0-5k Throttle Box

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4Springs
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0-5k Throttle Box

Post by 4Springs » Wed, 02 Jan 2013, 20:53

My Kelly controller requires a 0-5k resitive throttle input. I've had a bit of trouble, and thought I'd share my thoughts.

I bought one of these throttle boxes from EV Works: Throttle Box. They consist of a variable resistor mounted in a very robust steel assembly. There is also a microswitch that is enabled when the throttle is all the way off.
A few months after first using the car (about 18 months after buying the throttle box), the response started to become touchy. The resistor had started to degrade, resulting in jerky operation, especially at low speeds.
It was past the warranty time, so I bought a new throttle box.
This was a month or two ago, and now the new one has just started displaying the same symptoms. So for example I was showing someone the motor, with everything turned on and in neutral, when the motor started turning gently all by itself! I'll ask for a replacement under warranty.

This started me thinking about the safety of these 0-5k inputs. If I have a fault that causes the wire to break or otherwise come off the throttle box, the resistance will go high (open circuit). Does this mean that the controller will go full-throttle? Depends on the controller I suppose, but I can't see anything in the Kelly documentation that suggests it looks for high-resistance input. I'd try it out by putting my car into neutral and pulling the lead off, but I'm a bit wary of having the 800A controller full throttle on a series-wound DC motor with no load. I might take a few seconds to get things connected back up again, and by that time the motor may have exceeded its rated rpm. It seems like it would have been better to have a 5-0k throttle input. I would have thought a fault would be more likely to be open circuit than closed.
Anyway, I had the idea that I could use the supplied microswitch for a bit more safetly. I have now hooked it up accross the 0-5k controller input, so the input is shorted out whenever your foot is completely off the accellerator pedal. This will override a failure of the variable resistor or its wiring.

The only thing wrong with the old throttle box was the resistor, so I wondered if I could replace it. It is not a normal variable resistor, the entire 0-5k range is over about 40°.
I found one here, which looks like exactly the same part: resistor.
At $19.75 US the price is not too bad. Unfortunately the shipping charge to Australia is $100!

I found another possible candidate here: green resistor.
Price is much more reasonable at 3.15 UK pounds. Shipping roughly 30 pounds. The trouble is that this pot is not identical to the one in the throttle box, so I was not sure it would fit. Oh, and and is 0-10k, so I'd have to put a 10k resistor in parallel. I bought some to see if they would work.
Once they arrived, I found that I had to drill the hole out bigger, but managed to make one fit. So I now have a spare throttle box. The response was a bit different at very low resistances, but once I wired in the switch as above, it seems to be a good substitute. I have not tried this one in actual driving conditions, but I may have to fit it if the currently installed box gets any worse.


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Jeff Owen
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0-5k Throttle Box

Post by Jeff Owen » Wed, 02 Jan 2013, 22:59

4Springs
I have had the same problem with the Curtis pot box in my car. The first sign of the problem is usually a very small surge of acceleration as you lift off the throttle.
As a temporary fix, try pumping the throttle 5 - 10 full strokes before turning the car on each time you drive it. This seems to work for some cars and not for others, which may be related to the pot being too far gone.

A while back, the surging started again and I bought a new pot from Bylong but before I could install it, the problem went away. The car ran fine for months until one day at Weber's place, I showed the car to a visitor and demonstrated the motor running by operating the pot box manually by pushing on the arm. As I left Weber's house that day the problem returned. Over time and by pumping the throttle the problem went away and has not returned. I no longer operate the pot box manually by pushing on the lever and, so far, there has been no problem

I think the real issue is that the bearings in the pot are not up to having a lever hung off the shaft and that the contact of the wiper varies due to the side loads. There are 2 solutions that I know of.
1: EVWorks sell a Hall Effect throttle box. They also sell/sold an interface that goes between the throttle box and controller to make the controller think it is looking at a resistive pot box. This interface does not appear to be on their web page anymore.
2: Have look at http://www.digitalhometech.com.au/index ... path=68_69 These pot boxes were for sale a while back and he may still make them.



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Johny
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0-5k Throttle Box

Post by Johny » Thu, 03 Jan 2013, 14:34

Jeff Owen wrote:EVWorks sell a Hall Effect throttle box. They also sell/sold an interface that goes between the throttle box and controller to make the controller think it is looking at a resistive pot box. This interface does not appear to be on their web page anymore.
It's still listed as a product on Zeva's web site. Last entry on this page. http://zeva.com.au/Products/

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4Springs
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0-5k Throttle Box

Post by 4Springs » Fri, 26 Apr 2013, 18:30

Ok, I finally have some information to report on this topic.

Resistive Throttle Box:
The green resistors mentioned above were not good enough. I bought several of them, and each one failed within a few hours of driving.
Following up on Jeff's suggestion above, I found that Bylong sell a replacement resistor for their throttle boxes Link Here.
I bought one of these, and managed to make it fit the EV-Works box. It required a bit of persuasion using a drill and hacksaw, but now it is firmly attached. I have used this for the last couple of months with no problems.

Hall-effect Throttle Box:
I asked Zeva and EV Works about the Digital Pot Adaptor (DPA). It was a discontinued item, but they have now recontinued it.
EV Works also agreed to send me a Hall-effect throttle box as a warranty replacement for my faulty resistive one.
So I now have a Hall-effect throttle box and a DPA. I only got them working together today, so I'll see how they go. In theory this should be a better long-term solution.

Hope this info is useful for someone sometime!

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