working out HP for electric motors

[dwilfong]

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.

That is my point there are to many variables to do a true HP evaluation.

When I set up air compressors and pressure washers elc HP and gas,diesel HP out put requirements for the same pump are very different. It takes less elc HP to run the same pump on gas or diesel. The same pump that runs on 3 elc HP will take a 8 HP gas eng to run.

 

[jayt]

That is my point there are to many variables to do a true HP evaluation.When I set up air compressors and pressure washers elc HP and gas,diesel HP out put requirements for the same pump are very different. It takes less elc HP to run the same pump on gas or diesel. The same pump that runs on 3 elc HP will take a 8 HP gas eng to run.

This goes back to my original premise:

The problem with trying to compare peak horsepower values between electric and fuel is the power curve....

But the analogy does not demonstrate that the electric motors and fuel engines each somehow have a 'different' kind of horsepower. The electric motor is developing closer to its rated horsepower when driving the pump, while the fuel motor is well below its rated power (different efficiencies, etc.). It takes the same amount of horsepower to drive the pump given the same head, flow rate, losses, etc. Mechanical horsepower is mechanical horsepower regardless of how it is produced (motor or engine) - because it is defined as a specific amount of work. Hydraulic horsepower is not the same as mechanical horsepower because it is defined differently.

Gas and FE deliver their power differently, too differently to compare directly using the same units. Enough already.

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[dwilfong]

Touché B)

 

[lohring]

Torque is the amount of work being done, horsepower is how fast that work is being done. The speed versus time curve for an accelerating boat looks a lot like the horsepower versus rpm curve for the boat's engine. There are "dashboard dynometers" for cars that use this principle. The main difference is that in cars the drag is mostly proportional to the speed while in boats it is more proportional to the speed squared.

In racing I'm always interested in how quickly things are happening, so horsepower is a relevant comparison number. Dynos aren't just for internal combustion engines, though. It's always good to know the real power even though estimations are easier for electric motors than internal combustion engines. See below.

Lohring Miller

 

[dwilfong]

Cool water dino!

Talked about making a hyd pump dino last year on the form . Am getting all the parts to gather and have started on the designed. the one I am planing on will be a brake dino using a preset pressure as a base line on a flow compensating relief valve.

Have not decided on a data accusation system yet. The system used oh RC nitro drag cars looks promising.

some helpfull info http://www.herculesbulldog.com/proimages/Tech.pdf

 

[Mark Bullard]

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

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Remember you all are running three phase motors. The formula you gave is for single phase motors. So the correct formula is HP = ( 1.732 x V x I x EFF ) / 746. Of course you could build a Dyno. The formula is HP = (Torque (lb-ft) x RPM) / 5250.