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

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Keith Miles 214/08/2020 00:28:45
461 forum posts
6 photos

Well after all the preceding discussion, I have just discovered that Overlander no longer do any of the packs that I currently have!

My choice, of suitable capacity, from Overlander at least, is now either 6v/2300 flat, 4.8v 2300 flat or 4.8v 2300 square.

Am I the only one who feels, that as one gets older, obsolescence seems to accelerate as does expenditure?

Grrrrrr!

I’m 67 and there is no way, in my remaining lifetime, that I will willingly replace all of my servos and receivers or, for that matter, convert my IC models to electric for two reasons, my mortality and my wallet!

So, it seems to be either “revival” of my NiMh packs or Lithium and maybe a regulator!

The latter is looking like the front runner!

Interesting discussion, though!

smiley

Richard Wills 214/08/2020 00:37:27
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249 forum posts
7 photos

Keith anywhere you could use a 6v nimh pack, you can fit a 6.6v LiFE lithium pack unregulated straight swap.

Peter Christy14/08/2020 08:58:22
1868 forum posts

Barrie: Like yourself, most of my models are i/c powered, but I do have a few electrics - mostly smaller types. However, I do have an early 70's Schluter Cobra helicopter that I have converted to electric, but even on that I use a separate 4-cell NiMh battery pack for the radio gear (3300 mAH, sub-C cells - also helps with the CofG!).

In the absence of NiMhs, my preferred option is a 2-cell LiFe pack. This is a much more stable chemistry. It doesn't have the same reputation for spontaneous combustion that LiPos have, and yet can deliver plenty of current for even the most demanding servos.

One of my problems is that I have an awful lot of JR servos, and these are notorious for not being happy at higher voltages! The cost of high voltage replacements would be excessive, to say the least! However, I do have one (vintage) helicopter fitted with high voltage HiTec servos that runs very happily on 2-cell LiFe cells.

LiFes are stable enough to leave in the model for charging, whereas for LiPos, it is generally a good idea to charge them in a safe place (not surrounded by highly inflammable balsa or foam!).

I also don't like the use of regulators or battery backers! Down the years, I've seen these cause far more problems than they've solved. I know of at least two cases where the use of these devices has caused a dramatic reduction in range, and one where a regulator caused so much glitching that the model became dangerous to fly! It was cured instantly by going back to a 4-cell NiMh!

I know some ESCs have built-in regulators for the radio, but some of them have worryingly low current capacity.

To my mind, the best solution is the simplest, and that means using a good quality battery of sufficient capacity, the right voltage and low internal resistance. It also means having as little as possible between the battery and the receiver. My Cobra doesn't even have a switch for the radio! I just plug the NiMh in before the LiPo flight pack!

Keith: You're right! I hadn't realised that 2000mAH AA Eneloops were suddenly in short supply! I've certainly been unimpressed by the higher capacity versions! Just as well I have a couple of spares! To my mind, adding an extra cell is applying a sticking plaster rather than tackling the root cause of the problem!

Back in the NiCad days (shortly before they were withdrawn) I used to use a lot of 1900 mAH sub-C packs. These days I use the 3300mAH NiMhs for the same purposes (helicopters with lots of servos, larger models, etc).

Unfortunately, our hobby is a small consumer of batteries in the grand scheme of things. Most of the bigger manufacturers (Sanyo, Panasonic, etc) seem to be in a numbers race to attract the camera (and other domestic appliance) brigade. This is not necessarily to our advantage!

"Back in the day" we used to fly quite large models on 500mAH DEAC button cells! OK, the servos didn't draw as much current back then, but for all but the most serious flyers, 2000 mAh is more than enough for a day's flying! When I come to top mine up, I find that they rarely take more than 500 mAH.

Planned obsolescence is unfortunately something with which we now have to live. However, I'm an eternal optimist, and I'm sure something will be along soon to fill the gap in the market...!

wink

--

Pete

Trevor14/08/2020 08:58:41
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476 forum posts
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I was going to stay quiet on this but if Keith is considering switching to LiPos, I thought I may as well share my experience - just one more personal opinion to add to the confusion!

I always got on pretty well with NiCd batteries and continued to seek them out on stalls at shows well after they had officially ceased to be sold. Yes, I knew I was buying old stock but, such was my experience with the earlier NiMh packs that an old NiCd was infinitely preferable!

My poor experience with NiMhs was I believe exacerbated by the fact that, at the time they weren't getting a lot of use. Their self discharge rate was quite high and inevitably differed between cells. As a result, to be sure of charging them fully they had to be trickle charged, inevitably over-charging at least some of the cells. Not a recipe for a long life. I'm sure things are much better now with the low self-discharge types such as Eneloop, but I've no first hand experience of these.

I do a lot of electric flight and as my LiPo batteries begin to age, I now move them out to semi-retirement in the slope soarers, so I now have no NiMh batteries at all. Some of the slopers are over 30 years old so there's a good selection of old servos in their so 5v uBECs are used throughout, with 2s or 3s LiPos usually of 800 - 2200mah capacity. All the electric models also use uBECs (separate from, or built into, the ESC).

As others have said, there is no perfect solution. The main downsides of LiPos are the potential additional source of unreliability in the uBEC and the need to take a bit more care on the safety front. In most of the slopers, removing the battery for charging would be a pain so I admit to charge them in situ - but only outdoors. I always have a charger (and a 3s or 4s LiPo to power it) in my flight box. On arrival, the battery is checked in the model (you may need to buy extension leads for the balance connector). If necessary it is put on charge, out in the open, before flight. I usually only charge to around the 80% to 90% mark to reduce the stress on the battery in storage. The good side is that you don't need to bother with any battery checking or charging before going flying.

My radio gives me telemetry so I can monitor the voltage at the receiver. Unfortunately, due to the presence of the uBEC, this now tells me nothing about the condition of the battery! However, when the LiPos really begin to age, you will find that they drift out of balance due to uneven self discharge. This is the point to pension them off.

I hope this helps you in your pondering!

Trevor

Nigel R14/08/2020 09:23:48
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4066 forum posts
693 photos
Posted by Barrie Lever on 13/08/2020 15:29:19:

The biggest problem with NiMh's is that they have too high internal resistance and the voltage crashes when any serious load is applied, people over came this by fitting excessively large capacity batteries that had lower internal resistance.

Then you have memory issues, although Eniloop went some way to sorting that out.

Must respectfully disagree.

Internal resistance on AA Eneloops is low, datasheet gives 24mOhm. Compare with Panasonic's AA Nicad datasheet figure of 15mOh.

Terminal voltage at various loads for nimhs is well defined, tested, and the information available easily online to check.

As posted in the discharge curve, 5A can be held above 1V for 20+ minutes. That's around 2C discharge.

As compared with a 650mA nicad which Panasonic datasheets only lists - around 2C as maximum - 1200mA discharge rate. 5A would be around 8C discharge rate. I doubt that could be held up for very long.

I have not seen, and perhaps I am simply missing it, any evidence of memory issues on nimh.

IF operated in spec they are a perfectly good battery.

Nigel R14/08/2020 09:27:27
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4066 forum posts
693 photos

Posted by Trevor on 14/08/2020 08:58:41:

As a result, to be sure of charging them fully they had to be trickle charged, inevitably over-charging at least some of the cells.

Trickle charging does not overcharge nimh cells.

 

Posted by Peter Christy on 14/08/2020 08:58:22:

To my mind, the best solution is the simplest, and that means using a good quality battery of sufficient capacity, the right voltage and low internal resistance. It also means having as little as possible between the battery and the receiver.

Nail, head.

Eneloop AAs fit that bill, but I would say LiFe also do.

YMMV, etc.

 

Edited By Nigel R on 14/08/2020 09:30:59

Nigel R14/08/2020 09:38:53
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4066 forum posts
693 photos
Posted by Keith Miles 2 on 13/08/2020 18:04:55:

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!

Just set the charger to discharge at fixed current, 1C or 2C, until 1V/cell is hit, then stop. Don't worry about "true 1V", this isn't how the normal discharge test works. You'd really knacker the cell by continuing to hit it with every decreasing current until the voltage was stable at 1V.

Incidentally, Panasonic bought Sanyo. If interested, there is lots of stuff about commercial and technical history of the numerous iterations of the eneloop cell on wikipedia

**LINK**

"there is probably no such thing as a totally reliable battery that needs no monitoring, especially in applications where failure might be disastrous"

Absolutely right.

Periodic checks are the way to happiness.

Steve J14/08/2020 09:52:57
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2043 forum posts
60 photos

Posted by Nigel R on 14/08/2020 09:38:53:

Just set the charger to discharge at fixed current, 1C or 2C, until 1V/cell is hit, then stop. Don't worry about "true 1V", this isn't how the normal discharge test works.

That is what my charger does.

1~2000mah 4.8v eneloop #2.jpg

Periodic checks are the way to happiness.

Indeed. The Eneloop 2000 that the above graph is for is still going strong and is checked once or twice a year.

Keith Miles 214/08/2020 09:59:55
461 forum posts
6 photos

Some more useful posts, there, much of which gels with my own thoughts and echoes my frustrations!

Another “niggle”, for me at least, is finding alternative chemistries with the correct connector without having to buy or make up adaptors plus, of course having to make possible constructional adjustments to the model as well.

And, yes, I totally agree that the safety recommendations for Lipos, removal for charging for example, does not make them the most convenient choice for Rx packs especially given the general advice (but sometimes conflicting!) about storage charging!

I do take on board that LiFe, if it becomes necessary to change chemistry, seems to be, on balance (no pun intended) the more practical option, assuming that my 6v servos and receivers will tolerate the 10% over-voltage.

It does seem that a few 1000 and 2000 NiMh packs are still on some shelves, even if no longer made, but the worry might be about how long they’ve been sitting there!

As for 6v regulators, that seems to me to be an Etronix monopoly and stockists also seem somewhat limited and, yes, it does possibly add another element that might fail!

Is it my rose-tinted glasses leading me to the view that things were once much more simple?

Peter Christy14/08/2020 10:27:41
1868 forum posts
Posted by Keith Miles 2 on 14/08/2020 09:59:55:
Is it my rose-tinted glasses leading me to the view that things were once much more simple?

Entropy always increases! wink

--

Pete

Cuban814/08/2020 10:47:12
3029 forum posts
1 photos

I use these where I have the room - very good performance in terms of C rating (my own tests) and a reasonable price. **LINK**

The 2/3 A packs are also fine and I've used them before in smaller airframes - good for around 3A without sagging.

I found that LiFe packs upset some of my 6V max servos because of their higher voltage, so something that might be an issue.

Edited By Cuban8 on 14/08/2020 10:53:20

Richard Wills 214/08/2020 10:50:48
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249 forum posts
7 photos

I do take on board that LiFe, if it becomes necessary to change chemistry, seems to be, on balance (no pun intended) the more practical option, assuming that my 6v servos and receivers will tolerate the 10% over-voltage.

Remember 6v on a 5 cell nimh is the nominal voltage, below which the battery has very little usable capacity left. Fully charged it will be nearer to 7.5v so a 2s life pack supplies near as makes no difference equivalent voltage

Cuban814/08/2020 11:05:23
3029 forum posts
1 photos
Posted by Richard Wills 2 on 14/08/2020 10:50:48:

 

I do take on board that LiFe, if it becomes necessary to change chemistry, seems to be, on balance (no pun intended) the more practical option, assuming that my 6v servos and receivers will tolerate the 10% over-voltage.

Remember 6v on a 5 cell nimh is the nominal voltage, below which the battery has very little usable capacity left. Fully charged it will be nearer to 7.5v so a 2s life pack supplies near as makes no difference equivalent voltage

Agree in principle although I've never seen a 5 cell Nimh go to 7.5V unless really pushed by fast charging and getting a bit hot which I prefer to avoid........however depending on the servo and its spec even a couple of hundred millivolts above what a particular servo is happy with I've found can lead to poor centering and notchy behaviour. My Nimhs are timed trickle charged and normally finish at a little over 6.8V at 1/10 charge rate. On-load voltage at 2 or 3C is typically 1.25 -1.3V per cell depending on load and size of cell. I leave a bit of headroom and consider a cell exhausted at 1.1V so never get anywhere near down to 4.8V for a 5 cell pack. A full days flying with a six servo warbird always uses less than 50% RX battery capacity when I've checked - difficult to be exact might be a tad more or less depending on various factors on the day - flying style - a few more flights if the weather's been good etc.

I suppose the answer is for the manufacturers to spec their standard inexpensive servos for higher voltages rather than 6V (the old 4X 1.5V dry cells of ages past) or even just 4.8V max in a spec which raised a question on the forum a while back - don't remember the exact servo in question.

Pete Christy's sage advice about sufficient battery performance is so very true as is the keep it simple where possible approach. Trouble is the performance of RX batteries and even many UBECs is shrouded in mystery and never properly specified in simple and clear terms for the average consumer of those devices. Ask ten average non- techy modellers how much current their RX batteries can safely source or how it can be ascertained and I reckon you'd get ten blank faces or a couple of hopeful guesses - not ideal and the root of a lot of the 'brown out' panic that still persists.

Edited By Cuban8 on 14/08/2020 11:28:50

Martin McIntosh14/08/2020 11:11:50
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3527 forum posts
1220 photos

KM, don`t go near those 2300 packs since they are the ones which would not drive a couple of digi servos as I mentioned above.

I do not know why they term Eneloops as being LSD. Try charging a pack, leave it for a week then see just how much it takes to top it up again.

The reason I use twin packs and a smart switch on some of my better models is that if one suffers a problem it is switched out.

Back in the 70`s when I flew comps we only had 500 Deacs, sometimes 600`s and to counter a cell loss I added two more via a standard 5V 3A regulator. Really pushing my luck at a comp. which may require four flights plus the fly off.

Nigel R14/08/2020 11:39:00
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4066 forum posts
693 photos

Martin

They're "low discharge" compared to "standard" nimh, as in the first generation.

Although I think in fairness, having 75% charge retention after a year is pretty good.

As for the 2300 packs, if this is related to

"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)."

then I would assume you are talking about standard nimhs, not eneloops, and the older generation nimh had higher resistance and did not hold charge at all, plus if left to go flat they suffered damage quite easily.

Current Eneloop Pro datasheet quotes identical internal resistance to the current standard Eneloop.

 

Keith

"It does seem that a few 1000 and 2000 NiMh packs are still on some shelves, even if no longer made"

Component shop are showing stock of the normal eneloop 2000mAh AA packs.

The normal 2000 are still listed on Panasonic's website as a live product, as are the Pros with 2550mAh capacity.

One thing you may wish to note is that Eneloop Lite are NOT listed as made in Japan. The Panasonic website does, however, state the normal Eneloop and Eneloop Pro are Japan made. Read in to that what you will (although I my personal conclusion is that for RX packs I wouldn't touch with the Lites with a bargepole).

Edited By Nigel R on 14/08/2020 11:41:29

Barrie Lever14/08/2020 12:32:48
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294 forum posts
52 photos
Posted by Nigel R on 14/08/2020 09:23:48:
Posted by Barrie Lever on 13/08/2020 15:29:19:

The biggest problem with NiMh's is that they have too high internal resistance and the voltage crashes when any serious load is applied, people over came this by fitting excessively large capacity batteries that had lower internal resistance.

Then you have memory issues, although Eniloop went some way to sorting that out.

Must respectfully disagree.

Internal resistance on AA Eneloops is low, datasheet gives 24mOhm. Compare with Panasonic's AA Nicad datasheet figure of 15mOh.

Terminal voltage at various loads for nimhs is well defined, tested, and the information available easily online to check.

As posted in the discharge curve, 5A can be held above 1V for 20+ minutes. That's around 2C discharge.

As compared with a 650mA nicad which Panasonic datasheets only lists - around 2C as maximum - 1200mA discharge rate. 5A would be around 8C discharge rate. I doubt that could be held up for very long.

I have not seen, and perhaps I am simply missing it, any evidence of memory issues on nimh.

IF operated in spec they are a perfectly good battery.

Nigel did you get the internal resistance numbers switched around because 15milli ohm is better than 24 milli ohm?

I agree if operated inspec that NiMh's are a good battery, just that there a few better alternatives. On that basis down to the recycling centre with them.

B.

Bob Cotsford14/08/2020 12:40:04
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8739 forum posts
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Posted by Keith Miles 2 on 14/08/2020 09:59:55:

I do take on board that LiFe, if it becomes necessary to change chemistry, seems to be, on balance (no pun intended) the more practical option, assuming that my 6v servos and receivers will tolerate the 10% over-voltage.

Unless you are putting serious loading on your servos it won't be a problem, as has often been said 6v is nominally a 5 cell Nixx pack and those will easily exceed 7v fresh off charge much the same as 2S LiFe. As for receivers, I can't remember what 35MHz were rated at but everything that I've pwned in the last ten years have been rated for at least 9v.

Posted by Keith Miles 2 on 14/08/2020 09:59:55:

Is it my rose-tinted glasses leading me to the view that things were once much more simple?

or ignorance was bliss. We just bought the only option available (DEAC.NiCad) and the matching trickle charger and away we went. No telemetry, no intelligent chargers, just Lady Luck and an acceptance that you-know-what happens.

Barrie Lever14/08/2020 12:40:35
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294 forum posts
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Posted by Peter Christy on 14/08/2020 08:58:22:

LiFes are stable enough to leave in the model for charging, whereas for LiPos, it is generally a good idea to charge them in a safe place (not surrounded by highly inflammable balsa or foam!).

Pete

Pete

Bad luck having a load of JR servo's.

Are LiPo's really more unstable than LiFe?

To be honest I have never even had a LiPo puff up, but I am listening to what you say about LiFe.

I do like that bit of extra voltage that the LiPo gives, makes even an HV servo have a bit more zing !!

Anyhow it is all universes away from a centre tapped 4.8v DEAC running Logictrol servo's !!!

Best Regards

B.

Nigel R14/08/2020 12:54:01
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4066 forum posts
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Posted by Barrie Lever on 14/08/2020 12:32:48:

Nigel did you get the internal resistance numbers switched around because 15milli ohm is better than 24 milli ohm?

I agree if operated inspec that NiMh's are a good battery, just that there a few better alternatives. On that basis down to the recycling centre with them.

B.

Barrie, no not switched. Yes, 15mOhm is better than 24mOhm. But, both are quite good; note the internal resistance given in datasheets is only indicative - it is quoted at a frequency of 1kHz, an AC figure does not directly applied to our circumstance.

In the scheme of things the discharge curve is the best indicator of performance under varying loads. Both nimh and nicad have reasonable curves, I've already commented on the total time they could both hold up a decent output.

YMMV of course.

Maurice Dyer14/08/2020 13:17:02
102 forum posts

Ignorance is bliss on my part I suppose. One flight or six, my Nimhs get 8 to 12 hours and some are 6 years old.

Standard wall 1c charger.

Maurice

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