Sunday, September 18, 2011

Motor Overtemperature Indicator

The next disappointment from the EA kit is the handling of the motor temperature overheat indicator.  According to the manual, the wires from the motor temperature switch are wired to the red alternator light in the left-side gauge cluster.  Unfortunately, when I powered up the12V circuit, the light went on, indicating an overtemp situation.  This is clearly not the case, so I did some investigation.

The Warp 9 includes a temperature snap switch that *breaks* the circuit when too hot.  This action goes against the way the EA wiring diagram is designed.  I can only think that the Warp motor changed spec somewhere along the line and the EA manual wasn't updated, or the EA manual has been wrong all along.  Either way, I had to make this work.

The normal way to do this is with another small relay.  I wrote up the circuit below.

The key is to energize the relay through the overtemp switch circuit, but wire the "unenergized" terminal to the indicator light.  It will only light when the overtemp switch fires and breaks the circuit.

Luckily I found a cheap Tyco relay online, and mount and wired it into a small space in the front relay box.

With the circuit now wired up, I turned the switch and the light stayed off.

I then disconnected the motor overtemp switch wire, and the light went on!  Success!  I'm getting to be a real champ at diagnosing and fixing EA problems.