Nightmare: VFD in NYC - Powering a Schaublin 102 on 110V residential power

[cyanidekid]

I lived in an apartment that had ONE 15A circuit fed by a single 14GA cloth and black rubber wire pair from the fusebox in the basement 5 floors down.
Hells Kitchen in the 1980s, that was loads of fun. if you touched the 80 Year old wire, the insulation cracked like caramel on a cold day.

 

[reggie_obe]

Start by looking for the main breaker for your unit. Probably in the basement. One pole or two? Breaker size, wiring gauge and type from your main up to your panel?

 

[JST]

I did not see mention of this, only a 20A breaker. Although the 80% wire rating is continuous as mentioned, and highly unlikely to occur, but with the default VFD settings and a 1.5Hp it would far exceed the rated wiring capacity if turning deep cutting and/or repetitive cutting over minutes, which could cause significant heating. Given the age of the wiring, corrosion as well as insulation deterioration, it would not be advised. Where the breaker panel is and running a separate wiring would be ill advised in a rental unit.

...............................

If the wire is correctly sized for the breaker, that will not be an issue, The breaker will open if the wire is overloaded. Might take a while, but it takes a while to heat the wire also.

You would be scared to death at the ratings allowed for welders. Large overloads, but relying on the duty cycle, it works. Duty cycle does not get the wire too hot.

I didn't believe it, so I tested it. Sure enough, the wire got up to the nominal temp limit, but never exceeded it.

Very doubtful that you could get a dangerous or even near-dangerous situation with a breaker sized to the wire. I've seen tests where it took over 4x the wire limit current to start to do anything bad. The breaker will catch that, as shown in the time current curves.

If they have 20A on a 15A rated wire, that might be "edgy", for sure, but one cannot just assume that a circuit has been wired with bell wire and base everything on that.

 

[cyanidekid]

Start by looking for the main breaker for your unit. Probably in the basement. One pole or two? Breaker size, wiring gauge and type from your main up to your panel?

you can learn exactly the same information by pulling the cover off the panel in your apartment, and also the utility room is often locked, so just look in your place, in a relaxed manner, with the beverage of your choice...

If the wire is correctly sized for the breaker, that will not be an issue, The breaker will open if the wire is overloaded. Might take a while, but it takes a while to heat the wire also.

You would be scared to death at the ratings allowed for welders. Large overloads, but relying on the duty cycle, it works. Duty cycle does not get the wire too hot.

I didn't believe it, so I tested it. Sure enough, the wire got up to the nominal temp limit, but never exceeded it.

Very doubtful that you could get a dangerous or even near-dangerous situation with a breaker sized to the wire. I've seen tests where it took over 4x the wire limit current to start to do anything bad. The breaker will catch that, as shown in the time current curves.

If they have 20A on a 15A rated wire, that might be "edgy", for sure, but one cannot just assume that a circuit has been wired with bell wire and base everything on that.

yes, generally agree, but that kinda assumes all connections are good (at least decent), and ive seen some truly scary stuff in old buildings.
the wire, even if not an imminent fire hazard, will still throttle the current if it is 14ga. that's why I think a direct pigtail is a very good idea.

 

[JST]

Bad connections are equally evil for any sort of wiring. Yes, old buildings..... I've lived in them too. I grew up in a house built in 1914, with knob and tube 14 ga wiring, and live in a house built in 1933. No knob and tube, but plenty of 14 ga, in that delightful old cloth covered hardened rubber insulation.

Scariest thing in the 1933 house was an added circuit, wired with 14 ga aluminum wire, tied into a 40A stove circuit. I disconnected that virtually instantly, and did not pull a permit to do it, either. (there was a double 120V outlet wired in by the electrical panel, in addition to the one in the dining room that it served)

As for "throttling current", well, sort of. If you draw current within the limits of the wire gauge, it's fine. The issue is a voltage drop. At 20A, the drop is not that much added, 133% of normal max drop. And a bit less than double the usual heating.

If a 3% drop is taken as maximum, and you were at that already with 15A, then you would have a 4% drop at 20A. A drop of 4.8V instead of 3.6A.

It would certainly put a limit on fault current, if a dead short existed at the end of the wire. The max current with 14 ga would be less than with 12ga.

Might it, for instance, have some effect on charging of the bus capacitors in a VFD? "Some", yes.

Would that be significant vs 12 ga? That depends on the effect of 1/3 more resistance.

However, the most worrying issue with trying to run a larger motor in an old apartment, is what you and several of us already mentioned....... Is the wiring done correctly, does the breaker and/or outlet correctly represent the circuit capacity?

The outlet is no guide at all, 20A outlets are installed by landlords willy-nilly. The breaker SHOULD be a guide, but that depends if the box and breaker were installed by an electrician, or by the brother-in-law.

 

[jim rozen]

This seems to be a hit-n'-run by the original poster.

Either he tried it and it worked, he moved, or burned up the building trying it out. My approach would be to plug a 1500 watt heater into the receptacle and see what smoked up.....

 

[Nmbmxer]

I've not used those machines, but I've lived in an apartment and my neighbors complained about noise constantly from a reloading press. Id be more worried about them than power levels. To keep them from whining about machinery noise the material removal rates would have been far lower than 1.5hp. I can't imagine taking a cut heavy enough to eat up 1.5hp in an apartment setting.

SB9's used 1/4-1/2hp motors originally and that seems more reasonable. I'd get the 110-220V VFD and see how it goes, I just don't see you burying a carbide insert and spraying blue chips everywhere.

 

[JST]

It makes a lot of difference where you are in the building. On the first floor, you can make noise and it will be a minimal hassle to others, but you get other's noise as they clump about in their hobnailed boots upstairs. Never had any complaints about noise when I lived on the first floor in multiple apartments (but I wasn't running lathes and mills).

 

[microns]

Thanks to all for the replies, I didn't mean to go awol (or "hit and run" as someone said). I was doing more research on the lathe, the motor, and looking into the suggestions and comments that were posted here. One of the most important things I discovered was that unlike most other Habegger/schaublin 102s, which are equipped with 1.5HP motors, the one I am looking at only tops out at 0.9PS (roughly similar to HP), with a listed current draw of 3.2A. With these new specs in mind, it seems that I should be able to move forward with a 1.5HP VFD, that also does the voltage step up internally, like one of these: Weg - CFW300A06P0S1NB20 (without breaking), or Invertek - ODE-3-210058-1042 (with breaking). I suppose I could also do a 1HP VFD too, but as some of you mentioned it seems that oversizing the VFD is the way to go. I am not sure what it was about this motor/pulley/countershaft/belt set up, but it was enormously noisy, much louder than other 102s I've heard. For that reason, I am also wondering about a DC brushless motor as a replacement, but doing all of the mechanical work for that would also be a big task.

 

[microns]

I guess I should also re-state that wiring directly from the breaker box, or installing new circuit breakers is most likely out of my purview. I do have "access" to the breaker box; it is in my kitchen, and the lathe would be a room over, in the living room (yes, you can laugh at me). I will try to verify that the wiring is actually 12 gauge, or whatever matches with 20A breakers, but beyond looking at the wires in the breaker box (a bit scared to remove the front panel that covers the wires/everything except the breakers themselves), there isn't much I can do to verify what's in the wall, connecting the panel to the wall socket I'd be using.

 

[jim rozen]

1) photograph the panelboard in the kitchen.

2) for this motor a 1 hp VFD is perfectly adequate. You can purchase one that runs off 120 volts. Hitachi is a good name.

 

[microns]

I will post a picture of the panelboard when I get home tonight. As for the VFD, why is it that some people suggest upsizing based on HP/watts/amps, etc etc. I have tried to google this and search for past threads but I can't really get a clear answer.

Also, just to confirm; the best option would be to wire the motor for the low speed (looks like 1700 rpm), and use the VFD to vary up and down for there. A couple of people have mentioned this, but I am assuming this is has the purpose of giving you more torque at the lower rpms, while also still giving you speeds up to 3600 or so via the VFD potentiometer?

 

[microns]

Jim- here is my "breaker box." As you can see, it doesn't even have a main breaker switch that I can shut off, so I really don't want to unscrew this panel and see what's going on. I think some old nyc apartments have these sub panels, where the main breaker is somewhere in the basement.

 

[JST]

I will post a picture of the panelboard when I get home tonight. As for the VFD, why is it that some people suggest upsizing based on HP/watts/amps, etc etc. I have tried to google this and search for past threads but I can't really get a clear answer.

Also, just to confirm; the best option would be to wire the motor for the low speed (looks like 1700 rpm), and use the VFD to vary up and down for there. A couple of people have mentioned this, but I am assuming this is has the purpose of giving you more torque at the lower rpms, while also still giving you speeds up to 3600 or so via the VFD potentiometer?

Per the motor rpm, yes it will do something toward that goal.

Upsizing may have various goals. One is to ensure enough amps are available for the motor which might need more to supply low speed torque. Sometimes people will use a larger motor and VFD than needed, specifically so the current limit can be higher and the net output of the "de-rated" system will more closely match that of a lower power motor that uses a mechanical speed reduction.

Another is de-rating due to single phase input, although the voltage doubling VFDs should all be OK with single phase at full power.

Those are common ones, there might be others that folks are thinking about

 

[microns]

JST- thanks for the succinct summary; all of that seems to make sense to me. But then Jim thinks a matched HP VFD (1HP in this case) would be adequate. All of the threads I've seen feature both trains of thought but no one ever seems to invalidate each other. Some will just say match the HP, and some will say to over-rate it. I realize I'm probably going back and forth over a minor detail, but what would YOU choose in this case?

 

[jim rozen]

"...the best option would be to wire the motor for the low speed..."

No. Your motor is likely a consequent pole motor, and the low speed has 1/2 the hp of the high speed. If you use high speed, and cut the vfd to 50% speed, you get exactly the same effect as if you had wired it in low speed.

Also - your panelboard seems to be quite modern, suspect you'll have no problems running a 1 hp VFD from your 20amp branch ckt.

Be aware the VFD won't play well with a GFI if you have one feeding that circuit.

 

[markz528]

You really should not be sizing the drive based on horsepower. You should size it based on rated output amps.

Example why to oversize a drive - I will probably get too technical here, but an across the line motor starts to the left of the speed torque curve but a motor on a VFD always runs to the right of a speed torque curve. The advantage of the vfd during starting is that on a good drive you can potentially get substantially more starting torque than across the line start (based on speed torque curve of the motor). But in order to get this additional starting torque, the amps are quite high compared to running amps. This is where oversizing a drive really comes into play in order for the drive to provide the amps for the high starting torque.

But for an application like this, I would not get too hung up up on oversizing. The drive will have some short duration overload capability. My position is that for an application like this if the drive output amps exceed the motor full load amps then you would be fine.

 

[microns]

Thanks for the technical picture Mark. I understand what you mean about the sizing being based on amps, but I guess the uncertainty comes in while dealing with old Swiss motors like these. I think this one must be from the 60s. Is the 3.2A listed the FLA? If so, will it draw more than 3.2A now, 60 years after it was made, with more mechanical wear in the bearings and unknown condition of the electricals? Etc. That is why I was learning towards oversizing, as the 1.5HP VFDs are all roughly rated for 5.8-6A or so, while the 1HP ones are around 4.3A. I don't know just how much current the motor will pull, at normal load, or for big transients on start up, etc.

 

[JST]

There are also overload limits, with a time. Often there will be 150% current capability, with a limit of from 30 sec to 3 minutes, usually. Some will have a very short term 200% limit, possibly 2 to 5 seconds. Those get you through starts, even with reasonable inertia in the motor system.

For a high inertia system, you may need to think differently. Look at the accel figure. Often a slow accel will fail by exceeding the time/current curve built into the drive. The you may find a sweet spot of faster accel, which does not exceed the over-current limit, but gets the accel over with before the higher limit times out.

For "normal" systems, use of the accel parameter will get you a good start without a high current problem. Starting is not going to bother wiring, unless there is a loose connection. ANY current draw usually has some sort of problem in that case, so if the circuit runs ordinary household items, it will be OK with your VFD. That's not a "guarantee" , though.

What would I do? Probably install a smaller motor. I might get the larger VFD, and adjust the parameters to match, just so at some later time the original motor can be put back on.

There is always the option of not using the lathe at maximum, also. The motor pulls only the current it needs to run the load it has. Motors automatically do that, and you need not make any adjustments for them to do it. Just enter the motor parameters when setting up the VFD.

The motor is unlikely to draw more just due to age. A specific issue generally causes that, some added friction, a heavier load, or some issue with the windings. You would normally use the motor plate to obtain the motor ratings for the VFD parameters.

 

[jim rozen]

This is basically a 1 hp motor. A 1 hp drive will work well I think, set the accel times fairly long.