Thread: Fitch Williams 10hp RPC questions

First, thanks to everone who has contributed to this site. I've been reading for days and learning a ton.

I'm in the planning stages of an RPC build and I have a couple of questions.

1. In the Fitch Williams plan http://www.practicalmachinist.com/FitchWConverter.pdf there is a transformer to convert from 240V to 120V. Why not use a neutral wire and save on the transformer?
1a. If you did use a transformer is there an advnantage of going to 120V vs 24V?

I went through the parts list and looked up the grainger prices. (I used 150uF and 110uF for Cp and Cs just to estimate) the total is $367.76 without a motor or enclosure.
2. I see posts of people saying they are building whole RPCs for $200-$300. Where are these electrical salvage places?

control transformer 240V to 120V 4r874 $45.65
Cpf (run cap) 2ge81 $8.25
Cp (run cap) 2gu31 $14.69
Cp (run cap) 2gu30 $13.75
Cs(run cap) 2gu31 $14.69
(run cap) 2gu27 $10.57
C1 motor run contactor 5b109 $48.65
C2 starting contactor 5b118 $41.15
S1 on switch 5b453 $20.25
contact block 5b536 $12.98
s2 mushroom saftey switch 6b329 $33.65
contact block 5b535 $12.98
LT1 light 5b455 $58.10
resistors $5?
starter cap x2 4cu58 2x$13.7

Will:

Try this Ebay seller. I have bought many run caps from this seller. Normally they have 100uf in stock. Good luck

http://stores.ebay.com/Capacitor-and...QQftidZ2QQtZkm

Ken

I ended up spending a little over $300 for everything I used to build my 10HP converter. I bought stuff from eBay, surpluscenter.com, Home Depot, Grainger, local surplus stores and local auctions.

If you do buy caps from ebay, make sure they are rated for the proper voltage. I mistakenly bought some start caps that were rated for 165 volts rather than 220V. I bought them before I knew that they needed to be rated at 220V and the seller said they would be fine.

When I started the project, I didnot know what a rotary phase converter was. With a lot of help from the nice people on this board / the archives / and web links, I was able to build a phase converter that I am proud of.

-Joe

Thanks for the suggestions. I could cut costs a lot in that list but the switches and light look so cool!

will,

I buy my run caps from www.surpluscenter.com, buy my start caps and my potential relay new from Grainger. (I use a potential relay instead of the dual switches Fitch used. His method works good also)
I have just completed a 10 hp RPC and would be glad to talk with you. I spent about $300 on this one including the motor ($50 local buy) and a 16 x 20 x6 enclosure (also local buy).
I bought a contactor (60 amp) from eBay for $41 delivered and an overload relay for $23 delivered. You have to shop a lot of days to do this though.
I start collecting parts about a year before I plan to build so I can get good prices on everything. The one contactor would have cost about $250 list if I bought if from my local electrical house.

Bruce Norton
Kingsport, Tn

"If you do buy caps from eBay, make sure they are rated for the proper voltage"

Theoretical minimum for a start cap for a 240 volt RPC is 240 volts, AC. Practical minimum is 250 volts, AC.

Theoretical minimum for a run cap for a 240 volt RPC is 373.35 volts, AC. Practical minimum is 370 volts, AC.

thanks for the offer of help, ill gladly accept. ive read this http://www.practicalmachinist.com/ub...ic/3/2092.html

edit: i read the above post again and answered some of my own questions

overload relay i assume opens in the case of an overload but how is it wired?

thanks

also what is the advantage of the potential relay? it seems i end up with all the same parts and the same function

1. In the Fitch Williams plan http://www.practicalmachinist.com/FitchWConverter.pdf there is a transformer to convert from 240V to 120V. Why not use a neutral wire and save on the transformer?

Yes, you can do that. I've done that in my RPC because I was able to obtain 120V contactors much easier and cheaper than 240V ones.

1a. If you did use a transformer is there an advantage of going to 120V vs 24V?

No, no distinct advantage. If you can obtain contactors and relays at 24V cheaper than 240V, use them...so long as they meet specs for contact current sizing. Many remote light control and HVAC systems are 24V.

I think the potential relay versus Two start switches versus a time delay relay are all a matter of preference. I use the potential relay because I figured out how to use them about 17 or 18 years ago and I stuck with them. They are cheaper than a time delay relay. I also use multiple start / stop stations in the shop and I can do this with the potential relay or the time delay relay but can not do it as easily with dual start switches. It is all a matter of preference and what suits your needs.
With the potential relay you have one momentary start button and one momentary stop button. It does not get any simplier.

You asked about an overload relay. A magnetic starter (NEMA style) consists of a magnetic contactor and an overload relay. The relay senses current overloads and opens the seal in circuit holding the contactor closed. This will shut the RPC down in the event of an overload and it prevents any damage to your idler.
Go to the Allen Bradley website and look up full voltage magnetic starters. You will see some diagrams for wiring mag starters there and this should explain the concept.

Just had a note from Joe Lauver who is now testing his new RPC and his RPC shut down on overload last night. No damage to the RPC. Seems he put too much grease in his planer bearings and it did not want to start. I did not ask if the planer is in an unheated building but I suspect it is.

i still dont fully understand how the overload relay is wired. i understand how the NC contacts would break the control circuit and stop the motor but how does the coil sense the overload? is it wired in series on one leg of the RPC?

I was planning on running the output of the RPC to a breaker panel and from there to individual tools. wouldnt this system prevent overloads?

"With the potential relay you have one momentary start button and one momentary stop button. It does not get any simplier."

Dont take this as arguementitive but it seems in the FW plan (no potential relay) you have exactly the same parts minus the potential relay and you rely on the momentary action of your finger to do the job of the potential relay

Will,

The overload relay will have three in, three out with heater elements in series with them. When the heater elements sense the overload condition, they open up another separate NC contact on the relay (not the three in, three out at all). This NC is wired in series with the stop button which drops the voltage to the coil of the main contactor. The contactor won't have any idea if you hit the stop button or the overload relay tripped.


Hit Ebay for many of the parts at less than half of Grainger or others.


Lenny

ah it goes on all three lines. that makes sense thanks.

ive been browsing ebay but im a bit wary because i dont really know the specs for things i need. i know the specs for the caps but not really for the contactors and switches

I have just been doing the same thing. I have another line of questions a few posts back about the contactor sizing. The 10hp FW design calls for a contactor that is technically only sized for a 7.5hp motor. I found those contactors on ebay for $14.95.

The overload relay is more problematic. There are tons of overload relays, but most are the "hang on the side of the contactor" type and are quite specific for each brand of motor starter. There are also overload relays that uses heaters, some that are slightly adjustable via a potentiometer, & some that are solid state. Many, many to wade through. Most are the wrong size.

Any industrial start/stop momentary switch will work for you. The coil on the contactors are not current hogs so you can get by with most any choice. NOS or used ones of these are all over ebay so they should be easy to find. Some have built in pilot lights too.


Lenny

i figured most switches were up to the task of the contactor coils.

the specs for the main contactor in the FW plan are 40A inductive, 50A resistive 1HP @ 230 1ph, 10HP @ 230V 3ph
staying with those specs on an ebay contactor would be safe right?

There are three-phase amps and single-phase amps.

One three-phase amp equals 1.732 single-phase amps.

Which is why I usually recommend going up one NEMA starter size for an RPC, as the L1 and L3 contacts are single-phase, whereas the L2 contact, being "back fed" from the idler, is three-phase, with the sum of the three being a manufactured three-phase system.

how does NEMA size relate to the specs of the individual components?

http://www.conweb.com/tblefile/starter.shtml

NEMA size 2?

NEMA size 1 starters are rated for 27 amps. NEMA size 2 starters are rated for 45 amps. I think a NEMA size 3 is about 90 amps but do not have reference material in front of me.

You need to decide how much 3 phase amps you need then size the circuit to do the job. about 2/3 of the single phase amps will be converted into 3 phase amps. A 60 amp, 10 hp idler design will produce about 40 amps of 3 phase assuming you get some conversion from your load motors. A RPC will not start loaded motors any larger than the idler and it is best to use an idler one size larger than your largest load motor. Some folks prefer the idler to be 2X the load motor but I have not found that to be necessary if you build the circuit heavy enough and use Fitch Williams balancing technique.

These numbers are my preference--they are not carved into steel.
for a 5 hp idler, I use a 40 amp single phase circuit.
for a 7.5 hp idler, I use a 50 amp single phase circuit.
for a 10 hp idler, I use a 60 amp single phase circuit.
You will notice these circuits are larger than the ones Fitch Williams used. The difference is in how I use the finished product. I push the heck out of a converter and have had no failures in some 17 years of building and using designs with the above figures.
I presently have a very heavy duty 10 hp idler converter built for a 90 amp circuit. It is destined for a woodworking shop equipped with a 7.5 hp three phase dust blower and two 5 hp, 3phase machines. It will run all three at the same time. I will most likely put some balancing capacitors on the 7.5 hp blower to give the system even better capacity.
the moral of this story is: decide what you need then design a converter to do the job. There is no one answer that fits all. You need to learn how to wire up a magnetic starter before you do anything else. If you can not understand how controls work then you will have a tough time building a quality converter.

Again thanks for everyones patience and help.

When you say magnetic starter I assume you are refering to the contactors, switches, start caps, and overload relay, correct?

I understand how these parts work although this has been a learning process as I'm not very familiar with AC and 3 phase.

Not being familiar with AC and 3 phase I'm still learning about HP ratings and amps. I'm accustomed to DC where components are rated for volts and resistance and amperage is more clear.