Shaggy

Hello everyone, I have a dualsky 650w motor in my plane with a 3S 4350msh lipo batter and a 12x8 prop not I but it up to full power and it is pulling 300w at about 27amp not this does not seem enough, the motor is rated at 25amps, what can I do? as I do not want it to be under powered or burn it out.

Buck Rogers

What is the KV of the motor you have?

Shaggy

Hello Sorry about that the guy in the shop said KV is not that important, but it is 720kv

birdDog

I found this: http://www.vampowerpro.com/datasheets/xmotorspecs.pdf

I am asuming you have the XM3548CA-6

This gives you a burst current of 37 amps. Hopefully the motor should be OK at 27amp.

Might be kinda low KV for 3s. Most are spec'd out on 5s. Maybe a faster pitch prop?

Shaggy

Yeah that is the one, I am new to this and learning but I have worked out a 5S spec and that would be perfect it would give 462.52w at 25amps and 684.5w at 37amps, depending on prop of course.

So I think I will do that it is the only way to get the power I need.

The setup suggested would be 355.2w at 32amps and 488.4w at 44amps so it should be a nice power setup. with 3S

They do have a power setup which is 621.6w at 42amps and 888w at 60A but it is normally proped down so it will not be as mush as that, so I am somewhere in between. 4S

Do you think I am wright in going for 5S

birdDog

I am no master at this stuff but I have read quite a bit here at WF. Here is where your funding comes in. You could try to get a higher KV motor to still run on the 3s and give you the desired watts also. Personally I would talk with the salesman who states "KV is not that important". They dont print the amp load on the motor label, they print the KV on it for some reason. Maybe you could swap it out for a different motor?

Or you can try to increase prop speed and diameter until you might get too your desired wattage, Bigger diameter equals more torque and faster pitch equals more speed.

Shaggy

Yeah i did ignore his comment. Well I think by my workings on the other motors with high KV they will all be a little to slow but this motor being a 5S will give me about what I am after.

One thing though as it suggest an e flite motor and I went for a dualsky the e flite can use more amps than the dualsky on the same KV I should look in to specs more closely next time, I think I have learnt my lesson there.

birdDog

Hey Shaggy, You ought to see my pile of in-appropriate parts! You got a great motor! You will see that there is a tremendous amount of variables in the hobby.

Buck Rogers

I would disagree with the guy in the shop. KV is important as it determines the number of cells you need and also how big a prop you can use (slow KV usually means you can use a larger prop).

Anyway, as already pointed out, I would have thought a 720 kv motor would be more suited to a 4s (or even 5s) battery. With a 3s battery I'd normally be looking at around 900 - 1000 kv for a 12" prop.

You can always up the pitch or diameter (or both) to get more power out or see if you can swap the motor out for a higher KV version. Maybe this one would be better:

http://alshobbies.com/shop/lookupsto...?pc=5660&Desc=

Shaggy

Yes i did look at that one. Am i right in thinking that if i change the prop this will change my amps up or down depending on what i do but the best way to up the watts is up the voltage?

birdDog

You can almost put the watts wherever you want (within motor limits)with different sized props. More cells = higher rpm. Roughly 2880 rpm per cell.
More pitch = more speed and more watts
More diameter = more torque and much more watts. Then you have the issue of ground clearance or the motor getting too hot.

I am in the same predicament. I bought a 600kv motor but my chargers will only handle 4s. I am in the process of trying out some faster and bigger props to see where I can get to, hopefully without buying a diffrent motor or new batteries and a charger.

Ps. I REALLY like those style planes. I think my next will be some type of texan, trojan or mentor.

Buck Rogers

Actually, its not watts but amps that are the issue. The motor you have is rated at 650 watts using a 5s pack - thats about 35 amps. If you are using a 3s pack you still cant exceed 35 amps which means you'll have a max power output of just over 400 watts before the motor starts to get hot.

Its always better to measure the amps being drawn and compare that to the rated amps for the motor.