How to measure the Shunt resistance of your Controller

I made a video to explain the process of determining the shunt resistance (Rshunt) of your controller. This method will work, even if you have modified the shunt to increase your controller's amperage, as it literally measures the actual resistance directly, based on a constant current from an iCharger (Foam Cut mode at 10.0A) and measuring the voltage drop across the shunt, using the CA connector of the Controller.

We do this measurement on every controller we sell, and label the controller for the actual Rshunt value so you can program your CA accurately.

You can do the same for your own controllers with the proper equipment as shown in the video.

[youtube]okpFsoHNE7I[/youtube]

Cool, knowing the actual shunt value of your controller. Great idea to do that for your customers.

Thanks for showing how to do it for ourselves.

Stupid wifi is not working well enough to see the vid right now, but can I assume the method is essentially the same as here?
http://endless-sphere.com/forums/viewtopic.php?f=31&t=31548#p457115
or at least similar?

Yes, the same.

Very handy to have it in video form though, even easier to follow than Methods step by step.

Its very similar to methods' method, but I use a DMM instead of a CA to read the voltage drop in milliAmps. And I don't have to calculate anything. Just note the voltage drop and move the decimal over by one since I used 10A current to increase the resolution of the DMM.

Succinct and tidy video.

The procedure called out in the Methods post (traceable origin to Justin - not surprising ) can be found in the CA V3 Unofficial User Guide with a sample calculation and wiring illustration: "Appendix A. Calibrating the Cycle Analyst RShunt Value". Although this is in the V3 Guide it is applicable to the V2 as well.

A variation for calibrating the CA using an external shunt can be found in this post (e.g. for cases of using a simple length of wire as a shunt or a modified commercial shunt).

For one-off 'home' calibration, it can be slightly more accurate to use the target CA instead of an external DMM since the procedure then directly calibrates the CA and accommodates any existing CA calibration error. In the end, determining the shunt resistance is not the point of the exercise, but rather to cause the CA to read current accurately. Using the CA in lieu of a DMM may result in a CA RShunt setting that is not exactly the true shunt resistance but that results in more accurate CA current measurement - this is the slight difference between 'calibrating the CA' and 'finding the shunt resistance'.

• FWIW - the CA-vs-DMM approach can be of added value if the CA has ever been flashed with pre-3.0B20 firmware or any later firmware version with a filename of the form "XXXX_Cal.hex". Those files overwrite the unique per-CA custom calibration done at the factory and replace hidden gain settings with generic values. This 'generic calibration' is typically not off by more that a couple of percent, but if you are calibrating anyway, using the CA instead of a DMM may yield more accurate CA operation.