Diesel Horsepower

[TomG]

I'm guessing that the HP in an electric motor could be expressed in foot-pounds torque, but the HP unit used for electric motors is different than that used for vehicles. There are a number of HP definitions used. Just curious what the electric motor HP definition is.

I suspect that we'll see electric tractors before long. I think some prototype diesel-electric passenger vehicles exist now. I think it sort of hybrids with a fuel cell system. Maybe somebody knows something about them.

Of course, railroad locomotives have been diesel-electric for decades, and they pull pretty well. If I remember, locomotives use series wound DC motors. A series wound motor produces max torque (or is it draws max current, maybe both?) at 0 RPM, as opposed to a shunt wound motor.

Sounds a bit like this discussion. It's difficult to compare HP & torque measures in different engines without considering how the power distributes across RPM.

 

[TomG]

Thanks for the note. Hadn't thought about that, but it does relate to how power is distributed across time. I guess that if the stroke was long enough, the combustion slow enough, and there were enough cylinders, then the power output would be continuous. A flywheel wouldn't be needed.

Of course, power delivery in real engines is far from continuous, and kinetic energy has to be stored in rotating components to get an engine under load from one bang to the next. I believe that a theoretically ideal engine (one with no inertia or parasitic losses, and with instantaneous combustion) couldn't pull anything, no matter how much torque and HP it produced. All power would be delivered in an instant, and an instant after the power delivery, any continuous load would stall the engine. Just a curious thought.

 

[jdkid]

TomG ya right about diesel-electric in trains but i'm just thinking don't some of the BIG off road dumptrucks use the same gear in them?? and off the top of my head ya right about torque at 0 rpm in them ya just keep feeding the power in to them to make them faster(like a light dimmer)now electric motors here(new zealand)are sold in KW units (kilowatt=1000 watts) most tractors here are also sold in Kw and Hp rateings (1Kw=1.34Hp)or (1Hp=.746Kw) i'd have to go to sparky school to tell ya what it means in the real world but maybe someone here may know if we are on the right track
cya
JD Kid

 

[gordon]

Now Mark you know thats wrong wrong wrong---I have a puney hidden hitch on the back of mine often overloaded and I guess that would be the second time it would have been underloaded. The other time was when I got the bright idea to drive the truck back on a skidding lane with diesel in the back for the tractor instead of driving the tractor out.
Well needless to say floatation tires don't always float and it took my tractor and another to get it out---that was my smart move of the day that day. Oh and I got no work done that day trying to save a couple minutes cost me a few hours. I gave myself a forehead slap for that bright move.
Gordon

 

[Bird]

Wen, the HP of electric motors is just one more of the many things I don't understand. When I bought my current air compressor (60 gallon tank, 6hp motor, 120 psi), they also had a compressor sitting there with a 100 gallon tank, 175 psi, and a 5 HP motor. Now that "5 HP" motor was about 3 times as big as the "6 HP" one that I bought; both are 230 volt motors. The salesman told me electric motor manufacturers can rate them as anything they want to. He laughingly said they (the compressor dealer) call mine an "imitation 6 HP" while that other one is a "true 5 HP". I'm not sure I'd even want to hear the explanation for that; it'd probably just go over my head./w3tcompact/icons/laugh.gif

Bird

 

[gordon]

A D-C moter is a high torque moter a A-C moter is a low torque moter thats why a start capacitor is used to boost the voltage on an A-C to give it that jolt of voltage to get going. On a 110 volt A-C moter the start/run capacitor will give it a jolt in excess of 160-240 volts for a few seconds allowing the moter to start.
The reason D-C moters are used in locomotives because they are a high torque moter but with a lower h/p rating. But they need pulling power---torque---.
The reason that A-C moters are not as effective is that half the wave form is lost 60 times a second whereas on a d/c moter its a straight wave form in true d/c current.
How deep would you like to go with this?
Inductance/capacitance in a/c?

 

[_RaT_]

DC motors or the traction motors as they are called in locomotives today are used because DC motors are infinitely more conducive to the tpye of variable currents running through them. The dynamo generating the power needed for the traction motors does so at varying speeds. The diesel revs up, the dynamo increases its voltage/amperage output. In the end, its this ability of the DC motor to use constantly changing voltages that favors it as the choice for variable load situations. AC motors rely on 60 cycles for instance and that cannot or should not change. The voltage for AC is critical. To little and current goes up, heat goes up and it burns up. The diesels they use in the locomotives are more powerful then the one in Mark Chalkleys truck. Rat...

 

[PaulB]

Jim I don't have an answer to which motor will do more work, the one in my B1700 or the BX2200, but I do know that they are THE SAME ENGINE (model D905 - E), but mine has a lower rev limit than the BX. The bore and stroke are identical, and my guess is that all that is changed is the set point on the governor. Maybe my tractor with a BX governor would be a B2200?? As for power curves, these can be found at http://www.engine.kubota.ne.jp/english/product/ Mine seems to peak at 2200 rpm, which is exactly where it just plain sounds best by the way - coincidence or engineering, I do not know

 

[W5FL]

There I thought all topics changed to oil and this one started out in the oil & lubricants and is now about electric motors. I could discuss electric motors all day, but would rather find out if the other topic on Super UDT is all synthetic or not. /w3tcompact/icons/smile.gif

I also hate all dc motors (directly commutated) as the sparks at the brushes cause all kind of electro magnetic interference and that is pollution too.

 

[Anonymous Poster]

Since you were not sure if you wanted to hear an explaination, you can just read this one.

A horsepower in an electric motor is exactly the same as in any other kind of motor or engine. With tractors there more than one kind of rating for horsepower and the same is true for electric motors. With tractors the ratings that mean something are PTO HP and drawbar HP. The engine gross HP that manufactures always quote, can never be used and is only quoted for the "mine is bigger than yours" effect.

With electric motors the continuous HP rating is just what it says. The motor can put out that HP all day long and not overheat or fail (with a service factor of one). Sometimes you will see a service factor (SF) rating on the motor. I think this is just there to confuse people. If you take the service factor and multlpy it times the HP rating, the resulting number is the max HP the motor can put out continuously. Some motors will have a service factor less than one, which means they will over heat if used continuously at the HP on the nameplate. Maybe the motor on your compressor has a service factor less than one. That big motor on the other compressor may have had a service factor more than one.

Now for the "mine is bigger than yours" effect with electric motors. Many power tools you will see advertized do not quote max continuous HP, they instead quote max developed HP. The difference between the two is huge. A 1 HP continuous rated motor may be rated at 2.25 HP to 2.75 HP on the max developed scale. Max developed is a useless term that has no real world application except to increase sales to people that do not know the difference. Just so you know what the rating is, it is the max HP the motor can put out just before it stalls. As the motor is taking on a load it will start to slow down as the load gets greater than the max continuous rating. It will slow more and more until it stalls and stops turning. The max developed rating is taken mili-seconds before the stall occures. This higher load creates much more heat than the motor can dissipate, so if operated anywhere near this rating for longer than a few seconds the motor will overheat.

Andy