I need some help undersatanding 3 phase motors

[KeepItSimpleStupid]

I mentioned High Delta, because I thought April did.

3 phase anything REQUIRES a motor starter. Plan and simple. NO iffs about it. They can be electronic or the goofy things with the thermal overloads.

We would always put in something like this: https://www.grainger.com/Grainger/SQUARE-D-Combo-Motor-Starter-1H691?Pid=search It may not be appropriate for you because of the 120 control windings. Usually they contain a transformer to create the 120 VAC in the US.

I'm having a hard time finding a solid state motor starter. Anyway, the boxes above usually contain a disconnect, a transformer (to get the low 120 VAC control windings, 24 VAC might be common in au), A contactor with a thermal overload. An electronic version is only based on Full Load Amps and can be changed via a potentiometer.

A thermal switch is present in expensive motors which is a good place to put them.

There is a fuse for each phase and a fuse for the control voltage.

The disconnect is for safety.

The transformer gets a lower control voltage.

The Thermal/Overload relay is a contactor with an AUX contact. The AUX contact is normally used to give you a Start/Stop pushbutton and disengage with power failure.

We always added another switch that said ON/OFF/Dropout. There is a term called "HAND" that I'm not familiar with.

IF ON, the unit would stay on after a power failure. IF OFF, it would be OFF. If Dropout, then the system would turn off with a power failure.

With critical loads we would add a Three phase Protector. This device would protect against phase imbalance, reverse phase and would have both trip and start-up delays.

So, your risk depends on what it would cost to replace or repair and down time. When a pump cost $5,000 USD which is about the same as AUD $ or when the machine costa bout $15,000-$20,000 dollars and provides infrastructure to three other machines and the machine cannot be moved or shipped, it makes sense to invest in the full protection.

Management never sees the benefit, because it silently does it's thing. The utility company can drop a phase or the phase can get connected wrong. This can be very disastrous to certain equipment such as a compressor.

 

[april]

God help us. What bloody next? You are off in the dreamtime KISS.

 

[april]

That was a grilling?

For your motor I would start with a pair of 30 - 40 uf run capacitors and any starting capacitor between 250 and 400 uf. Relating to a starting relay I would suggest this one. **broken link removed**
It's in the same number range of the ones I use plus they are rather easy to take apart and fine tune if needed. Thanks I have a better idea of exactly what it does now.

I am not sure how you figure you only get a short time to measure things being that if the motor is up to speed it should be able to run that way for whatever time rating it has. If it does not come up to speed immediately I was worried there is not much time to measure before it burns something .but the push button seems like the best approach for me to start and see what happens on startup.

Relating to the voltage sensing relay for automatic starting as with my posts in the converter thread say most any voltage sensing relay will work being that internally they usually have some type of adjustments to raise or lower their pullin voltage point.

If you don't have a VSR you can just use a heavy duty normally open push button switch and use that as a manual starter. Turn the power on while holding the start button down then release the start button once the motor is up to speed.

As far as protecting your motor from future burnout from overloading I would suggest not using any power circuit over 20 amps. If you are still unsure then drop back to a 15 amp circuit until you have gained confidence in your setup. This is around what I have and it burnt out the single phase 2 1/2 hp so thats why I was cautious

My old backup air compressor is a 5 HP commercial unit with a stock 3 ph motor and that has been in service for over 10 years and has yet to ever cook a motor simply due to it having a 20 amp circuit. The breaker trips log before the motor ever has a chance to get too hot if it ever has problems getting up to speed in time.

Thanks tcmtech for that help I'm assembling the parts now and will post again when I see what happens. I mistook you for tvtech and thats what the red was about.

 

[tcmtech]

If you are there tcmtech , do you have any suggestions as to how to box up your device with safety in mind . You did not answer my question on the a/c potential relay.. I was looking to find one on Ebay and get a couple.

Here is what I typically use for for a box on converters up to around 7.5 Hp.

https://www.menards.com/main/electr.../6-x-6-x-4-pvc-enclosure/p-1716050-c-6424.htm If you dont have a Menards Home supply store most any bigger hardware chain store caries them as well. They are in the electrical section with the PVC conduit stuff most often.

They are a heavy PVC plastic which is easy to cut and drill plus all the components can be easily placed inside and secured with common RTV silicon.

I usually mount this right to the side of the motor where the original junction box for the wiring went.

 

[dr pepper]

You can use capacitors to run little 3 phase motors up to 370w 1/2hp on single phase 240v, you reconfigure the motor to delta config and put the cap from v to w on the terminal block, I've a couple of fans like this they've been running for years.
However for the size your talking as mentioned you'd have to use a drive, and even then you'd truggle to find one single phase in at that power.
Could you downrate the motor a little and fit a single phase motor?, you'd have to take sawing easier with less power.

 

[kinarfi]

After following and reading this thread, I feel I need to maybe apologize, go back and delete or change some of my posts, I'm still not sure about the use of delta for low voltage and WYE for high voltage, never seen done that way.
I've been an electrician for over 30 years with electronics back ground and worked as just about everything from residential to oil field to maintenance. In the oil field I had to do some strange things like tie to generators together manually to get a large motor started and then drop out the smaller generator after the motor was running and use #12 copper wire as a 200 amp fuse link in an REN fuse. I worked with roto phase, but didn't realize that it was the Miller system.
April, If I were to build what you need, this is how I would do it, assuming you working on your own house and when done, the saw more or less goes back into storage, If you're a contractor I would upgrade to voltage or current sensor relay to cut out the start capacitor and use a 3 phase starter switch in a NEMA 4 or better enclosure since brick cutting usually uses water.
I thought I posted this, this morning, but when I went back, it wasn't there.

 

[april]

You posted it twice -here and on tcmtech's Miller system thread -see comments there

 

[april]

You can use capacitors to run little 3 phase motors up to 370w 1/2hp on single phase 240v, you reconfigure the motor to delta config and put the cap from v to w on the terminal block, I've a couple of fans like this they've been running for years.
However for the size your talking as mentioned you'd have to use a drive, and even then you'd truggle to find one single phase in at that power.
Could you downrate the motor a little and fit a single phase motor?, you'd have to take sawing easier with less power.

Hmm - almost in direct disagreement except for small motors. Have you looked at tcmtech's thread on the Miller system? I don't understand what you mean by the underlined words could you explain. have you done this? I'm looking at doing it on a 6 HP motor actually.

If you look back a bit further dr-p you will see I connected a 2 1/2 HP motor but it was too much for it . I got it apart and the starter centrifuge was a little sticky and I suspect that pretty well wrote the motor off. Still runs but no power and gets hot so I think now I have burnt out one of the windings in it. When it ran properly though it did cut OK if I did not labour it but the load just free spinning was a bit too much I think.

I have found a 3 HP on Ebay for about $260 delivered and am considering getting this too , but I would also like to build and try tcmtech's system just to see.

I acid etched the placard and got some more info off it. Its 4.6Kw so 6.2 HP and is probably worth a thousand dollars or so ,so I'm concerned that I make a valid choice if I am going to attempt to run it. tcmtech thinks his Miller system will work well . Having some trouble getting big enough run capacitors. 60uF or so
Local electrician here wanted $1 per uF. $110 for 3 caps 50uF,30uF,20uF. They were second hand I think , saved from motors. Could barely see the markings. Geez they want to bleed you these days.

 

[tcmtech]

If you are having trouble finding the running capacitors just look online for air conditioner capacitors and power factor correction and the like. They are pretty common up to around 120 UF 370 VAC. I have bought them for around $11 a piece on eBay a number of times.

Here is a good place for surplus stuff. They have loads of motor run and motor start caps too! https://www.surpluscenter.com/

Local electricians are the worst guys to buy parts from. They are by trade a bunch of greedy weasels.

FWIW surplus center charges $6.29 for a new 60 uF 370 VAC motor run cap and a 105 -125 uf 250 VAC motor start cap is $2.99 each.

Relating to motor start capacitors there are two ways you can get the total capacitance you need.
You can either go with 250 - 300 VAC units in parallel or go with 125 - 150 VAC units in series however with the lower voltage units if you put two 125 VAC 1000 uF in series what you end up with is a 250 VAC 500 uF in circuit.

As a last resort you can also use a pair of DC electrolytic capacitors in reverse series connection to make a big motor start capacitor. I have been using a pair of 450 VDC 2700 uf electrolytics as the motor start capacitors for my 15 HP industrial air compressor for at least three years now without problems. I have them configured in reverse series + to + with the -'s as the input and output. The work out to the equivalent of being a single 450 VAC 1350 uf motor start capacitor. BTW at startup in the winter they can see as much as 130 amps going through them for up to around 10 seconds while the compressor gets up to speed.

BTW your estimate of your motor being worth around $1000 or so is way off. Used three phase motors sell for around $5 - $10 a HP in good working condition. I occasionally buy used ones in mixed lots of a ton or two at at time for around $1 - $2 a HP at commercial auctions just to scrap them out for the copper, iron, and aluminum.

 

[tcmtech]

I see you now say your motor is a 4.6 KW not 4.6 HP so you may need to go up a bit on your capacitance and the odds are you will be needing a 20 - 30 amp circuit to run it not a 15.

Now relating to the dual voltage argument here everyone is both right.

In some parts of the world 220/380 is a normal input for many motors with six leads working on 240/415 VAC systems yes they just change the the winding configuration from delta to wye to change the voltage.

Now in the US and other places that use 120/240 single phase or 120/208, 120/208/240, or 277/480 volt three phase power most motors have 9 leads and use two independent sets of Wye windings that are switched between series for 415 - 480 VAC or parallel for 208 - 240 VAC input.
However there are a number of specialty application motors that can have 12 and occasionally 18 leads that can be configured for multiple voltages and or winding configurations depending on the demands of starting torque, running torque, efficiency, or speed using either Delta, Wye, or mixed combinations of both configurations.

 

[april]

Crikey I want to come live where you are.
Those parts are cheap!

 

[tcmtech]

Well if you would fill in your info under your avatar pic we would know where you live and be able to make suggestions from that.

Surplus Center ships worldwide so there is no real reason not to buy from them.

 

[KeepItSimpleStupid]

God help us. What bloody next? You are off in the dreamtime KISS.

Management acted rectively, as usual, when the utility dropped a phase on us. Lots of damage. Most of the damage was cinfined to exhaust fans. An easy fix. Three pieces of equipment were out of service for a MONTH because of a compressor based liquid Nitrogen replacement system. Research nearly Halted. Nearly everyone used one of the pieces of equipment that it served.

 

[KeepItSimpleStupid]

A blurb on Wye Delta Starters: https://www.electro-tech-online.com/custompdfs/2013/04/50006-026-01E.pdf

 

[april]

I've placed an order, got all those capacitors and more for under a hundred bucks -wow, Thanks for the link
EDIT - They slugged me $75 for postage on top.

Here any order for any motor is always a Grand . They have had it that way for as long as I have seen but all changing now . The postal systems will have to take the load.

Found another 2 HP single phase I was going to try cause its old and twice the size of the other . Tried to start it and the thing blew the breaker on a 25A supply . Got to check out the wiring again to make sure its not shorted somewhere. I know its too small for this but I may as well clean it up and get it going while I'm tuned in.

 

[april]

Hmm so here is my order and its been shipped from the States already - $75 postage whichever way they sent it so I chose priority.

Got a 3 HP single phase on the way via EBay. This will probably run it and I have to get something going quick. $263 delivered
I want to try tcmtechs Miller system as well so that will be a longer wait.

Just as an aside , The rural power supply I am working with is actually 2 phase I think. Three wires in, one of which is earthed.
I was wondering what is the phase difference likely to be between them (180 seems logical) and could a Miller system be altered to run the three phase motor from this supply using both phases somehow ?

        QTY    ITEM                      DESCRIPTION                             AMOUNT
        *******************************************************************************

             3 28-1783-V            FUEL SHUT OFF VALVE FOR 28-1783-R & 28-17     11.97
             2 22-1225              25 / 5 MFD 370 VAC OVAL DUAL RATED RUN CA      9.98
             2 22-1227              30 / 10 MFD 370 VAC ROUND DUAL RATED RUN      10.58
             2 22-1231              40 / 4 MFD 440 VAC ROUND DUAL RATED RUN C     10.98
             2 22-1321              60 MFD 370 VAC MOTOR RUN CAPACITOR            12.58
             2 22-1217              45 MFD 440 VAC ROUND RUN CAPACITOR            13.98
             3 11-2397              SPST ON/OFF PUSHBUTTON SWITCH                  4.47
             2 22-1322              59-70 MFD 250 VAC MOTOR START CAPACITOR        5.98
             4 22-1324              105-126 MFD 250 VAC MOTOR START CAPACITOR     11.96
                                                                             **********
                                                                      PRODUCT     92.48
                                                                          TAX      0.00
                                                           POSTAGE & HANDLING     75.45
                                                                             **********
                                                                     TOTAL $     167.93

.

 

[tcmtech]

They don't really care what the source power configuration is just as long as the voltage is in the right range for the motor.

Around here our power is the three wire 120 - 0 -120 where you get 240 across the two 120 lines. It may have two line but its still single phase power.

 

[april]

Yes I'll have to look further in to that because this is 240V on either phase so if one is negative then perhaps I can get 415V ?

I was looking for another use for all those capacitors

 

[april]

Well the moment of truth has arrived. Big box of capacitors arrived today ( Isn't that brilliant service and quick) and its all wired up .Just have to get a suitable cord to connect up the single phase. Just a last check of my first try setup

Motor is in star (wye) configuration -see first post for photo of connections.
2 run capacitors of 46 uf each
1 start capacitor of 460uf with 1 pushbutton
Single phase line in is 240 V - 2 lines ,active and neutral.
Earthed all through

If there is anything wrong here shout out now
Fingers crossed...

Oh and I got a 3hp single phase motor and its up and running the saw now so the above is just to see for myself.

 

[april]

Well . Thats what I call marvelous.
Thank you very very much tcmtech for that very enlightening and useful piece of information.I know it will definately come in handy here.

I kicked it off with the above configuration and with a supply voltage of 236 Volts I had approximately 430 Volts on one line and 206 on the other while the motor was running. I noticed for the brief period before I cut the start capacitor circuit the motor seemed faster and stronger.

I changed the high line run capacitor to 10uF and was able to get a balance on both lines of about 235 V. Is this what I should be looking for ?

I'm very pleased with this and will post a confirming message on your thread for others that may wish to use this method.
At this point I cannot test it with a load for a week or two as the pulley is in use on the single phase motor.

There was no overheating that I could detect but when I get it set up with a load I will put a temperature gun on various parts of it to check.

Thanks again.