Purpose of 4.7Ohm resistor?

[Philip Lochner]

Should I have the 4.7Ohm resistor in the PC circuit as shown in the EXTERNAL wiring diagram when running TransControl fw? : http://www.msgpio.com/manuals/mshift/wiring.html

[jsmcortina]

Current limiting perhaps?

James

[Philip Lochner]

I can see no other reason either.

So, with the 2nd GPIO I built, I brought this resistor to a place where I could feel how hot it gets. I almost got a blister and I had not gone 50 meters yet... This was with a 20W rated 4.7Ohm resistor. The rest of GPIO showed no sign of hot spots. So I concluded that this resistor is the cause of my troubles.

So I removed it from the circuit and reduced max PC% to 40 hoping that would be low enough to protect the PC solenoid but high enough to drive with light foot. Now I have VSS issues again but my setup is such that the VSS sensor signal 1st goes to a TP500 and then splits to GPIO and the Speedo. The speedo also goes bonkers confirming that the TP500 now also has issues. I suspect its RF noise due to the higher PC currents resulting from the eliminated resistor.

Will now try doubling the value of the resistor....which should drastically reduce the watts into the resistor.

[Philip Lochner]

Doubled the resistor value.

VSS issues now gone.
Both resistors still get very hot, hot enough to burn a blister if I should hold my finger on it long enough.

Will now try 3 x 4.7 Ohm resistors...

[jamies]

try a flyback diode for the VPS and TCC if its PWM

[Philip Lochner]

I already had diodes on all solenoid outputs.

[slow_hemi6]

Doubled the resistor value.

VSS issues now gone.
Both resistors still get very hot, hot enough to burn a blister if I should hold my finger on it long enough.

Will now try 3 x 4.7 Ohm resistors...

You can see in the diagram it is shown as a 10W resistor. Even if it is only passing 5 or 6W then that is still going to be very hot.

[jsmcortina]

No matter what the rated power of the resistor, the heat energy has to go somewhere - you'll need a heatsink and some method to transfer that heat to air or by conduction to the vehicle's body.

James

[Philip Lochner]

This matter is now solved. See http://www.msextra.com/forums/viewtopic ... 32#p459732

A combination of:
1) using a 7.5Ohm resistor (2 x 15Ohm/5W in parallel); and
2) tuning for the highest % values of pressure that I can accept rather than the lowest values

the GPIO now does not get any hotter than the MS2 which runs the engine.