Questions about a 3 Phase motor for an RPC

I bought a used RPC and plan on using the motor for a home built RPC. The RPC is made by Cedarberg Industries. The motor plate has been removed, as well as the labels on all the capacitors in the panel. The only label on it states max motor size is 7.5HP, so I assumed it had a 15HP motor. Turns out it's 10HP. I'm not using the Cedarberg unit as is because it has a toggle switch that has to be turned on and off when starting the RPC. I want to put the RPC in another room and use a 3 wire start/stop circuit at the machine to turn the RPC on and off.

I made a test board to build the RPC before installing it in a panel. One start button powers the mag starter for legs 1 and 2, the other start button is a momentary switch for the start capacitors on leg 3.
When I finished the board I connected a 3HP motor I had laying around to make sure things were good before wiring up the 10HP motor. I connected one start cap (430-516 UF) on the L3 circuit to start the 3HP motor and it started fine. I measured 242v/193v/213v across the output legs, so all was good. I moved onto the bigger motor.

I bought new start capacitors, one 430-516 UF and two 630-750 UF, so a total of 1,690-2,016 UF, to start the 10HP motor (judging by the size of the start caps, the Cedarberg unit used three 630-750 UF caps). I started the 240v circuit, the motor started spinning, then I briefly pressed the start cap circuit button, maybe a 1/4 of a second. The motor started to spin a little faster, but it didn't spin up to full speed. I hit the stop button, waited till the motor stopped spinning, and started it again. This time I held the cap circuit button a little longer, maybe a 1/2 to 3/4's of a second. The motor did the same thing, spun with 240v, spun a little faster when power was applied on leg 3, but it still didn't come up to speed.
I was concerned about damaging the motor by holding the cap circuit on too long, so I decided to test the motor windings before going any further.

A ground check on all 9 wires showed none of the windings were grounded.
Continuity tested as follows -
T1/T4, T2/T5, T3/T6 checked good, and all 3 showed the same 1.5 ohms
T7/T8/T9 did not have continuity between them in any combination

Then I checked it again and found the following wires had continuity between them:
T1/T4 and T9
T2/T5 and T7
T3/T6 and T8

Before I took them apart, the 9 wires were connected for 240v as follows
L1(A)- T1/T6/T7
L2(B)- T2/T4/T8
L3(C)- T3/T5/T9

So the motor is Delta, not Wye. I read on this forum and others that Cedarberg doesn't share specs on their RPC's, but I called anyway to ask about the Model 75 RPC I had. I was politely told they don't give out any info or specs, not even a wiring schematic. The only thing he told me was the Model 75 RPC has a 10HP motor, not 15HP as I thought.

So, my questions are -
Is the motor good? Should a Delta wound motor have continuity between T7/T8/T9 or is the continuity above the correct way a 'good' Delta should motor should be?

Should I be holding the cap start circuit on longer, until the motor is up to speed, before I release the button?

FWIW - the wires coming from the mag starter to the distribution block are 6 AWG, all the rest on the board are 10 AWG. The motor is wired with a 10' long, 4 wire, 12 gauge SOOW cable. It lighter wire than I'll use when wiring the panel, but I figured this would be fine for testing purposes.

If things work out I have questions about the proper contactors and relay I need, but obviously have to get the motor working first.

This is a guess on my part, so keep that in mind.

Some rpc manufacturers have motors wound with extra windings for the generated leg, so it may make a difference which leads L1 and L2 connect to.

Though I do not know how it is done, it is possible to make some sort of connection which will allow the idler to self start in a consistent direction. I have a motor that does this that used to be a part of an RPC.

You say your motor starts turning and THEN you press the button for the start caps. Try putting the start caps on the other leg.

When you start it, press the start cap button first, then the start button. I suspect the motor is trying to start turning one direction, and the start caps are trying to spin it the other direction.

You have not mentioned balance capacitors, so I assume you do not have any installed. If they are installed, try removing them until you get the unit to run.

Here is a rig that uses ONE push button to start motor AND have start caps in the circuit - and taking my finger OFF the start button drops the start caps out of the circuit. Its easy with two contactors or "starters" working for you

(it isn't a RPC, just a way to run a 15 HP three phase motor on single phase)

How To Make An Old 15HP 3 Phase Go

have fun

I appreciate the comments, thanks.
When I was testing continuity, for whatever reason I thought it was a wye motor. When I didn't have continuity across T7/T8/T9 I assumed the motor was bad. When I figured out T7/T8/T9 had continuity with other lines (but not each other), and realized the motor was delta, it gave me a little hope. But in the back of my mind I'm still wondering if the motor is good or not.

I'd really like to hear from a motor guru that can confirm whether a delta wound motor does or doesn't have continuity across 7/8/9. That'll confirm whether there's a problem with the motor or not.
When I know that, I can resume trying to get it to run. I'll switch the 3rd leg power from L1 to L2 as suggested, and I'll start the 3rd leg at the same time as the other 2. I can't start L3 first, it's powered by L1 (or L2 if wired that way), but I can put power to L3 at the same time L1 and L2 are powered.

Also want to know if it's ok to hold cap power to L3 for however long it takes (2,3 seconds or more) to get it running full speed and stay there.

three phase - Identify unmarked leads on a 9-lead motor - Electrical Engineering Stack Exchange.

This link may be reassuring to you.

Capacitor start RPCs typically have a voltage sensing relay or a timer to remove the start caps from the 3rd leg, with the start caps being powered by L1 or L2 "after" the contactor- which is what you describe. In your situation, YOU are the timer to remove the start caps- but you want the contactor to "connect" them when it closes.

I cannot tell you how long is too long, but the capacitors will...
My 10 HP phase converter is up to speed in under a second, with less capacitor capacity. I would be getting anxious at 3 seconds.

How do you have them connected? It will make a significant difference. Please Wait... | Cloudflare

Lonster said:

I appreciate the comments, thanks.
When I was testing continuity, for whatever reason I thought it was a wye motor. When I didn't have continuity across T7/T8/T9 I assumed the motor was bad. When I figured out T7/T8/T9 had continuity with other lines (but not each other), and realized the motor was delta, it gave me a little hope. But in the back of my mind I'm still wondering if the motor is good or not.

im guessing this motor is a multi voltage delta motor. the continuity is normal for that style.

I'd really like to hear from a motor guru that can confirm whether a delta wound motor does or doesn't have continuity across 7/8/9. That'll confirm whether there's a problem with the motor or not.
When I know that, I can resume trying to get it to run. I'll switch the 3rd leg power from L1 to L2 as suggested, and I'll start the 3rd leg at the same time as the other 2. I can't start L3 first, it's powered by L1 (or L2 if wired that way), but I can put power to L3 at the same time L1 and L2 are powered.

Also want to know if it's ok to hold cap power to L3 for however long it takes (2,3 seconds or more) to get it running full speed and stay there.

Click to expand...

the caps in line to L3 is fine, it is just a fast charging battery for smoothing out the spikes and dips.

id be looking into load balancing caps and a seperate dedicated start caps for load balancing on both.

Lonster said:

I appreciate the comments, thanks.
When I was testing continuity, for whatever reason I thought it was a wye motor. When I didn't have continuity across T7/T8/T9 I assumed the motor was bad. When I figured out T7/T8/T9 had continuity with other lines (but not each other), and realized the motor was delta, it gave me a little hope. But in the back of my mind I'm still wondering if the motor is good or not.

im guessing this motor is a multi voltage delta motor. the continuity is normal for that style.

I'd really like to hear from a motor guru that can confirm whether a delta wound motor does or doesn't have continuity across 7/8/9. That'll confirm whether there's a problem with the motor or not.
When I know that, I can resume trying to get it to run. I'll switch the 3rd leg power from L1 to L2 as suggested, and I'll start the 3rd leg at the same time as the other 2. I can't start L3 first, it's powered by L1 (or L2 if wired that way), but I can put power to L3 at the same time L1 and L2 are powered.

Also want to know if it's ok to hold cap power to L3 for however long it takes (2,3 seconds or more) to get it running full speed and stay there.

Click to expand...

the caps in line to L3 is fine, it is just a fast charging battery for smoothing out the spikes and dips.

id be looking into load balancing caps and a seperate dedicated start caps for load balancing on both.

The way 9 wire delta motor are connected internally is 2 coils are connected to 3 terminals. So 3 terminals should show continuity to each other but not to any other set of 3 terminals! If one set of three have only 2 with continuity then one coil is probably open. Motor will run at 1/2 rated HP. You should check to housing/ground to see if coil is shorted to case. Megger is best if you have one.

Lonster said:

So, my questions are -
Is the motor good? Should a Delta wound motor have continuity between T7/T8/T9 or is the continuity above the correct way a 'good' Delta should motor should be?

Should I be holding the cap start circuit on longer, until the motor is up to speed, before I release the button?

Click to expand...

Fasten the motor to a board and wind a 6' rope around the motor shaft. Pull rope as hard as you can to spin motor and then turn 240vac on with no start capacitors.
If it doesn't start running on it's own by this method then start capacitors are not going to help.

I have used 100uf to start a 3hp motor and 210uf to start a 5hp motor. Start up time is short like 1/4 sec.

Your capacitor numbers appear on the high side. It's is not correct to assume that a capacitor is equal in capacity to another because they are the same physical size.

If Cedarberg won't provide info on cap sizing and wiring, you might need to find someone with identical model to figure those out. Were the old caps still there, maybe you can do some testing to calculate capacitance? Hope you got that thing cheap!

If you look at the wiring reference shown above, and Froneck's response, you will soon see the answer to the question.

Cedarburg made a lot of stuff. Most of it reasonably acceptable. Not the best, not the worst. (I went to high school with one of the Cedarburg offspring, also not the best, not the worst, for what that is worth)

Not sure why they chose to use a delta wound motor, but they did. The 10 HP is fairly conventional for a 7.5 HP unit.

So, when you apply power, you see the motor start? Might be good to know just why it starts.... I assume the run cap is connected at that point, so that appears to be starting the unit?

Also, just how do you KNOW it "does not come up to speed"? What RPM DOES it come up to?

Is it pulling excess current at that point? You can get conventional current for a 10 HP from UL or other sources. FLA is going to be somewhere around 28A, or a bit less. So the likely unloaded current will be around 12 to 16A.

If it draws more, it is probably not up to speed. If it draws about that, it is likely about at correct speed.

Speed may be something other than what you expect. Could be 3450 rpm, or 1725 rpm. or 1150 rpm (3600, 1800, or 1200 nominal, 2 pole, 4 pole, or 6 pole), for instance.

Did you ask Cedarburg if they could supply a correct starting capacitor?

Thanks for the replies everyone, the info is very helpful.

My mother passed away last week, I have to put this project hold while I take care of things. When I get back to it I'll post an update.

For now, here are some answers/comments on what's been posted.

*The wiring diagram Thiele linked, and Fronick's response, answered my question on whether the motor was good. I checked each winding for grounding to the frame - it passed the test, none of them are grounded.

*I'm using the Fitch Williams RPC instructions to build the RPC. When the motor didn't come up to speed (or so it seemed) after 2 attempts, I didn't try a 3rd time. I figured I'd test the motor before going further. Incorrectly assuming it was a wye motor threw me off track, I thought the motor was bad.

*When testing the 3 HP motor before moving onto the 10 HP, when I turned on the magnetic starter to give it 240v, the motor started spinning. When I pressed the momentary switch to give L3 a zap from the start capacitor/L1 circuit, the motor started spinning faster. I don't know how to word it - I could just 'tell' the third leg got power when I briefly pressed the start cap button. The 10 HP motor didn't start the same way. It started spinning when 240v was applied, but when I pressed the cap circuit button it didn't make any noticeable difference.

*My plan is to start the motor, then follow the Fitch Williams instructions on adding run caps to balance power across the 3 legs. When that's done I'll get the necessary contactors and relay and put it all in a panel.
The magnetic starter I'm using is something I bought to upgrade the crappy one on my planer. I'm just using it to turn the power on/off as I tune the RPC.

*Cedarberg has never been any concern to me. When I assumed the motor was bad I wanted to price getting it rewound (way too expensive!). I called Cedarburg to get the motor specs so I could tell the repair shop what I had. In my first post I was just commenting that they don't release information on their RPC's to the end user.

*I can't spin the motor with a rope, the rotor is enclosed in the motor housing. It doesn't have an output shaft.

*Start caps - I thought the motor was 15 HP when I bought the caps. I read start caps should be 100 mf per HP so I got two 630 mf and one 430 mf (240v) so I'd have least 1500mf when wired in parallel.


Thanks again for all the help and suggestions.

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Thanks for the replies, they're very helpful.

My mother passed away last week. I have a lot to take care of, so for now this project is on hold.
I hope to get back to it next week.

In the meantime, here are some answers:

J_R_Thiele said:

three phase - Identify unmarked leads on a 9-lead motor - Electrical Engineering Stack Exchange.

This link may be reassuring to you.

How do you have them connected? It will make a significant difference.

Click to expand...

Froneck said:

The way 9 wire delta motor are connected internally is 2 coils are connected to 3 terminals. So 3 terminals should show continuity to each other but not to any other set of 3 terminals! If one set of three have only 2 with continuity then one coil is probably open. Motor will run at 1/2 rated HP. You should check to housing/ground to see if coil is shorted to case. Megger is best if you have one.

Click to expand...

These responses answered my question, I think the motor is fine.
The start caps are wired in parallel.
I did a ground check on each coil when I was testing continuity, all were ok (none were grounded). A megger would be nice, but I probably would never use it again.

rons said:

Fasten the motor to a board and wind a 6' rope around the motor shaft.

Your capacitor numbers appear on the high side. It's is not correct to assume that a capacitor is equal in capacity to another because they are the same physical size.

Click to expand...

The ability to kick starting the motor would be helpful, but unfortunately it doesn't have an output shaft.
When I bought the start caps I thought the motor was 15 HP. I read somewhere that start caps should be 100mf per HP, so I bought caps to have a least 1500mf - two 630's and one 430.

thermite said:

Quit dicking around. Put Cedarberg in your rearview mirror.
If your idler is 10 HP., just go print-out PM's copy of the Fitch Williams RPC reference circuit and duplicate every last item, wire, and component value in it ELSE "close enough" 'coz close-enough will do just fine. RPC are not complicated animals.

Fitch used 10 HP for the reference circuit so it was easy to scale up or down.

Worry about fine-tuning the generated leg only AFTER you have it carrying YOUR specific load(s) and can determine whether you need to change anything at all .... or not.

Wishing won't rewind it, and rewinds cost more than new for small motors.

Click to expand...

Cedarberg was never a concern to me.
When I incorrectly assumed it was a wye wound motor, not having continuity across 7/8/9 threw me off track. I thought the motor was bad, I wanted to see what the cost was to rewind it (you're right, it's way too expensive, "estimated" price was north of $1000). I called Cedarberg to get the specs of the motor so I could tell the repair shop what I had. In my post, I was just commenting that Cedarberg doesn't share the specs of their RPC's with the end user.

I'm using the Fitch Williams design, that's what I've been following from the start. When I hooked the 3 HP motor up first....I can't put it in words.....I could just 'tell' the change in the motor when I hit the start cap circuit momentary button to put power to L3.
With the 10 HP motor, it started to spin when 240v was applied, but when I hit the cap circuit button, there was zero difference in the way the motor was spinning. I tried it twice, then decided to test the motor before trying again. As I said, assuming it was wye sent me in the wrong direction.
My plan is to get the motor running, then follow the Fitch instructions to balance the 3 legs with run caps. The magnetic starter is temporary, I bought it to replace the old, crappy starter on my planer. I'm using it to start/stop the motor while balancing it. When I have it balanced I'll get the contactors and relay and put it all in a panel.

JST said:

So, when you apply power, you see the motor start? Might be good to know just why it starts.... I assume the run cap is connected at that point, so that appears to be starting the unit?

Also, just how do you KNOW it "does not come up to speed"? What RPM DOES it come up to?

Is it pulling excess current at that point? You can get conventional current for a 10 HP from UL or other sources. FLA is going to be somewhere around 28A, or a bit less. So the likely unloaded current will be around 12 to 16A.

If it draws more, it is probably not up to speed. If it draws about that, it is likely about at correct speed.

Did you ask Cedarburg if they could supply a correct starting capacitor?

Click to expand...

The motor started spinning as soon as the mag starter gave it 240v, before I pressed the cap circuit button (which was a 1/4 second after I pressed the 240v start button)
When I get back to it, I'm going to hold the start cap circuit on a little longer and see what happens. I'll check the rpm with my tach and check amp draw if it comes to that.


Thanks again guys, I'll post an update when I start working on it again.

Lonster said:

... I'll check the rpm with my tach and check amp draw if it comes to that.
....

Click to expand...

If the speed's about right you're probably good to go. Unless you account for the high reactive currents (by checking the power factor of the unloaded unit) you'll be suprised at how high the amp-clamp meter reading will be. Don't let dismay. More important is to check the 3 line-to-line votages once your load machines are online. A good ballance would be 3 to 5 percent.

Initial problems solved

I got the problems sorted, I'm now working on balancing the legs.

Major problems were:

1. Not knowing what the motor sounded like at speed. The 3 HP 'test' motor was quite a bit louder than the 10 HP. I assumed the 10 HP wasn't coming up to speed when I first started it.

2. I used too much start cap power on the 10 HP motor, and was using a 10a momentary start button to energize the 3rd leg when starting it. A couple times doing that burnt the contacts in the start button switch, so it was no longer applying 120v + capacitor power when pressed. For longer than I want to admit, I didn't realize the start button was toast and thought the problem further downstream.

3. There's different windings - WYE or Delta? Who knew? (I don't want to talk about it)

4. Relating to #2, I assumed I fried the start caps and bought new ones. Turns out 2 of the 3 replacement caps I bought were DOA (USA made Mars caps bought from the US manufacturer).


So, now that I've got that sorted and have a running motor, I of course have more questions. To have a single push button start, do I just need to get a second contactor and a timer relay?

Can anyone point me to the correct parts needed?

I'm assuming the 40a 2 Pole contactor with a 240v coil linked here

And the Omron timer at this link - H3Y-2, 240V A/C Coil, 0-10S delay, 5A (with Socket Base)

To have a single push button start, do I just need to get a second contactor and a timer relay?

How I like to do that is to have a momentary switch for the start switch that has 2 sets of contacts. Use one set of contacts to trigger the auxiliary contacts on the main contactor. That contactor will stay engaged til you push normally closed stop switch. Use other set of contacts to engage a contactor that is hooked to starting capacitors. That contactor will open when you take finger off momentary switch. Sort of like starting an engine. Hold down start switch til motor is running. Just a bit longer than bumping start switch.

The RPC will be located in a different room, not close to where the 3 phase saw is. My plan is to have a 3 wire start/stop circuit wired to the main power contactor, that way I can run remote start/stop buttons for the RPC over to the saw.
I'm not sure what I need to do it. I thought just a contactor and a timer? Should the ghost leg contactor and timer relay have a 240v coils?

I sent you a PM and an email with an attachment. Did you get them?