Motor question, Old Frequency Converter

I am helping out a friend that recently purchased a piece of old wood working equipment. I was told that the motors on this piece of equipment were connected to a Frequency Converted that provided speed selection. Well, I had envisioned an old VFD. Once I went to look at the system I found that the frequency converter was what appeared to be 2 motors coupled together shaft to shaft. Both motors are 3 Phase AC motors. One is 30 HP and the other is 15 HP. Both motors are wired to a set of contactors that switch between the two and then to another contactor that switches to a knife box labeled LOW OFF HIGH. An output from this box appears to feed four motors of various HPs on the machine. Has any one seen this kind of set up before? If so, how does it work? Any help would be grately appeciated.
Thanks,

Did you by any chance notice what the RPM for the 15 and 30 hp motors was?

An 1800 RPM motor will develop approximately 3 Lb-ft per HP there fore if the 15 HP motor on this machine is 1800 RPM then the 30 HP would be 3600 RPM to create the same torque. This would allow 2 speeds with equal torque.

I cant say I have seen that specific machine but I have seen things similar, they offer 2 speeds which the box stating LOW OFF HIGH kind of verifies.

This looks like a "poor man's" two speed motor set up, and I think Ron called it right. Instead of buying a single two speed motor with separate windings the guy just bought two motors, one two pole, one four pole, or some similar combination. The "controller" is probably a two speed motor starter.

Depends on what you're trying to accomplish, but nowadays I'd replace this with a standard motor and a constant torque rated VFD.

The two motors that are coupled together are not mechanically attached to the machine. The machine has four smaller motors that seem to get power from the two larger ones. It’s almost like one of the two larger motors is being used as a generator. Is that possible? I have a pic that shows the two motors but I can’t get it to attach. If any one is interested I could Email it.
Thank's

Rday, If I understand your post correctly, there are four motors on the machine that change speed plus this "two coupled motor" assembly with the high-off-low speed switch.

Please advise where the incoming AC power connects and where the power for the four motors on the machine comes from.

You might want to double check that the four motors on the machine are possibly DC motors. That would make the "two coupled motor" assembly actually an AC motor driving a DC generator and you would have a typical M-G set DC speed control. These were common in the 1950's and were able to acheive remarkable precision, even being used in paper sheet tensioning systems such as web printers, etc.

Let us know on the above questions. Thanks.

Just noticed your last post which appeared as I was posting mine. You almost surely have an M-G set sytem.

The incoming power runs the AC motor at constant speed which is shaft coupled to the DC generator. The output of the DC generator powers the four DC motors on the machine and speed control is acheived by varying the field strength of the DC generator. This caused variable DC output of the generator which caused the four motors to vary their speed.

Reliance Electric made many of these systems and still has a few spare parts for them. However, for the most part, they are obselete and your friend will want to give serious thought to buying a new DC or AC drive system.

Don't be tempted to use the old DC motors on any new DC system. They were designed for nice smooth DC and if operated on the SCR-pulsed DC output from modern DC drives, will overheat severely unless derated at least 30-40%.

He said they were AC but I should have asked...did they both say AC or were you looking at the fact both have 3 leads coming from them?

We have an abundance of Reliance VS drives some are MG (motor generator), if he didnt get some kind of cabinet with it then you may not get them to work. Some of the old MG sets used tube technology while others used solid state BUT the fact is there is usually some kind of cabinet with the controls etc in it.

We recently hired a contractor to move 2 presses (paper) and they disconnected the motor leads without marking them, they assumed (because of 3 wires) that they were 3 phase.

DickDV,

I have the specs for the two big motors and I think that both are AC. Can one of the AC motors be used as a Gen? The four smaller motors on the machine are all AC motors, one is a 7.5 HP, one is a 5 HP, and the other two are 3 HP. I will list the specs for the two big motors for you.

The larger of the 2:
STAR KIMBLE
HP:25 Kw RPM:1200 Frame:444 Volts:220/440 AMPS:76/38
SEC VOLTS:367 SEC AMPS:45 POLES:4 REG:15 PHASE:3 CYC:60
PF:100 Service factor:1567
LEHMAN ELECTRIC COMPANY Chicago, ILL.

The smaller one.
HP:15 RPM:1140 Volts:220/440 AMPS:41.6/20.8
Frame:324U2 Type:L Form:B0W PHASE:3 CYC:60
Service factor:1.15 INS Class:B Code:G
AJAX Motor Company.

I don't have a wiring diagram of the motors to the switch gear I will try to get one tonight if possilbe. From the machine to the two large motors ther appears to be only three wires. These connect I assume to the four smaller ones. I am not sure though.

Any help is apperciated.
Thank's

This sounds like some sort of phase converter set up, although some of the details dont quite add up.

Well, Rday! You've got a really odd bird there! From the nameplate data I can see that the 25hp motor is a wound rotor motor which will give you variable speed thru the addition or subtraction of resistance in the secondary circuit.

If that is true, then the 15hp section must be an AC generator or alternator which, when rotated at variable speeds would produce a variable frequency output which would vary the speed of the AC motors on the machine. Trouble is, I don't see anything on the 15hp nameplate that indicates its an alternator.

I must say I've never seen anything quite like what you're describing. And I've been around for eons, it sometimes seems!

Maybe someone else has run it one of these before.

I will try and get a connection diagram and post it here. Maybe once we have the complete circuit to look at we can figure it out. :nodi: Or become even more confused.
Either way thank's to all.

this is just a long shot but i used to work in the wood working industry and im probably not telling u anything new, at a guess it sounds if this set up is either a two speed motor setup or a frequency changer set up, frequency changers tended to be used a lot with woodworking motors becouse u can obtain high speeds from a small motor and still have enough tauqe to do the job. (1 motor is used as a motor and the other as a generator it all depends on how its wired)
andy

It is very common to have woodworking equipment, especially "forming bits", operate at frequencies up to 400hz.

Synchronous-induction transformer sets were a common method of frequency conversion. This device consisted of "...a synchronous alternator on the lower frequency end and a slip-ring induction motor on the other, having the proper number of poles and run at such a speed that the slip frequency is the lower frequency of the set."

just an idea i had
you mentioned that the control was a selector LOW/OFF/HIGH is this possibly a manual star delta starter?
LOW being star and HIGH being delta?
andy

I have come across wooworking equipment with manual star/delta starters similar to what you mention. Could be what it is.