QX7/S ACCESS and 18650 Battery Issues

[HornPlayer]

I recently inherited a QX7S ACCESS transmitter and decided to go with it as my early QX7 was such a good reliable TX.
I quickly discovered that the 18650 cells combined with USB charging is full of pitfalls for old players like me. First of all I decided to check it out with 2 cells from another radio - it turned out they were getting a bit tired.

Lesson No 1: Do not assume that, just because a battery pack will switch the radio on and run it, that it has enough grunt to switch the radio off properly. The radio appeared to have turned off, the blue LED had gone out, but the audio circuit remained on with a small residual current draw and a low buzz/hum of white noise. Brand new batteries fixed the problem - as did a 2 cell lipo RX pack.

Lesson No 2: With new 18650 batteries installed and charged using USB via internal charging circuit cuts off at 8.3V - when the green charging light switches off. The radio will not start up at any voltage over 8.0V. I had to externally bleed off 400mA to get them back into usable range. It appears that the only reference to battery voltage in FrSky's sparse instructions is correct to the nearest mA of 8.0V - 6.0V. I haven't tested out what happens when voltage bottoms out at 5.999V and have no intention of chancing it and have set alarms at 6.5V

Strangely enough I have found no direct reference to these problems anywhere on-line although there are a few references to switch-on failures.

 

[gnichola]

The radio will run with up to 15V (15v was from the older Q X7S) 8.4, so I am wondering what batteries you had in there before and what is the battery range?

 

[HornPlayer]

The radio will run with up to 15V, so I am wondering what batteries you had in there before and what is the battery range?

View attachment 13632

Unlike my older QX7 which happily runs on a higher voltage range this radio come with a caution in the instructions to observe the battery range of 6.0 - 8.0V and it appears to have some sort of undocumented built-in protection to shut it down over 8.0V. I haven't struck anything like it before.
At 8.3V the TX switches on appearing normal and then immediately shuts down with the LED going RED. I was using brand new Samsung 18650 batteries and have now reverted to a 2s Lipo battery which is working ok.
The Open-TX screenshot shows a battery range that is not visible in ERskyTX. Is that menu item for display only or is it selectable and alterable? That is what my radio was showing before I changed it to erskyTX.
Before I blame a faulty switch for causing all my grief I am trying to eliminate the possibility that I have overlooked an adjustable radio system setting somewhere to allow for 18650 battery operation up to 8.4V which is the max voltage for that battery type.

 

[gnichola]

The battery range is adjustable, but I don't believe it really does anything other than set the range for the little meter icon. I also find it odd it won't run over 8.0v since the manual mentions 8.4.

 

[HornPlayer]

I think I am getting closer to the source of the problem. I reloaded Open TX to try the range adjustment - I cannot find that option in erskyTX - only a calibration adjustment.
I switched the radio off and removed my trusty 2s Lipo which does not cause any problems and went to replace it with the 18650 pack and as soon as the pins connected with the socket the speaker crackled and started buzzing again - with the radio still switched off. The only physical difference between the lipo connector and the 18650 connector is the little red fandango thingy inserted into the middle of the positive lead from the plastic battery tray. Both batteries are running at around 7.2V.
I think I will replace the connector and leads from the battery tray before I go any further.

 

[HornPlayer]

Problem has been solved. Faulty Main Board has been returned to FrSky for warranty repair after identifying PS voltage problem that started to occur from 7.7v and higher. I used a fully charged pack at 8.4v as per specs and when turning radio off it just kept continuously shutting down and restarting all by itself. Only way to stop it was disconnect battery.

 

[Landru]

Weird problem. Nice job getting to the bottom of it.

As an aside, after several years of use as my primary radio, my QX7 ACCeSS developed a funkiness in USB charging. It used to charge my 2S LiPo pack perfectly every time. Nowadays, the charge sometimes end up in the 'error state' with the green LED on the radio flashing and an incomplete charge. My workaround has been to pull the pack and balance charge it externally.