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NiMh Rx pack check report! ( And a warning?)

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Keith Miles 213/08/2020 13:35:12
501 forum posts
6 photos

I have a total of 9 Overlander, Eneloop Lite Rx packs, of varying vintages, some never used but merely stored.

I have 7 AA 1000mah Rx packs, 3 of which are White cells (2100 cycle?) and 4 Blue (500 cycle?).

Of the above 7, 2 of the White cells and 2 Blue were cycled and tested in April of 2018.

I also have 2 AAA 800mah packs, both White cells, that underwent the same process at the same time.

So, a mixed bag of used, unused, tested and non tested in varying combinations!

Feeling that it was high time to check/re-check all batteries, I elected to discharge all AAs down to 4v at 100mA, AAAs at 80mA and recharge at the same rates before then applying a 0.5C discharge load with my I-charger cut-off set to 4.8v.

A very long process but the results were interesting, to say the least!

Immediately prior to the 0.5C load test, all AAs were between 5.5 and 5.7 volts with the 2 AAAs at 5.4v and 5.7v.

Discharge time for the unused and newest AA (White) pack was 1hr 10mins (592mah discharge). Excellent! And a useful yardstick?

However.....

Discharge time for 5 of the AAs (White And Blue) varied between 37 mins (314mah) and 46 mins (386mah). Fairly even but a little worrying compared to the above result!

It gets worse....!

Discharge time for the remaining (and fairly recently used!) pack was 1 minute! EEEK!

The AAAs came out at 18 and 20 minutes (124/139mah).

So........

Firstly, at this point, there seems to be no obvious correlation, in general, within this “mixed bag” of “same make” Rx packs to explain the results, unless I’m missing something.

Secondly, there appears to have been a widespread deterioration in expected performance for reasons which I have yet to determine.

Thirdly, in at least one case here, it seems that a fully charged, in-service, not very old, battery at 5.5v might be less trustworthy than I thought it was!

Like most, I almost always fully charge Rx packs before use unless I know (or thought I knew!) how much safe flying time is left in the pack.

Since purchasing a modern charger some years ago, on my return to the hobby, I have also made full use of the information it provides particularly when recharging and regarding how much capacity has been used after flying sessions.

My models seem to be using no more than about 70 -80 mah per flight but a 0.5C load check seemed like a reasonable test value to include some “headroom” for test purposes.

With one possible exception (!), I’m not ready to scrap any of my packs just yet until I’ve done some more “experimentation” to see if I can improve or revive them.

There seem to be a number of views on this process on line but any additional input, or comment, from folks on this forum would be most welcome.

Nigel R13/08/2020 14:33:58
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4292 forum posts
715 photos

"I-charger cut-off set to 4.8v."

When you do your discharge test, do it down to 1V/cell.

If you discharge at 190mA on the AA you should match the datasheet conditions, i.e. expect 950mAh of discharge. I am not sure what you can actually determine from using 1.2V as the cutoff.

I have checked my standard AA Eneloop packs at 1C, that is 2A. Both my packs lasted around 50 minutes before reaching 1V/cell. I would consider that fine form.

Similarly to you, I am finding a discharge of around 80mAh from a ten minute flight with "the average glow sport model", although I have only starting monitoring this recently so don't have much data beyond that single figure.

Another point, personally, regarding "headroom" I am not sure about Eneloop Lite at higher currents. They just don't seem to be able to deliver nearly the same welly that the standard cells can.

There are some capacity tests reported here:

**LINK**

Eneloop standard discharge, note 4A (halfway between the 3A and 5A curve!) can be held for near 30 minutes:

And Eneloop Lite, that same 4A will cripple it before 12 minutes is out:

My take home from those graphs is that it isn't worth the 1oz weight saving from standard to Lite packs, I like a little headroom with my single points of failure.

Nigel R13/08/2020 14:37:22
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4292 forum posts
715 photos

PS, I picked 4A as that is the stall current for 5 old school standard analogues like a S3001 or similar - my personal data point for "the average glow sport model" when sizing these things up - i.e. it's a well matched battery to the average setup in a 40 or 60 size glow model.

Brian Cooper13/08/2020 14:55:48
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615 forum posts
27 photos

Yes indeed, discharging our NiMh batteries down to 1 volt per cell can certainly be an "eye opener" with regards to the health of a battery pack.

Beware of thinking that a brand new pack will be in good health. . It can be a lottery at times, with some old packs seemingly refusing to die, whilst (some) new packs can be distinctly "limp-wristed".

Cycling the charge/discharge a few times can put some "meat on the bones", but if a pack is old and has gone "moody" it really isn't worth taking a chance.

Former Member13/08/2020 15:29:19

[This posting has been removed]

Jesus Cardin13/08/2020 15:34:49
102 forum posts
22 photos

My personal experience matches closely to that of "Nigel R".

I have several 4 and 5 cells normal white Eneloop packs, some more than 5 years old and I always consistently get 1900-2050mah capacity in each charge.

When I got my first Eneloop packs I went a special route for charging and maintenance and it is I fully discharge at 0.5C (1A) to 1,0V per cell and then charge the packs at 0.25C (0.5A) and at the end of every process I always get near nominal capacity values, knowing all cells are OK and the pack fit for flight.

I have personally checked the AA withe normal Eneloop cells against similar AA gold Sony cells and I must confess Eneloop wins by far. After a few cycles to confirm nominal capacity for both brands packs, discharging at 1A makes an impressive difference: while Eneloop pack maintains just around 5.0V for more than an hour, Sony one fell to 4.8V -and even a bit lover- just in 12-15 minutes!

Bob Cotsford13/08/2020 15:37:35
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8847 forum posts
496 photos

As a stepping stone to full HV you can use LiFe packs as anything that's rated for 5 cell Nixx will be fine. I even ran older JR servos on 2S LiFe (6.6v) for years. Much more reliable than more recent nickel based packs in my experience.  I used 1100mAh packs on anything using standard servos.

Edited By Bob Cotsford on 13/08/2020 15:38:50

Keith Miles 213/08/2020 16:06:14
501 forum posts
6 photos

Nigel,

Many thanks. Some interesting points there.

First off, before seeing your response, I was about to report that the previously mentioned and seemingly “eeekworthy” pack just hit 4v within a few minutes at only a 100ma discharge! It was last used only a few months back in my PT19, so it seems that, by sheer chance, I might have dodged a bullet, there! For the sheer hell of it, and out of pure curiousity, I’ve just put it into “Forming Charge” to see what happens and because it’s a process I’ve never used before!

What concerns me is that I was regularly topping up before flight, noticing no obvious issue and ending up with a seemingly acceptable settled off load voltage of around 5.6 volts or more as with my other packs. Had this been a NiCd, I might be concluding “memory” effect but this is supposedly not an issue, of course, with NiMh is it? The pack has certainly never reached anything near the claimed 500 cycles nor is it anywhere near the claimed 10 year mortality limit! I’m currently baffled!

On your first point, my use of the 4.8 volt/500mA was purely to determine and provide a safe amount of “headroom” by seeing at what level of discharge the voltage dropped to the nominal 4.8v value. As you will note, the best pack of the bunch, unused and the most recently purchased, went down to 592mah i.e. almost 60% discharge (White/2000 cycle) which is way better than even the best of the rest at 38% discharge (Blue/500 cycle) and the former seems to be favourably comparable to the results that you have obtained from your packs, presumably 2000mah cells?.

On your point about Lite versus Standard, these just happened to be what I saw available at the time and my choice had no other technical basis other than capacity. Also, in practice, as I mentioned in another thread somewhere, I considered that there was little or no advantage, in practice, to using higher capacity as I rarely have more than three or four flights with any given model on any given day. I was also mindful of the fact that 2000mah of a given size will have higher resistance and less current/volt drop capability than 1000mah although again, in practice, and in view of your comments, it is something that I might reconsider.

All of that said, I remain puzzled by the seeming deterioration considering that Eneloops are supposedly the most robust and least fussy of cells in terms of storage and general use.

Once again, many thanks for your input.

I will report back further on the outcome of my “experiments” in due course, for those who might be interested!

At the moment, I’m not sure if my presumed vigilance in keeping an eye on the health of my cells has been sufficient or can be improved upon in some way!

Seems I certainly cannot rely on just regularly charging ‘em up or checking pre-flight voltage!

I’m also wondering how many models have bitten the dust, over the years, due to batteries that were seemingly okay but weren’t!

All of my crashes have happened for other reasons!

Former Member13/08/2020 16:22:26

[This posting has been removed]

Denis Watkins13/08/2020 16:23:22
4656 forum posts
132 photos

Wrong thread sorry

Edited By Denis Watkins on 13/08/2020 16:45:29

Keith Miles 213/08/2020 16:24:58
501 forum posts
6 photos

Thanks, Brian, Barrie, Jesus And Bob!

All good stuff, guys. Much food for thought for one who is still catching up!

One concession recently made, in view of the weight of the model and the additional number of servos, was to fit a 7.4 v 1000mah Lipo And 6v regulator in a Seagull Chipmunk, so I might be getting there, albeit slowly!

That said, I avoid chucking away otherwise good stuff if it will still do the job required even if alternatives might do it better, or differently.

I’m just puzzled as to why so many of my NiMh cells appear to have deteriorated for no obvious reason when they are supposedly resistant to doing so.

The head scratching continues......

Peter Christy13/08/2020 16:39:05
1921 forum posts

I have to say that I've never had a problem with genuine Eneloops, and all my packs are clearly labelled as genuine Eneloops (never come across a genuine one with a white case!). However, I always get the basic 2000mAH ones (or 800 mAH, in the case of the AAA cells) as the higher capacity ones definitely have a higher internal resistance.

Having said that, they are all used in what I would describe as relatively lightly loaded environments. The AAAs are used in my smallest single channel models, and the biggest I fly with the 2000s is a 60 powered KingPin (60s aerobatic model), though that does have four Futaba digital servos on board.

Never had an issue with them, though after the end of the lockdown - which followed a horrible winter - I did make sure to cycle them before use.

First of all, I discharged the 2000s at 1 Amp. Every pack still had between 60-70% of its rated capacity, despite having been left like that for over 6 months!. Following that, I trickled charged them at 1/10C overnight. The result? Full capacity restored!

It is not normally good practice to trickle charge NiMhs because of the danger of overcharging and venting. However, doing it *occasionally* will balance the cells, and NiMhs packs need balancing once in a while to maximise their capacity.

For larger models (some of my big helis), I use 3300mAH sub-C NiMh packs. These have no problems in even the most demanding environments, and can actually help with CofG issues in some models! wink

Oh, and ALL my packs are simple 4-cells. Never found the need for higher voltages. (And yes, I do have some DSM-2 receivers - some very old!)

I do have one helicopter that I fly with a 2-cell LiFe pack for the radio gear, but that has high voltage servos fitted.

I don't like the idea of using LiPos for flight radios. There are much better (and safer!) technologies around! I can tolerate them for the flight power, because such packs usually have quick access to remove / disconnect when things go wrong. Also, there isn't really much alternative!

But for normal small to medium size models, don't be too quick to write off NiMhs. They are very safe, and if looked after properly will give years of good service.

--

Pete

Keith Miles 213/08/2020 18:04:55
501 forum posts
6 photos

Pete,

On the “white case” issue, I only recently discovered, during my research into my current problems, that there have been, apparently, two incarnations of Eneloop. As stated in my original post, the first were apparently good for 500 cycles, the second for 2100 cycles, hence the apparent original colour coding.

I’ve also just noted, however, that my Overlander Blue cells are Panasonic and the White ones are Sanyo!

Make of that what we will!

Happy to read your comments in support of NiMh, for obvious reasons!

 

 

Couple of further points that come to mind.

Firstly, in terms of discharging to 1v/cell, nobody has yet observed that the end voltage is dependant on the discharge current applied which is why the voltage goes back up again when the discharge stops/current load is removed. To get a true 1v (flat) at the currents quoted would require driving the voltage below 1v (not a good idea, especially at high current) during the discharge.

So, if I want to obtain a truer 1v, I start with a higher current and gradually reduce it in stages. Sorry to be pedantic!

The second point concerns Rx/Radio battery testing in general and not necessarily NiMh.

Seems to me that probably the most reliable way to test batteries once the performance parameters required have been decided upon, is to perform a load test/discharge on the fully charged battery when new, at a given current load and to a desired level of voltage drop/capacity reduction, noting the figures obtained, and then occasionally thereafter, in similar fashion, comparing the performance over time with the original figures obtained.

In view of most recent experience where a crash might seem to have been imminent, despite my normal assumed “safe” procedures, that is what I intend to do from now on.

Telemetry, of course (more expense!) is an alternative or an added bonus in many circumstances.

Seems it’s never to late to learn. I certainly have and the process continues as do my battery investigations!

Oh, and as I type this, that Forming Charge has just completed after only 2 hours and 40 minutes with just 324mah of Charge at 6v cut-off! 

Methinks it’s on the way to my local recycling centre! At least it won’t be taking my PT19 with it!

 

Edited By Keith Miles 2 on 13/08/2020 18:28:24

Peter Christy13/08/2020 18:52:11
1921 forum posts

Keith, try the process I suggested. Discharge at 1 amp down to 1V per cell. Don't worry about reducing the current. Once the pack is "flat", trickle charge at 0.1C (200mA or so) for 10 to 12 hours. Then repeat the 1 amp discharge test.

You might be surprised by the result!

Of course, its always possible you *do* have some duff cells - I have some Vapextech ones like that, but I keep those for bench tests!

wink

--

Pete

Keith Miles 213/08/2020 19:31:34
501 forum posts
6 photos

Pete,

Rest assured all comments are noted. Currently (pardon the pun) I’m up for everything!

Bear in mind, mine are 1000mah packs not 2000mah, so my 0.1C is 100ma not 200ma and discharge current would, similarly, be 0.5A not 1A. I’m on the same page as you, though!

smiley

Duff cell report pending! It might take a while, unless I report one at a time. Some might be bored with this thread already and some might enjoy being kept in suspense!

smiley

Former Member13/08/2020 19:42:42

[This posting has been removed]

Martin McIntosh13/08/2020 19:42:47
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3631 forum posts
1245 photos

Just saw this thread and there are some very interesting points.

I have used Eneloops for years on both Tx and RX with mixed results. Back in 35mHz days I had a small aerobat which had two digital servos, the rest analogue and despite many Rx changes it glitched badly. I eventually realised that the high capacity NiMh cells could not supply sufficient current (not Eneloops but 4.8V).

I had a TN 44" Spit on 2.4, again 4.8V, (DSM2) which suffered a cell failure twice, fail safed each time and survived somehow. All models changed to 6V so that it would be unlikely to happen again.

Of my Eneloop packs, they are mixed Sanyo and Panasonic. Some retain full capacity for many years and others die off quickly. The best way that I have found to maintain them is to cycle a few times at 100mA discharge, 600mA charge. I am now changing everything possible to LiFe which are much cheaper, lighter, do no self discharge at all and require very little topping up for some reason. Likewise my JR Tx`s have Turnigy 1500 packs which last way way longer than 1900 Eneloops.

Many of my models now have two of Zippy LiFe 1100 or 1800 packs via a Failover switch; smaller ones a single 700. The former can easily supply even ten digi servos.

Richard Wills 213/08/2020 19:55:13
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259 forum posts
7 photos

Nimh batteries in my opinion are best used in their proper application, solar lights or the recycling!!!  There are much better batteries these days, LIFE packs in particular

 

 

 

Edited By Richard Wills 2 on 13/08/2020 19:56:38

Tim Flyer13/08/2020 22:02:27
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1352 forum posts
239 photos

I changed over all my NIMH packs to Life batters few years ago . I also moved my transmitter to LIFe power. I find better duration and much faster charging times to be a major advantage. The light weight of Life packs means it’s easy to run a twin battery RX power system in larger planes.

Keith Miles 213/08/2020 22:30:51
501 forum posts
6 photos

Always fascinating to read conflicting opinions. I have had the same experience when reading those of apparent professionals which doesn’t help to remove confusion!

in view of my most recent discovery, and I suppose that it’s something that I have subliminally known all along, there is probably no such thing as a totally reliable battery that needs no monitoring, especially in applications where failure might be disastrous. All batteries have a limited working life, whatever the chemistry, so it’s probably a good idea to have a reliable means of monitoring any Rx packs for their natural deterioration in order to know when to replace them before they fail in use. Doing so, I would suggest, might have prevented a lot of crashes and might help to prevent future ones!

I sense that even telemetry, whilst very useful, might not be an entirely reliable source of comfort or ideal safety net and I would not be surprised if models have crashed due to a weakened battery even where telemetry was fitted.

Just my own thoughts.

Oh, there goes the beeper! Forming Charge completed on the best of my packs. At least it will give me something to compare the rest with when I’ve got some more figures! I would rather resuscitate before, perhaps, buying direct replacements or, perhaps, changing my past habits for a new regime!

smiley

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