# Controller or pot box dead?



## johnsiddle (Jun 22, 2011)

Dougnutz said:


> Hi all,
> Old reliable didn't move this morning. I did a quick investigation and it looks like the pot box has died. I am running Curtis 1231c. Off hand I wasn't sure how to test the pot box but with only two wires (not counting the closed throttle switch) it seems like it would have to be some sort of variable resistor. I checked the input and output voltage across the range of it's motion. It measured just shy of 10v which remained constant despite throttle position.
> 
> This seems suspect to me I would expect 5v or battery voltage (12v) but 10 seemed odd. The fact that it doesn't noticeably change as I move the throttle makes me fairly sure it's a bad pot. But it's odd that it failed so completely and suddenly. It worked fine yesterday and died this morning.
> ...


Disconnect it from your controller and measure the resistance across the two wires you have. See what it measures throttle closed and then progressively move the throttle, it will either rise (if zero ohms at closed) or fall (if high value at throttle closed).
I do not know what the max resistance should be but I would expect it to be between 1Kohms and about 10Kohms.
But if it changes linearly then i would say it is OK no matter what the max resistance is and the fault might be in either the controller or wiring, although wiring is the lesser possibility.

I hope this helps.


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## Dougnutz (Aug 22, 2011)

Well, the pot seems to check out. It has .5ohm resistance at rest and about 5k at full throttle. Reasonably smooth progression from rest to full throttle. Are there any quick tests that can be performed on the controller? Or do you just test the motor directly and condemn the controller by process of elimination?


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## evmetro (Apr 9, 2012)

I don't know much about your controller, but have you verified that your main contactor is working?


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## johnsiddle (Jun 22, 2011)

Whilst I dont know anything about your controller, if there is only two wires then I would check that the both wires really connect back into the controller.
The 10volts may well be OK for that controller.

After that it may be down to to opening up the controller and having a look inside, or get someone who knows the controller and maybe has a circuit diagram for it to check it out.

It sounds to me like maybe the ground wire is not connected, where were you reading the 10v, between the wires or from ground/chassis to one wire.?


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## johnsiddle (Jun 22, 2011)

I have just had a thought, the throttle closed switch has not hammed in the closed position has it?

Test the switch before doing the next bit
If you can, disconnect it and try a live engine run (OUT OF GEAR OF COURSE).
If nothing try shorting the two switch wires and do the same. (OUT OF GEAR OF COURSE).


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## Dougnutz (Aug 22, 2011)

Thanks for all the replies. Here is what I have verified.
The main contactors closes with key on. 
The second contactor closes when the throttle starts to move, verifying it he throttle switch in the pot works properly.
The pot moves from about 0 to 5k ohm. Which as far as I can tell is correct for a Curtis.
The controller has three small connections. One has key on voltage the other two go to the pot. I removed each one and verified they are tight and clean,

The traction battery voltage is up to 151 (normal off charge voltage) the connections to the controller and battery are tight. I have not removed them yet to check for corrosion and arcing. I'll do that tonight.

I also put the truck in gear and moved it some to rotate the motor in case the brushes were resting on a bad spot in the motor.

So far it looks like the controller has taken a dirt nap. . I'm hoping someone has some more ideas. I don't really want to send this off to be repaired but I can't afford a new one right now.


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## Dougnutz (Aug 22, 2011)

well, last night I tore into things and confirmed my suspicion. The controller has expired.

I confirmed the motor works on 12v. The battery pack is healthy and charged. The contactors are closing properly. With no voltage drop across the contacts. The pot is near 0 ohm at rest and 5k open. The 12v key voltage to the controller is present as well as the case ground.

Since that is pretty much everything else in the circuit, process of elimination leads me back to the controller. I took it off last night and tried to figure out how to open it up. There were 8 screws in the bottom but I could not separate case. I'll have to find a disassembly thread somewhere.

At this point it's pretty much academic. I'm in the market for a controller. Probably a Zilla 1k or Soliton. Both are intriguing.

Any recommendations or pointers for either a controller or place to buy would be appreciated.

Thanks


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## onegreenev (May 18, 2012)

What is your aux battery voltage? What is the minimal voltage for your controller. I find low aux batteries the usual problem. Check that first. Make sure your aux is full. Don't assume it's good.


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## Dougnutz (Aug 22, 2011)

good point, I should have checked that. I merely tested with a logic probe. I guess I take the aux battery for granted and the car was fresh off the charger.

I'll double check the aux battery this evening. 

Thanks!


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## EVfun (Mar 14, 2010)

The Curtis 1231C controller doesn't use vehicle 12 volts. The ksi terminal should be connected to pack positive voltage. Weird things can happen if you power ksi with vehicle 12 volts. Here is a nice diagram of the correct controller wiring. Do not allow pack voltage to come into contact with either of the pot box pins, it will destroy the logic section of the controller.


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## domosher (Jul 10, 2011)

if I read you correctly you said that the voltage at the control pot box terminals was 10 volts if this is true and your pot box measures correctly that means one of the wires between the control and pot box is open. I repair these controls on a regular basis.


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## johnsiddle (Jun 22, 2011)

domosher said:


> if I read you correctly you said that the voltage at the control pot box terminals was 10 volts if this is true and your pot box measures correctly that means one of the wires between the control and pot box is open. I repair these controls on a regular basis.


This was my thinking, especially as the voltage did not change much when he operated the throttle.
If the pot is reading zero ohms when closed there has to be a zero (or very near) at the pot box.
I think the chassis/ground/-ve return from the pot box to the controller is open circuit, either at the pot box end, the controller or has been cut/broken somewhere in between.
Look for somewhere where there is movement when the throttle or brake pedal is moved.

He needs to check this out with a multimeter not a probe.


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## johnsiddle (Jun 22, 2011)

See if this picture helps you.
Basically the pot box MUST be connected for the voltage to change.
If it does not then you have a broken wire, marked red.
The exact voltages I can not be sure of because I have no knowledge of the controller, but the reading across the pot can not stay at any voltage with movement if it is fully connected.

The internal resistance in the controller is probably used to sense an open throttle/pot box and KILL all drive.


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## johnsiddle (Jun 22, 2011)

I have just realized I did not allow for a broken pot box wire when I designed my controller.
I shall have to modify it, an open wire could mean death....


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## Dougnutz (Aug 22, 2011)

Dougnutz said:


> I'll double check the aux battery this evening.
> 
> Thanks!


 
well the aux battery tested 12.5 with the headlights on. Not much of a load but I don't have any real loads in the truck anymore.


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## Dougnutz (Aug 22, 2011)

johnsiddle said:


> See if this picture helps you.
> Basically the pot box MUST be connected for the voltage to change.
> If it does not then you have a broken wire, marked red.
> The exact voltages I can not be sure of because I have no knowledge of the controller, but the reading across the pot can not stay at any voltage with movement if it is fully connected.
> ...


Thanks for drawing that out. It makes a lot of sense.
I wasn't testing like this and I have already pulled things apart. 

What I was testing was each wire to ground. I also checked resistance across the pot. Checking each wire to ground the voltage didn't move with the pot. I'm guessing that means the break in circuit is inside the controller.


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## Dougnutz (Aug 22, 2011)

EVfun said:


> The Curtis 1231C controller doesn't use vehicle 12 volts. The ksi terminal should be connected to pack positive voltage. Weird things can happen if you power ksi with vehicle 12 volts. Here is a nice diagram of the correct controller wiring. Do not allow pack voltage to come into contact with either of the pot box pins, it will destroy the logic section of the controller.


I bought this truck already mostly converted. The kit came from kta and includes a wiring diagram of the pack (high voltage circuits) and the 12 auto circuit. The diagram clearly shows the top terminal above the pot connections is connected to 12v + with the key. This isn't an official Curtis diagram but the truck has been hooked up this way for 6 years... So I didn't second guess the connection.

I did some digging and found an OEM manual here http://www.evsource.com/datasheets/curtis/Curtis_manual.pdf
Which shows the ksi connected to pack voltage. Quite strange.

Apparently this has been hooked up wrong for a very long time. I wonder if this explains they random stuttering under moderate load that has plagued me for the life of the truck.

At this point I have the Zilla replacement already ordered. But I does make me want to put the controller back on and test it out wired correctly...


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## johnsiddle (Jun 22, 2011)

You have all the info you need to sort this problem. Let us know how you get on.


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## johnsiddle (Jun 22, 2011)

Dougnutz said:


> Thanks for drawing that out. It makes a lot of sense.
> I wasn't testing like this and I have already pulled things apart.
> 
> What I was testing was each wire to ground. I also checked resistance across the pot. Checking each wire to ground the voltage didn't move with the pot. I'm guessing that means the break in circuit is inside the controller.


buy a 5k variable resister (preferably linear, but otherwise any will do just not so smooth) from your local TV/Electronics store and connect it across the terminals on the controller the read the voltage across the resistor, if the voltage never changes as you move the resistor then the fault is deffo in the Curtis, if the voltage moves, put the car OUT of gear, jam the throttle open (to operate the kill switch) then see if you can drive the motor by varying the resistor you just bought., if you can the fault is between the pot box and Curtis if it still does not drive then the Curtis is shot..... Simplessss....

Reading between the main chassi and any wire is meaningless...


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## Dougnutz (Aug 22, 2011)

Well EvFun was right. The controller works fine with the ksi terminal on pack voltage rather than aux battery voltage. This explains ALOT. Like why my voltmeter was not changing. With one lead connected to the pot wires and one connected to aux neg. It also explains why the Curtis controller has no ground for the ksi voltage. I always thought it was odd, but figured it was getting ground through the case. Which it was grounded to aux neg. 

I am back up and running now by adding a relay for the ksi circuit. 

I want to thank everyone who helped me run this down.

I am a little worried that something in the Curtis might be damaged but so far it seems to be back into a working state. Having been miswired for so long, then suddenly not working it makes me wonder what changed. 

Since the Curtis seems to be designed to operate in isolation from the cars 12v system I've been trying to figure out how this ever worked. I did a little testing and found that the traction battery and the aux battery are not completely isolated. If I hook my meter to the traction battery pos (144v) to the chassis ground I see 74v. My first thought was that mid pack there is something grounded. But mid pack is literally mid pack. Nothing around it to be grounded to. 

So I'm guessing that some component in the system is not completely isolated. The only thing I can think of is to start un hooking things until the two batteries are isolated.


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## EVfun (Mar 14, 2010)

Thanks for letting us know you found and fixed the problem. It is hard to have perfect isolation between the traction pack and the chassis. A little dust on the battery tops, a little carbon inside the motor... a lot of ways to have single digit milliamp connections between the frame and the traction pack. 

I recommend making up a set of multimeter cables with a 1000 ohm resistor between them. Then use that to check for voltage between the traction pack and the frame at different points (the charger should be off and unplugged.) For each volt you read that is 1 milliamp of leakage current. Anything less than 5 milliamps is generally considered safe.


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## Tesseract (Sep 27, 2008)

EVfun said:


> ...I recommend making up a set of multimeter cables with a 1000 ohm resistor between them....


A good idea in general because modern digital multimeters have very high input impedance (10M is typical) and so will read a voltage with no current to back it up. Loading down the input with 1k to 100k will eliminate capacitive/static charge buildup and get a "real" voltage reading between the (supposedly isolated) pack and chassis.

That said, do note that the power the resistor might have to dissipate here is given by the equation V²/R so, for example, a 144V pack with a hard fault to vehicle chassis will result in up to 20W of dissipation. Better use at least a 10W "cement" resistor and limit measurement time to a second or two, or use a bigger resistor, or one with a larger resistance value.


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## gunnarhs (Apr 24, 2012)

Dougnutz said:


> I am a little worried that something in the Curtis might be damaged but so far it seems to be back into a working state. Having been miswired for so long, then suddenly not working it makes me wonder what changed.
> 
> Since the Curtis seems to be designed to operate in isolation from the cars 12v system I've been trying to figure out how this ever worked. I did a little testing and found that the traction battery and the aux battery are not completely isolated. If I hook my meter to the traction battery pos (144v) to the chassis ground I see 74v. My first thought was that mid pack there is something grounded. But mid pack is literally mid pack. Nothing around it to be grounded to.
> 
> So I'm guessing that some component in the system is not completely isolated. The only thing I can think of is to start un hooking things until the two batteries are isolated.


 Regarding the 74 Volts I would start checking the wiring between battery pack and DC-DC-converter (if present)...


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## arklan (Dec 10, 2012)

> Apparently this has been hooked up wrong for a very long time. I wonder if this explains they random stuttering under moderate load that has plagued me for the life of the truck.


had this exact issue until it failed on and i had to hit the button
i also had the exact issue with reading the 74 volts from battery pack to ground, i narrowed it down to the motor and a proper multimeter showed 4.4mohm resistance
i was told this is nothing to worry about and to ignore it
if u put ur multimeter accross all of the batteries and see the voltage going down as u go through all the batteries its a pretty safe bet its the motor
carbon build up as evfun said


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## Dougnutz (Aug 22, 2011)

EVfun said:


> ...
> 
> I recommend making up a set of multimeter cables with a 1000 ohm resistor between them. Then use that to check for voltage between the traction pack and the frame at different points (the charger should be off and unplugged.) For each volt you read that is 1 milliamp of leakage current. Anything less than 5 milliamps is generally considered safe.


So I finally got back to this. I wired a 1k ohm resistor into some leads and measured the voltage across the resistor. The reading was .017 volts of leakage. I'm using a Fluke meter with a good set of leads so I trust the meter to be pretty accurate. So it seems (as most people mentioned) this is a non issue. 

As a side note the truck has been running better than ever with the controller KSI wired up properly. So I was tempted to send the Zilla back but I made the mistake of reading through the manual and all the features including the data stream. I've convinced myself to keep it. Now to wire it up 

I'll probably spin up another thread on this subject. I can't afford a lot of down time so I will be wiring the hairball up with just the basics this weekend. Then hopefully enabling more features and tuning it later.

Anyone on the market for a used Curtis


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