Adding series batteries and flight time?
 

If I have 2 batteries in series and I set the throttle for say 6 amps (less than full throttle) to a particular motor with a particular prop, that yields a certain motor RPM.

Now if I add another battery the same size as the first two and again in series so that now I have 3 batteries in series all the same size and capacity, and again set the throttle for 6 amps that yields the same power so the prop turns the same speed as with two batteries in series.

Now since I am taking current from each set of batteries at the same rate (6 amps) both packs will go dead in the same amount of time and the motor turns the same RPM in both cases.... So where did the extra energy go when I added the third battery? It seems it does not run longer and it does not run faster, something is wrong with this but I am not sure what?

Please help.

flierbk

RE: Adding series batteries and flight time?
 

If you're keeping the same throttle position, with an extra cell, it'll turn the prop faster, and pull more amps. To see the difference you need to use the same throttle position instead of amp draw. Adding batteries in series will not give you more runtime, it generally pulls more amps which will produce the same or maybe less runtime. To get longer runtime, you need to parallel the pack.

RE: Adding series batteries and flight time?
 

You might be confused about series vs. parallel.

Series is "daisy chaining" individual cells together, + to -, + to -. It will increase voltage, the speed the motor runs at a given throttle setting.

Parallel is "ganging" multiple packs together, + to +, - to -. It will increase run time, the motor will run longer.

Packs ganged together in parallel MUST have the same number of cells in each, the same voltage. If they don't, the packs end up fighting each other, and eventually get seriously damaged.

SOMETHING must change. Adding a cell in series will increase the RPM of the motor. Adding a pack in parallel will give you a longer run time.

From your description, it sounds like you did indeed add a cell in series. Did you measure the RPM with a tachometer, or are you just guessing by the sound of the prop?

RE: Adding series batteries and flight time?
 

The purpose of this test is .....................................? Adding a cell adds weight ,so the plane will not fly the same at the same rpm or amps. Any data from a test like this is going to be used for.............................?

RE: Adding series batteries and flight time?
 

Please notice I said that the current was adjusted to be the same in both cases, there is something wrong with this but I am not sure what it is, as you add energy in the form of more batteries in series, it MUSt be available for the motor, how does it show itself in the two examples? Something does not make sense! I need some critical thinking to answer this question.

Now if I add another battery the same size as the first two and again in series so that now I have 3 batteries in series all the same size and capacity, and again set the throttle for 6 amps that yields the same motor power so the prop turns the same speed as with two batteries in series.

RE: Adding series batteries and flight time?
 

When you added the cell and adjusted the throttle to get 6 amps the rpm changes I bet. More cells =more volts=moreRPM I guess this is a physics experiment and not a" powering an acft." question . You do not take into consideration the weight of the additional cell?

RE: Adding series batteries and flight time?
 

I follow What he is getting at. If you have 2 1 gallon cans of water connected together and put a 6mm hole in one it takes 1:00 minute to drain, 0:30 seconds a gallon. If you connect a 3rd gallon should it not take 1:30 to drain from the same 6mm or 6 amp hole.
It confuses me also. Help us both understand, I know the knowledge is out there
JimB

RE: Adding series batteries and flight time?
 

Using your water analogy, adding a cell adds PRESSURE to the system not the amount of water.

RE: Adding series batteries and flight time?
 

That is impossible. Adding a third cell in series will increase the RPM of the motor throughout the entire throttle range. The motor will be spin 3/2, or 1.5 times as fast as it did before, at any current setting. If the motor spun 2000 RPM on 2 cells at 6 Amps, it will spin 3000 RPM on 3 cells at 6 Amps.

Again, are you verifying this with a tachometer, or just by sound?

An accurate water analogy for adding cells in series would be stacking the cans of water one on top of another. Water pressure is determined by the height of the column of water. Electric pressure, or VOLTS, is determined by how many cells are in series.

RE: Adding series batteries and flight time?
 

Man Oh Man,
Do you know what this means. Basically the more knowledge I get the more tools I need to buy just to have them. I always had a cheap volt meter but then I wanted to measure Amps so I got a new meter that will do so. Now I understand the pressure thing and feel the need to measure RPM's so now I neeed to get a Tachometer. You know, A man and his toys. It was so much easier when I just has a basis RTF T Hawk. Plug the batteries into a wall charger and throw the sucker in the air. No knowledge No worries. HAHAHAHA.

This stuff is great
Thanks for sharing the know

Jim B