With a purely resistive load I got the following data with freshly charged batteries:
Load = ohms load at output of regulator
Vin = Voltage at input to regulator
Iin = current at input to regulator
Vout = Voltage at output of regulator
open circuit/5.79/760micro amps/6.06
Thus with a purely resistive load the regulator appears to behave as expected. It maintains voltage until the input voltage drops to around 3 V (I think the spec is 2.9V?) and when you run the numbers the efficiency based on power out divided by power in is around 85-90%. I did notice that at the 3.0A Iin current level there is a large voltage drop from my battery to the input of the regulator (around 1.5V, not reflected in the data above, I didn’t have enough DVMs to make all of the measurements simultaneously) so I need to check on why that is - maybe just the relatively small gauge of the wires).
I then took the same (now partially depleted) batteries and connected to the receiver and servo as I have in the past. I got the following data point when I stalled the servo;
Vin = voltage at input to regulator
Vout = voltage at output of regulator
Iout = current output from regulator to receiver and servos
In the end I’m still confused. I can understand the regulator output falling when the input voltage drops too low (as it did at with the 4.4 ohm load in the resistive test) but when I connect to the receiver and servos the input voltage appears to be staying high enough (3.65V) that it doesn’t seem like that should be an issue. Also, as the original data shows, when used with the receiver/servos the regulator output voltage won’t maintain the setpoint even at very low output current levels.
I am going to see if I can scrounge up a power supply to get the batteries out of the equation and if I can find a suitable one will collect more data. Any thoughts you have in the meantime are welcome.