Upping the start up torque of an electric motor

[randyjaco]

I picked up a 20's model Heston and Anderson 14 " bandsaw for cheap. The problem is that it has very little start up torque. Once it is running it seems to have plenty of power. I would like to keep the original motor if possible. The motor in question is a 1/3 hp Century. I can’t locate the capacitor, so that idea seems to be out. I have loosened the belt and blade, so the saw turns very easily. Still about the half the time, I have to spin the wheels to get it started. All the electrical connections are clean and fresh. The motor pulley is about as small as possible. Any ideas on what I can do to get this puppy to start up on its own?

TIA
Randy

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[Magicniner]

I would like to keep the original motor if possible.

Keep it,

on a shelf ;-)

[J Tiers]

Does the motor turn easily?

If the motor will not start on it sown, it has a problem that requires work (or in a practical sense, replacement)

Possible that the motor start switch is not closing well, is dirty, worn, etc. It does not seem to have any place for a capacitor, UNLESS it is old enough to have a "donut" capacitor in the end bell of the motor.

If old, 1920s as you say, it MIGHT have a donut cap, OR it might be a resistance start unit, with a big resistor inside the motor, in wiring case, etc. I had one of those on a die filer that I sold. It's basically a regular split phase but instead of having a high resistance start circuit, it has an actual resistor. Either could be intermittent or have changed value.

If a donut cap, and that is bad, you will have to find a way to install a modern one. Ditto for a resistor that is bad. It will be a big ceramic one, most likely, and they are not very common these days.

[train_backshop]

I believe it's most likely the start switch. It's located inside the motor one the non drive end. It may need to be cleaned.

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[darryl]

I guess the big question is whether there IS a start capacitor with that motor. Maybe under the base? If there is one, it's probably dried up to some extent.

If there isn't one, then the start winding and start switch are all that's left. It's not clear whether there is a start switch, but you'll know if you hear it clicking out when the speed comes up. If it's there, then it's likely that there is also a capacitor- though it's not strictly required. I've seen the odd motor that doesn't use one.

[randyjaco]

Yeah, I can hear a click in the motor a fraction of a second after I hit the power switch. But I hear no clicking out until I cut the power.
The motor turns freely.
There is no capacitor on the bottom of the motor. If it has a capacitor, it's well hidden. It's not viewable from the inspection ports.

[J Tiers]

The click when it starts is the switch opening the start circuit. The other one when you shut off is it closing the start circuit ready for next start.

That suggests there is no MECHANICAL issue with the switch. It may not close electrically, or the circuit may be dicey elsewhere than in the switch.

[darryl]

I would pop both of those covers and see what's under them. One obviously has the ac wire going into that cavity, the other perhaps is access to the switch contacts-? Or perhaps the wiring from the capacitor if there is one. If you can identify the cap wires, then it's likely possible to extend those to an externally mounted cap.

Often enough when I do a project I'll drill a hole to fit the ac supply wire, then push a steel rod through that hole and force it sideways- one side of the hole dimples inward while the other side dimples outwards. I push the wire through that and lay the wire flat to the panel, clamping it down with a sheet steel bracket. Good to go. You could do that with one of the covers on the motor. Gives you a low profile way to add a wire.

[flylo]

I'd take ik it off & take it apart & have a look see. After 100 years it may be done but may need cleaning, tlc, new wire inside, you won't know until you get in there & may be room to put the old base around a new 1/3hp as back then motors were motors & men where mwn. I have sone 3HPs big as bushel baskets.

[Paul Alciatore]

I would say it almost has to be one of four things: lubrication/bad bearings, start switch (if it has one), capacitor (again if it has one), and a broken/disconnected wire. Check those things and you have probably covered it.

Remove the belt and spin it. If it does not free wheel and coast for a while, lubricate and/or change the bearings.

Look for a start switch. If it has one, clean the contacts. It can't work if the contacts are pitted or corroded.

You have looked for a capacitor. If it has a start switch, it probably does have a start capacitor. Trace the wires from the start switch to find it.

Finally, look at the coils and the connections at the termination point. Undo each connection, one at a time and clean the wires. Then reconnect them. If there is a break in a coil it may show as a burnt spot or you may be able to find it with an Ohm meter. A break in a coil is hard to fix, but it may be possible.

That's about it. If it is not one of the above or at least if you can not isolate it to one of them, then just get a new motor. Or a new-to-you used one.

I didn't ask and you did not mention it, but we seem to be assuming that this is a single phase motor. If it is a three phase, one of the phases may be disconnected or have an open winding. This would cause it to operate in a single phase mode. But checking for this is covered in number four above.

[6PTsocket]

Does the motor turn easily?

If the motor will not start on it sown, it has a problem that requires work (or in a practical sense, replacement)

Possible that the motor start switch is not closing well, is dirty, worn, etc. It does not seem to have any place for a capacitor, UNLESS it is old enough to have a "donut" capacitor in the end bell of the motor.

If old, 1920s as you say, it MIGHT have a donut cap, OR it might be a resistance start unit, with a big resistor inside the motor, in wiring case, etc. I had one of those on a die filer that I sold. It's basically a regular split phase but instead of having a high resistance start circuit, it has an actual resistor. Either could be intermittent or have changed value.

If a donut cap, and that is bad, you will have to find a way to install a modern one. Ditto for a resistor that is bad. It will be a big ceramic one, most likely, and they are not very common these days.

Mouser or Digikey should be able to supply any resistance value and wattage, if required. A lot of,the newer high wattage ones are encased in an aluminum, finned heat sink. I have never seen or even heard of a donut cap before. You learn about some some interesting stuff here. I would never go this way and I do not offer the following as a practical solution. Assuming the motor would have sufficient torque if allowed to reach full speed, install an electric clutch between motor and pulley. Then of course you would need circuitry or a device to start the motor and then engage the clutch. Air compressors have pump unloaders to get the motor going. I wonder if something is not performing properly or this is even the right motor. 1/3 hp seems really small for the job. Just becsuse that motor and saw have been used together for many years, is no guarrantee that was a factory pair.

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[J Tiers]

The start resistor in the old die filer was a very non-standard case, and quite large. Made to take the start-up current for a short time, much like the capacitors are. it was roughly the size and shape of half a small fluorescent ballast. All ceramic case, same sort of ceramic as a PW-10, but obviously much larger. I have never seen another one.

Non-capacitor motors are actually quite common. Used wherever high start torque is not essential. They are not weak on torque, they just have a lower torque per amp of start current than a typical capacitor start unit. The capacitor gives a larger phase shift than the resistance does

[BCRider]

I've never seen a capacitor start motor that did not have a very obvious hump on it where the capacitor lived. At least no on smaller motors like this.

What it very likely has is a starter winding that is slightly out of position with the other windings. This is very common on small fractional HP motors. The switch feeds power to both the main winding and the starter winding and once it's up to speed the centrifugal force cuts the starter winding out of the circuit. I've always heard them called a split phase starting winding. But after looking up this "resistance" start method it had references to the starting winding being a higher resistance winding. So perhaps they are one and the same?

So the motor makes all the proper clicks for the start switch cutting out during power up and cutting back in on coast down. And it always starts in the proper direction? If that all sounds good then the starting winding is fine and the switch is fine. If the shaft turns freely with the belt off and can coast a couple or three turns from a wrist flick of the motor pulley with no belt it's fine too.

Such motors are known for their low starting torque. If your motor is taking forever to get up to speed then you might just need to swap it for a capacitor start type. Or if it's not something you turn on and off frequently and your idea of "a long time" is maybe 5 to 6 seconds then don't worry about it. If it's taking more than 10 seconds and you're doing frequent starts I'd start to worry about heat in the starting winding.

You asked about raising the starting torque. If this motor is a split phase switch starting winding motor as I suspect it is then there's nothing at all you can do. It is what it is.

[J Tiers]

The OP does not want to increase the start torque of a good motor, he wants to find out (and fix) why this motor seems not to start reliably. He makes reference to having to spin the motor manually to get it going.

That suggests that while the start system may be CAPABLE of starting the motor, it is not doing so every time. It intermittently fails to start.

That's a different problem from low stat torque as a design issue. The motor has some problem; loose connections, intermittent start switch, etc.

Since the motor has the same paint job as the saw, it is either original, or has been on there (and presumably working) since the last time the saw was painted.

[ulav8r]

Likely not much wrong with the motor. It is under-powered for the saw. The OP did not say, but I would suspect that a saw made in the 20's would have cast iron wheels. Even if they turn easily, they will have a lot of inertia to overcome. I would want at least a 3/4 hp motor for a saw that size unless it was running a blade speed of less than 300 fpm.