Battery telemetry on new ACCESS PLUS receivers

[MikeB]

The manual for the (non-plus) GR6 indicates the AIN2 input is for 0-3.3 volts only, so no internal voltage divider.
This explains your results compared to mine on a Rx with an internal divider.

Mike

 

[HENNY]

The manual for the (non-plus) GR6 indicates the AIN2 input is for 0-3.3 volts only, so no internal voltage divider.
This explains your results compared to mine on a Rx with an internal divider.

Mike

OK thank you

 

[benransom]

Hi David.
Some of the Archer Plus receivers now have a 10-1 voltage divider fitted to the Ain2 input on board the receiver so you no longer need the cheap external voltage divider. Be careful and check the manual the wording will say " Voltage Measurement Range via AIN2 (External device): 0-35V (Battery Voltage Divider Ratio: 1:10)"

FRsky making thinks easier.
Henny

I'm new to FrSky and Ethos, relatively new just to RC. I recently bought an X18 tandem and Archer Plus GR6, have them both configured w latest firmware and have several dozen flights, my glider still in one piece! I've got Vario telemetry working but haven't yet nailed LipO telemetry. I think I've learned enough in this thread to succeed in that using AIN2. But it bugs me that my telemetry shows an active RXBatt value (about 5volts). I thought with such obvious labeling -- RXBatt -- it might actually be that, or some ratio. It doesn't change with LiPo output, so what is it? And is it useful to know? Thanks

 

[HENNY]

I'm new to FrSky and Ethos, relatively new just to RC. I recently bought an X18 tandem and Archer Plus GR6, have them both configured w latest firmware and have several dozen flights, my glider still in one piece! I've got Vario telemetry working but haven't yet nailed LipO telemetry. I think I've learned enough in this thread to succeed in that using AIN2. But it bugs me that my telemetry shows an active RXBatt value (about 5volts). I thought with such obvious labeling -- RXBatt -- it might actually be that, or some ratio. It doesn't change with LiPo output, so what is it? And is it useful to know? Thanks

Ben The RXbatt sensor is 5 volts thats powering the receiver. If you were flying an IC plane this would be your 4.8 to 6 volt low voltage receiver and servo power source. This value is read directly from the receiver servo connectors. In an electric model you have a 2S to 8S motor power source. and this is where you have a second sensor to read your high voltage power source as well. AIN2 was originaly for early FRsky analog sensors. Today most sensors are digital and can be used with the S-Port connection. So being a bit innovative people said well maybe I could use AIN2 (Analog input-2) for something it wasn't original designed for.
I understand your question but this is what FRsky does really well, a number of flyers said, can I use AIN2 to measure my electric flight pack voltage, and they said yes but you need to add an external voltage divider. A lot of people said thats a bit messy so FRsky added the voltage divider to their newer receivers. It's a process that is evolving.

 

[Wayne]

I'm new to FrSky and Ethos, relatively new just to RC. I recently bought an X18 tandem and Archer Plus GR6, have them both configured w latest firmware and have several dozen flights, my glider still in one piece! I've got Vario telemetry working but haven't yet nailed LipO telemetry. I think I've learned enough in this thread to succeed in that using AIN2. But it bugs me that my telemetry shows an active RXBatt value (about 5volts). I thought with such obvious labeling -- RXBatt -- it might actually be that, or some ratio. It doesn't change with LiPo output, so what is it? And is it useful to know? Thanks

Can you tell us about the setup in your model? Then we can share some ideas.

If you are running a BEC to feed voltage to your receiver and servos, then this is the voltage that the RXBatt will see. With a BEC the RXBatt is of little value. You would need to add a voltage sensor before the BEC to see your LiPo's voltage. Frsky has a number of voltage sensors to pick from. They are all pretty easy to use.

The most common way to read a lipo is this sensor:

FrSky FLVS-ADV - Lipo Voltage Sensor

The FrSky Smart Port Lipo Voltage Sensor plugs into the balance port of your battery pack and allows you to monitor pack voltages while flying. No more guessing about your battery condition.

alofthobbies.com

It plugs into the ballance port of the battery and allows you to see each cell and total voltage. It is also a handy field meter thanks to the OLED display.

 

[benransom]

First, apologies for not being back into this thread and thanking you for replies since posting. (At the time I was brand new to everything Frsky including this forum.) I've been flying sporadically since then, and just recently poked back into the goal of measuring battery pack voltage via telemetry.

I'm working with two Frsky receivers (two different gliders) -- a GR6 and a GR8. My setup is simply connecting a small gauge sensor wire from the + side of the battery pack to AIN2. My receivers are the newer 0-35V AIN2 model, therefore safe with a 3s battery. With this, I can read ADC2 in in telemetry on my Frsky X18 TX. What I don't understand is why the reading is about 2/3 (~0.699) of the actual battery voltage. Fortunately, this ratio is pretty consistent through the battery voltage range, so within Ethos telemetry, I can multiply the ADC2 value by the inverse of 2/3 (~143.7%) to see a fairly accurate RX battery pack voltage on my TX. Seems to me this is a good method, but I'm a little sketch about it without understanding why the 0-35V AIN2 port reports 2/3 of actual voltage. Anyone know what's going on here?

 

[Wayne]

Here you go, copied from the manual, you need to adjust the ratio. Goto the telemetry section of your model setup:

 

[benransom]

Thanks Wayne -- That's what I have done, and I have the ratio that works. Just wanted to get some reassurance that this is the reasonable method... partly bc at first it seemed the ratio wasn't exactly the same from low to full battery or across different batteries. But I think now that was a testing error. I've now soldered my connection into the battery lead (esc side of the connector) and get very consistent results. (under 1% error across low to high voltage range and checking a random voltage of 6 separate batteries).

 

[Wayne]

Excellent!

Due to the divider and then multiplication, there will be a small error rate. But it is so darn simple, nothing extra to plug into the battery, surprised more folks don't use it. (Including myself!)