Converters

[WXYZCIENCE]

This is a picture of a 2kw converter that I built from an old McCulloh generator and a  GE 36volt dc motor.

The converter produces 240volts and is used to power my 1/2hp deep well pump. The pump draws around 7 amps at 240volts. This next picture is the motor driver computer, that was built by my brother. This computer senses the pump switch and regulates the voltage  and frequency of the converter.

The computer also monitors the 36volt battery bank. Converters require time to achieve start voltage.

The bank consists of 6 x 6volt flooded golf-cart type batteries. They are stored in a insulated box.  

The batteries are vented to the outside.

The box is purged by a fan when they are being charged. The converter's output is pure sine wave and has the kick needed to starts the induction motor in the deep well. The unit draws 1900 watts dc to drive the pump. I have figured the losses to be around 300 watts  but the pump only runs for 3 minutes to fill the pressure tank.

[behoof]

WXYZCIENCE

Nice job. Kudos to your brother also. Fortunatly for me my pump is 110v but regardless that's really nice setup you created. Thanks for sharing..

behoof

[WXYZCIENCE]

There are two coils in the alternator if I parallel them then the converter is 120v at 14 amp. I tested it on my 120v septic pump. We are adding a 120/240 switch to the unit we will be able to also start our air compressor. Joe.

[Nando]

WXYZCIENCE:

Please explain your first photo : 2kwConverter.jpg specially the external winding that the generator has at one end.

Thanks

Nando

[WXYZCIENCE]

Nando, Joe here, the coils on the left hand side are the original generator coils. The unit is a permanent magnet dual rotor design. I believe there are 4 magnets on each side. Can't actually see them. But I used another small magnet to test the flux. Will post another picture of a spare coil.

[oztules]

Nice system....but I'm at a complete loss as to how the voltage and frequency are varied, and what the exposed coil/s does/do on the left hand side.

I can't see how any magnetic flux effects them, or are they used in the voltage regulation .or ...nope, I just don't get it.

how does it work Joe??

......oztules

[WXYZCIENCE]

The computer measures the output AC voltage via a one bit A/D. The computer then controls the speed of the 36 volt dc motor by switching. The regulation can be held to within one cycle. We use a frequency tachometer to calibrate the output to 60 hz. The weight of the rotor and motor combined makes the output very stable. The computer also monitors the pump pressure switch, the battery bank level and alternator safety lockout relay. Step by step operation: 1. Pressure switch closes. 2. Computer wakes and does system check. 3. Computer turns on low current start contact. 4. Preset time to allow spin up approximately 1 sec. 5. Main power contact engages.6. Alternator safety lockout energized. 7. Ac voltage is at the measured.8 2nd Pump relay is energized. 9.The pump pressure switch opens. 10. Computer shuts down and goes back to sleep.  

[WXYZCIENCE]

There are 195 wraps of .056 guage wire on each coil. Here is a picture of the spare coil.

[oztules]

Thanks for that Joe.

Just to get this completly straight,... the pwm sets the rpm/input voltage of the 36v dc motor (sets 60hz +_1hz). By doing this, the voltage is roughly set to 240v. thereby mimicking the speed govenor of a petrol motor. (using inherant inertia to stabilise speed as well)

The coil design is unique to me, the flux cuts only the inner arms in this case?

Interesting gennie. Well done.

............oztules

[Flux]

The Mc Culloch generator is a strange beast. I have met a Homelite which I think is the same thing. It is the only commercial version of a dual rotor air gap generator that I have met. It used magnet steels ( alcomax or derivites) for the field.

As with all air gap designs the leakage reactance is low and regulation is good enough if the engine governors are good enough so they saved the complication of an AVR or compounding circuit and this must have offset the large cost of copper and expensive magnet steel.

For anyone who has never met the beast I can see why the picture is totally confusing.

Flux

[WXYZCIENCE]

For those interested the unit was calibrated by a frequency tach that I acquired a few years back. Here is a picture of the unit.  

I wanted to see how the meter lines up to the grid. As you can see, very close. Joe

[redeyecow]

   Great to see an old Mc Culloch genny being brought back to a useful purpose. Here's a picture of the one I have. It's got aluminum ribbon wire. Used to work great till the shaft to the engine broke. I think it's got 2 mags 180 degrees apart. It used to run about 3600 rpm for 60 cycles.

    I have a few 36V dc motors as I still run an old Delco for power. Running the Mc Culloch for a  pure sine wave would be worth the power loss for noiseless guitar amps etc. keith

[oztules]

Well don't that beat all.

If Danb reads this....Are there any other reasons that come to mind as to the demise of the diesel alternator you built using Cu ribbon.  If eddy currents in the Cu ribbon were to be the evil in the stator, it's odd that Al ribbon works ok at 3600rpm...now I am perplexed......eddy who??

....oztules

[WXYZCIENCE]

That is the exact rotor and many of the units came with aluminum ribbon wire. Also aluminum .060" wire. Can you count the number of wraps?. Do you have both of the coils? They worked good but he copper works better. Copper is heaver although. The weakness of the motor shaft was the models major fault. The rotor accepts a tapered shaft and with a little work you can machine a running motor to mate properly. I used the broken off shaft to gauge the taper. True center and balance is very important on these units because of the high rpms. I also played with the idea of rewinding 4 coils in this way reducing the rpms. I mounted the motor on rubber mounts. This helped in the balance and vibration. Also the coil you have is 120v. I just series two of them to get 240v. I see you cat is also involved. Joe.

[WXYZCIENCE]

Aluminum wire has one draw back "Heat". It does not like heat. It gets stronger the colder it gets. As the current increases the heat rises. This property is known as thermal runaway. Generators like this one have wonderful cooling, the air gap between the stator and rotor keeps the coils running cooler. Eddy currents are present in all wire that is cut by magnetic flux. Laminated plates, powdered ferrites, air cores are all used to reduce these unwanted currents. Generators that run under heavy loads suffer because heat build up due to eddy current heating. Especially if the cooling fins are blocked in anyway or the outside temperature is high.    Joe.

[Flux]

It's not aluminium that makes the difference, it's the fact that it is ribbon.

DanB used a rectangular section. Ribbon works if the flux is exactly along the thin direction. Willib has mentioned this in one of his latest posts. If the flux is not exactly along the thin edge then losses start to occur.

Dan's rectangular section I thought was thin enough to have got away with it but obviously not and any error in the flux direction will be much worse if the wire has significant thickness. as the projected area is much larger.

It may be a significant factor that the McCulloch was 2 pole. Frequency is lower and the coil is under a uniform field for much longer. The field at the edges of the magnet is always peculiar and with a large number of poles you are in this distorted field more often.

I think that if you use true foil that is wide and very thin and you are careful it will be ok. I did intend to try this but was put off by Dan's experience and also the difficulty of winding foil with interleaving insulation without having it excessively wide or risking shorts at the edges. The old Ford model T alternator had tape coils and they are not easy to hand wind, presumably they used a machine to feed the copper tape and insulating strip together.

Flux

[redeyecow]

  I only used one coil for 120v. The second coil was unravelling when I got the gen. as a give-away. Still use the Briggs on my garden cultivator as it is one of their good ones with good crank bearings. Here are  the specs that I measure:

        aluminum tape thickness  .008"

        tape width  .4"

        total coil thickness  1.73" at the narrowest point

        double rotor wt.   40 pounds with a bit of broken shaft

        each disk  1 1/2" thick

        diameter  9 1/2"

        air gap  1/2"

        windings approx.  150 ,   insulated with dark varnish

 The aluminum casing is .065" thick and covers the inner surface of the gap.  Eddy currents?

     Is there a way to make a 1725 rpm, 12amp,  32v dc motor run at 3600rpm without belting it?  This is the biggest I have at 1/3 hp. Maybe a bit light to run the McCulloch as a convertor although I mainly need the pure sine wave for sound equipment, not a lot of power. keith

[WXYZCIENCE]

Can you post a pic of the motor. My motor is 36v at 63amp rated 4000 rpm max. The coils limit me from using the motors full power. But it does allow me to get the unit up to speed fast and I can hold the regulation well. I cut back the power in what I call idle mode. Your amp probably only draws 200 watts. You will need to add 15%  more power because of the efficiency of the dc motor. Let say you have aprox. 85%, 230watts /32volt = 7.1 amps. dc. Joe