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Talk me out of buying a massive a 460v eletric motor and building a phase converter

arse_sidewards

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There's a 125hp 460v 3ph motor for sale locally at $300. I'm really thinking about buying it and using it as the rotating portion of a rotary phase converter since DIYing it is so much cheaper than a phase converter even half the size. I know I will only get a little less than 1/3 of the power rating of the motor available for starting other motors (only powering 2/3 of the phases at half the voltage) but even 30hp is plenty of hp for my needs. I just need something that can start 15hp while there's a 10hp load on it or vise versa.

So IBB, talk me out of it. :flipoff2:
 

arse_sidewards

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For $300, it's worth a shot.


How large is a 125hp 460V motor, size-wise? :eek:

Browsing similar motors on Surplus Center the shipping weights are in the 1000-2000lb range

I bet this one is under 1500lb considering the case configuration. If I wind up getting it I'll scale it.
 

M92PV4U

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I think it matters how the motor is wired if it's convertible from 480/240 but if you run it on 240v amps will go up and running it at slower speeds (vfd) reduces the airflow passed the winding which will cause it to burn up quicker.
And op forgot the pic so...
21989.jpeg
I'm not the one rewinding this motor my friend is.
 

larboc

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There's a 125hp 460v 3ph motor for sale locally at $300. I'm really thinking about buying it and using it as the rotating portion of a rotary phase converter since DIYing it is so much cheaper than a phase converter even half the size. I know I will only get a little less than 1/3 of the power rating of the motor available for starting other motors (only powering 2/3 of the phases at half the voltage) but even 30hp is plenty of hp for my needs. I just need something that can start 15hp while there's a 10hp load on it or vise versa.

So IBB, talk me out of it. :flipoff2:

Check the nameplate, its big, but still small enough its possible that it could be able to be wired for 208.

Not sure if your location but I've got a bunch of 25-400hp motors I could sell for scrap price if you have some kind of a business name to run it through.
 

Tin Roof

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Do you have nameplate info for this motor?

also, some power companies require motors over 100hp to be on a soft start due to the demand load at startup. Might want to check on that.
 

larboc

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Do you have nameplate info for this motor?

also, some power companies require motors over 100hp to be on a soft start due to the demand load at startup. Might want to check on that.

Could pull start it or spin it up with a small motor first. I've seen people rope start an RPC to keep from tripping the breaker.

VFD pc is the right answer
 

arse_sidewards

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I have 200A of service. If this motor can run on 220 with double amperage that puts me 40A over before you take power factor and efficiency into account. I am going to be way the fuck over 200A when I start this no mater what I do so I will have to come up with a soft start solution. If I can run this motor on 220v and derate it by half then I'm comfortably within my 200A service. This entire thing hinges on whether I can wire this motor up and expect it to draw the same amperage at any voltage. I would prefer a ~30hp motor since that's more in line with my power needs but I don't think I'm gonna do better than $300 at any size above 10-15hp.
 

arse_sidewards

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Looks like a hammered asshole. What does it actually say?:flipoff2:

What is the cost of a VFD to run the motor you have VS all the time you would pour into an alternative?

$200 for the cheapest Chinese 15hp one so $400 to run both machines plus another $100-200 each time I want to run something that's 3ph. Considering how cheap sub-5hp 3ph motors are compared to their 220v single phase counterparts having a phase converter that can provide 3ph to my basement and garage stands to save me a lot of money in the long run.
 

Blacksheep10

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Tried something similar. 25 hp 3 phase motor. Running it on 2 legs of single phase just spinning it (started it with another smaller motor) it was pulling 61a per legs when it tripped the service. I now have an American rotary that I run off of.
 

larboc

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Do you have nameplate info for this motor?

also, some power companies require motors over 100hp to be on a soft start due to the demand load at startup. Might want to check on that.

How would a soft start for 240v 200 amp single phase look/work/exist?
 

arse_sidewards

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Tried something similar. 25 hp 3 phase motor. Running it on 2 legs of single phase just spinning it (started it with another smaller motor) it was pulling 61a per legs when it tripped the service. I now have an American rotary that I run off of.

How exactly did you design your VFD. What was the capacitor setup?

How would a soft start for 240v 200 amp single phase look/work/exist?

Spin the big motor up to speed with a small one. :laughing:
 

Johann

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$200 for the cheapest Chinese 15hp one so $400 to run both machines plus another $100-200 each time I want to run something that's 3ph. Considering how cheap sub-5hp 3ph motors are compared to their 220v single phase counterparts having a phase converter that can provide 3ph to my basement and garage stands to save me a lot of money in the long run.

OK, I see what you are doing now. Considering some of the big iron you have drug home it makes sense. Three phase tooling is cheaper and less sought after so having a total shop solution would be nice.

My only VFD experience is an old school 3 phase buffer I converted to 110v single. Runs like a champ at half speed (1750 rpm) and will not stall with my 8 " buffs. It is actually hard to believe it is only rated as 1/2HP.

Now I am thinking of putting a couple other 3 phase motors that I've had kicking around for a while to work so it will be great to learn from this. Reminds me I need to drag that thread over to Shop and Tool and update it.
 

Black Sabbath

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$200 for the cheapest Chinese 15hp one so $400 to run both machines plus another $100-200 each time I want to run something that's 3ph. Considering how cheap sub-5hp 3ph motors are compared to their 220v single phase counterparts having a phase converter that can provide 3ph to my basement and garage stands to save me a lot of money in the long run.

Also don't forget to derate your VFD when converting single to 3 phase unless it is already rated for that use. But I also suspect anything involving a 125hp motor is going to come with a bunch of issues.

https://www.precision-elec.com/derate-three-phase-vfd-for-single-phase-power/
 

Dethmachinefab

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What is highest hp motor you want to run? I've built many of these and there are a few different ways to do it.
 

cj3a

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I needed one for a 20HP motor. By the time I price out the parts and the time it would take not to kill a bus load of nuns. I bought a 40HP from American rotary
 

PAE

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Yousa insane..

Just thought you should know.
 

DMG

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Don’t you guys have 3 phase in your shop?:flipoff2:
 

Dethmachinefab

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I need 15hp start, 30hp continuous.

This is for the mill you recently bought? A proper size capacitor on a momentary switch can be wired to make the machine run without buying anything else. It's the start function of a converter and the machines motor will spin up just like the rpc and provide 2/3 hp. Only good for stuff without big start up loads. Mills and lathes fine, mechanical press brakes and flywheel type machines no go.

You wire each of your shops 220v line into the two of the three 3ph loads. Off one of the 220v lines feed a rather high amp rated momentary switch into a capacitor and out to the third load on the machine. I'll get you a rough estimate on what cap size to use.

I've got a big turret lathe set up like this because a vfd was too expensive.
 
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arse_sidewards

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This is for the mill you recently bought? A proper size capacitor on a momentary switch can be wired to make the machine run without buying anything else. It's the start function of a converter and the machines motor will spin up just like the rpc and provide 2/3 hp. Only good for stuff without big start up loads. Mills and lathes fine, mechanical press brakes and flywheel type machines no go.

You wire each of your shops 220v line into the two of the three 3ph loads. Off one of the 220v lines feed a rather high amp rated momentary switch into a capacitor and out to the third load on the machine. I'll get you a rough estimate on what cap size to use.

I've got a big turret lathe set up like this because a vfd was too expensive.

Yeah, and the lathe. I have a 10hp motor that's gonna go on the mill but it's gonna go on the lathe until I find a 15. I really want at least 10hp for the mill and 15hp for the lathe. I'd need to up-size by 50% in order to get my desired hp. I'm not against doing that but 15 and 20hp motors don't show up on CL that often and when they do they're rarely under $300. Seems like just going with some sort of converter solution would be better because then everything is plug and play after that without losing power. That's if I can do it cheap enough though.
 

ThePanzerFuhrer

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I run my 10hp hbm off a cheap American rotary phase converter no problem. I think I have less than $300 in the whole setup. I can run my Bridgeport 1440 lathe and a bandsaw at the same time no issues.

Well holy ee fuck just looked at American rotary and boy did their prices go up. Thinking about it I bought my stuff in 2005.
 

The Internet

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200 Amp service is undersized @ 208. That said, if you get it started and are careful about its loading it may work. Or you may burn your shop down.
Coming from someone who has worked on that stuff, be careful with your ducktape solution.
 

arse_sidewards

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That motor wont go 208/240.


once they reach a certain HP it will be 460 for amperage reasons.

That's the whole point of this exercise. The motor draws amperage, not watts. How much voltage you pair that amperage with determines output. The only way I could run this motor is if I can plug it into 230 and get 1/2 the nameplate rating.
 
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