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[Solved] Min V to Go (Cell number) Function

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(@russellr150)
Trusted Member Customer
Joined: 4 years ago
Posts: 32
Topic starter  

Hi BrainDev,

Thanks for the ongoing  development of your products.

I tend to fly short flights and not overload my batteries.  For example on a 6S 5000 maH hour battery I will typically use less than 2300 mAh.  This is enough for one flight but not enough for two flights.  What I have discovered is that the resting voltage of 23.00 is not enough to trigger the low voltage warning.  A lower voltage eg 22.4 volts will trigger it.

Could you please consider either raising the trigger voltage or allowing the user to set an appropriate value.

Many thanks.

Acrow


   
(@customercare)
Reputable Member Admin Registered
Joined: 6 years ago
Posts: 1106
 

For greater clarity:
It is now calibrated at 3.82V (3.82*6=22.92V)
Would you like it to be triggered at 3.73V (3.74*6=22.44V)?

Although it is a popular opinion, the measurement of battery pack voltage can never be considered an accurate method of determining the state of battery discharge:

Battery pack voltage can vary a great deal if the measurement is made with the circuit "open" (battery disconnected) or with the circuit closed (battery connected powering the receiver and flight controller), but it can vary even more if the measurement is made while moving all 4 servos (or five servos in Nitro / Gasser models) and the measurement varies even more if the in addition to the above the motor is rotating and under stress (maximum collective pitch and tail rotor in counterthrust).

In short, the measured voltage can vary greatly depending on the applied load and circulating current.

The voltage drop of the battery pack caused by the circulating current depends on the internal resistance of the battery pack. The higher the internal resistance of the battery pack, the greater the voltage drop will be.

The internal resistance depends on the "C" value of the battery pack. (The higher the "C" of the pack, the lower the internal resistance of the battery pack and the lower the resulting voltage drops).

The internal resistance of battery packs also worsens (increases) as a result of cyclic charging and discharging of the pack (aging as a result of use). A battery pack that has made 300 flights will have a higher internal resistance than the internal resistance when the pack was new.

In addition to this, the internal resistance worsens (increases) considerably whenever the cell voltage under intense load drops below 3V.

Also, while the "Active FreeWheel" function increases flight duration (by a very small amount) because it recharges the battery every time the governor (internal or external) decelerates the motor RPMs when the collective pitch is reduced, in the long run it can damage the battery because there is no limitation on the maximum voltage and recharge current sent from the motor (which becomes a dynamo) to the battery and can adversely affect battery life. Better to disable it (in our opinion).

(A complete misuse by some users, fortunately few, is to land when by now the battery pack is almost discharged and as a result the motor has started to drop too low and the model has no sustenance. In this way Lipo packs are "destroyed" after only a few flights).

To check the above, simply turn on "ESC Battery Voltage" among the parameters to log in flight and after an aerobatic flight analyze the graph of the battery pack voltage trend.

To measure by how much the battery pack has discharged, the parameter of current drawn over time (mAh) should be used instead.

However, to be able to measure this parameter requires an ESC with telemetry capable of measuring the circulating current, and unfortunately there are still many ESCs that do not handle telemetry or there are inexpensive ESCs that among the telemetry parameters handled do not measure the current drawn (e.g., all HobbyWing from 60A and below).

For the reasons explained above, our flight controllers do not use the voltage value for battery discharge measurements.

Our flight controllers measure the BEC voltage (which is not the battery pack voltage) and do so only during tests performed at the completion of initialization while the servos are making the 4 vertical movements at the swashplate to measure the voltage drop when the servos are stationary and when they are moving and figure out if the BEC is capable of delivering sufficient current or if the contact resistance of the BEC connectors is too high.

The battery pack voltage is measured (but only if a telemetry ESC is used) only at power-up when the motor and all servos are stopped and with very little load and very little current circulating (only that of the receiver and that of the flight controller) with the one and only purpose of figuring out if you are going to take off with a battery that has not been fully recharged.

With this opportunity, we remind you that the measurement of the current discharged from the battery (mAh) is reset only by disconnecting the flight controller. So if you do not disconnect the battery between one flight and the next, the value of the discharged current will be the sum of the two flights.

Also remember that what drains the battery is not the receivers and flight controllers but is the movement of the servos and especially the motor. Leaving the model powered with servos stationary and motor off will discharge the battery by only a few tens of milliamps.

As for the logs, since the logs memory is circular, should there be any problems with the model in the last flight, the Flight Log from the last flight will still be available for analysis.


   
(@russellr150)
Trusted Member Customer
Joined: 4 years ago
Posts: 32
Topic starter  

Thanks for the detailed explanation.

I understood that the "Min V to go" warning was based on initial voltage only.

You ask "Would you like it to be triggered at 3.73V (3.74*6=22.44V)?".  The answer is no.  As stated in my initial post, I am seeking a higher value so that it will trigger this warning on startup if have failed to charge my 6S battery which has a no load resting voltage of 23.00 volts typically after flight.

With its current trigger voltage, it does not warn me if I place a "used" battery in my heli.


   
(@customercare)
Reputable Member Admin Registered
Joined: 6 years ago
Posts: 1106
 

Posted by: @russellr150
my 6S battery which has a no load resting voltage of 23.00 volts typically after flight.

Unfortunately, our Flight Control Units (but neither are all the others) cannot measure battery voltage at "no load" (open circuit) but only measure voltage when the batteries are connected to the four loads:
- of the ESCs' management electronics,
- of the receivers/satellites,
- of the flight controller
- of the servos internal electronics.
Four loads that cause an although slight load to the main battery which consequently has a voltage drop caused by the internal resistence of the battery compared to the voltage measured on the battery with no load (open circuit) or even worse measured by a battery charger which also raises the voltage by means of the even minimal holding current.


   
(@russellr150)
Trusted Member Customer
Joined: 4 years ago
Posts: 32
Topic starter  

Thanks again for the additional information.

My problem remains, however.  Can you raise the trigger voltage so that the "Min V to go" warning will activate for the case described?


   
(@customercare)
Reputable Member Admin Registered
Joined: 6 years ago
Posts: 1106
 

In the next version of the Firmware we have raised the minimum single cell voltage from 3.82V to 3.88V (3.88V * 6 cells = 23.28V). We hope that this small increase of 1.6% will not cause problems for other users using ESCs with different measurement tolerances but may be useful to you.


   
(@russellr150)
Trusted Member Customer
Joined: 4 years ago
Posts: 32
Topic starter  

Hi BrainDev,

Many thanks for tweaking this setting.  I look forward to testing it.

Regards

Acrow

 


   
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(@russellr150)
Trusted Member Customer
Joined: 4 years ago
Posts: 32
Topic starter  

This improvement was delivered in firmware version 3.4.139 in October 2023.

It works for me triggering the low battery warning of the swash plate after a 5 minute flight.

Thanks for listening to users' wishes.

Thanks to BrainDev for implementing it.

 

Regards

 

Acrow


   
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