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Electric Stunt => Gettin all AMP'ed up! => Topic started by: RC Storick on June 25, 2013, 03:23:16 PM
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I am getting ready to build my next generation E plane. I will be using a AXI 2826/12 730 KV with a TP 5S 2700 MAH battery. the question is why on my current eflight 25 4S 3000 do I use 80% and on the 5S set up being less MAH expecting to use the same 80%.
From what I am learning the plane needs to be designed around the battery and not the motor. Is my line of thinking correct?
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I'm not Dean, but I am an electronics engineer whose designed with batteries before.
The reason is because the total energy stored in the battery is roughly* equal to the pack voltage times the capacity. Your 4S 3000mAh pack sports a pack voltage of around 14.8V; your 5S 2700mAh pack sports a pack voltage of around 18.5V. Multiply that out and you end up with about 50 watt-hours** in the 5S pack and about 44 watt-hours in the 4S pack.
So you actually have about 13% more energy available to spin a prop in the 5S pack, in a plane with the exact same flying weight you should actually use a bit less of the total capacity.
* Roughly because the pack voltage goes down over time -- so the actual energy is less than what I'm calculating here. But the numbers should be proportional.
** 2700mAh = 2.7 amp-hour. 1 amp times 1 volt = 1 watt. So 2.7 amp-hour times 18.5V equals 49.95 watt-hour.
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so you are saying my thinking is correct? One more question. I am currently running a 45 AMP ESC will a 50 handle it?
The 45 and 50 weigh the same and I am shooting to loose two ounces off the nose so I am trying to stay away from the 70 amp speed controller. If I can use the AXI and 50 amp speed control along with a TP 2700 battery I can reach this goal. If not it's a useless exercise.
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so you are saying my thinking is correct? One more question. I am currently running a 45 AMP ESC will a 50 handle it?
Going from the 4S 3000 to the 5S 2700? Yes, it ought to work, at least if the airplane isn't too much heavier. In a world where reality always matched theory, if the plane weight was the same you could go down to a 2400mAh, 5S pack -- but you can never count on the real world actually reading the engineering books.
If you're doing OK with a 45 amp ESC with the 4S setup, then you should be fine with the 50 amp ESC as long as its honest. Because your voltage is going up by 20%, the current can go down by 20% and give the same power, so if anything you should be putting less strain on the ESC with the 5S setup (ignoring any issues because of the higher, of course -- I'm sure you're selecting an ESC that's rated for a 5S pack, so that shouldn't be an issue).
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I use those 5S batteries. They will haul around a 65-oz. Impact just fine, although I've run out of poop on calm, cold, days at low altitudes and fast lap times. One other variable is prop efficiency. The APC 13-4.5 prop is very efficient. Other props may not be and use more electricity. As light as you build, I'm sure you won't have trouble with the APC prop and that battery.
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Robert the castle 45 with the 5s TP 2700 did NOT work. Plenty of inverted LANDINGS. Lots of rudder repairs. Switched to ice light 50 never any problems. Get them while you can. Remember you can put ESC at your CG
I better be careful Randy is lurking LOL
Model,shark the ones you love.Power package axi 2826-12 TP2700 25c castle ice 50 Hubin timer himax disconnect switch.
Hope Orestes goes to NATS you can see package in a 63oz shark(home made) just like that west coast model.
Hey Robert would love to see the photo display you were showing of my Shark at Brodack I have lots of friends.
Jose Modesto
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Robert the castle 45 with the 5s TP 2700 did NOT work. Plenty of inverted LANDINGS. Lots of rudder repairs. Switched to ice light 50 never any problems. Get them while you can. Remember you can put ESC at your CG
I better be careful Randy is lurking LOL
Model,shark the ones you love.Power package axi 2826-12 TP2700 25c castle ice 50 Hubin timer himax disconnect switch.
Hope Orestes goes to NATS you can see package in a 63oz shark(home made) just like that west coast model.
Hey Robert would love to see the photo display you were showing of my Shark at Brodack I have lots of friends.
Jose Modesto
LOl Yes I am lurking... and by the way Randy has Ice 50s in stock :-) ... Robert can put them anywhere he wants to, even tip weight is OK lol
well actually not lurking I get paid big bucks by Robert to admin, and moderate here , and free vacations at world famous resorts "-) LOL
Randy
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Randy bring one to NATS for me
Thanks jose
I could not resist with all the fun u guys were having lol
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Its good to have friends. You dont need the display you have the plane. They also have the new 50 with no heat sink. It's only 1 ounce instead of 2. I already have the 50 and the motor just need the batteries.
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Hi Sparky,
Well, Tim did the math, yeah 80% on the 4S will be closer to 75% used on the 5S, and yes, you've got the right idea.
After all, the battery is ONLY between one fourth or one fifth the all up weight. The lighter you build, the larger the fraction.
Right off the bat, we look for a nice excess energy reserve but not too much for the dead weight ...
Then we look for "hero" cells from an energy per weight standpoint and a max power to weight standpoint. Yes, those TP2700's are among them.
Then, to further complicate matters, there's the weight vs line size break (you don't ever want to be just above the 40 or 64 ounce number!)
Of course, heavy ships aren't an issue for some folks.
later,
Dean
Howard,
please expand on "run out of poop". Did you run into the low voltage cutoff?
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The airplane slowed down toward the end of the pattern, sometimes landing under power. I think it happened with more than one battery, but one battery in particular was substandard. TP replaced it under warranty.