Now let's talk about sensor polarity.  The manual tells me to run the wire from the alternator thru the back side of the sensor (the PC board) and out the front.  So presumably positive is when current is flowing from the PC board side to the sensor side.  If I put this in the line from the battery, I want a positive number to indicate battery charging, don't I?  That would mean the wire should go thru the sensor in the other direction.

Rob,

 

Do not flip the logic.  A positive indication still will indicate the alternator is charging the battery.  A negative indication should indicate the ampere load discharging the battery.  I.E. As soon as the master switch is engaged (and the unit boots), you should see the battery discharge rate as a negative number, maybe -7 to -12 amps depending on how many basic things come to life (relay, engine monitor, turn coordinator, landing gear locked lights, etc.).  After engine start (and re-boot of the EPI), the main bus voltage should got to around 14.3 to 14.6 (SLA battery) and the ammeter indication should soon drop to fractions of an amp although mine is quite variable by jumping between charge and discharge (needle neutral).

 

You also said:

<<<<<

How would I use this device to determine whether the battery is charging or discharging?  To accomplish this goal, the current sensor would have to be on the wire from the battery (actually the downstream side of the battery contactor) to the main bus, and the alternator output wire would be connected to the main bus without passing through the current sensor.

Sound good so far?

>>>>>>

 

Nope.

I have the PC board mounted between the battery and the master relay.  Thus I can see the load from the master relay included on the display (one side of the coil is internally wired to the "bat" side of the relay).  If the alternator is capable of handling the electric load there may be a small positive charge going to the battery with the bus voltage at 14.3 to 14.6 (SLA battery).

 

BTW, my original sensor is still mounted on the firewall since I didn't want to cut and rebuild the line from the main bus to the plus side terminal of the starter relay - the same terminal to which the B-lead from the alternator is connected.  If I would have put a multi poled switch on the sensor to EPI lines, I could have monitored both the battery and the alternator load with a twist of the wrist. I already monitor the voltage of the main bus, essential buss and EI battery with a rotary switch.