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DX9 Tx Battery Warning, Warning!

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Keith Miles 212/01/2020 14:06:13
301 forum posts
6 photos

Firstly, my sincere apologies to readers of and contributors to another thread within which another issue arose regarding the Tx battery alarm feature and the related downing of somebody’s model.

During the debate, I made some comments about the low volt feature that were not correct!

Keeping the Tx batteries (and Rx batteries) fully charged has always been my practice long before modern computerised equipment and not intending to use it I gave the low volt alarm feature only a cursory glance on reading the manual and left it at the preset level.

The factory preset of 6.4 volts is “flat battery” territory for lithium, therefore not much use if you rely on alarms when you fly!

And Spektrum do not, understandably, advise what that safe setting should be nor at what voltage “loss of signal” will occur.

In the old days we used to fully charge for every session, I recall.

Happy days?

Once again, my sincere apologies for my portion of the previous confusion and tension that a recent debate created!

Denis Watkins12/01/2020 14:48:14
4057 forum posts
75 photos

The loss of signal estimate in the receiver instructions is 3.3v and the transmitter manual shows a chart on Page 8

Line D below, for Alarm voltage settings

" Digital Battery Voltage (an alarm sounds and the screen flashes

when battery charge gets down to 4.3V when using an NiMH

battery or 6.4V for a LiPo/Li Ion battery.) "

Many lads on here have suggested in the past to set these a tad higher

But fully charged, On site is normal for a flying day

Denis Watkins12/01/2020 14:48:15
4057 forum posts
75 photos

Meant to say that a 3.3v fall off is pretty common on circuitry

Where microprocessors ( chips ) are used, as they often don't work under 3v

 

Edited By Denis Watkins on 12/01/2020 14:52:22

Keith Miles 212/01/2020 15:12:53
301 forum posts
6 photos

Denis,

No chart on my page 8!

Not inclined to look at one or find it!

I also take the view that, sometimes, too much surgical inspection doesn’t help, it just tends to tempt people into pushing the limits until it ends in tears, theirs at best, someone else’s as well, at worst.

Lithiums, NiCd, NiMh, all have steady “charged” voltages followed by steep drop offs.

All have a “safe” working voltage. As soon as my Tx battery drops and stabilises at 7.3 volts, it gets recharged.

So my “tad” would be 0.8 - 0.9 volts!

Edited By Keith Miles 2 on 12/01/2020 15:34:16

Keith Miles 212/01/2020 17:47:14
301 forum posts
6 photos

Just been chatting about this feature with my brother-in-law who has much more DX9 experience (amongst other things!) than I do.

It has raised the question as to whether or not the audible low voltage warning comes in AT the set value or just BEFORE it.

I’m guessing it would be the former.

Does anybody know?

Obviously this could affect where best to set it!

Neither he nor I, have ever had the alarm go off, so we don’t know!

Currently, both our transmitters are showing 7.4 volts with his warning set at 7 volts and mine at 7.2volts.

If I find out before an answer comes back, I will pass the information on!

 

Edited By Keith Miles 2 on 12/01/2020 17:52:02

Keith Miles 213/01/2020 11:41:55
301 forum posts
6 photos

Oh, and during an indoor flying session last night, I was reminded of the audible “SYSTEM IDLE” feature.

So, that makes a total of THREE Spektrum DX9 features to avoid flattening batteries!

smiley

Keith Miles 219/01/2020 17:20:33
301 forum posts
6 photos

Update!

Had a few more flights this morning. End of session, screen still showing 7.4 volts.

On switching off, got a “low battery” warning.

Got home. Switched on. Screen showing 7.3 volts. No warning. Switched off. No warning.

Waiting to see, now, what happens when it gets to my setting of 7.2v.

Riveting stuff, huh?

smiley

Keith Miles 221/01/2020 00:58:41
301 forum posts
6 photos

Update 2!

Regular low volt warnings today with Tx display showing 7.3 volts but warning feature set to 7.2 volts.

So, it does seem to activate just before the value at which it is set. A good thing!

Just finished recharging the 4Max 4000mah lipo.

3800mah went back in i.e. the pack was 95% discharged at just 7.3 volts with just 200mah remaining!

And the originally fitted Li-On pack, of course, is only 2000mah!

Bearing in mind, also, the sudden voltage drop-off characteristics of both Lithium and NiMh cells, the message would seem to be clear if you want to avoid crashing a model!

Nigel R21/01/2020 06:47:25
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3398 forum posts
524 photos

It wasn't 95% discharged.

Figure on charging efficiency of 80% or so. I forget the exact figure.

Ie you put 3000mah back in the pack. Or thereabouts.

Gives 25% remaining. Assuming the 4000mah rating is honest.

The warning is there to avoid battery damage IIRC. Instant damage starts around 3v per cell. This is much lower than "flat" or fully discharged to 3.4v - which is a nominal figure trading off capacity per use against pack life of course.

During high discharge you could easily see 3v terminal voltage which instantly recovers when the discharge stops.

Keith Miles 221/01/2020 10:59:12
301 forum posts
6 photos
Posted by Nigel R on 21/01/2020 06:47:25:

It wasn't 95% discharged.

Figure on charging efficiency of 80% or so. I forget the exact figure.

Ie you put 3000mah back in the pack. Or thereabouts.

Gives 25% remaining. Assuming the 4000mah rating is honest.

The warning is there to avoid battery damage IIRC. Instant damage starts around 3v per cell. This is much lower than "flat" or fully discharged to 3.4v - which is a nominal figure trading off capacity per use against pack life of course.

During high discharge you could easily see 3v terminal voltage which instantly recovers when the discharge stops.

It took 3800 mah not 3000, from an indicated 7.3 volts. So, only 5% capacity remaining.

Yes you are correct that the warning is preset to an “anti-battery damage” level rather than “anti-crash” level, the subject of a somewhat heated debate in another thread recently!

And, as you say, one has to take stated specifications and reading accuracies into account.

Personally, I see no point in leaving the warning setting at the preset level especially if, as has been claimed elsewhere, the Tx suddenly switches off before the warning goes off!

I also note, from one Horizon video that when converting to a different cell type, Horizon man does not alter the preset,either, nor does he suggest raising it despite it being fully user adjustable!

In my view, better to keep batteries well inside the safe zone and away from that “cliff edge” especially if intending to do much more than one or two flights before recharging with, for example only 7 volts or less displayed on the screen!

And most of the time my 4 cell NiMh Rx packs are kept above 4.8v as well! 

I believe that fancy additional features are only beneficial if used sensibly and set up appropriately or they can, in some instances, have unintended and painful outcomes, or worse!

 

Edited By Keith Miles 2 on 21/01/2020 11:19:38

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