power to the controller by lifting my foot off the pedal in case of an emergency?


Well, here is the thing: logic states that the microswitch is a good safety, but reality is that same logical safety measure will most certainly end up destroying a Kelly controller. Disconnecting main power and then shoving it back on, full, WILL blow up most controllers, and Kelly/Logisystems has a history of doing that. When you are driving, your precharge circuit is completely useless and you are forcing full power to the capacitors, which will end their lives very quickly.

Maybe have it hooked up to another small switch in the cabin, like an emergency disconnect.


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## peggus (Feb 18, 2008)

If your pedal is properly adjusted the second contactor will never open or close under load, the controller will never even know it is happening, and certainly not blow up.

The zilla does not need this arrangement because the hairball controls the contactor and it is capable of detecting runaway faults on its own.






TheSGC said:


> Well, here is the thing: logic states that the microswitch is a good safety, but reality is that same logical safety measure will most certainly end up destroying a Kelly controller. Disconnecting main power and then shoving it back on, full, WILL blow up most controllers, and Kelly/Logisystems has a history of doing that. When you are driving, your precharge circuit is completely useless and you are forcing full power to the capacitors, which will end their lives very quickly.
> 
> Maybe have it hooked up to another small switch in the cabin, like an emergency disconnect.


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## edsammy (Jun 15, 2009)

does anyone else have any input?


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## dimitri (May 16, 2008)

It has been discussed many times in the past. I think the conclusion was that high pedal switch and 2nd contactor are from golf carts world, where people jump out of the cart without turning off the ignition key. IMHO, this is silly in a street EV. At best it doesn't give you any benefits, other than a little additional sense of security. At worst it causes continuous power interruptions which kill your contactor and/or controller.

I had same setup on my first EV since I followed EV America's schematic to the letter, but later I realized it was silly and just have one contactor in my 2nd EV.

In highly unlikely situation when you have runaway motor and your fuse did not blow and your main contactor does not open , what makes you think that 2nd contactor is going to have a different fate from 1st contactor? By this logic one should put 3 or 4 contactors in, just in case first 2 don't work


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## azdeltawye (Dec 30, 2008)

dimitri said:


> ...
> In highly unlikely situation when you have runaway motor and your fuse did not blow and your main contactor does not open , what makes you think that 2nd contactor is going to have a different fate from 1st contactor? By this logic one should put 3 or 4 contactors in, just in case first 2 don't work


 
In EHV transmission lines (345kV and above) it is standard practice to have triple redundant protective relay systems in place. Plus a breaker failure scheme at each terminal which adds another layer of redundancy to the protection.

I know this is a apples to oranges comparison. But when the stakes are high additional levels of redundancy are warranted.


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## dimitri (May 16, 2008)

azdeltawye said:


> In EHV transmission lines (345kV and above) it is standard practice to have triple redundant protective relay systems in place. Plus a breaker failure scheme at each terminal which adds another layer of redundancy to the protection.
> 
> I know this is a apples to oranges comparison. But when the stakes are high additional levels of redundancy are warranted.


That's why I would not object to mechanical emergency disconnect of some kind, which many people do in DIY EV, but jerking contactor every time you take the foot off the pedal is just plain silly.


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## peggus (Feb 18, 2008)

You don't seem to understand why the high pedal lockout is needed. Runaway is a fact of life when it comes to marginal controllers like Curtis, Logisystems and especially Kelly. 

The high pedal lockout kills power to the controller as soon as you take your foot of the pedal. Any other manual disconnect will take longer to activate, by which time you may already be halfway through the garage wall, or worse. 

Fuses and breakers will not save you in a runaway situation, they only protect you against hard shorts and ensuing fire.







dimitri said:


> It has been discussed many times in the past. I think the conclusion was that high pedal switch and 2nd contactor are from golf carts world, where people jump out of the cart without turning off the ignition key. IMHO, this is silly in a street EV. At best it doesn't give you any benefits, other than a little additional sense of security. At worst it causes continuous power interruptions which kill your contactor and/or controller.
> 
> I had same setup on my first EV since I followed EV America's schematic to the letter, but later I realized it was silly and just have one contactor in my 2nd EV.
> 
> In highly unlikely situation when you have runaway motor and your fuse did not blow and your main contactor does not open , what makes you think that 2nd contactor is going to have a different fate from 1st contactor? By this logic one should put 3 or 4 contactors in, just in case first 2 don't work


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## dimitri (May 16, 2008)

peggus said:


> You don't seem to understand why the high pedal lockout is needed. Runaway is a fact of life when it comes to marginal controllers like Curtis, Logisystems and especially Kelly.
> 
> The high pedal lockout kills power to the controller as soon as you take your foot of the pedal. Any other manual disconnect will take longer to activate, by which time you may already be halfway through the garage wall, or worse.
> 
> Fuses and breakers will not save you in a runaway situation, they only protect you against hard shorts and ensuing fire.


Oh, I understand your point perfectly. Crappy controllers are the fact of life because people accept them as such. If people weren't buying those crappy controllers, then runaway would not be fact of life.

Original poster asked for opinions, we all gave our opinion on the subject. There is no right or wrong here, its a matter of making choices based on available information. There are some benefits and some drawbacks in having this design, which is more important is a call each DIY EV maker has to make for himself.

BTW, I would not put Curtis in same line with Kelly and Logisystems. Curtis has a great reputation and works well if properly precharged.


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## dimitri (May 16, 2008)

Also, there is a pretty decent chance that contactor will weld on in a runaway situation since runaway current is likely to be higher than contactor's rating, that is where the fuse rated at the same level as contactor's rating would blow and save the day. So, you might be getting a false sense of security with 2nd contactor. Of course devil is in details, each case is different due to different pack sizes and currents involved and what current batteries can deliver in a runaway condition.


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## Dave Koller (Nov 15, 2008)

I compromised - have a second contactor - that has a latching control relay. BUT only disconnects on brake,parking brake,clutch or over-speed - etc. Still not the best - but a little of that margin of safety (along with the first contactor) - I did not like the idea of clunking every time one let up on the throttle - as Dimitri has stated - BUT I like the idea of disconnect in the manner I stated... You can see that at the end of my thread listed below my signature... 

I agree with Dimitri on the idea of a mechanical disconnect as added safety...


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## peggus (Feb 18, 2008)

dimitri said:


> snip
> 
> Original poster asked for opinions, we all gave our opinion on the subject. There is no right or wrong here, its a matter of making choices based on available information. There are some benefits and some drawbacks in having this design, which is more important is a call each DIY EV maker has to make for himself.
> 
> BTW, I would not put Curtis in same line with Kelly and Logisystems. Curtis has a great reputation and works well if properly precharged.


Sure there is a right or wrong: claiming the second contactor wouldn't help because the first contactor and fuse didn't help is just plain wrong. (the first contactor isn't even in the equation until you turn the key off) Claiming the contactor opens and closes under load is also plain wrong. 

Lets base our opinions on correct information at least.

As for the contactor welding, if it does you didn't pick the right contactor.

The Curtis has a number of design flaws, a couple of which makes it prone to runaway, that's just my opinion as a power-electronics engineer. That said, I am using one and they can be very reliable if you operate it below its specs and with proper pre-charging of course.


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## Tesseract (Sep 27, 2008)

peggus said:


> Sure there is a right or wrong: claiming the second contactor wouldn't help because the first contactor and fuse didn't help is just plain wrong. (the first contactor isn't even in the equation until you turn the key off) Claiming the contactor opens and closes under load is also plain wrong.


The devil is in the details, as the cliche goes. Let's assume for the sake of discussion that the throttle in question is a PB-6 and the microswitch turns off a contactor when the throttle returns to zero. This would appear to be an excellent safety feature because it automatically disconnects the motor controller from the traction pack with no thought on the driver's part. 

In order for this happy circumstance to prevail, however, the microswitch must de-energize the contactor AFTER throttle has hit zero, otherwise the controller will suck the input capacitors dry and it will be up to chance whether the precharge resistor will recharge the input capacitors before the driver steps on the accelerator again!

Additionally, the microswitch needs to re-energize the contactor BEFORE the throttle moves off the zero position. You would think that if the first condition were satisfied the second would be too, but that is not the case. All mechanical switches have hysteresis - some is intrinsic, and some is designed in. For example, it might take 15 degrees of movement to actuate a microswitch but require coming back 5 degrees to de-actuate it. There is 5 degrees of hysteresis in the actuation, then. 

Now, as long as the microswitch in the PB-6 has the proper microswitch with the proper amount of mechanical hysteresis (there are a bewildering number of options here, btw) and the microswitch is properly positioned with respect to the pot element and the pot element itself is a consistent length then everything will work fine. If any one of these is off, though, it is almost assured that the end result will be a contactor closing into a fully discharged input capacitor.

And it is not even necessary for the motor controller to fully discharge its input capacitors for contactor damage to occur. The very low ESR (for example, the Curtis 1221 has some 35 capacitors in parallel) ensures that the surge currents will be extremely high with only a 10-20V difference in voltage between the traction battery and the input capacitor, much less a 120V difference!

The huge surge current is not only rough on the contactor contacts, it also excites any stray inductance, producing equally huge voltage spikes. Boom goes the controller. This is almost assuredly what kills Logisystems controllers, btw, because when they heat up motor current often does not entirely drop to zero when throttle is at zero, and the precharge resistor can't possibly keep the capacitors charged up if even a couple amps are being delivered to the motor.

Unless you can make absolutely sure that motor current is at zero, the microswitch will actually be a safety HAZARD. 

My $0.02.


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## Dave Koller (Nov 15, 2008)

Tesseract:

Yep

Need a little logic to those switches and relays 

Hence the OVER complexity to my SIMPLE relay board....


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## edsammy (Jun 15, 2009)

thanks for all the input guys. i am going to try and rewire the system tomorrow. side question: can i use an RC timer circuit to delay the closing of the second contactor so the precharge can take place?


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## Dave Koller (Nov 15, 2008)

edsammy said:


> side question: can i use an RC timer circuit to delay the closing of the second contactor so the precharge can take place?


 Yep  **********************


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## peggus (Feb 18, 2008)

Yes, the devil is in the details. It is certainly possible to get it wrong. 

It doesn't really change why the high pedal lockout is needed. The Curtis and its ilk are riddled with single point failures that can lead to runaway, the high pedal lockout is the only backup preventing disaster.

If you don't want to have the contactor click-clacking every time you let off the pedal, you should at least have it open up when you press the brake as that is the second thing you'll do automatically in a runaway situation. Make sure you open up the KSI at the same time or you'll have problems if you accidentally press the accelerator an brake at the same time.

The best solution would be some logic that monitors current and high pedal lockout and only opens the contactor if the two don't agree.


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## Russco (Dec 23, 2008)

REAL controllers control the main contactor directly. The main contactor will close ONLY if the ignition switch is on, high voltage is available and has pre-charged the bus capacitors, the controller transistors are not shorted, and more. Only when these conditions are met, is the main contactor allowed to close. 

Examples of these controllers include the Zilla, Solitron, Russco.

THIRD WORLD controllers control the main contactor through the ignition switch only. These controllers do not check for high voltage, precharge, or shorted transistors. 

Examples of these controllers include the Curtis, Logisystems, and Kelly.

The THIRD WORLD controllers can benefit with a clank-clank open-the-contactor-each-time to try to comprromise the controllers safety deficiencies, but may have a timing problem , as discussed by Tes., AKA Jeffrey Jenkins. 

Just my opinion and 25 years in the controller business. 

Russ Kaufmann

RUSSCO Engineering

http://russcoev.com


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## Qer (May 7, 2008)

peggus said:


> The best solution would be some logic that monitors current and high pedal lockout and only opens the contactor if the two don't agree.


And add a delay for free wheeling current I presume...?










The slope of the PWM-curve is because the Soliton1 sample data with 10 ms intervals and thus the slope is false. In reality the PWM is completely cut exactly 1 ms after the knee in the PWM-curve.

As you can see there can be current flowing for something like ~70 ms after PWM is cut which such a safety circuit would have to take into account.


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## peggus (Feb 18, 2008)

Qer said:


> And add a delay for free wheeling current I presume...?


Not necessarily, just monitor the battery current, should drop to ~0 in less than one switching cycle. Thanks for the data though.


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## JRP3 (Mar 7, 2008)

Another plus for AC induction, they don't fail full on so you can't have a runaway. As far as I know...


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## Tesseract (Sep 27, 2008)

JRP3 said:


> Another plus for AC induction, they don't fail full on so you can't have a runaway. As far as I know...


No runaway, true, but if the stator windings are energized with DC then a significant braking torque is developed. Overheats the windings, too. Of course, any decent ac inverter is going to sense such a fault...


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## peggus (Feb 18, 2008)

JRP3 said:


> Another plus for AC induction, they don't fail full on so you can't have a runaway. As far as I know...


They're no more likely to runaway than a Toyota 

It depends on the designer, it is possible for software bugs and throttle failures to cause runaway even in AC controllers. Most well designed AC controllers have sufficient measures to prevent runaway, and power device failure can not lead to runaway like in a Curtis.


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