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Nimh Mythbusters test

some proper testing of how our battries hold up

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Lee Smalley12/01/2012 12:36:25
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unfortunately (or fortunately depending on how you look at it) work has gone mad busy and the chamber and my time that i had to do this test has gone right out of the window, i would love to do the test but i can't see it happening now, maybe i can do a smaller test that will take less time, lets see what i can do over the comming months
Steve Hargreaves - Moderator13/01/2012 09:58:38
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Posted by Codename-John on 11/01/2012 21:37:20:
Posted by Steve Hargreaves on 11/01/2012 09:59:35:
Give him a chance Funny Flyer....I think Lee is sneaking in after hours to do these tests....
 
Going by the dates of Lee`s original post`s he`s already had over 12 months and still no results ! lol
 
 
Ooops......I forgot last year was 2011.......I thought Lee had only jusy posted......
 
Come on Lee....get a bloomin' move on.....
Steve Hargreaves - Moderator13/01/2012 10:09:20
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I take your point about the capacity of the cells Peter....they must have achieved the figure somehow though.....perhaps though a 0.01C discharge rate at exactly 20 degrees C. Exactly the same conditions that we would use them in......I don't think!!!!
 
I guess its a bit like EU fuel comsumption figures for cars.....totally unachieveable in the real world.
 
I take your point about the impedence of our circuits but surely this is just making it far too complicated to be meaningful.....adding power factors & the like to our simple calculations would make for interesting debate but would be of little practical value.....
 
Regarding battery monitors then I always make a point of checking mine immediately after a flight......whilst "resting" in the pits batteries will recover slightly & give a higher reading the next time you switch on....for a minute or so anyway.....obviously they are not perfect but come under the "better than nothing" heading.....
Bob Cotsford13/01/2012 12:10:09
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good point about checking monitors after a flight Steve, also this highlights one good use for the telemetry that's appearing now. I reckon over half my models are now equipped with battery sensors that will give me an audible warning if the rx voltage starts to drop or if LiPo voltage is getting near the magic 3.3v/cell (courtesy of FrSky)
Peter Beeney13/01/2012 15:15:00
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Steve - I’ve never been convinced that these cells are anything more than what they appear. I’m sure that it would be impossible to achieve the capacity on the label, under any circumstances. All the other tests failed too, and they couldn’t be doctored. Mobile phone companies have had some problems with batteries, they even get past the people that are checking them! And look what they have to lose! For these consumable cells, 999 folks in a 1000 would not be fully aware of this, they just buy more replacements; and when I mentioned it to the supplier he simply ignored it. What else could he do?

Whenever the question about the 5 cell packs running down quicker than 4 cell crops up, I always get the impression that this always reads as though it’s going to be a lot quicker. I think this not always necessarily so. For starters it’s only 1.2V difference anyway; and I wasn’t actually talking about power factor, far from it, that’s something else, I was just trying to make it rather more simple, and consider the mechanical aspect, in terms of actual energy used over time. Thus for one or two reasons, in model planes, the 5 cell might last just as long, in terms of flying time.

As regards the power factor angle, sorry about that, but, as Erfolg might say, ‘ohh, I do like to slip them in’, this has always been dismissed as not applying to model aeroplanes, so therefore not very important, again something which I’ve never under stood. In a perfect world, an electric motor, such as used to power a model plane, with a power factor of 0.5 would use twice the amount of current as a motor with a factor of 1, for the same amount of power, in watts, produced at the prop. I’m not sure that I’d just want to ignore that. Although this never seems to get a mention anywhere, it’s possible it’s lurking in there somewhere, to a greater or lesser degree. I’m sometimes puzzled by what seems to be a rather high current when given for the no load revolution figures. Why is this. But again, this is perhaps not really the right place to dive into this.

I think I did say somewhere that a good place to fix the monitor is near the switch so that you eye catches it as you switch off. So great minds, as always, think alike! I did buy some bits to make an on-board audio low volt alarm to supplement the monitor, but at the moment it’s one of those I’venotgotarondtoityet jobs, I need more time. The GWS monitor is much better than "better than nothing", you can use all the battery power in perfect safety. I’m sure I’ve listed the discharge figures before in another thread, but I could soon do it again if it’s worth it. It only takes a couple of minutes with the right kit.
And although I certainly agree the voltage will recover, I don’t think it’s that much. One led perhaps, hardly likely to be the full range. I’m sure that once the leds have started to indicate that the battery is beginning to discharge you tend to concentrate on it a little bit harder. For me, that’s the whole idea.

We won’t even go near the brown out issue, I also have some problems with this, too…….

PB

Edited By Peter Beeney on 13/01/2012 15:17:08

Keith Simmons20/01/2012 16:11:27
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I found this from Giant Cod. Link it looks that Lipo batteries cannot maintain a discharge what it says on the label above 35C without suffering damage and some of the connectors supplied are not fit for purpose

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