# curtis 1231C and precharge



## madderscience (Jun 28, 2008)

I have heard some mixed signals on whether precharging a curtis controller (ostensibly to reduce the charge/discharge cycles on some internal components to prolong their lifespans) is a good idea or not. Precharging is typically done by having a small relay in parallel with the main contactor that feeds pack voltage to the controller through a large value resistor. The idea is to keep the voltage up on the internal components even when the main contactor is open (because you are off the throttle or whatever).

My car currently does NOT have a precharge circuit. I have had no problems to date, but the car is still fairly new (a little over 1 year on the road)

Should I remedy this or not? The paperwork that came with the controller did not recommend it.

Thanks!


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## Guest (Nov 10, 2008)

You need a pre-charge for your controller health and your main contactor health. The pre-charge is usually across your main contactor posts of the HV side. My set up has my main circuit breaker before the main contactor so when that is off I have no power going through the pre-charge resistor. When I turn on the main circuit breaker power is now going to pre-charge my controller. I let it sit a good 15 seconds then I can power up my main contactor and that circuit stays open while driving. Only when I shut down for the night does the pre-charge circuit get turned off. You may use a second main contactor that is used to bring power to the pre-charge resistor then after you wait a specified time you can power up your main contactor. I tap 24 volts off my main pack for my main contactor power. Full 72 volts through my precharge circuit but low amps.

Pete

Pre-charging is cheap insurance for a good long life for your controller and main contacts. 




madderscience said:


> I have heard some mixed signals on whether precharging a curtis controller (ostensibly to reduce the charge/discharge cycles on some internal components to prolong their lifespans) is a good idea or not. Precharging is typically done by having a small relay in parallel with the main contactor that feeds pack voltage to the controller through a large value resistor. The idea is to keep the voltage up on the internal components even when the main contactor is open (because you are off the throttle or whatever).
> 
> My car currently does NOT have a precharge circuit. I have had no problems to date, but the car is still fairly new (a little over 1 year on the road)
> 
> ...


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## Guest (Nov 10, 2008)

By charging up your controller caps you prevent voltage spikes and those can hurt the controller and main contacts. 



madderscience said:


> I have heard some mixed signals on whether precharging a curtis controller (ostensibly to reduce the charge/discharge cycles on some internal components to prolong their lifespans) is a good idea or not. Precharging is typically done by having a small relay in parallel with the main contactor that feeds pack voltage to the controller through a large value resistor. The idea is to keep the voltage up on the internal components even when the main contactor is open (because you are off the throttle or whatever).
> 
> My car currently does NOT have a precharge circuit. I have had no problems to date, but the car is still fairly new (a little over 1 year on the road)
> 
> ...


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## Tesseract (Sep 27, 2008)

madderscience said:


> I have heard some mixed signals on whether precharging a curtis controller (ostensibly to reduce the charge/discharge cycles on some internal components to prolong their lifespans) is a good idea or not.


I am quoting myself from another thread here:

***
The current that "rushes in" when the contactor is closed without pre-charging (called, appropriately enough, "inrush current") can be estimated by dividing the pack voltage by the capacitor bank's "ESR", or equivalent series resistance. Good quality electrolyics of the size typically used in this application have an ESR, each, of around 0.05-0.5 ohms. A bank of 10 in parallel will look like a 0.005 to 0.05 ohm resistor to the battery pack when the contactor closes. If the battery pack is 120V then the peak inrush current (ignoring Peukert effect, battery cable resistance, etc.) could be as high as 24,000A. This amount of current, if it doesn't cause the conductor to outright vaporize, will make it "jump". That's what hurts the electrolytics: the foil electrodes end up rubbing against each other which could wear through the thin oxide dielectric causing them to short out.
***

Now you decide if precharging the caps is a good idea or not


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## jlsawell (Apr 4, 2008)

And here is a beautiful tutorial on how to put it all together. I've done it for my setup and it only took about half an hour...

http://www.zeva.com.au/tech/contactor_jewelry/


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## judebert (Apr 16, 2008)

I'd like some way to have the whole thing work like a regular ignition switch.

When I insert the key at position 0 (off), nothing is enabled. 

When I turn the key to position 1 (accessory), the contactors and precharge circuits drop out. The car is not drivable in this position.

When I turn the key to position 2 (running), the contactors are latched into their present condition. During starting, this will be off; after starting, the contactors will remain on.

When I turn the key to position 3 (starting), the precharge circuit is enabled, allowing the controller capacitors to charge. Once the capacitors are charged, the contactors are latched on.

So, during normal starting, I start with everything off. I insert the key at position 0, and it key through position 1 (no change), to position 2 (still no change), and hold it at position 3 until the controller is charged and the contactors turn on. I then release the key, which moves back to position 2, leaving the contactors on.

When I'm done driving, I move the key to position 1, opening the contactors; the car is no longer drivable. Then I move the key to position 0 and remove it.

Is there an easy way to accomplish this? I hate the idea of my precharge circuit being on all the time.


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## patzke (Nov 1, 2008)

judebert said:


> I'd like some way to have the whole thing work like a regular ignition switch.
> 
> When I insert the key at position 0 (off), nothing is enabled.
> 
> ...


This makes sense and seems rather simple to do with a little time and a few relays. jlsawell posted a link to a tutorial showing a way to make a precharging system. Looking at it, the system is ALWAYS being precharged ... right? Design something using your idea, with the tutorial posted and you're good to go.




jlsawell said:


> And here is a beautiful tutorial on how to put it all together. I've done it for my setup and it only took about half an hour...
> 
> http://www.zeva.com.au/tech/contactor_jewelry/


That's wonderful, I will go get the parts for that today. Does this mean that the precharge circuit is always precharged?

If so, is this unacceptable?

*EDIT:* I continued to read on in the tutorial and got some decent ideas for the precharge system. Would it be efficient enough to have momentary switch on your dash you could hold for a few seconds while you're getting ready to start up to precharge your system? How long would an ordinary precharge cycle take? Anywhere from 5 ~ 20 seconds depending on how large of a resistor you attached?

OR would it be better to have it attached to your ignition which would trigger a relay, which would trigger your precharger.


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## rfengineers (Jun 2, 2008)

judebert said:


> I'd like some way to have the whole thing work like a regular ignition switch.
> 
> When I insert the key at position 0 (off), nothing is enabled.
> 
> ...


I built a step-start controller that does exactly what you describe plus it has an input that monitors the vacuum pump and waits until the pump stops before enabling the main contactor. I have been testing it for the past couple of days.

I expect to be offering them for sale in the next week or so. You can see the setp-start circuit board mounted on the back of my relay box in the attached picture.


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## jlsawell (Apr 4, 2008)

judebert said:


> I hate the idea of my precharge circuit being on all the time.


I'm curious as to why you feel this way.

As far as I'm aware, KiwiEV just mashes the contactor together, ZEVA uses the precharge resistor and has it on all the time. Both of these seem to be the ends of the spectrum and both work OK for their respective owners.


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## e_canuck (May 8, 2008)

jlsawell said:


> And here is a beautiful tutorial on how to put it all together. I've done it for my setup and it only took about half an hour...
> 
> http://www.zeva.com.au/tech/contactor_jewelry/


You are right. Beautifull. I am going to get some parts.

Thankx,

DP


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## JRP3 (Mar 7, 2008)

As I've mentioned in other threads, Alltrax controllers show the precharge resistor always connected. This may actually preserve the life of the controller by keeping the capacitors fully formed at all times. I have yet to see a good argument to switch off the precharge resistor, unless the vehicle will be sitting for weeks without being charged.


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## Guest (Nov 11, 2008)

Having the precharge on all the time even when the vehicle is off is in my opinion not a good thing. But having it on all the time while driving or during quick stops is not really a problem. If the caps are charged no further current will get wasted. Only when the caps need charged will the pre-charge pump out some juice. I want to set mine up so when I shut my key off the main contactor will shut off and a second contactor that will shut off that controls the pre-charge circuit. That way all will be off. For now as long as I manually shut off my main circuit breaker switch my pre-charge circuit is off. No leaking power after I shut down for the night. 

Pete : )

Best to keep it as simple as possible. More contacts mean more points for failure. It will most likely be just fine but you may want to have an idiot light for each contact switch just in case it does not work so you know if it is not working. LED's last for just about ever so those idiot lights are a good thing. Less electronics easier to fix and less to go wrong down the road. 

: )


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## JRP3 (Mar 7, 2008)

gottdi said:


> Having the precharge on all the time even when the vehicle is off is in my opinion not a good thing.


Why?
I should also point out that Alltrax recommends a much higher precharge resistor value than is used in the ZEVA article, depending on the voltage used.
48V 400ohm 10 Watt
72V 1000ohm 10 Watt.
http://evdrives.com/accessories.html
http://evdrives.com/Manuals/Alltrax/Doc120-046-A_TN010-Contactor-Fuse-Diode-Lessons-Learned.pdf


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## Guest (Nov 11, 2008)

Why? Only because it is just one more voltage discharge point. But it really is not a big deal. Power is only pulled from the pack when the caps discharge enough to need more. If you have decent caps in your vehicle the amount is negligible. I just like knowing that all power is off to the controller. It is no big deal to start it up again in the morning or when you decide to drive your vehicle. I may not turn it off if I am going to keep moving or will stop for a short time. I currently manually turn off my main circuit breaker so when that is off all power to the controller is off. Like I said in a previous post I still had one hell of a charge in my caps even after three days of non use. 

Pete : )

So in a nut shell it is just a personal thing. But I do need an easy way to shut off power and discharge the controller if and when I am working on the system. I don't really like that power floating around when my hands are in close proximity. So the main circuit breaker is my controller shut off and then I go for the battery cables before I do any work. 





JRP3 said:


> Why?
> I should also point out that Alltrax recommends a much higher precharge resistor value than is used in the ZEVA article, depending on the voltage used.
> 48V 400ohm 10 Watt
> 72V 1000ohm 10 Watt.
> ...


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## patzke (Nov 1, 2008)

gottdi said:


> Why? Only because it is just one more voltage discharge point. But it really is not a big deal. Power is only pulled from the pack when the caps discharge enough to need more. If you have decent caps in your vehicle the amount is negligible. I just like knowing that all power is off to the controller. It is no big deal to start it up again in the morning or when you decide to drive your vehicle. I may not turn it off if I am going to keep moving or will stop for a short time. I currently manually turn off my main circuit breaker so when that is off all power to the controller is off. Like I said in a previous post I still had one hell of a charge in my caps even after three days of non use.
> 
> Pete : )
> 
> So in a nut shell it is just a personal thing. But I do need an easy way to shut off power and discharge the controller if and when I am working on the system. I don't really like that power floating around when my hands are in close proximity. So the main circuit breaker is my controller shut off and then I go for the battery cables before I do any work.



Pete, 

What if you put a momentary push button on your dash to control your precharge system. Hold in for 10 or 15 seconds before you turn your car on. Then the system is only charged when you want it to be charged; when you first close the main contactor. Right?

*EDIT: I could not find the recommended 5W 180ohm resistors at my local radio shack, and they said they could not order them. What range or resistor ratings is acceptable for a precharge system?*


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## rfengineers (Jun 2, 2008)

JRP3 said:


> As I've mentioned in other threads, Alltrax controllers show the precharge resistor always connected.


Alltrax also insists that the main contactor MUST open when you let the throttle up. Do you know why they say this? It's because people repeatedly jump in and out of their electric cart to swing a stick at a little ball. When they jump out of the cart they do not turn off the key and carry it with them. If you regularly jump out of your EV and leave the key turned on in the ignition then you too should follow Alltrax's advice.



JRP3 said:


> This may actually preserve the life of the controller by keeping the capacitors fully formed at all times.


What are you basing this claim on? Electrolytic capacitors fail in this fashion if they sit unused for YEARS, not days or weeks.



JRP3 said:


> I have yet to see a good argument to switch off the precharge resistor, unless the vehicle will be sitting for weeks without being charged.


It's a saftey hazard. If all controller connections are fully protected from accidental contact then you are correct. However, I have yet to see a non-golf-cart that meets this condition.


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## judebert (Apr 16, 2008)

rfengineers said:


> I built a step-start controller that does exactly what you describe plus it has an input that monitors the vacuum pump and waits until the pump stops before enabling the main contactor. I have been testing it for the past couple of days.
> 
> I expect to be offering them for sale in the next week or so. You can see the setp-start circuit board mounted on the back of my relay box in the attached picture.


Very nice! Is it just that little circuit board? I could mount it behind the dash, I'm sure. But I bet there's at least one extra contactor.



rfengineers said:


> It's a saftey hazard. If all controller connections are fully protected from accidental contact then you are correct. However, I have yet to see a non-golf-cart that meets this condition.


That's my problem, as well. I can already get accidentally shocked while charging if I'm fooling around in the engine compartment. I want to fix that. An always-on precharge resistor would mean I can get shocked while the car is off, too. I definitely don't want that. And I'm willing to take the trade-off of waiting a few seconds whenever I start the car.


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## dimitri (May 16, 2008)

When talking about precharge you need to take in consideration how many contactors your EV has. I saw variety of schematics with 1 or 2 contactors. Depending on this, precharge can be done in different ways and have different overall impact.

In single contactor EV, if you hardwire precharge over main contactor, you will have safety issue because pack voltage will always be present on controller and there will be a slight drain of current to keep capacitors charged up at all times, even overnight, etc. In this case it makes sense to use some sort of relay circuit to close precharge few seconds before taking off. There are so many ways to do it, depends on your imagination.

In dual contactor EV, one contactor is closed by ignition and 2nd is closed by pressing the gas pedal. In this case just hardwire precharge resistor across 2nd contactor and give 2-3 seconds between turning the key and taking off. Safety and drain will be controlled by 1st contactor breaking the circuit when ignition is off.

As for value of the resistor, it can be between 100 Ohm and 1000 Ohm, depending on how long you want precharging to last. Some people even use 120V light bulb in plase of resistor, it helps to precharge very quickly, but has its own downside, like being made from glass, etc. Search for a thread on EVDL on the subject, very interesting reading.

As for not having precharge at all, some report years of EV use with no trouble, but why not have an extra benefit for very little cost? Even if it reduces chance of controller and contactor failure by 1%, why not have it?

I added mine last night, bought 130 Ohm 35Watt resistor on Ebay for couple bucks, whole job took 15 min. I happen to have 2 contactor setup because I used a kit from EVA and followed their schematics, so I just hardwired it.

After 3 months of use there were noticeable arcing marks on 2nd contactor, so I KNOW there will be a benefit from precharging in the long run.

Please note, I am not arguing that 2 contactor setup is better, both can be done safely and both have benefits, I simply differentiate them in light of precharge discussion.

YMMV...


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## e_canuck (May 8, 2008)

I have been reviewing my own equipment and I am now very confused.

I am using the Curtis 1231c so my Precharge resistor should be 750 ohm. That part is easy.

But what value should I get for the coil supression diode?

My contactors are from EVA. What is that small "thing-a-mabob" that is already on the contactor's terminal?










To my uneducated eyes they look like a resistor and a diode. So...Is the coil supression diode already there?

Thanks,

DP


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## frodus (Apr 12, 2008)

looks like it. The resistor is there to extinguish the current in the coil quicker.


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## rfengineers (Jun 2, 2008)

Frodus is correct. The diode is already installed across the contactor coil. That is why the coil has polarity markings.


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## rfengineers (Jun 2, 2008)

judebert said:


> Very nice! Is it just that little circuit board? I could mount it behind the dash, I'm sure. But I bet there's at least one extra contactor.


The step-start circuit is the blue circuit board in the picture. That is my test board, so everything is in sockets for easy upgrading. The final device will not use sockets since they tend to fail in automotive use due to vibration.

The three relays in a row are Precharge, Vacuum Pump and Contactor Enable. You are correct about needing at least one extra "contactor". The Contactor Enable relay is needed because the optoisolator can only sink 400 miliAmps and the Contactor draws 1500 miliAmps.


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## frodus (Apr 12, 2008)

And it happens to be installed in the correct polarity  

I honestly think they should come preinstalled on all contactors. Just clip them if you don't want them for some reason.

I got a Tyco EV200, its all built into the economizer.


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## Tesseract (Sep 27, 2008)

frodus said:


> looks like it. The resistor is there to extinguish the current in the coil quicker.


...and to limit the peak current through the diode when the coil kicks back.


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## JRP3 (Mar 7, 2008)

rfengineers said:


> Alltrax also insists that the main contactor MUST open when you let the throttle up. Do you know why they say this? It's because people repeatedly jump in and out of their electric cart to swing a stick at a little ball. When they jump out of the cart they do not turn off the key and carry it with them. If you regularly jump out of your EV and leave the key turned on in the ignition then you too should follow Alltrax's advice.


That's true but many EV's use the same setup and have the contactor open when off throttle. I see that as unnecessary but it's up to the individual. The main point is that Alltrax sees no problem leaving the precharge connected at all times, even when the carts are parked for weeks. They don't seem to be worried about the liability of shock from the caps.


> What are you basing this claim on? Electrolytic capacitors fail in this fashion if they sit unused for YEARS, not days or weeks.


I guess the point is that it doesn't hurt the controller to have the precharge always on, and may help it. I honestly don't know, but is it harder on the caps to be repeatedly charged and discharged, or remain charged?


> It's a saftey hazard. If all controller connections are fully protected from accidental contact then you are correct. However, I have yet to see a non-golf-cart that meets this condition.


It's not that hard to protect your connections, and how much hazard is it? High voltage yes, but what sort of amperage are we talking about?


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## frodus (Apr 12, 2008)

JRP3 said:


> It's not that hard to protect your connections, and how much hazard is it? High voltage yes, but what sort of amperage are we talking about?


If its only the caps that are charged (contactor disengaged), and you touch the + and - of the controller, its not enough to kill you, but it does give a little bit of a bite on a 156V controller.

I'm under the belief that if someone is that stupid to horse around near a controller, they deserve the little zap. I mean, come on, its not that hard to protect the connections. There should be NO OPEN busbar accessable under the hood of the car, and the connections should be protected enough so that hands cannot get near the bus. You should ALWAYS and I mean ALWAYS discharge the caps with a load before you work on a car. You cannot depend on equipment to keep you safe. Even if the controller has a built in discharging circuit, what if it fails? 

A GOOD ENGINEER/designer, would actually discharge the bus before working on it, and put a load or a short across the controller + and - bus the entire time he's working on the vehicle. That way if anything engages, at least the breaker or the fuse blows.

And yes, I'm an engineer that has worked on large scale control systems for GE Energy, H2E Incorporated and now Leviton. In every instance, you treat everything as if its got power on it. If you're stupid enough to touch those terminals without a safety in place, you deserve the next darwin award. I've worked around rectifiersthe size of a house that ran 1000V at 30kA (yes, thats 30,000A) for Intalco Aluminum Smelter, and we always discharged the bus manually via ground poles. On an EV, you can open the contactor, and put a jumper of some sort across the bus. Its the safest way to work around it if equipment fails. I mean, why else are you under the car.... to fix it? replace the controller? upgrade batteries?

People need to use more brains and count on themselves, not equipment to protect their lives.


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## rfengineers (Jun 2, 2008)

JRP3 said:


> That's true but many EV's use the same setup and have the contactor open when off throttle. I see that as unnecessary but it's up to the individual. The main point is that Alltrax sees no problem leaving the precharge connected at all times, even when the carts are parked for weeks.


You are correct, if there is no shock hazard there is no problem with leaving the precharge resistor connected and the HV on. Even over weeks or months the energy lost is negligible. Anyway, if an EV is to be left undriven for more than a week or two I would think that battery issues would become a more important consideration.



JRP3 said:


> They don't seem to be worried about the liability of shock from the caps.


 But there is a big difference between a professionally designed, mass produced vehicle and a DIY EV. From what I have seen of the various cars on the road today additional attention to shock hazards would be a good thing.



JRP3 said:


> I guess the point is that it doesn't hurt the controller to have the precharge always on, and may help it. I honestly don't know, but is it harder on the caps to be repeatedly charged and discharged, or remain charged?


 In theory, leaving the caps charged all the time is better, but we are talking about a MTBF (mean-time-between-failure) of a few percent. Not really worth considering.



JRP3 said:


> It's not that hard to protect your connections, and how much hazard is it? High voltage yes, but what sort of amperage are we talking about?


 At best a shock is unpleasent, at worst it can cause you to involuntarily do something else that has far worse consequences. You could drop a metal tool across a battery, you could draw back your hand across a sharp exposed metal edge (personal experience there, several stitches were the result).

I am just proposing an alternative to increase the safty margin.


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## judebert (Apr 16, 2008)

frodus said:


> I'm under the belief that if someone is that stupid to horse around near a controller, they deserve the little zap. I mean, come on, its not that hard to protect the connections.


Unfortunately, my car just isn't that well designed. Maybe it's my controller: all the connections are out in the open. I've painted them with insulating silicone (the kind you dip your tools in), and I've covered all my tools, but I've still managed to inadvertently make enough shorts that I earned the nickname "Spark Lad".



frodus said:


> A GOOD ENGINEER/designer, would actually discharge the bus before working on it, and put a load or a short across the controller + and - bus the entire time he's working on the vehicle. That way if anything engages, at least the breaker or the fuse blows.


That's a good idea! I'll be using it the next time I go look under the hood. All I need is a big resistor and a couple of alligator clips!



frodus said:


> You cannot depend on equipment to keep you safe. Even if the controller has a built in discharging circuit, what if it fails?
> ...
> If you're stupid enough to touch those terminals without a safety in place, you deserve the next darwin award.
> ...
> People need to use more brains and count on themselves, not equipment to protect their lives.


Exactly why I want more safeties. My main contactor is redundant; I've got two fuses and a breaker on the traction pack; I've even got an inertia switch. I used AGM batteries, so I shouldn't have any gassing, but I'm still paranoid about developing an electrical path to frame. What's the problem with a precharge circuit that's not always on? One less thing to zap me.



frodus said:


> I mean, why else are you under the car.... to fix it? replace the controller? upgrade batteries?


I'm having some trouble getting my batteries to make any sort of sense, so I'm among them regularly, measuring and whatever else I think will help.

Then there are the improvements: I've rewired my vacuum system twice. I'm planning on a new switch. After that, I want to get the tachometer working, then put a rev limiter in. Somewhere around the same time, I need to figure out why the heater is so unusual. In my fantasy world, I want to see about a Lee Hart Battery Balancer, an eVision, an maybe even an individual-unit battery monitor.

All those things requires being in among the electrons. 

And even if I do something smaller, like body work, paint, or windshield replacement, I can still get in among the electrons. Especially if something has gone wrong while I wasn't looking.

Here's the bottom line: when I turn my car off, I want it *off*. No precharge circuit, no DC/DC converter, no electrolyte trail from the batteries to the frame. *OFF.* I'm willing to put up with some 12V stuff for the clock and the meter, but I want a way to turn those off, too. 

It seems to me that's the best possible sense.


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## frodus (Apr 12, 2008)

judebert said:


> Here's the bottom line: when I turn my car off, I want it *off*. No precharge circuit, no DC/DC converter, no electrolyte trail from the batteries to the frame. *OFF.* I'm willing to put up with some 12V stuff for the clock and the meter, but I want a way to turn those off, too.
> 
> It seems to me that's the best possible sense.


do you have a main breaker and a main fuse?

If so, then tap the precharge AFTER the main breaker.

Then when you work on it, switch off the breaker, discharge the bus and you're done.

If not, maybe do a keyswitch precharge on accessory power, then when you turn the car to ON it engages the contactor.


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## Tesseract (Sep 27, 2008)

Folks, the debate over whether to protect your own selves from the consequences of touching exposed "high" voltage terminals is a bit, well, silly if you think about it. 

Here's what the UL says about this sort of thing: a product is considered safe if and only if a "tool" (e.g. - a screwdriver) is required to access anything energized at more than 42.4V. Clearly, no controller on the market meets this requirement, thus, none have UL approval (or, I should say, none would receive it should they pay for the testing to be done). Is this a big deal? Once again, that depends on *you*. Personally, I don't worry about *me* touching exposed parts, I worry about *lizards*. Yes, lizards. For some reason they really seem to like electrical equipment and I can't tell you how many times I've found one fried inside of industrial equipment, load centers, etc... So, think of the lizards; specifically, that they catch on fire when they inadvertently bridge the B+ and B- terminals on your controller...


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## rfengineers (Jun 2, 2008)

Tesseract said:


> Folks, the debate over whether to protect your own selves from the consequences of touching exposed "high" voltage terminals is a bit, well, silly if you think about it.


Anyone can make a missteak. Even seasoned professionals. Why, I remember that time I was testing a new system and used a pair of little 10-Amp jumper leads to supply power. Everything ran fine until I activated a device that drew about 25-Amps. The back of the car filled with smoke as the jumper lead insulation melted away.

Yeah, I remember it like it was just this afternoon....... Oh, it was this afternoon!! OOPS. Fortunately the only casualty was a pair of jumper leads.


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## e_canuck (May 8, 2008)

rfengineers said:


> Anyone can make a missteak. Even seasoned professionals. Why, I remember that time I was testing a new system and used a pair of little 10-Amp jumper leads to supply power. Everything ran fine until I activated a device that drew about 25-Amps. The back of the car filled with smoke as the jumper lead insulation melted away.
> 
> Yeah, I remember it like it was just this afternoon....... Oh, it was this afternoon!! OOPS. Fortunately the only casualty was a pair of jumper leads.


I did something similar myself. Once or twice.

I have a question about precharge resistor.

Acording to my Curtis manual I need 750 Ohm with a power rating of 25W.

My favorite electronic retail place as them but...He as to order them from "the head office". Minimum order is 15.

I will not buy 15 of them. So I want to assemble common resistor together.

How?

Thanks,

DP


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## JRP3 (Mar 7, 2008)

http://www.surplussales.com/Resistors/WireWound/WW510-1082.html


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## rfengineers (Jun 2, 2008)

e_canuck said:


> I did something similar myself. Once or twice.
> 
> I have a question about precharge resistor.
> 
> ...


If you combine resistors in series the resistance values add and the Wattage remains the same. {R1 + R2 + R3}

If you combine resistors in parallel the resistance combines as the reciprocal of the sum of the reciprocals. {1/((1/R1)+(1/R2)+(1/R3))} The Wattage increases since the current paths divide among the various branches.

For example, two 1000-Ohm 10-Watt resistors in series is a 2000-Ohm 10-Watt resistor. Two 1000-Ohm 10-Watt resistors in parallel is a 500-Ohm 20-Watt resistor.

It is OK to use a larger precharge resistor if you increase the precharge time. For example, I am using a 1000-Ohm resistor instead of the recommended 750 on my Curtis. That means that my precharge current for my 120-Volt (136-Volt when fully charged) will be (about) 120/1000 = 0.120-Amps instead of 120/750 = 0.160-Amps, so I need to increase my precharge time by about 25%.

Power is Volts times Amps, so the 750-Ohm resistor needs to be: 
136-Volts * 0.160-Amps = 21.8-Watts (25-Watts is a standard value).
OR, using the 1000-Ohm resistor:
136-Volts * 0.120-Amps = 16.3-Watts, with a 25% increase in precharge time.


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## rfengineers (Jun 2, 2008)

rfengineers said:


> I
> Power is Volts times Amps, so the 750-Ohm resistor needs to be:
> 136-Volts * 0.160-Amps = 21.8-Watts (25-Watts is a standard value).
> OR, using the 1000-Ohm resistor:
> 136-Volts * 0.120-Amps = 16.3-Watts, with a 25% increase in precharge time.


Ah, Another mis-steak! If you calculate current at 136-Volts it's 0.181-Amps (24.7-Watts) for the 750-Ohm resistor and 0.136-Amps (18.5-Watts) for the 1000-Ohm resistor.


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## e_canuck (May 8, 2008)

Tx JRP3 and rfengineers.

I have to absorb and do something now.

DP


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## Tesseract (Sep 27, 2008)

rfengineers said:


> If you combine resistors in series the resistance values add and the Wattage remains the same. {R1 + R2 + R3}


Er... um... Perhaps you've been spending too much time with the Smith charts??? I know they make my brain go fuzzy whenever I look at 'em for long enough... Because anytime you increase the number of resistors in a string - whether connected in parallel or series - the total wattage rating of the string goes up... So, for example, if you connect (10) 75 ohm, 5W resistors in series to make 750R the total string will be capable of dissipating 50W. Conversely, if 100V is applied to this string each resistor will see 10V and therefore will dissipate 1.33W (V^2/R); the total string will see 100V and therefore will dissipate 13.33W.

Now, this doesn't apply if all 10 resistors are bundled up tight - the ones in the middle will overheat...


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## rfengineers (Jun 2, 2008)

Tesseract said:


> Er... um... Perhaps you've been spending too much time with the Smith charts??? I know they make my brain go fuzzy whenever I look at 'em for long enough... Because anytime you increase the number of resistors in a string - whether connected in parallel or series - the total wattage rating of the string goes up... So, for example, if you connect (10) 75 ohm, 5W resistors in series to make 750R the total string will be capable of dissipating 50W. Conversely, if 100V is applied to this string each resistor will see 10V and therefore will dissipate 1.33W (V^2/R); the total string will see 100V and therefore will dissipate 13.33W.
> 
> Now, this doesn't apply if all 10 resistors are bundled up tight - the ones in the middle will overheat...


You are correct sir!


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## madderscience (Jun 28, 2008)

So for what its worth, here is what a Curtis rep said about it:

Here is what curtis said about the issue:

Hello Brian, 

1. Our manual recommends a pre-charge resistor across the main contactor. The resistor is primarily there to extend the life of cheap contactors. The resistor reduces the inrush current through the contactor and prevents contact welding. 

However, our largest distributor of 1231C controllers, Bob Batson of Electric Vehicles of America, has his customers go without the pre-charge resistors and he has not had any issues with wear on the controller or the contactors. Bob has used Albright SW200 contactors without any trouble. 

Also since the recommended 750 ohm, 25 watt resistor is hard to obtain, some convertors have opted for using a 120V, 25 watt light bulb.

2. We do not have a recommendation for minimum heat sink area. We simply recommend making it as large as practical. A plate with twice the footprint of the 1231C should be fine. Use a thin coat of thermal paste between the controller and the plate. A metal to metal contact is best for heat transfer. The paste is there to fill minor voids. Note that there is at least one finned heat sinks available online form some non-Curtis source.

Regards,

Wilfredo Chaluisant

Customer Support Engineer

Curtis Instruments


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## engineer_Bill (Jun 24, 2008)

Fry's has a variety of high wattage resisters. You don't need that high of wattage. Higher value resisters 1000OHM or higher. reduces current and can be a lower wattage, it takes longer to precharge, but still only seconds. If you use a light you can tell when the light dims that the precharge is complete. The capaciters dont have to be "full" to prevent inrush. Your main concern is arcing and welding of cantactor so all you need is to reduce inrush below that point. Or order some high wattage resisters from Fry's or another electronics outlet.


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## rfengineers (Jun 2, 2008)

I put a meter across the B+ and B- of my Curtis 1231C. Starting at zero volts and with 124-Volts from the battery pack it took 40-seconds to reach 110VDC using a 1000-ohm precharge resistor.

After opening the contactor the voltage began to bleed down rather quickly. I would estimate that after 60-seconds there was less then 10-volts across the controller input terminals.

It would be interesting to have similar data for some of the other popular controllers.

Now for the bad news.

I powered up my system with the car on jack-stands. The motor ran great and the wheels turned (in the right direction too!). I repeated the test, but on the third try the motor no longer ran. It seem that Curtis is not immune from the recent rash of controller failures!!


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## Tesseract (Sep 27, 2008)

rfengineers said:


> ... I repeated the test, but on the third try the motor no longer ran. It seem that Curtis is not immune from the recent rash of controller failures!!


Man, that sucks... You didn't by any chance have a scope connected across the motor terminals when you were testing it, did you?

(realize it's a long shot; asking anyway)


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## rfengineers (Jun 2, 2008)

Tesseract said:


> You didn't by any chance have a scope connected across the motor terminals when you were testing it, did you?


No, I didn't. There was no warning, it ran fine one moment and the next it was dead. Well, I guess I will have more time to finish the instrument cluster work! EV-Parts says it will be about three weeks to fix the controller.


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## Tesseract (Sep 27, 2008)

rfengineers said:


> No, I didn't. There was no warning, it ran fine one moment and the next it was dead. Well, I guess I will have more time to finish the instrument cluster work! EV-Parts says it will be about three weeks to fix the controller.


No warning, huh? Isn't that just typical... 

Since you are using the Warp9 motor, you might find this link interesting:

http://hitorqueelectric.com/gallery/v/custom_motors/warp9_101/

Mainly because the guy disassembles a Warp9 motor and finds a few "issues" with it. Specifically, the silver soldered joint for one of the field winding terminals was loose. Doesn't take much imagination to see how that could cause problems for a controller...

Not saying this *is* the problem, just suggesting it as a possibility.


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## rfengineers (Jun 2, 2008)

Tesseract said:


> Not saying this *is* the problem, just suggesting it as a possibility.


That's interesting. Wilfredo at Curtis suggested that I check for a shorted motor. What kind of resistance should I read across it?

I swept the motor with my vector impedance meter before I hooked it up. I will sweep it again and see if I get the same readings.


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## patzke (Nov 1, 2008)

rfengineers said:


> That's interesting. Wilfredo at Curtis suggested that I check for a shorted motor. What kind of resistance should I read across it?
> 
> I swept the motor with my vector impedance meter before I hooked it up. I will sweep it again and see if I get the same readings.



Im sorry to hear about the controller. 

At least they're sending you a new one!

How awkward though that you had it runnin a few seconds before, LOW current too - right?


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## Tesseract (Sep 27, 2008)

rfengineers said:


> That's interesting. Wilfredo at Curtis suggested that I check for a shorted motor. What kind of resistance should I read across it?
> 
> I swept the motor with my vector impedance meter before I hooked it up. I will sweep it again and see if I get the same readings.


Weeelllll, the field and armature resistances, should they be individually accessible, are probably on the order of 50 milliohms... what you really want to find is a shorted turn, a short to frame or an intermittent connection... Actually, I suspect the latter would be both the most difficult for a controller to cope with and the most likely to happen. No doubt you can imagine the consequences from interrupting a couple hundred amps through the amount of inductance in more than a few inches of wire, much less that of the motor and wiring together (use your LCR bridge to measure that, btw, and let us know how much inductance that Warp9 has... make sure to try different rotor positions to help smooth out the effects of any residual magnetism).


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## rfengineers (Jun 2, 2008)

Tesseract said:


> Weeelllll, the field and armature resistances, should they be individually accessible, are probably on the order of 50 milliohms... what you really want to find is a shorted turn, a short to frame or an intermittent connection... Actually, I suspect the latter would be both the most difficult for a controller to cope with and the most likely to happen. No doubt you can imagine the consequences from interrupting a couple hundred amps through the amount of inductance in more than a few inches of wire, much less that of the motor and wiring together (use your LCR bridge to measure that, btw, and let us know how much inductance that Warp9 has... make sure to try different rotor positions to help smooth out the effects of any residual magnetism).


The motor swept exactly the same as it did previously, raw data attached.

I hooked it up to a single 12V battery and it spins smooth as silk.

Patzke; Sorry, I did not note the current draw, but I don't expect it was very much with the drive wheels up in the air.


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## Tesseract (Sep 27, 2008)

Bang it with a rubber mallet, especially near the field terminals, and see if there are any disturbances. Might also need to spin the rotor.


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## rfengineers (Jun 2, 2008)

rfengineers said:


> I powered up my system with the car on jack-stands. The motor ran great and the wheels turned (in the right direction too!). I repeated the test, but on the third try the motor no longer ran. It seem that Curtis is not immune from the recent rash of controller failures!!


I have good new and I have bad news to report:

The good news is I should have my controller back before Thanksgiving!
The bad news is they couldn't find anything wrong with it. Which means, I don't know why my car stopped working!!

Any suggestions?

Here is what I know: 
The battery pack voltage at the B+ & B- terminals is 125VDC.
I read no voltage at the B+ M- terminals regardless of the pot box setting.
The motor turns when connected directly to 12VDC.
The pot box checks out OK with an Ohmmeter.
The system worked just fine several times and then quit.
The controller worked correctly when tested by EV-Parts. They tried it on the bench and in a test vehicle.


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## e_canuck (May 8, 2008)

rfengineers said:


> I have good new and I have bad news to report:
> 
> The good news is I should have my controller back before Thanksgiving!
> The bad news is they couldn't find anything wrong with it. Which means, I don't know why my car stopped working!!
> ...


Hi Joe.

You are better at this than I am. But I will try.

Are you using a potbox with a microswitch? Is the switch testing?
You might have a break in the wiring from the potbox or from the microswitch.

Is the potbox fused? with a valid fuse?

KSI relay?

Last try from me. His there a dead bug between the contacts of the contactor?

Good luck, we are all rooting for you,

DP


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## rfengineers (Jun 2, 2008)

Hey DP,

Thanks for the feedback, here are my responses.



e_canuck said:


> Are you using a potbox with a microswitch? Is the switch testing?
> You might have a break in the wiring from the potbox or from the microswitch.


Nope, no microswitch. I leave the contactor on as long as I am driving.



e_canuck said:


> Is the potbox fused? with a valid fuse?


No potbox fuse. A direct connection to the controller.



e_canuck said:


> KSI relay?


I though this might be the problem, but I connected the KSI input directly to the B+ with one of those handy "10-Amp Fuse" Jumpers while I was trying to figure out what was wrong.



e_canuck said:


> Is there a dead bug between the contacts of the contactor?


I really did look (with a small inspection mirror) at the contacts to see if there was anything in there, like a scrap of plastic left over from drilling holes in the box. They were clear.

Joe


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## JRP3 (Mar 7, 2008)

Did they open up the controller? I wonder if it could be an intermittent problem in the controller? I guess if you hook it up and it works that might be the problem.


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## rfengineers (Jun 2, 2008)

JRP3 said:


> Did they open up the controller? I wonder if it could be an intermittent problem in the controller? I guess if you hook it up and it works that might be the problem.


The tech said he was not authorized to open the controller. All he could do was check the operation and return it to a factory authorized repair center if it failed the tests.


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## CPLTECH (Sep 14, 2007)

*Here is what I know: *
_*The battery pack voltage at the B+ & B- terminals is 125VDC.*_
_*I read no voltage at the B+ M- terminals regardless of the pot box setting.*_

Not sure how much you have already done in troubleshooting this, but here are some suggestions and I see others have chimed in as well :

*KSI terminal (Key Switch Input)–* Must see pack positive voltage (~120V). Mine uses a 3A fuse and then goes thru the micro switch found on the pot box assembly. Measure from pack negative to the terminal as pedal is depressed enough to close switch contacts or will not go.

*B+, B-* *–* Not sure where you are placing the meter probes, so this may not apply in this case but may be beneficial to others on the forum… Just that I saw too many industrial maint techs measure incorrectly, even tho they saw a voltage but could not interpret correctly what they just saw. One must *always* measure across the two incoming terminals that make a device or motor do its work. (Saw where some would measure from ground to hot on a motor circuit. What if the neutral circuit was open? A motor uses ground for safety purposes only, not to make it rotate.) So, in this situation I would put one probe on the batt pack neg and one on the controller B+ terminal (should read ~120V). If missing, may be the 200A(?) contactor or ???. Likewise the motor must see the variable voltage (0-120V) across terminal M- to B+. Put the probes where you can measure the same voltage the motor has a desire to see. Keep in mind that the controller is only changing the “ON” time of the negative. The positive is not modified.

By the way, the big contactor on my unit went defective. Fortunately the previous owner threw in a spare at time of purchase. He must have known those devices do age with use/abuse.


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## Jimdear2 (Oct 12, 2008)

Here is a thought, If I have missed this suggestion from someone elsewhere, I appologize. 

Since you are powering the controller directly from the KSI, do you have to disable the High Pedal function in the controller. If you did disable it has it been reset by accident. On my controller, I believe this has to be done through software. If yours is also is done through software, is there a reset defaults function. 

By passing the high pedal switch with out disabling this function might be causing the trouble. 

JIm


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## rfengineers (Jun 2, 2008)

Jimdear2 said:


> Here is a thought, If I have missed this suggestion from someone elsewhere, I appologize.
> 
> Since you are powering the controller directly from the KSI, do you have to disable the High Pedal function in the controller. If you did disable it has it been reset by accident. On my controller, I believe this has to be done through software. If yours is also is done through software, is there a reset defaults function.
> 
> ...


Jim,

High Pedal Disable (HPD) is an optional feature that, as far as I know, is not included in the 1231C. It is one of those Golf Cart legacy things, like a throttle pot micro switch and plug braking, that are not used in on-the-road EVs.

Joe


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## tj4fa (May 25, 2008)

If you have one of those KLK fuses, check it for continuity. It might be blown.


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## ragee (May 25, 2008)

tj4fa said:


> If you have one of those KLK fuses, check it for continuity. It might be blown.


The same with a main power fuse if installed.


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## rfengineers (Jun 2, 2008)

tj4fa said:


> If you have one of those KLK fuses, check it for continuity. It might be blown.


I checked them all and, what-do-you-know, they are all SHORTED!!

Ha ha, just a little geek humor there (very little).

But seriously, you should not check fuses that way. The correct way is to measure the voltage drop across the fuse in circuit. I remember walking into the ET shop on board the USS Chicago one afternoon and finding one of our new techs checking all of the 1/32-Amp fuses with a Simpson 260 and wondering why they were all blown!!!!

The ohmmeter was, of course, blowing the fuse during the continuity check.


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## tj4fa (May 25, 2008)

rfengineers said:


> I checked them all and, what-do-you-know, they are all SHORTED!!
> 
> Ha ha, just a little geek humor there (very little).
> 
> ...


I'm not that smart when it comes to electronics and luckily never blew a fuse with an ohmeter (as far as I know). But a friend of mine went through a lot of jirations checking this and that and it came down to the KLK fast acting fuse was bad.


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## ElectriCar (Jun 15, 2008)

I would hope and recommend all of you who value your controller to fuse the pack near the controller. 

You want to use a "Semiconductor" fuse if you want to save it. All fuses are NOT the same even though they have the same amp rating.

For example, an industrial motor rated 100 amps may draw 300A or more on startup! Therefore a "Slow-Blow" or time delay fuse is required. A semiconductor fuse rated 100A would blow immediately as it should.

Semiconductor fuses are designed for just such applications as our controllers. The 1231 is rated 500A, or mine is at least. I'm running a 400A fuse but may upgrade to 500 as required. 

Hopefully I'll know before Turkey Day if I need a larger fuse as I'm hoping to be driving by Tuesday!!!


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## rfengineers (Jun 2, 2008)

My Curtis 1231C came back this morning. I installed it and it works just fine with the car up on jack-stands.

I lengthened my precharge timer to 30-seconds. I put a voltmeter across the contactor and measured 125.7-VDC. The voltage began to drop when I closed the precharge relay. After thirty seconds the meter indicated 40-VDC, then the contactor closed. I am using a 1000-ohm resistor, so lets see... the rc time constant is .... ought, ought, carry the naught. um, and the natural log of that is... Wow, 26-miliFarads of capacitance.

After the contactor opened the voltage rose quickly. It reached more than 75-Volts in 15 seconds, so there is a path for the capacitors to bleed off their charge.

According to Curtis the reason for the precharge resistor is to save the contactor contacts. How low of a voltage across the contator is low enough to close the switch?

There is a cute little calculator at:
http://www.cvs1.uklinux.net/cgi-bin/calculators/time_const.cgi
Just enter the size of your precharge resistor, the capacitance of your controller (26 miliFarads for the Curtis 1231C-77XX) and the percentage charge that you want, click "Calculate Now" and it will tell you how long to precharge. Cool.


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