Phase converter question.

[Larry Edgerton]

I have a 25 hp Rotophase converter in my shop and a new to me 20" bandsaw. The bandsaw is the smallest motor in my shop at 3 hp. Those of you that have a converter know how they growl a little at idle until the load is applied. My problem is that with the 3 hp motor the growling does not completely go away when the bandsaw is running. I assume that this is because the motor is too small for the converter but I am by no means an electrician.

So.......... my plan today is to wire in an additional old 5 hp 3 phase that I have around to run at the same time as the 3 hp and see if that quiets it down. I have a new 5 hp Baldor 3 ph that I could install in the saw, but I am not sure if it would be too large for the saw, so before I do that I am going to try the idler motor.

So.......... Those of you that know more than I, lets hear what you think. I plan on getting a Phase Perfect eventually for all the machines under ten HP, but it is not in the cards just yet.

Thanks, Larry

[David Kumm]

Can convert your DC to three phase as it will always be running with the saw? Have you checked the voltage balance of the saw? If that is within 5-10% I don't think the growling hurts the RPC, it's just the unbalanced voltage robs the saw of some power. Dave

PS. Watch CL and ebay for used PP. I've bought three that way for about half. Dave

[Larry Edgerton]

David

I am just picking up a used 7.5 hp cyclone/baghouse today and I thought of that as a solution, but it need to be at least repainted before I put it into service. I'm on my way to the shop now and will try the idler.

Once I get a few more things worked out in the new shop I am going to pay an expert to come out and help me make things right, but just not enough hours in the day for all the projects I have invented for myself. My own fault, a personality disorder that makes me have to be busy all the time.

I really want to be lazy.


Larry

[Rick Fisher]

Hey Larry

I have a 24" Bandsaw which came with a 3hp motor .. I swapped it out with a 5hp Baldor and can report that it was completely irrelevant to the saw..

I believe that most of the reason it didn't matter is that the saw never needed 5hp .. I have resawn 2x10 hardwood for 20 minutes and never heard the 5hp motor labor or even felt it get warm ..

My saw is an old Centauro .. new ones in the same size come with 5hp and/ or 7.5hp .. Back in the 80's they where 3hp .. I have seen 24" Laguna bandsaws with 10hp .. they come stock with 6hp ..

[Larry Edgerton]

Ok, today's trials......

I finished changing all the bolts on the bandsaw to allen heads, adjusted everthing, put on a new carbide blade and thought I would fire it up without the other motor idling and see how it cut. Had some 8" white oak in the shop I have to make into spindles with the saw so tried one. Saw cut straight and true, but about two feet into the oak it started running out of power, then it shut off. No reset, so I backed up and tried the planer on the same circuit. Nothing.

It blew a 50 amp fuse on one leg [3 ph] of the fused shutoff downstream of the converter. I put in a new fuse, tried the planer, worked just fine. Turned on the bandsaw and the same fuse blew, no load, in about 10 seconds. I had no more fuses so I drove thirty miles to the closest hardware, bought six fuses, and came home. Today was a wash other than I know the saw will cut well. I have no clue how to find the problem, I am electrically illiterate.

I may convert the saw to 5 hp single phase if I have the right motor around. I need to buy a book on industrial wiring as my new shop is out in the middle of nowhere. Is there an "Industrial wiring for Idiots"?

Larry

[Richard Coers]

Maybe the saw is wired for 460 and the phase convertor puts out 230? I think that is the numbers, maybe 480, but you know what I mean. Look at the motor plate and check the wiring.

[Scott T Smith]

Maybe the saw is wired for 460 and the phase convertor puts out 230? I think that is the numbers, maybe 480, but you know what I mean. Look at the motor plate and check the wiring.

What Richard said. Larry, in addition to my big generator I have a 30hp phase converter wired into my shop on a transfer switch. The system is setup so that choose between the phase converter or the generator for the 240 3-phase equipment (I have to use the generator for the 480 3-phase equip though).

I NEVER have an issue with running a low HP load off of the converter, and it does not "growl" from a low load - only an excessive load.

Checking the motor plate and the wiring is fairly simple to do. Also, check the circuit from the converter to the bandsaw; another potential problem is that the wiring may be crossed at the bandsaw with the generated phase going to ground somehow.

[David Kumm]

Have you measured the amp draw of the bandsaw? Since RPCs are only balanced at a point, usually towards the high amp end, a large rpc doesn't work very well with smaller motors. I run a 15 and a 10 together to cover the range. Sounds like the balance is out of whack and that is robbing the saw of power and causing your problems. Dave

[Larry Edgerton]

It is all wired for 240. I'm going to call in a pro tomorrow.

Thanks, Larry

[Larry Edgerton]

Faulty cable to the saw. New cable but had a section of ground making contact with the white wire. Replaced the whole thing, no problem. I would never have found that.

Thanks, Larry

[David Kumm]

Faulty cable to the saw. New cable but had a section of ground making contact with the white wire. Replaced the whole thing, no problem. I would never have found that.

Thanks, Larry

That would have been low on my list of things to check as well. Never had that happen. Did he check continuity between the wires and find it and did he say it was common? Dave

[Larry Edgerton]

I get leftovers[Free!] from a buddy that works commercial sites. It had damage from being crushed it appeared, but it had that good heavy rubber sheathing and did not show on the outside. Well, there was a slightly flattened out spot once we got looking real hard. Was not a manufacturing issue.

He put meters on both ends and it was drawing more at the shutoff than at the motor, so started looking at everything in between.