We need more imput from the experts, Please.  Why are batteries so expensive?
Are these R/C batteries, thus expensive because of the label "Hobby"? I wonder if there is an alternative. Like buying them separate or buying electric drill batteries and making your own batt. packs? Those drill batteries are less tthan  $100 and go up to 18 volts or more.

Fernando,

Battery prices may appear to be quite expensive but when compared to a regular IC engine set up, they are about the same. (or cheaper) When I fly one of my .60 size stunters with IC power, I burn about one dollars worth of fuel per flight.

Last year each of my Thunderpower 5S2P 4200 Pro Lite batteries cost me about $300.00. They are now down to $230.00 each. I expect to get around 250 to 300 cycles from each of my batteries. That's already cheaper than using glo fuel.

There is no denying that the cost of the support equipment (chargers, balancers, monitoring and test equipment) is not small and is not really an optional expense when dealing with large batteries.

As to the technology, we need batteries that have very high energy density and very high "C" ratings (the ability to dump the charge out fast) while also being lite in weight, small in size and safe. While some have in fact used electric drill motors and batteries in the R/C world,  I do not think that would be successful approach with control line.

Construction of my plane SHOCKWAVE began just over a year ago. Just eight months earlier the decision to build it would have been a definite no. It  was the announcement of the Thunderpower ProLite series of batteries that made it possible. Technology is changing rapidly and prices are comming down. I do not think you will see a $50.00 battery that will power a large stunter for three hundred flights in the near future but I also do not think that present prices are out of line with the alternatives available.

Kim.

Fernando,

Yes, when I say battery, I am talking about the whole pack. If you are using Lipo's it would be proper to also talk about how the "pack" was constructed. In my case my battery pack is described as "5S2P 4200 mah". (Milli amp hour) This means that I have 5 cells (each cell is 3.7 volts and has a capacity of 2100 mah) in series as a unit and two of those units in parallel. (total ten cells) giving me 5X3.7 volts = 18.5volts and 2X2100mah = 4200mah capacity.

Putting batteries in series causes the voltages to be additive but not the mah capacity. Putting cells in parallel causes the mah capacity to be additive but not the voltage. Then you need to look at the "C" rating for the battery. for a 4200 mah battery, a "1C" rating would mean that the battery pack can deliver its full load of power in the space of one hour. The Thunderpower ProLite 4200's are rated at 15C Continuous draw,  24C Burst. So this battery pack can deliver its full charge to the motor in as little as 1/15 of an hour or 4 minutes.

As to there being "4" batteries in a pack, realize that you can build a pack any way you want. You can have the simplest battery : "1cell", (say 2100 mah) so just one cell producing 3.7 volts at whatever mah capacity rating you want or you could have a "4S" pack consisting of just 4 cells in series (14.8 volts) at whatever capacity you want (say 2100 mah). If you needed more capacity but not more voltage you could have a "4S2P 4200 mah" battery which is still just 14.8 volts but is built of 4 cells in series and two of those in parallel. (total of 8 cells)

If you want to turn a motor at higher rpm then you will need more voltage. If you want to turn the prop at this same rpm for a longer period of time then you will need more mah capacity. Electric motors are VERY good at generating torque. Larger propellers with higher pitches are much more efficient than low pitch props. You should consider this when you are trying to decide on what combination will do the job.

One thing to bear in mind if you are designing a new electric stunter is that  the shape and weight of the fuel tank (battery) are dictated to you and the wires coming off of the battery may not come out of the corner or end that you want.

Kim.