Question re 3 Phase.

[Shedhand]

Can a sparky help me with some info please.
I have a 17 year old carbatac 12" table saw.
it has a single phase, 2hp motor drawing 11 Amps at max 2850 RPM. The motor has an overload switch which is so sensitive it trips even when ripping radiata pine.
I mostly work with hardwood from bull oak to red gum. So it takes ages to rip, say, a 600mm length.
I had 3 phase connected to my shed last year to run my big dusty. I had a lot of 3 Phase cable and switch gear laying around so it wasnt very expensive to do.
i spent today converting the table saw to 3 Phase.
i had an ASEA Motor in as new condition. 4 Hp, drawing 8amps at max 1450 RPM.
I took the old single phase motor off and mounted the 3 Phase motor in its place.
I removed the old single phase rocker on/off switch and all the wiring.
i wired up the motor and connected it to a rotary 3 phase switch to the correct terninals, Earth, L1, L2, L3. I made a cable to run from the 3 phase power point in my dusty shed to the 3 phase rotary switch. Checked everything was tight and right. Switched the saw on and it worked...except the saw runs backwards. 😕
Have I accidently reversed some wires? 🤷♂️
If so where would i hhave stuffed up and can you tell me how to get the saw cutting in the right direction?
thanks
mike.
INDEMNITY.
I accept all responsibilty for my work. No responsiblity or liability on your part for any advice you may provide.
mike gard



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[Bohdan]

Reverse any two of the three active wires.

[Shedhand]

Thanks mate! Do you mean any 2 of 3 (L1, L2, L3) in the switch on the saw? Or the plug end?
cheers
mike

[Bohdan]

Doesn't matter, any two.

[NCArcher]

Switch L1 @ L2 wherever it is easiest to get to.
You should be starting the motor with a 3 phase starter c/w thermal overload. A switch is not a good idea for 4HP.
Something like this
LE1M35U716 | Schneider Electric 4 kW Automatic 3P DOL Starter, 240 V ac, 3 Phase, IP65 | Schneider Electric (http://au.rs-online.com/web/p/dol-star-delta-starters/7447881/)

[BobL]

it has a single phase, 2hp motor drawing 11 Amps at max 2850 RPM. T

i had an ASEA Motor in as new condition. 4 Hp, drawing 8amps at max 1450 RPM.


Err...... no one spotted the difference in RPM?

At that speed that saw wont cut very fast no matter the HP difference..

[Bohdan]

Err...... no one spotted the difference in RPM?

At that speed that saw wont cut very fast no matter the HP difference..



Depends on what he used as a drive pulley. If he used one double the size of the original he is back where he started.

[BobL]

Depends on what he used as a drive pulley. If he used one double the size of the original he is back where he started.

Maybe he did but as he didn't say so in his post I'm still surprised no one said anything about it.

[Shedhand]

Hi Bob, i did wonder about that too but as the pulley is only a tad under twice the size i dont think it'll be an issue. The speed of the cut is less important than the damn saw cutting out all the time. If its too slow I'll just have to pedal faster. 😬 👍
Cheers

[Shedhand]

Thanks Bohdan. Works fine now. If i had 92 bucks to spare...anyway i never run it for more than the time it takes to rip something down. I might only use it a couple of times a week for about 15 - 20 minutes stop start in total.
cheers

[ian]

Sheddie

I think that NC Archer was referring to what happens to your circuit (and possibly the saw as well) every time you start the motor.

If I remember the little bit of Elect Engineering I did correctly, it's not a good idea to run a 3 phase motor in the start-up configuration, nor to start the motor in the run configuration.

[Shedhand]

Thanks for that Ian. I certainly dont want to fry anything! I'll see if i can pick one up off ePay. 👍 Unless one of our fellow forumites comes up with another solution/suggestion. Who'd be an electrician? 🙄

[Shedhand]

I'm looking at one on ePay! 👍

[BobL]

Thanks Bohdan. Works fine now. If i had 92 bucks to spare...anyway i never run it for more than the time it takes to rip something down. I might only use it a couple of times a week for about 15 - 20 minutes stop start in total.

15-20 minutes of ripping bulloak and redgum could still easily overheat a motor, and while its unlikely and hopefully the belt will slip, If the blade gets jammed it will only take about 3 seconds to start cooking the motor. At that point $92 is going to look cheap

[Shedhand]

Arghhh😳 Ok Bob! Point taken. Will put it in mothballs until i can get some spare cash together. Thanks for thewarning.👍

[themage21]

Shedhand,

The thermal protection is the main thing you need for protecting your motor. A 3 phase CB in an enclosure can do that job no worries, although $92 for a start/stop box is pretty competitive when you factor in what your own time is worth.

With rotary switches, well, depending on which one you used, it may not be rated for motor start (and particularly) stop function. Electric motors chuck out a high voltage spike when the current to them is suddenly interrupted, which if the contacts on the switch are not designed with consideration for, leads to premature death of the switch. It's less a safety thing and more a "it'll probably break sooner than you'd like" sort of thing. The DOL box in the link above has a contactor (big a*** relay), which snaps open far faster than a rotary switch will, which minimises damage from on/off cycles. For most larger equipment, it's far preferable to having switches which directly control on/off. It also normally deactivates on loss of mains, which is another important safety feature. Also, once you've got a control box, it's normally trivial to add emergency stop buttons on more convenient locations on the saw.

In the mean time, you should be right to use the saw, but the idea will be that you need to listen to your machine. If it bogs down, pull the work back and give it a break at no load speed before pushing on. If it stalls, stop pushing and/or power immediately. All the commonsense stuff that comes with being the owner of a machine that you plan on being the owner for for a long time.

It also helps your motor if you periodically remove it from the machine and clean it out. Being choked by sawdust is probably a bigger cause of death of woodworking machinery motors than anything else and the most easily avoidable.

You're probably already aware of all of this (to some degree or another), but I'd say it's pointless not using your machine for the sake of a switch. Change your habits to match the design of the machine - it'll make sure that it lasts longer even after you upgrade it later on.

[truckjohn]

It is worth googling up your motor and see if they recommend a separate motor starter. Some small motors dont need one.

chances are - if it starts and runs cool as-is, you are probably Ok. The danger would be if the motor hums and makes all sorts of commotion on startup or runs hot while running.

Switching from a 2hp single phase to 4hp 3 phase most likely resulted in a motor that hardly runs under any load even when sawing.

Now - if its running hot - I would check to make sure your bearings are good, guides are set right, and nothing is binding.

[BobL]

It is worth googling up your motor and see if they recommend a separate motor starter. Some small motors dont need one.
I have never seen a 4HP or even a 3HP and most 2HP 3 Phase motors without a starter.[/QUOTE]

Were not taking peanut currents here.
4HP at about 80% efficiency is around 9+A at 415V. If the blade jams this may cook a motor faster than you can switch it off, given it usually takes an operator a couple of seconds to work out what is going on. My guess is the OPs setup has one belt so hopefully the belt will slip.


Switching from a 2hp single phase to 4hp 3 phase most likely resulted in a motor that hardly runs under any load even when sawing.
Were also not talking about cutting hot butter north american timber here, but stuff that is up there along with some of the harder woods on the planet. These timbers will load up a Table saw very quickly and use every bit of the 4HP. This is almost certainly why the OP was having problems in the first place.

Just to give you an indication my 3HP saw pulls around 12A at 240V to rip aussie hardwood and it is very easy just to push a bit harder and hit 15A. The thermal cut out kicks within seconds if it reaches 17A. At that point that so called 3HP motor is outputting 4.4HP

[ian]

Just to give some perspective for truckjohn

Were not taking peanut currents here.

Just to give you an indication my 3HP saw pulls around 12A at 240V to rip aussie hardwood and it is very easy just to push a bit harder and hit 15A. The thermal cut out kicks within seconds if it reaches 17A. At that point that so called 3HP motor is outputting 4.4HPif this were a single phase US saw, the currents quoted by BobL would be about 24A and 30A on a 120V supply.

[Shedhand]

409854
Saw Model
409855

wiring from switch to motor
409856
switch type
409858
motor specs
409859
the motor.

Unlike the original 2hp single phase, this motor essentially starts at max revs whereas the old one started slow and built up to speed.
The ASEA motor is very quiet running compared to the old one. its mounted on a hinged plate with the weight of the motor provided the tension to the belt drive. there is only a single belt pulley on the arbor.
Comments welcomed.
cheers
Mike

[Bohdan]

With that single belt drive I think that you will have difficulty transmitting the full power of the motor without slipping so if there is a jam rather than the motor burning out immediately you will get a lot of smoke and will need to replace the belt as the burn will leave a bit of the belt narrower and this will cause a lot of vibration in the machine.

[BobL]

Thanks for posting the pics

The most obvious thing I can see is that's not a 4HP motor, that is a 4kW motor! so 5.4HP - even more of a reason to have a proper starter on it.

I agree with Bohdan that the motor won't transmit the power efficiently with one belt.
It also looks like the wrong size belt for the motor pulley, the belt is sitting too far down into the pulley, if the bottom of the belt touches the bottom of the pulley the belt will definitely slip and burn up

I'm not sure about whether put such a big motor on a lightly built machine is a good idea given the 2HP carbatec machine is not exactly a HD machine.
I figure a 50% to 100% increase in most motors should be OK but 5.4HP represents a 170% increase.
Probably OK for occasional use but I doubt the trunion is going to last long term given the amount of torque that motor can generate.
In that case leaving it at 1 belt is probably one way to save it although you should get the right size belt / pulley.

[Bohdan]

Thanks for posting the pics

In that case leaving it at 1 belt is probably one way to save it although you should get the right size belt / pulley.

Your right Bob I think that it is an A belt on a B pulley so the belt will have a real short life.

The A belt pulley groove is 13 mm wide at the top and the B is 17 mm. (or in the old numbers 1/2" and 5/8")

The correct change would need replacing of the pulley in the saw if it is, as I suspect, an A pulley, however you would probably get away with running a B belt on an A pulley unless it slips too much then you need to change the arbour pulley.

I suspect that the pulley on the motor is original and shows that the motor requires two B belts to transmit all of its power so if you were to change the arbour pulley you need to get a double. That however could result in a real monster of a saw.

[Shedhand]

A monster??😲i just took the pulleys off the big motor because they werent closed up properly due to rust and gunk. Cleaned up nicely and the existing belt is no longer so deep. But will get a new reinforced belt. And a replacement pulley for the saw arbor if its too narrow for the new belt. I have about 20kg of sheet lead which ill put under the saw where the frame crossmembers are so the saw doesnt leap about when i start it. Have also contacted my friendly sparky for a second hand switch to suit. My dusty is 5 hp so a start switch like its would be ok I'm assuming. I'm enjoying this exercise - even if it ends up on the scrap yard pile. Will pissibly sell my Gibson Les Paul to buy a new saw. 😉