# Rotary phase converter voltage

I recently purchased an older mill and lathe for my home and hooked up
a new rotary phase converter to allow for 220V 3 phase power supply.
The mill appears to run fine. However, when I power the lathe it turns
slowly for about 15 seconds and looses power. I checked the control
box and there are two componants (I forget what they're called) that
get hot and cut of power. Once they cool I retry with the same
result.Trying to troubleshoot, I first checked continuity in the
windings to make sure I had rewired the motor correctly from 480V to
240V and that checked out according to directions I found here on this
group. The next thing I checked was voltage at the 3 phase breaker. I
got 110V from L1 and L2 coming from my single phase panel, but I
measured 240V at L3 coming out of the rotary phase converter. That
seemed odd to me but I am not very familiar with 3 phase power. I had
assumed that 3 phase is 3 equal 110V lines. I will appreciate advise
from anyone who might suggest what my problem is, hopefully my motor
isn't shot. The motor is a 3HP Reuland and is "Y" wound.

Thank You
Hi "ss"
As you know, three phase power has three wires. The voltage measured from any one of those three to either of the other two will be the same voltage. If it is a 220 VAC, 3 phase system, the voltage will be 220 volts.
If you measure 110 volts between terminals in *any* 220 VAC three phase system, there is a major fault.
Is it possible that your measurements were taken from some "fourth" terminal to each of the three wires? Measuring three phase voltage involves only 3 terminals.
Jerry
How are you measuring the voltages? With respect to ground?
Suppose we call the two legs from the power line L1 and L2 and the leg generated by the rotory phase converter L3. If you measure FROM GROUND, L1 and L2 will measure 110 volts and L3 will measure something probably between 200 and 250 volts (In my own system, it measured 123, 124 and 221...). But, if you measure from L1 to L2, you will get 220 volts. And, if the phase converter is properly balanced, you will get 220 volts between L1 and L3 or between L2 and L3 (voltages are approximate). If it is not properly balanced, these readings may be off a little.
Anyhow, it sounds to me like you have a wiring error somewhere in the lathe or, possibly, the motor has a problem.
Jerry
the thing that gets hot is a protective circuit to keep from destroying the motor. A good test would be to remove the belt and see if the motor turns freely, and if so, if it will start unloaded and run smoothly. If it does, it may be that there is too much inertia in the lathe or that something is stuck, if not, then you probably have a wiring problem to the lathe or a damaged motor, or possibly a bad starter. Reading the voltages at the motor terminals when it is trying to start (read L1 to L2, L1 to L3 and L2 to L3) will tell you a lot - make those measurements as well and post all results here for more commentary
Since the mill runs OK, it sounds to me like your rotary converter just isn't quite big enough for the lathe. My RPC runs my mill fine and runs my lathe fine when the lathe is on low-range (3 HP) but my lathe behaves as you describe if I switch it to high-range (5 HP). The idler I'm using is a 5 HP. If I got a 10 HP idler (or added another 5) I'd probably be able to run the lathe in high-range -- but 1000 RPM is fast enough for me.
After all the good advice so far..Don gives you a hint to the next step.
Turn on the mill..and see if the lathe will now start.
The mill motor adds additional horsepower to the phase converter. If it starts with the mill running..you know you need to upsize the phase converter, or down size the motor on the lathe.
Gunner
Political Correctness
A doctrine fostered by a delusional, illogical liberal minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.
Gunner gives you a hint, or at least refers to one of the design caveats of RPCs which states:
"The idler motor HP should be at least 1-1/2 times greater than the HP of the load motor". That applies to voltage balanced RPCs. For unbalanced RPCs, a ratio of 2 X or greater is recommended.
Bob Swinney
Thanks everyone for your comments. I was testing voltage from each of the 3 lines to a ground so it sounds like the RPC is behaving correctly. I wasn't considering the possibility that my 5HP RPC might be inadequate since the supplier quoted it as able to supply 40A. I also didn't know that I could increase capacity by running the mill at the same time. One person commented that I might test the voltage at the motor during startup. Does that mean I should measure voltage between each of the 3 power leads (each contact having 3 wires attached) at the motor right as I turn on the lathe? Can turning the lathe on with this problem damage the windings? I will also try removing the drive belts. Thanks for the great suggestions! Stan
How can you tell if an RPC is balanced? Stan
I just spoke to a friend about my problem and he suggested that the "heaters" in the control panel may be sized for the lower amperage motor protection required by 480V wiring and that since I rewired for 240V, I doubled the load amperage which may be kicking them. Does that sound reasonable? Thanks Stan
yes, that sounds reasonable, but before you change them, try starting the lathe with no belt on it and with the mill running - with no load, it ought to start, I would think - just a guess though.
yes
I'm surprised the motor is Y wound, a dual voltage motor is normally connected Y for the higher voltage and delta for the lower voltage. Martin
Actually, no. The thermal cut-outs are there to protect against a prolonged overload. In other words, if the motor ran just fine, but you started working the lathe hard and then they tripped, this would be your probable problem. But your motor never gets started. It complains mightily for a while, then it trips... The thermal cut-outs are not your problem (even though they may be a bit too small), but they are probably saving you from making great quantities of smoke...
Either your motor is bad or, more likely, miswired. And a continuity or resistance test isn't necessarily going to find it...
Jerry
Hi Martin
It might be misleading to imply a Y connected 480 vac motor would likely be delta connected for some lower voltage. It is Very common for Y connected motors to be Y connected for either 480 vac or 240 vac.
Jerry
Oh hell yes. They are about half the amperage rating needed for 220, if previously run under 440
But that doesnt explain why it doesnt come up to full speed on high range.
Gunner
Political Correctness
A doctrine fostered by a delusional, illogical liberal minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.
If 4-5-6 are connected..that means its been at least partially wired properly for 220 on most..most..not all..but most motors
Reread your data plate again Carefully. Sometimes the wire numbers are damned hard to read after a gazillion years of hard use and some oil smutz on them. And dont try to clean each wire..you may well clean off the numbers completly. Been there..done that..sigh...had to take it to a motor shop.
Gunner
Political Correctness
A doctrine fostered by a delusional, illogical liberal minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.
It doesn't fall over when you fire it up...
Mine must be balanced then :o)
I tried running the mill at the same time as the lathe and it doesn't seem to make much difference. I should clarify that the lathe does seem to start easily and doesn't appear to be labored, it just doesn't continue to run. After 15 or 30 seconds it kicks off and won't start again for a couple minutes. Also it just seems to run at a slow speed. I may have to wait to get an instruction manual. My neighbor is an older machinist and he also has never seen this type of speed control. The Lathe is a 15" Cincinnati "Hydrashift". It has a round dial to select speeds which either isn't working or we can't figure out how it works. There is a label beside the dial that reads, "Select Speed, Dwell in Neutral for 2 seconds and jog". Has anyone here ever used this type of control. I've heard that Leblond has a similer setup.
Thanks, Stan
hell of a fine lathe. However..prone to electrical problems as they age.
Gunner
"Liberalism is a philosophy of consolation for Western civilization as it commits suicide" - James Burnham

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