3 phase converter running 3 idle motors
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  1. #1
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    Default 3 phase converter running 3 idle motors

    Hi everyone, new to the forum but been lurking awhile. I am starting to put together a wood shop and looking at some 3 phase machines but donít have 3 phase. What I do have is access to 5,10 and 15 hp 3 phase motors for idlers. The equipment Iíll be running have 7.5hp table saw, 10hp sander and 15hp moulder. Iím a one man show so only one machine will be running at a time. Do to needing various loads for each machine I was going to do a 3 idler phase converter so I donít have to run anymore then I have to plus cover the double rating for the moulder. I researched as much as I could but Iím not sure about how I have it laid out. Iíve included a diagram below.

    Iím bringing in the 100 amp 230v single phase into a North America 30 hp converter control panel (open to suggestions on others). Hooked to that will be the first 10 hp motor to create the 3 phase to go to a 3 ph breaker panel. From that Iíd power the other two idler motors when needed and bring out of it for power to the machines. Anything anyone would do different? What about balancing the other two idler motors since they are after the converter panel?46d363bf-cc45-4b1f-b257-9f2d24e2b059.jpg

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    I have a three motor RPC. I put control of all idlers in the control panel. I see no reason to put the control of additonal idlers somwhere else. But regardless, just place your balance capacitors at each idler. If you balance them individually, they will be balanced as a group.

    Why buy a panel for the first idler if you will have to build a panel for the other two?

    My RPC has three 7.5 hp idlers. Thermite has a multiple idler RPC with different HP idlers as you are considering. Both of us did this with the thought of not running more idler hp than needed. I only have start caps on the first idler and this is capable of starting the other idlers .

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    A three phase load center breaker panel is a GREAT idea. I did this for my son's shop.

    We treated this as a sub panel and ran the two hot legs from the single phase main to this. Each idler motor was on its own circuit breaker which went to a motor contactor and then the motor.

    His system has two idlers. When only one is needed, just turn off the breaker for the second idle motor.

    The control panel for the idlers brings in start caps for a few seconds when pushing the "start" pushbutton. Then a second timer relay brings in the run caps.

    IF the circuit breaker is closed on the second motor, a third timer relay brings in the motor and run caps - no need for starts here.

    No reason not to do a third.

    each load motor is on its own breaker.

    So, job 1 of the day is set the circuit breakers and push the "start" on the phase converter panel. If a second idler is needed later, just flip the breaker.


    This has worked perfectly for him for five years now.

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    I went this route because I have the breaker box and breakers for free and it would be easy for me to wire up, Most of my experience is with single phase. What would be an easy way to be able to choose how many motors I’m running and put it all through the control panel? If I have to buy capacitors to balance the other two then the free stuff isn’t exactly free and I might as well run it all through the control panel. I have access to some 3 ph stuff at work.

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    Where i am smallish used three phase generators are quite cheep, and can be used in an emergency and if your are handy..machinists, can be used as a heat source. So why does nobody ever consider them for running a shop? not wanting to highjack the thread but they never seem to be a consideration. what am I missing?

    I have four generators, 3 of which are three phase 6 - 5okw looking for for interesting jobs.

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    I think it was one of your post about his shop that gave me the idea for the breaker panel. Do you have a diagram on how you wired it? When it comes to this kinda stuff it really helps me to see it to understand it. Did you wire up your own control panel then? I’ve never wired in timer relays or capacitors so I’m learning.

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    Quote Originally Posted by seiner View Post
    Where i am smallish used three phase generators are quite cheep, and can be used in an emergency and if your are handy..machinists, can be used as a heat source. So why does nobody ever consider them for running a shop? not wanting to highjack the thread but they never seem to be a consideration. what am I missing?

    I have four generators, 3 of which are three phase 6 - 5okw looking for for interesting jobs.
    I think the biggest part you are missing is that fuel costs more than metered power. If you do not have power lines, or you have free fuel, the equation might change.

    OP, if you are a 1 person shop, instead of having multiple idlers, why not just start a few other machines and let them be the idlers while you start the machine you need to use.

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    Quote Originally Posted by dalmatiangirl61 View Post
    I think the biggest part you are missing is that fuel costs more than metered power. If you do not have power lines, or you have free fuel, the equation might change.

    OP, if you are a 1 person shop, instead of having multiple idlers, why not just start a few other machines and let them be the idlers while you start the machine you need to use.
    I did give that some thought but I don’t have dedicated shop space for everything right now. As I need it I roll it out and the other machine goes back to the wall. Someday I’ll have a dedicated shop. I thought about doing just two idlers for 20 hp then kicking on the sander or table saw till I get the moulder running and shutting it off but I read that’s a heavy load and might not be a good idea to only run 20hp of converter on a 15 hp motor. Plus I have the motors for free
    Last edited by NateF350; 09-10-2019 at 05:46 PM. Reason: Cause I can’t read

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    Quote Originally Posted by Karl_T View Post
    Ok I read through that and sort of see (I think) what you did with bringing in the single phase into the load center then breaker to motor control to motor for each idler. That then goes through the converter panel you made back to the load center? And then your able to put breakers in for each machine from there? If I come in to my load center like you did, then from breaker to motor how would I tie the 3 idlers together to go into my North American converter panel while still being able to run only the idlers I need? Just a manual motor control switch between breaker and motor? Sorry for all the questions this is the first I really have dealt with 3 phase and I’m trying to learn


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