# Curtis 1205X-4417 Fixed to Variable Plug Brake Modification



## zindello (Dec 5, 2014)

Hi,

As the topic states, I'm interested in hearing from people who have hacked apart older Curtis controllers and made modifications and who may have a schematic of the logic/control board in the 1204/1205 series controllers.

My situation is I'm using a 1205X-4417 controller with a 200A 24V Series motor for traction. I had intended to use the plug braking feature on the controller as the primary braking method, however unfortunately the -4417 controller (Which was ratted out of a pallet lift along with the motor) has a fixed 175A plug current, and is not variable with the throttle position (but rather set by the current limit pot of the controller).

Looking at the block diagram it seems that the fixed versions use the throttle position signal for variable braking and the main current limit for fixed into the plug current comparator. I'm hoping it's as simple as cracking open the controller and changing a jumper to convert it to variable plug braking which is needed for my application however a schematic would greatly assist me in figuring this out.

My only other alternative I had looked at was to remove the A2 lead from the controller and using a fairly heavy duty diode and a 1W 500 Ohm resistor implement my own plug diode and resistor and bypass the plug diode/detection in the controller alltogether. This would prevent the controller from detecting plugging and allow the user to vary the throttle in reverse and plug braking could still be provided. As far as the controller would be concerned, the unit would just be running in reverse direction and provide the same fine control as normal. If that proved to be still too effective I could switch in an additional resistor between the B+ and A1 on the motor to further limit total motor current.

I have a second controller that I can mess with for this experiment. The application is a miniature railway locomotive so the fixed (very high) plug current which is fine for rubber-tyred vehicles is unsuitable in my application and simply causes the wheels to lock up and then spin in the opposite direction.

Any help would be greatly appreciated.

If I can't get this to work with these units somehow I fear I'm going to have to go buy different controllers but given I got these "for the right price" if these can be modified to work in the situation that would be preferred.

Cheers,
Josh


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## major (Apr 4, 2008)

Hi Josh,

Interesting. But I doubt your plan to alter the plug circuitry will work. Several reasons. Have you studied the block diagram appendix A in the manual? There is no separate plug current sense. Just the usual current sense on the fets. Also, during the plug, the pwm frequency is altered.

Ever think about adding some extra field coil to the motor for a braking field? 

Got any photos?

major


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## zindello (Dec 5, 2014)

Hi Major,

Are you looking at the same block diagram as me? From the 1205x manual if you trace the following you'll see what I'm hoping can be done:

A2 -> Plug Detect -> Current Limit Comparators -> Plug Current Reference

At that point it branches off into 3 references, one for emergency reverse, one for variable plug (which goes to the throttle input) and one for fixed plug. From an electrical point of view the selection between variable and fixed would make sense to be either a jumper/link selection, or a software selection between two inputs. In either case, changing a link or cutting and detouring a trace to alter the input to a comparator is s no brainier - if I can get hold of a schematic for the unit.

Pics I'm not sure will help, but I'll add some if I can figure out how to upload them from my phone.

Cheers,
Josh


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## zindello (Dec 5, 2014)

Here's one photo that shows (kind of) the high power electronics.


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## zindello (Dec 5, 2014)

And here it is during testing hauling a 9 car (3000kg) train.


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## Tesseract (Sep 27, 2008)

For this application - high inertia/low speed - you really don't want to do plug braking; mainly because it requires additional energy from the battery and both that and the energy of the load, of course, get converted into heat in the controller and motor.

Dynamic braking - where load energy is dumped to a resistor grid - is kind of pointless if you have a battery pack while regenerative braking is so difficult to do with a series field motor you might as well say it is impossible. If you really need/want regenerative braking you either need to go with a sepex motor and controller (available for your power level at a reasonable price) or an AC motor and inverter.

Most low speed trains don't bother with any kind of motor braking, however, as there just isn't enough payback to offset the reduced reliability from increasing the drivetrain's workload.


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## zindello (Dec 5, 2014)

Hi,

I'm fully aware that it requires extra energy to provide plug/dynamic braking. At this stage the project is unfinished and there will be the addition of a petrol motor and a charging alternator to keep the batteries charged whilst the unit is in use. The whole point of going to a "controller based" setup was to take advantage of the electric braking available in the controller. The other alternative is compressed air, which is FAR more inefficient than plug/dynamic braking.

If I can't do that, then I may as well rip out the additional batteries and go to a straight petrol electric setup and build my own dynamic brake but that requires additional contactors, resistor banks, etc. It also requires the motor to be running every time I want to move it a short distance which is not what I'm after.

Also, given I'm running 210mm diameter wheels and they're geared at nearly 10:1 from the motor, from the motors perspective it's most definitely running at high speed, hence the want of (very effective) plug/dynamic brakes.

Oh and the drivetrain? Yeah that's dual row 1/2 pitch chain. A little electric braking isn't going to bother it one bit. As for heat I've added some fairly size able heatsinks to help with that and it will be getting fans also. This isn't my first dabble with high current electronics.

Anyway back to the main question ...

Is it possible to/is anyone familiar enough with/does anyone have the schematic of the logic board on these controllers so that I can asses the feasability of modifying the board to alter it from fixed to variable plug braking? I could trace it out but being quit a complex circuit thats going to take a lot of time if there's a source for what I'm looking for. Bypassing the internal plugging circuitry is also another option but I don't want to go down that path if the controller can be modified.

Cheers,
Josh


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## Tesseract (Sep 27, 2008)

zindello said:


> I'm fully aware that it requires extra energy to provide plug/dynamic braking.
> ...
> This isn't my first dabble with high current electronics.


And just how were we supposed to know that given that you just joined the forum this month and have all of 5 posts to your name???



zindello said:


> Is it possible to/is anyone familiar enough with/does anyone have the schematic of the logic board on these controllers so that I can asses the feasability of modifying the board to alter it from fixed to variable plug braking?


There is no "logic board" on these controllers: they basically use a few comparators to form the pulse width modulator (not even a dedicated PWM chip!) and sense the voltage drop across the MOSFETs when on to obtain a crude sense of motor current. If the 1204 sense motor current in the same way as the 1221 (and it probably does) then it would require some nasty kludging to implement variable current plug braking. That said, I don't know of anyone who has bothered to reverse engineer the $250-$300 1204 controller, but Otmar of Cafe Electric/Zilla fame did reverse engineer the higher power 1221B and published his efforts here: http://cafeelectric.com/curtis/


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## zindello (Dec 5, 2014)

Hi,
Sorry if my post came across a little blunt, I've been struggling to find someone who's familiar with what I'm trying to do. Next time I'll provide a full scope of the project instead of a limited specific scope/question. I came here as a last resort.

Thanks for posting that link, I'll have a look at that article tonight when I get home and see if it can help. I understand the tech in these controllers is fairly old which is why I was hoping it would simply be a case of altering the Input to the plug reference unit. I could kludge it by adding a "braking switch" that reversed the field, switched out the current limit pot to the throttle on the loco as well and use that to vary the plug current, but there has to be an easier way.

Cheers,
Josh


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## major (Apr 4, 2008)

zindello said:


> Hi Major,
> 
> Are you looking at the same block diagram as me? From the 1205x manual if you trace the following you'll see what I'm hoping can be done:
> 
> ...


Thanks for the photos. Just curious. And photos of neat stuff (EVs) often times brings more replies 

As far as I know, Tess posted about the only known actual schematic. And that block diagram you reference is different than the one in my manual. I think it is newer; for the 1204/5M controllers which have a plug for the programmer and list programmable plug features on the sales brochure


> Programmable, variable or fixed plug braking modes.


 Sorry, I lost the link to that document. So it appears the newer model 1204/5 would do what you want. However the programmer is like $800 not included. I think member frodus will rent them to members. Or if you're close by, I could drop by with mine. BTW, please go to the CP and list your location for us.

I don't think your ideas to hack the plug terminal (A2) will work. If it was me, I'd add the extra coil on the motor field and install a dynamic braking resistor in the A2 circuit. 

As for battery power consumed during plug (or dynamic) braking, it is fairly insignificant; just field excitation power. There can be quite a bit of power to dissipate coming from the kinetic energy. That's why the braking resistor would be nice. Otherwise, plug braking relies on the armature, brushes and A2 diode to dissipate the energy. I think your motor could probably withstand it because I imagine the duty cycle to require relatively few stops and no long descents. 

Like Tess said, modern separately excited DC or AC motor/controllers would regenerate and be the best solution. Another way, if you have the space and weight availability, add an alternator coupled to the drive line. Use resistors across the armature winding and excite the field with low voltage/power source.

I think there is an electrical solution. Neat project.

major


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## nimblemotors (Oct 1, 2010)

I tore apart a 1204 controller.
Just threw away the logic board and made my own and upgrade all the parts as well, but this isn't needed if you only want the original 36volts and 200 amps.

Heck of a lot easier and better than trying to figure out all the analog stuff.


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## PapaGolf (Dec 11, 2014)

pretty cool to see someone still messing with the old curtis controllers!
I am almost done reverse engineering a 1204 logic board. I've got the schematic almost perfect. As soon as I can figure our where the output of the limit integrator connects and figure out what some of the values for resistors are ill be set. Be warned though, this is a work in progress so compare carefully!

As for what I'm doing with it, this was originally a 1204 24-36v controller for my golf cart. Long story short I embarked on the challenge of making it good for 48. and a challenge it has been!

As for your problem, these controllers basically use a comparator (LM339 in my case) read through voltage dividers from B+ and A2. This is at the top center of the schematic. When A2 exceeds the value of B+, the comparator grounds its output. This does three things, 1. changes the voltage divider for the oscillator, 2. provides a resistance to the limit integrator for throttle limiting and 3. Changes the current limiter output. 

Could you post a picture of your logic board? 

I know everyone's going digital but I've been hard pressed to beat the reliability of these curtis logic boards. Eventually I'll be turning to the atmega for mine but for now it's been a nice analog refresher!


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## PapaGolf (Dec 11, 2014)

While we're on the topic of plug braking... Does anyone know if there is a threshold over B+ that A2 has to hit before they go to plug mode or is it simply that A2 has to be above B+?

also, I found out that in my 1204 the A2 diodes are 50v and 50A each. That's probably why the high voltage guys have burnt them up!


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