Hello people!

I'm having problems with my Attopilot 180A voltage and current sensor.

I know people had similar problems but can't find any solution.

Here is my story:

I have 1.000 mm octocopter (6S 16.000 mAh), around 50 A at hover, Pixhawk.

I've installed Attopilot 180A voltage and current sensor in order to have voltage, current, but most importantly for me, mAh reading to be as safe as possible when flying. I also have Futaba 14SG with telemetry so I'm also tracking my battery status (voltage) on the transmitter.

The problem is that Attopilot doesn't seem to have linear voltage (nor current) output under load. I've ruled out everything else because I did the following:

1. I've calibrated the voltage reading with handheld voltmeter and fully charged 6S. The voltage info on the OSD/MP is absolutely correct without load.

2. When I start to draw about 10-20 A, voltage on the OSD/MP drops too much, 0.4-0.5 V under actual value (measured with inline watt meter and handheld voltmeter)

3. Interestingly enough, when I connect 4S pack, without any load the reading is perfect. So, conclusion is that when current starts to flow shit start to happen.

4. Now, to rule out the Pixhawk, I've measured the output on the Attopilot alone and compare that to the voltmeter. Here is what I get: 24,87 V (no load) -> 1,579 V; 24,67 V (around 7A) -> 1,559 V; 24,49 V (around 10 A) -> 1,546 V; 24,41 V (around 20 A) -> 1,537 V

If you start doing the math you will see that Attopilots voltage drops too much when under load. So, if I calibrate the voltage reading with no load, then the reading will be inaccurate when under load. If I calibrate it under 10 A load, then it will be inaccurate without the load and under different load (50 A).

Since these Attopilot board are very simple devices I don't know why is this happening. Should I try to buy another Attopilot 180A board (or any alternative if something like that exists) or I can fix this somehow

Thanks a lot!!

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Replies

  • God dammit I'm not alone on this. It has to be a bad ground reference or some ground loop while we have load. I already cut the attopilot ground trace so the ground comes from the pixhawk after the bec and attopilot shunt resistor but I still have a 0.2v voltage diference between my own voltage divider and the attopilot reading.. I'm probably going to discard the voltage reading from the attopilot and use my voltage divider but still I would like to understand why this is happening.
    • Thank God I'm not alone in this.

      In  fact, I've ordered second attopilot 180 A because I thought that maybe I damaged it while soldering. I was very careful with second one when soldering and it's the same.

      Yesterday something came across my mind. I'm using anti-spark 150 (AS150) connectors. Positive connector basically has 5,5 ohm resistor built in. Could this be the problem somehow (even I don't see how)? Are you using anti-spark connectors?

      Thanks!

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