# Req: How to determine "Horsepower" of small electric 12v motors, any help appreciated!

The problem is, I have some small 12v electric motors that I would like to use in the miniaturization of a project (for demonstrations). Is there any way to determine
the approximate "horsepower" of a small 12v electric motor of unknown source and unknown specs, other than it being 12v?
Any and all help will be appreciated, Robo
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snipped-for-privacy@nowhere.invalid wrote:

1 horsepower = 746 watts. You can calculate watts by multiplying voltage times amps and factoring in efficiency. You can't really get horsepower just from the voltage of a motor.
Here's a page to get you started -- search on Yahoo etc to get more.
http://www.elec-toolbox.com/Formulas/Motor/mtrform.htm
-- Gordon
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On Fri, 04 May 2007 05:28:32 -0500,

You could make a small dynamometer using another dc motor as generator with a variable resistor load. You would need to be able to measure the rpm and the torque being produced by the motor being tested (possibly using a torque arm on it and a cheap digital scale).
http://en.wikipedia.org/wiki/Dynamometer
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Thank You. This is a great page. I should have stated it better in that I meant, not "other than it being 12v", but knowing it is 12v and using other "common" hobby tools, like multimeters, to calculate the horsepower. This page you referred me to is going to be very helpful. I will have to take a guess at efficiency, but it is going to be a lot closer than I could have done without your help.
Thanks again!

Thank you as well. I think my biggest problem with this method, although probably more accurate, would be a simple way of measuring speed with common hobbyist equipment.
Thanks again
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On Sat, 05 May 2007 18:37:17 -0500,

If you have a multimeter that has a frequency meter built into it, then you probably could use that to measure the rpm. There may be other ways to measure the rpm. Below are ways from the old days to measure the rpm of phono turntables using a fluorescent light as a strobe source. To measure the running motor torque, the torque arm on the running motor could be a thin bamboo skewer with a weight on the end, with the torque being calculated by the amount of distance the skewer is rotated from a bottom verticle position in the side/upward direction.
http://www.extremephono.com/ftp/60Hz.PDF http://www.myvintagetv.com/strobe.htm
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Hi Robo,
a very simple way is to put a load on your motor with or without any gearbox. One way to do it is built anything with a kit like your Meccano.
Power (in Watts) is simply Voltage mutlitplied by Current.
Then, take two multimeters and any tranformer (10x1). Make sure that you have one multimeter with high amp capacity. You mount an electrical circuit with the power source, motor and transformer. Be careful to put the one side of the transfo in your circuit and the 10 side will where you will connect the ampmeter set on the highest range. The Amperes that you read have to be mutliplied by 10 in order to get your motor current.
Here you go.
LHR
snipped-for-privacy@nowhere.invalid wrote:

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LHR wrote;

Hey LHR, thanks! That I can do with the palytry collection of eletronic equipment I have available. Thank you again! This is very helpful, and I might add difficult to ferret out of the internet as I have tried. This is a good group to get help from on these kinds of problems.
Robo
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On Thu, 10 May 2007 00:03:34 -0500,

That will tell how much electrical power is being used by the motor, but doesn't really have anything to do with the actual shaft horsepower output of the motor.
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Sorry, my header for the above should have been Re:, not Req: Robo
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Chris, Yes, I am naive about electrical calculations, that's why I asked for help. And no, I am not selling anything. This is for my own curiousity and understanding. The phrase "for demonstrations" was meant to keep this short and simple. It is for me and some fellow robotics hobbyists.
I can't afford to create a full scale model. I have some numbers as to how much horsepower is used on full size equipment which uses gasoline engines and are rated in horsepower, which is a unit of work (mass, distance, time).
I realize that there are transitional differences in going from scale to scale, and torque, horsepower, power ranges, engine speed, etc. I know what I am getting into on this level.
I am not an expert, but I need to start somewhere. If the initial requirements by calculation prove to be too much, then I will save myself a lot of time and expense. My hobby is robotics, but I still don't want to waste my time on something totally impractical.
I don't want to get everyone involved in a discussion about all the scale transitional differences. But as an example, if I wanted to create a scale boat, plane, car powered by small electric motors, and the scale model was exact (I know!), and the real boat, plane, car is powered by xxx horsepower motors, etc. (not necessary to point out the differences), I want to determine if any popular cheap small electric motors could emulate the same performance. To do that without building the model, I would like to calculate out the project first on "paper". Therefore, to be able to calculate a *rough* scale of horsepower supplied by these motors. Trying to keep it simple at this stage.
Thanks,
Robo
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Unless you are buying an electric motor for a boat...then it may be HP in USA, or kW in the real world
Cheers
:-]
Dale
snipped-for-privacy@nowhere.invalid wrote:

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I find use of the word "horsepower" somewhat suspicious in any engineering discussion. In a strictly mathematical sense, as Gordon points out, one horsepower is indeed about 0.746 kilowatts. In common usage, however, a kilowatt is a unit of measure used by engineers to calculate things whereas a horsepower is a unit of measure used by salesmen to sell things. That you seem to believe that simply by using the correct quantity of horsepower you can accurately demonstrate something with a scale model strikes me as naive. The physics of most systems scale in nonlinear ways. What exactly is this project and what are the parameters you hope to estimate?
-chris.

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