Desperately In Need Of Help

I am new to this forum. I ran across this forum while looking for an answer to a problem that I have had for several years. The problem is that I have a Jet engine lathe, model# GH-1440A, gear head lathe. This lathe has a two speed electric motor. The speeds are 900 RPM'S on the low side and 1800 RPM'S on the high side. On the high side, the full amperage load is 13.4 and on the low side the amperage is 8.2. The motor is rated at 3.4 HP on the high side, 1.5 HP on the low side. I have built a 10 HP rotary phase converter with unbalanced phases. This will run my J2 Bridgeport mill and it will also run my Jet lathe on the low side with no problem. When I change to the high side on the Jet lathe, it will not run and kicks the breaker out on my phase converter. I have been looking at the WNY phase converter panels and panel kits. I have been thinking about buying the 10 horse panel kit that they offer on their web site, but don't want to waste the money if it will not do the job of correcting the problems that I am having with my jet lathe. Any help or input will be greatly appreciated!!!!


This is a great forum and I have enjoyed read everyone's input. Keep up the good work because we can all learn from everyone's input!!!!

I would buy some run capacitors and try to balance your existing 10 HP design, it will help, and might be enough to start the lathe in high. (Try balancing the generated phases about 10% above the utility phase.)

If balancing does not help, you could try adding a second idler motor when you wnat to use the lathe in high, or just idling your Bridgeport.

-Joe

kicks the breaker out

Click to expand...

How big is this breaker?

I ran 40 amp on a 7 1/2 HP unbalanced idler

John Oder

It sounds like you need to balance your phase converter. Unbalanced, the generated phase will sag under starting load. Balanced correctly, you can really stiffen the generated phase and also decrease your idling current with power factor correction capacitors.

You have recieved two good answers: balance the converter with run caps and make sure you have the converter designed for 10 hp. You need a minimum of 50 amps single phase while 60 amps will be much better. If you have it on a circuit smaller than 50 amps then no replacement converter panel will help you any.

Phase Converter 2 speed motor

Myberry,

I think your problem is the two speed constant torque motor. You have balanced your converter for a 1-1.5hp motor ( the bridgeport and low speed lathe). You are then asking the converter to start and run a 3.4 hp motor (hi speed lathe, 2x the hp). I don't have any RPC's but I think your problem is independent of the the type of converter (RPC or STATIC). You may be able to balance the converter at 3-4hp but without a cap change it may run ok at 1.5hp but it can't run balanced at all hp. A VFD would not have this problem.

I have a 13 x 36 Clausing Colchester 900/1800rpm 1.5hp/3hp two speed motor. It is set up to run on a VFD (3hp) or a static autotransformer phase converter. The VFD works fine on any setting. In order for the static converter to start and run the lathe with a collet setup at 40 rpm or a 10" 4 jaw at 1800 rpm I had to wire a relay to the lathe control circuit so that the relay could determine whether the lathe was being run at hi or lo motor speed. The relay then added start caps and run caps as necessary to properly start and run the motor at hi or lo speed.

With your set I don't know if you can set up a similar arrangement but that is how I solved the two speed motor problem.

Joe

Since someone mentioned a Colcehster 13 x 36 lathe, 3/1.5 hp two speed motor I will add that I have one of these and run it from a 5 hp RPC. it will start in any speed and this includes my 8" Buck chuck. It does not over tax the phase converter. The converter has overload protections and the 3 phase circuit is fused at 15 amps with time delay fuses. I have never blown a fuse nor tripped the overloads. The RPC is on a 30 amp single phase circuit. I can run the lathe and my 2 hp Bridgeport at the same time as long as I start them one at a time.

Two Speed motor

Hi Bruce,

I agree. I think a 5hp RPC could easily run the 1.5/3hp Clausing colchester. My point was that Myberry may have only enough capacitance for 1-1.5hp. I think this is consistent with all the other posts. It seems his set up is not capable of the capacity of his idler.

"You may be able to balance the converter at 3-4hp but without a cap change it may run ok at 1.5hp but it can't run balanced at all hp."


Joe

Joe,

You may be correct about the balancing. I balance the RPC for maximum output and never worry about what size motor is connected. I have never encountered a problem with this technique and I have been using it for 20 years.

I balance the idler unloaded and bring the two manufactured phases up until one of them is 10% above line and the other is a little less and the manufactured leg current is less than full load amps, as measured with a clamp-on amp meter. For a 5 hp, I use a 30 or 40 amp single phase circuit and for a 10 hp, I use a 60 amp single phase circuit. I have used as high as 80 amps on a 10 hp when there are some 7-1/2 hp motors to start.

If any additional balancing is needed then do it at the load motor starter. I have needed this only one time.

I think a big part of the Jet lathe problem is the motor itself. I have a machinist friend with a Jet 12" lathe and he has gone through two motors in three years.

Bruce Norton
Kingsport, Tn

Either that... or...

Either any of the above, or he's got a circuit breaker that is insufficient, wrong type, or not quite landed tight enough.

Berry- I've run into SOME circuit breakers that just don't perform properly, and I'll name one example: the Square-D HOMline... But ANY brand/model breaker can exhibit nuisance tripping. IF you have a breaker that is (by itself) hypersensitive by some defect, or the breaker model and type are typically hypersensitive, you'll get what you noted. I found out about the type I mentioned before, and it was not a good day to be around me... I replaced 'em with another brand/type that was compatible-enough, and never had problems since. Your homemade panel could be using any type of breaker- you didn't specify, but could be that it's just simply not the right capacity or type. I believe type HACR is the most appropriate, and as others have noted, you'll need in the vicinity of 50A. My experience has been that if you have enough circuit breaker to START the idler, you've got enough to RUN the load. Now, clearly you won't be able to start the RPC with the JET ON (yikes!), but I'm assuming you're not attempting to do that...

Next, if you have wires landed on the breaker, but they're not quite tight enough, you'll get tripping... because the breaker has a magnetic trip mechanism, AND a thermal... and if the breaker is getting too hot (typically a bad connection will percolate heat into the thermal elemenet), it'll trip for no-apparent-reason. Make sure they're snug.

Last- if you have even a CLOSELY balanced 10hp RPC setup, it shouldn't have any problems bringing up any 4hp-and-down load. Try starting the RPC, then the Bridgeport, and while the bridgeport is spinning, fire up the JET... if it starts, you've eliminated the breaker and feeder, it's down to balancing and connections. With yours being 'unbalanced', realize that the RPC idler won't be able to whump out a whole lotta generated-phase current at a vector suitable for starting torque... the result will be longer, slower start time, hence high start current and nuisance tripping. Guys that run unbalanced RPC setups typically do so with a 10:1 ratio (10hp of idler for 1hp of load)... and they run fine, but you're probably seeing the limit... Get run caps in there... get a half dozen 600V (or higher) motor run caps of a variety of sizes and hook 'em in per the usual way, and see what happens.

Thanks for the help

I greatly appreciate the input I have received and I have ordered an assortment of run capacitors. I am going to try to balance my phase converter but I am not quite sure how. Is there anyone that could post a drawing showing where the run capacitor should go? Does anyone know what size of wire I should be using to go from the phase converter to the load motor on my lathe?

Thankyou very much for all the help.