Building an RPC and transformers.

[matt_i]

Good job there, I'm interested to see your L1-L2, L2-L3 and L1-L3 digital voltmeters working.

Also, be careful of the open shaft on the idler, it seems benign enough but would wrap up a person before they could react...you could cut off the shaft (neanderthal!) or just fabricate a "can" to enclose the end.

 

[Matt Matt]

Good job there, I'm interested to see your L1-L2, L2-L3 and L1-L3 digital voltmeters working.

Also, be careful of the open shaft on the idler, it seems benign enough but would wrap up a person before they could react...you could cut off the shaft (neanderthal!) or just fabricate a "can" to enclose the end.

I don't have a little voltmeters set up and running on the 20 hp 15 kVA portable cart yet. But I think it would be fun to add. Even though I don't have a video of the L1/L2, L2/L3, L1/L3, The L1/L2 stays perfectly constant under started upload(as it is natural). But L2/L3 and L1/L3 take some hard drops, but recover to pretty good voltages. Maybe I'll shoot a video with all the metres in action on the 5 hp RPC.

Here's a video of the 20 hp 15 kVA set up.

And then with 5 hp 6 kVA set up.

And then here is a test with 2=>5 hp motors.

And then here's a test with the 2=>5 hp motors both properly balanced.

All of these tests are coming are off of a single phase 40A feed line which has a 40A GFCI.

 

[navycryppie]

I've got both, and it does work well, for me.

RPC is a surplus auction 20HP Baldor then ended up costing nothing because I sold the other two in the lot. From there I purchased a North American Phase Converter controller box and wired it up, learning lots about wye and delta in the process (had a licensed electrician check it all before firing it up).

Fast forward to the next auction buy, a three phase Miller CP-300 welder that, as it turns out, was a 480V unit. Found an appropriate step-up transformer, thank you Craigslist, and have had it all going for about 6 months now. I did add a switch so I can add or remove run caps depending on if I need the extra kick to start up the compressor or evened out for welding.

When I get a moment I'll post a few pics of the setup. Idler is outside the shop in it's own doghouse on a concrete pad with vibration isolators. I also mounted a box below the control panel that shows volts and amps for each leg.

 

[larry_g]

As someone who has an RPC, I'm quite aware, thanks.

I'm saying RPCs generate 3 real 3 phase, so a 3 phase transformer should have no problem being on the output of a properly balanced and loaded RPC.

It's been a long time since I built mine, but it is still running 10+ years later. The RPC does not generate true three phase because the three legs are not truly 120* out of phase with each other. Now would this cause an issue going through a transformer? I don't think so but I'm not intimate with all the different transformers and how they work.

lg
no neat sig line

 

[Matt Matt]

It's been a long time since I built mine, but it is still running 10+ years later. The RPC does not generate true three phase because the three legs are not truly 120* out of phase with each other. Now would this cause an issue going through a transformer? I don't think so but I'm not intimate with all the different transformers and how they work.

lg
no neat sig line

It sounds like you've tested that these are not out 120°? How did you test this?

 

[larry_g]

It sounds like you've tested that these are not out 120°? How did you test this?

I haven't tested it, just foggy memories of research many years ago.

lg
no neat sig line

 

[Matt Matt]

I haven't tested it, just foggy memories of research many years ago.

From what I have tested, 9 times out of 10 the phase orientation is bang on with a RPC (except for under extreme load starting). The third leg moves a bit, but the voltage lag is the criminal.

This is purely my evaluation.

 

[firebirdparts]

I built one using a voltage-sensing relay that cuts out my idler start cap. Before I built it, I got to looking online for good expertise and I discovered that I knew a guy personally who was good at them. He had built several using a motor starter to control the idler and the voltage-sensing relay. You can find a lot of plans at practical machinist forum. They have a whole forum section about phase converters and whatever other interesting issues come up from powering machinery.

 

[navycryppie]

Pics attached. Drywall is (hopefully) going up this week, pending a no rain day to get it home.