Motor HP to Replace a 10 HP Diesel Drive Engine

Mechanical horsepower - Unit Converter

That is a rather amusing converter..... It equates one mechanical horsepower to 0.7457 watts.

Sir, we tried a 10 Hp, 440V, 3-Phase to drive the hammer mill but the motor tripped when we started to load the limestone at 20% opening of the control damper.F.Y.I.

Your dilema is lack of initial starting torque.

There is no way an "off-the-shelf" 10 HP electrical motor will have the same torque available during initial starting as the 10 HP diesel engine.

Starting a hammer mill requires a lot of torque initially from the prime mover to get the mass of the shaft and hammers rotating.

You need to:

1. Review the torque requirement of the application.

2. If the motor you currently have on hand meets the torque requirement, you need to review the manufacturer's motor overload protection allowance settings and adjust the time delay curve to maximum allowed. (Normally 125% of LRA x time allowed.)

2. If your existing motor does not meet the torque requirement: Select the proper electrial motor that has the correct torque curve to meet the demand of your load. (Maximum torque required at start during locked-rotor status with torgue decreasing exponentially as rotational speed increases.)

It might be in your best interest to consider installing a VFD (if the motor you are using is compatible) so that the torque curve can be manipulated to meet the acceleration and torque requirements.

I didn't test drive it first.

Well, the truth is not a compromise.

Quite right.

It's not that simple. At the worst though, you can take the HP at the speed of the engine to determine torque, then use the torque and the speed of the electric motor to determine he HP rating of the motor. It's not even that simple because of transmission differences, losses and the fact that electric motors have a different torque - speed step response that favors needing less HP. But doing it this way will err on the side of having more than you need rather than not enough. I've done that many times and it has always ended like that, but can have the unfortunate effect of smoking drive belts if not careful.

Thank you for your comment. Can it possible to install a bigger motor say 25 HP then control the load by using the flow damper of the inlet of the Hammer Mill just to avoid trippings. Is there a need to add the number of belts from existing 3 pcs.? Pls. comment from your experience sir!

I've had the experience that you can get away with an electric motor of LESS hp than the nominal rating of the diesel engine. The only exception I can think of here is if you are replacing an ancient diesel engine that might have had a very conservative HP rating. This might be seen in a pre-WWII one cylinder diesel or the like.

However, you need to be careful that you keep a few things in mind:

1. Ensure that the normal operating speed of the load when driven by the diesel engine is the same as when you have converted to the electric motor. You may have to deal with a different drive to do this--a gearbox, belts and sheaves, etc. You cannot use a variable frequency drive to alter the motor speed in lieu of a gearbox because the VFD may not be able to operate the motor at the full output at the desired speed.

2. Ensure that the fusing and overloads on the motor are not set conservatively...some electrical guys like to put in fuses that barely will allow a motor to run, let alone put out full hp or even 110% hp (that you may need momentarily). This is especially true if your load takes a lot of torque to get started. The motor will handle it but you may see nuisance trips if the overloads heat up too much at startup. The true test of this is to see if your motor is getting hot while running the load. Most motor nameplates will tell you what they are rated at for in temperature rise--it is usually +40C over ambient. That is pretty hot, so you can push your motor quite a bit, as long as you are keeping an eye on it. Most standard 3 phase motors can put out 150+% of their nameplate HP for short periods of time. They just heat up faster.

Hope this helps!

Jon.

Thank you, we are using a Yanmar Diesel Engine. Maybe I will refer to the supplier/manufacturer of our existing Hammer mill maybe they have units with same model driven by Electric Motors.

What a good idea.

Write to a reputed motor manufacturer and ask them to recommend a suitable motor/starter to match your machine characteristics.

<...Write to...>

Why not telephone instead, and cut out the response delays?

Yes, Sir well taken because engines have their own flywheel. we need to determine the ratio of the diameter for Hammer mill Pulley vs. of the motor to maintain same torque. Thank you.

Make that call [#14↑].

I have read all the good replies ( all good) depending on finances you may consider adding a flywheel and a mag drive this will absorb shock waves and is speed adjustable as well as perform a very gentle start up. You will also save some energy as the motor will run at most efficient speed.

Stick with the 10hp 3ph motor.

Fit a star/Delta starter box. (Installation by Electricians only)

Adjust Star run timer to allow maximum speed before switchover to Delta.

If need, increase drive pulley size by 10% to 20% to compensate for the faster running electric drive motor

Ummm,

I think on the sheaving, if you want to compensate for the faster motor, you need to DECREASE the driveR sheave size or INCREASE the driveN sheave size.

Decreasing the drive sheave size is usually the less costly alternative, but you may have to consider that a smaller sheave will transmit less hp/belt. If you only have 3 belts now, depending on their size (I'm assuming V-belts) you may have to check out the HP rating of the overall drive. Your industrial supplier can usually do this for you.

If this is an old drive, be aware that sheaves wear out and you probably can transmit even less hp/belt than what the catalog might say!!

Jon.

Thanks!

By the way, how did you start the load with the diesel engine? Did you have some sort of mechanical clutch? Did you start the engine from a dead stop against the load?

Jon.

Yes sir, we engage the clutch as the engine reaches its rated speed. Thanks.

If I understand correctly, the load is not simply an inertial load, but the hammermill will have a very large friction load from the limestone that is pushing through the hopper against the rotor that you are trying to start rotating.

Okay, then...you will have a problem with an electric motor that is only belt-connected to the hammermill. As at least one other poster has suggested, you will need some sort of mechanical means of allowing the electric motor to come up to speed before it sees the load from the hammermill. This could be a torque limiting drive that attaches to the motor shaft. Another consideration might be to empty the hopper before you shut down the hammermill so it can be started under just the inertial load of the rotor.

Here's a link to a typical oil-filled mechanical soft start.

Hope this helps,

Jon.

Sir,Wye start has too low torque to overcome inertia. MAybe it can be applicable when no limestone are at hopper of hammer mill and start loading as the motor attain its rated speed. It is not practical to unload all the limestone every start-up. Thanks

i

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