Startomatic speed change for 60Hz

[jimboz]

My startomatic is designed for 50 Hz and I'm thinking of cutting the generator v-belt diameter down to get 60 Hz (1800 RPM) at the generator shaft, I'd appeciate any comments/concerns.

Thanks,

[Combustor]

Hello Jimboz,
                 Your Start o matic alternator will have a harmonic regulation system which is quite sensitive to speed variation and increasing it from 1500 to 1800 rpm will send it way, way over voltage.  It is not uncommon to finetune output voltage by small adjustments to rpm where frequency is not critical. My CS 8/1 delivers about 250v at 52Hz  no load and about 220v at 50Hz full load. If I want to maintain 240v at full load I need to tweak the governor to hold 52Hz  at that load. So the voltage/frequency relationship is quite critical.  Unless someone here knows a way to modify the voltage regulation I think you are stuck with a 50 Hz machine. Just my thoughts,  Combustor.

[millman56]

Hi Combustor and Jimboz,     

I have the reverse of this problem with a Markon 4 KVA 110 Volt 60 HZ transformer regulated alternator, when series connected and run at 1500 rpm it will only make 200 or so volts despite trying the different tappings on the transformer to try and increase this.   
When I get a spare hour I`ll disconnect the rectifier and fit an AVR to see if this will provide enough excitation current to make 220/230 Volts.   
If my little scheme works then it would be a fair assumption that it would work the other way round on an SOM alt.

Mark.

[BruceM]

An AVR is the modern way to solve the regulation problem.   If your harmonic excitation is way too much at 1800 rpm, great, adjust it to the maximum, then you can use the harmonic as the excitation source for an AVR, instead of the mains.  The AVR can only limit whatever source is used. 

There is only one advantage of the old harmonic winding frig for regulation-  only the bridge diodes need be replaced in case of EMP.  A spare AVR, and bridge diode in a foil wrapped box will also solve that problem.  I just read the post EMP story "One Second After" by William Forstchen. Chilling.

[mike90045]

.... I just read the post EMP story "One Second After" by William Forstchen. Chilling. 

Link to online or hardcopy ?

[DirtbikePilot]

You could do what I'm doing with my parents' startomatic generator set. I'm using the existing generator for starting only and adding a ST generator to the system. I got some various sizes of pulleys to see what rpm I need to run it at to get at least 3000 watts at 6000 feet elevation. I'm using a double v-grooved pulley for the ST generator.

[BruceM]

http://www.amazon.com/One-Second-After-William-Forstchen/dp/0765356864/ref=sr_1_1?ie=UTF8&qid=1390070528&sr=8-1&keywords=One+second+after

[jimboz]

Looks like i've got some studying to do.  I thought speed controlled frequency and the field current regulated voltage and/or power factor.

[BruceM]

You've got it right, Jimboz, except for power factor

Since the field current is a function of the applied voltage, you can look at it as either current or voltage.  You can always just add more resistance to reduce the output voltage and current and keep the harmonic excitation, if you don't mind some voltage variation with load.

Power factor (PF) is a measure of the mismatch of voltage and current waveforms on the line load, and is only a factor in that if the power factor of the load is bad, the generator must have enough "head room" in it's design to provide the extra current.  Also, a very poor (0.5) PF load  such as those presented by some bad switching power supplies in battery chargers will tend to "chop off" the top of the AC waveform.  This is a problem for AVRs that don't do true RMS regulation, but it may also be a problem for other devices on the load which were expecting a sine wave with an appropriate peak voltage.  Newer designs with power factor correction spread the current load throughout the sine, boosting voltage when it's low, bucking it down when it's high, matching the current waveform to the (sine) voltage.

[Listerfever]

Hey Dirtbikepilot
Your set up sounds like one of the ideas that I have considered. I watch these 50hz to 60hz threads come to life and die quickly without ever seeing a plan that I feel comfortable trying with my 8/1 SOM. Can you give more details of your set up, maybe pics ? I was considering adding a pulley next to the flywheel with belts going the opposite direction to a marathon gen. I also plan on using the DC to charge batteries for off grid solar set up. Does anyone know the output amps of the DC ? Any input on this subject is appreciated.

[listeroil]

Jimboz

Heres a few pages of genuine 1967 Lister manuals. The show how Lister just changed the pulley to get the higher revs for 60 hz. It should be quite easy to get your generator to produce 230volts 60 hz.  There are 2 big fat adjustable resistors in your top box one is to adjust the AC voltage and will need setting down to 230volts when you increase the revs.  The other is for the battery charging and that will need setting down as well.  If you want 110 volts out of it you will need a 230 to 110 volt stepdown transformer.













Mick

[jimboz]

Thanks for replies.

I really like the idea of modifying the pulley diameter, I hope I can get my head around the regulation issue though.

With some heavy studying I think I'll be able to grasp the circuitry and tuning of the fields via resistors, etc.  Harmonics throw me for a loop though, when you gents use the word harmonics, what do you mean?  Can you provide a more laymen's understanding?

It might all be for naught if I can't find a place to rewind the gen though.

[BruceM]

When we refer to the "harmonic" we are talking about an extra set of windings on the stator which are used to provide the DC excitement of the rotor.  The harmonic windings are located on the stator such that increased current on the AC output windings cause an increased voltage on the harmonic winding. So a "harmonic" winding regulation system is thus a somewhat self regulating system.  An adjustable dropping resistor (2-8 ohm) is used after the harmonic winding to fine tune the output voltage.  The harmonic output is AC, typically very spiky, but it is rectified with a full bridge rectifier, and the large inductance of the rotor windings filters it out to a more average DC level.  

There is a huge step increase in the harmonic output when a surge load, like starting a motor, is applied.  While voltage regulation isn't as tight as I'd like (I prefer an AVR - electronic regulation), the harmonic system does work adequately for most situations and does a good job of starting motors and other surge loads.  

An AVR electronically monitors the AC output voltage and adjusts the excitement DC power going to the rotor in order to maintain the desired fixed voltage, regardless of load.  Some AVR's use the output AC to provide that small amount of DC, others will use either the line AC or the AC from a harmonic winding.  In the latter case, you'd bypass the dropping resistor to insure that the AVR had sufficient power input to meet the load demand.

Best Wishes,
Bruce

[needenginerunnin]

http://www.amazon.com/One-Second-After-William-Forstchen/dp/0765356864/ref=sr_1_1?ie=UTF8&qid=1390070528&sr=8-1&keywords=One+second+after

or

try you tube, full audio book sit back and enjoy I did

[listeroil]

The generators on SOMs are strange beasts and not like any other.

Their AC output comes out of the rotor and through the AC sliprings to output.

The field windings are part of the stator and intertwined with the DC start windings. The same starter windings also act as a DC generator when the engine is running and feed back through the big resistor(SFR) to the field windings. There is no AVR on a SOM generator head just the big adjustable resistor (SFR) in the top box. Which you use to adjust low power voltage to 230 volts and another smaller one auxiliary field resistance (Y) in the back of the generator near the brushes that you adjust at full power to 230 volts.
 
Mick