wattage verses amperage

[sprintkat]

ok - lets se if i got this right
if i have 2000 watt motor, the more voltage i put to the motor, lets say 22.2v 6s2p, the less amperage it needs to move the boat which is 90 amps
then if i put 2x3s2p at 5000 mah with a 30c discharge, i would have 150 amp at my disposal or would tht be 300 amps

[Diesel6401]

Is not wattage vs amperage, the 2 are directly related to each other.

Watts = Voltage x Amperage.

In boating the actual wattage number isn't typically a major factor like it is in airplanes. AIrplanes have a more charted out approach and typically the amps are always going to be less then most fast electrics boats. In boating amperage (which does effect the wattage number) is our biggest enemy which is why proper higher voltage setups are typically better as they will pull less amps to achieve the same amonunt of wattage. We focus on the amp and rpm numbers in boating rather then the wattage output of the system. That wattage is always going to be there, it's just the way we achieve that number is what makes all the difference.

Using the batteries you listed here is how this works out in series and parallel circuits.
(two) 3s 5000mah 30c

Series:
6s 5000mah 30c (approx 150amp)

Parallel:
3s2p 10,000mah 30c (approx 300amps)



* In order to reach 6s2p, you would need (two) 6s lipos.

[de-pro]

Is there a direct relation between the wattage of the motor and how many amps it draws?

[Boaterguy]

you could kinda think of it that way. a motor that uses (terminology?) 2000 watts and 20 volts will use 100 amps to get to that wattage.
if a motor uses 2000 watts and 200 amps will need 10 volts to reach 2000 watts.
most motors can actually take more than stated on the page.

[Insaniac]

Is there a direct relation between the wattage of the motor and how many amps it draws?

Yes. For a fixed battery voltage, say 14.8v (4S), the higher wattage motor CAN draw more current for a given setup IF you prop up for more speed. Take a UL-1 motor (~2040Kv) which I think is probably about 800 watts, versus say an ARC ducted fan motor (~2000Kv); because the ARC motor is rated at 2000 watts peak, you can pull a lot more amps using a bigger prop and get a LOT more speed. Only caution is you need a bigger ESC.

[graill]

Is there a direct relation between the wattage of the motor and how many amps it draws?

Sounds like you have a winter project in the form of electrical theory and application. My assuming from your OP.

Dividing the wattage by the voltage gets you theoretical amps. Amperage heats things up, also not having enough potential, insufficient esc with low amp rating, small wiring, can also heat things up as the reserves are depleted to quickly and bad things happen (heat), also excessive boat weight for your setup, and as a couple folks already pointed out poor prop choices. Alot to learn.

A motor that works harder draws more amps. Take a freewheeling motor just starting, it will use more amps to start rotation but then those will drop down once rpm levels off, unless of course it continues to work harder and harder it will then draw more and more amps.

Your boats weight, setup, your skill soldering, and selecting quality parts that work well together, batts, esc's, motor, driveline, prop, water conditions. Electrical boating is a fine art and a fickle mistress that does not tolerate bad math.

My Dollar and two cents.

[de-pro]

Great info.
I was more referring to the power the motor produces. Example is a Leopard 4082. It produces 3500 watts of power or 4.7 horsepower across all their kv motors. However the amps draw ratings are different. For example a 1600kv draws 120amps versus a 1200kv only draws 82 amps. Both produce the same power though. Are we talking apples and oranges between the power motor produces versus the amps it draws.

[Brushless55]

Great info.
I was more referring to the power the motor produces. Example is a Leopard 4082. It produces 3500 watts of power or 4.7 horsepower across all their kv motors. However the amps draw ratings are different. For example a 1600kv draws 120amps versus a 1200kv only draws 82 amps. Both produce the same power though. Are we talking apples and oranges between the power motor produces versus the amps it draws.

with those, the lower the kv the higher the volts to get the same 3500watts out of them..

[Punisher 67]

Lets expand this a little bit more

There is an electric motor constant of 1355 that applies to every electric motor regardless of wind or type of magnet .

If a motor has a KV of 1355 its KT will be 1.0 inch once of torque per AMP drawn . So now lets compare a 1600kv motor to your 1200kv motor

1600kv / 1355 = .8468 inch/oz torque per amp drawn
1200kv / 1355 = 1.129 inch/oz torque per amp drawn

now lets assume to spin a 45mm prop at 30,000 rpm will take 150 inch/onces of torque .

the 1600 kv motor = 150 / .8468 = 177.14 amps to pull that load
the 1200 kv motor = 150 / 1.129 = 132.85 amps to pull that load

1600kv motor will need 18.75volts to pull 30,000 rpm...........30,000 / 1600 = 18.75V
1200kv motor will need 25.00volts to pull 30,000 rpm...........30,000 / 1200 = 25.00V

1600 KV motor = 18.75Volts x 177.14Amp = 3321 watts ( volts x amps )
1200 KV motor = 25.00Volts x 132.85Amp = 3321 watts ( volts x amps )

Can you see the pattern here

To round this off the 1600 kv motor on 4 cells will need 177.0 amps to accomplish this task
the 1200 kv motor on 6 cells will only need 132.0 amps to accomplish the same task

[JT13031]

One thing that needs to be pointed out as well. Just because a motor is rated at 2000W oesn't mean it is going to produce 2000W of power. It's only going to make the power it needs. The rating is what the motor can handle. The more load you puyt on it the more pwoer it will make

[Punisher 67]

To be honest there are a lot of factors that come into play with any given motor .

[de-pro]

Thanks Punisher, thats the info I was looking for

[HydroMike]

Thanks Punisher, thats the info I was looking for

Still looks like I need to learn a little more good info now all I have to do is to keep it in my head lol

[Rich]

Lets expand this a little bit more

There is an electric motor constant of 1355 that applies to every electric motor regardless of wind or type of magnet .

If a motor has a KV of 1355 its KT will be 1.0 inch once of torque per AMP drawn . So now lets compare a 1600kv motor to your 1200kv motor

1600kv / 1355 = .8468 inch/oz torque per amp drawn
1200kv / 1355 = 1.129 inch/oz torque per amp drawn

now lets assume to spin a 45mm prop at 30,000 rpm will take 150 inch/onces of torque .

the 1600 kv motor = 150 / .8468 = 177.14 amps to pull that load
the 1200 kv motor = 150 / 1.129 = 132.85 amps to pull that load

1600kv motor will need 18.75volts to pull 30,000 rpm...........30,000 / 1600 = 18.75V
1200kv motor will need 25.00volts to pull 30,000 rpm...........30,000 / 1200 = 25.00V

1600 KV motor = 18.75Volts x 177.14Amp = 3321 watts ( volts x amps )
1200 KV motor = 25.00Volts x 132.85Amp = 3321 watts ( volts x amps )

Can you see the pattern here

To round this off the 1600 kv motor on 4 cells will need 177.0 amps to accomplish this task
the 1200 kv motor on 6 cells will only need 132.0 amps to accomplish the same task

Well put Punisher, now if we could only get the actuall numbers for each prop . . . . I think that will be a valuable tool.

[Punisher 67]

Yes Rich that would be a valuable tool - that was all just an example I have no idea if I was even close with the actual torque figures related to that prop .