Voltage measurements always wrong

ArduCopter Copter 3.2
1

I am using a APM 2.8 and 3dr clone power module.
My voltage readings on MP are always wrong. I have calibrated the voltage monitor multiple times but it always shows a very high voltage…and therefore no low battery alarm.
I sent the voltage monitor, ran the motors at half throttle until 9.3v and no alarm (set for 10.2v). The monitor still showed about 12v.
Also interesting that when I am only connected to USB…no battery…that MP still shows about 12v and current drain while just sitting on the table.

2

@bobt2000,
Maybe your clone 3DR Power Module is not functioning like you think it is?
Regards,
TCIII GM

3

Yes, sounds like a bad clone, this is not normally an issue people ask about.

4

Is it normal to see a battery voltage displayed on MP when its only plugged in to USB…no battery connected ?

5

As far as the power module goes…what voltage should I get on the pins to the APM?
I measured them all and don’t get the battery voltage on any of them, so I’m not sure how the APM knows what to display.

6

@bobt2000,
Like members have pointed out, your clone 3DR Power Module may not function the way a genuine 3DR Power Module does so it may be incompatible with Mission Planner.
Regards,
TCIII GM

7

I can accept that maybe the module is defective but there has to be a way to test it. It came with the APM so I’m sure it’s compatible.
I’ll just keep googling it I guess.

8

the power module have really 4 signals, +5V , GND , current and voltage - on the original one there are clearly marked labels and test-pads.
The 6-pin DF13 connector just uses two wires for 5V and GND.

To test - you would check the voltage pin, that similar to the current pin, should show a lower voltage, proportional to input voltage.
if you feed it 16v , maybe you should measure 1.8volt , if you then apply 8v, you would expect to see 0.9v from the power module.
(I am not sure about the real divider, but you get the point )

9

I appreciate the reply.
I selected the APM 2.5+ and 3DR module, selected voltage only and it seems to be fine (better).
It’s within .2v most of the time.

Thanks again.