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Member postings for Keith Miles 2

Here is a list of all the postings Keith Miles 2 has made in our forums. Click on a thread name to jump to the thread.

Thread: Capacity checker accuracy?
26/01/2020 11:48:25
Posted by leccyflyer on 26/01/2020 09:20:03:

I've never looked at or knowingly read off the % remaining on a battery, but regularly hear folks say that their battery is at 35% or whatever. All my gear displays the voltage per cell, which is what I use - if it's <3.85v/cell it needs charging and if it's >4.1v/cell it;s fine to fly. If it's in between, then I'll pop it on the charger before flying. I have enough batteries to not have to need to try to eke more than one flight per charge out of them and I only charge at the field.

 

Entirely sensible BUT voltage is never a definitive measurement of capacity and becomes even less so over time as cells naturally deteriorate and capacity reduces.

Capacity is something that cannot be instantly and accurately measured as some seem to believe.

As I said, in an earlier post, I have had small LiPo batteries that read 4.1 volts and originally gave a comfortable four minutes flight time and after about two dozen flights, this dropped drastically to a matter of seconds, in some cases, whilst still charging to an indicated 4.1 volts on a very basic dedicated charger.

Monitored charging and/or monitored discharging is the ONLY way to ensure that batteries remain in sufficiently good condition for flying model aircraft and, for that purpose, a good charger would seem essential.

So-called “capacity checkers”, by contrast, are not “essential” as marketing might suggest, and should never be relied upon as a either a primary or reliable source of capacity information.

Edited By Keith Miles 2 on 26/01/2020 12:13:08

23/01/2020 09:53:52

Trevor,

Good system! I know one or two flyers who do the same as you do.

23/01/2020 09:42:21

In my case this was one of four almost new 3000 mah batteries, each of which have had only two or three flights.

Also, the model has been tested for current draw at full power with several props for the purpose of determining a safe initial timer setting on the transmitter.

All four batteries have also been monitored on the charger, at the flying field, after flight and all four have shown an expected amount of recharge and no signs of any discrepancies or lack of capacity.

The fact is that the checker used was showing 93% discharge when, in fact, the charger was showing just under 70% discharge. That’s a BIG discrepancy irrespective of temperature issues and other suggested factors.

As voltage is being used to provide capacity information for a battery with a fairly constant working voltage, it seems to me that unless it can accurately and consistently measure to at least two decimal points, it can’t be trusted.

Furthermore, as Frank acknowledges, it will not tell you anything about a reduction in maximum capacity of the battery over time but, if anything, will only provide a not necessarily accurate percentage reading of the existing capacity.

Yes, they can be handy for a quick check if you get your used and unused batteries mixed up at the field but for that job you only need a simple voltage checker not a supposed “capacity” checker.

Again, however, full voltage also does not guarantee that the capacity matches what is printed on the label, only a monitored discharge and charge will do that.

Edited By Keith Miles 2 on 23/01/2020 09:49:02

22/01/2020 22:19:15

Here’s another thing.

So, you land your model, put your checker on the battery and the checker says, for example, 30% remaining.

So, what do you do with that information?

Not take-off again with the same battery, one hopes!

Also, I don’t see a need to check batteries before flight when they should already be charged for use.

I will accept that it might be a handy device, perhaps, in some circumstances, but certainly not a necessity nor something to place too much faith in.

 

 

Edited By Keith Miles 2 on 22/01/2020 22:24:12

22/01/2020 21:47:55

Yep! Seems that my doubts are well founded!

My electrical mind suggests that the only accurate way to see how much charge is inside a battery is by measuring discharge current over time (the very definition of ampere hours!) until minimum voltage is reached and by, similarly, measuring current over time to maximum charge voltage to check maximum capacity.

For that, I prefer my charger although, admittedly, the process takes much longer and my charger doesn’t fit into a jacket pocket!

And further to my earlier point about full voltage not necessarily indicating full capacity, many in the hobby will also recall the legendary NiCd “memory effect”!

Frank,

Totally agree with you there but many modern, and not too expensive, chargers are as good as it gets, in practical terms, for monitoring and testing the condition (or deterioration) of one’s packs.

Edited By Keith Miles 2 on 22/01/2020 22:04:25

22/01/2020 21:19:50
Posted by john davidson 1 on 22/01/2020 20:48:04:

If one cell has packed in the checker can be tricked into seeing a three cell as a two and give a totally false reading

Not sure about that, unless two of the three positive outputs became one, thereby connecting two cells in parallel, in which case, assuming no internal damage was caused, you would still get three voltage/capacity readings, I would have thought, two being identical.

Alternatively, I would also have thought that an open circuit on a cell would provide a zero reading on that cell.

Do not all “capacity” checkers give a voltage/capacity reading for each cell or just some of them?

Happy to be educated!

Not that I’m inclined to buy one!

22/01/2020 20:46:30

Allan,

Ditto!

smiley

22/01/2020 20:45:01

Bruce,

Where, indeed?

At least one would seem to be wildly inaccurate, unless it was just having a bad day!

I can see how they might be fairly accurate at the top and bottom end, given the wider voltage differential but it’s the bit in the middle (the majority of the working capacity) where the voltage differences are very small, that intrigues me, especially for a cheap device.

Unless I am very much mistaken, capacity cannot be measured directly so “ capacity checker” is also a bit of a misnomer, in my opinion.

As for top voltage denoting full charge, that ain’t necessarily true either. I have had a number of small LiPos that charge to 4.2v only to last, in some cases, just a few seconds in my little helis! So, a voltage measurement, especially off load, is not a definitive piece of information concerning capacity or battery condition.

22/01/2020 19:33:29

Traditionally, I have been an IC flyer.

I bought my first electric model about four or five years ago, a palm sized quadcopter, since when I have added a number of similar small helicopters, a couple of small fixed wing park flyers and a Mini Wot4. I recently bought a Max Thrust Riot. Despite this limited collection, I have a 540w power supply and an I-Charger 208B.

From the outset, I have noted the wide use of pocket sized battery checkers but given the fairly flat discharge curves of the battery types commonly used, I have always doubted their accuracy and, therefore, how useful they really are especially when compared with the re-charge information provided by most, if not all modern and popular chargers.

Someone used a very popular model of battery checker today, post flight, on one of my Riot LiPo batteries and it, apparently, read 93% discharged after a five minute flight with a slightly higher pitch prop.

When I later recharged the 3000mah battery concerned, the charger put back, in fact, 2086 mah.

So that would make the checker out by 25%, albeit on the safe side!

So, I would be interested to hear if anyone else has had the same experience with these “convenient” and “pocket sized” devices?

 

Edited By Keith Miles 2 on 22/01/2020 19:34:14

Thread: DX9 Tx Battery Warning, Warning!
21/01/2020 10:59:12
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

21/01/2020 00:58:41

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!

Thread: Max Thrust Riot versus Wot4
19/01/2020 18:15:51

Just been doing some more testing, including a “head to head” with another similarly configured 3S Riot V2.

Firstly, there was no difference between the two in speed/power terms. One has the supplied 12x6, mine has APC.

Also, Just re-read the review which quotes 300watts/ 27A, on the supplied prop as “not far shy of 100w/lb”. Article also quotes weight as 3lbs 7oz (3.43). I make that about 87.5 w/lb. A BIG difference!

Unlike the review figure of 30A (for 330w) on an APC 12x6, I only get 27A on the same prop. My model weighs slightly more at 3lb 8oz, so similar power/weight of 87w/lb and well short of the 100!

Manual quoted weight for mine is 1480g (3.25lbs). So, at 300w, that’s still only 92w/lb.

At 330w (if you can achieve it!), I get figures between 96 and 101 watts per pound, based on the aforementioned weights.

It’s even clearer to me now why many owners have converted to 4S to get it to better match its description!

And that is my main criticism of it and certainly not its price!

I have suggested to Century a 4S Riot V3 i.e. no modifying required.

I would simply say, judging by the response that I received, don’t hold your breath!

Maybe they are happy with sales and happy to have a model which seems to me, in its current form, to sit in a category of its own?

If so, I can’t argue with that.

Thread: DX9 Tx Battery Warning, Warning!
19/01/2020 17:20:33

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

Thread: Trial Flights - Promoting the Hobby
17/01/2020 09:30:35
Posted by Tom Sharp 2 on 17/01/2020 01:00:38:

Having family youngsters in the club can be a two edged sword.

At one club I am in, one member had his son join. Trouble was he kept shouting at his son whenever the lad made a mistake. So much so that the poor boy told his dad where to stuff his planes and walked away never to be seen at the field again.

I would suggest not a “double edge sword” for a club, but perhaps one for the parent concerned, one who might seem, on the face of it, more discouraging than encouraging!

You say “his” planes.

Maybe that was the problem?

16/01/2020 00:07:41
Posted by Tom Sharp 2 on 15/01/2020 23:48:17:

'Trial Flights' is rather off putting, sounds as if the club is judging the newcomer.

'Experience Flights' would seem better.

Newcomers are hardly Donald Trump! They are not “on” trial. The hobby is on trial.

In full-size aviation, the former infers “hands-on” with a qualified instructor, the latter “hands-off” not requiring a qualified instructor. There are also legal implications in that world!

Edited By Keith Miles 2 on 16/01/2020 00:15:18

Thread: Can Superphatic glue go off?
15/01/2020 23:32:18
Posted by McG 6969 on 15/01/2020 12:02:02:
Posted by Keith Miles 2 on 15/01/2020 11:37:16:
Posted by Piers Bowlan on 14/01/2020 13:04:08:

I keep most of my glues in the fridge which keeps itself at +2 degrees so it doesn't damage the vegetables.

Why keep glue in a fridge to avoid damaging vegetables?

smiley

... it is well known that most of the solvents allow most vegetables to keep their natural 'green & shiny' colour...

... mind you, there are some exceptions like radishes, cranberries and even strawberries... even if the two latter ones are fruits.

Cheers

Chris

Interesting....I might experiment with some parsnips....

15/01/2020 11:37:16
Posted by Piers Bowlan on 14/01/2020 13:04:08:

I keep most of my glues in the fridge which keeps itself at +2 degrees so it doesn't damage the vegetables.

Why keep glue in a fridge to avoid damaging vegetables?

smiley

Edited By Keith Miles 2 on 15/01/2020 11:38:08

Thread: battery c rating
15/01/2020 11:24:12
Posted by Simon Chaddock on 14/01/2020 19:17:17:

Now if you can build a plane that only needs well under 1C from the battery to fly:

a) it will be able to fly for along time and

b) It will still be able to fly with significant battery degradation but just not for so long. wink 2

Which brings us nicely back to "fit for purpose" and "used appropriately"!

smiley

Thread: Trial Flights - Promoting the Hobby
15/01/2020 11:14:17
Posted by Supersavage on 15/01/2020 09:45:41:

As a new member of the BMFA I found their website and their membership portal thing really bad to use, even more so if you're viewing it via a phone. I spotted this thread the other day and I couldn't find anything about trial flights.

I tend to agree, there!

Not very "joined up" is it?

On the "Trial Flight" issue, I would have thought that it is something that should hardly need "promoting", as such unless the club, or group, for whatever reason, are reluctant to attract new members or if site restrictions prevent it.

My club has only been somewhat cautious about general advertising for reasons that have nothing to do with discouraging new members or potential new members but rather with protection of the site and its facilities and equipment. That said, we are a BMFA club and have our own website.

We have always offered "trial flights" to interested visitors and, indeed, recently invested in some new equipment for training purposes.

Also, we have hosted a cub scout group. Great fun! Many of the parents lived in the nearby village and, apparently, were unaware of our existence, despite many years of flying IC models, as is still the case!

Thread: battery c rating
14/01/2020 17:24:11
Posted by Andy48 on 14/01/2020 13:58:42:

Can I reiterate what I said at the start, and that is that a higher "C" rating does appear to equate to a longer battery life. There is probably a simple explanation for this in that you are stressing the battery far less by drawing well below its maximum current rating and therefore you get a longer life. From my anecdotal observations, the extra life expectancy is well in excess of the extra cost of getting a higher "C" rating equivalent.

And I think that most would agree with you. Your reasoning is entirely sound, and correct.

The “C” rating is, really, a thermal rating and relates to both current and internal resistance.

No battery, unless of excess voltage, will do damage to a load.

Conversely, excess load (stress), can certainly damage a battery, short term or long term, in the same way that high charge rates will reduce battery life.

So, a battery of correct voltage and high “C” rating will not “kill” but, if anything, in some installations, a high “C” battery might be regarded as “overkill”!

That “headroom” thing again which will only affect size, weight and cost considerations.

And on Mike Blandford’s point, all batteries deteriorate over time, even if well maintained. This is almost certainly down to a natural deterioration in their internal chemistry.

Edited By Keith Miles 2 on 14/01/2020 17:39:17

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