3 phase

True enough if your machine isn't too big. My Mazak M4 is going to "the Kid's" place. I can't run this 20 horse lathe in the three highest gears at my place using a 25 hp phase converter. I told the kid I'd make him a 50 horse unit. But, I doubt he'll be able to run his Matsuura bed mill at the same time with its 12 horse spindle.

he's also got a huge miller three phase wire feed welder that would like real three phase, not to mention future purchases.

Keep in mind we like to play with big toys

Karl

I bought my clients at Gossco, a very nice 480 vt, 8" bench grinder on a stand , with lights and the whole tamale, for $0.99 from Reliable tool, a few years ago. Baldor motor that was ONLY 480 volt, oddly enough.

The guy at the auction who bought it for $75..was a bit pissed off when I told him it was ONLY 480volt

Gunner

Interested in a minty+ Airco PhaseArc 350 3ph mig welder? 300 Amps out the torch. Spray transfer...not a problem

They were running it on 480 when I loaned it to them.

Make you a hell of a deal.

Gunner

Good deal. I once sold a 7" Baldor grinder, 440v only, for $150.

Gunner, what would happen if you tried to run it from 240v? I had a few 440v machines run from 220v, they seem to run, although I am sure they produce less power.

Karl sez: " True enough if your machine isn't too big."

It is true as long as it is capacitor balanced and the idler motor rated HP is more than that of the intended load motor(s) on the order of 2 X or so.

Bob Swinney

I'm pretty sure there's more to it when you start to exceed 200 amps during startup on a 200 amp service, but you're the expert here. I do know starting the mazak on real three phase isn't an issue and it totally dims the lights and kickout breakers on my system in the higher gears.

Karl

No idea, though Id suspect if it ran, it would run slow and with little power. And likely overheat the windings to the point of burning out before long.

Small wall mounted transformers however are cheap enough. In fact..I brought 4 home last weekend. 5 kva or so if I recall. 440-220 3ph and reverse.

Gunner

Not quite. The balance is a function of the load. Tune it for proper balance with one machine (load) and if you turn on a different one with a different horsepower, the balance will be off a bit, as will it be when you turn on a second machine while the first is running. (Each extra machine adds to the rotary transformer capability, but does not add to the tuning capacitance.)

Though I guess that you could tune for a no-load balance, and add tuning capacitors to each load machine's motor and keep things a bit closer.

Certainly under certain circumstances, you can lose seriously using a rotary converter. An example would be with the old Bridgeport Series-1 CNC mill with the BOSS-3 through BOSS-5 controllers and stepper motors. The stepper motor voltages are controlled by a saturable reactor to tune for either slow step and stationary (lower voltage and current) or fast step (higher voltage to overcome the switching inductance of the motor windings). Each axis presents a load on only one phase, so the balance shifts with X-axis, Y-axis and Z-axis moves -- with load on one often causing the other two to be higher. The problem is that the motor windings are stepped with power transistors which just barely had enough maximum voltage rating, and an unbalanced rotary converter can start popping transistors -- ones which are now hard to find and thus expensive.

And this is neglecting what imbalance might be introduced by other loads connected to the same rotary converter.

Enjoy, DoN.

Filament transformers? ;-)

A plasma cutter.

As a side note..Ive got a 25 hp Hitachi VFD I brought home last week from So Cal, if anyone is interested. Probably late 80s/early 90s, but appears to be unused.

Gunner

Gunner

karl

I've used tubes with dual, 1.5 VAC, 1000A filaments. The two filaments had to be balanced to less than 1/100 volt difference to prevent hum in the audio & video outputs.

GACK!!!!!

Good lord...one could cook a 5 course meal over those.

Metal or glass shell?

Gunner

gunnerasch at hotmail dot com

Whats it worth to you?

I have all the manuals etc etc

It appears to be a Toshiba Tosvert G2

Im going to LA in a couple hours for the day..but Ill try to check it out before boxing it up and shipping it. Damned thing is heavy...

Looks like this one

So its a Toshiba rather than a Hitachti

Still interested?

Gunner

Don sez:

Not quite. The balance is a function of the load. Tune it for proper balance with one machine (load) and if you turn on a different one with a different horsepower, the balance will be off a bit, as will it be when you turn on a second machine while the first is running. (Each extra machine adds to the rotary transformer capability, but does not add to the tuning capacitance.)

Well, it depends on how sensitive to additional "load" your RPC is. Tuning, (actually power factor correction) in a well designed RPC is quite broad and is proportional to the ratio of load to idler motor HP. In a good RPC voltage regulation over minor load variations is no problem. Don's implication is correct; balance is a function of load. Good RPCs are designed to operate with a fairly constant load to idler ratio. That is reason is it good practice to have a 1.5 to 2, or greater, ratio.

A RPC is a strange animal, indeed. Think about it. The load(s) and idler are connected in parallel but in order to feed a 3-phase load from a single-phase source the currents do not flow in parallel ! Balancing caps provide series resonant tuning from each side of the single-phase line to the manufactured phase. Current flow is quite complex and defies simple math reasoning. It can be shown that currents try to flow in opposite directions at the same time. The math system of "symmetrical compoinents" is required to sort it all out.

Bob Swinney

(actually power factor

ratio of load to idler

problem. Don's

to operate with a

have a 1.5 to 2, or

My own converter gives decent voltages (close to one another) both with and without load. I did test it.

Iggy sez:

"My own converter gives decent voltages (close to one another) both with and without load. I did test it"

"Decent" is not a very definitive expression, so readers will have a hard time qualifying their voltages. Also, you failed to mention if your RPC had correction caps or not. Per my statement that: RPC idlers and loads are connected in parallel but their currents do not flow in parallel (by the classic definition anyway). It follows that if the idler to load ratio is great enough you don't really need to worry about PF correction caps. This in keeping with the well known characteristic of a very low impedance swamping any regulation effects in a parallel connected load.

(actually power

ratio of load to

problem. Don's

to operate with a

have a 1.5 to 2, or