The difference is how electric motors are rated vs how gas engines are
rated. Gas engines are usually rated at their peak power. Electric motors
are usually rated at a continuous-duty power rating, or a one-hour rating,
or some other period of time depending on the application. A starter motor
would probably be rated for a much shorter period of time, for instance.
Also, most electric motors can deliver much more than their rated output
for a short period of time. It pretty much has to do with thermal loading
and how much heat the motor can dissipate. For instance, the forklift motor
I used in my electric drag bike was rated at 4.5 HP for an hour. I actually
got around 35 HP out of it for about 14.25 seconds or so.
So, it's not that a HP doesn't equal a HP, but for the same application
you'll need a different HP rating for a gas engine than you would for an
electric motor.
Also, a lot of wound DC motors, that is motors with a bunch of copper
windings on the armature, can handle rpms of up around 5,000 to 7,500
without any trouble, even if the power rating is at a lower speed. At
speeds above that the windings start lifting up which pull the commutator
bars up into the brushes which brings everything to a messy stop in a hurry.
Henry Deaton
SF, CA
At 11:19 PM 1/26/2003 -0500, Bill \"Pokey\" Bennett wrote:
>Ok I may be setting myself up here, but I will stick my neck out.
>Somewhere years ago I saw a conversion factor for converting from an AC
>electric motor to a gas engine drive on hydraulic pumps. I can not remember
>what the number was, but do remember it was NOT one for one. I know I know
>how can HP not equal HP. Think it maybe because of torque and rpm because
>typically a hyraulic pump would be running at 1750 rpm with an AC electric
>motor, and with a gas engine would be running closer to 3600 rpm.. Now here
>comes another thought. Dry sumps run at half speed so lets say around 4500
>rpm. Now most DC motors run around 2400 rpm. Now a pulley swap to get pump
>speed and I have given up half my torque capability.
>
>Bill
>"putting on bullet proof vest"
/// unsubscribe/change address requests to majordomo@autox.team.net or try
/// http://www.team.net/mailman/listinfo
/// Archives at http://www.team.net/archive/land-speed
/// what is needed. It isn't that difficult, folks.
|