Phase Converters

[EastCoast Yota]

I just got a 10" pedestal grinder from work and noticed that it is 3 phase 220V. Does any one have any ideas on what I should get? I think the grinder is only 2HP. I have seen alot of phase converters for sale on EBAY but not sure if they are worth buying.

[Eric]

A static phase converter will cost around $100 and it will only produce about 66% of the rated output of the motor. Cheap and easy for a grinder.

If you were operating a mill or drill press, I would recommend a VFD....much more expensive, about $250. Way too many features that you will never use for a grinder.

[ray balcom]

Please expand on your phase converter experience ....can you control motor speed with it? ...i need one for my lathe and beside my contact relays are shot...

[Eric]

Originally Posted by ray balcom

Please expand on your phase converter experience ....can you control motor speed with it? ...i need one for my lathe and beside my contact relays are shot...

A static phase converter basically takes single phase input power and applies it to the motor's windings with a start capacitor between the generated leg and the two provided by you. The start capacitor delays the AC signal long enough the create a phase shift which creats an imballance in the motor and casues it to spin. After the motor reaches a specific RPM, the start capacitor is switched out of the circuit and the motor creates its own third leg called the generated leg. Since this is a generated leg from the 3 phase motor spinning, it doesn't have power to spin the motor so you are really driving the motor with only two poles = 66% power.

A Variable Frequency Drive (VFD) basically take single phase input voltage and electronically creates a 3 phase output. With this you actually get drive power for all 3 legs unlike the static converter where you only drive 2 legs. A VFD is so complicated and has so many features that it would take me too much time to talk about all of them. Bottom line is that it converts 1 ph input to a 3 ph output and allows you to control the output frequency which spins the motor faster or slower.

For example, if you want to run the motor at the set pulley speed, you set the output freq to 60 Hz. If you want to spin if faster, just increase the freq to 90 Hz and the motor will spin 50% faster. If you want to spin the motor slower, just lower the freq. However, don't run the motor at lower speeds for long periods of time since most motors have a built in cooling fan which need specific rpms to keep cool.

Other benefits are high starting torque, over load protection, stall prevention, adjustable accel and decel ramping speeds, accel and decel S-curve settings, automatic torque and motor slip conpensation, dynamic breaking, DC braking, skip frequencies, programable analog and digital inputs and outputs, relay outputs, RS232/485 comm, PID loops, and removeable keypads with speed potentiometer for easy adjustments and programming.

Here is a pic of the 2 HP VFD that I use at home with my Bridgeport.

[camo]

thanks for the tech eric. gives me a understanding of what is happing inside my little $100 static phase converter box.


i bought mine from one of the companys on ebay. paid under $100 for it and i use it to run my variable speed bridgeport mill, variable speed doall bandsaw and burrking sander. all three seem to work just fine in my applications using the el cheapo method of phase converting.

[Eric]

I can add tech for electrical stuff since that is what I do for a living (design flat panel TV/LCD processing equipment)

Don't get me wrong about using static converters....they are cheap and work just fine, but they just derate the HP of the motor......this is why you change gears/pulleys with them and you won't have any issues.

[JeepinDoug]

Het Eric, Could you post up a brand and model number for that VFD.
Thanks, Doug

[Eric]

Originally Posted by JeepinDoug

Het Eric, Could you post up a brand and model number for that VFD.
Thanks, Doug

Automation Direct has two different VFDs that I would consider for low end motor control such as milling machines, lathes, drill presses, grinders, motors etc. The GS1 and GS2. I use the 2HP GS2 (model # GS2-22P0) with 230V 1 or 3 phase input and 3 phase output. The GS1 is basically a stripped down version of the GS2 since it doesn't allow dynamic braking or have a removable face plate for remote mounting/control. I believe it has fewer digital/analog inputs and outputs.

I really like the GS2 over the GS1 since you can add a braking resistor to allow for dynamic braking. This basically lets you hit the stop button and you can control how the motor is stopped. If you are tapping holes, you may want the instant stop instead of coasting to a stop. It basically converts dynamic energy (rotating cutter) and converts it into electrical energy (current) through the resistor to disipate it as heat. The other cool thing about the GS2 is that it has a removable face plate that you can mount anywhere you want and just run a cable back to the VFD. This allows you to keep the power wires shorter, keep the AC Drive (VFD) in a box or away from flying chips, grinding dust, etc and still be able to use the keypad to set up the parameters and adjust the pot for fine tuing of the motor speed. If you mess up the keypad, they only cost about $30 to replace.

So, to wrap this up, any VFD will work to drive a 3 phase motor from single phase power. There are so many different VFDs to choose from, but remember this.......they are only made by a few different companies so they are practically identical except for packaging and firmware. A more expensive one doesn't mean really mean that it is better. The expensive ones are designed for applications that need all kinds of fancy control and feed back loops etc that you are wasting your money buying one.

Any brand VFD will work and what you are looking for is a "volts per hertz control mode". You don't need sensorless vector or flux vector control mode".

Automation Direct has decent ones for our home shops.
GS1 1HP - $159 does not come in 2 HP for single phase input

GS2 1HP - $199
GS2 2HP - $266
GS2 3HP - $313

They don't make one bigger than 3 HP for single phase inputs.

[JeepinDoug]

Eric, thanks, I definately want to be able to rigid tap in a Bridgeport.

[EastCoast Yota]

Thanks for the info. Eric. I saw a few on E-Bay I just wasn't sure if they were worth buying. I plan on getting a mill and a lathe someday, but for now I think the Static converter will do for the grinder.

[Eric]

Originally Posted by EastCoast Yota

Thanks for the info. Eric. I saw a few on E-Bay I just wasn't sure if they were worth buying. I plan on getting a mill and a lathe someday, but for now I think the Static converter will do for the grinder.

No problem on the info.

One thing I forgot.....while running, the VFDs can cause interference with the radio or TV. They do have different carrier frequency bands that you can switch to help reduce the amount interference.

E-bay is a good place to get old ones which may not be as good as some of the newest technology out there, but they will still work. Just make sure you get one that is rated for your motor's output voltage. You can't use a 480V output VFD unless your motor can run on 480V. Some of the older ones need to be derated to use a single phase input which sucks. So if it says 3 phase in/out, you will not get the rated HP since you are using it as a single phase input. Most of the newer ones will say "1 PH / 3 PH input and 3 PH output" and they don't need to be derated to run at full capacity.

Drop me a note if you are about to get one and I will check it out for you.

The Static phase converter will work just fine for a grinder since you probably won't be pushing so hard on the motor to stall it.

[AJ Johnson]

what about for 3 phase plasma cutters? I saw one of those on ebay, and it seemed like a good deal.. I also have a 3 phase hot tank that I've never installed...

[Eric]

Originally Posted by AJ Johnson

what about for 3 phase plasma cutters? I saw one of those on ebay, and it seemed like a good deal.. I also have a 3 phase hot tank that I've never installed...

VFDs are AC Motor Drives (they are designed to opperate AC motors).

[Dusty Booger]

I bought a static phase converter for my old LeBlonde lathe off Ebay. I think it is an Anderson converter. It has trouble on start-up. In fact you have to manually spin the lathe to get it going. However, once up to speed it does fine. If you had the money, I would not go with the static converter. I plan to upgrade- it just hasn't been a priority since I can get by. If I were to do it over again, I would have just spent the extra coin the first time.

[fj40guy]

Originally Posted by Dusty Booger

I bought a static phase converter for my old LeBlonde lathe off Ebay. I think it is an Anderson converter. It has trouble on start-up. In fact you have to manually spin the lathe to get it going. However, once up to speed it does fine. If you had the money, I would not go with the static converter. I plan to upgrade- it just hasn't been a priority since I can get by. If I were to do it over again, I would have just spent the extra coin the first time.

Dusty,

You have a BAD Static convertor. You shouldn't have to spin the lathe to get it going. Either the cap, relay, or your wiring is hooked up incorrectly.

Note the static convertors are "rated" for a certain size 3 phase motor. If the lathe motor is 2hp, you need a static convert witha "1 to 3 hp" range. Too large or too small of a convertor will not work.

Tom