MoTeC Global Forum

All,

Earlier this year I spent some time with an o-scope and finally the guys at MoTec East here in the USA diagnosing a problem with our M84. Seems like when using the "output test" function the outputs will only swing from ~3.3V to ground. They respond correctly to the configured polarity...etc...just the wrong voltage swing. Upon further testing and inspection, simply toggling the polarity in the ECU manager shows that it will swing the full voltage range. Also it functions normally under ECU running conditions (ie turning on fans and pumps and so-forth)

It should be noted that the outputs were floating...ie not connected to anything
or
the outputs were being used to drive the Vgs on a N-channel fet

This leads me to think that there's some fail-safe within the firmware that is current sensing or something similar...that keeps a floating load from being driven high. (open wire and the High-impedance of the FET gate would act similar).

I was just wondering if this ever made its way out to Aus or if you guys have experienced something similar or could shed some light on whats going on.

thanks!

-John

When testing the ECU output as a low side drive,The output behaves like a switch with one end connected to ground.
When you turn it on you see nothing because it it at ground voltage which is 0V. If you had a load connected to +12V you would have seen the 0-12V toggle.

When you do a test with the high side and low side option enabled the output is controlled by 2 switches, one connected to ground and one connected to +12V. At any time only one of the switches are turned on.
this is the reason when doing the test you see the output switch between 12V and ground.