-
Hobart 2812 Sometimes spinning backwards
-
fixbear wrote:
You can only test one and measure the micro-farads with a dedicated capacitor tester. And they are not cheap. Hell, I don ‘t even own one. I can check if a capacitor works, but I can not measure how many MF it is capable of. That requires a very specialized machine/ instrument.
In my twenty years in the military (until 1998), we had Simpson 260s and then were upgraded to Fluke DMMs. Up until then, the only way I’d learned to test a capacitor was by using the OHMMETER (YOU know that crude method). Back then, though, my need for testing a cap was a RARE occurrence. My occupation THEN was working on power generating equipment.
In 1998, I entered THIS trade. Hence…I’ve always preferred Fluke meters (because of my familiarity with them). The first meter I bought (in ’98) had a capacitor test mode. The other prerequisite features it had to have were to test µA (flame sensing circuits) and temperature.
Later on, THAT meter was replaced by this Fluke 116:
However, for the sake of expedience (and convenience), I’ve never actually done that testing method.
-
WELL. The bad-Man comes back from retirement to chime in again.
-
That is reactive power. To really test a start circuit requires a scope and phase angle. Induction moves phase angle back, capacitance moves it forward. I actually found a improperly installed substation transformer on a power distribution grid that was built different than the other two. Phase angle of A phase was 4 degrees behind where it should have been. Lot’s of motor load unbalance and vibration. Amazing how they suddenly stop talking and involve lawyers when you show a power company engineers that they are wrong. They actually told there employees they could not talk to me. Yet they provided me a $45,000.00 ABB solid state motor control to place on the service supply for the plant. I had previously worked very closely with there meter and test personnel.
I know that there are test and meter manufacturing company’s that claim things, but I need to see proof before I believe them. Knowing what I do about Capacitors, voltage, time, and return all falls into it. I have yet to find a hand meter that will do that.
-
fixbear, even if I lived to be 150, I don’t think I could ever learn the things you know.
-
Oh how I miss my Simpson 260. I loved that meter. Wish a fiend I loaned it to hadn’t died before returning it. But, I do like my Flukes as well. I use a 87 for the field. A $400 meter with capacitance, but does it accurately measure it. NO. I’ve also had the use of a 980, but it is beyond my budget. I do own a field Oscilloscope and TIF, UEI and belkan meters as well. None approach the flukes for stability, accuracy and usability. And the 80 series are as rugged is it gets.
-
Likewise. We have both had our life experiences and have learned from them. It’s the pleasure of passing it on and learning for each other that is the best part. When I was a scoutmaster, The reward of seeing the light come on in a boys eyes with a discovery was one of the greatest rewards a man can have.
-
What you have pictured here is a PSC motor. Not a split phase.
-
But, let’s explore why a capacitive start, induction run motor runs backwards. To understand this we have to know how the motor is made and why it can run in reverse.
The motor is wound with two or four poles, but also a extra set of winding’s a few degrees ahead of the run winding’s. The start winding’s have more turns and a finer wire than the run winding’s. Normally the start winding and the run winding get power at the same time. The calculations on where to place the start winding in electrical degrees is different than mechanical due to capacitor charge time and inrush delays etc. Suffice it to say that the run winding is almost dead center till there is rotation of the rotor. That gives capacitor time to charge and energize the start winding to create the start torque. Also why start inrush current is 17 times full load run current. If the rotor winding line up slightly ahead of the run winding and the start is delayed by say a starter contact resistance, the rotor will move to the reverse rotation till corrected by the start winding. Once momentum is developed, if fast enough to carry over a pole the motor will run in reverse. Rarely is that amount of momentum developed, but it does happen.
So from this, we know that if the capacitor starts the motor normally after a reversal the place to look is the start control and wiring. Doesn’t matter whether a centrifugal switch, potential relay or current relay. They all are designed to drop out the start winding at 75%.
I once had a South Bend lathe that regularly would not start without a push on the chuck. Or would start backward. The reason I dug into this many many years ago.
So, eritech1, you may want to replace the relay
-
Wow thank you all for taking ur time and helping me, i had no time answer anything yet because I work crazy hours and really hard, I’m sure u experienced that years ago lol.
but any way I will call the customer back at the end of the week to see if they experienced the issue again and if they do I will definitely put that relay in. I have them in stock so I”m not worried.
There are two relays in there the one ectofix mentioned earlier wich is electronic start switch and the black relay.
-
>To really test a start circuit requires a scope and phase angle
I would *love* to get a call at a mom & pop place on a slicer or mixer, and drag out a bunch of meters and a scope, and maybe even a wifi router with all ports with cables in them or something. A satellite dish even.
Spend a few hours fiddling with the knobs, then replace the capacitor. Pack it all back in the truck. They’d talk about it for weeks.
Log in to reply.