Building 10 Hp Rpc

Upgrading from a 5hp to a 10 hp, 5hp I bought complete 4 years ago,. My new lathe popped a starter cap on the 5 hp rpc. I have a 10 hp motor and encloser. 220V is wired in my garage. I figured to use a Run capacitor of 280 mfd, and a Starting capacitor of 600 mfd.
I just have a few questions.

First, What is the difference with a starting cap and a running cap? I know what they do different, but do they have to be a specific starter cap or a running cap?

Second, can I use ballasts from floresent lights, if the value is the same?

Third, I want to use a timer relay, I found one from McMaster a HVAC Motor starter relay 240V?

Fourth, do my values sound right?

Fifth, Should I use 10 gage or 6 gage for a 10 Hp?

Thanks

"First, What is the difference with a starting cap and a running cap? I know what they do different, but do they have to be a specific starter cap or a running cap?"

Start caps are electrolytic, and are designed for momentary application, only, and even then only a few such applications per unit time.

Run caps are oil-filled, an are designed for continuous application. These may be used for momentary application, too, but the capacitance-to-volume ratio is quite low, so electrolytics are preferred for starting.

However, if a machine often cycles between run and stop, or FWD, OFF and REV, it is usually best to use an oil-filled cap in place of an electrolytic for starting.

Start caps must be rated at least equal to the line voltage. 250 VAC is common for a 240 line.

Run caps must be rated at least equal to 1.56 times the line voltage. 370 VAC is common for a 240 line.

Ok that makes sense, using my 5 hp as example the running cap is larger (oval), compared to the starter cap.

electromech13

Ballasts from lights would be oil filled run caps. I have used these as long as they are 370 volts or higher rated. I have seen some rated 330 volts but do not use these. I seem to remember having some of these that are 28.5 mfd.

For a 10 hp idler,
Start caps will be about 900 to 1000 mfd for fast starting and minimum lights dimming
Run caps, about 160 mfd on the primary phase (Cp) whichis the same phase the start caps are connected on. About 120 mfd on the secondary phase (Cs). These values will work for normal efficiency motors from the 70's, 80's up to the mid 90's. A high efficiency motor will be different (I do not like them for idlers)

A timing relay can not handle the start caps directly. You will need to use the timer relay to control a contactor (at least 40 amp, 3 pole rated) and put no more than 450 mfd on any one pole. I use a 270-324 mfd cap on each of the three poles so I have a total of about 900 mfds.

If you want to run a full 10 hp with this idler, then you will need a 50 to 60 amp circuit. The cost is about the same, so build a 60 amp. and use #6 wire. If you want to run only 7-1/2 hp then use a 40 amp circuit and #8 wire.

There are lots of plans around. I personally do not like time delay relay controls as the start time is very short--in fact it is faster than I can get my finger off the start button for a 10 hp with a good starting circuit. If the start circuit stays in too long you will have a growling sound from the idler, if it is too short you will pull a lot of amps on startup.
the start timer needs to operate in the range of 0.5 to 3 seconds. Make sure you get one that is rated for no more than 10 seconds. I would prefer one rated for 5 seconds max.

Thanks toolnut
Well the plan I was going to use sounds like it won't work. So I will search some more. The 10hp idler will be running a old 5 hp, 3 hp, and a 2 hp, plus a welder once in while.

Honestly why do you think you need more than a 5hp then ?? The way I understood it is you can run 1 or 20 (5) hp motors with one 5hp rpc ?? IE you do not need a 7.5hp rpc to run a 5hp and 2 hp motor both at the same time ?

Bill

The 5 hp rpc I have ran great till I hooked up the Gisholt 5hp lathe. When I tried the lathe for the first time it let the smoke out of the run capacitor, the lathe ran, and the rpc growled. I did get it to start again by spinning the idler motor, again the lathe ran, and the rpc growled, but this will not work as a permanent fix. I was told that since this Gisholt my be as old as 1928 or 1929, that the motor would not be a true rated 5hp, it could be as big as a 9hp. Does this make sense? Could I be way off. I figured that I already have a 10 hp idler motor, I might as well upgrade. the 5hp Rpc also growls when I use my welder.

Im looking at George Carlsons design. Seems simple.

George Carlson's design has some bad flaws. I have helped several people fix them. It works as long as you have no run capacitors but when you add run caps the thing gives lots of trouble.

Fitch William's plans are vastly superior. Be aware the 10 hp Fitch Williams plan is really a 7-1/2 hp circuit with a 10 hp idler. This is a very good way to build a 7-1/2 hp RPC. If you want full 10 hp then scale the plan up to 60 amps by increasing the circuit, contactor and wire sizes appropriately.

The only thing I can suggest is look for plans that are fully functional not just simple.

The guy that said you can run twenty 5 hp motors from one 5 hp RPC has no concept of Power. Twenty 5 hp motors is 100 hp and that would take a 500 amp single phase circuit, if you want to run all of them at the same time. RPCs do not generate power. You have to put all the power you need into the RPC plus some to cover the internal losses.

The welder will be your largest problem. You will need a 10 hp idler just to get about 25 amps of three phase and it will need at least a 50 amp single phase circuit-I prefer a 60 amp circuit. You get no conversion from a welder so the idler has to carry all of it.

Other folks have posted about running a welder from a RPC. Might be worthwhile to start a new post asking for the experiences other poster have had with this.

I understand that you need to be able to pull all the power you use thru the RPC itself, 20 motors was a hypothetical illustration.

Lets say 2 motor on one RPC, if it is a 5hp rpc you can run (2) 5hp motors on it as long as you are within your maximum current draw...IE (2) 5hp machines do not need a 110hp rpc to run at the same time.

Bill

I had no problem running anything in my shop 3 hp mill, 2 hp lathe, and the miller MIG welder, all on a 5 hp RPC with two caps run, start and a relay. Never popped the breaker 30 amp. I could run the lathe or mill and the welder. I never had enough arms to run all three.

electromech31 said:

The 5 hp rpc I have ran great till I hooked up the Gisholt 5hp lathe. When I tried the lathe for the first time it let the smoke out of the run capacitor, the lathe ran, and the rpc growled. I did get it to start again by spinning the idler motor, again the lathe ran, and the rpc growled, but this will not work as a permanent fix. I was told that since this Gisholt my be as old as 1928 or 1929, that the motor would not be a true rated 5hp, it could be as big as a 9hp. Does this make sense? Could I be way off. I figured that I already have a 10 hp idler motor, I might as well upgrade. the 5hp Rpc also growls when I use my welder.

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to throw some light on old time motor ratings when i did my apprenticeship in electrical engineering ( not house bashing ) I had to do a year in the armature/stator winding dept. I was surprised to find the details on one armature was the same for a 5 hp to a 25 hp motor plate ? the same thing happened with some old ac motors as well , evan bigger swing.

I asked the winder ( he was old about 55 ) he said that when a customer asked for a 5 hp motor the stores man just stamped 5 hp on the next guy wanted a 25hp you guessed it out came the 2 and 5 punch

treat all old motor ratings with great skepticism better to take the amp reading and work from that

I just found out that the Gisholt is a 42 or 43. I have ordered parts from WNY Phase Converter & Supply for a 10 Hp converter. From what I understand is that a 10 Hp with starter and running caps can run upto a 10 hp, with no adjusting caps, but if it had adjusting caps it would run a 10 hp.