RPC questions

I hate to disillusion you, but what you have there is not a rotary converter, but a cobbleded up static converter. It will still work, just won't stay balanced under varying loads. The running caps are the big can type metal cans, 6-8" tall rated for your PEAK voltage, not rms. You should have a bank of them with clip-on jumpers to adjust the phase angle to get optimum balanced current & voltage. The inductor in a static converter normally has taps to vary the inductance too. Your pony motor is a fixed inductance. Bugs

Start capacitors are typically electrolytic and housed in plastic covered cases. They give a lot of mfds per volume, but are only momentary rated. They blow up if run continously.

Oil filled ones are used for run capacitors and are often found in steel cans. Though as an electronics tech I can say that one can find electrolytics with that form as well. I only mention this as if you scrounge you might well come across some like that. Folks who source from motor repair shops can pretty much depend on the electrolytics being in insulated housings.

Often the oil-filled ones will say this, stamped on the side.

The 17 mfd 600 volt ones might be usefull during the tuning phase.

If based on the hanrahan site you will need about 150 then I would dither that value in units of maybe 1/4 of 150, or so. Something like 40 or 50 mfds per change.

Typically the voltages are listed as:

L1-L2

L2-L3

L3-L1

You had just L1, L2, L3 listed. But if you spec them by pairs (because that's how you are measuring, one hot leg to another) then it makes it clearer.

Peter Haas has a good diagram here:

But notice that he calls the incoming line L1 and L2, the generated leg (which I think you are calling the wild leg) he calls L3. I *think* that is the convention in general, don't be confused by it.

So the balancing capacitors are C(1 to 3) and C(2 to 3). Power factor correction is by C(1 to 2).

I take the belt off my pony motor once the thing's running.

Jim

Gunner's phase converter includes a 10 hp idler motor with pony motor to spin it up. In what sense is that static?

Hmm. Lemme think.....

None.

Jim

Jim, can you help me clarify a power factor correction question? Assuming wild leg == L3, I have caps on L1-L3 and L2-L3. That greatly cuts down on vibration and humming noise. Just awesome. What I am wondering about is whether I would cut down on stray currents (power factor) if I added some capacitance on L1-L2. Which I could do, although I am space limited.

That would be power factor correction if you did that.

You need to obtain and read the information provided in the jim hanrahan paper, and also what fitch williams has written on the subject.

Because I've not ever done this I think you should hear about it from the experts.

Jim

Really? Odd. All those links and all the discussions here have lead me to believe its a RPC.

Good to know. My commercial and plainly marked Rotary Converter, seems to be miss marked, and doesnt have any taps.

I wonder if I should sue the maker?

Gunner

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

There are tons in the North corner inside the main store building - remember, San Fernando Road runs on a diagonal. (Stupid surveyors always taking the easy way out...)

Go in the front door, and hang to the left along the SF Road wall, all the way to the wall (before the "Back Room" door) - that corner. With the Variacs and Sola Ferroresonant transformers. There's also a center aisle that has smaller values boxed up.

Now telling the oil filleds from the regular electrolytics will be a bit of a challenge, unless you have some old reference catalogs handy that tell you what series numbers you want.

And you might find some PCB oil-filled models in the pile, you don't want those. I forget the year they officially eliminated PCBs, but it was a few years between that and when they started marking the cases "No PCB's" leaving a grey area where they were clean but not marked. Then you get into translating date codes...

For the usual small values I just go over to Johnstone or Grainger. The new ones are cheap enough, you know they're run caps because they're marketed as such, and you know they'll last at least a few years.

Apex is better for the really odd stuff they simply don't make anymore, or that would be radically expensive if bought new.

I've had Apex quote a price on a few used parts that approached the current new price of an in production item like a solenoid valve, and had to pass - if I pay full price, I want a warranty too.

-->--

SNIP

Hey Gunner,

A year ago now, but walk in and bear right, to the end of the big rack along your left. Turn left (you should be able to see the door to the "back-yard" directly ahead) and on the end faces of the second or third rack, they were about knee to waist high. Oil filled for "run" caps. They have some others too, but I forget where, and you want oil-filled for running anyway, not electrolytics.

Take care.

Brian Lawson, Bothwell, Ontario.

Thanks Bruce and Brian.

Gunner

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

You need oil filled capacitors. They should be labeled NO PCBs. A new 100 uF run cap costs $11 on ebay, see item 7572846399. It is not that much, although you may possibly need a few. My 10 HP motor is very nice because it starts on just 184 uF between kegs 1-3.

By the way, I tried a capacitor between legs 1-2 (for power factor correction and reduction of idle amps). It worked great and reduced idle current from 15-17a to just 7 A. I am very happy.

Thanks. I tried adding a (I think) 110 uF capacitor between legs 1-2.

That did WONDERS for the idle current (corrected power factor). It went down from about 15-17 amps to about 7 amps. Adding more capacitance did not help, so I think that 7 amps single phase is close to the real draw of these two motors at idle.

I also did more things like added 1 and 3 phase receptacles on the RPC, etc, and tested my RPC with my CyberTig, at full power. The difference between this one and what I had before is enormous.

1. There is no more screeching noise and vibration of the RPC at full load. It hums almost as quietly under full load as it does under no load.
2. There is no more huge voltage drop: L1-L3 and L2-L3 is about

Under full load, the amp draw of the RPC is about 85 amps from the wall.

This makes me wonder if simply shorting my welder at say 100-150 amps would make it into a garage heater.

Although oilfilled capacitors are entirely suitable as run capacitors they're mostly a historic overhang from the days when paper dielectric and foil electrodes was the norm. The reason for the oil filling was to impregnated minute residual voids in the dielectric. In DC operation these are pretty innocuous but,under AC stress, ionisation in unfilled voids eventually leads to failure.

With modern capacitors, AC rated plastic film types are both cheaper and smaller. These use metalised polyester or polypropylene film. Because they are void free, oil filling is unnecessary. A useful source is power factor correction capacitors for industrial fluorescent fittings. These are typically housed in oval or cylindrical aluminium containers with tag connections. An alternative construction is housed in a white or grey plastic cylindrical plastic container usually with flexible flying leads rather than tags. 40 uF units are readily available and, since they're pretty small it's not difficult to parallel up to the value you need. They will feel surprisingly light because very little metal is used in the construction and will be marked with the VAC working voltage.

Intermittent rated AC rated start capacitors are pretty well always mounted in black cylindrical containers usually with tag connections. Slightly heavier for their size than plastic film and about three times as many uF per unit volume. Best bought new from a motor supplier.

Jim