i have pictures of a working model made from 90% recycled parts.
I have a "static converter" on my Avey made from 100% recycled parts. Air conditioners and well controllers are good sources of potential relays and start capacitors. I got some nice 660VAC oil-filled capacitors for run caps out of an obsolete power conditioner. The cabinet once held lighting controls for a microwave tower, which also supplied some terminal strips. No photos, though.
 
Another good source of information on RPC can be found on metal web news. I used this back in 2001 to build my first system.
 
I made this motor starter for HM supporter, Bamban's Bridgeport Milling Machine
6/16/2016


the box is very simple to hook up to any motor.
you simply hook the box up to your idler motor and distribute the 3 phase circuit from the idler motor to whatever you'd like to run.
in my home shop, i have a 5 hp and a 7.5 hp RPC's wired in & ready to go at the push of a button.
i use the 5 hp most of the time,
but when i want to fire up my 300 amp POWCON 3 pahse welder- it needs a bit more juice, so i run the 7.5 for that or anytime i need to run larger capacity motors.

on your BP,
this box, as configured, only has the capacity to start the motor in one direction.
because the start capacitor in the box is starting the motor with a strong bias in one direction of rotation.
a 3 phase motor is happy running forward or reverse, they truly are bi-directional the efficiency and power output is equal, regardless of direction of rotation.
but since we are tricking the motor on start up to believe it has 3 phases( but one of the phases is a burst of 120VDC @ 200UF momentarily)
after the motor is running, it creates it's own 3rd phase, the start capacitor is no longer in the motor circuit after you let up off the green(start) button.
you'll wire the output of the box to your BP's drum switch, then the drum switch to motor.

sequence of operations:
after the box is wired in, to start the BP you'll pick a direction on your drum switch F or R- then push the green button- the mill will run in that direction.
you will push the red (stop) button on the box, power is cut to the BP's motor.
if you'd like to restart in the same rotation, simply push the green button again and then the red button to stop once again.
to reverse the motors' rotation select the other direction on the drum switch and push the green box button, the motor will run in reverse until the stop button is actuated.

one point of information, the drum switches are normally open center switches.
that is that they don't conduct electricity between poles in the center position and are isolated.
that being said, there is potential for possible motor damage if you were to mistakenly switch directions on the drum switch before the motor came to a complete stop.
get into the habit of stopping the mill with the red box button.
 
Last edited:
Is their any sort best practice (rule of thumb) for determining a cap value per horsepower for running. I read about 50 mf for starting. not sure about the run side of things though. Thanks in advance.

charles
 
Hi Charles,
generally speaking for normal service, somewhere around 20 uf per hp of running capacitance is all that's required, unless you are running very heavy loads.
 
Back
Top