PMU voltage reading incorrect? - help wanted

[aerialindo]

Hi all, we have been flying S800 for more than a year now and achieving great video results! We named him Sebastian .

However, recently something strange has happened. Sebastian's flight times have been getting progressively shorter each time we fly - this has been happening over the past week.

What happens is - the battery shows depletion very fast - we have to land just after 1.5 minutes as the battery is showing 22.5 volts. We land, then it jumps to 24 + volts. (that is a very big difference between loaded and unloaded).

The charge takes 15 minutes more or less and only puts in between 500 and 1000 amps and is fully charged at 25.2 volts.

You will be thinking the batteries are all nuked. Thats what I thought, so, bought 4 new sets (8 pieces) of new batteries. Charged the batteries and did flights to break in the new batteries - same thing!

So I have no idea what it is except maybe some PMU issue.

We have a 3 day job starting in 2 days, a bit nervous.

Perhaps others have had the same issue and have a solution?

Appreciated.

Aaron.

 

[aerialindo]

Some more info/insight for you all.

We just did a test flight - hovering only. We plugged in a little battery checker to help figure out what the problem may be.

Ok - we are hovering for 2 minutes - the iosd is telling me a reading of just 22.4 volts - yet at the same time (whilst it is still hovering), the battery checkers reading is 23.9 volts.

When we land, naturally, the voltage goes up because its not under load. The battery checker now says 24.3 (which is about the right amount of difference). The iosd is also sending back the same reading of 24.3.

So, when under load, the PMU for some reason reading the battery 1.5volts lower than what it actually is - but it is accurate when not under load. (actually, that is one test flight example, it can be up to as much as 1.8 volts inaccuracy.

Plugged into WKM assistant, everything looks fine - expect for a little dialogue box pops up saying warning, low voltage (there is a fully charged battery connected.

Really hoping someone here may have had the same problem as us and knows what to do.

Thanks.

Aaron.

 

[Old Man]

Perhaps a slowly developing resistance issue inside the PMU from a deteriorating electrical component? If you had a spare it would be something to swap out for a comparison.

This is risky but if a few test hover flights, say 5 or more, provided solid data of higher battery voltage for evey test flight you could reduce the low voltage level through the assistant to get the work done. I doubt anyone has a PMU for sale independent of an entire control system. You would need to perform the test flights in a manner that let you see the battery checker for the entire duration of the test. This is something I do with new birds to establish initial flight time estimates.

 

[aerialindo]

Hey old man! Thanks for your reply. It seems that could be the case, but why then does it only effect the under load reading? Yes, for now we will run timed tests per battery using the battery checkers and turn off the voltage protection all together so there's no chance of descent when above gtr ocean over a cliff! I'll check about spare parts with my dealer tomorrow... Thanks again.

 

[Rgolfer]

Perhaps a slowly developing resistance issue inside the PMU from a deteriorating electrical component? If you had a spare it would be something to swap out for a comparison.

This is risky but if a few test hover flights, say 5 or more, provided solid data of higher battery voltage for evey test flight you could reduce the low voltage level through the assistant to get the work done. I doubt anyone has a PMU for sale independent of an entire control system. You would need to perform the test flights in a manner that let you see the battery checker for the entire duration of the test. This is something I do with new birds to establish initial flight time estimates.

Actually you can get a PMU unit here.

http://www.amain.com/DJI-Naza-M-V2-Power-Management-Unit/p263588

 

[Old Man]

I'd be all over that and pay the extra for over night shipping, if possible, if I was in the OP's shoes.

 

[aerialindo]

Update again. Replaced the PMU - didn't solve the problem. Replaced the iOSD - didn't solve the problem. So I am out of ideas. Anyone?

 

[Cheshirecat]

I am seeing something similar.
I get a 0.5 Volt difference between what the IOSD is showing on screen and what i am reading through my telemetry on the TX, the sensor for the later is on the Herkules board.
But on landing the resting voltages match up, i am flying it on the Herk readings alng side the drawn current and not seeing any loss of flight time (16Mins fully laden, 20 without the Gimbal and camera)

I am running ver 5.26 on the WKM and also have an unexplained problem with the motor mixer on that version so i plan to revert to an earlier version (after my RPQS assesment)
I will check back in to see if you have resolved your issue if not i will let you know if a firmware revert addresesd it for me.

 

[aerialindo]

Heya, well, sorry that your having the same problem as I. It's a little bit weird hey! How'd you go with the firmware change? I think I'll buy a quanum telemetry for now until we upgrade to s900 and A2....

 

[Scott Drysdale]

A corroded or worn battery connector will function as a resistor creating a voltage division circuit between battery and the load...... net result is that you will always get less than the full voltage at the load end relative to the power supply end.
And as the current demand increases at the load end so does the temperature and resistance increase on the battery connectors.

This was the root cause of issues I have experienced on several occasions including vehicle security system failure while I was in the driver's seat as well as a field installed RTU that would receive SCADA host polling signals but would brown-out when trying to transmit. The vehicle security system would lock me in or out of the vehicle (with keys inside) at random intervals and even activate the audio alarm....... which could not be stopped until the battery was disconnected!!!!......

All issues were resolved once I cleaned the vehicle battery posts.

This is another possible cause for problems people are experiencing with FC failures during flight.

 

[aerialindo]

Thanks for that. I've just replaced all batteries and connectors thinking that may be the issue.... Sounds like that was fun for you trying to figure out what was going on. !!

 

[Cheshirecat]

Heya, well, sorry that your having the same problem as I. It's a little bit weird hey! How'd you go with the firmware change? I think I'll buy a quanum telemetry for now until we upgrade to s900 and A2....

i Have not regraded yet, i am not changing anything now until i have completed my Civil Aviation Authority flight assessment in a couple of weeks (missed it once due to a technical hitch and leaving alone until then) i will let you know what i find.

 

[aerialindo]

Good idea, be sure. Yea that's something I should look into also. Do you know if that covers you internationally?

 

[gtranquilla]

In addition to the voltage division situation: http://en.wikipedia.org/wiki/Voltage_divider

There is also the infamous, intermittent grounding issue..... happens a lot with computers and vehicles..... with somewhat similar results!

And it is not fun having your vehicle security system turn against you, play games with your head, lock you out with your keys in the ignition......
then do it all over again after you found your spare keys...... evokes extreme aggravation as does a faulty MR FC system.

Thanks for that. I've just replaced all batteries and connectors thinking that may be the issue.... Sounds like that was fun for you trying to figure out what was going on. !!

 

[aerialindo]

Gotta squill I wish I was there to film it! Lol

 

[Cheshirecat]

Good idea, be sure. Yea that's something I should look into also. Do you know if that covers you internationally?

It is UK specific and a legal requirement for professional work, i believe there is a initiative to harmonise this across Europe and i understand Australia has a very similar setup and Maybe NZ as well.
In the US the FAA are way behind to the frustration of many, i expect over time that as the industry develops and matures thing like certification will start to harmonise but right now i don't know of a global program to cover operators.

 

[Old Man]

A civil Pilot's license is an international certificate. It will be interesting to see if the same extension will be granted to sUAS certified people.