Determining winding polarity on a 1phase dual voltage ac motor - Page 1
Forum section: electronics / repair

author: Rjc987
author_rank: Contributor
timestamp: June 02, 2022, 09:22:37 pm
content: Hi guys!Quick question, I have a Edwards vacuum pump with a GE single phase 1/3 hp 110/220 V AC induction motor that I’m trying to figure out but the wiring from the windings were completely destroyed, insulation and all turned black and cracked off, and the termination board was completely destroyed so there is no way to differentiate any wires. I stripped it down and crimped some new wires onto the windings, put a new termination board and starting switch in, and traced out the windings, but that’s when I ran into a problem. There are three winding, 2 run windings at 3.1 ohms each, and one start winding at 4.2 ohms but 5 wires - the end of one of the run and start windings are spliced to one common wire. I assume I would want to put them all in parallel with the start winding going through the centrifugal switch for 110v, however how can I determine what the polarity of the windings are, i.e. which ends are supposed to be connected together? Take a look at the terrible schematic below. Also note that I broke out the common windings into two separate wires for testing purposes

author: kamocat
author_rank: Newbie
timestamp: June 02, 2022, 11:00:55 pm
content: I would expect magnetic coupling between the windings to indicate which way you should connect them.Power up one of the windings (with a decreased voltage, if you wish) and compare the phase.If you don't have a scope, you can do this by putting two windings in series, but only powering one of them (like a center-tap transformer).If it produces double the voltage end-to-end, then it's the wrong way.Alternatively, you could try both orientations and see which works better. Make sure there's an appropriately sized breaker so you don't burn up your coils.

author: james_s
author_rank: Super Contributor
timestamp: June 03, 2022, 12:25:01 am
content: If you get it wrong the motor will run in the wrong direction so you should be ok to try it and if it spins the wrong way reverse it.

author: Rjc987
author_rank: Contributor
timestamp: June 04, 2022, 05:50:59 pm
content: Ok, so I don’t have access to my scope at the moment but I used a variance to output 5vac and measured different windings in series combos but the results are confusing me. The windings need to be in parallel for 110v, correct? The common for the start and run#2 are really messing with my ability to visualize the results. Some orientations I get 9-10v (wrong) most I get about 5v but some I get a few hundred mv to around 1v as well. I assume those just mean the windings are on different sides of the motor and not really overlapping yes? Can anyone draw any conclusions from this chart? The first 2 tests gives a solid 5v for common being live and the start and run2 being neutral, but then when I power run1, regardless of polarity, I get 10v if I’m measuring run1 in series with run2 but if I put it in series with start, it gives me 5v. I know run1 and run2 are probably on opposite sides of the motor with little overlap since I get a few hundred mv on one if I power the other, so could that affect it?

author: Rjc987
author_rank: Contributor
timestamp: June 04, 2022, 05:52:56 pm
content: Btw here’s all the combos I’ve tried to map out the motor fully. Some are duplicates but only a few