Eneloops unsuitable for flight packs ?

[Steve Hargreaves - Moderator]

Yes the lower temp will definitely affect the batteries...by how much......ah...that is the $64,000 question...as my German work colleagues like to say " Ve do not know...ve must make a test"

I don't know but I would think the Vapex instants use a similar chemistry/technology to the Eneloops.....there are several brands on the market of these LSD cells now....

I have seen figures for the Vapex cells that suggest a max discharge of over 6A but I've no idea what this does to the voltage....

[John Cole]

Pat (and Steve) the corresponding data for Eneloop XX can be found here .

You can take out 1600 mAH at 5A before they drop on load to 1.1 V.

Pretty good, eh! To think I managed for years with a 400 mAH NiCd.

[Peter Beeney]

I’ve often wondered about aeromodellers and their electrical bits and bobs. There has always been many ideas about how this and that works, and what we should and shouldn’t use, but unfortunately as far as I’ve always been able to see there has been very little if indeed any hard evidence to back any of this up. Taking this thread as an example, it appears that some modellers are saying that Eneloops should not be used as receiver packs. Has anyone ever put forward any proven evidence of why they should not be? I suspect not. From the evidence that has been shown, however, by the pilots that have used them, they certainly appear to be more than perfectly adequate. So perhaps it might be an idea to try find out why this concept is so prevalent.

I don’t think that by any stretch of the imagination a receiver plus servos load can be described as ‘high’! There is more than enough evidence to prove that this is in fact comparatively very light. A typical 6 lb sports model will consume an average up to 200 mAh, admittedly there will be many little servo operating spikes, but they don’t amount to much, and I have done some practical tests on this, such as locking servos so that they can’t turn, a situation that if it should occur in the air would render the battery pack a bit unnecessary anyway. This was checking volt drops, and it still didn’t fail! Of course, as the model size increases, the servos and power pack need to be increased in line with this, but it’s all still relative. A man can steer a full size plane around the sky with generally little effort, it’s a bit like driving your car, too, the engine does all the work moving the vehicle, the driver is simply changing direction.

With regard to the ‘swiss roll‘ type of cell construction, I think generally all cylindrical cells are made like this. At least, all the one’s that I’ve opened have been. The resistance of the cell will largely depend on the total surface area of the plates; the bigger the area, the lower the resistance.
There is a Bolder 2V lead acid cell, 73 mm long by 24 mm diameter, weighing in at 77 grams, with spirally wound plates that are only 0.21 mm thick, made from at lead-tin alloy that is only 0. 05 mm thick, for maximum surface area. When fully charged has an internal resistance of equal-to or less than 2 milliohms; ≤ 0.002 ohm. It has a phenomenal performance, one novel trick is to wire 6 in a series pack, weighing about 0.5 Kg, and then start a car a number of times before it needs recharging; and then that only takes ten minutes!

I’ve previously searched without success for these, so they may not be obtainable in the UK.
I always been a bit sceptical about the brown out scenario, too, but that’s just me, I guess I’m a minority of one. However, I have tried to replicate this, again without success, three times now, which I have described in previous threads, but I have to qualify this by saying I’ve only been able to use my Spektrum AR500 receiver. To get a true comparison, I need to test at least a number of other types, but I’m not inclined to go and buy more receivers just for this purpose. One day, perhaps, I might be able to borrow one or more to try them.

So, I’m inclined to believe that whilst Spektrum equipped models may crash, it’s not always because the battery voltage has dropped to the very low level that it would appear to have to so do. There are many questions surrounding this set of circumstances, but I’m sure it will remain as part of the aeromodelling scene for a long time. I bought some Eneloops with a view to giving them a workout or three, but I’ve used then for other applications. However, I would personally not hesitate to use them as a receiver pack, at least for a normal model, 5 or 6 standard sized servos; and up to 60 powered; and, of course, if you also have the very desirable on board voltage monitor then it’s most unlikely you’d run out of watts accidentally anyway. In fact, there is a very simple little check that anyone can do, provided you have such a monitor. Just stir both sticks for a short while, if the top green led stays lit when the battery is charged then all is definitely well, if it runs up and down the scale a bit it’s still probably ok, that does tend to happen, if it gets into the red at all then there could well be a touch of resistance in the circuit, which is most likely the battery but not absolutely certainly so. I’d be more inclined to check this one out first.

[Peter Beeney]

PART TWO

Temperature as far as modellers are concerned is not likely to be much of an issue, nickel cells are pretty much given as ok down to around minus 20 degrees C, and I for one would not be flying in this anyway, and the Vapex cells with the 6 amp discharge rate I have tried. I’ve been here before on the forum, I did buy some just to have a look, and they were a total failure in every respect. I did mail the man, and he told me that I was doing it all wrong. However, when I started to explain that, amongst other things, I was checking the cell voltage at the cell terminals, which is the best and correct way of doing it, he declined to reply again.

Having said all that, they’d still be ok as a rx pack, simply because the demand is so slight. Although they were down by about 45% in capacity there was still plenty; and that I think is the answer.You need to check you own individual packs, irrespective. I’m sure good brand names are still the best bet, but again that’s not always necessary so, a pack of 4 from the 99 pence shop, for £1:98, AAA size, 800 mAh, are as good as gold!

As always, just a few of my observations, not necessarily the view and opinion taken by management……

PB

[Myron Beaumont]

Peter

Well spoken .Do you know,I \always used to just make sure everything was as well prepared as possible ,and still do .It's only reading the forum that I've almost become paranoid about other peeps so called failures or inadequacy of their equipment that I've began to worry about my gear .As I've mentioned some time ago ,I've never even experienced a glitch in over thirty years ! I'm maybe thinking I'm one of the fliers (most of whom never experience problems either and don't talk about their "success story" that is writing in positive terms about not having any problems..I surely can't be the only one ?

Touches balsa wood Glad that other Futaba owners don't have spasmodic problems as well .Hint!

Edit---And Hitec

Edited By Myron Beaumont on 23/03/2012 20:44:44

[andy watson]

I just bought a couple of packs of these eneloops- but I am not exactly sure why!

To me there is only 1 advantage to standard packs- their low self discharge rate. It might be theoretically advantageous to be able to leave a plane in storage for a month and then just go and flyl but is there anyone that would actually do that? I know I would still charge the pack before flying- so the LSD rate becomes irrelevant.

I am also slighly concerned by the "cliff edge" drop in voltage. Whilst I am comfortable my packs are far too big to be exhausted, things might happen to make this happen. Perhaps most important is my ability to test the rx battery with a little voltage tester. A gradual decline would register on the monitor, but a sudden drop might not show if it was just about to drop, but might go straight into LV during the subsequent flight.

[ken anderson.]

one of our older members at our field yesterday was using eneloop's in a large extra....2.4ghz/futaba/6 servo's...and reports he has had no problems ... and has been flying same model for a while now....

ken anderson ne..1 ...eneloop dept..

[Steve Hargreaves - Moderator]

Ah there you are Peter......I was hoping you might put in a comment or two as I know you have an opinion on this issue from your previous posts....

@ Andy Watson....yes its a good point Andy....I wonder if Eneloop/LSD users do just charge their packs when they come back from the field & then take them out again in a day/week/months time...theoretically I suppose you could..in fact this is exactly what you are supposed to do with them.....personally I don't....I always "top them up" the day/evening before a session....

And yet I still wonder......I was flying my LSD equipped Yak 54 on Saturday (54" span...70 4 stroke)....a quick stir of the sticks (moving all 5 standard servos) will drop the voltage monitor from top green to bottom red, or rather I should say it will make the bottom red flicker briefly before going back to top green when I release the sticks. I still fly it on 35MHz so no possible "brown out" issues.......

[John Cole]

I use Vapex Instant LSD both for Rx and Tx. I charge after flying (to above 5.5v and 11.0v). If I'm flying electric then I charge my LiPos at the same time. I'm then ready to go the next time I want to fly. If there's a gap in my flying I check, but rarely need to top up.

I use Futaba 2.4 GHz, so no chance of brown-out. Low Rx voltage kicks in the fail-safe. Never had it happen.

[Steve Hargreaves - Moderator]

Interesting John....you are using them as intended.....how do you check them? Just on a voltmeter & anything over 5.5V is OK? How long would you leave them before you would "top up" before flying?

Slightly off topic but I fitted a 3 cell LiFe pack to my Futaba 10C about a year ago & this has been fantastic...I charge it after about 3 hours use (on the Tx timer) & only put around 500mAh back in....theoretically I should get 9 hours out of the 1800mAh pack.....3 hours use is a lot of flying for me so it equates to several months worth of flying....I think I have only charged it about 3 or 4 times since I fitted it....

[John Cole]

With a digital voltmeter which has a Futaba plug attached.

If I haven't flown for a few weeks, I check them. But I also check my Tx using the built-in DVM and usually do that before I set off (just in case I've left it switched on). If the Tx is fine ....

[andy watson]

I popped one of the new eneloops into the vulcan last night- just to check a few things.

I thought nothing of it, and left it plugged in for about an hour. After the hour I happened to reach over the battery and felt a noticeable warmth. I unplugged the battery and the battery pack was uncomfortably warm to hold.

Is this normal? It worried me yesterday. The was basically no load on it.

[Steve Hargreaves - Moderator]

I would say definitely not Andy.......I can see a pack getting warm if being charged but not under load.....unless it was a very high load ie several amps continuously which is an application you probably shouldn't be using these batteries for anyway.

Current must have been flowing around the battery somehow Andy.....it couldn't get warm just sitting there.....where might the current have come from? I'd check your wiring......

[John Cole]

NOT normal. Put a meter between the battery and the plane and see if it is REALLY no-load.

Eneloop quote a voltage drop of 0.15v @ 4A so that would generate 10W of heat per cell so if it got warm I would guess the draw to be significant.

[Lee Smalley]

oh dear why do you listen to such people who have no idea what they are talking about, i have 20+ packs of LSD nimh packs both from makes SANYO and Vapextech i have had a pack in my Yak for 3 years it has a 23cc engine in it with all metal geared servos 6 off i fly more than most, about 6-7 flights a day and after each day they are about 60-80% and need about 500mah put back in if you are sucking constantly around 2-5 amps (not spikes) then your installation is rubbish and if your flying something that is massive with so many digi servos that the current draw is in the danger area for these type of cells then you are an idiot for trusting such a model to a few AA cells, please guys can we not rake over this stuff again these cells are fine for the majority of models we fly!!

and the reason i use LSD packs is that if the model is stored.... even for a week it only takes half an hour to an hour to put the charge back in as its only lost a few 100 mah simple.

test and debate all you want experience tells me all i need to know !!

[Myron Beaumont]

Lee

So I'm not the only one with no problems as I suspected & mentioned in this thread a couple of days ago. It must be other peeps not doing things right !The ones we hear about probably (to coin the lager advert terminology) on the forum as against us others that manage alright . .By the way I'm still using a 600 mAh Tx battery nicd ,about five years old I think , in one of my trannys (Hitec Optic 6) with complete confidence .Just bung it on the wall charger the night before flying .I do charge up my "Instants " before flying the next day regardless of what's been taken out of them like others seem to do .Habit I suppose .Of course there is no peak detection on my Tx charger @ 150 mA (Fusion cheapo £9.99) ,only on the Rx ,so I just leave the Tx on for maybe 4 or 5 hours .No probs so far .

Edited By Myron Beaumont on 26/03/2012 14:32:21

[Peter Beeney]

Steve, I think I would not be entirely happy with that situation regarding your wobbly monitor. I’ve certainly no wish to want to tell you what you might do in this case, so I’ll just say what I’d do if it were mine. I’d consider in the first instance the battery is the biggest suspect because generally speaking none my other models have this problem. Also I would view this as possibly a bigger load of trouble in the pipeline, and it may be closing fast! To quote one pack that I’ve used recently as an good example in another thread, an homemade pack, not LSD, circa. 2005, this is 5 UniRoss AAA 800 mAh NiMHs, still right up to spec and the top green only stays lit when I waggle the sticks, even after I’ve had several flights. It’s in a 6 lb hack model, which is quite quick, so some servo loads. Therefore I’d be somewhat suspicious if anything deviates from this, my other models are exactly the same. I’ve done this rather more than normal recently, in view of what has been said in some threads on the forum.

My procedure would be this. Firstly I’d recheck the monitor, so that I’d know exactly what voltage the receiver was dropping to, I could do that on a battery discharge using an accurate voltmeter. If that were ok, and I’d be extremely surprised indeed if it weren’t, then I’d plug the battery straight into the receiver and try that, so as to try and determine where the higher resistance point may be. This should prove it to the battery or the switch harness. If it’s definitely the battery I wouldn’t want to speculate the reason until I’d had a good look at it.

To try and back this spiel up, I will recheck my monitor, it’s the GWS one, and I’ll also hook up my pack of 4 Eneloops to this receiver, the one’s that I bought recently, just to see what happens. They appear to discharge just fine, but the monitor will sort them out. These monitors are quite sensitive, and the scale is about a volt, so it’s possible that I’d be happy with some slight deviation, but I have to say that the leds going right down into the red when the servos operate would firmly grab my apples, anyway.

Not perhaps entirely related to Eneloops, but definitely batteries, we’ve had another couple of incidents very recently, a fellow modeller wanted to check out his model after some mods but was unable to because fortunately, due to my persistence, he’d installed a monitor and that was in the red. Reason unknown, but at least it saved a potentially serious incident.

However, within minutes another model was flown, this was a nice little scale plane, and had just changed hands, the previous owner was more or less passing it straight on, it was not his scene, and had not used the supplied battery because he was unable to test it. This is a Sanyo 2500 mAh 5 cell pack of AA’s, it had been on charge all night and within a couple of minutes of taking off the model spiralled in and was wrecked. When I checked the battery it was completely flat. Now, on a test charge/discharge it’s perfect. There’s very little I can say about it all really, but there is a clear message to see, I think.

I’m sure that in fact most folks don’t have any problems, but this just goes unannounced. It’s the occasional, but nevertheless the ongoing and persistent incidents that come to the fore, it’s easy if you are familiar with this stuff, but many folks are not, and when you don’t know the answer the question is always difficult. I just try and help others in trouble the best way that I can.

I’ve just at a little fiddle with a v. m., a GWS, and the bottom red led is lit down at 4.115 volts. It extinguishes totally at 4. 012 volts. So if you get a blank screen at any time you know you are at 4 volts or below, and I believe the brown out is supposed to occur at 3 volts, although my AR500 doesn’t.

Just another piece of useless information……

PB

[nasa_steve]

Posted by Andrew767 on 22/03/2012 16:51:52:

Posted by nasa_steve on 22/03/2012 16:32:57:.

Steve....In what planes?....How many servos?

Thanks Andrew

hi Andrew

3 of my models have Eneloop 2 have 4 cell and one a 5cell packe all three models have at least 4 servos each one funfighter a 60 sized model and one 90 sized model, although that said the 90 is a Seagull Navion which has 7 standard servos three of which are digital two metal geared and one cheapy standard on the throttle. the 60 sized model is an Sbach with digitals all round and is powered by an Eflite Power 60 electric on 6 s lipo. On average i would possibly get 4 flights on each in a session.

incidentally i would'nt even consider flying anything larger on AA cells and all of my bigger models are sporting sub c receiver packs right up to a 50cc petrol model. my general rule of thumb is if its 120 classed or above then its sub C's or decent li-po with a regulator/u-bec

nasa

[Lee Smalley]

Why Steve, that's your choice and I respect that but there is no need just to base it on size, the decision should be based on servos, type of flying, and current draw my yak only has very brief spikes of 1 amp with all servos moving, even under load these 1amp spikes are less than 10 seconds long its well within what the pack can cope with, but I allways use 5 cell packs anyway

[Steve Hargreaves - Moderator]

Peter...you have just triggered my inate paranoia.......I will now have to dig the battery out from its hiding place & check it over......but thank you for the kick in the pants I probably needed to investigate it.....its kind of been niggling away for a while.....I did cycle the battery just recently & got around 1600mAh both in & out of a 1700mAh battery (I forget the exact figures) at a 0.3A discharge/charge so I figured there couldn't be that much wrong with it!!!

On a more general point, all this talk of large currents to the servos is slightly academic anyway IMHO....the typical servo plug & socket we use for our batteries is only rated at 3A continuous.....

[Lee Smalley]

Yep

[Peter Beeney]

Steve, Is it worth having a quick look at the monitor first? Some of them have been a bit iffy in the past, particularly when they have a limited range, considerably less than a volt in some cases, where I think the manufacturer is trying to err on the side of caution. Probably not that easy if you’ve not got a variable voltage supply, but if you’ve got a voltmeter and an old potentiometer it might just be possible to cobble something up. The GWS version consumes around 20 milliamps, so it might be a touch of poke and hope.

As you say, it would seem there’s little wrong with your pack in terms of capacity. I lashed up my pack of 4 Eneloops temporarily to a model and admittedly they are fully charged but however hard I tried to stir the sticks the top green did not deviate one iota. So there is no voltage drop there to speak of. Which does rather point to the possibility that you might need to get up close to your pack for a good look.
Regarding the large current flowing, I’m sure the 3 amp limit is only a guide, I’d be confident the standard plug and socket will survive at least 5 amps indefinitely; and the airborne discharge rate is very intermittent; and overall quite low anyway, at least from all the evidence that I’ve seen. As far as the low voltage effect goes, a 35 MHz receiver will stop working at 2.8 volts, my 2.4 Spektrum AR500 switches itself off at 2.7 volts, and coincidentally at that point, 2.7V, usually a servo stops moving. It still turns on but there’s not enough push to make the motor turn.

Frankly, if your power supply ever gets down to this level, for whatever reason, then you’re probably in unrecoverable territory anyway, and there’s only ever going to be one outcome, and that might involve the use of a certain plastic container. I notice the EU are now talking about outlawing the use of plastic bin liners, will this be the one move that successfully manages to severely curtail the flying of model aeroplanes, I ask myself? We won’t have any means of carrying them home……

Of course, if the problem persists, and you are not able to easily spot the cause, you can always just disconnect the monitor and throw it out. That will ease any paranoia, and the ensuing crash will then come as total surprise, instead of being a long drawn out affair!

Only kidding, and the very best of luck with it all.

All in all, this does rather make you wonder why there seems to be an idea in some quarters the Eneloops are not suitable as model aircraft radio receiver supply packs!

PB

[Steve Hargreaves - Moderator]

Posted by Peter Beeney on 27/03/2012 21:20:06:

Of course, if the problem persists, and you are not able to easily spot the cause, you can always just disconnect the monitor and throw it out. That will ease any paranoia, and the ensuing crash will then come as total surprise, instead of being a long drawn out affair!

So this begs the question is a surprise crash better than one you have been expecting........h'mm maybe I will just leave that one hanging...

But you are right Peter....I will dig the battery out & attack with my DVM & see what is going on.....I am in great danger of actually taking my own advise here & just replacing the battery if I have a doubt about it...

[Peter Beeney]

Steve, If you did a test discharge with your voltmeter and the monitor all tied up together and then note where each led lit and extinguished that would soon give you a clue as to what level the voltage is dropping to-.

It will be interesting to know what you find is the reason for the voltage excursion.

PB

[Steve Hargreaves - Moderator]

My charger will link to the PC & record all the data so I might rig it all up when I am in the office & watch what happens.....sitting watching as each LED on the monitor goes out might be quite dull.....better than X Factor but dull just the same!!!