Shopsmith Forums

you mentioned it would not start on slow speed ? any idea why ? Like JPG said ? one would think it would spin easier on low because less tension on the belt and pulleys ? is something binding ? also there are places on the shaft inside the headstock that need oiled ? can you spin the shaft with your hands ? how about the shaft bearings ? as far as measuring the amps on the motor there are several ways to do it safely , depending on the tester you have one would be with a clamp on tester at the breaker box if it is close enough to your work station and one would be at the power wires in the control box in the head stock this may require removing the headstock , clamping it to a bench and bench testing it . from your description , JMO it sounds a lot like a pulley or tension issue , does the belt get hot ? my'n did something similar when I got it,, it was the speed control pulley not releasing when the speed was adjusted . good luck .you got this .

Summary Version: I tried to simplify this explanation but it remains tedious. The problem described (slows down and stops when the CB trips when something is attached at high speed) is normal behavior for an overloaded motor condition. That condition could be, and I suspect is, caused simply by the combination of high speed and something attached.

Since you said you had a general knowledge of electricity I'm going to go for more of a layman's explanation of some of what I see as information that might not have been effectively communicated (mainly by me).

Measuring Amps - Two common methods are in-line and clamp-on. For simplicity, clamp-on is the only one we'll consider. The measurement device has a loop that one power wire, hot or neutral for AC, passes through. It will not work if both power wires pass through the loop.

Typical SS AC Induction motor in a headstock - You don't need to check your label, but there are three parameters on it important to understanding it: Current/Amps, HP, and RPM. They are rated at Max HP only, so for this discussion it is 13.2 - 13.5 Amps, 1-1/8 HP, and 3450 RPM all at the same time. While the motor is starting it will draw way more current and produce way less power at speeds from 0 - 3450. After startup it will run at a speed ranging from 3450 to a little bit faster than that as determined by the mechanical load. A hard limit of 3600 RPM exists only on paper, in practice it will never reach that speed so the RPM range is narrow. In this speed range, 3450+ RPM, Amps and HP are inversely related to RPM. So as load on the motor is increased, RPM will decrease slightly while Amps and HP needed to balance the load will increase.

That is important because 3450 RPM and 1-1/8 HP are critical in this discussion. If the load causes the speed to go below 3450 everything changes. Amps become inversely related to RPM and HP. This is an overload, the motor is drawing more than its designed steady state current and generating potentially damaging heat. A few things can happen in this state:
A) It is my understanding and experience that AC SS motors have no internal overload protection, ruling out one possible outcome. But SS has used several motors so self-protection gets an honorable mention.
B) The overload is removed and things recover. Usually the operator is involved, senses the overload, and changes the load (e.g. slows the feed rate).
C) Unlikely in the case of a power tool, but the load diminishes with RPM to the point that balance between power produced and required is achieved at current and temperature levels that exceed the design but can be sustained.
D) The motor burns up.
E) The Circuit Breaker trips.

Now I'll apply that to the headstock I provided AC current values for. We know the motor is turning 3450+ because Amps are reasonable. As I increase headstock speed Amps start increasing, motor speed is pretty constant, but actually decreasing slightly. This continues, varying from less than 8.0 up to 12.5 Amps, and I believe this motor was marked 13.2 on the plate. The additional work, as seen by the motor, accounting for that 4.5 Amp change consists of spinning some belts, bearings, and shafts faster than before, all the same parts are in motion.

Assuming your headstock is similar, you are then adding burden to that load, meaning more bearings, shafts, a blade, etc. It follows that your AC current would be greater than 12.5 Amps, perhaps significantly greater. In other words, you are perhaps experiencing normal operation for the abnormal test case you're creating. And that you are experiencing the best possible outcome with the CB tripping.

-David

Is it possible that the contacts have fused together, keeping the start winding's engaged , as described in this post by Bill Mayo.

https://www.shopsmith.com/ss_forum/view ... 248#p48248

rpd wrote:Is it possible that the contacts have fused together, keeping the start winding's engaged , as described in this post by Bill Mayo.

https://www.shopsmith.com/ss_forum/view ... 248#p48248

It IS possible and was mentioned quite early above.*

* May have been a different thread!

We have not determined why lack of starting torque at slow speed setting. Is it possible that the start switch is opening too fast at slow setting, and failing to open at fast??? Loose mount???

I think you folks have given a straight forward and narrow path that should solve the issue , My point and I did not fully explain it .by measuring the load at the breaker it will tell you if the load is too high for the breaker , measuring the load at the headstock will define how much of the load is being consumed by the headstock, in brief,, if the load on the breaker is too high do not increase the breaker size ,chances are the wire is not rated for doing so , instead reduce the breakers load by adding another breaker for the headstock . if the load is with on the parameters of the breaker replace the breaker . jmo

Hey guys! Sorry for the hiatus! Reading back through these posts, but in brief answer, I'm okay with live wires, as long as I have the right gear. Rubber gloves etc, I do have electrical clamps, wires and the multimeter. I am going to snap a photo of each of them. I want to get this running so bad before my job opens again.