Setting up LiPo power consumption alarm on Taranis

[Stephen Belshaw]

Have I got this right?

 

I want an audible warning when my battery gets to 75% capacity, so in the case of a 2200mAh pack that would be 550mAh

I have an FAS40 current sensor in the model, in Telemetry on the Taranis I add a new sensor which I call Power Consumption

In Logical Switches I put in the formula a<x where a is the power consumption and x is 550mAh

In Special Functions I select the logical switch to play the value selected above

 

Et voila?

 

 

[Ron Gray]

The FAS40 measures current flowing through it, not the capacity of the battery. You could change it so that you are measuring volts instead of amps, not as good but good enough.

 

http://rcdiy.ca/battery-capacity-remaining/

Edited November 24, 2022 by Ron Gray

[Stephen Belshaw]

"The FAS40 measures current flowing through it, not the capacity of the battery"

 

Isn't the Taranis doing the calculation for me?:

 

[Ron Gray]

Ah from your first post I thought thou were referring to just the current, my mistake!

[Andy48]

5 hours ago, Stephen Belshaw said:

Have I got this right?

 

I want an audible warning when my battery gets to 75% capacity, so in the case of a 2200mAh pack that would be 550mAh

I have an FAS40 current sensor in the model, in Telemetry on the Taranis I add a new sensor which I call Power Consumption

In Logical Switches I put in the formula a<x where a is the power consumption and x is 550mAh

In Special Functions I select the logical switch to play the value selected above

 

Et voila?

 

 

Sounds exactly right. I also have a momentary switch (I added a second switch as they are so useful) that plays a series of values whenever I need it. The ones I use are consumption, flight time, RSSI and battery voltage. This is very useful when someone calls an emergency just as I am thinking of landing.

 

Edited November 24, 2022 by Andy48

[Tim Kearsley]

I might have got this wrong but if you want the warning to first sound when the battery consumption reaches 550mAh shouldn't the function be a>x?  In other words no alarm until the cumulative mAh is greater than 550mAh.

Apologies if I've got this wrong and confused things!

 

[Stephen Belshaw]

8 hours ago, Tim Kearsley said:

I might have got this wrong but if you want the warning to first sound when the battery consumption reaches 550mAh shouldn't the function be a>x?  In other words no alarm until the cumulative mAh is greater than 550mAh.

Apologies if I've got this wrong and confused things!

 

Mmmm, now I'm confused! My assumption was that the alarm would sound when the capacity was down to 550mAh? If I made a>x would I need to enter 1650mAh as the amount consumed??

[Frank Skilbeck]

1 hour ago, Stephen Belshaw said:

Mmmm, now I'm confused! My assumption was that the alarm would sound when the capacity was down to 550mAh? If I made a>x would I need to enter 1650mAh as the amount consumed??

That's what I would have though, unless you can set 2200 mah as the start value and then have consumption count down from this. Counting up is preferable IMHO as then if you put in a different capacity battery it still works. One thing that could be useful is to use the trigger value not just be an alarm but to start a timed readout, so when you hit 1650mah it then reads out the mah every 10 seconds or so.

[Neil R]

I use - and love! - the FrSky current sensors, but yes they are only able to support the calculations and act on what you have taken out not what might be left. So >1650 is correct here. Since the sound pack I use has both 'Battery Low' and 'Battery Critical' options I create two different warnings e.g. at 70 and 85% usage. I suggest you also check out and understand the 'reset flight' options to ensure you take-off on any subsequent flight (with either a new or the same battery) at the right start point.

I note the newer FAS40 ADV sensor can also monitor battery voltage - if at cell level (especially) I assume this could be used to give a truer indication of imminent battery expiry. Hopefully somebody can educate us both on this! 

[Tim Kearsley]

I think the way the original question was phrased was slightly misleading - "I want an audible warning when my battery gets to 75% capacity" - I took that to mean an alarm would sound when the battery got down to 75% capacity remaining - though I did think that was a rather odd point at which to be warning!

So yes, if the requirement is to alarm once the battery has 25% capacity remaining then for a 2200mAh battery the logical switch is a>x where x = 1650.

I generally use FrSky Neuron ESCs, which have telemetry built in and, like Neil R, I use a dual warning - one for "battery low" and one for "battery critical".  These are set up to nag at 10 second and two second intervals respectively, so that I don't overlook them!

It's best to back up these consumption warnings with other checks, such as cell Voltages, as the consumption warnings only work properly where a fully charged pack is put in the model.  If you accidentally put in a part-charged battery and rely only on consumption warnings you could get a nasty shock.

Edited November 25, 2022 by Tim Kearsley

[Graham Bowers]

Must admit, I just monitor lipo voltage and get notification when Cels gets down to 3.7 V under load.  On recharge, the various packs always accept about the same amount of charge in mAhr.

[Ron Gray]

If you look at rcdiy there are a few entries regarding battery capacity / consumption etc (also the link above to a Lua script).

[Andy48]

This is my standard setup for a 3300mAh battery:

 

 

 

 

It tells me when the consumption has reached a certain point. Its simple but effective. There are more complex ways where you can input the capacity of the battery first, but this too has its problems. While I have standardised on 3300mAh, over the years some have been replaced with 3200mAh or 3000mAh batteries. Either way I know when I get the third warning it is time to land, though I don't normally leave it that long.