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Nimh Mythbusters test

some proper testing of how our battries hold up

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Lee Smalley07/12/2010 14:03:47
2125 forum posts
68 photos
2 articles
Hi guys i have read lots of stuff about Nimh and the problems that some people think they have, some people have done testing but they seem to fall down in one area or another one was using old packs and another was using 2amp discharge and then wondering why the voltage sat down so much! so I have decided to sort this out once and for all!!! and so this is what i propose to do.
I have 3 packs all brand new
1 sanyo eneloop 5 cell
1 vapex instant   5 cell
1 JR supplied pack  4 cell
1st test charge holding ability
discharge all and then recharge using same charger all charging at 0.5C
hold in the boot of the car for 1 week bring back up to 20 deg c and check capacity at a discharge rate of 600mah
i am using 600 as it really  is the max  that the average sport flyer will see
2nd test voltage level under load at 0 and then 20 deg c
again the packs will be cycled and allowed to rest for an hour before going into a chamber held at the test temperature whilst being subjected to a constant load of 600mah the voltage of the packs will be logged every minute for 3 hours
before you lot ask i operate a calibration lab and have the use of an enviromental chamber to carry out these tests the voltage will be logged with an 5 1/2 digit agilent datalogger, i have limited time i can do these test (as i am at work at the time) but if you would like any other tests carrying out them post them here and i will see what i can do give me a few days to get the discharge boards built and tested and then we will make a start, in the meantime any questions fire away!!

Edited By Lee Smalley on 07/12/2010 14:04:46

Doug Ireland07/12/2010 23:23:50
2088 forum posts
42 photos
Sorry Lee but I don't see the point in these tests other than for purely academic interest. Most people just recharge battery packs prior to use anyway and are not that interested in their ability to hold a charge over a certain period of time.
sparks5908/12/2010 03:18:58
217 forum posts
105 photos
Whilst Doug makes a, no doubt correct, observation of what most people do, I do think your proposed tests have value. At least we will all know the truth about these batteries in certain sets of circumstances.
I'm looking forward to seeing your results Lee.
James4008/12/2010 06:45:31
885 forum posts
3 photos
Go for, it's a great idea. I think the one thing RCM&E sadly lacks is back to back testing of products so the consumer knows what's best for their money.
Bruce Richards08/12/2010 07:45:41
1849 forum posts
I think these test will be very useful. People recharge their batteries before each use because that is what they have always done not because it is necessarily  the best way to do it. More information on the subject will be most useful.I have to say that the Instant Cells in my Dx6i have on ly ever been charged 3 times in the year I have had it and even then they did not take a any where near a full charge each time.

Edited By Bruce Richards - Moderator on 08/12/2010 07:46:48

r6dan08/12/2010 08:08:27
1110 forum posts
46 photos
I think it is a really good idea go for it,maybe some lipo testing in the future?
Brian Parker08/12/2010 08:31:14
538 forum posts
Just use Sanyo Eneloops and charge every other full moon.
Seriously, It might prove informative if you could include a budget supermarket ‘4 pack’ for comparison.
Stephen Grigg08/12/2010 09:34:02
8691 forum posts
1128 photos
Sorry to sound nieve Lee are these batteries  RX batteries or power to motor batteries please ?
Ian Jones08/12/2010 10:30:42
3219 forum posts
1397 photos
Do it Lee.
When I arrive at the field with a fully charged battery pack  I want to know  that when I land I will stil 95% or more capacity left. If I make two flights and the capacity is down to around 50% then the pack goes in the bin. Hardly scientific but it keeps me out of trouble.
The ability of a battery pack to hold it's charge can be the diffrence between a landing & a crash. I check my flight pack at least every other flight so that I can monitor & get to know how a pack is behaving and it would be useful have something to measure against.
Then there is storage of course. A pack unused for 6 months - will it be dead or just in need of charge? I've found them quite unpredicable. What should I be expecting?
Your results will make intersting reading.
Allan Bowker08/12/2010 10:53:19
1627 forum posts
227 photos
Any test is worthwhile Lee, even if we think we know what the result will be.
Your work should confirm or prove otherwise.

Biggles' Elder Brother - Moderator08/12/2010 11:03:21
15748 forum posts
1460 photos
Experiments are always good Lee - go for it. I'm predicting a set of very positive results.
Only one observation, 600mA is still a discharge rate way more than these batterries will see in service in a sports model. I seriuously doubt they would see that rate of discharge even momentarially - let alone for 3 hours!
Myron Beaumont08/12/2010 11:03:56
5797 forum posts
51 photos
I have several Rx packs that I've had for about   18 months (Instant 2100mAh ones) Three times I've checked their voltage over that period of time which only dropped about 0.2 volts.every 6 months . The second time I checked them ,not knowing what to expect , I recharged for a short while to "Top them up". Although never flown I worry a bit that maybe I'm using the wrong technique ie NiCds ritual having read somewhere that they don't like a top up or that maybe they should be flattened every now and then & then re-charged at 1C .Complicated isn't it ? Queries abound don't they ? Just who do you believe? Carry on the tests Lee !
Myron (trying to get ready to move house )
Lee Smalley08/12/2010 12:56:18
2125 forum posts
68 photos
2 articles
Totally agree BEB 600mah is too much really but there are people out there who claim to be pulling AMPS!!! yeah right, i have decided on this as its about in the middle of what people are claiming from 100mAh to 2 amps and its the load using the components i have here to make the constant current dump boards up with
i have included the 4 cell pack from JR as this is the nearest i can get to std Nimh packs they do not claim to be LSD cells !!
Doug the reason for the test are because people are still repeating the old myths about the poor old Nimh cells and this is based on very old data, and lets face it if the data goes the way i think it will you no longer will have to top up before flying (providing you use LSD cells)
Lee Smalley08/12/2010 13:00:05
2125 forum posts
68 photos
2 articles
sorry Mr Gigg they are Rx batts only
Lee Smalley08/12/2010 13:06:06
2125 forum posts
68 photos
2 articles
the test equipment i will be using

environmental chamber

agilent voltage logger
Lee Smalley08/12/2010 13:07:24
2125 forum posts
68 photos
2 articles
ohh and everthing is calibrated as well i will also be calibrating the current dump boards when i have built them
Peter Beeney08/12/2010 13:37:24
1587 forum posts
59 photos

          One additional test you might consider including is a pack of Vapex VAP-ACC-AA2900 2900 mAh AA cells. These seem to be available from a number of sources, from at £10.99, free delivery, or Amazon, £2.99 + £4.99 delivery via Component Shop, or £2.99 delivery via Digital Additions. Thus in this respect they perhaps come in the ‘budget’ bracket, although of course they don’t claim to be low self-discharge cells.
There was a very comprehensive and high performance specification published on these cells, which strangely, or perhaps significantly, now seems to have disappeared. The nearest I could find was at Firesupport, £7, where they advertise a 3C discharge rate plus a one hour charge rate. Also, and I quote, a high shelf life (80% initial Capacity storage). Whatever that means, exactly?
   I did a run on a pack of 4, from idle curiosity. As I’ve been tinkering with batteries for fifty years plus I felt this seemed to be a little bit too good to be true and thus it proved to be. Big time! The capacity proved to be 1800 mAh, and all the high rate tests collapsed the moment I tried to start, i.e. the voltage fell below one volt per cell, 4 volts.
   The capacity test that I did was the standard one that charges to 150% of capacity and then discharges at one tenth C, down to 4V/cell; if it doesn’t pass this it won’t pass anything!
   So I discharged the cells until flat then charged at 0.1C, 290 mA, for 15 hours, left for 24 hours, and then discharged at 300 mA until the pack reached 4 volts. Which it did at 1800 mAh.
   Discharging straightaway after charging made no difference. The 3C discharge rate was in the original spec., in theory it should discharge for 20 minutes at 8.7A down to 4 volts, in my case it was probably less than 20 milliseconds.
   Having said all the above, as I’ve said before in these threads, this would still fly a model as a rx battery, all day, simply because the power demand is so light. It’s just that it’s nowhere near the super battery it claims to be.
   A comparison check would be very useful indeed, as I tend to think this is not a rogue pack, another set of figures would at least make that a little clearer.

   Regarding the low discharge aspect, again, as I’ve said before, I’ve run a little check for more than six years on a standard Ni-MH. This doesn’t seem to lose capacity over time in a very short time, so I don’t have any issues with low shelf life.

   I agree with you, I use all nimhs, or nicads, they are all old, they simply refuse to wear out! But there are faulty cells in some pilots packs occasionally, and I’ve always said a regular check-up does help to catch these before they are able to cause any grief.

   Good Luck with your testing.

Biggles' Elder Brother - Moderator08/12/2010 16:04:30
15748 forum posts
1460 photos
Looking at that environmental chamber and the data loggers you really do mean to nail this one - once and for all don't you
I assumed you were going to stick them in the fridge at home! (Or even on an external window ledge in this weather!)
Go for it man - the applicance of science!
PS Glad to see your employer is right behind you on this one Lee
Stephen Grigg08/12/2010 16:37:11
8691 forum posts
1128 photos
Ive a 5 cell pack in my Harmon Rocket thats been chaged only twice this year and the Rocket gets used the most,When I put the battery check on it its never been below 99%
Ian Jones08/12/2010 17:01:19
3219 forum posts
1397 photos
Oops! I found that with one pack - then I changed the settings on the battery checker to 5cell/6volts. Fortunately I realised before any critical loss of capacity occurred.

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