how to get 110V single phase from milling machine control circuit .
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  1. #1
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    Default how to get 110V single phase from milling machine control circuit .

    But only when the spindle motor is turned on
    forward or reverse .
    The reason is to activate the (I think it's called)
    potential relay or drop out relay in my rpc .
    It is a timed relay that when
    supplied with the 110v on motor start up will send
    a little extra oomf for 1.2 seconds max.to get the 6 hp 50hz spindle motor going when I've got it in top speed .So the 110v has to cut out when spindle is shut off .Standard circuit with fwd. and rev. contactors
    There is a 220 to 110 transformer already in place
    that was for a work lamp . I'd be happy to lose the lamp if I can use the transformer for this other need .
    Any help would be most appreciated .
    Ted

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    Do you have the current wiring diagram plus interconnect for RPC and Mill.
    Your lamp transformer should be able to feed both a lamp and a second device like a relay, this is more likely if the original lamp was incandescent and you have change to a LED or CFL.
    I am more confused on how you expect to get the RPC potential relay to add extra to the RPC output.

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    The capacity to the generated leg needs to be adjusted for the load. Apparently his circuit is adding what amounts to a starting capacitor to get the spindle motor running.

    Bill

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    Thank you for the help .
    Bill is correct . As I understand my rpc will add a starting capacitor to overcome the mill motor under load .The rpc starts my 5hp lathe just fine and the mill some times. We checked the
    3 legs and they were within 10 percent .Will check again .
    10 hp rpc might be marginal for starting 6 hp motor ?
    Ted

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    I know I would not fly such a tactic unless the RPC was running a dedicated, lonely motor. A cap can cause 3P voltage imbalance, or a transient spike and damage something.

    From experience, I have used a 10HP RPC to start a 10HP motor, and it will start instantly. To tune an RPC properly, it MUST be loaded as you will see the voltage balance change with load and will have to find a good mid point for capacitor tuning.

    I would not be trying to use a timing relay and cap to help the RPC start a load. A capacitor ampacity is a fixed value based on voltage and frequency. Start caps can blow up if left in circuit too long or used too often.

    I recommend resistive heating loads on the RPC so you can monitor the voltage and make adjustments.

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    Thank you for the warning huleo .
    I will take heed .
    Ted

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    Quote Originally Posted by Thompsonguitars View Post
    As I understand my rpc will add a starting capacitor to overcome the mill motor under load .The rpc starts my 5hp lathe just fine and the mill some times.
    Ted... a rotary converter consists of a three-phase motor, powered by mains on two legs. A three-phase motor will RUN on single phase power (like two of the three cylinders of an engine firing), but it will not START from a dead stop, on single. A self-starting RPC has some device, that upon power-up, applies enough phase-shift to the 'generated' leg, to 'kick' the motor into motion. The 'potential' relay you see in most RPC designs controls the 'start' function. It detects presence of voltage on the 'generated' leg. When there's no voltage, the relay contacts close, which applies mains power through a capacitor (phase shift) to the 3rd leg, causing it to push the armature in one direction.

    It does 'not' provide boost...

    It sounds like your mill's motor is imposing much more start current load than your system is able to provide.

    Which is curious... if your mill's spindle motor is substantially smaller than your RPC, then there's something else thta isn't quite right.

    It could be that your mill motor takes a long time to start due to it driving a high RPM spindle with lots of inertia (i.e. a wood router) or... there's enough resistance in the motor leads or some other element between RPC and spindle, that is limiting current to the motor, hence, it's slow to start.

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    Quote Originally Posted by Thompsonguitars View Post
    There is a 220 to 110 transformer already in place
    that was for a work lamp . I'd be happy to lose the lamp if I can use the transformer for this other need .
    A typical 110V relay coil wont draw any more power than even a very low-Wattage incandescent lamp, and most LED ones. Yer fine on that part, should be able to run BOTH, as the relay is only activated briefly.

    Any other issues with yer RPC are .... other issues.

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    Thank you all for the input .
    I think my rpc is just not up to it .
    Going to look into American Rotary ADX 15 .
    Will be on here with more questions before going ahead .
    Ted


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