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Help troubleshooting a starting issue with large motor via RPC

StillwaterWW

Plastic
Joined
Apr 14, 2021
Ok, I will try and make this as concise as possible and include the details that may be relevant...

I’m having an issue starting a machine I just brought in - Wadkin BEM shaper / spindle moulder via my RPC. It will start and try to come up to speed for 2-3 seconds and then the overload / contactor / coil trips and cuts it off.

Shaper specs -

12 hp / 27.4 FLA @ 230v, 3 phase, dual voltage motor with belt drive to spindle.

Photos of the contactor / overload protection / coil below. I am not convinced that this is the right size for the machine at low voltage, but maybe someone can confirm.

The outside of the control box has a 480v sticker on it, but the (12 wire) motor leads appear to be wired for low voltage according to a few places online I saw, however current motor lead wiring does *not* match either schematic shown in the provided paper wiring diagram that I found stuffed inside the junction box so I scratch my head and pull at my beard....photos below of J box, paper diagram found and written diagram on the back of said paper that shows how motor is currently wired.

RPC - (photos )

Kay MA-2-R-VS 10hp with new caps and fed via #4 awg on dedicated 60 amp 230v breaker from main single phase panel. 3 PH MLO subpanel with (1) 30 amp Branch & receptacles and (1) 20 amp Branch / receptacles. Obviously I am plugged into to the 30 amp receps with appropriate plug on the machine in question.

This is on the edge of capacity for this RPC but I thought it would start it. Obviously I may have misjudged, but I’m confused about the contactor on the machine that controls the overload protection (Moeller), which is what is actually tripping. See photos, The highest setting for overload is 16 amps...which makes sense for the machine @ 480v but is way under @240v...but the motor seems to be wired for low voltage / 230v.

So the questions are - is my RPC underpowered? Is the overload protection / coil / Contactor wrong or underpowered for a low voltage setup?

Can anyone confirm via photos if my 12 wire motor wiring is correct for low voltage?

What am I missing?

Other notes -

I have verified via multimeter that the wild manufactured Leg is passing through contactor and not the leg involved with going to the little transformer in the control box and, I would assume, not involved with operating mag coils on Contactor, but I am new to this type of troubleshooting.

I have been using this RPC for a few years now to start both a 9 hp SCM planer with large cutterhead and 9 hp sliding table saw (and several other smaller motor machines) with no starting issues. The RPC is not tripping it’s breaker or appearing to struggle in this situation.

I was able to get the Wadkin shaper to start and run normally but removing the drive belt that connect motor to spindle. It pegs the onboard amp meter to 90+ at startup / inrush and then settles around 10 amps at “idle” with no belt load.

This shaper had been sitting around for years unused / building sold / new owners don’t really know about it, but I did see video prior to me buying of it starting and running what appeared to be fine, but am unsure of details of their power source, but is likely metered 3 phase (unsure of voltage.) It had a 250v rated plug on it when it came to me.

Whew...that’s hopefully enough for someone to go on. I’d appreciate any help troubleshooting this and happy to provide more details and photos of relevant details as needed.

-Phillip
 

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The RPC motor is at 10 Hp max and the shaper motor is at 12.5 Hp.
RPC is a little on the light side. A 15 - 20 Hp might make it.
Test by adding a 5-10 Hp motor in parallel to the existing RPC motor.
 
Ok, thanks for the reply.

Am I wrong in thinking that practically speaking, this is all based off amps and not HP? I have seen many different interpretations via manufacturers / motors / etc at putting a HP figure on something but where the rubber meets the road is the FLA at a given voltage, no?

RPC manufacturers seem to rate and market the “HP” stats of their units in different ways from what I have seen. Kay does not market the same way that someone like American Rotary does. I realize that I am trying to start a “12 hp” motor with a “10 hp” RPC, but where is the real, accurate calculation done in this equation? HP or Full Load Amps?

So if I have an RPC being fed 60 amps single phase and outputting 30 amps 3 phase (someone please correct me if im wrong...) then it’s not a stretch to think that it will start a 27.4 amp motor with no tooling load is it? Especially when it has been starting a 9 hp / 24 amp planer with 5” diameter cutterhead as a load for the last 3 years.

I tested with another smaller 3 phase motor on same branch running first before starting shaper and same result.

What of the details of what appears to be an undersized (5HP / 16 amp) O/L starter. This does not make sense to me and is the piece of the puzzle that is tripping, not the RPC.

I am not trying to be contrarian, and more trying to make sure I understand this properly and it’s not all adding up to me.

Thanks again for the reply.
 
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You have a 5HP motor starter trying to start a 12.5 hp motor, makes sense to me that its tripping on startup. Starter was sized for 480V supply, you have half of that requirement.
 
You have a 5HP motor starter trying to start a 12.5 hp motor, makes sense to me that its tripping on startup. Starter was sized for 480V supply, you have half of that requirement.
Thank you for the reply and confirming what I was concerned about. It doesn’t make sense considering the motor being wired for low voltage, but I do not know the history of this machine so assuming much of anything is unwise and trying not to work from assumptions.

I will look into sourcing a starter sized for 12hp / 30 amps + @ 230v.
 
Thank you for the reply and confirming what I was concerned about. It doesn’t make sense considering the motor being wired for low voltage, but I do not know the history of this machine so assuming much of anything is unwise and trying not to work from assumptions.

I will look into sourcing a starter sized for 12hp / 30 amps + @ 230v.
Don't immediately spend money on this yet. Get any 5 Hp 3 phase motor and connect to your current idler.
Of course you would start one at a time and make sure your wire size can handle the current.

If this was me and I was faced with getting a larger idler in the 15 - 20 hp range, I'd be checking my math.
The larger the idler the more it takes to get it spinning.
 
Ok, thanks for the reply.

Am I wrong in thinking that practically speaking, this is all based off amps and not HP? I have seen many different interpretations via manufacturers / motors / etc at putting a HP figure on something but where the rubber meets the road is the FLA at a given voltage, no?

RPC manufacturers seem to rate and market the “HP” stats of their units in different ways from what I have seen. Kay does not market the same way that someone like American Rotary does. I realize that I am trying to start a “12 hp” motor with a “10 hp” RPC, but where is the real, accurate calculation done in this equation? HP or Full Load Amps?

So if I have an RPC being fed 60 amps single phase and outputting 30 amps 3 phase (someone please correct me if im wrong...) then it’s not a stretch to think that it will start a 27.4 amp motor with no tooling load is it? Especially when it has been starting a 9 hp / 24 amp planer with 5” diameter cutterhead as a load for the last 3 years.

I tested with another smaller 3 phase motor on same branch running first before starting shaper and same result.

What of the details of what appears to be an undersized (5HP / 16 amp) O/L starter. This does not make sense to me and is the piece of the puzzle that is tripping, not the RPC.

I am not trying to be contrarian, and more trying to make sure I understand this properly and it’s not all adding up to me.

Thanks again for the reply.
Doesn't matter. Given a 5 Hp motor of different makes, the FLA is not always the same. The older heavy motors usually draw more current.
I've got one at 12 A and the other one is at 14.2 A. Both 5 Hp. A amp here or there doesn't make a difference until you get to the edge.
I remember Yes's album, Close to the Edge.

The equation people here use is:
Target motor Hp is 2 times the idler motor Hp. That means 22 Hp, so a 20 Hp idler motor is what you will need.
Your 10 Hp RPC and 9 Hp planer together works. Possible that your boundary condition for stalling has been reached with
the 12 Hp motor.

The RPC should have a OL on the idler motor. I do this. You should have your idler with OL set closer to 11A and not 16A.
But I don't know how the RPC is wired. Draw up a diagram and post it. Or take a picture of the RPC internals.
 
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You have a 5HP motor starter trying to start a 12.5 hp motor, makes sense to me that its tripping on startup. Starter was sized for 480V supply, you have half of that requirement.
The way I read this: The idler 10 Hp motor is connected to a 12.5 Hp target. The idler is running, the target is connected and 2-3 seconds the OL occurs.
The OL is caused by the target, not the free-running idler. I have used a 3 Hp starter on a 5 Hp motor for a long time.
 
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Thank you for the reply and confirming what I was concerned about. It doesn’t make sense considering the motor being wired for low voltage, but I do not know the history of this machine so assuming much of anything is unwise and trying not to work from assumptions.

I will look into sourcing a starter sized for 12hp / 30 amps + @ 230v.
Look into it but hold your water, I mean wallet.
 
I don't see where the comment about 5 HP comes from. The RPC is rated for a 10 HP start.

If the overload in the shaper is popping, that suggests that the RPC is providing the current, but the overload may not be capable of carrying the current, because it is only 16A. A 28A load would open it, and the starting load will really overload it.

Of course, we do not know what wires are supplying the current. It may be that the generated leg is falling too low, and the shaper might still not start on a higher current overload unit.

But what I am seeing is that you have a high inertia load, that will take some time to spin up. During that time, current will be high.

At the same time, you appear to have an under-rated overload. And you are running from an RPC, which usually will be a little slower in starting a motor, especially one with a high inertia load, such as you have. Plus, the RPC is a little under-rated.

It may well have started on a powerco 3 phase supply, because there are generally no weaker legs on the powerco supply. Even an open delta is stiffer than an RPC that is at, or slightly under, the required rating.

For a test, you can either bypass the overload entirely, or bypass it with some motor-rated fuses of the correct value (35A). See if the motor will start in a reasonable time. I'd call around 5 seconds a "reasonable" time.

Hit the "off" switch if the motor bogs or takes too long to start. I'd go up to maybe 10 seconds, and if it is not going full speed by then, or current is still high, hit "off".

If it does start OK, then the overload is the issue. If not, then the overload is still an issue, but the RPC is also weak. Try the extra motor.
 
I don't see where the comment about 5 HP comes from. The RPC is rated for a 10 HP start.
It comes from the rating on the manual starter, 5 Hp for 230 V and 10 Hp for 460 V.
A 10 Hp start at 430 V compared to a 5 Hp start at 230 V. Buy another starter? I wouldn't.
Unless this starter switch is going to be cranked for an elevator going up and down all day.

I use a 3 Hp starter with a 5 Hp motor for a lot of years. Still using the 3 Hp starter from 2001.

Not critical that the Moeller starter be upgraded. But it wouldn't hurt.
Since the use is occasional and a big dollar item I would not replace.


You see the little box to the right. An auxiliary switch that can be used with start/stop push buttons.
 
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Is it not the undersized starter that’s what is tripping and preventing the motor from starting? 3HP starter on 5 hp motor is not 5HP starter on 12 hp motor.

It seems I need to either replace with a proper size and/or bypass the O/L to be able to properly assess if the RPC can start the load or not, no?

I hear you about the cost of a starter that size off the shelf. Hurts to consider.

A larger RPC is ~4-6x times more than that, a properly sized VFD is ~ double that cost. I’m just trying to figure out how to make this work with the most reasonable amount of extra cost.
 
Do the cheap (no-dollar, low-dollar) tests first... You may be able to ID the problem positively.

The overload is not going to work well regardless. You have a 27A motor on a 16A overload, it's probably going to trip when you do not want it to, especially if you run it near full power..

The contactor, well, if it is rated low also, it is technically overloaded, and thus is being used "off data sheet". It may work fine or it may do something nasty like weld shut when you don't want it to.

If it is a US made contactor, probably fine. They tend to be rated conservatively. it appears not to be US however.

If european, as it appears to be, the rating may be different from what you expect. They are often selected to "just barely work", at the bare minimum rating to give acceptable life at specific conditions. I'd expect trouble when doubling the current.
 
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Is it not the undersized starter that’s what is tripping and preventing the motor from starting? 3HP starter on 5 hp motor is not 5HP starter on 12 hp motor.

It seems I need to either replace with a proper size and/or bypass the O/L to be able to properly assess if the RPC can start the load or not, no?

I hear you about the cost of a starter that size off the shelf. Hurts to consider.

A larger RPC is ~4-6x times more than that, a properly sized VFD is ~ double that cost. I’m just trying to figure out how to make this work with the most reasonable amount of extra cost.
Your RPC box has no start or run capacitors. Wonder about if you ever measured the line-to-line volts.
If the RPC OL is strictly monitoring idler current and it trips at the max setting then you can say it's a undersized starter.
It's also a undersized idler too.
 
I don't think he showed any of the innards of the RPC.

He showed the nameplate of the RPC, but the innards are on the Wadkins shaper, as I understand it.
 
I don't think he showed any of the innards of the RPC.

He showed the nameplate of the RPC, but the innards are on the Wadkins shaper, as I understand it.
Yes, that’s correct. The RPC has 8 caps (4 start and 4 run, iirc) though I can’t remember off the the top of my head what uF.

Traveling today for family vacation so access to machines for the next week is nil, but i will be trying to figure out the best/cheap way to test with removing O/L and ~35 amp fuses to further isolate once I get back. Im not an electrician but can maybe manage to order the right parts and wire it up to test.
 
Pics 2-4 are the switch box on the Wadkin shaper. The 5 HP O/L is on the Wadkin shaper.

The only photo I showed of the RPC in the original post was the spec plate from the top of the unit.

These are some photos of the RPC. The (8) caps are in a separate enclosure box on top of the idler...found a few pics from when I replaced caps.
 

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