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Van Norman #12 has difficulty running higher speeds off static PC

shaggy

Hot Rolled
Joined
Sep 29, 2010
Location
Oakland CA
...or, POS static converter won't properly run VN12(!)

Long story short... My new-to-me Van Norman #12 w/ GE 1-1/2 hp 3 ph. motor - runs just 'OK' at the slower speeds on a Phase-A-Matic PAM-300, which came w/ the machine, but w/ that setup will not pull the two highest spindle speeds.

So I hooked up a 3500rpm 3HP 3-phase motor as idler motor, using the PAM-300 as starter. I'd hoped even this bare-bones RPC would be a vast improvement, however it only just pulls the second-highest speed, but still not the top speed.

I haven't yet rigged run caps or compared legs - it was a quick and dirty setup, by which I hoped to see some improvement over the static converter.

I'm not sure w/ this setup if the PAM is completely out of circuit once the idler motor is running (Previously I'd tried switching the wild/center leg OFF with a toggle switch, to no discernible effect).

A few thoughts.. the VNs 1-1/2 horse motor is getting pretty light-on when compromised by a static converter. Add to that the VN12s helical drive spindle and gearbox, which require substantial torque to get in motion.

I have no illusions about the static converter. It's basically crap, but probably good enough for starting an idler motor.

What I don't understand is why the 3HP idler motor is (so far, and set up the way it is) providing such limited improvement.

Next on my list is a/ make the idler motor remote -- the din of it up close prevents hearing any problem in relays and switchgear, and b/ measure the 3-ph legs once the setup is underway and under load. Maybe add basic run caps, nothing fancy.

Speaking of run caps, what sort of values are we talking about for a ~3HP rig? I see up to 150uF added to the legs on one design. That is a lot of run caps - I'm used to seeing on the order of 3uF, 7.5uF for oil-filled -type motor caps.

I like the idea of keeping the machine, motor and switchgear original, so a VFD has little appeal (though I'm open to persuasion).

But I need this (basic as possible RPC) to be no-fuss. I don't want to get anal about precision-balancing run caps, etc. I believe an RPC can be as simple and effective as I've read, and that I'm almost certainly missing something.

Thanks for any feedback!
 
anything less than a 5hp motor which might be 90% efficient, is mostly useless as an idler.

the reason isn't easy to understand but basically induction motors are inductors combined with rotational inertia and resistance.

the open circuit voltage of most any 3 phase induction motor when run from single phase is 240v/210v/216v, and this corresponds to the 7:1 ratio between locked rotor current and full load current.

problem is, the voltage ratio is fixed by the air gap inductance but the energy wasted in the coils to get the voltage is inversely proportional the the size of the motor.

so you take the efficiency squared and then take 85% of it, and you get the voltage you'll get out of the generated leg of the RPC at the rpc's full load. problem being this voltage has to be above 75% to generate any torque at all in the driven motor.

motors above 5hp have similar efficiency as they do power factor, above 10hp the power factor stays constant at round 90% and the efficiency creeps higher at >93%.


a 3hp induction motor is probably 75% efficient and 80% power factor. without adding a lot of capacitors, it will provide starting torque only and will not run a 1.5hp motor at full load. Edit: what i mean is, it will not provide a high enough voltage on the generated leg to prevent the driven motor from burning out at full load.

so the usual rule of double the size of the idler sort of works. 90% efficiency squared times 80% powerfactor is 64%

so in the case of hypothetical 100 volt system with an idler twice the size of the driven motor, you would have gotten 64 volts out but instead you get 82 volts (because the idler is twice the size as the driven motor), which is enough to start and run the driven motor, but no where near enough voltage to

100 minus 64 is 32 volts drop, divided by two, (since the driven motor is half the size, so you get 18 volts drop).. which is only 18%, within the range of: it works, don't fuck with it.

the other saving grace is: a 30 pound motor takes about 30-60 minutes to burn out at modest overload. if you burn out a motor at lathe or milling machine duty.. you're doing something else wrong.

also, provided you don't exceed 57% nameplate hp from the driven motor, you don't need any contributing amps from the rpc at all. the motor will run fine on single phase without overheating provided you can get it up to speed.
 
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I have made several RPC's and had the best performance with 6 pole idler motors.
The 3450's are almost useless, and noisy, the 1725's can get lots done except plug reversing motors and very hard to start motors. The 6 pole are the best, and 8 pole are basically useless unless waaay oversized , but they are very quiet.

My home shop and the shop where I keep my '41 Monarch MG EE are all run with a single 3 HP 1140 RPM idler in each shop.
Both motors have a service factor above 1.2.
They have approx 75 Uf of run caps and a 216 - ? start cap that is switched in for .2-.3 Sec with a time delay relay powering a 30Amp double pole relay.
When the timer times out, the DP relay drops out and disconnects the start cap.
Dirt simple, no hard to find voltage relays etc.

NO I have NOT tuned or balanced this setup at all.

I plug reverse my Bridgeport, my DSM-59. MY B&L plug reverses his old Bridgeport with a FM Pancake motor, with an 1725 RPM idler the RPC would reverse when the BP was reversed when tapping. But with a 1.5 HP 1140 RPM idler he can plug reverse when tapping.

Hope this helps,
Bill

After reading the post above this one, and getting the info in my post figured out 20+ years ago, I didn't know this wasn't supposed to work!
 
Thanks very much johansen for your time to reply, and the clear explanations. One thing I didn't get, in your last paragraph re 'exceeding 57% nameplate hp' - could you please expand, particularly in context of what I see as my machine's main issue, i.e., smallish main motor receiving reduced power, plus machine's relatively large required starting torque)? And what might be my best practical solution for running off 240V single phase?

-cheers
Shaggy
 
Thanks Bill. Nothing like having had the actual experience, and knowing what works. This is my first with RPCs. I'm glad I got off my ass and am doing it, with the help I know I can count on here.

Yes, it is a noisy little bugger, and I kind of knew it would be (and that a 3-horse 1750rpm will be ~twice the size). It's just that I chanced on this motor locally at the exact right moment for only 40 bucks, and as it was recommended over a 1750rpm motor in the Phase-A-Matic literature, quote: "A good quality 3450rpm Y-wound 3-phase 220V motor is the best choice; 1750rpm motors can be used in applications not heavily loaded".

I'm looking as we speak for a slow-speed 5-HP, or larger, but it may take a while. Unfortunately they do not seem to be selling as cheap as used to be suggested, I think before the popularity of DIY and off-the-shelf phase converters.
 
"So I hooked up a 3500rpm 3HP 3-phase motor as idler motor, using the PAM-300 as starter."

You want to be sure the phase a matic is disconnected when you using the idler. One good way to do this is, is to pony motor start the idler.

You say the idler won't work on the higher VN speed ranges. What happens when it fails, does the idler stall or the VN motor just fails to start, or maybe
trip breakers/fuses/overloads?

You are using an idler that is about twice the hp of the load motor, which is just about the minimum for this application. Because the VN has a lot of
starting inertia this could be a problem.

1) check the voltage balance phase to phase when the VN is running on the lower speeds. If the manufactured leg is low this is a bad sign and consider
some tuning capacitors to bring this up

2) consider a four or five hp idler motor. Idler speed motor does not matter that much. Another approach would be to sister another idler motor on the first once
the first is started. Or, if you have another three phase machine with, say, a 1 hp motor on it, start that one first and this will assist in starting the VN. The
aux. motor hp is added to the idler hp.
 
Yep, it's like having a big shop vac always on - distracting :) Hardly meant to be left on all day right next to ya, this one. More like off a big table saw. And the bearings have seen better days. Maybe I'll find a proper use for it after this experiment is over.
 
Yep, it's like having a big shop vac always on - distracting :) Hardly meant to be left on all day right next to ya, this one. More like off a big table saw. And the bearings have seen better days. Maybe I'll find a proper use for it after this experiment is over.


I only mentioned the noise factor of a 3,450 rpm idler because that's what I got when I bought my first RPC from Phoenix on eBay. It was almost unbelievably noisy. It shrieked like a Banshee. It had to go.

I ran if for about 3 months until I built my own from notes offered in this section of PM. I used a motor from eBay - a 5hp, 1,750 rpm one built by Boston Gear Co.
It handles my 3 hp mill with no trouble and is very quiet.
 
Jim, on the 3-horse idler, when trying to get to the highest speed the main motor just keeps chugging, but can't get anywhere near it. Curiously there's no immediate indication of o/load from the PAM or the switchgear, but of course I shut if off anyway as soon as I see it's not going to make it.

Before hooking up the idler motor, with only the the PAM, it (PAM-300) would go constantly in and out of overload / start cycles, and never get to speed, main motor rpms cycling up, then down, o/load light on, then off.
I believe it's relatively the high starting torque of the machine that is my problem.

Next step will be finding a larger, slower idler motor. (If a PAM or switched cap will get it started, I don't really want the additional moving parts of a pony motor.)

--thanks
 
Jim, on the 3-horse idler, when trying to get to the highest speed the main motor just keeps chugging, but can't get anywhere near it. Curiously there's no immediate indication of o/load from the PAM or the switchgear, but of course I shut if off anyway as soon as I see it's not going to make it.

Before hooking up the idler motor, with only the the PAM, it (PAM-300) would go constantly in and out of overload / start cycles, and never get to speed, main motor rpms cycling up, then down, o/load light on, then off.
I believe it's relatively the high starting torque of the machine that is my problem.

Next step will be finding a larger, slower idler motor. (If a PAM or switched cap will get it started, I don't really want the additional moving parts of a pony motor.)

--thanks


FWIW I've got two VFDs for my VN22L, one for feed motor and one for the spindle motor.
I'm thinking both will typically run at 60hz but always gives the option of more fine
tuned feeds, etc.

The 1-1/2hp and 2hp 1140 RPM motors seem happy on the VFD with limited testing. I had pulled them apart, cleaned and re-greased the bearings. They make some "VFD noise" but not too bad, and I can always play with the carrier frequency if desired.

I know you want to go the RPC route...

-Phil
 
Would this (below) be a good quiet (and efficient) idler motor? A guy reasonably close has some for $225 each.
 

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1983-ish I built an RPC using a GE 30hp (scrap yard special) as an idler, gaggle of run caps to balance line-to-line, etc. Would not start the 5hp motor in my Van Norman #2 medium, but started all other 6 machines in the garage just fine. Ended up installing a 10hp GE motor (scrap yard special again) and the problem went away. Maybe you need to replace the machine motor as well as use a larger idler?
 
1983-ish I built an RPC using a GE 30hp (scrap yard special) as an idler, gaggle of run caps to balance line-to-line, etc. Would not start the 5hp motor in my Van Norman #2 medium, but started all other 6 machines in the garage just fine. Ended up installing a 10hp GE motor (scrap yard special again) and the problem went away. Maybe you need to replace the machine motor as well as use a larger idler?

Dang. Just a minute before I was going to write maybe I should change the old 1-1/2 horse motor for a 3 or 5 HP, and run it 'however'. Would the poor phase form become a moot point, i.e. with power to spare from the bigger motor? Doubtless inefficiency would still exist and have to be paid for (in upped power bills, perhaps).
You put a 10 on yours? What was your final verdict on why the machine was hard to start, and was it just in the high speeds?
 
I buy mine here < $50

This one is very similar to mine: Used Machinery & Industrial Equipment | HGR Industrial Surplus

Item # 0420-001-0016 $38.00 + shipping.
I would have them post a photo of the inside the motor junction box to make sure it has all it's 9 leads. If only 3 leads, I would pass.
4 connections of 3 leads is wired for the low voltage, 6 connections of 2 is the high voltage.

Bill

Looks like it sold while I was posting about it.
 
Dang. Just a minute before I was going to write maybe I should change the old 1-1/2 horse motor for a 3 or 5 HP, and run it 'however'. Would the poor phase form become a moot point, i.e. with power to spare from the bigger motor? Doubtless inefficiency would still exist and have to be paid for (in upped power bills, perhaps).
You put a 10 on yours? What was your final verdict on why the machine was hard to start, and was it just in the high speeds?

Keep in mind a No 2 Medium is more robust conventional horiz. mill, 10 x 50 table, very comfortable with the 10hp motor. Never figured out why the OE motor wouldn't start well....I tried all I could think of as a noob, checked winding's, connections, etc. Very frustrating at the time as it was my first trip down the mysterious (at the time) 3 phase machine path. Also running other smaller 3 phase motors in the same circuit can help with starting an ornery motor.....switch on another lathe or mill before the problem child motor.

Bill, HGR is a viable option these days. No such thing in the 1980's that I was aware of. Besides the scrap yard in town was 2 miles from the house. No pickup truck, eyebrows were raised when I had them load the 30 horse into the trunk of my '71 Grand Prix. Fun times....
 
Thanks Bill. I'll find one locally (CL), might have to pay a bit more ($200 odd, for that one in the pic above), so not too bad, plus pick up is free, and no tax.
 
Live 'n learn -- I did not know they made different flavors of VN12 :)

Not a variation, completely different animal. the 12 is a smaller lighter universal Vertical-Horizontal tool room acrobatic type machine.
The No2 Medium is a more stout (around 4000lbs) traditional horizontal machine that had vertical head attachment available but not built in.

Van Norman Size
 








 
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