3.1-rc7 and BATT_AMP_PERVOLT

This parameter’s description says for the 3DR Power brick it should be set to 17, which is what mine was at with 3.0.1. Today I upgraded to -rc7 and the first thing I noticed was my current was 92 amps. I did some digging, and set this to .17 rather than 17, and the amp draw looks closer to what it should be.

Is it possible that either with the new version of MP or with rc7 that there is scaling that was removed for this attribute, but not correctly, and that is why I am having to modify to .17 rather than 17?

If not, what else can I look at?

I have a Power Module (from HobbyKing) and when I choose 3DR Power Module, it shows a BATT_AMP_PERVOLT ratio of 18.0018 which is more close to the maximum allowed voltage for the Power Module. The docs however state it should be 17.

In any case, I needed to select “Other” for type to be able to enter the correct measured voltage, because this was off too (about 1V too low). I ‘calibrated’ by measuring my 4S LiPo with a DVM, switching to “Other” as battery monitor type and entering the voltage directly in the topmost field. Will this be OK for the full charge curve of the battery?

I fly FPV with MinimOSD so I can keep a direct eye on it to see if I see any strange values.

Thanks, so I’ve done that as well (selecting Other) and what happens is the voltage gets set properly, and the current gets set just about right, and then during flight neither of the values ever change - they stay locked at those “at rest” values. This leads me to believe that since the APM is not properly measuring voltage and current, it is not making the appropriate adjustments to the compass offsets that are based on Current.

I haven’t uploaded rc8 or the full version yet, but I’ve noticed my OSd is saying those values are all over the place, in conjunction with what Mission Planner is saying, so I don’t think it is an issue with just the mavlink connection, etc.

If the values do not change with type “other”, this is because this type expects signals to be !easured from A1 and A2 as defines in the parameters list. If you indeed use the PM the signals are !measured by the PM connector, not via A1 or A2.
I personally use attopilot with voltage and current signal lines connected to A1 and A2, selected type “other” and calibrated with the measured voltage value. It works fine.

when you use “other”, do you put exactly the voltage battery measured with a voltmeter?
the battery voltage displayed on HUD is what you measure? on Mission Planner hud, voltage is variable, 0.1-0.2 v and not sure if I should use the peek, or medium or low.

Hi criro,
Yes I measure with a voltmeter and I try to have the drone as stable as possible so as to minimize the measurements variations. Indeed it is not obvious to have a fixed measurement. You can be happy if you succeed to get a precision of 0,2V. Anyway you must consider the reading as an approximative indication of the charge state of your battery. By security I type into the field the reading of my voltmeter minus 0,2V to be on the safe side. Afterwards the display on mission planner should correspond to reality (more or less 0,2V).

I do the same for current measurement by using a turnigy wattmeter installed between my battery and the PDB (plugs in series between your battery and the connector of your PDB). I then spin the motors so as to read about 10 amps on the wattmeter and I copy the value (for ex 9.89 or 10.06) onto the measured current value in mission planner (battery monitor/Other). There too there is a bit of unprecision but it is unavoidable.Anyway I just consider the displayed amp value as a rough indication of the consumption and I DO NOT use it to trigger a battery low event. I only base the battery failsafe on the voltage reading which I trust a bit more than the current reading.
This is my experience and it might be different for others.
Hopes it helps

I just need to figure out why mine is crazy. Oddly when I disarmed last week, the voltage reading changed from the static version before I took off to the actual voltage. The current didnt change though. This is on a craft that was working fine.

I’ll stay at it, Randy gave me some stuff to check so hopefully I can get it true again.

The note above about “Other” going to the analog ports, I didn’t realize that, so when I get home from my travels this week that’s one of the first things I’m going to start looking at. I am also wondering if the cable that connects the PM to the APM is not good.

Yes Josh and please check that you connect the voltage signal wire and the current signal wire to the correct A1 and A2 pins on APM. The first time I was setting that up, I wrongly connected to A2 and A3 (I skipped a PIN by distraction) and the readings were crazy or static…(looks like what you are experimenting)

It is a 3DR power module and only has the one cable to the PM port. I’ll have to make a mod to the PM that I would prefer to avoid to do that.

Right now Randy wants me to measure a few points on the module first and then I’ll check the cable too. I doubt a cable is making the current sensor read 92A at rest, but, you never know.