# [EVDL] Pot box design



## EVDL List (Jul 27, 2007)

If a EV moves when not occupied, then it does not have the safety circuits 
install to prevent this operation. Any time you are out of the EV, then you 
should have the ignition key and/or control circuit shut down and the brakes 
lock up with a mechanical pull lever.

If you want to do test and/or maintenance of a EV while it is activated, the 
drive line should be disconnected if you have a transmission which is place 
in neutral or block the contacts of a reversing contactor to prevent motor 
control power going to the motor.

A main battery power shut down is done by two safety contactors that is 
control by the main ignition control circuit and may be back up by one or 
two emergency shut down switches.

A motor rpm sensor circuit is also install where you can limit the motor 
rpm.

A pot box circuit should be design where the resistance is a certain minimum 
ohms, then the motor controller shuts down. Also when there is a maximum 
certain resistance or wire come off and/or cut or shorts, then the motor 
controller also shuts down.

In my EV call Transformer I, it has two safety contactors that can shut down 
the battery circuit under full load if needed. The ignition key on the 
steering column does this, plus four large lighted rocker switches on the 
console of which any one can also shut down battery circuit.

De-pressing the accelerator to where the pot resistance goes below 150 ohms 
or goes above 7K ohms the motor and/or over speed of the motor, the motor 
controller shuts down in a Zilla.

I am going to do a modification of this where I am going to replace the 
transmission shifter with a straight line cable shifter that has a extra red 
lever that if you happen to have your hand on the shifter knob, I can flick 
it with one finger to do a shut down.

Another mod I did, was to have the motor rotate while I am servicing the A/C 
and testing and checking out the accessory drive system, I either had to 
have some one sit in the EV and press the accelerator or using a stick 
against the accelerator pedal.

I install another 5Kohm pot which I can switch in series with the existing 
5K pot and can manual adjust it to a set rpm I want. I leave this second pot 
pre-set to give me about 500 rpm idle speed. I use a on dash selector 
switch that can either select ON - OFF - IDLE control circuits.

I also found if the route I am going on only require slowing down or to a 
very short stop and go, I will at times set this switch to IDLE, where the 
motor do not go below 500 rpm. I did a 1 mile run test using the IDLE 
control and found than I am using less battery energy during the idle run vs 
the no idle run.

Every time I have to restart the motor, my motor and battery ampere is about 
two to three times greater, if I do idle the motor at this time.

To see if this true for your EV, if you are using a transmission, when 
coasting down to a stop, put the transmission in neutral to let the motor 
freewheel during the short stop. Sometimes the motor will continue to spin 
until you take off again. Then see if there if any energy difference in 
your run.

Roland






----- Original Message ----- 
From: "Mark Grasser" <[email protected]>
To: "'Electric Vehicle Discussion List'" <[email protected]>
Sent: Sunday, May 25, 2008 9:20 AM
Subject: [EVDL] Pot box design


> If and when I ever get there (building a speed control) The throttle
> position sensor gives me chills, reading about full throttle incidences.
> Remember the story of the sparrow just taking off at full speed during a
> demonstration day, probably not the same thing because as I remember it 
> was
> not occupied.
>
> Anyway, why not two pots, one pot is used to create the location of the
> window of a window comparator and the other pot has to stay within the
> window and is the input of the controller. If the second pot voltage 
> leaves
> the window there is a hard shutdown of the controller.
>
>
> Mark Grasser
>
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
> 

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## EVDL List (Jul 27, 2007)

Ian concluded: "...BUT, after building that I decided it really doesn't make
sense using 
a potentiometer for something so critical, using a hall effect sensor 
makes so much more sense because there's no friction surfaces to wear 
out."

EXACTLY.
It's kind of funny that so few home-built EVs are being built with the more
reliable non-contact sensors available (whether Hall Effect or Inductive).
Personally, I don't think I could trust a pot box without having detailed
specs from the manufacturer of the potentiometer itself.
And even then, I have had so many stereos over the years that developed
noisy volume controls due to pot degradation that I'd never feel secure
without at least a small capacitor on the wiper. Still, they work for most
people and we don't hear too many horror stories here.

But why is no one mentioning inductive throttle sensors (ITS)?
Several EV controllers (e.g. all of the DCP controllers) are built to work
with an ITS as are many of the golf cart controllers (Curtis 1206 and
Alltrax AXE controllers). EZ-GO makes an ITS including a fully encapsulated
coil assembly and a high-MU slug for mounting to your throttle linkage.
There's only 2 wires to connect and there's absolutely no possibility of
intermittents in that sensor----unless you break it or the slug falls off.

The ITS has its own downsides (cost is main one: e.g. EZ-GO ITS is $159 from
EVparts: http://www.evparts.com/prod-SP1117.htm ) including perhaps a
potential vulnerability to extraneous HF signals or nearby moving metal.
However, the fact that these sensors avoid the primary pitfalls of a pot and
are directly compatible with some of the better EV controllers, it is
astounding that almost no one mentions using an ITS for control of their EV.
I highly recommend it over all the complex schemes that I now hear folks
coming up with to make them feel good about the weak link in their throttle:
the pot. I have used an EZ-GO ITS for control of my 36v powered boat for
5yrs now.

-Myles Twete
26ft Reach Of Tide scow barge cruiser: www.austinev.com/evalbum/492


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## EVDL List (Jul 27, 2007)

> 


> > -Myles Twete wrote:
> > 26ft Reach Of Tide scow barge cruiser: www.austinev.com/evalbum/492
> 
> Make that http://www.evalbum.com/492
> ...


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## EVDL List (Jul 27, 2007)

> Myles Twete wrote:
> 
> > It's kind of funny that so few home-built EVs are being built with the
> > more reliable non-contact sensors available (whether Hall Effect or
> ...


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## EVDL List (Jul 27, 2007)

Thanks for the correction.
I intended www.austinev.org/evalbum/492 , which maps to www.evalbum.com/492



-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of JS
Sent: Sunday, May 25, 2008 10:34 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Pot box design

> 


> > -Myles Twete wrote:
> > 26ft Reach Of Tide scow barge cruiser: www.austinev.com/evalbum/492
> 
> Make that http://www.evalbum.com/492
> ...


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## EVDL List (Jul 27, 2007)

So, what are the specs on a typical pot that is acceptable in throttle use? 
I am thinking of a slide potentiometer that is rated at 100,000 slides, and
has a linear range of 60 mm. It only 0.2 watts though. What wattage should
they be rated at? 

-Paul




> Roger Stockton wrote:
> >
> > Myles Twete wrote:
> >
> ...


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## EVDL List (Jul 27, 2007)

> Myles Twete wrote:
> > Ian concluded: "...BUT, after building that I decided it really doesn't make
> > sense using
> > a potentiometer for something so critical, using a hall effect sensor
> ...


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## EVDL List (Jul 27, 2007)

Depends how you design it.
Automotive RPS or PPS (rotary position sensors or pedal position 
sensors) are robust enough and specified to 5...10 million trouble free 
rotations. 

Well after all I've read today using an automotive position sensor is
probably a good idea, it is made for a quarter revolution so that part is
right, not sure about the 10 million rotations. I'd still use two or three
of them. You have to remember.....on an ICE if you lose the pot your
throttle cable can still close the throttle, the car won't accelerate
without the butterfly being open.




Mark Grasser



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## EVDL List (Jul 27, 2007)

Regarding use of ITS sensors, Victor added: "Inductive/hall sensors will
require to modify input of the controlled device."

Maybe---depends on the controller.
Alltrax controllers offer the programmable choice of at least a half dozen
different sensors and pot configurations.
Both Alltrax and the DCP controllers work with the ITS without requiring
modifying any input HW.

-MT

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## EVDL List (Jul 27, 2007)

I know of modern cars where the throttle has no linkage to 
the butterfly, because it is drive by wire, the throttle
is only driven by an electric motor which is controlled
by the computer reading the oxygen sensor and controlling
the injection, so it can make sure the mixture is right.

I do not know if this is try in many newer cars, as I
no longer am very temped to look under the hood of those
modern vehicles that use dinosaur technology, though my
Prius has an interesting mix and this is where I see the
throttle butterfly on a motor and the go-pedal only be
tied to an advanced potbox.

It may be interesting to select a vehicle (or multiple)
that already have the control you want and scavenge it
in a wrecking yard, why order expensive new replacement
parts that are marked up from sitting on a warehouse shelf?


Cor van de Water
Systems Architect
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water IM: [email protected]
Tel: +1 408 542 5225 VoIP: +31 20 3987567 FWD# 25925
Fax: +1 408 731 3675 eFAX: +31-87-784-1130
Second Life: www.secondlife.com/?u=3b42cb3f4ae249319edb487991c30acb

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Mark Grasser
Sent: Sunday, May 25, 2008 1:28 PM
To: [email protected]; 'Electric Vehicle Discussion List'
Subject: Re: [EVDL] Pot box design


Depends how you design it.
Automotive RPS or PPS (rotary position sensors or pedal position
sensors) are robust enough and specified to 5...10 million trouble free rotations. 

Well after all I've read today using an automotive position sensor is probably a good idea, it is made for a quarter revolution so that part is right, not sure about the 10 million rotations. I'd still use two or three of them. You have to remember.....on an ICE if you lose the pot your throttle cable can still close the throttle, the car won't accelerate without the butterfly being open.




Mark Grasser



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## EVDL List (Jul 27, 2007)

> Mark Grasser <[email protected]> wrote:
> >
> > Depends how you design it.
> > Automotive RPS or PPS (rotary position sensors or pedal position
> ...


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## EVDL List (Jul 27, 2007)

Evan,

I, for one, can supply Wabash dual TPS; they are
2.5k per channel, include integrated kick down switch. $75.
1k Bosch machines are available too, but the
cost is beyond what an individual would spend
unless ultimate reliability is a priority.

The source you mentioned is good, just make sure those
are automotive grade products. Being in the UK,
there is disadvantage of dealing with weak US currency.

Victor
'91 ACRX - something different



> Evan Tuer wrote:
> 
> > Where to get a TPS? It used to be that the major electronics
> > suppliers carried them. Now, they don't seem to - I don't know why.
> ...


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## EVDL List (Jul 27, 2007)

Hi Victor,
I believe these pots are closer to $20 but your point about the
currency stands. As I'm in the UK it's the sensible choice for me
anyway.
These products are definitely at least "automotive grade" and probably better.
As I say, the one I was looking at (CP17) was chosen for the PSA
electric vehicle pedal sensor of which tens of thousands are in use.
I have never heard of an actual pot fault in practice although it is
easy to suspect sometimes.
Of course the location in the car footwell is much kinder than stuck
on the side of an ICE with all kinds of fuel, oil, dust, salt and
water contamination as well as heat and vibration to contend with, so
a top of the line TPS is probably overkill for EVs anyway.

Wiring problems can occur but even with a single 3-wire pot, the
vehicle is either properly controlled or cuts out for safety. Of
course if you have a controller which can deal with dual or triple pot
input then you should choose something like that, but I think the
common controllers do not.

Cheers
Evan



> Metric Mind <[email protected]> wrote:
> > Evan,
> >
> > I, for one, can supply Wabash dual TPS; they are
> ...


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## EVDL List (Jul 27, 2007)

I didn't realize you're in UK. Go for it then, you're in good shape.
These appear to be right grade units judging from the photos and
downloadable specs. $20 is very low price if this is what I think it is.

Please leave guitar pedals for others to play.

Victor



> Evan Tuer wrote:
> > Hi Victor,
> > I believe these pots are closer to $20 but your point about the
> > currency stands. As I'm in the UK it's the sensible choice for me
> ...


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## EVDL List (Jul 27, 2007)

I have been considering linking one of these:
http://usdigital.com/products/ma3/
to a tiny 8-bit microprocessor driving a digital potentiometer such as one 
of these:
http://ww1.microchip.com/downloads/en/DeviceDoc/22017a.pdf

This would be a fairly simple project and would yield a very high 
reliability throttle position sensor that interfaces any standard 5K pot 
input.

Jon 

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## EVDL List (Jul 27, 2007)

Jon,

While I'm sure this can be fun project to tackle, it is a solution
looking for a problem.

A micro still needs input, from up/down buttons or encoder or
... different pot .
it needs software that can lock up (watch dog or not),
it needs a power supply which has to be clean and stable,
it all has to be environmentally protected/sealed and immune
to EMI from near-by high noise controller/inverter or battery cables.

How do you plan to repair it when it fails?
Replace for a new PCB with new components?

Do you really think just one passive element of high quality
is worse solution than all that above? Just wondering.

(If building/learning process is more important than outcome,
it's of course different story...)

--
Victor
'91 ACRX - something different




> Jon Wagner wrote:
> > I have been considering linking one of these:
> > http://usdigital.com/products/ma3/
> > to a tiny 8-bit microprocessor driving a digital potentiometer such as one
> ...


----------



## EVDL List (Jul 27, 2007)

> Do you really think just one passive element of high quality
> is worse solution than all that above? Just wondering.
>
> (If building/learning process is more important than outcome,
> it's of course different story...)

yeah you're right about that one! it did seem like a fun tinkering project, 
but the reliability comment was a little far fetched... 

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## EVDL List (Jul 27, 2007)

With everyone discussing so much about the pot box
and in response to a question on the US Electricar list,
I thought it might be helpful to cross-post my answer
and give you a bit of info from my factory converted EV,
using 2 parallel PB-6 operated by one throttle cable
(we are talking about an S10 truck, but Prizm should be same setup)
=========================================================
I opened up my accel box (rather cheesy-looking but solidly
welded together box with screw-on lid and 2x PB-6 ganged together)
and found following:
2x parallel (only the wiper contact is returned separately from each
potbox to the controller) so on a 4-wire configuration, both are 5.6 kOhm
so the combination reads 2.8 kOhm
and the full scale is reached in the first 30 or 40 degrees, after that
(the last 10 to 15 degrees) the wiper is shorted to the "high" lead.
No doubt that if you opened the pot itself, you would find the normal
270 deg trace but 240 degrees or so is covered in metal deposit
and the last 30 deg gives the 5.6 kOhm variation we see.
For the markings on the pot:

PMC98191
CM44675
20 9419
MEXICO

Each potbox is marked:
PB-6
Curtis PMC

It seems they have their own product number for this pot.
If they use the common year-week marking, it was made in wk 19 of 94
so in early May 1994

Hope this helps,
===========================================================

Cor van de Water
Systems Architect
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water IM: [email protected]
Tel: +1 408 542 5225 VoIP: +31 20 3987567 FWD# 25925
Fax: +1 408 731 3675 eFAX: +31-87-784-1130
Second Life: www.secondlife.com/?u=3b42cb3f4ae249319edb487991c30acb

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Victor Tikhonov
Sent: Tuesday, May 27, 2008 9:38 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Pot box design

Jon,

While I'm sure this can be fun project to tackle, it is a solution looking for a problem.

A micro still needs input, from up/down buttons or encoder or ... different pot .
it needs software that can lock up (watch dog or not), it needs a power supply which has to be clean and stable, it all has to be environmentally protected/sealed and immune to EMI from near-by high noise controller/inverter or battery cables.

How do you plan to repair it when it fails?
Replace for a new PCB with new components?

Do you really think just one passive element of high quality is worse solution than all that above? Just wondering.

(If building/learning process is more important than outcome, it's of course different story...)

--
Victor
'91 ACRX - something different




> Jon Wagner wrote:
> > I have been considering linking one of these:
> > http://usdigital.com/products/ma3/
> > to a tiny 8-bit microprocessor driving a digital potentiometer such as
> ...


----------



## EVDL List (Jul 27, 2007)

here's a curtis replacement potentiometer for the PB-5 and PB-6:
http://www.tecknowledgey.com/catalog/product_info.php?cPath=54_55&products_id=464&osCsid=3f414d829b3a7d92152e063b8ebbaba5

Its 40 degrees 0-5K and is a direct replacement from a company in New York
for $18.45.

Not bad when you consider everywhere else is above $30.




> Cor van de Water <[email protected]> wrote:
> 
> > With everyone discussing so much about the pot box
> > and in response to a question on the US Electricar list,
> ...


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