Electric to gas motor conversion equivalent

I am going to buy an 18" Woodmaster planer on Saturday and I am thinking that I may end up converting it to run on a gas engine since I do not have enough power to the sawmill/lumber building. The electric motor is 220V 23 amp 5 HP single phase 3450 RPM and I am wondering what size of gas engine I would need to provide a similar amount of power. It is a belt drive so I can change the pulley size to make the speed match. I have gotten the impression through the years that a gas motor produces less useful power than an electric motor of the same HP rating but I do not even know if that is true. Any advice will be much appreciated.
Zach

Not exactly sure, but I think a "gas horsepower" is about 1/2 of an "electric horsepower".

I have 2 12" planer with 5 HP motors, and I think that is barely enough to do the job. Try for a 15 HP gas engine. Or maybe you could fabricate some method of putting a pto shaft on it to run it with a tractor

1HP is one HP.
No matter if it's 1HP electric, two stroke gasoline, four stroke gasoline, two stroke diesel, four stroke diesel. Water turbine, gas turbine or steam turbine.
Where the confusion lays is the concept of intermittent overload capacity.
That 5HP electric motor maybe able to make 10HP for a few seconds when the planner is over loaded. You are non the wiser unless an ammeter was indicating current and a tach was showing increased rotor slippage.
A 5HP gasoline engine is going to wheeze to a stall when a 10HP load is applied. The 5HP gasser engine does not have a torque rise and intermittent overload capacity of the 5HP electric.
Try running a 10HP load with a 10HP gasoline engine,then with an 5HP electric motor. The 10HP gasser will keep running for hours.The 5HP electric motor will carry the 10HP load for about a minute before tripping the thermals.

Well here is a true story. I have a compressor that had a 12hp gas engine on it and now a 6 hp electric. The problem with gas and electric is the gas does not have the same torque as the electric has so you need a higher HP gas then electric to keep up with the load. So no HP is not the same across the board and it comes down to torque power

As others have said 1HP equals 1HP, however as we all know all horses aren't created equal, so to speak. Think about it this way, it might take one Clydsdale 1 minute to drag a 1000 lb weight 10 feet, but it will also take a dozen minature ponies to move the same weight the same distance in a minute. The difference is the power or torque created by the Clydsdale vs the ponies.

That said, what your concerned about will be the torque, and the torque characteristics are completely different between gas and electric power. In that respect a 5HP gasoline engine isn't going to work to replace a 5 HP electric motor. I know that when converting an air compressor from an electric motor to an engine you need to go with an engine of at least double the electric HP. Now most compressors typically turn in the 1800 RPM range and many engines typically reach their Peak HP in the same RPM range so you've got that working against you. In your case your wanting to turn at 3450 RPM or nearly double the RPM where the engine is gonna reach it's peak torque so if you went with a pulley stup to increase the speed you in effect will be decreasing the torque with the increase in speed. If it was me doing the conversion I'd go with a minimum of a 18 HP engine and prefferably a 20 plus HP engine and direct drive everyting through some sort of coupling. I say this because knowing it's a planer the speed of the blades is important to the finish and that speed is going to rely directly on the torque output of the engine being high enough to prevent the engine from bogging when the blades hit a hard spot and slowing everything down. Too going with anything other than direct drive you lose a certain amount of HP through the 'drive device' so close coupled is the best way to tget the greatest amount of torque transmission to the machine.

Short of getting into a lot of math that 'only and engineer' could understand,((((((((see the link))))))) that's about it in a nutshell. Over the years I've converted several compressors from electric to gas and rule of thumb has always been 1 HP electric is equal to 2 HP gasoline or diesel, and I know of at least one conversion that has been worked hard and is going strong on Dad's service truck since 1986 so the rule must work. In your case though it would be better to be safe than sorry, especially if your buying a new engine, and know that you'll have enough UMPH to do what your wanting, and not wind up with an engine that's too small and has to be pulled off and replaced with a second, larger engine. The price difference between say a 18 HP and a 24HP plus isn't that great, especially when you compare it to the cost of two engines....... Hope this helps, and Good luck.
Good explination here

Wayne
I agree with everything you said except the close coupler.
I think he would have a problem with vibration using a coupler.
I would think the best way to go would be belt drive a heavy
fly wheel, something around a hundred pounds or so.
The fly wheel would allow for the use of a smaller engine and
would help with the load from hard spots in the wood.
If the fly wheel was set up on a Jack shaft he would be
able to fine tune the speed and eliminate all vibration from
the engine.

Scott

My dad once had a large HEAVY planer (I think it may have been a 24") that had been converted by amish to a gas engine. It had a twin cylinder 18 horse.

I have a friend than has a big sawmill operation, went all electric a few years ago, told me about 2-1 ratio. Also a flyweel would only help for the first foot of the board, what about the rest of it?

Thank you all for the advice. I forgot to say in the original posting that the planer has a separate 110v motor that runs the rollers and has a variable feed rate of 0-16 fpm. I am thinking that that would make it possible to reduce the load on the engine when planing wide boards or tough spots, but I am not totally clear how it works till I get the planer tomorrow. I've got a lot of useful advice to ponder now, thanks very much.
Zach

Maybe find a generator that will handle the load.
Then your feed motors will operate as they are designed to operate.

Hello Zachary Hoyt,
Multiply kilowatts by 1.341 to obtain H.P.
50% more H.P. for start up load, and you
should have all the power you need.
Guido.

Thank you very much, that formula helps a lot. According to my calculations 23 amps x 240 volts = 5.52 kw x 1.341 =7.40 HP, so I would need an 11 hp engine to equal the electric motor. Now I can start looking for an engine.
Zach

Yes, it is true that 5.52 KW equals 7.40 HP however, that assumes 100% efficiency, which is not true. If we use 80% for the motor efficiency we get 5.92 HP; the rest of the electricity goes to waste heat. Since your motor is listed as 5 HP the 5.92 number would suggest a SF (service factor of 1.2) for a short term overload condition.

Including the SF for your motor we need to find a gasoline engine which has 6 HP at 3450 RPM at its rated (not maximum output) output. This engine should be equivalent to your current electric motor.

HP = [Torque x RPM] divided by 5252 and we want to solve for torque. Therefore we have, Torque = [6 x 5252] divide by 3450 = 9.1 ft-lbs. Now, we can look at engine performance curves for a engine that makes approximately 9.1 ft-lbs torque at its rated output.

I have performance curves for Kawasaki engine so I will use Kawasaki egines for an example.

Case I: Kawasaki Model FE170D - 5.5 HP at 3600 RPM, maximum output. This engine has 8.0 ft-lbs torque at its maximum output so there is no point in looking at the rated output torque.

Case II: Kawasaki Model FE250D - 8.0 HP at 3600 RPM, maximum output. Checking the "recommended" maximum output (rated output) performance curve at 3450 RPM, I read 6.6 HP which calculates to a torque output of 10.0 ft-lbs. Therefore, this engine should replace your current electric motor when run at 3450 RPM and using the current pulley size.

This engine is a single cylinder, air cooled, horizonal shaft and runs on gasoline. Kawasaki also makes similar engines in 9.5, 11.5 and 13 HP versions. The point of this reply is not so much as to dictate this is the size engine you must purchase but rather to show the sizing method. Using a larger engine simply means it will not have to work as hard and provides for additional over load capacity. Finally, I used Kawasaki because I have the data, there are many other engine manufactures to choose from.

Hope this helps.

This 1HP electric = 2HP gasoline has came about because electric motors are expensive and they are minimal sized. With the knowledge that a 5HP electric may see an average of 5 to 6 HP.
That 5HP electric motor maybe making 10HP at times, then down to 2HP. That is why the typical electric to gasoline swap make it appear that 5HP electric = 10HP gasoline.

Russ
Can you elaborate on how a flywheel would only help for the first foot of the board?
Flywheels have been in use since 1038 and are still used to this day for just the problem Zachary would have using an ICE on his planer.

Below is a link that will explain how and why flywheels work.

The ironworker in my shop has a flywheel, the buzz saw in my yard has a flywheel, one is electric powered and one has a hit and miss engine. Their both there to store energy and maintain rotational speed.

Scott
Flywheel

Would it cost less to run wire to the building.Ive run a 12 planer for many years and would not want a gas engine running near the planer,The fire hazard from dry planer dust and shavings is high.A 10 hp gas engine will cost a lot.You also have exhaust gas to deal with.

(reply to post at 22:07:22 10/28/11)

Click to expand...

Flywheels only store/release energy and do not add to the power or torque of an ICE or electric motor on a steady state basis. Therefore, a flywheel is most effective for intermittent loads. You provided two examples of applications for a flywheel, a buzz saw and ironworker, both are intermittent loads. A buzz saw making intermittent cuts throught 10 inch diameter logs can make good use of a flywheel. Conversely a flywheel would be ineffective when the same buzz saw is used as a saw mill cutting a sustained load on a 10 foot long log.

Flywheels make a engine/motor "appear" more powerfull on intermittent loads only. In the case of a planer a flywheel would help if only if one were using it on short boards.

Electric motors produce more torque than a gas engine of the same HP rating. To get an idea of engine size vs electric motor, compare power washers. Typically what is powered by a 5hp gas will be 3hp electric.

At the same rpm and the same HP, the toque at rated power will be identical.
What the electric motor has going for it is momentary over load capacity to carry 2-3 times rated load. Loads that would stall a gasser of the same rated HP.