Quote:
Originally Posted by bsmith0404
Is that millisecond surge enough to register it on a typical meter/surge protector? Does it drop down to regular running amps right away or does it hang around the 5-7 amp surge that I had been told about for a bit until it’s had time to run up.
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Some Digital Multi-Meters (DMM) will have a "hold" function that you can engage, some do not. If yours has it, it will lock on the highest amp reading it sees until you clear it.
Just as soon as the rotor inside the motor starts to move/turn, the current will start dropping from it's peak value which is called inrush current or LRA....and depending on the rotor mass and what the motor is trying to turn, the speed at which the current takes to drop down to FLA is a variable length of time. I've seen large 3ø motors (1500 HP up to 20,000 HP, take up to 2 or 3 seconds to come up to speed. Smaller motors like most of us encounter, it's usually in the milli-seconds range.....and again, once the motor starts to turn, the current starts dropping and the length of time is dependent on the load it encounters, to get down to the "normal" amount of current that it uses.....which usually is a value that is pretty close to the listed FLA rating for the motor.
That is why I stated that if an A/C compressor has not had time to equalize the internal pressure between the high side and the low side refrigeration loop, the motor would be starting under a high "load" than if it had equalized the pressure. Think of your camper and truck starting from a dead stop on flat and level ground and accelerating to say 50 mph. Then think of that same truck/trailer combo trying to start from a dead stop...but going up a 10 degree incline and accelerate to the same 50 mph. That puts a lot more stress on the engine and it uses more fuel to do the same work....and...it takes more time to get up to speed. In the example of the truck and trailer, the engine has to overcome the effects of gravity. In the case of the A/C compressor, it would have to overcome the higher than normal pressure in the system because the refrigerant has not equalized inside the Air conditioner refrigerant loop. Another example might be a 10 speed bicycle. Try starting from a dead stop in first gear, vs. starting from a stop in 10 gear....and getting the bike up to 10 mph. Hope this helps...