Run another motor BEFORE the VFD?

I've installed a TECO FM50 to run the 2hp motor on my Hendey lathe, and frankly I'm impressed. Now I have to install permanent wiring and a 220 1ph plug rather than trail the cord across the floor to the present outlet. I have existing 220 1ph at the new location for my Hendey shaper and would never run THAT motor while using the lathe, but I'm concerned what would happen IF the shaper were started by mistake (both plugged in, only one running). Perhaps this is a bad idea and I should run a new dedicated circuit?

Hi George!

Well, if the shaper is running, and you start the motor (being driven by the TECO), one of several things can happen.

1) It will start, and run just fine.
2) The branch circuit breaker will trip from overcurrent (if the shaper is a heavy load)
3) The TECO will see voltage fluctuations that it doesn't like, and fault out
4) The TECO simply won't start (not likely).

Obviously, if the branch you're running these two off of is insufficient for the two machines, but properly protected, you'll get a breaker trip, which is obviously a preferable result.

I don't believe there's any action that would occur that risks damaging the TECO- any side-effects would be performance oriented, with the worst-case being a FAULT condition of the drive.

One of the 'bonus' features of doing this, however, is that the TECO will reduce the startup inrush applied to your line by the machine it drives... it is, in effect, a soft-start system, so you may find that both your shaper and lathe running at the same time, as long as you don't accelerate the lathe really hard or take heavy cuts with the shaper, would work amicably.

I currently run a 2hp lathe, 1hp mill and 1hp surface grinder, all 3 phase in a shop with only single phase power available. I have a 7hp static converter running a 7.5hp 3 phase motor which serves as a generator. This is all supported from a 50A two pole breaker. From this I have wire from generator to terminal disconnect and the lathe, mill and grinder wired together at disconnect. I have a fusable disconnect for each piece of equipment and fused according to its name plate amp load. Your static converter and generator motor need to be at least 50% bigger than the total hp rating of your equipment. I have run all three at same time with no problems. Starting and stopping has not been a problem although I have not had them all try and start at same time. My arms are to short.

I forgot this post was about VFD. In regaurds to the post I made earlier. I am running VFD on my Bridgeport Mill and KO Lee Surface Grinder.

George Andreasen said:

I've installed a TECO FM50 to run the 2hp motor on my Hendey lathe, and frankly I'm impressed. Now I have to install permanent wiring and a 220 1ph plug rather than trail the cord across the floor to the present outlet. I have existing 220 1ph at the new location for my Hendey shaper and would never run THAT motor while using the lathe, but I'm concerned what would happen IF the shaper were started by mistake (both plugged in, only one running). Perhaps this is a bad idea and I should run a new dedicated circuit?

Click to expand...

Lathe, 2HP 230V 3 phase = 6.4A, current draw from 1 phase supply = 11+amps full load

Hendey shaper, probably 2HP 220V 1 phase? another 12+ amps.

If you have a 15A or 20A 2P breaker feeding this, the circuit is too small to run both motors and the breaker will likely trip if you put a load on both. But if you are not using the shaper and just left it running unloaded when you start the new lathe, probably no problem. If the lathe is running unloaded (via the VFD) and you turn on the shaper, I doubt if the VFD will notice, however the inrush of the shaper motor may be too much for the breaker and it will trip.

The others have explained the situation pretty well. Just to add my support, I have a planer on a vfd and sometimes run other machines including a 5HP shaper off the same convertor (not the vfd) at the same time. As long as the amperage (& appropriate sized wiring) is there, anything (any motor) running with minimal load _before_ the vfd just balances the 3ph output of the idler motor. OTOH if the load before the vfd is for some reason too heavy, the vfd will trip from under current or out of limits voltage, but it won't hurt it.

The nicest way to deal with shop generated 3ph is to feed it into a separate distribution panel/load center. Very flexible, easy to safety, easy to add circuits too. The panels can often be found at junk yards. Just get one with breakers that are still available, cause the breakers are the expensive items.

What I'm getting at, is in your situation, everything before the vfd is basically "the panel" whether you have a proper one or not. A "proper" one makes it easier to see and deal with, but is not intrinsically different. IOW, if your convertor fed a panel with other distribution, and your VFD/lathe was only one item, you would probably not be worried as long as there was enough juice to the panel for all the loads.

smt

Thanks everyone, looks like I can safely have both machines on the same circuit as the shaper motor is only 3/4 hp 1 ph (sorry, forgot to mention that). It's very doubtful that I'd have both running at the same time...in fact it just isn't going to happen at all. My concern was whether another motor in line with the VFD feed would cause any problems for it or not if it were started accidently.

HOWEVER......I just came in from the shop and realized that I could extend the existing 220 1ph a lot easier than I first thought. Guess I should have moved a few things and looked at my conduit setup before asking. So, the point becomes moot......I'll leave the existing outlet where it is and run new conduit/wire overhead and stick a new outlet on the end, thus keeping it on it's own circuit after all.
Thanks again and everyone have a safe New Year!