Would this Baldor 10 h.p. 3 ph. make a good 6 h.p. output RPC?

[Danl]

I need to make an RPC capable of handling startup of the 6 h.p. 220 volt 3 ph. motor on my new-to-me Nardini 1440 lathe. I'm wondering if this 10 h.p. 3 ph. motor motor would do the trick, using a start capacitor? And if so, what any idea on sizing the start capacitor?

Thanks,

Dan L

[flylo]

Your motor plus this eBay item number:300526178147
& your all set. It will run 1 machine 10HP but up to about 40HP if you start the larger motors first.

[J Tiers]

That should do the job. It's a 1760 RPM motor, meaning it will be reasonably quiet.

The service factor of 1.15 suggests it will respond better to overloads, and may have a bit less voltage drop than other motors, which is all to the good if true.

The 1760 rpm means it is a lower slip motor, with a low resistance rotor, which is good for an RPC. It WILL mean a higher locked rotor current and start current.

[lakeside53]

Actually.. probably not. If the Nardini has a 2 speed motor, the motor is a pig. A 15hp rpc will not start it in top gear high speed. There was a thread on this recently.

As for "start capacitor"... there is more to it than this. Dig around on this site and other about building an RPC. You will need to balance the output voltages with capacitors also.

[J Tiers]

Was that one a Nardini also? I did not connect this with that one.

Well, the motor will make a good RPC, but if the Nardini basically needs powerco 3phase to work, it might be light.

However, this motor oughtta have a better shot at it than some.

[lakeside53]

The initial thread was not but the same issue with the Nardini was referenced in it.

[flylo]

That was a 7.5hp Nardini I think & this is only a 6hp. The ebay box & the motor work great, we did aa 7.5 for a friend & it runs quiet & smooth. Fot $189/shipped all wired & ready to go is the way to go IMHO.

[PStechPaul]

I think the way to determine an approximate size for a run capacitor is by using the impedance that will provide the full load operating current at the rated voltage. This motor draws 27 amps at 230V at 60 Hz, or 8.5 ohms. X(C) = 1 / (2 * PI * f * C). Thus C = 1 / (6.28 * 60 * 8.5) = 311 uF. A start capacitor would probably be 2x to 3x that size.

[Rich Carlstedt]

Dan
For capacitors you want about 100 Micro Farad (240 volt) starting Caps per horsepower and 15 Micro Farad Run capacitors ( Metal/Oil filled at 370 volts) also per HP .
The start Caps are usually Plastic cased (Paper in the old days)
The above is for a 240 volt system
Do not use lower voltage caps !
If you get higher voltage units than the above, be aware that they will have less MF rating at a lower voltage.

Used Caps can be found in Air conditioning repair discards, so if you know a A/C repair guy the cost is $0 as they also have potential relays that are tossed.
You can undersize the above caps, but realize that less MF you have, means longer start cycles and that's what blows out Caps as they can only stand so much heat. Some convertors need a minute or more between consecutive starts or they blow. The above should get you about a one second start. If you don't mind, you do not need a cutout relay , but instead use a heavy duty push button and use it like your ignition switch in the car, when you hear the engine run, you release the key . In the instant case, you push the button in, and then turn on power and when the motor comes up to speed, you release the button. Its not automatic like some RFC's but is simple and cheap.

What others have said about the Nardini motors is true . The starting ranges between low and high speed will drive you nuts. The motor is a hog. ( I did a 15 inch 7.5 HP one, I know).
To handle it, it's possible to add more caps to the difficult speed range as long as you know which leg is the manufactured leg in that set of power leads and for that speed only.

Hope this helps
Rich

Forget the "balanced Voltage " claims that you hear about !
What you want to measure is amperage. I balance all my RPC's by amps as "Amps are Power"
Voltage is " potential" and does not do work ( batteries have voltage but do nothing till the amps flow)

[polaraligned]

If it is a 2 speed motor, you may be in the same boat I found myself in. I cannot get my 15 hp RPC to start up my 7.5 hp lathe properly in the high range.
See last post on this page for the damming videos of the generated leg taking a beating on the high range. It seems that you need a much larger (than the 2x rule of thumb) motor for running the high speed range on these 2 speed motors.

http://bbs.homeshopmachinist.net/threads/71866-Problems-Running-7-5hp-2-Speed-Motor-on-Lathe/page4?highlight=victor+lathe

[j king]

I had a guy help me build my RPC. I purchased a large bank of capacitors.6 caps I believe.it was from a electric furnace I believe I was told. It starts a 15 hp motor with no help. I do have a contractor wired into a cap to start it up and then release the contractor once up to speed. Works great. The bonus is I have a hydraulic car lift with a 3 phase motor on it. I can run that without the the RPC running because the caps are so large. I am not an electical guy so can't explain how it works but it does very well.
I know people don't believe me but I swear my power bill goes down or doesn't change when I run the RPC for the shop.

[smithdoor]

Use for start Capacitor Value = 60-80MFD per Motor HP
For run capacitor use 1 to 2 MFD per HP
Use a Standard A/C Style Potential Relay

For more detail see

http://www.homemodelenginemachinist.com/downloads/files/three-phase-converter-292.pdf

From my past this will start over 15 HP. My old shop. Most time I use a 1 1/2 hp 3 ph motor and would start 3 hp motors/lathe with no load

Dave

I need to make an RPC capable of handling startup of the 6 h.p. 220 volt 3 ph. motor on my new-to-me Nardini 1440 lathe. I'm wondering if this 10 h.p. 3 ph. motor motor would do the trick, using a start capacitor? And if so, what any idea on sizing the start capacitor?

Thanks,

Dan L

[wierdscience]

The 60-100 mfd per HP is the correct range.The last RPC I built I use a centrifugal switch to handle the start,which is nice since the RPC will start just like any other single phase motor at that point.It also gives you another advantage where if you get a load spike that tryies to stall the RPC the centrifugal switch will drop the start caps back in and give the system a boost.

The motor in question should work fine,since it is the same model Baldor motor that Ronk and several others use for their RPC converters.

[Doozer]

Being 10hp, the Baldor is likely delta connected
on either voltage, which is good for an RPC
as delta seems to generate a more stable wild leg.
I have a 6hp Leeson for an RPC in my shop.
It is 1200 rpm and delta connected;
runs everything really well.
The motor on that Nardini should be a WEG,
which are good heavy motors.

-Doozer

[smithdoor]

The Potential Relay is use on seal motor like A/C and Water pumps works just like a centrifugal switch.
They say this will start a A/C type motor at 20 HP. Some parts of word they only have single phase to use and will start even large motors. I had place in the hills that to get three phase 15 years ago would cost from the power company $10,000 or more plus the cost of the meter ring. I can use single phase lower in cost.

Dave

The 60-100 mfd per HP is the correct range.The last RPC I built I use a centrifugal switch to handle the start,which is nice since the RPC will start just like any other single phase motor at that point.It also gives you another advantage where if you get a load spike that tryies to stall the RPC the centrifugal switch will drop the start caps back in and give the system a boost.

The motor in question should work fine,since it is the same model Baldor motor that Ronk and several others use for their RPC converters.