Charger XLR Pinout

[flyinbrick]

Does anyone know what the pinout of pin 3 on my charger is for my Izip E3 Peak? I bought another charger with a 3-pin XLR, but only pins 1 and 2 are connected, no connection on pin 3. I want to know if it is safe to use. It does charge the battery, however.
It's a 48V 2A charger, identical to the one supplied by EM3EV for their dolphin battery, except the em3ev charger does not have the 3rd wire soldered in (solder pad is empty).
As far as I can tell, the third pin is a voltage sourced from the charger. It measures 2.55V relative to output ground when charging the battery and 5.0V relative to output ground when plugged into power but disconnected from the battery. When tried tracing it - one of the traces lead to an empty pad labeled NTC2 (right side I f the board in the photo) so is this some sort of thermal shut-off signal option by the charger manufacturer if the device were there?

 

[flyinbrick]

Bump... Anyone know?

 

[dnmun]

if the NTC was to be located inside the charger then it implies that the third pin is used to provide a reference voltage to the BMS of the battery that will turn off the charging when the charger overheats.

does that make sense?

 

[flyinbrick]

Thanks, yes, that does make sense. There were also traces that lead to some other components so I'm guessing that the intent is to supply some logic output on that 3rd pin whether that NTC is there or not. The 2.5/5v level is puzzling - doesn't conform to either TTL or CMOS logic levels. I'm not interested enough to figure it out all the way as my 2-wire charger seem to charge the battery just fine.

 

[flyinbrick]

I found the answer in case anyone is wondering:
https://www.maximintegrated.com/en/app-notes/index.mvp/id/5681
the 3rd pin on the charger is the thermister pin. 5V is sourced from the charger. When connected to the battery, the thermister in the in the battery forms the lower leg of a resistor divider and drops the voltage in half - hence the 2.55V I measured while charging.