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Old 09-18-2012, 08:55 PM
  #1
MetallicaJunkie
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Default Explain this please

how is this device able to tell how much capacity a LiFe or LiPo has in it from just plugging a battery pack to it? http://www.futaba-rc.com/accessories/futm4166.html
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Old 09-19-2012, 02:31 AM
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Default RE: Explain this please

"*The remaining capacity (criteria) display is based on voltage at no load. Since it may differ largely from
actual remaining capacity according to the battery type, use it as a criteria only.
*From the standpoint of the battery characteristics, immediately after charging and discharging, the
remaining capacity display will change until the battery stabilizes. The voltage stabilizes about 30
minutes after charging and discharging.
In addition, because of the different discharge characteristics, when the specified capacity was checked
after use, a remaining capacity lower than the actual remaining capacity may be displayed even for the
same type of battery. Judge the remaining capacity with the stable state value as a criteria.
*When the remaining capacity (criteria) display reaches 20% or less, recharge the battery.
*When the remaining capacity (criteria) display exceeds 95%, since the battery is almost fully charged,
refrain from charging it. Overcharging will cause the battery to deteriorate."

from the manual below



http://manuals.hobbico.com/fut/br3000-manual.pdf

if you download the manual, don't freak out because just the first half is in Japanese
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Old 09-19-2012, 03:38 AM
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Default RE: Explain this please

One other fact to point out is that LiFe packs have a very flat discharge curve with a very sharp knee at the point of exhaustion. This means that the voltage remains fairly constant throughout the discharge process of that pack. For this very reason, devices such as Voltwatch2 and such devices can give you a false sense of security with regard to remaining charge in an LiFe pack. So, use these devices carefully and monitor your flight times.

It's really best to know how much battery you would consume in a normal flight and base the remaining charge on the overall capacity to determine how many flights you can safely have when starting out with a fully charged pack.

I am extremely conservative when it comes to flight times and battery duration. I will not fly if I think I am approaching a point where I would be leary of the remaining charge in a pack. There is just to much to lose. Lose the plane, that's one thing. Crash it into a crowd, or into someone's property, well, that's a very different situation and it just isn't worth it to get "one more flight" that day.

CGr.
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Old 09-19-2012, 08:25 AM
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Default RE: Explain this please


Quote:
ORIGINAL: CGRetired

One other fact to point out is that LiFe packs have a very flat discharge curve with a very sharp knee at the point of exhaustion. This means that the voltage remains fairly constant throughout the discharge process of that pack. For this very reason, devices such as Voltwatch2 and such devices can give you a false sense of security with regard to remaining charge in an LiFe pack. So, use these devices carefully and monitor your flight times.

CGr.
Absolutely.

I've seen posts here from people who INSIST that voltage can be used to determine the charge state of LiPo's, LiFE's, A123's and other Polymer batteries.
Unfortunately that doesn't really work, because of the relatively flat discharge curves.


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Old 09-19-2012, 08:30 AM
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Default RE: Explain this please

thanks for the replies... .. i think ill just monitor my batteries the old way by seeing how much many mah's it takes to fully charge them after a few flights...and just check em under a load between flights
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Old 09-19-2012, 08:47 AM
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Default RE: Explain this please

I have a question that deals with this thread, I hope you don't mind )), is there a product that measures amount of mah's one uses during a flight? I know more radios have telemetry built in and I would think that would be a handy feature to measure power draw. I know that you can get something like it for larger lipos.

Thanks

Jon
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Old 09-19-2012, 10:01 AM
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Quote:
ORIGINAL: Minnreefer

I have a question that deals with this thread, I hope you don't mind )), is there a product that measures amount of mah's one uses during a flight? I know more radios have telemetry built in and I would think that would be a handy feature to measure power draw. I know that you can get something like it for larger lipos.

Thanks

Jon
Don't the Castle's ESC effectively do this automatically via their flight logging?

The software produces a great chart showing instantaneous amp draw and averages. This can be used to easily calculate total draw if it doesn't do so already.

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Old 09-19-2012, 10:33 PM
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Default RE: Explain this please

Just like lipos are at 50% at 3.85 volts life can be checked for capacity as well. What is required is a much better meter. Life do not have a flat discharge curve, yes they drop off very slowly but they do drop off and with a good meter they can be checked for capacity that way.

I have no experience with the above meter but I have used a voltmagic for the past 4 years on A123 and it has been bang on regarding capacity left. It works just like a voltwatch on a NIXX battery and when I hit the yellow light I put back in the same amount each and every time so I know it works.

http://www.voltmagic.com/
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Old 09-20-2012, 03:19 AM
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Quote:
ORIGINAL: MetallicaJunkie

thanks for the replies... .. i think ill just monitor my batteries the old way by seeing how much many mah's it takes to fully charge them after a few flights...and just check em under a load between flights
This will certainly work fine and save a few dollars to boot. I was very skeptical going in to A123 and now that I have them I am amazed that I don't need a voltmeter at all. It is a waste of extra dollars in this case. I just charge and fly initially, come back charge and see the usage. After that only charge to top off.

As a matter of fact since switching to all A123s it seems to me that I have a far better grasp as to how my planes use the batteries than I ever did with a voltmeter. Voltmeter may show voltage, but we have to remember it does not show capacity. Now, I know exactly how many times I can fly and the super bonus is that you can charge them so fast it is amazing. Plug the charger up and in minutes you are charged and ready to get back in the air.

I hardly ever pull out a voltmeter any more. The only time I use one is to check my NIMH ignition batteries and I really would not need to do that as I have developed a consistant pattern in how I use them. I know you can get used to using a voltmeter on A123, I just think it is additional time and cost that is no longer needed.
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