diesel hp VS electric hp

[martincn35]

Hi,
I would like to know if,when replacing a diesel engine with an electric motor someone need to look for the same HP for the electric motor as the hp the diesel had.

Martin.

[Matthew Edmondson]

probably not the exact same HP, because electric motors have more torque at lower RPMs than an internal cumbustion engine

[Dave Grason]

Electric motors smell better, too.

Unless of course you're using biodiesel and then your engine smells like french fries. Yumm.

[kens]

HP is HP no matter how you get it.
The things that make 'different' HP is power/weight ratio, and the RPm that you produce that given HP. (and this defines torque)

Example; if you make 50hp @ 3000rpm, then it dont make a difference if you getting it with gas, diesel, electric or otherwise, as long as you are talking about 50hp @ 3000.

[ttownshaw]

In the words of Homer Simpson...mmm french fries and the smell of electric motors.

[upspirate]

check this site out....replacement for diesel & an electric outboard:

http://www.solidnav.com/index.htm

[bob smith]

Question:
If the power cord leaks juice, will it shock you when you mop it up?

Bob Smith
Chester, SC (Electrified in the late 1800s)

I am an expert of electricity. My father occupied the chair of applied electricity at the state prison.
W. C. Fields

[Ltjamesd]

In doing research for my own Solar Powered boat plans, I learned that the correct formula to convert gas HP to Electric HP is 2.73.
In other words one (1) Elec hp = 2.73 Gas hp. Electric motors also have a more even or consistant torque level through out the entire RPM range.

[AaronStJ]

In doing research for my own Solar Powered boat plans, I learned that the correct formula to convert gas HP to Electric HP is 2.73.
In other words one (1) Elec hp = 2.73 Gas hp.

Huh? With all due respect, that makes no sense. One horsepower is one horsepower is 33,000 foot pounds per minute, no matter what energy source is supplying it.

[Cranky Badger]

Aaron, that might be an 'anecdotal' ratio based more on experience than math...though it sounds a little specific for that.
With an electric motor conversion you free up hp by not spinning the drivetrain and accessories,so the hp that the prop sees is closer to what the motor can actually produce.
At least, that's how I took it.

[Ltjamesd]

I'll find the exact tech specs and post it on here. I also read another post here that talks about commercial operations converting their gas 350 Merc to 150 hp Electric, meaning equal power conversion. In the mean time here are a few quotes:
"Electric motors are upwards of 90% plus efficient. Internal combustion engines are 30% to 35% at best. That is another reason for a guideline if you need or have a 30hp gas engine. A 12hp electric motor would be almost the same. 30% of an IC's energy is wasted in the heat from the exhaust. IC engines are terribly inefficient."

"From contributor T:
It is generally accepted that an electric motor will give what can be construed as horsepower at about 2 1/2 times the rate of a gas engine. It has to do with the electric motors ability to keep its rpm up with a correspondingly high amount of torque over a wide range. Electric motors start up with very high torque, level off slightly under, and maintain that level throughout."

"From contributor C:
It's true. In most all cases, a machine that requires 10 hp will require 2 to 3 times more if equipped with a gas engine."

I'm just sharing what I've read from reliable sources, like motor manufacturing companies, and it's how I'm planning my project. I'm not trying to get into a Physics lab arguement.

[Ltjamesd]

"The OSSA Powerlite system incorporate two 25kw generator (combined 67 hp) driving two 35hp propulsion motors. These replace the twin 75 or 100hp Yanmar engines that have previously used on sisterships along with a "Mini 8" Fischer Panda generator."

http://www.ossapowerlite.com/customers/ ... ast_47.htm

http://www.solomontechnologies.com/m_recreational.htm

This might be helpful. Have fun exploring.

[Cranky Badger]

James, as the new guy I hope you don't take any of this personally. The folks here like to kick stuff around but everyone gets along.
Thanks for the additional info and links BTW.
I'd be interested in a thread on where you're at with planning your solar project.

chair of applied electricity

That is just too funny...

[Kevin Morin]

AaronStJ, seemed to me to bring up the reason for the confusion in this topic and the seemingly conflicted sources or references. AStj used the physical constant [33k ft.lb/min=hp] and asked how were the two different types of machines changing 'physics'- isn't one HP one HP "all the world over"?

I think that what has happened here is the rating methods, and the labeling methods versus the physical constants creates an apples and oranges conversation? I don't think electric motors and reciprocating engines have universal testing standards so they don't have common ratings, and the difference is in the rating methods and numbers that follow.

First, reciprocating internal combustion engines are advertised by total [possible] hp which is [unfortunately] too often measured by cranking the engine to highest redline and the applying a brake to the running engine and measuring the heat generated to stop the engine running. That heat amount is "converted" to Hp. This isn't the Hp at the top of the torque curve, nor is it really usable Hp because you'd have to run the engine at that condition to see that horse power.

Fueled engines most often are rated with peak possible, all out, redline pushing revs, and that is more or less 'ad speak' instead of there hp at peak torque or in 'cruising' rpms. So the 100 hp diesel is really delivering 35 or 40 hp to the shaft at 'normal' operating conditions, compared to anywhere near 100 "advertised, named, and possible" hp that the advertising/marketing guys have labeled this engine.

Now electric motors are more often specified by engineering types as opposed to the advertising guys, the latter tend to exaggerate, or 'hype' as we say now, compared to the former type who by training are more conservative in their labels and terms. Electric motors are often rated by math; the mass of the rotor and shaft multiplied by the revs gives a momentum and that is often converted to foot pounds and divided by 33k as AaronStJ noted. This means the electric motor is more often rated at its 'normal operating' conditions instead of at some 'ready to explode' condition.

So if one torque producer is rated by advertising people and the other by engineers who don't care about ratings being higher than the 'other guys'- just 'workings'; the 2.5:1 ratio seems more like a difference in how we've all come to talk about these two types of torque producers - instead of any real difference in the real world, physical constant facts, or some magic of one type of power over the other.

I think the reason for the 2.5:1 ratio is the amount of exaggeration used to rate reciprocating engines. To dial out the 'adspeak'; divide the advertised horse power of an engine by 2.5 and that is 'useful' power rating. Once that's done it quickly levels the difference between motors and engines and could put us all on a common conversational footing in terms of the useful work these torque producers will provide.

cheers,

[Nova SS]

This means the electric motor is more often rated at its 'normal operating' conditions instead of at some 'ready to explode' condition.

BUT its so much fun to use them when they're on the ragged edge of exploding...lol