I'm setting the heater current, and I am not getting the current to drop low enough after heat-up to enable the drive pump.

If I disconnect the heater (after initial power-up) then the heater current drops to zero and the circuit enables.

Wondering, does the sensor need to be in the exhaust gases as well, to get the temp up??

 

Disconnect the heater? Do you mean unplug the o/2 sensor?

If the red led comes on with the sensor unplugged from the "controller", but does not come on when the sensor IS plugged in...

The unit is not getting enough voltage.

It needs as least 13.2v for proper sensor heater operation.

Hal

 

no the o2 sensor will heat itself up in free air no problem.

and Hal is right you gotta watch your voltage, it won't work in my car unless i have alternator voltage. battery itself wont cut it. my bench supply put out 13.7 and it worked fine. my living room was very lean! (lots of o2)

 

I meant I just disconnected the heater wires, so the heater current dropped off.

My Bench supply was at about 13.6. The LM317 Reg has al litle over a volt drop out, so yeah you need to be above 13 for it to run.

 

I found the prob, or at least a way around it.

They spec the heater at 9.7 ohms at 800'C (full op. temp), and mine only gets to 1.09 Amps w/ 8.97V across it. this works out to 8.2 ohms. So the current will never drop to the expected level.

I guess there is some discrepancy between heaters? Also, I've got 15 feet of 24AWG feeding it, but that cant be more than a half ohm total..

Anyways, I increased R38 to 1.65K Ohms to trigger the drive cct a little earlier. ...