Build your own phase converter?

forrestM · June 05, 2024, 11:45:50 AM

Hello,

I'm going to need to power a 18hp 3 ph machine but I only have single phase. I know it is cheaper to make your own, so I was wondering what the cost might be, and what kind of headache is involved. Do I need to find a 36 hp motor for the converter? It's powering a 3 headed moulder. The 3 heads come on one at a time, not all at once. Not sure if that makes a difference.

scsmith42 · June 05, 2024, 06:21:23 PM

Croman Converters in CA sells kits for converting a 3 phase motor into an RPC. They cost around $400 as I recall, and you need to provide your own 3 phase motor.

I run a 15hp Woodmizer Edger off of a Phase-a-matic 30hp RPC. It struggles when we run 8/4 oak through it. I have to fire up a bunch of other 3 phase equipment to help the edger (counterintuitive - I know).

For a single piece of equipment, a VFD might be a better (albeit more expensive) option.

They are pretty simple to build. My experience is that 3,600 RPM motors work better than slower RPM motors, but I've had other knowledgeable folks tell me the opposite...

Don P · June 05, 2024, 07:02:25 PM

@teakwood is running a molder with several VFD's. Scott is right, the rotary doesn't need to be double the total but should be double the largest motor. As you bring more motors on line the system balances better, up to a point. I'm running the sawmill blower on a homebrew RPC but will probably get a VFD for the industrial tablesaw.

Larry · June 05, 2024, 09:46:08 PM

Shop built rotary phase converters can range from stupid simple to very sophisticated. On the simple end it would be a 3 phase motor equipped with a large pulley, single phase input, and three phase output. Shove the pulley with your boot to get the motor spinning and turn on the single phase. Lots of step ups with the top dog being a capacitor bank to get things started. Kits use capacitor's and are great for somebody without experience. For sensitive equipment, phases may need to be balanced as they can vary widely off the motor generator. For running a moulder I wouldn't worry to much about balancing. Don't neglect safety. I like a motor starter on the single phase input so the converter won't try to restart after a power failure. Circuit protection is also needed on the 3 phase side.

Check out the first thread at this site for lots of good design help. Practical Machinest Phase Converters

For 3 phase motors to use for the generator check out the local junkyard. Most sell motors for scrap prices. Take a ohmmeter to check the windings and your nose. Use your nose to check for a burnt smell from the motor. Bearings are easy to replace. I've bought lots of bargain price 3 phase motors at the junkyard and as of yet have not gotten a bad one. Auctions are good places to find motor starters, and circuit protection equipment.....price a new 3-phase breaker!

The first rotary phase converter I ever saw was a boot start in a old small machine shop. The owner told me his dad built it and the thing had been running for 20 years without issue. Cheap and reliable but not OSHA approved I'm sure.

teakwood · June 06, 2024, 08:06:35 AM

I would use a 30hp motor if you go the rotary phase converter route, maybe later you will add another machine. I have one (20hp) for my planer 15hp and the sawmill 7.5hp, was flawless for 3 years, yesterday i had to replace all the running capacitors (100$), now i'm back in business.

for the moulder i went with the VFD's as my moulder has 8 motors and a phase converter would a have been way too big. you need ONE vfd for every motor, count in lift and advance motors, suction,.... it's not only the spindle motors who need a vfd

YellowHammer · June 06, 2024, 08:50:23 AM

I have a commercial one, but I have a buddy who built one himself with just a 3 phase motor. One of the issues with a home built is that most people don't add boost capacitors to compensate for the startup inrush of the machine hooked to it, or have booster capacitors to deal with a fast heavy load input. Capacitors are basically reserve batteries that come on line when needed. Mine was dragging a little on my Straight Line Rip saw, I called up the company, they sent me a couple more run capacitors, I wired them in and problem solved.

I also run a 3 phase generator. As a general rule, phase converters lose voltage (increased voltage drop) on the manufactured leg as they get near capacity, and generators make cleaner and maintain full voltage as they get near capacity.

Larry · June 06, 2024, 12:40:26 PM

This is the box where I balanced the phases using capacitors on the last one I built. To balance properly I load up the driven motor to near full capacity than add or subtract capacitance to keep all 3 phases at the same voltage. I found a balanced phase converter will start a much bigger motor than would one would expect. Depending on the intended application I don't always go through this extra step.

teakwood · June 07, 2024, 08:06:21 AM

This is my setup, 20hp outside and the starter panel

and these are the vfd's for the moulder

rusticretreater · June 07, 2024, 10:05:46 AM

Quite a few VFDs. Sounds like quite a machine.

teakwood · June 07, 2024, 07:52:49 PM

@Larry

Well, the new capacitors didn't fix the problem. Maybe some of you can help me out. My motor is reving up and down, i can hear the rpms varying. have steady income Voltage monophase, steady outcome three phase 238V, 242V and 245V on the three legs, amps is 13A, 16A and 17A, the system works fine but what could be the problem of the rpm drops??

Larry · June 09, 2024, 09:33:21 PM

I don't have a clue. Wild guess would be some kind of mechanical issue.

I did have a similar problem one time but it was my cockpit error. I wired a dual voltage motor for 480 and tried to run it on 230 volts.

rusticretreater · June 10, 2024, 01:12:02 AM

No expert here. I am just following the thread as I want to learn new things. But my intuition tells me that your electricity flows need to be rated/tuned to bring a balance into the system. A leg with output of 245v @ 17A is a lot more flow than one with 238v @ 13A. You have three outputs with markedly different rates of electrical current. My 1 1/2 cents.

YellowHammer · June 10, 2024, 06:36:04 AM

Had anybody got experience with one that is in the 60KW to 80kw range? For example, my planer is about 65 hp, 480 3 phase, and I was thinking of running a converter off 220 single phase, instead of my generator.

teakwood · June 10, 2024, 08:50:02 AM

Quote from: rusticretreater on June 10, 2024, 01:12:02 AMNo expert here. I am just following the thread as I want to learn new things. But my intuition tells me that your electricity flows need to be rated/tuned to bring a balance into the system. A leg with output of 245v @ 17A is a lot more flow than one with 238v @ 13A. You have three outputs with markedly different rates of electrical current. My 1 1/2 cents.

Very good point, actually one leg is not 17A it's 26A, so even worse. is there an electrical gismo i can hang into the system that tunes the phases? how is that called? maybe i can by one of amazon

doc henderson · June 10, 2024, 09:10:45 AM

the DPS phase shifter I got only goes to 50 hp and is 220 three phase. I had to go through 3 of them to get a good one.

Larry · June 10, 2024, 11:37:50 AM

YellowHammer, do you have enough amps on the single phase supply to support a additional 65 HP motor? I'm on a rural electric coop and they meter me with a electronic gadget. If I ever tried to start a motor even close to that big they would disconnect my service in a heartbeat due to the inrush current.

rusticretreater · June 10, 2024, 12:36:53 PM

@teakwood

3-phase AC Current Regulator

Something like this:
https://www.amazon.com/60A-200A-Three-Phase-Voltage-Regulator-thyristor/dp/B0CQJXKZ6W?th=1

teakwood · June 10, 2024, 08:54:18 PM

thanks rusticretreater , i will order one. is the 40A big enough if the 3 legs bring 14, 16 and 26A??

Can you then help me where it needs to be installed?

YellowHammer · June 10, 2024, 09:21:56 PM

If I remember correctly 3 phase voltage should be within 3% under full load amps at least that's what good phase converters say they will stay within.

I have commercial power and they have already run a an unused 200 amp 220V service for my use, and if I peg that, I will get them to run another, bigger service.

rusticretreater · June 11, 2024, 01:08:22 AM

Quote from: teakwood on June 10, 2024, 08:54:18 PMthanks rusticretreater , i will order one. is the 40A big enough if the 3 legs bring 14, 16 and 26A??

Can you then help me where it needs to be installed?

Seriously, I have no experience in making three phase power.

In old cars the regulator would go between the power source(generator) and the load(battery) so it didn't overcharge the battery. So this would go between the motor and any other electronics. I'm sure the device instructions would be specific on this.

If you read the post by Larry above you see that he also tunes it by using capacitors as well.

Here is some homework:
https://gruppoenergia.com/blog/choose-voltage-stabilizer-correctly/

Machinebuilder · June 12, 2024, 07:47:58 AM

Robert,

just a quick ball park calculation

65hp is about 220A @220V.

I need to go digging for some books to figure out more.

I never had to mess with convertors.

scsmith42 · June 13, 2024, 11:30:44 AM

Quote from: Machinebuilder on June 12, 2024, 07:47:58 AMRobert,

just a quick ball park calculation

65hp is about 220A @220V.

I need to go digging for some books to figure out more.

I never had to mess with convertors.

Plus you need the additional amps to operate the converter. I think that you'll need a 400 amp service minimum if you pony motor to spin up the converter before engaging it's power. That should reduce the current inrush significantly.

Larry · June 13, 2024, 12:33:09 PM

Since my power company is so down on motor loads the last converter I built is a pony start. You can't even see the tiniest blip on the input when it is started.

YellowHammer · June 13, 2024, 05:45:09 PM

Yes, those are the kind of numbers I was thinking, I guess I will just go back with the generator solution for my planer. I run phase converters for most of my other equipment, but limited to 30hp. Works great...but...

teakwood · July 13, 2024, 08:48:09 AM

Quote from: teakwood on June 07, 2024, 07:52:49 PM@Larry

Well, the new capacitors didn't fix the problem. Maybe some of you can help me out. My motor is reving up and down, i can hear the rpms varying. have steady income Voltage monophase, steady outcome three phase 238V, 242V and 245V on the three legs, amps is 13A, 16A and 17A, the system works fine but what could be the problem of the rpm drops??

@Larry after some electrical help and explanation from Larry i had the electrical system checked and it was all good but didn't solve the problem. so the next thing was to check the bearings although there was no obvious damage when turning the rotor by hand, just a tiny tiny click when rotating slowly. so i dismantle the motor which isn't hard but everything is heavy on a 20hp motor. the bearings seemed ok but i have already ordered them so what the heck. even having them in the hands and turning them there was no noticeable damage. after putting the motor back together with the not cheap new bearings (150$) the noise was gone. must have been a slightly touched ball in a bearing that caused the noise.