Induction Motor as Generator C-2C

[glort]

I have been playing with my Induction motor setup and learning some things.
I got the meter to spin backwards quite nicely after wiring it direct to the AC supply and was generating in both starr and delta configs with the caps set up in different arrangements.  I Did some vids of each setup I'll get round to posting on Youtube as well.

The motor I have is a 3 phase 5.5 HP, 4Kw unit. It is wired with 3 legs coming out of the machine.

I did a Vid of it the other day producing over 2.1KW when being driven by my little 165 2.2Kw Rated Diesel. Don't understand how that is possible but I measured it several ways and it seemed to be correct.

After I was playing with the thing, I noticed some C 2C wiring diagrams and realised I had the thing wired wrong.  I put the caps across 2 legs and took the power off the pair that had no cap.
Today I went out and rewired the setup by just moving 1 wire so the output was across the C1 pair. Instead of the expected improvement, I couldn't get he machine to come near holding the load. The open circuit voltage would be over 600 ( yes, I know, not good for 450V caps) but as soon as I dropped the stove element load, the excitation would crash. I tried it with 500W loads and it was OK but a lot more variance between no load and loaded voltage.

I then re wired it across the 2C legs and the same results.  When I tap the load across the legs with no cap, the engine holds the load no problems and the variance between the open circuit and loaded voltage is a lot less.

Is there something I'm Missing?
Every C2C diagram I can find shows the load tapped off the C1 legs. Tapping it off the legs with no cap works much better on my setup.


I also found this paper: http://journal.uniten.edu.my/ojs3/index.php/jee/article/download/263/99

Which mentions a C2-RR configuration that supposedly increases the efficiency of a C2C setup from 50% to 86%.  ( page 3-4 on the PDF)
I tried it without ballast ( as there is no indication what cap value or resistance to use)  and just using various light loads in addition to the main load but couldn't get any advantage out of it over just wiring a cap across each leg and using 3 individual phases. I used the Double cap value I use in the C2C setup which should have worked if anything was going to.

I have to admit I don't really understand the paper descriptions so I was wondering if anyone could put this into simple language for me?
They refer to 2 phase power which I take to be 2 phaseS as far as I'm aware there is no such thing as 2 phase. It's either single or 3 phase.
The way I read the paper, I should be able to get my 2Kw off one phase and another 40% of that off the other phase.  This doesn't seem to be the case so I'm wondering where I'm going wrong? I want to be able to get max power off a single output or at leas 2-2.4KW as our standard appliances are rated up to. Also makes load balancing a lot easier.

The caps I was using for the C2C were 50Uf and I connected 2 in series to get the 25UF on one side. I tried 50 and 100 but clearly that was far too much and the motor was creating significant drag even with no load at all.  Halving the caps worked perfectly.

One thing I noticed with the setup was again, the legs that had NO caps across them held the load a lot better than the one that did.
I was going to wire Both outputs across the 2 legs with no caps but in testing this arrangement I gave the engine too many revs and got the voltage too high trying to stabilise the start up load and Fried My killawatt meter. Bloody annoying and I lost interest after that.  Time for that new AC Current Clamp Meter. 

Can any of the boffins here shed any more light on how to practically set up this C2-RR config?

[Dualfuel]

Dear Glort,
Just caught your post. When I was doing the induction motor generator bit, I used three sets of caps for 3 phase. I found a very simple way of connecting everything...I had to because it is too complicated for me to think through...so if I had a motor that was wound in a delta, I would lay the caps out in a delta on a piece of plywood. Like an actual shape of a delta. I would draw a delta on the plywood and run the leads from the motor over to the picture and place them in the corresponding places, then I'd simply jumper over from the picture to the capacitors. Spin the motor while arcing one set of caps across a 12volt battery and off I'd go...taking power off the set up varies with what I needed, 110vac was half a leg, while 208vac was a whole leg.
I did the same thing for motors wired in a wye (Y)...they were more a pita because you have to fish out the center tap and break it up if you wanted 110vac.
I would find the sweet spot on the engine, then get pulleys to match 60 hertz on the motor, then I would series parallel caps until the voltage matched.
Then scrap went through the roof and I sold all my big three phase motors, and bought actual generators.

[LowGear]

I want single phase 240 volt power.  Are you paralleling the phases to get a single phase output?

Casey

[glort]

I sort of go on the mental picture of ABC for the terminals.  I don't have any problem working out the connections and in this case it's all pretty easy. One take off on AB with a cap and the other takeoff on BC so you have a shared point as the neutral. There really isn't much to stuff up.

I have played with wiring the motor in Delta and wye as our 2 phase is 414/440 and single is nominally 230 now but my home supply measures out generally around 245.
it's easy to tap off each leg with a common neutral ground but I'm more interested in having plenty of available amps off one line hence the C2C.

I found if I give my engine a good hard rev for a couple of secs the caps will tend to self energise without being flashed.  I usually idle the motor down with loads connected and then take a ground wier and put it across 2 terminals and then I can change connections without having to stop and restart the engine.
I take off the ground clamp, unplug the loads, bring the throttle up ( I have a set screw on it so I can put it back to optimum RPM) and then give the thing a blip for a couple of sec.  On the multimeter you can see the volts slowly come up then when they get to about 50 it's a couple of big jumps and it energised.
I have gone to flash the windings a few times when they had come up and that makes for an interesting electrical crack!    

IF I could get a big motor I could drive it with the diesel I Pulled out of my mercedes and I'd have plenty off each leg and I doubt an imbalanced load would make much difference if it were only a small load to what each leg was capable of.
That said, Like you hopefully I'll buy myself a good genny head this year.  I'm also hoping to get a 2 Cylinder Kubota engine from my brother in laws boat as he has an oversize gen head for the engine and has since scored a bigger engine. I think the motor he is replacing is about 18 HP so perfect for my generation purposes.

Amazing how they put more power in these boats than a lot of homes are wired for or would have as backup!

[glort]

I want single phase 240 volt power.  Are you paralleling the phases to get a single phase output?

Casey

I don't know if parallelling the phases is the correct term but in essence I guess that's what it is.
With C2C you are basically using the caps as electronic time delays to get all three legs off the motor into Sync.  They are 120o apart so if you tried just putting them together they would clash and short.

You can tap off each leg in Wye or delta for 1/3rd the motors output or with the C2C you can get the total output in one phase which is what I and you seem to want.
I'm getting a single output at the full amps, I'm just getting it with a wiring connection different to all the info I can find!