Electric motor starting

[slowzuki]

'Nother mill Q!

For the mill I am aquiring soon, I can get a 10 hp TEFC single phase electric motor for a good price.  It can run on 208-230 or 460 v but I only have 230 V service.  At 230V it pulls 48 amps.

I have a welding receptacle rated at 50 amps.

The motor will only draw the full amps if it is loaded that high so I could put 40 amp thermal overload protection to prevent it from being a danger to my wiring.

To keep the amps down when starting I can either spend a fortune for a soft starter or I'm thinking about using a 3/4 hp pony motor to start the bigger motor.  If the pony motor can get it almost up to speed it should be fine.

Anyone see any flaws in this thinking?  I tried looking for a pair of 5 hp's but they cost much and weigh more than the single 10 hp.

[Rod]

I am using a 40 amp breaker for my on and off switch on a 10 HP motor and it seems to work fine.

[D._Frederick]

Slow-,

Check the circuit breaker that your 50 Amp welder receptical is on, if it is 50 amps or larger you should not have a problem. Since you are starting the motor on your saw mill without a load, the starting time from start to full rpm is small your breaker will stand the load. Also check the guage of wire from the breaker to the receptical, you should have at least an 8 guage. The biggest problem you will have is not stopping the motor after every cut. You will burn the starting windings out if you start the motor too often.

[Danny_S]

What about starting the motor without bandwheel load and then tensioning the bandwheel belt after?

[ladylake]

Slowzuki
Are you sure it's single phase. I've never heard of a single phase using 460. Far as starting I'd try it and if you pop breakers go with heavyier wire or breakers.

[slowzuki]

Isn't 460v the leg to leg voltage on 600 V 3 phase service?

My welding setup is 40 amp cartridge fuses to 6 gauge running to the garage to the NEMA 50R receptacle.  The heavy wire was incase I replaced the 40's with 60's and replaced the welding receptacle with a subpanel (its 4 wire with one conductor unused)

I'm glad to hear people are running 10 hp on a 50 amp breaker, I was thinking it would pop it.

With the info given, I think I will just provide a declutching mechanism for the bands and skip the pony motor and buy that motor!

Ken

[Stan]

If you have trouble with starting current, you can rig up a capacitor starting arrangement. I get 346v phase to phase on a 600v Y system. 600*(1/1.73) A delta system would be 600 volts phase to phase and 346v phase to ground.  :P

[J_T]

 Sounds like it is 3ph from here  ??? Like 208-240 low voltage or 440 high 3ph

[Stan]

If it is a 3 phase motor, buy it anyway you can use it as a phase shifter.  ;D

[slowzuki]

I picked up the motor and it is single phase.  It came with a contactor for direct starting but has a nice set of instructions for connecting a series / parallel switch.  Somehow this reduces the starting current to 1/4 the direct start method.

Anyone know where one could find a switch like this?  I assume the power factor or output of the motor is terrible when switched for starting then improves when switched to normal.

Ken

[Buzz-sawyer]

Hey Ken ...I was not suprised you deciced to use zuki parts for milling!!!
Sounds like a really good design to me.
On the motor starting, the key is higher voltage, means lower amperage....so switching to the higher voltage option to start  will greatly reduce the amp load....so a simple switch will do it

[D._Frederick]

Slow-,

I think what you have is a starter for 3 phase, some 3phase motors can be started on Y connections which reduces current and then switched to run on a delta connection which increases current.

You can get electonic control soft starters for single phase motors, but they cost more than the motor.

[slowzuki]

D. Frederick, I thought they were talking 3 phase too but the wiring you talk about is detailed in the next section of the owners manual under the 3-phase section.

I'll open up the wiring box to see and maybe scan in the diagram from the manual.
Ken

[slowzuki]

Ok heres the skinny:

The motor is wound so by a simple rewiring, it can be run as single phase on the following voltages:

With the windings in parallel, 200 - 220 V
With the windings in Series, 400 - 440 V

The motor basically has 2 motors wound inside of it.

You can temporarily connect it in series so you are running a 400 V motor on 200 V giving a reduced voltage start up.  The 2 sets of windings are higher resistance so the current flow is less.

Once it is turning you switch it back to normal.

I think I like this!  Theoretically you could run it on only one winding and have a bit less than 5 hp motor, I suspect all the unused windings would bugger up the power output though.

[donald_harby]

I teach industrial motors and controls at a technical college and have worked with industrial motors for years.  Induction motors will generally pull about 1.5 to 3 times there rated current for a very short time during start up.  On large motors the voltage is sometimes reduced to lower the current.  You could do this by wireing it for high voltage then switching to low voltage once it is upto speed.  On most controllers the voltage is switch when the motor gets to about 75% of rated speed.  You could make a very simple reduced voltage starter using a couple of relays and a time delay relay.      

[Rod]

I just used a 40 amp breaker in a box and used that as my on and off switch,cost $28

[D._Frederick]

Slow-,

ON the 10 hp single phase motors I looked at, GE and Baldor, they only had the 220 volt windings. I have a 5 hp single phase Baldor that I wanted to run on a 6KW generator and it has both 220 and 110 volt windings, so I wired it up with a switch to start, using 110 and then running on 220. It worked OK with very light loads like a fan.

[slowzuki]

D.F. you're absolutely correct! The manual warns against loading too much when starting.  I was looking in my friends electrical wiring text and it shows the torque curve is cut by lot.

I will use the pulley clutch.

Rod, I'm glad it works off the 40 amp breaker, I'm more concerned for the future if I'm running off a gen-set.  I don't want to have to way oversize the generator just for starting.
Ken

[chisel]

You can get electonic control soft starters for single phase motors, but they cost more than the motor.

Is an "electronic control soft starter" different than a magnetic starter? I found a cheap 10hp motor for the bandmill I'm building, but it may not be worthwhile if "they cost more than the motor."

[D._Frederick]

Chisel,

AN electonic soft start is not a magnetic switch, it works by generating an output voltage to the motor that reduces the frequency and the voltage amplitude, then slowly increasing them to normal as the motor rpm increasess.

If you have minimum of a 50 amp service to a 10 hp single phase motor, you should be able to start it directly with line voltage.

[ruffusca]

Hi Ken,
We meet again.
The band mill won't have much starting load unless you're using incredibly heavy wheeels. I'd try going without a clutch if possible, one more thing to build and one more thing to give trouble.
My 20 inch band saw runs the same blade as a mill when re-sawing. It has heavy cast wheels and starts with a 2 hp motor on a 20 amp breaker with no trouble. The shaper made me switch to the 20 amp breaker. With a heavy cutter it would trip the breaker when spinning up but the band saw never does
Greg.

[chisel]

Chisel,

AN electonic soft start is not a magnetic switch, it works by generating an output voltage to the motor that reduces the frequency and the voltage amplitude, then slowly increasing them to normal as the motor rpm increasess.

If you have minimum of a 50 amp service to a 10 hp single phase motor, you should be able to start it directly with line voltage.

Thanks for the explanation. It's very clear to me now. Ok, I can start a 10hp 1ph motor with 50 amp service, but if I want to start/stop the motor after every board is cut, I would need the soft-start, correct? Or else I would burn up the motor?

Does the soft start take longer to start a motor?

The elec. motor seems like a lot of hassle vs. gas, but I like QUIET!

(sorry, quiet)  ;D

[D._Frederick]

Chisel,

A 10 hp motor starting on full line voltage turning band wheels will be up to full speed in less than a second. A soft start is programable, depending on make, I didn't look it up but would think it would be under 5 seconds max.

An induction motor has a limit of how many starts an hour it can have. A single phase is more limited than a 3  phase because of the starting winding an phase shift capacitors.

If you are building a mill, keep the band wheel diameter 24 inches and larger so that you will not have to stop the blade after every cut. On my mill with 19 inch wheels, I have pulley system to tension the drive belt that I use as a clutch.

Tell me about gas engines-fowled spark plugs , dirty carburator, water in the gas, lot of noice. The 10 hp motor will work the pants off of a 25 hp gas.

[Bruce_A]

Gasoline and clutches are for lazy sawyers or old folks.  Electricity is for rock and roll.

[chisel]

D_Frederick,
Thanks for your very informative replies. This forum is great!  8)