Maybe Ill use a 10 hp. Ive got that 1501 Clausing with the 7.5 hp motor. Its a bit slow to start on my 5hp Star International RPC (old bastard) and doesnt like starting in Low range.
I can get by a bit by firing up the OD grinder at the same time, which acts as a slave, but its still under powered.
Gunner
"In my humble opinion, the petty carping levied against Bush by the Democrats proves again, it is better to have your eye plucked out by an eagle than to be nibbled to death by ducks." - Norman Liebmann
Well nobody would be dumb enough to leave the darn thing on all night.
Ahem.
Trouble is, this converter is really really quiet. I simply cannot hear it running inside the little root celler it sits in. The rubber stoppers do a great job of vibration isolation, and I think it's a pretty high quality motor to start with.
I've got it powered off of a 15 amp breaker, through number
12 wire. The fuses in the knife switch are 10 amp, so it's on a pretty short leash. I've had momentary lapses of grey matter on occasion and threw the knife switch *before* spinning the idler up - and the result is that it grunts for about a second before one of the fuses pops.
Still a drop-out contactor is now on my list-O-stuff to do.
Until then I'll just be sure to turn the damn thing off before leaving the shop, religiously. Maybe a note on the cellar door, or a big red light in parallel with the drive.
This is news to me. Where did you read that? For a reasonably sized rotary converter (at least 50% larger than the driven motor) you can develop full hp on the driven motor.
Code smode. At work, I follow code to the letter, at home, I follow proper practices based on safety. Often times not to "code"
I picked up about a half case of semi rectangular caps, about 2" thick, by 5" wide by about 8" tall.
Only problem is..they are about 7fd. Not sure what they can be used for. But the price was right.."can you use those? Toss em on your truck"
Gunner
"In my humble opinion, the petty carping levied against Bush by the Democrats proves again, it is better to have your eye plucked out by an eagle than to be nibbled to death by ducks." - Norman Liebmann
Ill try just it. Ive got a nice 10hp in my motor pile. I assume that I have to spin it up to data plate rpm? Which is better, a 1725 or
3600 rpm motor? And what is a drop out contactor and how does it work?
Gunner
"In my humble opinion, the petty carping levied against Bush by the Democrats proves again, it is better to have your eye plucked out by an eagle than to be nibbled to death by ducks." - Norman Liebmann
What you need to do Jim is connect the power also to an electromagnetic lock on the door. That way, as long as the RPC has power the door cannot be opened. Keeps people out too. You know, can't stop in the middle of a cut so you can't shut off the power. Come back later when I'm finished. Mebbe get you out of a chore or two. Then again, mebbe not... ERS
Jim sez: "... or a big red light in parallel with the drive."
Better yet a 110V, 7-1/2W night lamp wired across the manufactured phase. Yeah, I said, 110V night lamp because they are cheap, so don't forget the 2k Ohm, 10W, series dropping resistor. Mine is glued to the inside bottom of the 3-phase start-switch box. The night light is contained in a nice socket on the wall along side the start box, so it comes on with the RPC.
Gunner sez: " Ill try just it. Ive got a nice 10hp in my motor pile. I assume that I have to spin it up to data plate rpm? Which is better, a 1725 or 3600 rpm motor?"
Immaterial, my good man! Pretty much, anyway. Some say the 1725 rpm machine is quieter. You don't have to spin it up to "name plate" speed -- just a good pull on the rope will do it, but have something set up so's you can switch on the power soon after spin up. In other words, don't walk across the pasture to the switch, or the spin will be all gone before you get there!
Anecdotal evidence suggests the slower motor is better. I've never seen anyone do this with a motor that runs slower than 1725 though. I would steer away from the 3600.
A drop-out contactor is simply a large three-pole relay that take the place of (or is in series with, for you belt-and-suspenders types) the knife switch.
The coil to pull that relay in is operated with a start/stop pushbutton ciricuit - best is if the coil is 240 volt, so one end of the coil goes to one incoming line, then it goes to a normally closed pushbutton, and then to one of the outgoing (load side) terminals of the relay, on the other phase.
The load is switched by two dedicated contacts, it's the third one that runs the coil itself. Then you put a normally closed pushbutton across that third contact set on the relay.
So the drill is, load is off, coil is off. When you push the 'start' button (normally open one) it engerizes the relay briefly, and the contacts suck in. At that point you can take your hand off the button because the third set of contacts are now closed, and provide juice to energize the coil.
Normally you turn the thing off by briefly interrupting current in the coil with the normally closed button.
But if there's a power dip, the relay drops out - and will not suck back in until you hit the start button again. All the newer hardinge stuff is wired this way - try it. Start up the spindle, and leave the levers on 'run' while you unplug or otherwise disconnect the machine. When you plug it back in, the machine will not start until you hit the go button the electrical box.
This is now an OSHA requirement for all moving machinery - the idea is that the spindle should not start unexpectedly after a power fail, if the machine is left on 'run.' I had to go and put contactors like that on all our shop equipment - grinder, drill press, etc.
Though, now that the drill press is VFD driven, they have a "no restart" feature built in.
And btw if you do implement this, be sure to *fuse* the contactor circuit appropriately. Most times the wiring is number 16 gage or so, and it should have a fuse rated for much less than the 20 amp branch circuit rating!
Where are you applying the clamp-on ammeter? If between the junction of the two motors' wires and the static converter, there
*should* be no current once the motors are started.
However, if you clamp around one or the other of the motors, you should see some current at least. (Mostly the amount would be based on the horsepower and the loading of the smaller motor.) Perhaps if both motors are equally lightly loaded, they are each generating about the same voltage for the third phase, and as a result, are generating very little current between them. Put a serious load on one motor or the other and see whether there is a visible upswing in the current.
If you take the time to tune the 20 HP converter for better balance, and once that is done, you start adding capacitance across the
240 feed from the wall, you will eventually reach a point at which the current is at a minimum, where more capacitance will increase the current again.
Note that the extra current will not cost you anything (other than nuisance trips on the circuit breaker) -- *if* you are on a residential feed. If you were on a commercial feed, they could (and probably would) charge you based on the reactive current. But if you were on a commercial feed, you probably would also have three-phase power available and not need to make a rotary phase converter.
On Thu, 26 Aug 2004 12:27:16 -0500, "Robert Swinney" calmly ranted:
SEVEN FARAD, not microfarad, Bob. To test, don't you hook 'em up across a wall outlet then check with the leads on either side of your tongue? If it zaps, it's good? (Kids: don't try this at home.)
- Inside every older person is a younger person wondering WTF happened. ---
On 26 Aug 2004 09:22:39 -0700, jim rozen vaguely proposed a theory ......and in reply I say!:
remove ns from my header address to reply via email
D'OH. Now I have to find it again!
I do take your and Don's point that the big muvva idea and some tuning sound OK. It would appear that I was getting muxed ip with the static converter.
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"The static converter is basically only a start circuit that once the motor starts, disengages and lets the motor run on single phase power. The disadvantage of this method is that the motor winding currents will be very unbalanced and the motor will not be able to run above about two-thirds its rated horsepower. The rotary converter provides current in all 3 phases and although not perfect, will allow a motor to provide all or nearly all its rated horsepower. If the motor has a service factor of 1.15 to 1.25 then you should be able to use full rated horsepower. The service factor can be found on the motor nameplate and is usually abbreviated S.F. "
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"Either a static converter or rotary phase converter can make it possible to run a three phase motor on single phase power. The Static Phase Converter does not actually generate three phase but only starts an electric motor and then allows the motor to operate on only two of the three windings in the motor. This being the case, the motor then is running at 2/3 of its rated Hp.
A Rotary Phase Converter does provide full rated three phase power to operate equipment without this loss of Hp. Rotary Converters are always the best way to go, if you size them correctly for the application."
Apart from that, I can remember discussions here about it.
***************************************************** I have decided that I should not be offended by anybody's behaviour but my own......the theory's good, anyway.
On 26 Aug 2004 00:17:46 -0400, snipped-for-privacy@d-and-d.com (DoN. Nichols) vaguely proposed a theory ......and in reply I say!:
remove ns from my header address to reply via email
I am probably thinking of the fact that the rotary part of the converter needs a driver that is at least 1.5 times the power of the driven gear, because of the trouble with the fact that it running as if started by a static...on two legs only.
***************************************************** I have decided that I should not be offended by anybody's behaviour but my own......the theory's good, anyway.
On 25 Aug 2004 13:18:31 -0700, jim rozen vaguely proposed a theory ......and in reply I say!:
remove ns from my header address to reply via email
I have to admit that
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's prices are quite surprising, if you use a free or very cheap 3PH motor that you supply.
As far as I can tell they design to suit your motor, and the price for a panel is it.
***************************************************** I have decided that I should not be offended by anybody's behaviour but my own......the theory's good, anyway.
I sort of suspected that. The thing is, most of the techies here (and that is not a derogatory term) love to do stuff the
*right* way, the best way. And they have the design princples down to an iota for rotary converters like that.
The deal is though, if you simply oversize the idler motor a lot, you don't need to do any tuning or power factor correction at all, if you are only running a couple of
1 hp or so machines in your shop.
In my case it's a five hp idler that runs small machines, and there's no tuning or fancyness involved.
Sure you can run the same machines on a two hp idler motor, but once again, the 5 or or so hp motors seem to be easier to come by for free, at least around here.
On Thu, 26 Aug 2004 19:13:59 -0500, "Robert Swinney" calmly ranted:
Grid? Oh, you must mean ex-Governor Davis's fine, triple-priced CA electrical grid. Gotcha. No, he'll just have to saw off some of the cap height so they measure up, er, down.
- Inside every older person is a younger person wondering WTF happened. ---
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