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Topic: Monitor Battery Levels (usage fluctuates)  (Read 766 times) previous topic - next topic

Immortal_Conqueror

May 15, 2017, 08:26 pm Last Edit: May 15, 2017, 08:33 pm by Immortal_Conqueror
Hello, I'm looking for advice on how to monitor the battery levels of a quad-copter. Since the usage of power will change depending on what actions are done i'm somewhat at a stand still. I had been considering merely monitoring the voltage and use a voltage graph for the battery however this isn't reliable.

I plan to have 2 of these in a series circuit on the quad-copter.

The idea I had to monitor the battery usage is based on how Smart phones keep a track of their battery levels, only simplified. What seems the most logical is a Columb counter. Here's a lightweight one. 

It looks feasible, however I'd welcome any easier ways to monitor the battery levels.

Additionally, the temperature won't be a problem, I can use the on-board temp. system to calculate and fix the temp. error.

vinceherman

Are you trying to predict flight time?
You can monitor and compare to a graph like you said.  There are many studies online like this one

Mostly, I have always flown the bird starting with a fully charged battery.  I monitor the time I flew and check the state of charge when I am done.  If the SOC is too close to my bottom threshold, I shorten the max flight duration.

MarkDerbyshire

There are already good and proven monitors out here with the hassle of building one yourself

Eagle Tree Systems

Immortal_Conqueror

I am, however many of the Li-PO batteries have a constant flow then drop traumatically, as such 1 minute the readings would be 96% the next 5%. This wouldn't be ideal.


 
There are already good and proven monitors out here with the hassle of building one yourself

Eagle Tree Systems
The system looks good, but it has wayyy to many extra features that I'd never use. Also, $80 (don't forget tax) to merely monitor power is a bit high; in my case a simpler design such as the Columb counter would be better. But you did give me a good idea, thanks. Here's a simple one that's perfect.

Boardburner2

#4
May 16, 2017, 08:26 pm Last Edit: May 16, 2017, 08:44 pm by Boardburner2
Hello, I'm looking for advice on how to monitor the battery levels of a quad-copter.

I have tried this using a telemetry module but abandoned it in favour of using a timer as the information did not prove useful in practice.

It may be useful for something like a photography drone though.  

EDIT

Or anything else where the drain is relatively constant.

sdturner

Monitor the current and count the Amp-Hrs taken from the battery?. Add a voltage measurement and count the Watt-Hrs?

Boardburner2

#6
May 17, 2017, 01:50 am Last Edit: May 17, 2017, 01:51 am by Boardburner2
That is what the OP is proposing. Coulumb counter.

100 Amps for 1 second is the same charge as 10 Amps for 10 seconds  assuming constant voltage.
With a quadcopter both situations are feasible.

However both conditions have a different effect on remaining charge.

100 Amps for 1 second is also very likely to reduce terminal voltage.
The charge monitor has to take this in to account.
Testing and calibration is needed for the battery, this is probably done for the likes of cellphones and the eagle tree unit but is probably a bit tedious for a one off.

Immortal_Conqueror

That is what the OP is proposing. Coulumb counter.

100 Amps for 1 second is the same charge as 10 Amps for 10 seconds  assuming constant voltage.
With a quadcopter both situations are feasible.

However both conditions have a different effect on remaining charge.

100 Amps for 1 second is also very likely to reduce terminal voltage.
The charge monitor has to take this in to account.
Testing and calibration is needed for the battery, this is probably done for the likes of cellphones and the eagle tree unit but is probably a bit tedious for a one off.
The popular batteries have proper documentation of their voltage changes depending on their battery level. The one I selected has this documentation which I can use. However, the fuel gauge i'd need to buy needs to have the capability to use this data, if i'm understanding this correctly.   

I have tried this using a telemetry module but abandoned it in favour of using a timer as the information did not prove useful in practice.

It may be useful for something like a photography drone though. 

EDIT

Or anything else where the drain is relatively constant.
I see your point. But how'd you use a timer to monitor your battery levels? Or do you have any other ideas on how I could continuously measure the battery levels?

Boardburner2

#8
May 19, 2017, 11:57 am Last Edit: May 19, 2017, 12:30 pm by Boardburner2
I see your point. But how'd you use a timer to monitor your battery levels?
As vince herman has already suggested.
As does everyone else i know.

Battery use and charging/storage makes every battery different anyway.
I use a marker pen to label each one with how it performed last time.

A suspicious one gets relegated to an arduino project or a ground based model rather than risking it on a flying model.

RC transmitters come equipped with a timer for just this reason.

EDIT
I use An A,B,C method, the professional drone users keep a log for each battery which details charging storage and use.

Immortal_Conqueror

#9
May 19, 2017, 08:16 pm Last Edit: May 19, 2017, 08:24 pm by Immortal_Conqueror
Looks like I'll need to go with the log then. As such; would this be a good template to properly monitor each of the batteries?  (see attached) I drew this up quick so don't be too harsh. xD


Edit:

Boardburner2

I think a date field is needed.

Stored for over a day the charge should be reduced to approx 40 % for longevity.

You may find online a template that the pro flyers use to obtain their licence.
It is a good way to monitor battery state over time.
I use my own somewhat simpler method

Boardburner2

Something that could work is to monitor battery voltage when in low power operation and indicate when 40% capacity is left by audible, led or telemetry.

Then you stop doing hi G manoeuvres which could cause brownout , 40 % being enough to retrieve your model.

For the likes of fixed wing or photo drones probably 30% is enough margin.
 

Immortal_Conqueror

#12
May 22, 2017, 08:00 pm Last Edit: May 22, 2017, 08:06 pm by Immortal_Conqueror Reason: Missing Links
Something that could work is to monitor battery voltage when in low power operation and indicate when 40% capacity is left by audible, led or telemetry.

Then you stop doing hi G manoeuvres which could cause brownout , 40 % being enough to retrieve your model.

For the likes of fixed wing or photo drones probably 30% is enough margin.
 
Good idea, I'll be sure to include that feature.

Here's a good log I found.

I'll continue to look into fuel gauges for li-po batteries, hopefully I can find one that can take new readings for each battery to calculate an accurate estimation of the current battery levels.


Here's the log
//You'll need to download it and open it in excel to see it correctly.

CrossRoads

Check sparkfun.com, they have several "fuel gage" chips on breakout boards for monitoring LiPo charging and discharging, etc.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Boardburner2

#14
May 22, 2017, 09:24 pm Last Edit: May 22, 2017, 10:05 pm by Boardburner2
Good idea, I'll be sure to include that feature.

Here's a good log I found.

Looks comprehensive.
Ones i have seen are paper and slightly simpler, i will try to get a copy at the W/E.
(CAA seem to like paper with lots of signatures).

[/quote]
Check sparkfun.com, they have several "fuel gage" chips on breakout boards for monitoring LiPo charging and discharging, etc.
The chips for those seem to be available in 1 or 2 cell types.
My quad however uses 3 or 4 S batteries.
None of the applications docs i have seen show them as being suitable for flying models.

The popular batteries have proper documentation of their voltage changes depending on their battery level. 
Yes but they do not give much information about how they perform for sudden high currents.
A 45C battery should not be discharged at a rate higher than this, testing has indicated it could be as high as 100A for a short period. I gave up after that although it may well be possible with enough time and testing.
Any idea how the eagle tree unit works ?

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