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Old 07-11-2012, 12:45 PM
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Default [EVDL] Circuit drawing for potbox modification.

Did anyone draw the circuit that modifies the Curtis pot box to be less "touchy"? Had something to do with placing a resistor with it. In the 0 to 500 ohm part. Making it take much longer to ramp up. Lawrence Rhodes......

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  #2  
Old 07-11-2012, 02:15 PM
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Default Re: [EVDL] Circuit drawing for potbox modification.

Hi Lawrence,

The first and simplest modification is to place
a resistor parallel to the potbox, though this
might avoid you from ever reaching full on, so
it may be necessary to also add other resistors,
but the first thing I recommend to try is to
add a parallel resistor, somewhere between 5k to
10k Ohm if your controller is expecting a resistance
as input. If your controller can take an input
voltage instead, then it may be better to use a
much lower resistance (I am currently using about
500 Ohms in parallel to the potbox and also a
pullup resistor to +5V of about 200 Ohms to allow
the voltage to go to 3.5V.
These low resistor values cause the bottom 2/3 of
the potbox to become unused (which is good as that
was the area that was bad in mine) and only the top
1/3 will first give a s-l-o-w decrease in resistance
and then progressively faster.
Since my controller takes 3.6V as "off"; 3.5V as "idle"
and the lower the voltage, the higher the motor output,
this mod was exactly what I needed.
You will need to measure your potbox and controller
voltage what values your setup need, then you can
decide how to best modify your potbox to get the
desired result.

Note: I have seen suggestions that as soon as you
engage "reverse" you add a resistor across the
potbox to not only reduce its sensitivity, but also
limit the max throttle since it is rare to encounter
a situation that requires max throttle in reverse.
It can be as simple as a 12V relay coming on with the
reversing light and its contact connecting a resistor
across the potbox, if your setup is that a lower
resistance lowers the output. In my controller, I
would still need only a single contact but connect
the potbox to a voltage divider.

If you tell me what your controller needs then I can
suggest how to implement it best.

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: xxx@xxx.xxx Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203

-----Original Message-----
From: xxx@xxx.xxx.edu [mailto:xxx@xxx.xxx.edu] On
Behalf Of Lawrence Rhodes
Sent: Wednesday, July 11, 2012 10:35 AM
To: xxx@xxx.xxx.edu
Subject: [EVDL] Circuit drawing for potbox modification.

Did anyone draw the circuit that modifies the Curtis pot box to be less
"touchy"? Had something to do with placing a resistor with it. In the
0 to 500 ohm part. Making it take much longer to ramp up. Lawrence
Rhodes......

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  #3  
Old 07-11-2012, 02:27 PM
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Default Re: [EVDL] Circuit drawing for potbox modification.

The advantage of using AC, like ALL production cars use, you can program the
controller to adjust all the parameters of the throttle, including power and
speed in reverse that doesnt require a the transmission.

--
View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/Circuit-drawing-for-potbox-modification-tp4656438p4656442.html
Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com.

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  #4  
Old 07-11-2012, 11:15 PM
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Default Re: [EVDL] Circuit drawing for potbox modification.

[quote] Cruisin <xxx@xxx.xxx> wrote:
> The advantage of using AC, like ALL production cars use, you can program the
> controller to adjust all the parameters of the throttle, including power and
> speed in reverse that doesnt require a the transmission.
>

That is NOT and AC vs DC thing. It is 100% how the controller is designed.

--
David D. Nelson
http://evalbum.com/1328
http://2003gizmo.blogspot.com

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  #5  
Old 07-12-2012, 11:35 AM
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Default Re: [EVDL] Circuit drawing for potbox modification.

I guess I didn't make it clear how my pot box works. My Curtis starts at 0 ohms and goes to 5k. I need the 0 to 500 ohm area to stretch out a bit. So the time it takes to go from 0 to 500 ohms is extended. My problem is jerking at start. The pot is too sensitive. I need feedback. As it is now I have to be very ginger with the pedal and it takes me a few seconds to do a smooth start in gear. I could just use the clutch but that would be defeating the advantage of the electric drive and wear out the clutch. Lawrence Rhodes......

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  #6  
Old 07-12-2012, 01:35 PM
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Default Re: [EVDL] Circuit drawing for potbox modification.

Lawrence,

Probably the simplest is to get a "logarithmic" pot,
the type used in volume controls which ramps up
slowly in the beginning and faster towards the end.
That is because just like your vehicle control, you
do not want the Watts from an audio system to be
linear with the control, otherwise a 100 Watt system
would nearly always be operated in the first 1/100 of the
control range and be very touchy - just like your throttle now.

It is possible to use a linear potbox and build an electronic
circuit with Opamps and FETs that convert the linear range
to logarithmic, but as Lee pointed out you want the potbox
as simple and error free as possible, so I suggest looking into
getting a logarithmic pot.
Make sure that the direction it turns has the start when the
pedal is up (pot turned all the way counter-clockwise)
otherwise you make the problem even worse with an audio pot.
I do not know how easy it would be to modify a potbox for
working the other way around if that is the problem, I have
never seen a Curtis potbox in real life.

Success,

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: xxx@xxx.xxx Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203

-----Original Message-----
From: xxx@xxx.xxx.edu [mailto:xxx@xxx.xxx.edu] On
Behalf Of Lawrence Rhodes
Sent: Thursday, July 12, 2012 9:26 AM
To: xxx@xxx.xxx.edu
Subject: Re: [EVDL] Circuit drawing for potbox modification.

I guess I didn't make it clear how my pot box works. My Curtis starts
at 0 ohms and goes to 5k. I need the 0 to 500 ohm area to stretch out a
bit. So the time it takes to go from 0 to 500 ohms is extended. My
problem is jerking at start. The pot is too sensitive. I need
feedback. As it is now I have to be very ginger with the pedal and it
takes me a few seconds to do a smooth start in gear. I could just use
the clutch but that would be defeating the advantage of the electric
drive and wear out the clutch. Lawrence Rhodes......

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| Please take those discussions elsewhere. Thanks.
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  #7  
Old 07-13-2012, 09:25 AM
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Default Re: [EVDL] Circuit drawing for potbox modification.

[quote]Cor van de Water wrote:
> Probably the simplest is to get a "logarithmic" pot,
> the type used in volume controls which ramps up
> slowly in the beginning and faster towards the end.

I like Cor's approach. They even often have a built-in switch (intended
to turn the radio on/off). It may be a challenge to find a high quality
logarithmic pot, though. They are normally used for audio, and most are
very cheaply made.

But there are a few more things to check first.

1. The Curtis 1221 and 1231 series controllers have an adjustment
on the side to control the rate of acceleration. Look for three
screws on the side of the case. The one farthest from the other
two is the acceleration ramp control. Remove the screw, and turn
the trimpot behind it counterclockwise to slow down the rate of
acceleration. That may solve your problem!

PS: Use an *insulated* screwdriver! Put tape around the metal
shaft so it won't short anything inside the controller to the
case! Preferably, kill all power to the controller before making
this adjustment.

2. Are you sure the potbox isn't just dirty? Curtis uses cheap
unsealed pots, and the potbox itself is not sealed. It's common
for water, dust, bugs, etc. to get inside and damage the pot.
They can be cleaned with spray contact cleaner as a temporary
fix, but the problem will return.

3. The pot may also be defective. I have completely smooth throttle
response right from zero with a Curtis 1231C controller. The
Curtis pot went bad after a few years, causing the same sort of
jumpy response you reported. I replaced it with a higher quality
sealed pot. No more problems!

4. You can also slow the throttle response by putting a 100-470uF
electrolytic capacitor across the potbox terminals. The higher
the capacitance, the slower the response. This 'fix' also tends
to mask the jumpiness of a dirty or failing pot.

5. The standard Curtis potbox setup is 0-5k ohms, with 0 ohms
being off, and 5k ohms being full on. Make sure you have this
kind of controller to work with a logarithmic taper pot.

Curtis has several other options. Some reverse the resistance
range, so 5k is off and about 400 ohms is fully on. 0 ohms is
interpreted as a short, and turns the controller off. Others
need a 0-5 volt input for the throttle. Again, exactly 0v
or 5v is interpreted as a fault, and turns the controller off.

6. Curtis only uses about 45 deg. of rotation of the pot for 0
to full throttle. Most pots spread their resistance over 300
deg. If you replace the pot with a conventional or logarithmic
one, it needs to be at least 20k to get 0-5k with only 45 deg.
of rotation.

--
Ring the bells that still can ring
Forget your perfect offering
There is a crack in everything
That's how the light gets in.
-- Leonard Cohen, from "Anthem"
--
Lee A. Hart http://www.sunrise-ev.com/LeesEVs xxx@xxx.xxx

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