Furnas Motor Starter, Size 0, Rebuild / Upgrade

[woodchucker]

Thanks for the explanation.

 

[toolman_ar]

You are welcome.

When I purchased my air compressor the guy asked; "do you need a starter?"

My response was maybe... tell me what it does...

My understanding of how this equipment works and why grows every day. I am still a beginner.

 

[bazzystar]

I need help diagnosing a delta Rockwell band saw. It has a 1.5 hp motor and a furnas magnetic starter. I had received this project from another person who couldn’t figure it out. The goal is to switch it over to 220 3 phase. I have no power to the unit when I plug it in. No noise. Nothing. I’m a newbie and electrical is not my strength.

 

[Bi11Hudson]

I need help diagnosing a delta Rockwell band saw. It has a 1.5 hp motor and a furnas magnetic starter. I had received this project from another person who couldn’t figure it out. The goal is to switch it over to 220 3 phase. I have no power to the unit when I plug it in. No noise. Nothing. I’m a newbie and electrical is not my strength.

Good evening, Sir;

I just found your post, thought to throw a little archaic knowledge your way. It has been so long your problem probably has been settled. Then the post from bazzystar showed up. A similar problem. Please understand, I am (was) an industrial electrician in my earlier years, before the BSEE. I have respect for the power of OSHA and other mommy government agencies but hold them in very low regard as a working man. In my day on the foundry floor, I usually was attired in sneakers and a ball cap. When the molten iron slung out, you ran. Didn't stand around to get burned. /// End rant (not) ///

What you both are dealing with is a "pre-OSHA" starter. Some desk jockey decided a third heater was necessary. If the current of the unprotected leg is too high, that current has to be in one or the other protected legs. Thus only two heaters on a three wire system. If you want to meet OSHA regulations, by all means add the third heater. Otherwise, just don't worry about it.

Some basics on "starters" vs relays: A starter is no more than a high current relay with an overload deck. They can be dealt with as two separate devices in one package. So, first thing, consider the power supply voltage. Probably 240 or 480, that old it may be listed as 208 or 220. No matter, it's a range, not an absolute. Look for the starter coil, check the voltage there. It may be as low as 24 volts. There may be a transformer somewhere. Low voltage control is not uncommon, then or now. Check the motor voltage while looking, too. Note it but take no action right now.

Next is a three wire control station. That's the probable way, but it may be just a latching push button on a locally controlled machine. I have a drawing of a three wire station if you need it, but I don't want to look for it right now. The control station will be wired in series with a contact on the overload deck. When the overload trips, the concept is to drop out the control station.. So, from the standpoint of control, there is the line(1), a 3 wire control station, the coil, the overloads and line(2). On 120 volt control, that last may be a neutral. On a transformer(low voltage), if one line is grounded, it will be that one. These leads will be the two small wires on the overload assembly.

Next up is the power leads. If the starter is marked (some are, some not) find L1, L2, L3. They will be at or near the top. That's a convention far older than I am, power "flows" down from source to load. The "L" leads go through a set of contacts to the "T" leads. The "T" leads then go to the overload assembly. One of the leads will jumper down past the overload deck. The connections may be wires or just buss bars. At the bottom of the overload assembly(deck) are the terminals for the motor. Why "T" leads for a "M"otor is beyond me. It's just the way things are.

Now to the root problem. Wrong word, but I'm slow tonight. An overload has two general methods of operation. The first is a "bi-metallic" strip that bends as it heats. And much more common from what I've seen, a "solder pot". Every manufacturer uses a different technique. One has a "flat pack" with a ratchet wheel on one side. Another is the use of a post mounted in the overload assembly. The "heater" is a separate coil of wire that is calibrated for motor current. In any case, the heater/overload MUST be calibrated to motor current.

Look at the motor nameplate for "full load amps" or "FLA". A "nine wire motor" is what I am most familiar with, a dual voltage 240/480 Wye wound motor. There are many, often changable, wiring configurations. And even more for single phase motors. Motors deserve a goodly sized book on their own, with overloads a couple of chapters therein. To keep it simple, just determine whether to use the high or low voltage current rating. I will try to stay away from writing a book here.

Back to the overloads, there should be a chart inside the starter case. Likely age has worn it out. On used equipment, it is rare to have the chart in hand. Worst case, find a true electrical supply house, lay an overload on the counter telling the salesman you want one like this but. . . Let the salesman do the research work. That's what he's paid for. However it is accomplished, the overload "heaters" must match the rated motor maximum current. If they are too small, there will be niusence trips. If they are too large, the motor may be burned up. And motors ain't cheap.
For testing purposes only, Do Not run the motor in service this way. A fire in the making. . . The overload heaters can be replaced with a wire of suitable size. There will be no protection. But it can be run unloaded for a short time to test the rotation and the like.

Lastly, for "bazzystar, post: 802303", I tend to shy away from digital instruments for electrical work. They usually work but there are circumstances where you don't get a valid reading. A couple of 240 volt lamps are more reliable than a Fluke on the mill floor. A "Simpsom 260" is far better suited for electrical work. For electronics, I have a couple of Flukes. But for electrical. . .

Assume the line cord is plugged in and the circuit is good up to the starter. There will be no indication short of getting shocked that power gets that far. Press the start button. The starter coil should pick up. Unplug the cord. Connect the motor. Try again, the motor should run. What that does is prove each portion of the circuit. The most likely reason it doesn't is the overload heaters are not in circuit. Unplug, mount the overloads, and try again. Short of the heaters, if any portion of the trials fail, it's time to trouble shoot.

There's much, much more to trouble shooting. And should be done locally. Finding a "qualified" electrician is the best bet. The best I can offer remotely is http://www.hudsontelcom.com/uploads/ShopElex.pdf. Just keep in mind that wiring a house does not an electrician make. Find one that knows motors. . . It's past 2 AM and I'm more interested in what movie to watch than an unqualified man trying to shoot a motor system. If I can help, I will. But on my time, not right now.

Bill Hudson​