3PH (that's Phase not Horse Power) from 1PH

[Jaeger_S2k]

I was just looking around, as channel 5's signal was pants and found this, admittedly it's from across the puddle, but .....

From contributor J:
Here is a very simple and crude way to make your very own rotary phase converter for $53.00.

First buy a used three phase motor which typically runs about $10 per hp. Second, go to the hardware store and buy a lawnmower string (seriously!).

Run your single phase power to the motor (2hots and ground). This needs to be a switch or a plug so you can turn the motor on in an instant. Splice the power leads from the machine you want to run into these wires. Connect the third leg from the machine you want to run to the third leg in the motor.

To start your phase converter, wrap the lawnmower string around the shaft of the motor, and pull on it just like you would to start a lawnmower. While the shaft is still turning fast, either plug the motor in or flip the switch.

The motor will run on single phase power. Your lawnmower string took the place of the capacitors that commercial phase converters have wired to the third leg. Somehow, once the motor is running, it generates the power in the third leg.

I know this may sound strange, but it is not very different from your $1400 phase converter. They are nothing more than a typical 3ph motor, a switch, and a capacitor bank wired into the third leg.

I used this setup to run a 7.5hp inverted pin router until I had a shop with three phase. I learned this trick from a guy who had a machine shop in his house. He used this to run his CNC mills and lathes.

From contributor W:
Contributor J, you are 100% correct - your setup *will* run a 3-phase motor. However, there are a couple problems with creating 3 phase this way:

1) Without proper capacitors, the three legs will be *very* unbalanced, both in terms of voltage and current draw, resulting in an uneven load on the machine's motor windings, less than full HP availability, and possibly premature failure of the machine's motor.

2) Without a proper isolating means (disconnect or plugs), circuit protection fusing, and motor running over current protection, don't let your insurance guy or the local inspectors see this arrangement!

I don't recommend that anyone who is not comfortable with electrical codes try to build and install their own converter.

Contributor J is correct in that you can build a 3 phase converter for low cost. The shop I worked in used one for 15 years. What he forgot was that if you wind your rope around the 3 phase motor backwards. your machines will run backwards.

Now having seen what some have down with compressor farms .

Who's had a go at this?

 

[irondarren]

Actually i have a proper 3 phase converter up to 4kw. I do get the felling you might be in breach of part P wire regulations lol. but basically its how it works run a 3 phase motor on single phase to generate the other phases. Mind if you want a small converter 1.5kw they do some neat inverter units that let you mess with the ac frequency, switch the phases to run a motor backwards etc. they arent that expensive.

 

[Jaeger_S2k]

I'll have to have a word with my Electrics Inspector (he's doing inspections 1st fix and 2nd fix of my electrical works on behalf of LBC, no Hitch it's not finished yet) I now sub for him installing electrics, plumbing and gas
Could be interesting over a beer.

 

[madkayaker]

rotary phase converters are old school but work!

 

[Luke]

Yes, they work, but inverters are better but then i would say that

 

[madkayaker]

having fully read the post (I'm awake now) I wouldn't recommend running a motor in this way!

 

[shenion]

You can get cheap static phase converters to start a 3-P motor. Basically just a capacitor and contactor. There are lots of designs floating on the internet. The better ones disconnect the cap when they sense the motor is up to speed.

I have an inverter on my lathe. The inverter and 3P motor were less than $100 off ebay. With an inverter, i can run the motor from 200 to 2000 RPM. Muc easier than changing belts.

3P motors are cheap off ebay as many swap them out for single-phase and then dump them. An inverter can be had for as low as $99 new for small HP. 2 HP for $155.

 

[Jaeger_S2k]

So just to help my brain as it's stumbling over this.
You stick an inverter switch (capable of the HP you need) on the 3PH motor and it plugs/connects to the single phase. This allows a cheaper more efficient 3 PH motor to work.
Is this economical? I'm thinking these 'new' inverters will be intelligent and only draw what they require?

 

[shenion]

Yes, my inverter runs on 110V 1-phase and provides 208V 3-phase. Note, it does not step up the voltage 208 is 3 110V phases.

I have a 1/2HP motor and through the inverter it draws less then 8A under full load. Not real efficient, but only draws as much as it needs.

There are special inverter motors that can run 0.5Hz to 200Hz or more. Mine is a generic 60Hz, 1740 RPM motor. It still runs well from 30 to 90 Hz. Below 30 it has very little torque and above 90 it starts getting inefficient.

A description of the Variable Frequency Drive (VFD or inverter) is on my lathe pages here.

 

[madkayaker]

that's the best method. You will need to check if the motor is duel voltage and will run @ 230V as the cheaper inverters only switch the voltage. The data plate will say 400V and 230V (might say higher and lower than this)

 

[Jaeger_S2k]

That's cool, I'll do some more research on these.

 

[shenion]

Both motors i have can be wired for 208-220 or 400-460. Most seem to be able to be jumpered for dual voltages.

Edit: be sure the inverter will work on single phase. There are many that are 3P in and 3P out. Some will work on 1P in.

Here, below 1HP, they will work on 110V single-phase in, above that they are 220 1P or 208/460 3P.

I was suprised how inexpensive they are. Now that i have one on the lathe, i would not want to be without it. I can flip the fwd/reverse switch and the motor slows down, stops then reverses. Real smart control with all kinds of protection form over loading.

Another note: It will trip my GFCI breaker instantly. Regular motors on inverters will have a bit of capacitive leakage. This fools the GFCI and trips it.

 

[piman]

Hello Shenion,

your American domestic electrical supply is, if I understand correctly, three phase 208\120 volt 60Hz, and the 120 is used for light loads and 208 for the heavier ones such as air conditioning and ranges? I understand that these may still be single phase units however. So is your supply commonly just two phases and neutral or are all three brought into the house. You are probably aware that our supply is twice your voltage so most houses only have a single phase brought in, i.e. 240V?

For me, for single units an electronic 1ph to 3ph inverter is the way to go, modern ones are so sophisticated and incorporate so many advantages particularly with protection and slow speed running that years ago would heat the motor excessively, not any more.
For a multiple machine set up a rotary converter is probably better from a cost point of view.

Alec

 

[shenion]

In the US and Canada, residential power is 220V with a center tap of ground. Lights, outlets all work on one of the phases to ground (the breaker panel alternates each circuit on each phase.) Big items like ranges, A/C etc run across 2 phases for 220V.

110/220V is an old term. It is usually near 120/240 (mine is typically 122V.) I have seen it referred to as 117V as that is more of the average value.

3-phase here can be 208V (120V line/neutral *3), 220V, 380V (220 *3), 460V. 208 is most common as you get 3 110V circuits. Industrial buildings will often have 380 with a transformer in the utility room to generate 110V.

Note: I I was to go with 3-phase, I would get less voltage for single-phase things like my Airco (208 vs 220).

Residential areas usually only have 1 phase at the pole. If I wanted 3-phase, i would have to pay for them to run 2 more phases from 2 streets away and the cost of 2 additional transformers on the pole.

Note: one difference I see is here we have HV power delivered closer to homes. If I remember right the pole will have something like 3600VAC (have seen over 7kV mentioned.). Each transformer runs at Most 3 houses with short 00-gauge lines. When I was in the UK, I though it odd how few transformers I saw and how many houses I saw wired together.

My house is shared with 2 other houses on a transformer that I think is rated at 450A. So my big Airco does not bother my neighbors when I fire that beast up

I worked in a officice that had 220V 3-phase with the neutral not in the center (it was 18V up one leg.) Was a real odd unbalanced setup. We actually melted one of the 000-gauge feed lines as all 110V had to be on one phase.

On inverters, yes, the protection and smarts are a big plus. On mine, there are dozens of parameters to set including rated motor current, acceleration, deceleration, frequency range and idle current. It makes it impossible to overload the motor.

In my case, my 70-year old lathe came with an old 1/3HP motor. I removed it to look at trying to straighten the shaft as it must have gotten knocked. I found cloth-covered wires that were falling apart. Saftest option was to just replace it.

I checked suppliers and a good motor was $200. Ebay had all kinds of 3-phase motors for $20. I found an inverter for $27. So had a replacement with variable speed and smarts for about $80.

 

[piman]

Hello Shenion,

you see transformers in rural areas, local distribution is 11KV\415v and yes there are lots of houses fed from one cable, typical modern domestic feed is 100amp maximum, so I expect fairly substantial feeder cable sizes (mostly underground, except for rural areas)

I hadn't expected the sort of split phase system that you describe, and I have never seen anything like it in the U.K except for industrial power sockets that are fed from 110v centre tapped to earth transformers so that the maximum voltage to earth is 55v as a safety measure. All U.K. portable tools in industrial sites must be 110v not the more common 'hobby' 240v tools. This existed long before the arrival of sensitive fault monitoring breakers that are now common and required in U.K. domestic installations.

Alec

 

[madkayaker]

Hello Shenion,

you see transformers in rural areas, local distribution is 11KV\415v and yes there are lots of houses fed from one cable, typical modern domestic feed is 100amp maximum, so I expect fairly substantial feeder cable sizes (mostly underground, except for rural areas)

I hadn't expected the sort of split phase system that you describe, and I have never seen anything like it in the U.K except for industrial power sockets that are fed from 110v centre tapped to earth transformers so that the maximum voltage to earth is 55v as a safety measure. All U.K. portable tools in industrial sites must be 110v not the more common 'hobby' 240v tools. This existed long before the arrival of sensitive fault monitoring breakers that are now common and required in U.K. domestic installations.

Alec

Can be 230V now with RCD

 

[irondarren]

those 3 phase inverter converters are an old trick for running variable speed for a forge motor.

 

[R Kraft]

3 phase motors are handy to have around.
I use the things as phase converters as transformers and generators.
You might have a look around: http://www.redrok.com/engine.htm
Robert

 

[piman]

Hello MK,

"Can be 230V now with RCD "

I didn't know that but I bet that few works will be going to the expense of fitting rcds to their 240v sockets. Does that also apply to the likes of construction sites? What about the requirement for periodic operation tests of the services? As I said with 110v the maximum voltage you could get to earth is 55 volts, so fairly safe.

Alec

 

[Jaeger_S2k]

Does that cover trailing sockets with RCD fitted (like what I have)?