# What is a Pedal Interlock?



## MemphisPapa (Feb 16, 2012)

I'm looking for some help finishing the connections for my Curtis 1238R controler. Pin #9 says it is the Pedal Interlock and goes to the "N.C. Throttle Switch" then on to the the menu button that returns to Pin #10 on the controler. What is the Pedal Interlock? What is it for and why do I need it? What is the N.C Throttle Switch?
I'm in my first build and am so close to the first run. I just am not sure about this one. Thanks ahead for the help.


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## major (Apr 4, 2008)

MemphisPapa said:


> I'm looking for some help finishing the connections for my Curtis 1238R controler. Pin #9 says it is the Pedal Interlock and goes to the "N.C. Throttle Switch" then on to the the menu button that returns to Pin #10 on the controler. What is the Pedal Interlock? What is it for and why do I need it? What is the N.C Throttle Switch?
> I'm in my first build and am so close to the first run. I just am not sure about this one. Thanks ahead for the help.


Hi Memp,

The common throttle pot assembly is the Curtis PB-6. It comes with a microswitch activated when you lift (throttle off position). This is called an interlock. When the throttle is off, the controller gets a signal from the interlock switch and inhibits the motor.

N.C. means Normally Closed for the switch contacts. The microswitch on the PB-6 is SPDT and can be wired for NC or NO (Normally Open).

Do you need it????? Maybe. If you have the programmer, you can disable the function. If not, and your controller has been programmed for it, then you could hard wire it.

I use it on the brake pedal instead of the throttle. That way if the throttle gets stuck, the brake switch turns off the motor. On the brake, use a NO instead of NC switch.

And the return isn't thru the menu button, it is to B+. The menu button return is also B+.

You should be able to download the complete manual from the Curtis website. See page 12.

Good luck,

major


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## Hippie Djohn (Oct 24, 2011)

It is for redundancy.
IMO it's a very good thing to have.
It could be quite serious if the car take off by itself.


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## MemphisPapa (Feb 16, 2012)

Thank you for the explanation.
In my case, for the HPEVS with an AC-50, is this the trigger for regeneration braking? The diagram I got with the motor and controller shows it spliced with the 12V supply (from the controller) on one end of the menu button. The other side of the menu button is going back to Pin#10 on the controller. What I would like is to activate regen with the brake pedal, not with the lack of throttle.


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## Hippie Djohn (Oct 24, 2011)

MemphisPapa said:


> Thank you for the explanation.
> In my case, for the HPEVS with an AC-50, is this the trigger for regeneration braking? The diagram I got with the motor and controller shows it spliced with the 12V supply (from the controller) on one end of the menu button. The other side of the menu button is going back to Pin#10 on the controller. What I would like is to activate regen with the brake pedal, not with the lack of throttle.


Use a pressure transducer connected to the hydraulic system and the brake input on the controller instead. That works much better. To make a switch work reasonably, you need access to the VCL if HPEVS already didn't configure this ?


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## Hippie Djohn (Oct 24, 2011)

As said before redundancy on the throttle signal is VERY good idea !!! I've seen a car out of control due to a faulty throttle input.


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## MemphisPapa (Feb 16, 2012)

The brake light switch is located on the master cylinder. Could I use that switch with a relay to work as an NC switch from the brake and maintain 12V isolation?


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## Hippie Djohn (Oct 24, 2011)

MemphisPapa said:


> The brake light switch is located on the master cylinder. Could I use that switch with a relay to work as an NC switch from the brake and maintain 12V isolation?


The brake input only accept 0-5V. 
Why not use a pressure sensor instead ? 
It is 10 times easier to do and there are already predefined parameters for it.
it work absolutely great !


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## mizlplix (May 1, 2011)

> Originally Posted by MemphisPapa
> The brake light switch is located on the master cylinder. Could I use that switch with a relay to work as an NC switch from the brake and maintain 12V isolation?
> 
> The brake input only accept 0-5V.
> Why not use a pressure sensor instead ?


The simple answer is yes.

When you use your relay, you can use any current value you choose to signal the controller. The brake switch IS a pressure sensor. No need to add another to be kept maintained.

Miz


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## Hippie Djohn (Oct 24, 2011)

By using the brakelight switch, the brake signal becomes an on/off signal.
This will reduce the regen brake performance or make it operate harsh and if the pedal interlock input is used you really compromise safety.

With the pressure transducer (not a simple switch) mounted to the hydraulic brake system you will get a very smooth regen braking without sacrificing safety. 
The sensor should put out between 0 and 5V in your pressure range (typically 0-100 bars is fine) and with the already defined brake parameters it super easy to setup.
I'm 100 % sure that you will not regret if you do it.


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## ricklearned (Mar 3, 2012)

I'm thinking of using a brake pot. My theory is I can start the regen before the brakes get pressure by using the pedal freeplay. I may have to play around with the programming. Is that a viable alternative to the pressure transducer?


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## MemphisPapa (Feb 16, 2012)

Is the pedal interlock the input for the regent brake or is it a safety switch that keeps me from accidental acceleration through the back of the garage when I turn the key from off to on?


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## ricklearned (Mar 3, 2012)

The interlock is a safety device. The thread had digressed to talk about regen, so I thought I would ask a related question. Sorry about the inadvertant hijack.


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## major (Apr 4, 2008)

ricklearned said:


> The interlock is a safety device. The thread had digressed to talk about regen, so I thought I would ask a related question. Sorry about the inadvertant hijack.


Hi guys,

Well yes, the interlock is a safety mechanism. However the systems which I favor are AC with regen proportional from the brake pedal via a pot in the freeplay zone before the friction pads are brought into play. These systems have a priority given to the regen signal which overrides the accel signal if both are present. Therefore the regen input pot functions as the interlock inasmuch when you have your foot on the brake, the throttle is completely defeated. The same priority can be used with the pressure sensor, which sounds like a nice way to go. 

I think the Curtis controllers use a static return to off strategy in which the throttle must return to zero command before the motor is given power upon initial start up. It is a nice feature which prevents undesired acceleration if you have it floored by mistake when you turn on the key.

There are a number of ways to be smart about safety in the EV design, but somehow a fool can always find a way to wreck it 

major


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## Ivansgarage (Sep 3, 2011)

major said:


> I think the Curtis controllers use a static return to off strategy in which the throttle must return to zero command before the motor is given power upon initial start up. It is a nice feature which prevents undesired acceleration if you have it floored by mistake when you turn on the key.
> 
> major


Major I think Miz was working on his dash panel one time, It was laying
on the throttle and he turned the key on and it took off, if was on jack stands. Saved his ass..


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## major (Apr 4, 2008)

Ivansgarage said:


> Major I think Miz was working on his dash panel one time, It was laying
> on the throttle and he turned the key on and it took off, if was on jack stands. Saved his ass..


The feature may be only on the lower voltage/power models and offered by other controllers as well for forklifts and utility EVs. Both Static Return to Off (SRO) and High Pedal Disable (HPD). Seems like these would be good features for EVcars as well.

And yes, by all means, jack those wheels up when working on your EV with the battery connected. Crap can happen in a hurry


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## Hippie Djohn (Oct 24, 2011)

major said:


> Hi guys,
> 
> Well yes, the interlock is a safety mechanism. However the systems which I favor are AC with regen proportional from the brake pedal via a pot in the freeplay zone before the friction pads are brought into play. These systems have a priority given to the regen signal which overrides the accel signal if both are present. Therefore the regen input pot functions as the interlock inasmuch when you have your foot on the brake, the throttle is completely defeated. The same priority can be used with the pressure sensor, which sounds like a nice way to go.
> 
> ...


Thank you, that is more or less what I've been trying to say..


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## ricklearned (Mar 3, 2012)

major said:


> Hi guys,
> 
> Well yes, the interlock is a safety mechanism. However the systems which I favor are AC with regen proportional from the brake pedal via a pot in the freeplay zone before the friction pads are brought into play. These systems have a priority given to the regen signal which overrides the accel signal if both are present. Therefore the regen input pot functions as the interlock inasmuch when you have your foot on the brake, the throttle is completely defeated. The same priority can be used with the pressure sensor, which sounds like a nice way to go.
> 
> ...


Yes that is exactly what I want to do. You say it so elegantly, Major.


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## Hippie Djohn (Oct 24, 2011)

This is why you want redundancy signal on your throttle !!!

http://translate.google.com/transla.../koert-ned-af-loebsk-skraldebil-turist-draebt


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