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Schematic for a 20 HP RPC. That's more than the 5hp rating on the potential relay.

m-lud

Stainless
Joined
Sep 4, 2016
Location
Missouri
I have made a couple RPCs over the years with this basic diagram. All were for five HP and under.
I'm now building one for a Baldor 20 hp motor rated at 47 amps.
OIPOSAHYPLJUUUU.jpg

View attachment 324673I

In searching here for information here on the forum I found this Thread by Peterh5322.
RPC Topologies Using Potential Relays (practicalmachinist.com)
I understand what he is saying. I think!
He is using a relay or a magnetic motor starter and using the coil of the relay as a switch for the potential relay to make and break the potential relays start capacitor cycle. Therefore using contacts that are rated for the load well over what the potential relay is rated for.
Peter contributed a lot to the forum.

Here is peters schematics.
Small_RPC_LE_5_HP.jpg
Large_RPC_GT_5_HP.jpg
I understand these schematics but am not sure of myself enough to build my RPC.
Its been many years since Peter drew these schematics.
Is there a schematic out there more like the first one i posted?

I found this photo of a 25 HP RPC on ebay that I can pretty much follow how its wired but prefer a schematic.
FFFFF.jpg

I have searched but my key words aren't getting a good schematic.
My start caps. = around 240 micro ferads. Is that satisfactory for my 47 amp 20 HP motor.? I can buy more

I realize a motor with no load wont be pulling those 47 amps. Accept while starting up. I have a good strong 220 amp service with only a row of 110 outlets on the service.
I have been using a 5HP RPC but now need a 20 HP..

Thanks Mike
 

thermite

Diamond
I have made a couple RPCs over the years with this basic diagram. All were for five HP and under.
I'm now building one for a Baldor 20 hp motor rated at 47 amps.
View attachment 324684

View attachment 324673I

In searching here for information here on the forum I found this Thread by Peterh5322.
RPC Topologies Using Potential Relays (practicalmachinist.com)
I understand what he is saying. I think!
He is using a relay or a magnetic motor starter and using the coil of the relay as a switch for the potential relay to make and break the potential relays start capacitor cycle. Therefore using contacts that are rated for the load well over what the potential relay is rated for.
Peter contributed a lot to the forum.

Here is peters schematics.
View attachment 324679
View attachment 324681
I understand these schematics but am not sure of myself enough to build my RPC.
Its been many years since Peter drew these schematics.
Is there a schematic out there more like the first one i posted?

I found this photo of a 25 HP RPC on ebay that I can pretty much follow how its wired but prefer a schematic.
View attachment 324683

I have searched but my key words aren't getting a good schematic.
My start caps. = around 240 micro ferads. Is that satisfactory for my 47 amp 20 HP motor.? I can buy more

I realize a motor with no load wont be pulling those 47 amps. Accept while starting up. I have a good strong 220 amp service with only a row of 110 outlets on the service.
I have been using a 5HP RPC but now need a 20 HP..

Thanks Mike

The technology hasn't changed in over a hundred years, so "technically" either of Peter's schematics - or Fitch Williams - can be "scaled" - up or down.

And of course a(ny) type of sensitive relay ... with low-amperage contacts .. .can switch a contactor with MASSIVE contacts. The "load" the smaller relay sees is only that of the actuator coil of the heavy contactor.

The greater concern is that a 20 HP RPC WILL HAVE a rather nasty starting load even with NO machines loading it's own output.

Even with a contactor that can manage it, that - motor inrush, plus the start capacitor (or gang-of) - is going to hammer your supply resource to the point where either of "pony start" .. or staggered-start of successive smaller idlers - might be the better option than capacitor start of one large idler.

EX: Just the ONE starter/control I already had (Phase-Craft)..

- starts my 10 HP Weg.

One contactor, each, no other starter/control, can then add:

- a 3 HP.

Now we are at 13 idler HP..

- add a 7.5 HP

Now we are at 20.5 idler HP.

- add the second 7.5 HP.

Now we are at 28 idler HP.

In actual use? That sole Phase-Craft can also start a lone 7.5 HP idler. Or kick the 3 HP online "yesterday"!

:D

Really MINOR mod.. or maybe NO mod, and your existing 5 HP starter/control could probably bring a 7.5 HP online first instead of the 5 HP. Then add the existing 5 HP. Then add a second 7.5 HP.

So go search for two 7.5 HP you do not already have.

- three contactors

- put the balance caps for every idler on the idler-motor side of the contactor.

And with but two new idlers as the "big bucks", you could have any of:

5 HP

7.5 HP

12.5 HP

15 HP

20 HP.

No big deal as to starting .. except a skosh more TIME to stagger-start.

And the largest single inrush load is only 7.5 HP.

Never 20.

Or you could do it with two 10 HP idlers, still only one starter/controller, ... and trade the 5 HP away?

The other "plus" is that by associating the "run" caps with each idler.. rather than "pooling" them all the time as a single array, it is easier to select "enough" idler HP to start even a nasty load (I have ZERO clutches...) and then.. drop-back to a better match of the generated load to the actual running load.

I've been lucky as getting "NOS" never even once wired-in idler motors off "scratch & dent" .. apparently salvaged from shipping damage returns..wherein I have to patch a cracked or dented fan housing or such.

Not really all that much work for the money saved..
 

m-lud

Stainless
Joined
Sep 4, 2016
Location
Missouri
The technology hasn't changed in over a hundred years, so "technically" either of Peter's schematics - or Fitch Williams - can be "scaled" - up or down.

And of course a(ny) type of sensitive relay ... with low-amperage contacts .. .can switch a contactor with MASSIVE contacts. The "load" the smaller relay sees is only that of the actuator coil of the heavy contactor.

The greater concern is that a 20 HP RPC WILL HAVE a rather nasty starting load even with NO machines loading it's own output.

Even with a contactor that can manage it, that - motor inrush, plus the start capacitor (or gang-of) - is going to hammer your supply resource to the point where either of "pony start" .. or staggered-start of successive smaller idlers - might be the better option than capacitor start of one large idler.

EX: Just the ONE starter/control I already had (Phase-Craft)..

- starts my 10 HP Weg.

One contactor, each, no other starter/control, can then add:

- a 3 HP.

Now we are at 13 idler HP..




- add a 7.5 HP

Now we are at 20.5 idler HP.

- add the second 7.5 HP.

Now we are at 28 idler HP.

In actual use? That sole Phase-Craft can also start a lone 7.5 HP idler. Or kick the 3 HP online "yesterday"!

:D

Really MINOR mod.. or maybe NO mod, and your existing 5 HP starter/control could probably bring a 7.5 HP online first instead of the 5 HP. Then add the existing 5 HP. Then add a second 7.5 HP.

So go search for two 7.5 HP you do not already have.

- three contactors

- put the balance caps for every idler on the idler-motor side of the contactor.

And with but two new idlers as the "big bucks", you could have any of:

5 HP

7.5 HP

12.5 HP

15 HP

20 HP.

No big deal as to starting .. except a skosh more TIME to stagger-start.

And the largest single inrush load is only 7.5 HP.

Never 20.

Or you could do it with two 10 HP idlers, still only one starter/controller, ... and trade the 5 HP away?

The other "plus" is that by associating the "run" caps with each idler.. rather than "pooling" them all the time as a single array, it is easier to select "enough" idler HP to start even a nasty load (I have ZERO clutches...) and then.. drop-back to a better match of the generated load to the actual running load.

I've been lucky as getting "NOS" never even once wired-in idler motors off "scratch & dent" .. apparently salvaged from shipping damage returns..wherein I have to patch a cracked or dented fan housing or such.

Not really all that much work for the money saved..

My 5 H.p. RPC will start a 7.5 hp.
I was going to add another Idler motor to the 20 HP so your point of starting with smaller HP and building up to start the 20 would be better.
I really need more than just the 20HP anyway. Ill be running a American Pacemaker that has a 20Hp . Its a much larger and heavier wound motor so it should have at least equal to a 25Hp or better.

I considered taking the smaller diameter 20hp Baldor and putting it in the Pacemaker and using the big 20 HP motor for my RPC. Reason for that would be to give more room in the pacemaker too change drive pully size to raise the RPMs of the lathe from 800 to about 1200 to 1500. The extra room would allow keeping the 8 like new belts on the lathe. Getting off topic here

That heavier wound 20 hp motor may make a better RPC. ???

I may consider a pony motor start. I want a clean setup.
My 220 electric service comes directly off a trunk line 500 feet from my transformer. No other homes involved. My shop has its own service

I appreciate your help Bill.
I'm still searching. There is so much information here its just finding it.
 

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
One advantage you have is that the Pacemaker will have a clutch. That means the motor can start under a minimal load, without a lot of moving parts. That would be an easy start compared to starting some smaller machines in full speed setting, where everything has to be started along with the motor.

You MIGHT get away with less than what is often stated to be needed. Most would specify at least a 30 HP idler for a 20 HP motor, and maybe a 40 HP. A 20 HP idler can supply the current to run a 20 HP load, just, and probably will start it at the minimal load with the clutch out.

Probably depends on what load you will have on the Pacemaker.
 

thermite

Diamond
My 5 H.p. RPC will start a 7.5 hp.
I was going to add another Idler motor to the 20 HP so your point of starting with smaller HP and building up to start the 20 would be better.
I really need more than just the 20HP anyway. Ill be running a American Pacemaker that has a 20Hp . Its a much larger and heavier wound motor so it should have at least equal to a 25Hp or better.

I considered taking the smaller diameter 20hp Baldor and putting it in the Pacemaker and using the big 20 HP motor for my RPC. Reason for that would be to give more room in the pacemaker too change drive pully size to raise the RPMs of the lathe from 800 to about 1200 to 1500. The extra room would allow keeping the 8 like new belts on the lathe. Getting off topic here

That heavier wound 20 hp motor may make a better RPC. ???

I may consider a pony motor start. I want a clean setup.
My 220 electric service comes directly off a trunk line 500 feet from my transformer. No other homes involved. My shop has its own service

I appreciate your help Bill.
I'm still searching. There is so much information here its just finding it.

Your "old" 20 HP Pacemaker motor would make a fine RPC idler BUT.... it MIGHT also be easier to start than the newer same-HP Baldor motor.

Major-maker's have been pushing "running" conversion efficiency UP. But it has made many of their newest motors much harder to start than the older ones.

You probably will NOT need any more that 6 to 12 HP "running", so a staggered-start "dial an idler" rig could be better than pony start for one large one.

If you have both the 5 HP and the 20 HP already on-hand, then adding a ten might do yah:

5 +10 = 15, + 20 = 35.. and that should start the Pacemaker.

Then drop one - or maybe even two.. for normal running - light or heavy?
 








 
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