Jrk12v12 using brushed motors

Hi and happy new year to the forum!

We use the 12v12 Jrk’s for quite heavy duty work, we swing a 2.4m dish in 2 directions (az/el). We use 12VDC brushed motors and max ampere 6A (noted sofar).

We have burned 2 x Jrk’s and wonder why?

Could it be that the brushed motors act as generators and overload the 12v12:s? If so, we need something to prevent too high voltage from the motor into the Jrk, a crowbar? If so, I found the LM431 crowbar application interesting.

Here is a video when we tracked a satellite with a 2.4m dish, it worked about ~1h then the elevation Jrk burned
http://www.youtube.com/watch?v=kbkgu9Kairo Notice: it is always the elevation unit that burns (it got the toughest job)

Suggestions appreciated,
Patrik, Vasa Finland
Jerry Martes, Los Alamitos CA US

Hello, Patrik.

I am sorry to hear you are having trouble with your jrk 12v12 controllers. Do you have the specifications for your motor (particularly its stall current)? How and when did you measure the 6 A current draw? What are you using to power your system?

The stall current of a motor can be much higher than the current it draws while running normally, and it will briefly draw that much current when starting abruptly (and twice that when reversing direction abruptly). If your motor’s stall current is higher than what the jrk can handle, it might be damaging the jrk if you are not taking precautions to limit the current, such as setting an acceleration limit or using current limiting.

- Kevin

Hi Kevin,

We used a 12 volt battery the last time the jrk failed. We used an EXTECH 380941 current meter that measured current less than 7 amps while the jrk current plot never exceeded the 80% line.

The dish moves with less than 10 foot pounds. The gear reduction between the motor and the load is 1,372. The load on the motor is quite small.

Now, we hope to overcome the possible problem by using caps at the motor input


I have talked to Jerry Martes several times over email and phone. I’d like to correct something:

Actually it was one jrk that broke twice. The second break occurred after we had repaired it for him.


Hello, Patrik.

It seems unusual that you’ve experienced failures with the jrk 12v12 twice, and since the driver on the jrk should easily be able to handle a 6-7 A current, I suspect that your motor might occasionally be drawing far more than that. Specifically, I am concerned that it could be drawing current in very short-duration spikes that your current meter might not be able to catch. Do you have access to an oscilloscope you could use to measure the motor current?

Additionally, if you have a way to obtain the stall current specification of the motor, that would be useful for helping determine whether it could ever draw too much current for the jrk.

- Kevin