An ohmmeter as a tool in a wood shop?

[frank81]

[*]An old school analog engine analyzer that is essentially a specialized multimeter. I can set up points and do several engine diagnostic tests with it.

How do you set points with a multi meter? I always just use a playing card to set the gap, then advance or retard using the timing marks on the flywheel. Is there something else I should be doing?

[JPG]

How do you set points with a multi meter? I always just use a playing card to set the gap, then advance or retard using the timing marks on the flywheel. Is there something else I should be doing?

'DWELL';)......

[billmayo]

OK I'm a meter junkie. I have:

• An old school analog engine analyzer that is essentially a specialized multimeter. I can set up points and do several engine diagnostic tests with it.

I never realized there were so many until I started making a list.

I only have one Shopsmith.

When I set up my motor repair and rebuilding station, I found a new still in the box an "old school analog engine analyzer" I had stored that I believe I brought in the early 1960s. It has a 10" analog meter with a 0 to 100 ohm scale that I use. I believe it is accurate to .1 ohm when set up. I do not use the other cables and scales on the analyzer at this time. Any one has seen the analyzer has never seen one before or even knew about one. Before the digital age.

[artlinux]

Recent posts in this thread by joshh and Dusty may not have drawn the correct conclusions about electrical measurements and calculations of the power being consumed by the SS motor.

Ammeter and voltmeter measurements at the point of SS plugin to a wall receptacle or extension cord, measure independent values of current and voltage. The nature of alternating current power systems is that current and voltage values only peak at the same time in resistive circuits such as baseboard electric heaters. For such heaters, separate current and voltage measurements generally provide good values to calculate power measured in Watts (for example 9 Amps of current x 120 Volts = 1080 Watts of heat).

Motors are a special case. Because motors use coils of wire in their design, the current and voltage waves do not normally peak at the same time. The logical measurement and calculating techniques used above for baseboard electric heaters does not work as simply for motors. The formula for motors is current (Amps) x voltage (Volts) x pf (power factor is the measure of how much the peaks of current and voltage are different in time from each other) = Power (Watts). Except in industrial plants where such measurements and the use of power factor correcting capacitors to resolve the power factor problem are used, such measurements are too expensive for any benefit in home shops.

Motor efficiency and power factor vary greatly with motor load in a home shop application. This alone makes an attempt to measure motor power too complex for any useful comparison to a SS rating of 1-1/8 hp.

[JPG]

Recent posts in this thread by joshh and Dusty may not have drawn the correct conclusions about electrical measurements and calculations of the power being consumed by the SS motor.

Ammeter and voltmeter measurements at the point of SS plugin to a wall receptacle or extension cord, measure independent values of current and voltage. The nature of alternating current power systems is that current and voltage values only peak at the same time in resistive circuits such as baseboard electric heaters. For such heaters, separate current and voltage measurements generally provide good values to calculate power measured in Watts (for example 9 Amps of current x 120 Volts = 1080 Watts of heat).

Motors are a special case. Because motors use coils of wire in their design, the current and voltage waves do not normally peak at the same time. The logical measurement and calculating techniques used above for baseboard electric heaters does not work as simply for motors. The formula for motors is current (Amps) x voltage (Volts) x pf (power factor is the measure of how much the peaks of current and voltage are different in time from each other) = Power (Watts). Except in industrial plants where such measurements and the use of power factor correcting capacitors to resolve the power factor problem are used, such measurements are too expensive for any benefit in home shops.

Motor efficiency and power factor vary greatly with motor load in a home shop application. This alone makes an attempt to measure motor power too complex for any useful comparison to a SS rating of 1-1/8 hp.

Well said!!!!!!

Add the 'detail' that the currents may not be 'sinusoidal'(easily reduced to mathematical equations).

[frank81]

[quote="JPG40504"]'DWELL']

That's what the playing card is for.

If both sides are gapped correctly, there is nothing you can do about dwell because its machined into the cam. At least on all the stuff I've worked on.

[JPG]

That's what the playing card is for.

Card thickness is a physical dimension.

Dwell is a percentage of time.

Related, but only loosely so.(i.e. gap can only approximate a dwell percentage). Granted tis usually adequate!;)

[artlinux]

I tussled with myself about adding this complexity of harmonic content of current and voltage waveforms to my post. It seemed to just add extra complexity to a conclusion that the calculation of power (Watt) consumption by the motor is not reasonably possible in the home workshop.

I see a similar background / experience in your reply.

Art

[billmayo]

Motor efficiency and power factor vary greatly with motor load in a home shop application. This alone makes an attempt to measure motor power too complex for any useful comparison to a SS rating of 1-1/8 hp.

I built a test setup to test DC motors and controllers many years ago. As a separate task, I put several different Shopsmith 3/4 HP and 1 1/8 HP motors in this test setup. Measuring the voltage and current amps with various loads, I found the 3/4 HP motor could use less amps some times at different loads but less than 10% difference. I have always used the 3/4 HP motors in my personal Shopsmiths. I find proper alignment and sharp saw blades are must more critical than HP for the Shopsmiths.

[JPG]

I tussled with myself about adding this complexity of harmonic content of current and voltage waveforms to my post. It seemed to just add extra complexity to a conclusion that the calculation of power (Watt) consumption by the motor is not reasonably possible in the home workshop.

I see a similar background / experience in your reply.

Art

Agreed! Keyword 'calculation'!



I cannot 'imagine' what a discussion here about 'imaginary' power would produce!:D

We might get by with 'apparent' power!:rolleyes: