Calling in the experts…Please help troubleshoot my used Unisaw I recently found on CL…
I’ve been restoring a Unisaw model# 34-806 (3ph 5hp Marathon Motor – 3480rpm) The saw has a LVC magnetic starter and is being operated with single phase power using a Phase-A-Matic PAM-900HD static converter- Which is sized correctly 4-8hp (and proper operation has been recently verified/tested by the Phase-A-Matic company)
I have been restoring this saw from the ground up…I have replaced all the bearings both arbor and motor assemblies, taken everything completely apart, cleaned, and repainted the Chassis etc. I am now to the point of trying to get this 3ph motor to run correctly on single Phase power and am running into problems. I am able to get the motor to start fine but it only runs freely for appoximetly 1.5-2mins. (with no load or pulley installed) then the saw’s overload protection trips and the motor shuts down. (The 30-amp circuit breaker does not trip.) I have replaced the original overload relay and associated “heaters” in the saw’s starter panel (thinking the relay may have gone bad) with a new one of the exact same specification (model and make). Then I verified the “Heaters/fuse elements” are sized correctly to the Motor’s full load amp rating (12amps @ 240v) listed on the motor nameplate. After the motor shuts down about 30 seconds later the outside of the motor case and rotor is very hot to the touch and remains so for about 15 mins.
Other relevant info:
All associated power wiring is 10-gauge wire and all connections have been tightened and verified. The power panel is about 130 feet away from were the dedicated table saw outlet is located. Then there is an additional 15 feet of wire length and phase converter to the saw itself.
I did replace the motor bearings (NTN bearings- original spec)…I made sure to do this carefully to ensure proper seating on the rotor- so I do not suspect it’s a misaligned bearing problem. I also made sure to apply Exxon motor bearing grease to the bearings and bearing inlets prior to reassembling the motor case. The rotor spins beautifully smooth if your rotate it by hand. The motor windings appear to be intact with no overt signs of damage such as discolorations or fowl odors. Also I successfully performed a series of electrical tests to confirm the integrity of the motor’s windings as outlined at the bottom of this website (very useful tests I might add): http://www.homemetalshopclub.org/news/may05/may05.html
When the motor runs you can hear a very faint pulsing oscillation sound, if that makes sense, it’s not a constant humming sound (i.e. as the motor rotates it makes a slight pulsing sound). I have also verified the cooling fan of the motor is pointing in the correct direction – in order to cool the motor.
1. Does anyone have ideas what could be causing this problem or had similar experiences?
2. Does anyone know the effects of using a static phase converter in relation to the proper sizing of magnetic starter heaters? Meaning since the motor, when started with a static phase converter, is unbalanced electrically speaking. (The motor is only running with 2 of the 3 winding series and not with 3 phases) – does this fact change or alter the “full load amperage rating” of the motor? Stated differently: Does running a 3ph motor on 1ph power increase current draw (FLA) of the motor?
My last option, if no one has any other ideas, will be to purchase a replacement 1ph motor. I am leaning towards a 3hp Baldor motor, but it has 3450rpm rating and the original Marathon motor had 3480rpm rating so I may have to purchase a new pulley to balance with the new motor?
Thank you in advance for your insight!!!
See attached pictures for reference: