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Capacity checker accuracy?

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Keith Miles 223/01/2020 09:53:52
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Trevor,

Good system! I know one or two flyers who do the same as you do.

Nigel R23/01/2020 10:18:56
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Checker says 95%, I know I've charged the battery and I fly with it.

Checker says much anything else, battery goes home for charging, I don't fly it.

If it consistently reads <25% when I land, I decrease my flight timer a bit.

These things are just voltmeters, really. And quite cheap ones at that.

Capacity can only be rated at a particular discharge rate (usually something quite low) from fully charged to fully discharged. Manufacturer's idea of fully charged and fully discharged is likely to vary from yours. The temperature affects matters, too. An exercise for your normal charger to perform, if you want. You probably know this already.

Erfolg24/01/2020 21:30:08
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11551 forum posts
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I make no pretense of being an electrical engineer. Nor do I pretend to know much about electricity and even less about Electro-chemistry.

I do use a % and straight reading voltage checker, which provides a reading for each cell and across the battery. I mainly use the Tx timer to decide when to land.

I also am conscious as to how the model flies during the flight, to a degree.

When i become suspicious all is not well, I also have a internal resistance meter. I have a good idea about the IR when new, also when tested. If a cell shows up (normally towards the middle of the battery) as being higher than the rest and all relative to when new, I guess it is goosed.

My methods are subjective, have not always avoided embarrassing moments, but hey, this is the real world, where NPL standards are not useful, and judgment is probably as good as it gets.

leccyflyer26/01/2020 09:20:03
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I've never looked at or knowingly read off the % remaining on a battery, but regularly hear folks say that their battery is at 35% or whatever. All my gear displays the voltage per cell, which is what I use - if it's <3.85v/cell it needs charging and if it's >4.1v/cell it;s fine to fly. If it's in between, then I'll pop it on the charger before flying. I have enough batteries to not have to need to try to eke more than one flight per charge out of them and I only charge at the field.

Keith Miles 226/01/2020 11:48:25
301 forum posts
6 photos
Posted by leccyflyer on 26/01/2020 09:20:03:

I've never looked at or knowingly read off the % remaining on a battery, but regularly hear folks say that their battery is at 35% or whatever. All my gear displays the voltage per cell, which is what I use - if it's <3.85v/cell it needs charging and if it's >4.1v/cell it;s fine to fly. If it's in between, then I'll pop it on the charger before flying. I have enough batteries to not have to need to try to eke more than one flight per charge out of them and I only charge at the field.

 

Entirely sensible BUT voltage is never a definitive measurement of capacity and becomes even less so over time as cells naturally deteriorate and capacity reduces.

Capacity is something that cannot be instantly and accurately measured as some seem to believe.

As I said, in an earlier post, I have had small LiPo batteries that read 4.1 volts and originally gave a comfortable four minutes flight time and after about two dozen flights, this dropped drastically to a matter of seconds, in some cases, whilst still charging to an indicated 4.1 volts on a very basic dedicated charger.

Monitored charging and/or monitored discharging is the ONLY way to ensure that batteries remain in sufficiently good condition for flying model aircraft and, for that purpose, a good charger would seem essential.

So-called “capacity checkers”, by contrast, are not “essential” as marketing might suggest, and should never be relied upon as a either a primary or reliable source of capacity information.

Edited By Keith Miles 2 on 26/01/2020 12:13:08

leccyflyer26/01/2020 13:03:24
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I agree completely - the only accurate measure of capacity is to properly cycle a pack under an appropriate load and monitor it on test to determine what it can safely deliver. In practice though, in most sports applications I've found that the excess of power available is such that it isn't anything to really worry about and I prefer to determine the longevity of a pack in the air by having a comfortable flight and landing with power in the tank.

On rare occasions I'll push it a wee bit too far and land with the pack at a slightly lower indicated voltage that I'd ideally like. I use a timer with the more critical models, but tend not to use one routinely - I should probably change that.

I was far more organised and religious in the old NiCd and NiMh days, regularly cycling and monitoring the capacity of my flight packs, but we didnl;t have the surfeit of power available then and needed every mah we could get. Contrary to the popular perception though we actually were able to fly electric models successfully before Lipos were ever thought of,

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