208V 3 phase motors are reversing while powered

[scubasteve]

I am having a problem with 2 of 4 208v 3phase motors on a
marina travel lift.All 4 motors are connetcted to the same source.However 2 of the motors are connected by a heavy duty
cord.I have troubleshot most of everything.I have 205v to
each motor but they struggle to run and some times not at all.At one point while they were running they reversed direction by themselves.Could this be an out of phase condition,dirty relay contacts,brushes.???i am stumped

 

[rhatcher]

Anything is possible from the description you have offered. However, based on the fact that two motors are 'hard-wired' and two are powered by a cord, I will take a guess that phase rotation is the problem. Note that phase rotation determines the direction that an induction motor rotates.

Guessing sucks though, so as a way to check this, you should use a phase rotation meter to ensure that all four motors see the same phase rotation. If you don't have one of these, you may try operating the motors independently to see which way they turn. If possible, unplug the cord and operate the lift on two motors. Then, operate the lift on the two motors supplied by the cord. If they direction is the same, then there is a bigger problem. Let us know.......

 

[scubasteve]

rhatcher thanks for your response.I have isolated the motors as one of my trouble shooting steps.And if i get them to run the startup is slow and gradually increases.
Most of the time i hear the relays energize and the motors hum.the motors are 3 phase 208v but only have 3 conductors
to each.I cant seem to grasp that.They were running fine
until yesterday and i belive i have eliminated loose
connections,shorts,and the typical good stuff.I hope this
info helps;and again i appretiate yours.

 

[jclough]

Boy Steve, It sure sounds like you have a phase that isn't working. Is this a three phase motor induction motor or one of the brush type universal motors? Sounds like the former but have a peek and let us know. Name plate info would be nice. Is the motor connected to power through a relay (motor starter)? More to come but first things first.

 

[BJC]

Sounds like you don't have an engineering problem but an electrican problem. Get a good electrican to go over the thing and fix it. The worst thing I ever worked on was a manlift that used two 208 three phase motors driving pinion gears up and down a rack gear. Very simple in theory but very hard to make right. Lots of contactors, limit switches, brakes etc.
Get someone who knows what to do and let him ( or her ) do it. IMO you tripping over a dollar to pick up a dime. All you have to do is drop on boat, or fail to get it out of the water and you'll probably loose the money it cost to get it fixed correctly.
Knowing when to quite is a good thing.

 

[jbartos]

Suggestion: It would be nice to know where the 205V was measured and if motors were running since cords may have many shortcomings, e.g. small AWG, run over by something, etc.