jrk12v12 too often connection lost!

Hi all!.
I am using 3 jrk12v12 (plugged via usb) to handle my 3 12v motors using a 10turn pot to each one of my jrk.

Ok the little jrk working good but often I get connection lost!
In 10 tests I get 4 or 5 times that one of my jrk lost the connection with the pc.
And all the 3 jrk have suffered this problem so I think it’s impossible that all my 3 jrk are all broken!

When this happen I have to unplug and replug the usb cable and the problem is solved. (I tried these tests in 2 different pc getting the same problem)

So, why is that? I think the jrk is not optoisolated. Can be this the problem? or maybe my USB cables?
And if the problem is the optoisolation so I need just to optoisolate all my 3 usb ports right?

I would just to can to use my 3 jrk continuously and without problems!
Please help me!! :unamused:

Hello, aldoz.

I’m sorry you are having trouble with jrk.

Could you give me more details about what you are doing? How is everything being powered? Are all three motors/jrks running at once? Do you have any more info about your 12 V motors, like a web page or datasheet?

If you are using Windows, could you look in your Device Manager and describe the entries you see for the jrk? There should be three entries during normal operation. What entries do you see when the system is in this bad state? What are the jrk’s three LEDs doing when it is in the bad state?

Please try getting your system into this bad state and then connect the jrk’s RST line to GND for a few seconds. Does that fix the USB connection?


Hi David and thx for the answer!
I try to answer to your questions:

Ok this video show you my 3dof system and you can see the main cable design :

My 3 jrk are plugged to 2 car batteries.
The 3 jrk are set to 22.5 amps max current instead 12 amps max current (but I get some problem with my jrk set to 12amps max current) .
I am using alluminium heatsinks for each jrk and 2 fans to provide fresh air.

My motors are winch motors 12v 25amps max
here an ebay page:

ebay.com/itm/Master-Lock-12- … 12&vxp=mtr

Yea I am using windows 7 64bit and in the device manager I can see 3 entries when all is ok:
Pololu jrk 12v12 Command Port (COM5)
Pololu jrk 12v12 TTL Port (COM6)
Comunication port (COM1)

these 3 entries for each jrk.
Unfortunately I have not seen the device manager when I had the problem. Tomorrow with new tests if (better say when… :frowning: ) I will get the problem so I will go to watch the device manager entries!.

When the problem come so I can see just the yellow light slowly flashing (should mean that the power alimentation is ok, in fact the jrk is plugged to the battery. But no green light!!)

Do you mean the input RESET pin? the 4th pin starting from up in the main description jrk pic? How I can connect this pin to GND? and you mean the GND pin? the 8th pin right? I need just to make a bridge from RESET pin to GND pin?

Thanks for all the information.

I’m pretty sure COM1 is not associated with a jrk, but each jrk should have two COM ports and one entry in the “Pololu USB Devices” list. Let me know what you see in the Device Manager when the system is in this bad state.

How did you connect 3 jrks to 2 car batteries? Are the batteries in series or parallel or neither?

It looks like your motors are pretty big and you aren’t using any acceleration or duty cycle limiting on them. If the jrk abruptly switches from a duty cycle of 0 to a duty cycle of 100% forward, the motor will briefly draw a current equal to its full stall current (> 20 A). This could cause the voltage on the jrk’s VIN line to spike downwards and that could cause problems. If that is the problem, shorter leads from the car batteries to the jrks could help, and adding a capacitance of a couple hundred microfarads between the jrk’s GND and VIN pins could help. How far are the batteries from the jrk?

Since the jrk’s green LED is off, it means that either there is no power being supplied on the USB port, or (more likely) that the computer has stopped sending any packets to the USB port. I suspect that some kind of electrical noise is getting back to the USB port and it is shutting off to protect itself.

Yes. That pin is labeled RST on the back of the board, and RESET in some of our pictures. You can connect it to GND using any type of wire. If you have a F-F premium jumper wire that would be best, but just a normal wire will work if you are careful to not short anything out. Any pin on the jrk that is labeled GND will suffice.

If this method of restarting the jrk works for you, I might be able to make a special version of the firmware that does it automatically. Still, this would only be a workaround and it would be better to do something that prevents the problem from happening in the first place.


Hi david and really thank you for help.
So, my batteries are in parallel.

Yes the problem may be because of this, I thinked about it too. Please tell me if I understand you when you write “shorter leads from the car batteries to the jrks could help”…
Do you mean to have shorter power cables from jrk to batteries? these my cables are 1 meter long so I think not too much…

About the “adding a capacitance”, do you mean this? :

If not please can you add a picture of what you mean? (sorry but my english is really on my limits…)

The batteries are 1 meter from my jrk.

Dude it would be great! but before I need to do some test and get again the problem to answer to your question about device manager list.

tomorrow I will have time to do all these tests and tomorrow I try a new configuration of PID, duty cycle, accelleration, pid period and integral limit too from mine friends using jrk too. I notice that all these parameters was not too optimized so I am curious to see if I can solve the problem just using a more optimized jrk config utility settings.

For now THANK YOU very much and as soon as possible I will update here my situation! :slight_smile:

I’m not sure if this is your problem or not, but I think it’s a bad idea to connect two car batteries in parallel. One car battery should be able to provide enough current for all three jrks.

Yes, I mean shorter power cables from the jrk to the battery. Maybe one meter is too long. Shorter, thicker cables might help.

By “adding a capacitance”, I mean adding a electrolyitc capacitor to each jrk. It should be close to the GND and VIN lines of each jrk. This would be the schematic:

If that doesn’t solve the problem and you’ve already tried turning the acceleration way down, then I think those motors are just too big for the jrk 12v12 to handle.


Hi again david!
So today I made a lot of tests and I have other informations about the problem of the jrk lost connection.

Here the vids of what my platform do and what ask to the jrk12v12 :

You can see that sure I am asking much to my little jrk but they works really good!!

I tried many settings about PID, duty cycle, accelleration, pid period and integral limit too and I find a better and more precise behaviour of my motion system but unfortunately the “lost connection” error back today and many times.
From what I understand (and I am 80% sure about) more the motor get effort more the percentage of possible error grows.
I lowered the duty cycle and accelleration and I get less errors.
Here the errors:

And now the news! When I get the error (or the first pic error or the second too) I watched the device manager and I see that the situation here is the same of when all the 3 jrk are working without problems.

here the pic, I have this exact situation when my 3 jrk are working good and when one or more jrk stop to working after a connection lost:

See the next REPLY of this thread to see the device manager pic! I can’t attach more of 3 pics!

Do you think you can handle the problem with the reset method which you were talking to me? or making a new firmware making in automatic this reset?

And I notice too that the jrk had the green and yellow flashing lights exactly like when they are working correctly and powered (other day I told you that there was just the yellow light but I think I was mistaken).

So when I get this error I can’t to move the motor from jrk config utility, I can’t move the motor from x-simulator (the software I am using for my motion system) and I must to unplug and replug the jrk to back to have control of it.
When I replug the jrk then I can move again the motor from the jrk config utility and from x-sim too.

Thank you for the scheme, I speak about that to my electrician team mate! I MUST to solve this problem and all the theoretical solutions are loved here!!!

and remaining in the “external components” matter to solve this bad problem, please, take a look to next reply of this thread to see the pic of the schema about 6 relays that should solve finally this bad connection lost error.
I already test this method time ago and WORKS!! No more the jrk providing the current from batteries to the motor!
The relays will think about the motor power alimentation and with this method I can get ALL the truly motor power with really less suffering for the little jrk!.

In fact the jrk will handle just the order to positions and feedback so I am pretty sure (I hope!!!) that no more problem related to too many amps request from motors or bad and very big amps peaks!.
Please tell me what you think about!.

I stop to use this method just cause I was pretty sure I could use directly the jrk to handle without problems my winches motors… but as you told, probably I am a bit over the jrk12v12 performances…

A last thing, why 2 same models car batteries in parallel is not a best choice?

For now again thank you a lot, your help it’s really precious mate and sorry for my bad english…

here the device manager pic. If the 3 jrk are working or NOT working the situation is always this:

Here the relays schema to avoid the jrk handling the current from battery to motor leaving it really relaxed and fresh!. Will be the relays to handle the current from batteries to motor!:

Another thing you can try is a USB opto-isolator. If the problem is that electrical noise is getting to the USB port then something like this might help:

circuitsathome.com/products- … -populated
lipoly.de/index.php?main_pag … _id=209711

I have not tried that product myself and I don’t know how good it is, but if you do try it let us know how it works.

Also, please try setting the PWM frequency of the jrk to 5 kHz instead of 20 kHz. This might reduce the errors.

Did you try connecting the jrk’s RESET to GND yet?

It’s a bad idea to put two batteries in parallel because if they are at different voltages then a lot of current flow as they equalize. Then during normal operation, if the batteries have slightly different internal resistances then they will be used unevenly.

I don’t really understand your relay schematic but I think it will not work. Bidrectional control requires four relays. The jrk outputs a 20 kHz PWM signal that allows it to have fine control, but relays are basically on or off.


Hi again David, I am really curious about the opto isolation and sure I will to try it!
Tomorrow I will try to change the PWM frequency.
I was thinking that these winches motors needed to use 20 khz. But I will make this test!

About the reset solution so I have not tested yet (damn…) but I will to test it too.

Ok, so 2 parallel batteries are not the best choice (I was dubious too about to use 2 parallel batteries) but the connection lost problem also happened when I was using a single battery for each motors so probably the main problem is elsewhere.

About the relays schema, it’s works good! :slight_smile: Already tested, from jrk config utility moving the motor (with a pot for feedback) on various positions, clockwise and anticlockwise, exactly as I am using my system without the relays)

BUT sure I can’t edit the duty cycle and accelleration anymore. I will to obtain MAX power of pure and total 25amps making the jrk avoid to get bad amps peaks or too high amps inside his little silicion body! :slight_smile:

Tomorrow I will go to buy the 6 relays needed and I will update you about!
(the little bad thing is that you can hear the click click sound when the relays are working, lucky this noise is really low.)

I am curious about your electrolyitc capacitor method!. If I will find the right time so I will do all these tests!
I really love the jrk12v12 and I would to obtain the maximum from my motion system continuing to use these little powerful motor controller boards!