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Sep 15, 2019, 02:02 AM
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FrSky Taranis Q x7 - telemetry RxBt = 3.1 V ?


Hello everyone.

Can someone explain me why RxBt is showing me this value? ''3.1V''

I have a Taranis Q x7 with a X8R receiver.
I just want a warning when the battery (Lipo 7.4V 1300Mah 20C) is at 6.2 - 6.4 Volt.
Or that each/a cell is below 3.2 V.
But when I tested this battery with my LiPo checker it showed me that it had 3.69 V and 3.66 V left in his cells. But my taranis is showing me RxBt = 3.1 V

What can I do? Is something wrong with the receiver or am I missing a setting?

EDIT 15 september 19' :
After a lot of searching I found some kind of solution in the manual of OpenTX.

''Ratio
The multiplier to use to get the correct reading; Usually in volts. Using a multimeter measure the voltage. If the multimeter voltage and sensor voltage do no match adjust the ratio until they match.''


It seems that inside the editing mode of the sensor RxBt, there is a option called ''Ratio''. this is where you need to adjust the amount of Voltages read and the actual Voltages measured by a LiPo checker of Multimeter.

But 5 min later, the sensor read 7.9 V, but when I checked it with my Lipo tool I still had 4.10 V in each cell = 8.2 V.
So I again adjusted the ratio.

So a 2 cell battery needs the ratio at 22.0. Atleast for me.

Greetings
Last edited by Ginovv; Sep 15, 2019 at 03:24 PM.
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Sep 17, 2019, 08:41 AM
Happy FPV flyer
Kilrah's Avatar
RxBt gives you the supply voltage to the receiver. That will always be 5V in a typical electric setup since it's regulated by your BEC.
You cannot get your battery voltage without an external sensor.
Sep 17, 2019, 09:06 AM
Carbo (-nator) ;-)
Quote:
Originally Posted by Ginovv
Can someone explain me why RxBt is showing me this value? ''3.1V''
Do you supply your RX with 2s directly? With the default ratio (13.2) for RxBt your radio should show you the correct supply voltage. If it shows 3.1V, something is wrong. Connector/cable or A/D converter (unlikely).
Last edited by Allerhopp; Sep 17, 2019 at 09:14 AM.
Sep 17, 2019, 02:21 PM
Registered User
Thread OP
Quote:
Originally Posted by Allerhopp
Do you supply your RX with 2s directly? With the default ratio (13.2) for RxBt your radio should show you the correct supply voltage. If it shows 3.1V, something is wrong. Connector/cable or A/D converter (unlikely).
I just figured it out. Thanks for replying!

I found a simular forumpost somewhere else.

You're probably using a BEC which gives a constant 5V to your receiver, so you can't use RxBt to read your battery voltage, you need an extra sensor.

Also it seems you might be confused, RxBt is the supply voltage of the receiver, but what you say suggests you're trying to look at it to see the radio's battery voltage.


I just ordered mini voltage sensor from HK, hopefully they come with the cable I need. Smartport -> Sensor

And yes after setting the ratio back to 13.2 it was back at 4.99 V - 5.00 V.

Again thanks for replying, I didn't got any answer from other forums. New to the hobby, so maybe it's a stupid question?
Sep 18, 2019, 01:43 AM
Registered User
Quote:
Originally Posted by Ginovv
I just figured it out. Thanks for replying!

I found a simular forumpost somewhere else.

You're probably using a BEC which gives a constant 5V to your receiver, so you can't use RxBt to read your battery voltage, you need an extra sensor.

Also it seems you might be confused, RxBt is the supply voltage of the receiver, but what you say suggests you're trying to look at it to see the radio's battery voltage.


I just ordered mini voltage sensor from HK, hopefully they come with the cable I need. Smartport -> Sensor

And yes after setting the ratio back to 13.2 it was back at 4.99 V - 5.00 V.

Again thanks for replying, I didn't got any answer from other forums. New to the hobby, so maybe it's a stupid question?
Verwijder de sensor en laat OpenTX hem opnieuw vinden. Voor RxBat moet je nooit aan de ratio komen, deze is VAST. Als de waarde niet klopt standaard is de ontvanger kapot.


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