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Rx battery power

Old 03-04-2003, 09:27 PM
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kirknik
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Default Rx battery power

Now that i invested in a voltage meter, at what level should I no longer fly? I'm talking about my reciever battery. The transmitter warns me at 8.5v but I wonder when the receiver battery is no longer safe.
Old 03-04-2003, 09:37 PM
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greenboot
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Default Rx battery power

My lawyer advises me not to say anything but here goes anyway. I don't take off with less than 4.8. That is very conservative, but it only takes a couple minutes to field charge between flights.

You need to get to know your battery pack. Discharge it some time with a 20 ohm resister and record voltage over time. You will develop a feel for how the voltage drops rapidly, then levels off around 4.8 (the nominal voltage) for a long time. Finally it drops more quickly.

The other thing to be aware of is "surface" voltage. An almost dead battery will appear to have full voltage after a small amount of charging.

Tom
Old 03-05-2003, 08:59 PM
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Jemo
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Default Rx battery power

The transmitter warns me at 8.5v


I would never let my TX go that low.
Old 03-05-2003, 10:10 PM
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MinnFlyer
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Default Rx battery power

While some people swear by them, I would never rely on a voltmeter. Battery packs (Rx) are rated at 4.8 volts, but will charge to over 5 volts. At 4.8 you don't know if you're near the end of their cycle or the beginning.

My rule of thumb (it may not be scientific, but it works for me) is to fully charge the pack for 16 hours, then I will get 3 flights (4 if I'm feeling lucky).

The rest of the day, I'm either chewing the fat with the guys, or flying someone else's plane. So if I get 3 flights on my OWN plane, That was a good day!
Old 03-05-2003, 11:35 PM
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mglavin
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Default Rx battery power

You can safely run NiCad and NiMH batteries down to 1.1V per cell. a 4.8V battery is comprised of four 1.2V cells, so 4)1.1 = 4.4 volts. A five cell 6.0V battery can be discharged to 5)1.1 = 5.5V.
Your TX can be discharged to 8)1.1 = 8.8V.

Static voltage is not an accurate method to decide on when enough flying has elapsed. A LOADED volt meter or ESV is an acceptable method to utilize to determine if you should fly or not fly. However this is NOT the best method available to determine when to fly or not. The best method is to cycle your battery pack(s), note the mAh capacity, log the elapsed time flown, discharge the battery pack and again note the mAH capacity that was available after the recorded flight time, calculate the consumed power and divide by time flown and you have a KNOWN average power consumption, you can use this info together with the LOADED voltage test data to decide weather it's safe to fly or not.

1400 4-cell battery, cycled and capacity rated at 1420mAh.
Logged 36 minutes flight time, discharge the battery. 880mAh recorded available capacity. 540mAH was consumed flying. 540 divided by 36 = 15mAh per minute consumed.

1420-880=540, 540/36=15mAh average per minute.

Theoretically you can use the entire capacity of the battery pack, we as modeler's seldom due, in fact most charge far more frequently than is required, but do so for that warm fuzzy feeling.

A very safe NO fly number would be around 50% of the rated capacity. At 15mAH a minute you could fly for 47 minutes...

The secret is to log the accumulated flight time, become familiar with your models displayed and LOADED voltage readings, use this info to recognize a prematurely low voltage reading. Low voltage readings recorded/noted sooner than normal are indicative of abnormally high current draw, a bad cell or a battery thats degrading/loosing it's capacity.
Old 03-06-2003, 04:56 PM
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greenboot
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Default Rx battery power

One thing I've noticed about using a loaded voltmeter is that the reading is not effected very much by the load. At least for a fully charged battery. On my meter, I can switch the load on and off.

What this says is that the load doesn't really cause any drop in voltage. So why is it so important to have a LOADED voltmeter, I'm not sure. If I'm uncertain about a battery pack, I leave the load on for a minute or so to get rid of the "surface" voltage, then watch to see that the voltage remains stable.

Tom
Old 03-06-2003, 06:21 PM
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MHawker
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Default Rx battery power

The load is very important, and although I don't know this for sure (Red?) I would imagine it gets even more important the more drained your battery gets.

I built a "load" from Red's website and on a freshly charge 4.8V pack, I get about .2 or.3 volts less with a load than without. So, if I checked it with a normal meter that showed 4.8v, I would fly. But, subtract even a .2v drop with a load and that would cause me to charge that pack first.

Mike
Old 03-07-2003, 07:58 PM
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Whirley Bird
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Default Rx battery power

[i]
The rest of the day, I'm either chewing the fat with the guys, or flying someone else's plane. So if I get 3 flights on my OWN plane, That was a good day! [/B]
Well,
If you went with a bigger amp rating you can get in more flight time.
4.8 [email protected] 600 mils vs [email protected],600 mils= more time flying.
Old 03-07-2003, 10:41 PM
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Ladyflyer
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Default Good point .

Larger batteries and /or field charging are safe bets.
Voltage readings even under load can be trouble.
In a series string it is possible to have 1 cell discharge to

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