Odd potentiometer - Page 1
Forum section: electronics / repair

author: thf
author_rank: Newbie
timestamp: July 02, 2014, 09:29:29 am
content: Greetings allI'm in a process of repairing a gas pedal for a electric car. In that unit, there is a 5k 1 turn pot. It has a somewhat odd characteristic, and i have not been able to locate a replacement.Its a CP16110-M50 5KOK ES84 from Colvern Ltd, and the resistive span is around 12 degrees. The rest is either 0 or 5k ohm. Illustrated: -00000000000000000012345555555555555555555+ (360* represented, in kOhm)Anyone know what that sort of specialty is called, or know a manufacture with such a potentiometer?Regards Troels

author: Rerouter
author_rank: Super Contributor
timestamp: July 02, 2014, 09:37:43 am
content: what is the model of car?, most of them only rely on a voltage between 0 and 5 Volt (e.g. 0.82-4.2V for a large number of Mitsubishi)The actual pot is called an S-curve pot, but that curve is unusual from what i have seen, most are linear or audio (2 linear slopes)

author: thf
author_rank: Newbie
timestamp: July 02, 2014, 09:48:23 am
content: Its a speederbox from unknown manufacturer, mounted in a "airport trolley tractor/car".Its indeed linear, and the odd bit is that the change in resistance only happens on a very small span at the middle of the 340* pot turn. The rest is either zero or 5k.

author: Andy Watson
author_rank: Super Contributor
timestamp: July 02, 2014, 10:19:25 am
content: Quote from: thf on July 02, 2014, 09:48:23 amCould it be a break in the track? 12* could easily be the width of the wiper.

author: thf
author_rank: Newbie
timestamp: July 02, 2014, 10:54:05 am
content: Unfortunately not, i cracked it open because it puzzled me aswell.. The carbon area is only at a small part of the rotation.Better illustration:

author: amyk
author_rank: Super Contributor
timestamp: July 02, 2014, 11:15:25 am
content: What is it about the control that needs such a pot? Is it only turned that small amount? You mention it's a gas pedal, so if it's turned the full amount all the range of control would be all concentrated in a narrow range - no power until almost halfway down, and full power just slightly beyond that - which doesn't make sense. I would replace it with a linear pot of a suitably larger value, configured so that it gives the 0-5k when turned the same small amount.

author: thf
author_rank: Newbie
timestamp: July 02, 2014, 11:28:27 am
content: Quote from: amyk on July 02, 2014, 11:15:25 amThat is the correct assumption. Its directly attached to the pedal shaft, so i guess its just to create a deadzone. I think the max speed of the vehicle is around 25km/h and often slower, so perhaps it was made like this to ease the motor going, instead of just on/off adjusting.Remember that 12 degrees a 12,5cm long footpedal is around 3cm travel. But a larger degree up to the max rotation of the pedal shaft is also viable. Though there should be some deadzone to avoid problems in both ends.

author: Rasz
author_rank: Super Contributor
timestamp: July 02, 2014, 11:44:28 am
content: Quote from: amyk on July 02, 2014, 11:15:25 am>"airport trolley tractor/car"might have a weird motor controller that doesnt really like being half throttleor the mechanical part of the pedal limits movement to only that 12' part of the potedit: didnt see last post, so the controller is just extremely simplistic and has no notion of dead zones internallyIf all esle faild you could bodge something with ordinary pot, micro and a digital pot ()

author: amyk
author_rank: Super Contributor
timestamp: July 02, 2014, 12:22:42 pm
content: Reminds me of the time I tried a trolleybus - the pedal travel was only ~1cm and maintaining a constant speed was rather difficult.

author: thf
author_rank: Newbie
timestamp: July 02, 2014, 12:59:00 pm
content: The travel is further than the 12*, so it must be a rather simplistic motor-controller. ( I have not seen the rest of the car, just the "speederbox"). And i cant argue why the original manufacturer has chosen this rather novel pot design. Other than limit other people from repairing them on component level.Does anyone know what type of pot it is? The characteristics-wise. Is it "just" an extreme S curve?Thanks for the input so far

author: Rasz
author_rank: Super Contributor
timestamp: July 02, 2014, 01:43:34 pm
content: option number 2 - mechanical bodgeget 150K linear pot and conductive glue/paintuse paint to short carbon track like in the original (obviously dont paint on the track itself, just on the edge)

author: Fraser
author_rank: Super Contributor
timestamp: July 02, 2014, 02:21:30 pm
content: Potentiometers with delta R over a limited circumferance are common in accelerator pedal applications, due to the small arc of movement available. The 340 degrees of movement is purely due to a standard format of potentiometer chassis being used. Have you considered contacting Colvern ? Many companies like Colvern are happy to assist if you send them a nice friendly email. Colvern becale AB Electronic Ltd in 1997.http://electronics.zibb.co.uk/profile/a+b+electronic+ltd/gb/romford/rm7+9lp/26006343www.abelectronic.comAurora

author: thf
author_rank: Newbie
timestamp: July 03, 2014, 06:40:36 am
content: Thanks Aurora, i would have started to contact them if i could find them. I guess you had more luck than meAB Electronic Ltd is also an obsolete name/company, but i found references to Proxistor and then TT Electronics, so i have contacted the later. Hope they can either help me or direct me to the right company/person.Bodging something together is not really a viable option, as its commercially used and quite a safety issue.

author: thf
author_rank: Newbie
timestamp: July 03, 2014, 09:49:22 am
content: TT Electronics in Germany responded and gave me a quote. Sometimes its detective work that solves the day

author: wagon
author_rank: Frequent Contributor
timestamp: July 06, 2014, 12:07:23 pm
content: I repair a lot of 'mobility scooters' and the throttle pots on those have those funny small ranges. Could be a good low cost way of getting the part needed.

author: Zepnat
author_rank: Regular Contributor
timestamp: July 06, 2014, 12:40:14 pm
content: Welcome Wagon.

author: wagon
author_rank: Frequent Contributor
timestamp: July 06, 2014, 12:46:49 pm
content: Thanks mate.