Thread: Does this 3hp motor require a starter?

If it was mine I would include a starter like the one you have linked to (Electrician Supplies). If you wanted an extra E-stop somewhere else on the machine, a starter makes it easy to connect.

No, this can be started happily without a starter.

It could be as simple as a switch like on the dust extractor
but a DOL starter like on the existing 3ph motor is a much better option for the new motor, gives you options to remote stop/start/estop with thermal overload for motor protection plus the no start after a power failure, a starter of the right size will do either 3ph or single ph with the appropriate wiring change


Pete

Hi Stinky.

I was looking for (3 phase) starting options for my old 50s/whatever thicknesser last year. It originally had a Nilsen manual change-over star-delta starter which basically managed what your motor does automatically - start off with a low-draw arrangement to get the motor started then change to a higher-drawing running mode.

I went to the local Laurence & Hanson and merrily asked about star-delta starters ... and choked at the $1000/$2000 price range

The simpler magnetic starting "box" was quoted at around the $150-$250 mark, which I was resigned to until I saw it was much larger than I had on my other machines. This turned out to be one with replaceable components inside the box, but there was a significantly smaller "box" - the size I was expecting - rated at the 8/10amps I had worked out the motor needed - for $40 or $50 or thereabouts. It didn't have replaceable components, but it was the right size and the right price and is a good unit. (Again this is for 3 phase starting)

One hiccup. It worked great on the thicknesser - excepting only one thing. I had worked out the running current needed - but not taken into account the starting current.
The thicknesser would start to wind up for 4 or 5 seconds then ... click. "What the ??" quickly followed by "Doh - you idiot"

So the starter went onto the hollow-chisel morticer (which only had a 3 phase plug) and works great, and for the moment I just use a simple 3-phase switch on the thicknesser which starts and runs no problem at all.

Definitely go for the mag start - it shouldn't be expensive for single phase - and you get the safety of the magnetic off and current protection - just make sure you allow enough current draw to get your machine started

Cheers,
Paul McGee

G'Day Stinky,
A 2.2kW single phase motor will draw around 14.3 amps while running. This is not huge and won't cause any undue stress on the system. Starting however is another matter. The motor can draw in excess of 60 amps while starting. While this draw is momentary and a normal switch may cope ok for a while it will eventually fail. This is why we have starters. Motor starters either reduce the starting current or are built to handle it. The DOL (Direct On Line) starter you listed will do the job and it is an excellent price. It is a 3 phase starter with a 240V coil on the contactor. These can be used for single phase with a little bit of rewiring as Pete mentioned.

Originally Posted by NCArcher

G'Day Stinky,
A 2.2kW single phase motor will draw around 14.3 amps while running. This is not huge and won't cause any undue stress on the system. Starting however is another matter. The motor can draw in excess of 60 amps while starting.

14.3 A?? you might be getting your instantaneous current confused with your RMS current ?
The 2.2kW rating will almost certainly be an RMS power so by my reckoning ; 2.2kW/240V = about 9A.

My TS is supposedly rated at 2.2 kW and I routinely have a current meter connected to it. Free running it draws about 5 A. It draws 8 A ripping 50 mm pine with a moderate feed rate. Crosscutting 50 mm Jarrah it draws around 10 A and above 12 A it sounds like it is really working hard and I don't like to have it under this sort of load for more than a few seconds. BTW I have had it all the way up to 17.5 A before it tripped the breaker. When starting I have never seen it draw more than 35A but I agree it could be as high a 60A for a fraction of a second.

Originally Posted by BobL

14.3 A?? you might be getting your instantaneous current confused with your RMS current ?
The 2.2kW rating will almost certainly be an RMS power so by my reckoning ; 2.2kW/240V = about 9A.

Hi Bob,
If you have a power factor of 1 and efficiency of 100% your FLA (full load amps) may be around 9 but i'm pretty sure you don't have either of those especially with an inductive load. Although it may never run at 14.3 amps that is what you have to allow for.
Edit: from the catalogue its 13.67A but that assumes a PF of 0.95.

Originally Posted by NCArcher

Hi Bob,
If you have a power factor of 1 and efficiency of 100% your FLA (full load amps) may be around 9 but i'm pretty sure you don't have either of those especially with an inductive load. Although it may never run at 14.3 amps that is what you have to allow for.
Edit: from the catalogue its 13.67A but that assumes a PF of 0.95.

Agreed, which is probably why they recommend a 15A breaker ?

I had previously considered that "starters" were only required for 3ph motors and particularly this was where the star/delta connection had it's part to play.

However, it appears that "starters" can be useful for single phase motors too judging from the foregoing comments. I had assumed that the addition of capacitor starts (and in some cases capacitor run) was to permit the high starting currents that occur with induction motors.

Early 1ph induction motors did not have capacitors and potentially that did pose a problem, although I suspect that because we had fuses, which have an inherent time delay, high current draw at startup was tolerated: More so than with our modern circuit breakers.

Perhaps the experts can explain whether there is any relevance to my comments.

Just as an aside with 3ph motors I was originally taught that starting current can be typically 4 to 7 times that of the running current. Whilst something similar occurs with 1ph motors my impression is that although it may not be so high it persists for longer.

I make that statement from having watched 1ph and 3ph bench grinders of the same HP starting side by side.

Regards
Paul

Originally Posted by BobL

Agreed, which is probably why they recommend a 15A breaker ?

Yep.

Originally Posted by Bushmiller

Early 1ph induction motors did not have capacitors and potentially that did pose a problem, although I suspect that because we had fuses, which have an inherent time delay, high current draw at startup was tolerated: More so than with our modern circuit breakers.

Regards
Paul

Paul, fuse wire can have a slower rupturing time and it is possible to get "slow blow" cartridges for HRC type fuses. If you have a highly loaded piece of equipment that occasionally trips the breaker on startup you can replace the breaker with a 'D' curve circuit breaker that is designed for motor circuits. It will allow a high inrush or starting current but still provide protection at the rated amperage.
The start capacitor on a single phase motor is there to get the motor turning. It makes one winding lag the other so the magnetic fields effectively push against each other to provide the rotational movement. If your start cap fails the motor will just sit there and hum. The run capacitor found on some motors is for higher torque applications where the start winding isn't switched out when up to speed.

Thanks all.

It looks like the starter may be the way to go and the price at Electrical Supplies seems very reasonable compared to what I have found to be a similar thing from Clipsal ($300+). Thanks to whoever on the forum posted their detail on another tread.

Given that the new motor is single phase is the 5.5KW 240V Control from http://electriciansupplies.com.au the one to go for?

As per their details how do I know how many amps I will need for the overload?

Sorry to ask so many questions but it really isn't my strong point. And for those wondering I will not be wiring it myself. My father in law was an electrician in the navy so I will have him look at it for me and if he cant do it I will go to my electrician. Past experience has told me Stinky and electrics dont mix

Originally Posted by Sir Stinkalot

Given that the new motor is single phase is the 5.5KW 240V Control from http://electriciansupplies.com.au the one to go for?
Yep that's the one.

As per their details how do I know how many amps I will need for the overload?
They are adjustable and come in ranges, for instance 7.2 amps to 15.5 amps. I can't remember the standard ranges but just ask for 13.67Amps.

They can also come as a set value and you adjust the dial as a multiplier. i.e. a 10 amp O/L adjust the dial to 1.2 for 12 amps or 1.5 for 15 amps. Too much information. just ask for 13.67 amps.

Thanks NCArcher ......

To throw another one into the mix thanks to another supplier I found on the renovation forums:

Direct Online Starter 18Amp 240V Coil - DOLSTART/D18 Sparky Direct - Online Electrical Wholesaler- Electrical Accessories

Would this fit the bill or should I just go the 12amp version?

Just out of interest does the DOL trip protecting the motor if the current draw exceeds 18amp?

Cheers

Stinky.

You need the 18Amp version. The amp rating on those ones is the maximum setting on the thermal O/L. Still a great price for a starter.
The circuit breaker protects against an instantaneous high current spike, like a short circuit, the thermal overload protects against continuous draw of higher than rated current. If you motor is labouring, say from a colapsed bearing, it will still try and turn at the same speed but will require more and more current to maintain the speed. Additional current will overheat the motor windings and without the thermal overload protection the insulation would eventually break down and the motor would 'burn out'.