How much power should I expect?

[BuckeyeDennis]

The voltage drop is easy to calculate, if you have a good wire-resistance table. The one below has all the details, both for solid wire and for all sorts of stranded-wire construction.

https://www.calmont.com/wp-content/uplo ... -gauge.pdf

Let's assume a 100 ft. run of 14 gauge solid wire. From the table, the maximum resistance of the wire is 3.5 milliOhms/ft. (The chart gives it as Ohms/1000 ft). Now keep in mind that the current has to travel in both directions in the cable, so for our purposes we actually have 200 ft. of wire run. At a 15A current draw, the voltage drop in the house wiring is 15 A * 0.0035 Ohms/ft * 200 ft = 10.5 V.

Most induction motors are designed for a maximum input-voltage variation of about 10%, so much more voltage drop than that could be expected to cause motor performance problems, including reduced output power and overheating.

The above chart says that the nominal copper cross-sectional area of stranded wire is close to the cross-sectional area of solid wire, but it varies a bit with the stranded-wire construction.

Contrary to the conventional wisdom that I found with a Google search just now, the maximum DC resistance of 14-gauge Calmont stranded wire is almost always less than that of their solid wire. The weird thing is that the nominal copper cross-sectional area deviates in both directions. Perhaps as you put more strands in the wire, the strand-diameter tolerances tend to average closer to the mean?

[RFGuy]

The voltage drop is easy to calculate, if you have a good wire-resistance table. The one below has all the details, both for solid wire and for all sorts of stranded-wire construction.

https://www.calmont.com/wp-content/uplo ... -gauge.pdf

Let's assume a 100 ft. run of 14 gauge solid wire. From the table, the maximum resistance of the wire is 3.5 milliOhms/ft. (The chart gives it as Ohms/1000 ft). Now keep in mind that the current has to travel in both directions in the cable, so for our purposes we actually have 200 ft. of wire run. At a 15A current draw, the voltage drop in the house wiring is 15 A * 0.0035 Ohms/ft * 200 ft = 10.5 V.

Most induction motors are designed for a maximum input-voltage variation of about 10%, so much more voltage drop than that could be expected to cause motor performance problems, including reduced output power and overheating.

The above chart says that the nominal copper cross-sectional area of stranded wire is close to the cross-sectional area of solid wire, but it varies a bit with the stranded-wire construction.

Contrary to the conventional wisdom that I found with a Google search just now, the maximum DC resistance of 14-gauge Calmont stranded wire is almost always less than that of their solid wire. The weird thing is that the nominal copper cross-sectional area deviates in both directions. Perhaps as you put more strands in the wire, the strand-diameter tolerances tend to average closer to the mean?

Thanks Dennis. You are right...I forgot to calculate both directions for voltage drop since this is single phase and I forgot the return path. Thanks for pointing this out. Still, less than 5% for my 12AWG (100') example. I can't explain the DC resistance difference you observed, but I just wanted to share the pic below as a visual for anyone that isn't aware. Stranded wire is always larger in size than solid for the same AWG in order to give the same cross sectional area you end up with voids (air spaces) between the stranded conductors.

stranded_solid_wire.jpg (6.75 KiB) Viewed 1060 times

[JPG]

Gee y'all had fun while I was briefly 'away'.

I think the reason we condemn an extension cord is as already mentioned, using one with too small wire and ignorance of what size is being used or that it matters. Ditto using a cut off extension cord as a power cord replacement. I gotta say #12 is the goal there($$$ vs benefit)

On one occasion, I ran a headstock on a #12 (? foot) cord outdoors to plane some oak. It was for sure over 50 foot long.

The increase in startup to speed time was very obvious.


As for 100' runs in a house, IIRC earlier someone stated that runs over 100' require increasing the branch wire to the next larger size according to 'the code'.

I agree #10 is overkill.(unless a VEEEEERRRRRY long run for a 15A branch; 20A branch, see previous sentence.

[chapmanruss]

HopefulSSer,

I would like to get back to the original problem to better understand what is going on. At this point can you tell if it is the motor actually slowing down or is it slippage in the system, belts or the Gilmer clutch or a combination of both. I don't recall how much slippage the clutch should have off hand. It has been several years since I worked on one. Too much and you cannot drive anything with the spindle. Too little and you end up with the problem Magna originally had of breaking belts which is why one of the earliest changes made to the Mark 5 headstock was going from the fixed drive sleeve assembly to the clutched drive sleeve assembly. On the Mark 5's with the Gilmer belt the slippage points are the Motor to Idler shaft V belt and the Gilmer Drive Sleeve Assembly Clutch if it has the clutch. The original Mark 5's made in 1954 without the clutch in the Drive Sleeve Assembly only had the V belt as a slippage point. The Poly V slippage points are both belts. If it is the motor slowing and stopping what sound is it making. Is it trying to work or giving up under the load.

[DLB]

HopefulSSer,

I would like to get back to the original problem to better understand what is going on. At this point can you tell if it is the motor actually slowing down or is it slippage in the system, belts or the Gilmer clutch or a combination of both. I don't recall how much slippage the clutch should have off hand. It has been several years since I worked on one. Too much and you cannot drive anything with the spindle. Too little and you end up with the problem Magna originally had of breaking belts which is why one of the earliest changes made to the Mark 5 headstock was going from the fixed drive sleeve assembly to the clutched drive sleeve assembly. On the Mark 5's with the Gilmer belt the slippage points are the Motor to Idler shaft V belt and the Gilmer Drive Sleeve Assembly Clutch if it has the clutch. The original Mark 5's made in 1954 without the clutch in the Drive Sleeve Assembly only had the V belt as a slippage point. The Poly V slippage points are both belts. If it is the motor slowing and stopping what sound is it making. Is it trying to work or giving up under the load.

I think I recall a thread where someone, probably Bill Mayo, discussed rebuilding the clutch and testing it for in-spec. So he must have had a specific value for the torque at which it should slip. Sounds and recovery time would be vastly different between a stall and slip. Also with a slip the machine is still 'trying' but with a stall the power drops to near nothing. I know that on mine, at saw speeds, it was always a stall. I presume clutch slipping might occur at lower spindle speeds where there would be more torque available. I never experienced a slip on the Gilmer, at least not that I know about, so this is somewhat hypothetical.

- David

[JPG]

viewtopic.php?p=32871#post32871

[JPG]

viewtopic.php?p=32871#post32871

Thank You MickyD!

[DLB]

viewtopic.php?p=32871#post32871

Thank You MickyD!

Yes, thank you MickyD! Take the fact that I thought Bill Mayo wrote this as a complement, as it surely is.

- David

[JPG]

Bill Mayo was the source of 10-20 ft.lb value. MickyD had conversations with Bill. So Bill does deserve credit!

[DLB]

Heavy-gauge extension cords are expensive so I would imagine most people would shop on price and buy an under-sized one….

So I just did a bit more precise estimation and my choices are:

• Plug the SS directly into a 15A outlet fed by 38’ of 14/2, or….

• Plug the SS into a 20A circuit with 67’ of wiring consisting of 52’ of 12/2 to the outlet and 15’ of brand new 12 ga. extension cord

I also did the sanding disk test and with some force the clutch will slip (as it should). Now the question becomes just enough force or too little? I don’t know and don’t even know how I would know!

EDIT: thinking about it, if I can stop the motor then I guess the clutch is ok. It would slip under shock load but it holds under a slower progressive load increase....

IMO you should be fine on either circuit. The 3/4HP motor will have an amperage rating on it, that is at max HP. Mine is 8.5 Amps, so it is going to be close to that. It would be somewhat lower when the motor is running but not producing full power, and way higher for a brief time during startup. There is an assumption there that your voltage is good at the panel. If there is a difference in start-up time using one circuit I'd use the one that it starts the fastest. On paper the 15A circuit looks slightly better, but may not provide the much higher start current that the motor wants.

- David