Made a Rotary Converter.....I now have 3 phase 415v Mwahaha (Video)

[WorkshopChris]

I think the ready built rotary phase converters from Transwave ect don't need the capacitors changing as they are matched to the idler motor only which is constant.

Yes but they have a voltage monitoring relay, that drops extra capacitance in the circuit as is seas a volt drop from a motor starting as a boost.

 

[snoozer]

My head is slowly starting to hurt

 

[MBB]

For what it cost for the materials and switch gear etc I could probably bought one from Transwave ready made cheaper.

 

[God mode restorations]

I wish I understood electrical like you guys do. It baffles me. Hold my hat off to you chaps.

 

[Fazerruss]

For what it cost for the materials and switch gear etc I could probably bought one from Transwave ready made cheaper.

I keep thinking the same. If I were to build it from all new components then you aren't far off the mark. For a decent size 3 phase motor could be pushing 300 quid alone. Caps are around £6 to £13 each depending on size.

 

[addjunkie]

For what it cost for the materials and switch gear etc I could probably bought one from Transwave ready made cheaper.

My static is one of theirs, but the guy there told me, to just wire in another motor, and the inductance smoothes the voltage on the generated phase, allowing the lathe to stop, and suds pump for example to run away drawing next to nothing quite happily.
I have the additional motor, just not done it yet.

 

[Hood]

My static is one of theirs, but the guy there told me, to just wire in another motor, and the inductance smoothes the voltage on the generated phase, allowing the lathe to stop, and suds pump for example to run away drawing next to nothing quite happily.
I have the additional motor, just not done it yet.

30 or so years ago I had one of their statics, did as you say and wired a motor in parallel with my lathes input and it worked great. I could go forward to reverse without having to wait for the motor to stop in between, worked great.

 

[Tilly819]

Right here we go...

Any chance of the circuit for the one you made? Because we know it works and easier for lazy people like me than trawling the net.

I am afraid I do not have a diagram. There is a chap on ebay though who sells them for about £10. I bought a set of out of curiosity and his system works in the same way as this one does.

Very tidy. I’ve a similar setup, with the addition of a 3ph transfromer. Spitting out 7.5kw Any idea what the transformer is doing/for.

If you have one with a transformer then the rotary converter is converting your single phase 230v to three phase 230v then the transformer steps up the voltage to 415v.

Looks really good and well executed. However I don’t understand how it works. Doesn’t the motor need to be driven by another motor ?

No the idle motor as it it known in the converter gets its power from the single phase supply and and additional excitation from the start capacitors. Once it is going and in the star configuration it will self sustain, having a bit of a flywheel on the shaft helps with this. The two un-powered coils then induce a voltage creating the additional 2 phases (i think they are all the correct words). This then allows you to run other 3 phase machines as if you had an actual 3 phase supply in the workshop.

A 3 phase induction motor will start (and run) on single phase with just a capacitor wired across live and the spare wire of three. You lose a lot of efficiency and the start-up torque is very low but once it's up to speed it'll run well enough. Also, once it reaches it's running speed the fact that it relies on 'induced' currents means that the un-powered leg of the three phases gets a voltage generated on it.

Up-side is that you really can generate 3-phase from single phase very simply. Down-side is they are not terribly efficient and draw a lot of current from the mains.

Yes, yes and more yes. This is the exact reason I built a converter rather than just using Caps on the lathe. My lathe is a Harrison VS330TR which is full vari speed and Direct on line start. Therefore it has A LOT of starting inertia therefore needs a lot of starting current. Also I now have the converter so I should just be able to plug in any machine in future and it should just work.

If wired like this when it switches to star mode in theory would the neutral stay grounded? In theory this design is negating the need for a step up auto transformer as the motor sort of does this between 1 and 3.
I would have thought you would need a big idler motor though as you are pulling a lot of current through just one set of motor windings on the 240v supply in.

View attachment 148373
I'm interested in expert opinions on this as I would like to build one eventually but I want it to be a "safe" design.

There was this fella who said he had done so but hasn't done a third video with an explanation...

The video you have linked to is where I got most of my information, If you look at the diagrams he shows. That is the same system I have used. At that point the only tricky bit is working out how to do the switch gear. There is also a link to another video that might be useful in my video description.

How do you adjust capacitance for differing loads/machines ?

At the moment I am not. My plan is to monitor the voltage and current for each machine as and when I get them. Then if I need to do some additional balancing I will do it at that specific machine so there are not knock on effects on other machines.

Thats what i am trying to get my head around, spent 20 years around various phase converters. Supply looks very light gauge cable on the 16 amp plug, i would expect big volt drop on start ups.

Voltage drops to about 150V @ ~60A on startup for ~1 second while the motor is in Delta. Once in Star the voltage comes up to 248 ish and current is ~3.8A when idle. I may beef it up a little as I inevitably will end up doing some optimisation on it in the future. I can't just let anything that works just work......It must be optimised....

I also would expect the idler motor to be at least 3 times the size of the total load put on it.

The idle motor is 4KW and the lathe that I start at the end is 2.2KW. I'm expecting it to work to around 75% of the idle motor. Ie. I recon it will run a 3KW machine. That is a proper wet finger in the air kind of approximation though.

For what it cost for the materials and switch gear etc I could probably bought one from Transwave ready made cheaper.

I have not added it up properly yet but I recon it cost about £350. But that also includes building the trolley. So some steel and plywood etc. A lot of it boils down to how cheap you get the motor. I think mine was £50 off Ebay second hand.

Hope this answers a few questions. So glad you all enjoyed it

Cheers.

 

[RichardM]

Nice job, but my head now hurts too and it's not from beer.
Must see if they're clearing any motors out at work.

 

[Justme]

I dont get how the claimed current consumption can be correct.

During start up prior to switch over perhaps.

But surely once up to speed the 240v is supplying the force to rotate the device.

That force must be more than the output.

 

[Pete.]

I dont get how the claimed current consumption can be correct.

During start up prior to switch over perhaps.

But surely once up to speed the 240v is supplying the force to rotate the device.

That force must be more than the output.

Current consumed is proportional to current demanded. When the motor is idling it only demands the necessary current to keep itself spinning. When you put a load on it the current consumed is a product of the current required to keep it spinning PLUS the current supplied to the device being powered through it.

 

[Justme]

Current consumed is proportional to current demanded. When the motor is idling it only demands the necessary current to keep itself spinning. When you put a load on it the current consumed is a product of the current required to keep it spinning PLUS the current supplied to the device being powered through it.

That would be my understanding too. The video claims a very low current draw.

 

[Tilly819]

On start up the converter pulls about 60A for ~ 1 second while the motor is in Delta. If it was left in delta the current would drop to something sensible after the initial inrush required to overcome the starting inertia had passed. As it happens that coincides with the change over to star. It is not changing to star that drops the current. With the converter idling, Ie no load attached, the output current is 0. No load = no current demand therefore the 3.8Amps at idle is just the current required to run the machine on its own. (friction, heat, noise, air resistance etc)

When the load is connected (the lathe is started) there is again a surge in current as the lathe has to overcome its starting inertia. Once this has passed and the lathe is up to speed each of the 3 phases is drawing around 2.5A @ 400v = 1KW per phase. The single phase supply is 248v @ 8 Amps ~2KW.

Now to address the point about getting more out than you put in... If only that were possible.

I assume that the thought process here has been as follows...

1KW/phase x 3 phases = 3KW output with only a 2KW input. Which I completely agree is not possible.

What this does not take into account though is the phase angle and shift within the three phase side of the circuit. If you look at the three phase, each phase is 120 degrees apart therefore the peak voltage and current occur at a different point in time on each phase.

Now i'm not an electrical engineer so that is a kind of educated guess as to the reason for the numbers. I'm also not taking into account efficiency. If someone can give a more in depth explanation I would be very interested to hear it.

TLDR -> Yes current consumed by the single phase supply is proportional to current demand by the three phase load.

Cheers

 

[Hopefuldave]

Re something for nothing - the delivered 3-phase power is root three times the power per phase, so for your 2 kw input, 1 kw per phase output, you're actually delivering about 1.7 kw to the powered machine - pretty good efficiency if that's what you're getting, about 85%!

Dave H. (the other one)

 

[Tilly819]

Re something for nothing - the delivered 3-phase power is root three times the power per phase, so for your 2 kw input, 1 kw per phase output, you're actually delivering about 1.7 kw to the powered machine - pretty good efficiency if that's what you're getting, about 85%!

Dave H. (the other one)

Thanks for the clarification, I thought someone would know the correct maths. Cheers

 

[HughF]

Interesting..... I’ll draw out the circuit from my boost converter sometime for reference. It’s a very soft starting converter

 

[WorkshopChris]

When the load is connected (the lathe is started) there is again a surge in current as the lathe has to overcome its starting inertia. Once this has passed and the lathe is up to speed each of the 3 phases is drawing around 2.5A @ 400v = 1KW per phase. The single phase supply is 248v @ 8 Amps ~2KW.

What are the voltages on load at the lathe phase to phase & phase to neutral?

 

[Tilly819]

No load
Sup (V) = 242 (I) = 3.1

Output P1-P2 (V) 428 (I) = 0.1
Output P1-P3 (V) 440 (I) = 0
Output P2-P3 (V) 417 (I) = 0.2

On load
Sup (V) = 238 (I) = 7.4

Output P1-P2 (V) 408 (I) = 2.2
Output P1-P3 (V) 404 (I) = 2.3
Output P2-P3 (V) 395 (I) = 2.0

I will have to get in there with a meter next time its on to get phase to neutral values. These values are from some pics I took of the displays.

Cheers.

 

[steviec_lj]

That’s something like 90% efficiency..

Maybe I need to make one of these too

Did you purchase “plans” from eBay?

 

[Hopefuldave]

I make it 87% - pretty impressive... Not up with VFDs though, they're usually in the high 90s!
They also don't draw most of a kw with no load :/

@Tilly819 - have you fitted power factor correction caps to the 240v input side?

Dave H. (the other one)