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battery duration

Old 10-10-2007, 11:32 PM
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spitfire66
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Default battery duration

Hello Again! I have a question concerning battery duration. I have a 4.8 vot 1500 mah batter (new). How much flight time can I expect after the battery is fully charged? I was always told never to attempt a flight when the voltage drops to 4.8 on a loaded voltmeter. Another question I have is how long after a day of flying (maybe 30 minutes of flight time) should I leave my batteries charging? I have the standard jr charger with 50 mah of draw.
Old 10-10-2007, 11:42 PM
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KitBuilder
 
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Default RE: battery duration

Pick a nice charger that cycles, etc.. I had a 1200mah nimh pack that was about 9 mos old. .recently it started showing 600 mah after full charge [>:] .. You'll never know whats going with your batteries with the standard wall wart type chargers. Please don't take this as gospel by any means but I think maybe the general rule is a typical 4 channel with standard flying.. nothing crazy pulls approx. 350mah per hour?? I would not extrapolate that to mean you could fly 3 hours. I think batteries lose approx 5% per day of the charge... and condition, storage, etc can affect that as well.

What type of batteries are you talking.. nicd or nimh. I beleive the nimh are less susceptible to memory issues but I cycle mine anyway.
Mike
Old 10-11-2007, 06:09 AM
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Flying freak
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Default RE: battery duration

If i were you i would just play it safe and get a somthign like this to check your battereies http://www2.towerhobbies.com/cgi-bin...&I=LXWW16&P=ML I check mine before EVREY flight also you will need some charge leads http://www2.towerhobbies.com/cgi-bin...&I=LXL335&P=ML to go between the tester and the wire.

Steven
Old 10-11-2007, 09:53 AM
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Default RE: battery duration

1500MAH battery is 2 1/2 times the capacity of a battery that comes with a flight pack. If your running 4 or 5 servos your good for 5 perhaps 6 flights....remember if you like to gun the engine on taxi, or flying in heavy winds, doing 3D, or the airplane isn't in trim and you have constant stick inputs your battery won't last as long.
If you're that worried about it get an expanded scale voltmeter that puts a load on your batteries and check the batteries after each flight at first...it won't take long to figure out how long you're good for
Old 10-11-2007, 11:50 AM
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roknHS
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Default RE: battery duration

I have a similiar question concerning Nimh batteries. I just purchased a JR 2700 mah 4.8volt Rx battery for a bigger plane.........four sub-C cells in a flat configuration.
I'm trying to form charge it for maximum performance..........I have read not to use a peak detecting charger for form charging so I'm using a wall wart that says it will put out 150mah for a Rx battery.........my last charge was 27hours and when I discharged it on my Accu-Cycle I got 1900mah out of it.........my next charge I'll let it cook for probably 36 hours and hope to approach that 2700mah mark.......How many mah's should I expect from this fully charged battery? Will I get a full 2700mah's?

Also, when I left this battery on the charger for 18 hours, (18 X 150mah = 2700mah's),
then let the Accu-Cycle discharge it at 250mah I only got 1700mah out of it........why didn't I get closer to the 2700mah capacity?

I believe my Accu-Cycle discharges to 1.1 volt per cell or a total 4.4 volts for the pack.
Old 10-11-2007, 02:40 PM
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Default RE: battery duration

Spitfire,
4.8 volts is the rated voltage of the battery.
You can let your voltage drop to around 1 volt.
A lot of people have their own preferences ranging from about
.9 to 1.1 volts per cell.

If you figure each flight is 15 minutes and you are good for 3 hours
that would be 12 flights for the day. That sounds like a lot.
My flights are usually less than 10 minutes so that would be 18 flights.
Our wind comes up long before I could get close to those numbers.
Essentially, I think you're doing a lot of worrying for nothing.

Good Luck,
KW_Counter
Old 10-11-2007, 03:39 PM
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Default RE: battery duration

Roknhs, you may not be charging with enough current. Check out these articles, they should clear this up for you.

http://www.masportaviator.com/ah.asp?CatID=2&ID=146
http://www.masportaviator.com/ah.asp?CatID=2&ID=149

Spitfire, flight time will depend on how many mA your plane draws. I have read that for a standard 4 servo trainer/sport plane you should figure about 110-125mA per 15 minute flight. You can figure the safe number of flights from there. Regarding when it's safe to keep flying, most people won't fly if their 4.8V rx battery shows 4.65V or less with a 250mA load placed on it.
Old 10-11-2007, 06:00 PM
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spitfire66
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Default RE: battery duration

I'd like to thank you for your input. You guys are always helpful. My aircraft is a super decathon with 5 servos and it sounds like I am doing a lot of worrying for nothing. I had a guy overemphasize that you can't fly your aircraft very long when I was starting out and always left me wondering how long the flight pack would actually last. I think I will be done flying before the airplane is. Thanks again.
--spitfire
Old 10-11-2007, 08:41 PM
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Default RE: battery duration

The standard receiver pack is 600 millamp HOURs. That means it should nominally deliver current at a 600 milliamp rate for 1 hour. A normal rate of discharge for 4 servos and reciever is probably on the order of 250-300 milliamps, assuming you're not banging the sticks around constantly. At that rate, you should have roughly 2 hours total flight time (300 milliamps x 2 hours=600 milliamp-hours)

If you fly for 10 minutes each flight (a typical flight time), you should be able to get 10-12 flights on a fully charged battery.

Now scale up to your 1500 mah battery. The math is left as an exercise for the student.

As for a cutoff voltage, your best bet is to use your radio on the ground and discharge the battery with the plane. Measure the voltage frequently and determine the voltage at which your servos become sluggish. Thats the voltage to avoid. If you've been measuring frequently, you should now have an idea of what the voltage was 10-15 minutes before you hit the minimum voltage. Add .1 volts and make that your no fly voltage.

As for charging, the typical wal-wart charger is not a constant current charger, but is normally a constant voltage current limited charger. That means that it delivers a maximum of 50 milliamps. As the battery approaches fully charged, the current is going to drop off. So your 1500 mah battery would require a MINIMUM of 30 hours (1500 mah/50 ma)to charge, and more likely will require over 40 hours to fully charge.

Many fast chargers allow you pick a charge rate, and most battery manufacturers recommend a C/10 rate, so if you can select a 150 ma charging rate, it should take about 10 hours to charge. You can probably go as high as a C/5 rate (300 ma) without worry.

Brad
Old 10-14-2007, 05:08 PM
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feihu
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Default RE: battery duration


ORIGINAL: spitfire66

Hello Again! I have a question concerning battery duration. I have a 4.8 vot 1500 mah batter (new). How much flight time can I expect after the battery is fully charged? I was always told never to attempt a flight when the voltage drops to 4.8 on a loaded voltmeter. Another question I have is how long after a day of flying (maybe 30 minutes of flight time) should I leave my batteries charging? I have the standard jr charger with 50 mah of draw.
During normal flying, the amp draw is about 300ma. So for a fully charged 1500mah battery, you can expect to fly 1500mah/300ma = 5 hours.

When the voltage drops to 4.8 on a loaded voltmeter, for practical purposes, the pack is depleted and you should not fly.

After 30 min of flying at 300mah, you will have used up 150mah; just to replenish that, you need at least 150/50= 3hrs+ charge at 50ma; you might leave it on charge until you fly the next day or so.

To fully charge your 1500 pack at 50ma would take 1500/50 = 30 hrs + , but at 50ma, which is really a trickle charge, you may never get a full charge depending on the self-discharge characteristics of your battery.

Suggest you charge at 150ma (.1C) for 14 hrs for a good full charge.
Always charge at this rate the night before flying.

NOW HERE IS AN IDEA THAT MIGHT YOU MIGHT CONSIDER -

Charge your rec'vr pack from the JR tx output but make sure the polarity connection is right. The output from the tx into the rx might be anywhere from 100 to 130 or so. I just measured the output from my ACE tx-rx charger and I got 130ma charge into 4AA2500mah cells.
Thought you might be interested.

feihu
Old 10-14-2007, 10:17 PM
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BillS
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Default RE: battery duration

Occasionally after flying I like to cycle the batteries down and compare the ma left to the battery ma. The comparison will tell how much longer you could have flown.

Bill
Old 10-15-2007, 06:59 AM
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Flypaper 2
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Default RE: battery duration

Get an ESV, Expanded Scale Voltmeter. It's your gas gauge. When the batt. gets down to 5.2 volts, give it a recharge. I get four flight out of a charge in a 1/4 scale plane with a Spektrum 4.8 V batt. Check the batt. before each flight. Fast field charger charges it in about an hr.,

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