working out HP for electric motors

[David Kingston]

Guys,

Im trying to calculate out the HP of an electric motor to compare to nitro.

I know that the HP will be more theoritical but just after ball park figure...

I just got asked what the comparable horse power range would be so it might help to work on the setup, and stating point with prop work.

Motor is a 1521/1.5d

battery 5s 6000mAh poly RC pack.

cont. watts on motor is 2250Watts

Dave

 

[Ub Hauled]

Guys,Im trying to calculate out the HP of an electric motor to compare to nitro.

I know that the HP will be more theoritical but just after ball park figure...

I just got asked what the comparable horse power range would be so it might help to work on the setup, and stating point with prop work.

Motor is a 1521/1.5d

battery 5s 6000mAh poly RC pack.

cont. watts on motor is 2250Watts

Dave

Dave, this motor can output 2880watts with it's recommended 30sec burst voltage and amps...

that would be the equivalent to 3.86HP

With your cell count (5s), 1998watts or 2.67HP, considering the max rated 30sec burst of 90amps

 

[David Kingston]

So how did you work this out....?

I remember talking to Jorge' some time back and his figures were slightly higer in HP that that, but i accidently deleated the email that had the calculations in it.

Dave

 

[Ub Hauled]

So how did you work this out....?
I remember talking to Jorge' some time back and his figures were slightly higer in HP that that, but i accidently deleated the email that had the calculations in it.

Dave

22.2v nominal x 90amps = 1998watts (2.67HP)

if you use more amps or more volts the output will be higher, but remember that every motor has a limit. Keep in mind that this is with the

factory data... people sometimes push it harder then this... therefore having more output.

 

[David Kingston]

so how do you get 2000watts to 2.67HP

whats the conversion here.

calculated out my setup to be

5s = 18.5v normal.

120 - 150 amp setup.

Therefore 2220 - 2775watts

Dave

 

[lohring]

Dave

There are 746 watts in 1 HP. Volts times amps gives watts. However there is some loss in the speed control, batteries, wires, and motor, so the output power will be about 80% to 90% of the volts times amps input with a good lipo, brushless setup. Brushed motors are not as efficient, especially with lead acid batteries. By the way, I doubt that many engine manufacturers do accurate testing and I suspect that their power figures are overstated. I have done a lot of testing on gasoline engines. Pipes and tuning make a huge difference. A change in pipe alone can add 1/2 hp to a stock Zenoah.

Lohring Miller

 

[drwayne]

Guys,
Im trying to calculate out the HP of an electric motor to compare to nitro.

I know that the HP will be more theoritical but just after ball park figure...

I just got asked what the comparable horse power range would be so it might help to work on the setup, and stating point with prop work.

Motor is a 1521/1.5d

battery 5s 6000mAh poly RC pack.

cont. watts on motor is 2250Watts

Dave

PolyRC... 6000 mAh 5S 18.5volt 25C/40C pack

equates continuous 120/200A(30sec)

equates continuous 2220W/3700W )30sec)

equates continuous 2.97/4.96hp (30sec)

actual lower due losses of efficiency

VxAxC/746=hp

cheers

DocW

 

[Ub Hauled]

so how do you get 2000watts to 2.67HP whats the conversion here.

calculated out my setup to be

5s = 18.5v normal.

120 - 150 amp setup.

Therefore 2220 - 2775watts

Dave

Oh crap. I just realized that I was using 6s instead of your stated 5s.... DUUUUUUUUUH... my bad, that was ridiculously shortsighted of me...

If you are pushing the system to 120-150amps your figures would be right (@ nominal). The biggest "power thief" would be the efficiency of the motor and the voltage drop due to quality of the cells at the amps you mentioned. All cells drop voltage when under pressure, cheaper cells will drop more then good quality cells... the impedance are low on this particular motor and most of the times low on the ESC as well... higher discharge cells (high C rate) have lower impedance, specially when pre-heated to 100-110 prior to use, they will drop impedance to about half. Longer thin wires are a bad thing to have on board, you wanna use short big gauge wires... the biggest problem with long wires is the ripple current issue, that will fry the ESC and/or more parts.

Sorry about the confusion...

 

[jayt]

The problem with trying to compare peak horsepower values between electric and fuel is the power curve. Engine performance is really a function of the area under the power curve, and the curve of an FE motor simply has more area for the same peak number. The average 4 hp electric motor will give superior performance to the average 4 hp nitro motor in the same hull. It's just physics. You can calculate the numbers, but then all you have are numbers. The reality can be much different.

.

 

[Ub Hauled]

The problem with trying to compare peak horsepower values between electric and fuel is the power curve. Engine performance is really a function of the area under the power curve, and the curve of an FE motor simply has more area for the same peak number. The average 4 hp electric motor will give superior performance to the average 4 hp nitro motor in the same hull. It's just physics. You can calculate the numbers, but then all you have are numbers. The reality can be much different. .

Jay said it all...

Electric does not have to spool up, we have full HP from "get go".

 

[David Kingston]

Jay

Yeah, not directly relating electric to the IC motor, but it was required to compare. Basically the boat i am getting together (dont want to let the cat out of the bag just yet) but it takes HEAPS of ponies to get going fast and hard.

I think my motor selection is right for this application. Time will tell...

Im comparing my 3.5mac 33inch mono to my 1521 33inch mono, the electric wins hands down. Instant power and acceleration, just cannot run it for as long as the nitro...

Im hoping that a 1527/1.5d would be of equal power to that of a 80 or 90 engine.

While i am on the topic...

What sort of props would be worth while staring with on the 1527/1.5d in a rigger on 5s. . .

I was going to run 1460's then 1657's.

Ive run the motor before with 55mm props in monos and it works wonders so hoping i can swing the bigger lifting props in a rigger hull...

Dave

 

[jayt]

I'd go straight to 1655s and 1755s if the rigger is set up right. Hold on....and watch for heat, particularly if your pond is small and requires lots of on and off throttle.

'

 

[Mark Bullard]

The proper formula is

1.732 x E x I x EFF x PF / 746 = HP

E = volts

I = amperes

EFF = efficiency (decimal)

PF = power factor (decimal)

The manufacture will have to give you the Efficiency and Power Factor

 

[dwilfong]

I am building a Kep's rigger for FE and have bin using this info for set up.

http://www.offshoreelectrics.com/conversion.htm

Lots of good info for making calculations.

 

[pda75]

Dave
There are 746 watts in 1 HP. Volts times amps gives watts. However there is some loss in the speed control, batteries, wires, and motor, so the output power will be about 80% to 90% of the volts times amps input with a good lipo, brushless setup. Brushed motors are not as efficient, especially with lead acid batteries. By the way, I doubt that many engine manufacturers do accurate testing and I suspect that their power figures are overstated. I have done a lot of testing on gasoline engines. Pipes and tuning make a huge difference. A change in pipe alone can add 1/2 hp to a stock Zenoah.

Lohring Miller

small comment : in Europe 1 HP = 736 W and not 746 W !

Just to let you know that US and european HP are slightly different.

in US, 1 HP is the required power to lift 550 pound by one feet in one second

In europe 1 HP is the required power to lift 75 kg by one meter in one second

 

[Ub Hauled]

small comment : in Europe 1 HP = 736 W and not 746 W !
Just to let you know that US and european HP are slightly different.

in US, 1 HP is the required power to lift 550 pound by one feet in one second

In europe 1 HP is the required power to lift 75 kg by one meter in one second

there should be only ONE universal standard... metric system rules... much more precise and easier.

IMO of course.

 

[dwilfong]

HP is a very vague concept. As has bin stated it is the time it takes to move weight a certain amount of distance. torque is a much more constant measure of power.

 

[jayt]

Mechanical horsepower is not a vague concept at all, it is a measurement of actual work performed. Torque is a measurement of the moment of force, not of power.

Now which is more vague? BTW horsepower of IC engines is calculated directly from torque and rpm.

The formula for calculating the horsepower of an electric motor is: HP = (V x I x Eff) / 746.

The efficiency varies with voltage and load, so a simple calculation is difficult. The above formula is accurate enough though. BL motor makers often furnish efficiency, Kv, impedance and resistance values. Seldom can you obtain additional technical information.

http://www.elec-toolbox.com/Formulas/Motor/mtrform.htm

.

 

[dwilfong]

Mechanical horsepower is not a vague concept at all, it is a measurement of actual work performed. Torque is a measurement of the moment of force, not of power. Now which is more vague? BTW horsepower of IC engines is calculated directly from torque and rpm.

The formula for calculating the horsepower of an electric motor is: HP = (V x I x Eff) / 746.

The efficiency varies with voltage and load, so a simple calculation is difficult. The above formula is accurate enough though. BL motor makers often furnish efficiency, Kv, impedance and resistance values. Seldom can you obtain additional technical information.

http://www.elec-toolbox.com/Formulas/Motor/mtrform.htm

.

My point is you need a torque value to calculate HP. You will not have any HP if you cant apply torque. IE prop slip ,wind resistance ,water resistance,drive line efficacy. True HP is how much it weighs and how fast it can cover a measured distance.
The coefficients for elc ,nito ,gas and diesel are all different. They can all claim the same HP but can not do the same amount of work.

 

[Ub Hauled]

My point is you need a torque value to calculate HP. You will not have any HP if you cant apply torque. IE prop slip ,wind resistance ,water resistance,drive line efficacy. True HP is how much it weighs and how fast it can cover a measured distance.
The coefficients for elc ,nito ,gas and diesel are all different. They can all claim the same HP but can not do the same amount of work.

That would be virtually impossible to do...

why don't you just get the all data of the motor and use the true pitch of the planned prop, I am sure you can get the necessary data from all the motors you would like to compare. At least that way you can have a constant throughout.

All the inefficiencies will be the same on all tests as long as same prop is used.