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Old Nov 27, 2008, 04:32 PM
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When does a 6 volt battery become unsafe to use?

Basically i have been hearing numerous answers to the following question: If i have a 6 volt 2000 mAh nickle metal battery being used in an avistar with a stock futuba reciver, under load what charge amount (6 volt, 6.5 volt, and so on) should I stop flying at.
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Old Nov 27, 2008, 06:41 PM
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Carlyle Harper's Avatar
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5.8 to 5.9v
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Old Nov 28, 2008, 09:45 AM
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Quote:
Originally Posted by airplane7794
Basically i have been hearing numerous answers to the following question: If i have a 6 volt 2000 mAh nickle metal battery being used in an avistar with a stock futuba reciver, under load what charge amount (6 volt, 6.5 volt, and so on) should I stop flying at.
When you say "6 volt battery" I am assuming you mean 5 cell battery. If so, you can safely fly down to 5.5 volts with no worry. At that point you will still have about 5 to 10% of the stored energy available before the voltage takes a nose dive.
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Old Nov 28, 2008, 12:38 PM
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Please note that you must read the voltage under a 200 to 250 mA load. An unloaded voltage is meaningless.

Bill
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Old Nov 28, 2008, 01:39 PM
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Denmark
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I would say somewhere around 7.0 Volts.
I just made a curve of a 6-pack of mine at C and as You see it goes south at 7 and fast.

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Old Nov 30, 2008, 01:36 PM
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The previous post demonstrated what a 6-cell nimh pack does. I believe the original poster said he has a 6-volt nimh pack, which most commonly refers to a 5-cell nimh pack. Nonetheless, the readings from the 6-cell pack confirm my 5.8-5.9v lower limit on a 6-volt pack. How you ask?
See if you can follow the logic.

A nimh cell has very little power left once it gets below 1.2v/cell. The nimh cells I have will bleed off to 1.2v/cell and sit there under load until they are just about drained then the voltage will start to fall off a cliff. The above graph demonstrates just this when you break it down to the cellular level (chemistry anyone?)

So a good working voltage for a 5-cell pack is 6 volts. When you get to below this with only a 250 milliamp load (not very much), the voltage falls off very rapidly, possibly resulting in a receiver failsafe especially if you have high current servos. A sudden spike in servo current would then depress the voltage even further because the cells can't handle it at the end of the charge, and then you get a failsafe or glitch followed by the mysterious crash, the cause of which eludes many people, because the battery seems to check out ok after the crash (since it had time to somewhat recover to pass the 250 milliamp load test again) and therefore they eliminate this as the cause of the crash.
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