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...
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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
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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