OK for all you folks who are interested in the A123 batteries, I have some real world data for you.
This data was collected today, 11/23/2007 flying my 106” 100cc Giles G202. The plane weighs about 27 lbs., has a DA-100, 6 5955s and 1 8711 on the rudder. No matchbox, the ailerons are on a Y cable on 2 channels, 2 servos per channel. The linkages are as close as I could get them mechanically and there seems to be no real binding although there is probably a small amount of mismatch at extreme throws, it’s hard to get it perfect.
In the plane I have a single A123 2300mah pack that goes to two switches through a Y and then into the receiver using two standard JR servo connectors. It’s a JR 921 2.4 GHz. Receiver and I use a JR X9303 transmitter, not that it really matters.
I made two flights of about 10 minutes each, with (apparently) 3-4 minutes of recorded data from the startup period. I did a range check, taxied around a bit, the usual.
When flying I flew a lot of typical IMAC type maneuvers, loops, hammerheads, humpties, lots of rolls and point rolls, and a lot of snaps. I flew several multiple snap sequences of 3 or 4 rolls in an effort to put as much stress on the electrical system as possible.
I used my Eagletree systems elogger V3 and the included software that downloaded it to my PC and analyzed it.
Before doing my flight test I tested the logger itself by running my battery tester through the logger and then recharging. The Eflight power meter said I used about 1430 mah, the elogger said I used almost exactly the same and the Cellpro charger recharged to pack and said it put in 1431 mah. Close enough; all 3 readings agree within a fraction of a percent, I think we can trust the logger’s data.
I collected data samples 10 times per second, or every 100 milliseconds. Any event lasting less than 100 milliseconds could theoretically have been missed. Any voltage spike or current surge lasting greater than 100ms will certainly have been recorded, and a shorter duration event would have had to be positioned exactly between the sample periods to be missed, making hidden events even more unlikely. I think that what we see here is a good representation of exactly what happened.
My only disappointment was the fact that I was unable to save the graphs off as a jpeg file which would have been useful in making this report. The best I could do was to take a photo of the computer screen which is not real clear. In the photos the pink traces indicate current draw, the blue line shows voltage.
So, on to the data. What did I learn?
The freshly charged pack started out at 7.05 volts. It took about 5 minutes of usage/flying to come down to 6.6v, and another 3 or 4 of flying for it to settle in at the 6.5 volts that it stayed at for the rest of the test. Average voltage throughout the test was 6.58 volts, and the lowest voltage recorded was 6.12v. According to the graph voltage dipped below 6.2 volts about 6 times, probably during the extended multiple snaps. The voltage dips coincided with spikes in current usage as one might expect. This A123 pack is not going to allow reboots, you’d need to melt the wires to pull it down to 3.5 volts.
What about current demand? The maximum current drawn in both flights was 11.56 amps. There were about a dozen times when current draw went over 6 amps, and a half dozen times when it exceeded 8 amps. Again, the voltage drops coincide with the current spikes.
The average current demand throughout most of the 2 flights was in the 2 to 3 amps range. It never fell much below 2 amps and rarely exceeded 3 amps. Based on my recollection of the flight, the big current draws were in long snaps and long knife-edges. The rest of the time power usage was fairly modest.
Total power used was 479 mah; this is pretty consistent at around 25mah per minute of flight time. A single 2300 mah A123 pack will support at least 60 minutes of flight time plus all the messing around that goes with it with probably a 25% cushion at the minimum.
So, what do we know? On a plane of this size, especially if it uses multiple rudder servos, you should probably have 15 amps available in bursts, and that burst should not pull the voltage down much if you want your flight performance to be consistent. But you can probably fly IMAC basic with no more than a 1200mah Nimh pack since that type of flying rarely draws more than 3 amps.
I would speculate that a 40% plane with 14 servos could easily require double this amount of power, needing burst current of 30 amps but living between the bursts easily on 5 or 6 amps. I’d use dual 2300 packs on a 40%, if not for the added current then for the redundancy, but I have no problem with using one A123 2300 on a 40% plane since one pack will easily burst over 30 amps.
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Thanks for the foot work Tom. Its nice to see the real data. I always wondered just how many amps we were pulling. I would love to see a similar test with a 7.4v regulated system in the same airplane such as the TurboReg that SmartFly offers. I'm wondering if the voltage would be more stable?
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Thanks, Jason I love it when my airplane is on fire...as long as the fire stays inside the engine!
Thanks for the foot work Tom. Its nice to see the real data. I always wondered just how many amps we were pulling. I would love to see a similar test with a 7.4v regulated system in the same airplane such as the TurboReg that SmartFly offers. I'm wondering if the voltage would be more stable?
A month ago I couldn't spell enginne ear, now I are one.
During 90% of the flight the voltage was between 6.42 and 6.52 volts, as stable as you will ever see, During the other 10% of the flight there were spikes down as low as 6.12 volts, though only for very short durations that coincide with heavy current draw.
I have tested Li-Ions, I can assure you that a single 2400 Liion (remember this was a single A123 2300mah pack) would have dropped far below the 6v line and the current draw would have never reached 11.2 amps, they just don't have that kind of capability. A dual setup might have drawn the 11.2 amps, but with a fairly expensive regulator setup. Lipo's cold maintain the current level, but not Li-Ions.
More importantly, I seriously doubt that any pilot in the world could see a difference in performance if the batteries momentarily drop by 0.4 volts. And if he's a world class pilot he'd be using at least two packs which would probably keep the voltage fluctuaton down to a quarter volt or less.
Still, it would be interesting to see. The problem is I can't install the data recorder in a 2 pack system, all the power must go through a single connector to be accurate and A123 is the only battery which can supply adequate current to do this. It would be possible with Lipoly with a really good regulator or with no regulator, and then you are also testing the regulator.
I'm not curious enough about it to do it though, this A123 setup is lighter and cheaper and performs extremely well, there is a point of diminishing returns where spending more money yields so little gain it's not worth while.
Maybe someone else will do some testing on a more conventional system with regulators.
TF
< Message edited by rctom -- 11/24/2007 4:11:04 PM >
Tom---You do good work !!! So it looks to me you can get 8 flights out of that size pack with no problem. Does that sound about right ?
Yes, that's about right though when you start using them I'd suggest that you work your way up. I would fly maybe 3 flights and then recharge and see how much the batteries will accept, the Cellpro charger will tell you how much it put back.
It IS possible to set up a plane with a servo mismatch that can draw a lot of current all the time. If you do this you may pull more than you think, so start out safe and work your way up to learn how far you can go, but I would not be surprised to get 8 flights.
Also, even if you can get 8 I'd stop at 6 just to be safe. It only takes a few minutes to recharge, about the same amount of time it takes to find your destroyed plane and put it in a trash bag.
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Tom--Yes sir I hear what you're saying. I hardly ever fly more than 6 or seven flights in one day any how. Usually 4 or 5 practice flights doing 2 sequences per flight and my brain is mush anyway, but it's nice to know the batteries will give that many flights B-4 needing a fill up. I understand that on my set up I may use more or less mah per flight than your example. I will surely go with these batteries on my new airplane set up. Just have to decide if I should use them on the ignition or not. Thanks again for all your good work and help to us on this project.
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quote:
ORIGINAL: rctom
Also, even if you can get 8 I'd stop at 6 just to be safe. It only takes a few minutes to recharge, about the same amount of time it takes to find your destroyed plane and put it in a trash bag.
TF
A better practice would be to plug in the charger while you refuel your plane. The cells don't develop a "memory' and won't mind a quick hit on the charger between flights or after every other flight. It will take about as long to refuel the plane as recharge the battery.
When cells recharge as fast as these there is no reason to stretch out the number of flights between charges.
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quote:
ORIGINAL: BTerry
quote:
ORIGINAL: rctom
Also, even if you can get 8 I'd stop at 6 just to be safe. It only takes a few minutes to recharge, about the same amount of time it takes to find your destroyed plane and put it in a trash bag.
TF
A better practice would be to plug in the charger while you refuel your plane. The cells don't develop a "memory' and won't mind a quick hit on the charger between flights or after every other flight. It will take about as long to refuel the plane as recharge the battery.
When cells recharge as fast as these there is no reason to stretch out the number of flights between charges.
Well charging batteries while fueling a glow model may be the thing to do, but being a retired firefighter I find the idea of electical current flowing around in close proximity to an exposed gasoline situation, to be a rather hazardous one...
Now normally you wouldn't have a problem, but there's always that little slip/malfunction which is responsible for disaster. Fumes, puddle from the vent line, drips etc. Then all it takes is a spark from disconnecting your charger, the lead from the charger's battery gets pulled/knocked off, an airframe electical switch which is not explosion proof gets turned on, well you get the idea.
Am I paranoid? Possibly, but as you said it only takes a few minutes to charge so why take the chance to save a few minutes?
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You did this with only 2 standard servo connectors plugged into the RX for power? Did I read that right?
I thought a standard servo connector was supposed to melt when it got over 4 amps. The tests seam to indicate that a standard servo conector can handle over 5.5 amps in a surge. You were not running a continuous load on the connectors at 5+ amps though. Your tests indicate the average/continuous load was somewhere in the 2---3 amp range. I can see 2 servo connectors being able to handle that load. All my reading on this site had me believing there was no way a standard servo conector could handle 5.5+ amps--even on a momentary burst.
Thanks for the research.
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Airplanes have expiration dates. It''s just not printed anywhere on them. I''m not really an airplane pilot; but I did stay at a Holiday Inn Express last night.
You did this with only 2 standard servo connectors plugged into the RX for power? Did I read that right?
I thought a standard servo connector was supposed to melt when it got over 4 amps.
Urban myth. I posted some other tests earlier where I did continuous load tests on both batteries and connectors.
With a standard JR servo connector I was able to pass 6 amps continuous (and I mean for like 3 minutes) with no fluctuations or heating. When I bumped it to 8 amps after about 30 seconds holding the connector between my fingers I could sense a slight warming, but it never got what you would call hot. I doubt I would have noticed the temperature rise if I had not been looking for it. I would not be surprised to see 10 amps pass easily for a few seconds, possibly more. I can test that if anybody cares.
My conclusion was that 2 servo connectors are perfectly adequate for any 35% plane unless something is seriously malfunctioning. They will easily pass 12 amps continuous (a current draw which you will never see), and will pa
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Real world data on power requirements - 
