Motor Generator Looping Question

[Kajunbee]

Will submit question separately.

 

[Kajunbee]

I have a couple questions about current and voltages in the setup I posted . Both of these motors are wired to turn the same direction. Since there facing one another the motor with 4" pulley is spun in opposite direction. In this configuration low speed ( com to red ) shows 140 volts. If I swap the rotation wiring of motor with 4" pulley output voltage drops to 125volts. hertz readings are 74 and 73.50 in second direction. Would this slight change in frequency lower voltage that much.
My second question is about amp readings when I loop them together as shown in diagram. When I place amprobe on main feed I read about 7 amps. When I place meter on common to prime mover I read 6.85 amps. When I place meter on common of gen. motor I read around 1.70 amps. The 1.70 amps is what has me puzzled. The amp draw on main feed and prime mover are almost the same. So where is the 1.70 amps going. I'd be satisfied with a guess.
I do not have access to a power analyzer and the ones I've seen are expensive. Is there a poor boy way of determining which direction current is flowing in this setup.

 

[BradtheRad]

Please confirm, do you really have pulleys of different diameters, yet both motors turn at the same speed?

 

[Kajunbee]

The 1075 rpm in diagram is motor speed on tag of both motors. Prime mover has 5.25 " pulley and second motor which acts as generator has 4" pulley. So second motor should turn roughly 20% faster than prime mover. Prime mover is wired up high speed ( common, black) and second motor is wired up to low speed ( common, red ).
I disconnected the belt and the prime mover on high speed draws 4.5 amps no load . Second motor draws 1.3 amps on low speed no load.

- - - Updated - - -

I don't have a tach to give you exact rpm under load. If prime mover is turning its rated speed (1075 rpm) second motor would be roughly 20% faster.

 

[KlausST]

Hi,

I don't have a tach to give you exact rpm under load. If prime mover is turning its rated speed (1075 rpm) second motor would be roughly 20% faster.

5.25 : 4 = 1.3125 means 31.25% faster. Maybe there is some slip...

*****
My comment to your configuration:
Two motors fighting against each other. It just causes power dissipation.
A waste of time and energy.

About your question.
When only one motor is connected to mains..it acts as a motor. It drives both engines.
The electrical power it draws is: P = V × I × cos(phi)
It is:
* loss in wiring
* loss in motor windings
* loss in magnetics
* mechanical loss (bearings, air movement..)
* loss in transmission
* mechanical loss of second engine (generator, not electrically loaded)
* a little magnetical loss in second engine

*****
When both motors are connected electrically, then the faster one acts as generator, the slower one as motor.
But both are fighting each other.
You can't calculate currents, because you don't know cos(phi).

Klaus

 

[FvM]

Is there a poor boy way of determining which direction current is flowing in this setup.

Use a current transformer or shunt and a two channel oscilloscope to determine I-V phase angle

 

[Kajunbee]

. The high speed ( common, black) generates lower voltage than low speed ( common, red ).is this because number of poles active in stator.
High speed - 100 volts no load
Medium speed - 125 volts no load
Low speed. - 140 volts no load
Also can exact rpm of generator be calculated from the voltage output and frequency.
High speed - 100 volts , 74 hertz

 

[schmitt trigger]

So where is the 1.70 amps going. I'd be satisfied with a guess.
.

You are only seeing the magnitude component of a vector. Without the angle information, all we can guess is that the angle of the other motor is opposite and thus on the vector sum they cancel each other.

 

[Kajunbee]

FVM suggested using a current transformer and two channel scope to find I-V phase angle. A couple friends of mine said they would put it on there scope and try to analyze it for me . They have about 40 years experience each in TV and radio repair. But since they don't do this type of analysis everyday they admit that and engineer would be much more thorough.
Is this a pretty straight forward test. Would there be any other variation of this test to get a more detailed analysis. Also, I do not want to damage there equipment. Is there any extra precautions so that there equipment isn't damaged. A schematic of where to to place probes and transformer on my setup would be greatly appreciated.