Jeti receiver voltage alarm query

[Graham Bowers]

Context is a cooking 5 servo model, Black Horse twister AKA SLEC / Precedent Funfly. 54inch span and .35 powered, Fut S3001 / S3003 servos, brand new switch. Flown recently on FrSky and changed over to Jeti. I'm using it to get used to the new kit and it had about 4 flights on Jeti prior to yesterday.

 

Receiver is a REX6 with the Rx low voltage alarm set to 4.5 Volts. The pack is a 4 cell Overlander low self discharge 2300mAh NiMh bought new by me and never flattened, but could be a bit aged - can't remember. Fully charged at 0.7A that morning. It took about 350 mAh.

 

I got a Rx low voltage alarm on the first turn on the 4th flight yesterday so landed immediately, no drama. The resting voltage after the flight on telemetry and direct measurement was 5.1 V however stirring the sticks would consistently trigger the alarm. Parked it up for the day.

 

On Frsky I had the voltage alarm set a little lower (possibly too low??) at 4.2 V and crucially, with a 1 second delay.

 

I've not found any way to set a delay on the alarm setup on my DS-12 transmitter, and can't find any mention of delay, or absence of delay in the documentation.

 

This morning at home I tried another brand new switch, no difference. So believe the switch is not a factor.

 

Next I tried another identical Rx pack that showed 5.1V resting, and didn't get an  alarm. That pack had been used recently in another model and is less than a year old. So will cycle the other pack to see how it does, but probably retire it to bench duty and replace with new.

 

The Jeti question. Is there a delay built in to the Rx alarm function, either Tx or Rx end, to take account of sag under load please? If so, is it user settable?

 

General query. Am I being too conservative setting the Rx pack alarm to 4.5V?

 

Thanks

 

Graham

 

 

 

 

 

 

Edited September 3, 2023 by Graham Bowers

[Trevor]

There are two low voltage alarms. The receiver will send an alarm immediately when the voltage drops below the set level. Also, the receiver continually sends its measured voltage back to the transmitter and the Tx will sound an alarm when this voltage drops below its (separately) set level. It does sound like your battery is past its best but if you are happy to continue using it, you could lower the Rx alarm (or even turn it off entirely) and then think what you wanted to do with the voltage telemetry in the transmitter. I've never tried to do exactly what you suggest but I'm sure it's possible.

 

Trevor

[Graham Bowers]

1 hour ago, Trevor said:

There are two low voltage alarms. The receiver will send an alarm immediately when the voltage drops below the set level. Also, the receiver continually sends its measured voltage back to the transmitter and the Tx will sound an alarm when this voltage drops below its (separately) set level. It does sound like your battery is past its best but if you are happy to continue using it, you could lower the Rx alarm (or even turn it off entirely) and then think what you wanted to do with the voltage telemetry in the transmitter. I've never tried to do exactly what you suggest but I'm sure it's possible.

 

Trevor

Thanks for that. Given the clue, I was able to find the relevant Harry Curzon video that gave the detail on the two Rx voltage alarms. He didn't mention any delay up to the point I watched it, which was when he moved on to voice files. I suspect the delay function doesn't exist in Jeti however I will watch it all the way through later. I'm off flying soon 😉

[Dickw]

3 hours ago, Graham Bowers said:

...................

I got a Rx low voltage alarm on the first turn on the 4th flight yesterday so landed immediately, no drama. The resting voltage after the flight on telemetry and direct measurement was 5.1 V however stirring the sticks would consistently trigger the alarm. Parked it up for the day.

..............................................................

 

Do you not have a telemetry log of the voltage during the flight? That would give you a better idea of what is happening than a "battery resting voltage".

If the voltage is dropping when you stir the sticks, that tells me that the power supply is inadequate for the applied load, and the purpose of a voltage alarm is to warn you of that situation. Trying to hide the on load voltage drop sounds an odd way to proceed to me.

 

Dick

[PeterF]

I have always been sceptical of these type of high capacity AA cells. Because they have high capacity they are seen as being very good but I have always believed that their current capacity is limited. The Overlander datasheet states maximum discharge current as 1.15A, that is 0.5C. Therefore, as we undoubtedly discharge them at higher rates they will age quicker than expected.

 

Just to confirm, I have not found a delay function on the low RX voltage, but you could probably set an alarm function up with the delay if required.

[Graham Bowers]

@DickwTelemetry log is a good idea, thanks.  I'm new to Jeti so haven't used that functionality yet.

 

I was quite surprised to get a low Rx voltage alarm on a model I've flown on Frsky so the ensuing thought processes were to try to understand how much is due to the measuring system (Jeti) and how much is due to the limitations of the supply.

 

I'd expect any power supply system to experience voltage sag when a current demand was placed on it, so the crux question to me becomes "how much is too much"? Perhaps I've been living near the edge without knowing it!

 

@PeterF Your statement statement about the limitations of these cells is interesting. I've been moving to AA Rx packs 5 cells of that chemistry on some models, Sub C NiMh  or LiPo on others to be honest. I'd just picked a simple "cooking" model to get stared with Jeti and am learning more than I bargained for 😉

 

Thanks for confirming the absence of delay. On OpenTx it's a function of a logical switch that can be applied to any parameter. Perhaps applying it to Rx voltage isn't best practice 😉