RPC first build questions

I'm in the process of putting together a RPC. I picked up a 10HP 3phase motor and put together a very quick and dirty RPC to see if I could get the RPC motor spining and see if I could get another motor running. I have been able to successfully do that, but now I need to put something together that is a bit more permanent and safer.

I have been doing a fair amount of reading and am trying to determine what I want to do while putting this RPC together, if I want a pony start RPC or cap start.

My current situation is I have a seperate two car garage which the 3 phase machines are in, its about 150-200' from the main house. Last year I dug a trench and ran a conduit between the two buildings and then ran wire between the main 200AMP panel in the house to a 100AMP panel in the garage. I can't remember what the wire size was that I pulled, but I do remember it was sufficent for 100AMP sub panel work.

My intention is to run #6 wire to a remote cabinate which will be the connection center for the 3phase RPC from a 60 AMP breaker in the sub-panel. I would like to mount the RPC motor outside in a doghouse or up in the attic of the garage in order to minimize noise, but this remote mounting makes pony starting a bit more difficult. My other concern is the current inrush when a 10HP RPC is started with caps. I understand you should have between 50-100uf of capacitance per HP so I am looking at 500-1000uf. How much inrush current would that cause? Is it likely I am going to cause light flicker/dimming in the garage, main house, neighboorhood? Will I be poping circut breakers regularly?

I'm probably going to put the RPC together in phases, a simple push button start to begin with a more automated system later as I aquire parts etc... Any downside to a plan like this?

Thanks in advance for the advice.
Jay

I also have a 10 HP motor that I used to make a cap start RPC. I run it from a 100a subpanel very similar to your situation. I also used the uf/hp formula for capacitance on the start circuit. I do not notice any flickering of the lights or any other effect on start. The unit did start with a pretty loud bang, but I removed start caps until it starts with a small "bump", now. The unit does make some noise, but it is less than my mills or lathe, so it is not very loud or obtrusive. It mainly serves to remind me to shut it down when work is finished. Regards, Clark

Clark -Thanks for the info. I think I will give the cap start a try. It seems like I can get the the start caps from http://www.surpluscenter.com . I'm going to buy 7 caps with some differing sizes so I can mix and match them a bit in case I get a hard start condition as you noted.

I buy a lot of start caps from these folks http://stores.ebay.com/HVAC-4-Sure

The shipping is free. the caps are generally pretty small in size compared to others. Have had 0 problems. Dont forget to install some 15,000 ohm, 4 watt resisters to prevent torching your relay contacts.

You will likely end up with something around 500MFD for start caps depending on your amperage potential and how many run capacitors you use (they help with the start load)

I usually use the 270-324 mfd electrolytic start caps and install 3 of them for a 10 hp idler. It seems to work fine and with no unusual noises. I notice the surplus center has some chinese ones real cheap and have no idea how well they work. I have been buying mine from Grainger for years but the price keeps growing. Some notes you may be interested in: in rough numbers, 300 mfd will yield about 30 amps current. This should help you size your wiring and switching for the start caps.

Thanks toolnut I will start with 3 of of the 270-324 mfd's and go from there. Looking at the 3 places noted, Granger is $49 for the 3 plus shipping, surplus center is $24 with shipping and the ebay seller is $22 with shipping, but the granger and ebay ones are only 220v and the surplus center ones are 330v. I'm going to go with the surplus center ones.
Regarding the wire sizing, would 3 300 mfd caps yield 90 amps? And then should I then be using #2 wire size? Looking at some of the schematics some show the usage of #10 wire. My thoughts had been to use #8 from the panel to the RPC #10 in the RPC and #12 out to the lathe and mill. Was my sizing totally off?

Stelradcoal,

There are several ways to design RPCs. For my homebuilt RPCs, I use a 60 amp circuit for a 10 hp Idler and run power from a single phase breaker to a 60 amp contactor in my RPC panel. This contactor turns off all power beyond itself so only the control circuit is active when the main contactor is de-energized. Wiring from the single phase panel to the rpc panel must meet local codes for the amp rating and would likely be #6 but check to be sure. Inside the rpc panel I use a 40+ amp start contactor to handle the start caps. I use a 3 pole contactor and wire one cap through each pole and use #10 wire as I only have 30 amps through each pole. I do this to avoid the large wire problem. The start contactor is controlled by a Steveco 90-66 potential relay and drops out the start contactor when the idler is up to speed. I also use an overload relay to protect the idler from overloads, thus the rpc will shutdown when overloads occur. I have never had one other than when I deliberately created one to test the overload circuit. Drop me a PM with an email addy and I will send you details about this. I will be slow as I will not be online much for the next week.

Sorry to dredge up a 5 year old topic, but heck is my topic so whatever.

Long story short the last 5 years passed while I occasionally worked on the 3 phase converter toolnut sent me build plans for. I've finally got it running and hung in the garage and wiring to the machine tools.

But I had an issue. I wired it for 24vdc controls and all seemed to work, staer stop no issue, start machine no issue. After the. converter ran the first time for a longer period (10-20 minutes) the 24vdc coil on the ABB contactor burned out.

I'm not sure what caused it, but it looks like there are two parts to the coil, a pull down connection and a hold down connection. I only had power to pull down. Should I have it to both? Continously? Could it be something else?

Sent from my SAMSUNG-SM-G891A using Tapatalk

I'm trying to learn how to build my own RPC. This thread looks like the one you have built may be a good place for me to start. Do you happen to have a copy of the plan that toolnut sent you? I'd like to take a look at it and see if I can use his plan for my RPC.

AC coil contactors have a built in current reduction when the armature is closed. When it is open, the inductance of the coil is low and it draws a high current, sufficient to push enough magnetic flux through the large air gap. When it closes, the air gap reduction increases the coil inductance and the current drops to a small holding one.

DC contactors do not have this effect working for them and any but small ones need a means of limiting current once it is closed. The usual solution is to have a resistor in series with the coil that is shorted by normally closed contacts. When it pulls in, these contacts open and add the resistor to the circuit. I don't know anything about your conmtactor but there is likely something of that sort on it. It may also switch to a higher resistance coil, two windings in one coil assembly.

Bill

DC contactors may also have the same size foot print on a flat steel panel. But they are taller and will not fit in some enclosures.

Thanks for the input. RonRock - I will attach the 3 docs ToolNut sent that I followed to get me this far.

This whole build has been a learning experience for me. There is a lot of information out there and you really need to study up. In fact, I should have studied the information about the contactors better and I may have not had the issue.

9100 thanks for the information, once I read that I looked up the contactor data sheets and it made more sense to me now. In fact on these coils there is an A1 A2 and A3 connection - A1 and A2 are supposed to connect direct to the power supply. A3 is supposed to connect to A2 through a NC terminal on the contactor, so it drops out once the pulldown is complete.

I'm bench testing the coil/contactor now and will stick it back in the converter some time in the next few days. Then I can get back to actually setting the machines up! I'm attaching a picture of the coil wire diagram. My reading is + to A1 and - to A2 with the connection the the normally closed terminal from A2 -> A3. Let me know if it seems wrong.

RonRock - I cant upload them - too big or something. Shoot me an email and I will send them to you.

Jay

Well I am finally getting back to work on my 7.5 HP RPC.

Thank you again for the plans stelradCoal. Also thanks to toolnut for doing the plans.

I plan to follow the plans for an RPC with a 24V remote station.

I have started sourcing the parts and ran into a problem. It seems that the Steveco Potential Relay has been discontinued. At least by Grainger but Grainger does have an alternate part number.

SUPCO
Relay,130-270 V
Item# 4MG77

https://www.grainger.com/product/STEVECO-Relay-4E655

Is this part correct? The plans state that the Steveco should not be substituted.

Is there an optional relay that is still available? Or another source?

Ebay only shows 1 listing for the Steveco 90-66 and it is an Essex 128416-1354UR 5G1.

Priced @ 34.99.


As an aside bit of info, I considered buying a Phase Craft RPC. For the price it might be a better way for me to go. But they don't have a 24V switching option. And besides I like to DIY and learn along the way. But if this relay is going to be an issue the PC might still be a better way. Opinions?

Ron,
I have a work around for the Steveco 90-66 and you will need the new plans. I am very slow to get these things out now days due to health problems and trying to work 9 hour days.
I need an email address to send the updated plans. You can send a Private Message or e mail me and I will get them t o you. If I do not respond in a week, drop me a reminder. I no longer have a computer at home and will need to stop at the library to send the plans.
I know of at least one RPC being built from these plans and it worked ok. Please check the wiring for a DC contactor and wire per the manufacturers specs. I think I used A.C. contactors.
Bruce

toolnut said:

Ron,
I have a work around for the Steveco 90-66 and you will need the new plans. I am very slow to get these things out now days due to health problems and trying to work 9 hour days.
I need an email address to send the updated plans. You can send a Private Message or e mail me and I will get them t o you. If I do not respond in a week, drop me a reminder. I no longer have a computer at home and will need to stop at the library to send the plans.
I know of at least one RPC being built from these plans and it worked ok. Please check the wiring for a DC contactor and wire per the manufacturers specs. I think I used A.C. contactors.
Bruce

Click to expand...

PM sent Bruce.

stelradCoal said:

My intention is to run #6 wire to a remote cabinate which will be the connection center for the 3phase RPC from a 60 AMP breaker in the sub-panel. I would like to mount the RPC motor outside in a doghouse or up in the attic of the garage in order to minimize noise, but this remote mounting makes pony starting a bit more difficult.

Click to expand...

Placing the idler motor outside will invite rust formation inside the motor case. I would not do that.

stelradCoal said:

My other concern is the current inrush when a 10HP RPC is started with caps. I understand you should have between 50-100uf of capacitance per HP so I am looking at 500-1000uf. How much inrush current would that cause? Is it likely I am going to cause light flicker/dimming in the garage, main house, neighboorhood? Will I be poping circut breakers regularly?

Click to expand...

I would not use something as crude as a pony motor, although it works. Look into a soft starter. They are not hard to build. But I'm looking at it from my perspective. If you don't have the background in the area the simple answer is: get some.