Battery Capacities?

[Robert Cracknell]

I have been cycling some of my Rx packs to check on their condition and capacity and I have come up with a few points which I feel could warrant input from the forumites.

 

The packs in question are all 4.8v, 2600mah Rx square packs made up from welded Vapex AA Ni-mh cells. They range from less than a year old to some at 6 years old.

 

The charger is an Overlander D100V2, and the settings for this exercise are;

 

Discharge Rate 1.5A

Charge Rate      1.5A (57% C)

Cut off voltage   4.0v (1.0v per cell)

 

The first point is that none of the cells took anywhere near the rated capacity of 2600mah, The best I could achieve before voltage cut off was reached was 1960mah. The others varied between this figure at best at 1550mah at worst. The discharge figures more or less mirrored these.

 

Secondly, discharge times varied as well with the newer pack discharging the fastest. This was not measured but simply an observation from the side by side display on the D100V2

 

This raises a question or two….

 

The full capacity of the cell clearly cannot be extracted unless the 1.0v/cell limit is breached, i.e. the remaining capacity is only available by taking the cell to damagingly low levels. How do we assess the working capacity of these packs? Maybe we should be looking for ‘Real World’ ratings, perhaps expressed as a percentage of the claimed maximum.

 

The voltage drop  was also noted and at a 1.5A load the voltage dropped quite quickly to around 4.3/4.5V. What is considered to be the minimum operating voltage? The voltage would hold at this for much of the discharge cycle.

 

All input and comments appreciated….

Edited April 9 by Robert Cracknell
Spelling

[Simon Chaddock]

Robert

The conventional wisdom is that high capacity AA NiMh cells have a high internal resistance so have to be charged and discharged very slowly to reach their claimed capacity. There is of course no guarantee how or even if the manufacturer ever achieved what "It says on the tin".

If you are getting out what you put in at the sort of rates you are using then that likely the best you will get.

If you know the actual discharge rate your TX requires and use that for both the charge and discharge you see a higher capacity. 

 

Remember the old NiCd AA cells were only 500mAh. They did have that capacity and with a lower internal resistance could deliver a good 10C (5A) at a push.    

[Robert Cracknell]

Thanks Simon

Perhaps I'll repeat the procedure but at 0.1A charge which is as low as the charger will go..

Thanks

Rob

[Engine Doctor]

With Nimh cells i have found that anything above 2000mah capacity are more prone to failure and drop their voltage drastically under load as IR increases. I lost a good model sone time ago when a cell in a 6v 2700mah pack packed up. When checked the pack showed 6.3 v but as soon as any load was put on it the voltage dropped to zero ! Just one cell cost a lot of grief .Up to 2000 mah they seem fine. I now only use the ready charged or LSD type as they seem even more robust than  the standard type.

[John Lee]

According to the manufacturer's UK site Vapex cells have a capacity of 2500mAh and this is rated at a discharge rate of 0.2C (500mA)

[Robert Cracknell]

John

Isn't 500ma too low for a Rx and 4 servos?

Rob

[Martin Harris - Moderator]

That rate would be for the purposes of standardised testing rather than a maximum discharge rate.  The voltage will drop as the discharge rate increases and that is the critical factor.  The site linked shows a maximum discharge capability of 7.5A  - in other terms, 3C.

[Jesus Cardin]

Just now, Robert Cracknell said:

John

Isn't 500ma too low for a Rx and 4 servos?

Rob

No, it is not too low for Rx plus 4 standar servos. Probably the opposite: in a trainer or sport model current consuption might be arround 300-350mA.

Edited April 9 by Jesus Cardin

[Martin Harris - Moderator]

The concern would be voltage depression with several servos under load or stalled rather than average current draw.  However, if the maker's data is to be believed, the plugs and wiring are likely to be the limiting factors.

[Nigel R]

What vapex cells are they? They do "standard" and low discharge types (marked as "instant" i think).

 

Your results look about expected for standard type. Although the variance is quite large.

 

Low discharge are better for our purposes,  in my opinion. Those should show 80pc of the rate capacity when cycling at 2C.

[Peter Christy]

12 hours ago, Engine Doctor said:

With Nimh cells i have found that anything above 2000mah capacity are more prone to failure and drop their voltage drastically under load as IR increases. I lost a good model sone time ago when a cell in a 6v 2700mah pack packed up. When checked the pack showed 6.3 v but as soon as any load was put on it the voltage dropped to zero ! Just one cell cost a lot of grief .Up to 2000 mah they seem fine. I now only use the ready charged or LSD type as they seem even more robust than  the standard type.

 

Quite correct!

 

In AA sizes, anything over 2000mAH is pushing your luck! You will be much better off sticking with 2000mAH rather than going for the higher capacity. 2000mAH is quite adequate for most of our applications. Don't get fooled by "the bigger the number, the better" syndrome. It ain't necessarily so!

 

I've never had an issue with genuine 2000mAH Eneloops. My personal experience with Vapex has been mixed...

 

--

Pete

 

[Robert Cracknell]

Nigel

The batteries are described as 'Racing Battery' at 2600mah.

See photo....

Rob

[leccyflyer]

Agree with the comments on AA sized NiMhs which have stated capacities >2000mah. I've never had much luck with those and at least a couple of those packs have fallen over and failed to deliver anywhere close to that claimed capacity in a very short time.

[Phil Green]

I dont know about the battery, but to me, everything about that label says "Avoid"   🙂

[John Lee]

1550387430392308810.pdf

 

This is the manufacture's data sheet for those cells.

 

I had a Rx pack of them sold by Component Shop but scrapped it after a year or two. I've otherwise stayed with genuine Panasonic 2000mAh Enerloops for AA NiMh, the oldest of which will be 14 years old in June this year and still going strong.

Edited April 10 by John Lee

[Engine Doctor]

I used to buy my batteries from 7dayshop.com but when Covid struck the supply chain fell down and they no longer list them. I still hsve some left so ok for a while. I have some of their AA cells made into Tx pack probably 8 or nine years old and some AAA packs in models a  few years old and working fine giving good voltage etc under load . Never been a fan of Vapextech cells . I bought some when they first appeared and they didnt last very well. What to use when my stock is used up ? 

[Robert Cracknell]

E.D.

The consensus on this thread seem to point to Eneloops......

[Peter Christy]

E.D.: Genuine Eneloops still available from Overlander (AAA-800mAH, AA-2000mAH).

[Nigel R]

ED, Eneloops are gold standard, as RX batteries are a single point of failure, I spend out on the best here. Of course, options exist to have multiple packs with failover type setups, but the best option is almost always a simple setup with reliable parts. Plus, Eneloops seem to have good shelf life. Anywhere stocking ripmax clobber will carry eneloop packs:

 

http://www.ripmax.com/Item.aspx?ItemID=O-4EN2000AASF&Category=090-010

 

 

I expect someone will be along to say how good LiFe or LiPo packs are soon... 😈

Edited April 11 by Nigel R

[Bruce Collinson]

Interesting nobody seems to have mentioned LiIon which Jeti put in Txs and suggest/recommend for Rxs too.   What's their downside?

 

BTC

[Martin Harris - Moderator]

Dunno.  11 years on, the original battery (more correctly, cell) in my DS16 is still performing well.

[Peter Christy]

14 hours ago, Bruce Collinson said:

Interesting nobody seems to have mentioned LiIon which Jeti put in Txs and suggest/recommend for Rxs too.   What's their downside?

 

BTC

 

They are fine for Tx use. Many modern Txs use them (FrSky, Radiomaster, etc). For Rx use, they are heavier than LiPos for the same capacity and the voltage is slightly different.

 

These observations assume that the voltage is correct for the application. Most modern transmitters (2.4 GHz) are quite happy operating in the 6-8volt range. Older transmitters (27/35MHz) require either 10 or 12 volt, depending on their age. Similarly, for LiPo/LiIon use in receivers, you need to be sure that both the servos and receiver can accommodate the higher voltage.

 

My own preference is either Eneloop NiMhs or LiFe cells for airborne use. Both can be charged safely in situ. LiIon and LiPo both have a chequered history in that respect.....! I wouldn't want to charge them in a model.

[Neil R]

Peter  - you keep saying that Li-Ions are heavier than LiPos.  I'll inverse your 'for the same capacity' caveat, and instead say that 'for the same weight' I'm personally seeing Li-Ions having up to 50% extra capacity.  I'll put some numbers at the bottom of this post which you can check yourself.

 

I've assumed for Li-Ion we're talking about twinned 18650 or 21700 cells, so typically 2500 / 3000 mah and 4500 / 5000 mAh respectively. For Rx packs of lower capacities I accept you'd probably still be looking at LiPo or LiFe, and in such cases the final weight will likely be less.

 

My own thinking is that the main current disadvantage for Li-Ions is the poor availability of mass produced made-up packs and hence the current higher prices (noting that Nick Mann on the BMFA Classifieds is doing his bit in presumably smaller volumes).

 

For actual electric flight packs the advantages of Li-Ion have started to win me over much more - I've just DIY built a couple of 4S Molicel packs, which like LiPos also charge to 4.2V, and for just a few extra grams I have replaced a 2800 mAh LiPo with a 4500 mAh Molicel pack. Given that these are essentially Electric Vehicle & Laptop cells I personally will have no qualms about charging in situ, and I'm going to worry less about returning them to storage charge if not used on any given day. It's the recent improvements in discharge 'C' rates for the Molicels in particular that have started to make these flight packs more viable.

 

The data I just googled was:

 

Li-Ion 18650:

 Molicel P30B     3000 mAh         48g ea;  x2 and add ~10g for leads  106g                

 Samsung 30Q   3000 mAh         46g                                                      102g

 Samsung 25R   2500 mAh         44g                                                       98g

 

Li-Ion 21700

 Samsung 50S   5000 mAh         65g ea; ditto                                        140g

 Moilcel P45B     4500 mAh         72g                                                      154g

 

LiPo:

 Nano-Tech 2s   2000 mAh                                                                     110g

 Turnigy 2s         3600 mAh                                                                     173g

 

LiFe:

 Nano-Tech 2s     2100 mAh                                                                     115g

 Nano-Tech 2s     3000 mAh                                                                     183g    

Edited April 12 by Neil R
added bit about C rates.

[Peter Christy]

Yes, I'm talking about relatively small packs. I've only got one model I would call "big", and it isn't that big in the greater scheme of things! 😁

 

However, I'm still very wary of LiPos and LiIons. Its not that long ago that laptops and cell-phones were catching fire in airliners and on trains! The technology hasn't changed, though the quality control has, hopefully!

 

I do use both LiPos and LiIons. The LiPos because for traction motors there is no real substitute, and the LiIons because I've got two transmitters that came with them. My preferred technology for both transmitters and receivers is either NiMh or (if the system can take the higher voltage) LiFe - purely on the grounds of safety! Remember that even Boeing were having trouble stopping LiIons catching fire in their Dreamliners! Mind you, given their recent history, that's probably not a good example....! 🤣

 

If you are comfortable charging them in situ, then that's your call. Personally, I'm not. But that's just me being very cautious. I have seen a couple of horrible accidents caused by momentary short circuits when the chap connecting things got distracted for a moment. There's an awful lot of energy stored in those cells, and you don't want it being released all at once!

 

<Gets off soapbox!>

 

😁

 

--

Pete

 

[Robert Cracknell]

Since my original post about cycling Rx packs I have bee experiencing some rather strange problems with my Overlander D100V2 charger.

I was cyclng a 4 x AA Rx  square pack and the display showed ‘D’ for discharge and a start voltage of 4.14V. As the cycling went on I noticed that the pack voltage began to rise. From a start of 4.14V it slowly rose to 4.23V. As I had set the cell cut off at 4.0V (1.0v/Cell) I thought there is no way this is going to finish so I cut the process short. I recorded the latter part of the rise by videoing the display.

A couple of days later I was cycling a 4 x AAA 800mah flat pack with a discharge of 1.0A and a charge of 0.5A and, foolishly, went into the house to make a cuppa leaving the pack discharging. When I came back about 10 minutes later I could smell something hot and within a few seconds one of the cells on the pack split open and was extremely hot. I am sure it was still on the discharge part of the cycle but even if it wasn’t 0.5A is below 1C and should not have caused the cell to rupture,

I raised this with Overlander Support (the charger is just over 3 years old) about 2 weeks ago and apart from being told that they have reported this to the manufacturer I have no answers.

Given the volatility if LI-Po cells I am not going to risk putting any of these near this charger!

Has anyone had any similar experiences with a D100V2…?