Changing the motor voltage to 220 V AC

[markba633csi]

They are a bit more efficient on 240 because of things like copper loss, eddy current losses and stuff like that. It's a small amount, around 3% I think
Because the resistivity of copper is a constant, when you double the voltage and halve the current the whole system gets more efficient, the wiring in the wall, the motor, everything. Less voltage drop means more power delivered to the load
This is why automotive electrical systems went from 6 volt to 12, less copper required, less weight, etc.

 

[stioc]

Well said Craig. I'm not an electrician either but that doesn't stop me from playing one Just added two 20 amp breakers to the panel and ran 12ga wiring for 12 outlets. And I'm in the middle of running a 220v line too.



But the reason I asked if there's an advantage is because my mill's 2HP motor is rated for 16A at 110v and 8A at 220v which I'm assuming are peak amps -because my 15A breaker has never tripped. Of course it's possible I have a bad breaker, I need to put my Kill-A-Watt plug on it.

 

[Karl_T]

All horses aren't the same. Sears came out with a supposedly 4hp air compressor 20 years ago. it ran on 110. that's when I coined the terms "sears horses". They are just ponies.

A true 1 hp should draw 750 watt with a 2:1 temporary overload.

As for that 2hp mill on 110, you just need to be aware not to push your mill to the limit. easier said than done - something will go harder than you expect sooner or later. if you ever rewire, move etc. upgrade it to 220.

 

[mksj]

So a few things to clarify, it is one thing change the wiring on the machine from 120 to 240V single phase if designed to do so. But a whole different proposition changing out the motor to 3 phase and adding a VFD. There are a multitude of factors that determine the load requirements and electrical sizing of the socket, and the requirements of the equipment you plan to use. Looking at the Hp alone, well that can be anything depending on the actual current being drawn at the rated voltage, what load it is operated under, and for how long. You often see vacuums rated 4-5Hp, but plug into 120VAC 15A sockets, the real continuous Hp/current is much lower. A VFD on the other hand can draw upwards of 200% of the motor amperage for up to a minute, so the maximum size 120VAC VFD is around 1.5 Hp and this requires a 20A plug/breaker. As other's mentioned, most 120VAC sockets are 15A, so trying to run a 2 Hp motor off of that is not wise. The running Hp/current under no load is less, but current and resistance is what cause heating in the wire. Use a smaller wire at a higher current = more heat and eventually damage and possibly fire.

Breakers are designed to protect the wiring, but the assumption is you are not overloading them based on the socket/plug rating. Breakers are also designed with different trip curves, depending on the age and wiring, it may not be working at 100% of spec. Wiring in a house and also appliances have a safety margin built but there may be some de-rating based on the the wire ratings and associated equipment. A breaker is usually designed to trip based on current over time, so you can pull higher peak currents over a specified time. The motors with very high starting currents to not trip the breaker, as long as the current quickly declines.

If you plan to go to a VFD, then you need to replace the motor and for the most part you would not be using any of the current machine controls/wiring, so a complete rebuild. The only available VFD's for 2 Hp are 240VAC, the VFD manual will usually specify a 30A breaker, it may run off of a 20A breaker if you dial down some of the VFD load parameters or have light duty use. It will run, and may be fine, but for continuous use with load I would use a 30A breaker. The circuit breaker is supposed to be sized to ~125% of the VFD full load rated input current, does not matter what the VFD is connected to.

 

[stioc]

@mksj thank you for the informative post. I agree, if I upgrade it to a 3 phase motor (and a vfd) I will be running it off of single phase 220v and at least dual pole 30amp breakers with 10ga wiring. The original question was out of my curiosity if there's any benefit to converting a 110v wired motor to 220v.

Speaking of converting to a 3 phase motor I found this article helpful...even though it specifies Automation Direct's products but I learned about the NEMA frame sizing which I didn't know. This will certainly help finding a motor that fits with minimal modifications.

Converting a Mill/Drill and Installing a VFD

Modern VFDs have the ability to take single-phase electricity, convert it to three-phase with full power, speed control, reversing ability, and more.

library.automationdirect.com

 

[WCraig]

the reason I asked if there's an advantage is because my mill's 2HP motor is rated for 16A at 110v and 8A at 220v which I'm assuming are peak amps -because my 15A breaker has never tripped.

We as the operators of machines like a mill, lathe, table saw or whatnot control how much load we put on the motor. If you push the mill quickly through a long, deep and wide cut, you could well trip the breaker. Most of us recognize the stress we're putting on our machines and don't push them to their limits. On the other hand, things like a water pump or air compressor face pretty much the same load every time they run.

Ideally, if you were to continue running the mill on 120 volts, you'd want to put it on a 20 amp circuit so you have some headroom over the 16 amp full load draw. I agree that 240 volts makes sense if adding the circuit isn't prohibitive.

Craig

 

[rock_breaker]

I have a 220 volt air compressor at the far end of the shop from the breaker box and a 220 volt Enco lathe within 8 feet of the mill and they are both within 8 feet of the breakers, it is an opportunity to reduce the heat potential. My band saw is is close to the compressor outlet so I installed a 220 volt switch, a polarized plug and changed the motor connections. Again this is about reducing heat in the wiring.
Have a good day
Ray

P.S. Mark thanks for the info.

 

[RockingJ]

I had problems with my RF mill when running on 115 V. The centrifugal switch burned up the contacts. The centrifugal switch is what turns off the start windings in the motor when it comes up to full speed. I had to replace the switch.

If your wire is properly sized for the rtotal load on it, the wiring should not heat up, if it is getting warm then the wire size is too small and needs to be addressed!

I have learned not to use the horsepower ratings of motors now days, go by the amp draw or Kw rating. If you look at the HP on my RF mill it is rated at 2 HP but the amp draw is closer to 1 1/4 HP. Obviously Chinese HP isn’t the same as the rest of the world!

The mill may run better on 204V since the voltage drop through the wiring will not be as big of a factor.

 

[FOMOGO]

Not by any means an electrical guru, but it has been my experience that on dual voltage motors, running on 240 will always feel like you have more available power. I have an ancient Craftsman radial arm saw that had a tough time ripping 2x material. Rewired it for 240 and it was night and day difference. Same story with my old Buffalo 8" grinder. Mike