The evolution of battery technology never stops to amaze me. We always seem to benefit greatly in the electric flight world from lighter weights, longer duration, and increased current delivery capability.

Shown here are three different battery technologies in a common shape made popular by Zagi wings and similar models.

From top to bottom, we have:
[ul][*] Thunderpower [link=http://www.hobby-lobby.com/thunderpower.htm]TP420032[/link] 3s2p, 4200mAh, 11.1v Lithium pack (8.9oz)[*] Sanyo ([link=http://www.flydma.com/batteries/batteries.asp?path1=batteries]DMA[/link]) 8-cell, 1700mAh, 4/5AUP, NiMH pack (10.2oz)[*] Sanyo 8-cell, 800mAh AR, NiCd pack (9.6oz)
[/ul]

All packs can deliver 20-30amps (or more), and, weigh similar amounts , but the energy density winner is clearly the ThunderPower Lithium technology. Additionally, the TP Lithium pack has the equivalent voltage of a 10-cell NiCd pack which allows for better peak burst performance!

If we based our flight time on a 20amp draw, we can see the duration improvement from the various packs below:

[ul][*] 800AR NiCd pack = 2.4 minutes[*] 1700 NiMH pack = 5.1 minutes[*] 4200 TP Lithium pack = 12.6 minutes
[/ul]

doesnt the lithiums cost twice the price of the 1700's though?

all well though, thanks for the post, i am planning to get a zagi sometime soon.

I've considered putting Li-po's on my E-Zipper MkII with a 16/15/3. Are batteries in parellel a necessity or is a simple 3s sufficient? Is it the difference between amps & volts? I have to admit, I don't understand the difference.

Thanks,
Brad

Volts is the speed at which the electrons are flowing throught the wire. Amps is the amount of electrons flowing. If you are contiplating using lipoly batteries, you have to match the current draw of your motor/prop combo to the ability of the battery to deliever that current. What prop will you be using? To find the current draw, you can use a computer predicition, manufactor's data (http://www.megamotorusa.com) or use an amp meter or wattmeter.

Hope this helps.

John

Lithiums are still more expensive on a "per-mAh" basis, but that price is slowly coming down. When we start seeing LiPoly-powered cordless power tools, you'll really see prices start to drop. Many people find the increased duration, reduced weight, and resulting increase in performance well worth the additional cost, though.

Case in point, my Wattage Crazy 8. If not for LiPolys, I probably would've given up on it. With CP1300 NiCds, the thing was a tail-heavy lead sled. Going to 3S2P Etec 1200 packs and a slightly smaller prop saved the plane.

Here is a practical example. I'm finishing an Alfa Models P47. I put an AXI 2212/34 outrunner brushless motor in it. What lipoly battery will work? Checking the manufactor"s data:

AXI 2212/34


Small and very robust but light weight (57g with 14cm long power wires) brushless motor with rotating case suitable for all models of 300-400 size wich surprised you with very high power can deliver. Hardened steel Shaft have 3,17mm and is supported by two large ball bearings wich ensure very good mechanical stability. Thanks to using newest materials this motors achive in their weight category extremely high efficiency and high load possibility. A new future in AXI design is a provision for radial mounting.


Specification
Voltage range 6-10 cells
2-3xLi-Poly
RPM per Volt 740 RPM/V
Max. Efficiency 77%
Max. Efficiency Current 4-8 A (>70%)
Max. loading 10 A / 60 s
No load Current / 12V 0,4 A
Internal resistance 345 mohm
Dimensions 27,7x30 mm
Shaft Diameter 3,17 mm
Weight 57 g
Recomended model weight 300 - 700 g
Propeller range 2xLi-Poly prop 12"x8"
3xLi-Poly prop 10"x5"
10 cells prop 10,5"x7"



Recomended speed controller:
ModelMotors 0810-3
ModelMotors 1210-3


Accessories for AXI22xx/xx.

Radial mount set for AXI22xx/xx.








Examples of use - AXI 2212/34 Motor Prop. w/o gearbox Battery I/A RPM U (V) P- OUT (W) P- IN (W) Efficiency (%)
2212/34 9x6 APC Slow 3xPi-Pol 7,2 5770 10,2 58 73 79
2212/34 10x4,75 APC Slow 3xPi-Pol 6,9 5850 10,2 56 70 80
2212/34 10x7 APC Slow 3xPi-Pol 9,4 5170 9,9 69 93 74
2212/34 11x4,75 APC Slow 3xPi-Pol 9,4 5160 9,9 69 93 74
2212/34 11x8 Gr. CAM gear prop 3xPi-Pol 9,3 5200 9,9 69 92 75
2212/34 10x7 Aer Glas elektro 10x N500AR 7,7 6030 10,8 64 83 78
2212/34 10,5x7 Aer Glas elektro 8x N500AR 6,2 4990 8,8 43 54 78
2212/34 10,5x7 Aer Glas elektro 10x N500AR 8,3 5810 10,6 68 88 76
2212/34 10,5x8 Aer Glas elektro 8x N500AR 6,7 4840 8,8 45 59 77
2212/34 10,5x8 Aer Glas elektro 10x N500AR 8,9 5610 10,5 70 93 75
2212/34 11x8 Gr. CAM gear prop 8x N500AR 7,5 4620 8,6 49 64 76
2212/34 11x8 Gr. CAM gear prop 10x N500AR 9,9 5350 10,3 75 101 74


I'll be using a 3s lipoly pack and an APC 9x6 prop. The data says 7.2 amps (Sorry, I know its hard to read the table, but the current draw is listed after the prop size).

I have 3s Kokam 1500 packs that can handel a 8c draw or 12 amps (8x1.5=12).

I can use this pack.

2nd case. I have a Multipex twinjet with 2 mega 16/15/4 motors in parallel with APC 6x4 props. I measured the current draw at 40 amps. With the same packs, I used 3 in series (a 3s3p). They can handle 36 amps (3x12=36 amps) continuously, so I used this battery, but I knew that I could only use full throttle in short bursts. Well, I liked doing full speed passes so I changed props to 5x5 to drop the current to 34 amps and I can now fly all the high speed passes that I and my club mates can stand.

Sorry about the long post, but I hope that I answered your questions.

John

Thanks for both of your posts, John. In my attempt to understand the volt vs. amp difference, I had their functions reversed. I am glad to learn from someone who has a working knowledge, because I sure didn't.

I like word pictures, so how's this for a representation.... Volts are 'how much water pressure' amps are 'what diameter is the garden hose'.

Thanks again,
Brad

Brad,

That is a good analogy for the supply end. For the demand end, think of your motor, gearbox, and prop as all affecting how far the flow valve can be opened.

Greg,
Excellent..... yes excellent analogy for the demand end. I think I got it now!

Thanks a bunch,
Brad

That's a good analogy, but not 100% accurate.

Here's a better one.

Think of the electrons as a bunch of tiny workmen moving around a track (the circuit). The strength of the workmen is determined by their voltage. The current is the number of workmen that can work per second. The amount of work they need to do is the resistance.

So if the voltage is high (stong guys) you dont need as many of them (current) to get the same work doen. Alternitively if if they are weak you require more of them to do as much work.

If you reduce the workload (ie resistance) but keep up the strength (voltage) each guy finishes his work quicker and more of them can move around the track (higher current).

Help
I have a zagi xs and a wattage cap 232ep what size poly lith battery should
I use and should I put the batteries in series
I think they both have a 30 amp speed control
thanx
Tom

Hi Tom,

For the Speed 400 Zagi XS, a pack like the 3-cell [link=http://www.hobby-lobby.com/kokam.htm]FM15003[/link] Kokam 1500mAh may be a good fit. The dimensions are on the Hobby Lobby site so you can compare them to the 1800mAh folded pack from Trick RC.

For the Wattage CAP 232, use two of the Kokam packs mentioned above in parallel or the [link=http://www.hobby-lobby.com/thunderpower.htm]TP420032[/link] ThunderPower 3s2p 4200mAh pack.

Since the voltage will be higher than the normal stock packs, try to limit your use of full throttle to short bursts of 10-15 seconds during the first half of the flight.