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Running a 3 phase VFD with a rotary phase converter.

alcro1998

Cast Iron
Joined
Nov 10, 2020
Location
Central Ohio
Hi, I am in the process of converting a monarch DC drive to an AC drive. I am looking at getting a 10hp inverter duty motor and a 10hp vfd or sensor less vector drive.

I am wondering if I will fry the vfd or vector drive if I run it off a rotary phase converter?

Thanks
 
It's probably doable, but why? We'll need more background. Why not hook the AC motor directly to the rotary phase converter? If you want to control speed with the VFD, then why not upsize the VFD to support the 10hp motor? If you already have a 20+HP phase converter, it should work, just seems like a complicated setup without much advantage (unless you already have all the equipment lying around).
 
It's probably doable, but why? We'll need more background. Why not hook the AC motor directly to the rotary phase converter? If you want to control speed with the VFD, then why not upsize the VFD to support the 10hp motor? If you already have a 20+HP phase converter, it should work, just seems like a complicated setup without much advantage (unless you already have all the equipment lying around).

he would need a ~20 HP 3 phase converter to safely run a 10HP motor from single phase input.

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The only reason I would have an RPC in series before the VFD was if I had other 3Phase motors to feed on the RPC at the same time and only one of them needed speed control. A 25 HP RPC and a 10HP VFD may be cheaper than 2 20HP VFDs to run 2 10HP motors at the same time. Potato tomato.
 
My RPC is only 15hp. I am using the vfd for speed control. I did read that most vfds can run off single phase so it sounds like it would just be better to snag a 20hp rated vfd and run it off single phase correct? My biggest concern was the cost difference between a 10hp vfd and a 20hp vfd. Thanks for all the responses!
 
Imo you should download the manual of the VFD before you buy it.

Some allow incoming phase loss to be turned off as a parameter.

Above 5hp, all standard reliable bets are off on what can do what with single phase input, from what I have found.

If you have a 10EE my opinion is you need to do some serious measuring before committing. That is a big motor + gearbox in a tight space and for what gain? My free advice is to use an EE for finishing sizing and detail. It can do it all but send hogging cuts to bigger machines.

Monarch makes some excellent large ones as well.
 
Thermite can be... well, Difficult at times. But his analysis is dead on. If you're running a 10 hp motor (seems like overkill) than you're fine with a 10 HP VFD. I run a 7.5 with a 10 HP VFD right off 250VAC single phase, but only because that's what I could get at that moment. All my other VFD run equipment is straight matched 1-1 with no issues whatsoever. I'm assuming you are talking about a 10EE application? Again, you are probably never gonna need 10 HP. Even when pushing dull CNMG cutters, I doubt I hardly ever surpass a need for 3 HP. Don
 
Thanks for all the replies, especially THERMITE for the extremely in depth replies. It looks like I can do what I initially wanted to do and run it off a RPC.

The system is actually for a 1000ee so I will have a 4 speed geared head which will help in keeping adequate torque at low speeds. The original motor is a 20hp dc motor!!! so 10hp is not overkill at all haha. I bet a new DC drive for the system would cost me at least an arm and leg so that's not an option!

I don't think I could ever ask for a full 10hp and my current lathe is only 5hp while they both have about the same swing.

Thanks again! Just wanted to make sure I wouldn't fry an expensive vfd with "dirty" RPC power.
 
For $1500 that would work well. The dc drives I looked at were $5,000. The other issue I’m running into is that I only have 50 amp 220v single phase to run the lathe and I’d assume I need more than that for a 20hp dc motor.

I’m planning on spending somewhere around $600-1000 for the AC conversion which seems reasonable. I do already have a 15hp RPC and I talked with a guy who should have a 10hp baldor inverter duty motor for $200 so all I am left with is a VFD.

Thanks for all the help and suggestions it is greatly appreciated.
 
How balanced is your RPC? My older Kay fried a vfd as the wild leg was too high. I needed to do some work on the unit if I wanted to run vfds using it. I avoided rather than fixed the problem by swapping to a Phase Perfect and by running the smaller machines off single phase. Newer rpc are better balanced so you might be golden but checking first is better than my method of diagnosing what went wrong. Dave
 
Unfortunately it would be impossible to get more than 50a unless I ran all new power to the shop. I’ll just have to make something work with the power I have.

I thought that 50a single phase would have been enough since I don’t really plan on putting too much of a load on anything.

I suppose I could go with a smaller motor if I needed and it probably would be fine for me since a 5hp lathe has always been more than enough for me. Just kinda seems like a waste to me going from a 20hp DC motor to a dinky 5hp one. Maybe 7.5hp would be adequate?
 
Don't I need more power to get the full range of speed from the DC motor? I thought that less power meant lower speed.

Also I do not have the lathe in my possession at the moment so I don't have any decent pictures of it.
 
Hi, I am in the process of converting a monarch DC drive to an AC drive. I am looking at getting a 10hp inverter duty motor and a 10hp vfd or sensor less vector drive.
...

What's wrong with the original drive? You're not going to be able to cobble together anything remotely as good as the original 1000EE/13EE drive. If it's an issue with the C16J tubes, there are solid-state replacements available from Scissio Controls - Products. If it's simply because you don't understand the drive, think it's too primitive or whatever, than let's please have a discussion.

Cal
 
What's wrong with the original drive? comic sans ms]Cal
He doesn't have the power to operate it.

You need to stop screwing around with my posts. If you want to quote me, quote me, but if you keep up the "comic sans ms]" jibes and other adolescent BS, I'm going to have to tighten things up a lot. OK? If you have something useful to post, fine, do so in a clear and concise manner, but save the gibberish for elsewhere.

Cal
 
I am hoping to pick the machine up on Sunday. I did not take a peek at the motor when I saw it for the first time but I just assumed that it had the original 20hp motor still inside. Once its in the shop I will start going through everything right away. Been waiting to get the space for the machine for a couple months and everything finally lined up!
 








 
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