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4s battery on apprentice 15e (vs 3s)

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Old 05-21-2013, 09:42 AM
  #1
Droiddr
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Default 4s battery on apprentice 15e (vs 3s)

Hi,

According to what I see the ESC on the apprentice can take 3 or 4 s packs.
Nowhere can I see if the motor can take it. I don't see max current or max voltage specs anywhere.

Do you think the motor can take the 4s pack?

The best to all!
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Old 05-21-2013, 09:57 AM
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Default RE: 4s battery on apprentice 15e (vs 3s)

Find out what the spec for the motor AND the esc on that plane are. It's rather important.

Why do you want to put a 4S battery pack? Just remember that there are more considerations than the voltage rating of the pair to deal with. If this is a serious increase in voltage from the original setup, you really have to be concerned with torque limitations.

I had a small three channel plane that came with a two cell pack but offered a three cell as an option. I had both and flew it with the two cell pack and it flew ok, but was not exciting enough. So, I put the three cell on without thinking about it and hand-launched the plane at about half throttle. When airborne, I pushed the throttle to full and heard this strange noise and watched the plane flutter to the ground. When I walked up to it, I noticed that the wires leading from the ESC to the motor were tightly twisted around the shaft that held the motor mount in place and tore the ESC out of it's mounting position and right up against the base of the motor - it was mounted using velcro. Nasty. The motor was a throw away, by the way.

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Old 05-21-2013, 10:02 AM
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Default RE: 4s battery on apprentice 15e (vs 3s)

Hi

As stated above,

The ESC says 3 or 4 cell pack, 30A.
I can't find the specs for the motor anywhere. (manual, website etc).

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Old 05-21-2013, 10:10 AM
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Default RE: 4s battery on apprentice 15e (vs 3s)

Difficult to say IF it can handle 15 volts but if it can and you run the 11x8 prop you will probably be over the limit of the 30amp ESC.
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Old 05-21-2013, 11:09 AM
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Default RE: 4s battery on apprentice 15e (vs 3s)

Call Horizon and ask them ~~ 1 888 959 2395 . ENJOY !!! RED
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Old 05-21-2013, 01:00 PM
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Default RE: 4s battery on apprentice 15e (vs 3s)

The Eflite BL-15 950KV is rated at 34A continuous and 42A burst

The Motor used in the Apprentice has a lower KV rating so it is LIKELY to be at least 35A continuous capable if not 38A.

Assuming the LOWER rating for safety...

The ESC is rated for 35A continuous. Given that vendors LOVE to make their figure look as good as possible this is likely to be 30Amps AT 11.1v.

So that means the ESC can deal with 35 x 11.1 = 388 watts

If you increase the voltage you must keep the equivalent current draw about the same... sooooo...

388 watts / 14.8 = 26.25 A

You will therefore have to DECREASE the prop size to stay within this wattage range...

Pushing the numbers through ThrustHP...

14.8 x 840kv = 12432 RPM

388watts / 745 = .52 HP

You would need to drop down to a 9x6e prop to draw .54HP which should be within the safety range.

That will produce a static thrust of 2.95lbs but a prop airspeed of 70mph.

The 11x8 prop with the 11.1v pack produces about .67 HP which means that the original electronics were set up to run closer to the "edge", assuming you would use throttle management to keep things cool. The original setup provides 3.82lbs of static thrust and produces a prop speed of 70mph.

If you switched the 14.8v setup to a 10x5 prop you would get 4.49lbs of static thrust but only 58 mph prop speed...

So increasing the pack voltage CORRECTLY will onl net you more THRUST but less SPEED.

IMHO it's not worth doing, particularly on a trainer plane...

A 3D plane would be another matter....

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Old 05-21-2013, 01:29 PM
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Default RE: 4s battery on apprentice 15e (vs 3s)

Makes perfect sense,
very enlightening!!! thanks.

I will do some empirical testing. I don't have a proper stress gauge, so I will use a fish scale for now

I will try my existing setup, buy a current/ voltage meter (or watt meter). I can put on the battery and measure static thrust with the standard setup.

I will then try the 4s battery and will slowly increase the throttle until it reaches a too-high point or is acceptable (doubt it). I will measure current and stress to make sure I don't burn anything in the process.

Then try other props and measure the same things.
It will be an interesting experience.

Thanks for the lesson!





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Old 05-21-2013, 05:21 PM
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Default RE: 4s battery on apprentice 15e (vs 3s)

Since the ESC can go a bit higher than what your current system already has ( pun not intended ).... your limiting factor is your motor.

Even if you increase the motor's capacity, you in turn have to increase the capabilities of the ESC.

You can achieve the same results by just using a large prop or a prop with a deeper pitch.... and keep the same voltage.

Anyway it is all a balancing act with electrical systems.

With a glow or gas engine, all you'll do is bog the engine down if you put too large of a prop on it.

With electric propulsion it is the other way around, the prop will draw more current and blow the electronics.

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