Kv and amperage question

[Prodrvr]

If voltage and prop stay the same, you change motors from a 2860 3300Kv to a 2848 4370Kv, how much would the amp load increase? Is there a formula for this, or simply trial and error?

[Fluid]

Too many unknown variables, only experimentation will provide an answer.


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[sivadmatt]

Kv is rpm per volt. Amps and volt is watts. I'm sure they're equation for it but it's going to be extremely lengthy and complicated and explained in watts.

[Prodrvr]

Thanks guys. Maybe I'll just pick up the motors and see how it goes.

[sivadmatt]

It is all on the prop

[Fluid]

You will make an expensive mistake if you choose the wrong Kv for the voltage you intend to use. Most beginners choose motors with too high of a Kv for their application. The Kvs listed in the OP are excessive for 4S for example. Both will quickly fry any speed controller in most applications. On 3S and 2S respectively they would be much more appropriate and reliable.

It's not "all on the prop", the hull design and setup are also critical. We could be of more help if we knew the exact boats and voltages.

Feel free to ignore the above. It's your money.


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[Prodrvr]

You will make an expensive mistake if you choose the wrong Kv for the voltage you intend to use. Most beginners choose motors with too high of a Kv for their application. The Kvs listed in the OP are excessive for 4S for example. Both will quickly fry any speed controller in most applications. On 3S and 2S respectively they would be much more appropriate and reliable.

It's not "all on the prop", the hull design and setup are also critical. We could be of more help if we knew the exact boats and voltages.

Feel free to ignore the above. It's your money.


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This is a 3s setup. It's the HK flowmaster. Comes with 3300Kv motors. I was looking on Kershaw Designs website and found these Gen 4 4370Kv motors for 3s. For $37 each, thought I'd try them out.

[Prodrvr]

As I go along with this boat, I may end up gutting it, reinforcing it, then put some more significant power in it. Or, just play with it a while and build something more worthwhile...and bigger! 36" is just not enough hull for me.

[785boats]

You do realise that you will be trying to spin those motors at over 48,500 revs. The drive lines will probably flog out very quickly for a start.
Also, the fact that they are a shorter motor, they will draw more amps with the same prop. And also the increased revs will draw more amps with the same prop. Double whammy. The 60A ESC's will not survive in my opinion.
Have a read through this from nearly a year ago. A lot of info in the first 6 pages. A great motor upgrade in post #3. But the motors supplied in the boat with some larger ESC's & props will surprise you.

http://www.rcgroups.com/forums/showthread.php?t=2418315

[Prodrvr]

You do realise that you will be trying to spin those motors at over 48,500 revs. The drive lines will probably flog out very quickly for a start.
Also, the fact that they are a shorter motor, they will draw more amps with the same prop. And also the increased revs will draw more amps with the same prop. Double whammy. The 60A ESC's will not survive in my opinion.
Have a read through this from nearly a year ago. A lot of info in the first 6 pages. A great motor upgrade in post #3. But the motors supplied in the boat with some larger ESC's & props will surprise you.
http://www.rcgroups.com/forums/showthread.php?t=2418315

Cool thanks!

[Lightknight]

Even if you went down in prop size ( as you must) its hard to see how the amp load would not increase by 35-40%. That's a big increase and will put the spotlight on both Motor and ESC cooling. I doubt that HK builds much unused capacity into their set-ups.

[Prodrvr]

So the load would increase that much even going with a smaller prop? That's a lot!

[Lightknight]

I am not sure why you are going to a shorter motor, though it will reduce the amp increase a bit. So definitely reduce prop size given the smaller can.
I run a TP 2860 5400KV and it draws almost X1.8 times the current than the Leo 3650 4200KV it replaces. as a guide I could use a 37mm prop with the Leo and a 32-34mm prop on the TP.

[dontrinko]

Is there a relation between KV and amps? IMO; only for a certain motor size if at all. The amp draw will depend also on the load.
There are tiny 3300kv motors and there are large 3300KV motors.
They may produce the same rpm for a certain voltage but the current draw under load will be totally different. The load is mostly the propeller. Don