My $45 homemade 10 HP phase converter is WORKING!!!

Chuckle...Ill try to explain this...

Most US homes use single phase power. This means there are two wires in the outlets, plus a ground. It can be 120volts or 240 volts, but there are just two "hot" wires (over simplification for ease)

Industrial machines use for the most part...3 phase power. There are 3 hot wires. and will not run properly on only two. They heat up and burn out quickly or refuse to start.

There is a lot of surplus industrial machines available, for very little money that work very well for home use. Even a moderately worn industrial machine is likely 3x as well made as a brand new Chinese big box store machine. An example would be a Ryobi table saw from Home Depot, versus a Delta UniSaw from an industrial auction. One might last a year or two...the Delta the rest of your life.

So a way must be found to allow a 3 phase machine to be run on single phase power. Hence we have rotary and static converters (and a few other ways) which make up the 3rd hot wire.

Such a converter allows you to run industrial type machines on the 240 volt power that comes into your house. Plug the converter into your electric dryer outlet and now you can use that Delta UniSaw, as an example. Lathes, milling machines, drill presses, heavy industrial welders, etc etc are all available, and most often are not even available in single phase models. Hardinge Lathes, are an example. Due to many factors, the machine cannot easily be changed over by replacing the motor with a single phase one. So has to be run on

3phase power. Again..we use a converter to generate that third hot wire so it can be run off your dryer outlet.

Help any?

Gunner

Liberals - Cosmopolitan critics, men who are the friends of every country save their own. Benjamin Disraeli

Liberals - Cosmopolitan critics, men who are the friends of every country save their own. Benjamin Disraeli

"Ignoramus9394" wrote in message news:Xy4Ge.6053$ snipped-for-privacy@fe12.usenetserver.com... | I do not mind installing an overload relay, as such, except that it is | a cost issue. Fuses are cheaper. (unless I can find something at that | junkyard). Realistically speaking, the idler is not going to bind. If | contacts to capacitors break, yes, I could have a stall issue, which | would be addressed by properly sized fuses. | | A relay is more exciting and possibly a little more convenient (it is | resettable, I do not need to buy new fuses when a fuse burns out), but | in reality will provide about same protection. | | Am I mistaken? |

Your 220V home circuit breaker has two poles, but each pole is connected so that if one leg has an overcurrent, it will trip, taking the other leg out with it. Otherwise, one leg will still be hot, presenting a very ugly hazard. Fuses cannot provide this protection, and as such, are a single shot deal. Overloads, on the other hand, have various trip conditions that can be selected for, and they take all three phases out at the same time, which is the safety you need.. Ask your supplier for assistance in picking them, I don't have that information at hand anymore. While motor starters have the contactor and the overload physically attached to each other, electrically they're pretty much the same so one brand ought to be usable with another even if you can bolt them together. Just for the sake of the record, a motor starter consists of a set of three large contacts, possible auxiliary contacts (usually clipped or screwed) and the overload. The overload has three fuse looking elements that are called heaters. When the heater gets to a certain point in its thermal cycle, it will bend and trip the overload, which actually just opens it's own auxiliary contact and the contactor opens up. The solenoid on the contactor is wired through this overload contact, so in order to reset it you usually have a reset button to push. To add a little more confusing information, starters are given sizes, according to NEMA, thus you have a starter for a given range of motor sizes.

has a lot that info that might help you understand better. The overloads are sized to match as well.

Thanks. That's very helpful!

i

I

As I remember instructions, the contactor does drop out when the 240 single phase power is lost. That assumes that you use buttons to engage the idler.

Jerry

Jerry, I am a little confused, what particular contactor are you talking about? My definite purpose furnas contactor? If so, I believe (and will verify it tonight) that it is stupid and closes when 110V is applied to the coil, that's all.

i

Like many other people, I put a 3 pole relay in my RPC. Two poles transfer the pair of hot wires through to the drop-out contactor and the third pole completes the circuit that drives the relay. If power to the RPC is cut, the relay cuts out and doesn't reconnect when the power comes back on. A simple magnetic safety switch.

I got the 3 pole relay for a few bucks from surplus center. Knowing your scrounging ability, you could probably come home with the relay and a few dollars more than you left with.

Pete

You are probably OK. I didnt read the right instructions. I understood that your contactor wouldnt drop out and stay out whenever the the 240 power failed. I thought the instructions showed the contactor was held in by a connection in the contactor, which opened whenever the power is lost . I'd have used good push butons to start and stop a 240 volt idler.

Jerry

What they are refering to is a specific way to connect the contactor and 2 push buttons together. Push the NO start button and the contactor engages and the machines starts and runs. Push the NC Stop button and the machine stops. A key part is that the power for the contractor is supplied from the back side (not the line side) of the contactor so that the contactor will drop out and stay out if there is any interruption in AC power. The start button momentarly supplies power from the line side to the contactor to start the machine. I think this is called 3-wire control.

chuck

I'll check them out. It is an interesting idea, but I am not sure why the need for it though.

Let's say, hypothetically, that I have a single phase mill. Power goes out. The proper procedure is to turn off the mill and go do other stuff.

If I forget to turn the mill off, it will turn back on again, with the obvious consequences.

Now, let's say that I have a 3 phase mill. Power goes out. What are the possible consequences of me forgetting to turn it (and RPC) off?

The answer is, the same as in the single phase example above. The phase converter itelf will not be damaged by returning power, it will simply restart.

If so, then, logically, I need to install similar relays on single phase equipment as on 3 phase equipment. And yet no one does this with single phase equipment.

Protection of RPC itself cannot be the reason, since it starts just fine when power is restored.

What am I missing?

i

I see. I plan to install a regular household light switch to control the contactor. UP means run, DOWN means stop. I will have two electrical boxes on the outside of my RPC: one for incoming single phase power and the switch, another for outgoing power. I may also install a Square D disconnect on the outgoing side of the converter. I already bought that disconnect used.

i

Thanks. I understand this, I was simply saying that I do not have such a switch. I am not quite sure if I really need it, either.

i

You can use your furnas contactor as a drop-out device. You wire it to hold in, using the third contact.

The other two contacts carry the incoming 240 volt lines to the motor.

This way a control circuit (which really should be derived from the same incoming 240 volt lines via a 240:120 transformer) with two pushbuttons can run the thing, and the buttons don't carry the load currents.

Jim

It would be best if you did. All you need are the two pushbuttons (one NO, one NC) to implement this function, because you already have a spare contact on the furnas relay.

Jim

You are correct. I believe this is acceptable for a residence but I SUSPECT its not allowed for industrial applications and that is why its commonly used.

There are some applications were auto restart is not allowed and this is why they make make single phase motors with manual reset overloads too. I have noticed lots of warnings in Grainger catalog about auto reset thermal overloads on motors. They want to make sure that the person working on the machine isn't surprised and injured when it restarts by itself.

Some VFD will also not allow auto restart. My Boston fincor VFD will not start the motor when power is applied with the switch in the RUN position. In this case the switch has to be moved to stop and the reset button pushed. The Teco drives are not as smart. They attempt to do this but will auto start if the power is gone long enough for the VFD to forget its previous state. I am still somewhat dissapointed in this. All my VFDs will flash overload and wait for manual reset when the motor is overloaded. This is done to emulate the 3 wire control and autodrop out of the contactor.

Most people here tend to treat their shops in a conservative manner and implement some of the industrial safety measures for their own safetly. A good friend of mine lost a finger when a machine started on its own. I want to keep mine.

chuck

There are a couple of reasons to use a drop out contactor. One is to protect the RPC and any other 3 phase motors you put on it; even though your RPC is normally self starting, it might not start when there is an additional 3 phase load on it. If the power goes out when the RPC is running and some additional 3 phase machine is also running, and you forget to turn either off, then when the power returns the RPC run capacitors will be trying to start two motors simultaneously. You have only verified that they can start the RPC by itself.

The other is simply that it is not generally a good idea to have machines starting up unexpectedly, as they might when you forget to turn something off when the power fails. This case isn't any different for single phase machines, and they should have the same sort of relays. Of course as you know they often don't.

allan

This IS done on at least some single phase equipment....My Delta Unisaw has a magnetic switch that works that way. If power is lost, the relay drops out and the saw will not restart when power is restored, until ya press the button again.

I guess the idea is that the machine may not get turned off when power fails, and you may not be around when power returns.....

Posted FWIW....

Jeff

Thanks. I have become convinced that I need such a relay. What I would like to find, for not too much money, is a relay with start/stop buttons and overload protection for a 10 HP motor.

What is the proper name of such a thing and where should I look for it. It is very painful to explain what I need, without knowing the proper name for it.

i

Chuck, thanks, I am convinced. I will look for something like that. Any tips will be appreciated.

i