RPC - All the parts but lacking the brains

[Tinker.in.the.shop]

Hi All (UK resident),


Last year I purchased some plans for a rotary phase converter (220v single-phase input >>> 415v 3-phase output) that used a similar HP running motor as I would need, so it was ideal as all the components listed would be of a suitable capacity for my use.
I started gathering contactors and misc. parts that I would need including a good quality motor for the idler/slave.

I'm not electrically minded, but I do understand general safety and I'm always extrememly cautious when working with anything electrical.
As I was working my way through the wiring diagram, it was no more clear in my mind what exactly was going on in the system to make it work so troubleshooting has been difficult.

Short story, I put it together how I thought the plans dictated but the RPC doesn't work as intended. I got as far as the slave motor starting but it didn't sound right and was not running at it's normal RPM. And some wires became very hot very quickly so I never tested it for more than a few seconds.
I tested the slave motor with a vfd and it runs perfectly, the bearings are good etc.

I had no luck finding anyone locally that could assist me. I emailed back and forth with the chap who made the plans but he could only help to a point.

Is it even worth me going into more detail here? As I bought the plans, I don't think I'd be able to post the diagram without breaking copywrite but basically I believe it uses capacitors to start the slave motor in one config and then a timer kicks in switching it using contactors to the other config and then should be generating 440v 3-phase.

Initial general advise is welcomed. Tried to keep it brief initially.
Cheers,
-Tinker

 

[Karl_T]

here's another write up on how to build one. Is yours similar?

Can not help much without seeing what you got and what you are trying to do.

 

[JimDawson]

I find it difficult to believe that it is possible to make a RPC output a voltage greater than the input voltage, without the use of a transformer on the output.

Please provide the schematic for the unit you are building.

 

[Tinker.in.the.shop]

I can't provide the schematic due to copywrite however I was told that this chap built his RPC to a very similar design.
I believe the use of a duel phase motor which switches between delta/star is partially how the system generates the "415v"
ALthough not exactly the same, it explains briefly the principle behind the 220v single to 415v 3ph.

around 10:20 mark

 

[JimDawson]

OK then, I stand corrected.

But it makes my brain hurt thinking about how this works.

The best advice I can offer at this point is to recheck the wiring step by step to make sure it is wired correctly. Wires should not be getting hot.

 

[markba633csi]

It actually works? I would have said impossible- guess I'll have to watch the video
-M

 

[Karl_T]

Engineering 101 - got a problem you can not solve - break it into smaller problems and do one at a time.

The video shows (about 10:30) you got what we in the states call a standard RPC with a delta motor. pretty standard stuff for many of us.

Then after its running in delta, just switch the wiring over.

So, let's get it running in delta. I see one minor issue - the above RPC also drops the start caps when switching wiring so you will need to just drop start caps after one second.

 

[markba633csi]

Yep, I see. You create a rotary auto transformer. Very clever, and nifty
The switching is not exactly trivial- need a clear schematic for a project like this

 

[Tinker.in.the.shop]

Thanks for the comments so far. I'm sure the schematic is simple to those with the right mind. For me I never had to look at anything other than extrememly simple wiring diagrams so Its a learning curve!

Good point made about getting it running on Delta first. I did get the motor to start but it was definitely not running at it's rated RPM and sounded almost, "gravel-like" as mentioned though running on a vfd it sounds smooth as butter!

Hoping to get some time this week to take it back to bare components and start rewiring from fresh. I'll keep updating,