Author Topic: Difference between 3 phase STC and Stamford heads???  (Read 11926 times)

apogee_man

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Difference between 3 phase STC and Stamford heads???
« on: August 12, 2009, 07:43:59 PM »
I've been looking at both of these heads.

If both are 12 wire designs, what's the difference between them?  Is it only that one design uses brushes and the other doesn't?

I've been toying with what Bob presented (splitting the stator and using it to charge batteries). 

Seems like it's a doable idea that might just work extremely well...

To that end, what's the difference between these generator designs and will either work fine?

Lastly, can a 3 phase head also be wired to operate in single phase instead?  Is it just as efficient as a dedicated single phase head or "will it work" but less efficently because it's "converted"?

Finally, is there any difference in efficency between the STC design and the Stamford designs?

(Also, I'm assuming that the ST is single phase, and the STC is 3 phase.  If my assumptions are incorrect, please let me know...)

Any info would be much appreciated!  I've been searching the web but haven't been able to find answers to these questions...

Thanks,

Steve
« Last Edit: August 12, 2009, 08:02:54 PM by apogee_man »

Doug

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Re: Difference between 3 phase STC and Stamford heads???
« Reply #1 on: August 13, 2009, 03:03:55 AM »
Some 3 pahse heads can be econnected for single phase.

I have no idea how the Chinese wound the STC
It's a Good Life, If You Don't Weaken

adhall

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Re: Difference between 3 phase STC and Stamford heads???
« Reply #2 on: August 13, 2009, 04:07:20 AM »
For what it's worth, a number of years ago I used a 12-wire Stamford head to make a frequency convertor (60Hz to 50Hz). I know that one could be connected for single phase output--it used a zig-zag winding configuration. I don't remember if this configuration gave full rated output power--somehow I doubt that it did. And I don't know if this is generally true of all 12-wire heads.

Looks like I don't know more than I do. That happens as you get older...

Best regards,
Andy Hall
JKSon 6/1, 5 kW ST Head, 1992 Dodge RAM Cummins 5.9L Turbodiesel, 2001 VW TDI 1.9L Turbodiesel, 2006 Jeep CRD Turbodiesel, Yanmar FX22D Diesel Tractor

Doug

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Re: Difference between 3 phase STC and Stamford heads???
« Reply #3 on: August 13, 2009, 04:13:57 AM »
I beleive its full output Andy. I'd need to look at the connction diagram is been a few years.
It's a Good Life, If You Don't Weaken

adhall

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Re: Difference between 3 phase STC and Stamford heads???
« Reply #4 on: August 13, 2009, 04:51:59 AM »
Doug,

I'm thinking that the output power is only 2/3 the full rated output. Here's why:
Basically you have one leg with two windings in parallel (low voltage connection) and the other six windings make up the zig-zag configuration in a weird looking series/parallel circuit. The zig-zag connection produces that phase shift the results in the two legs being 180 degrees out of phase so that you have "normal" North American 120 / 240 VAC three wire power. That being the case, you have two 120 VAC legs at the rated output current instead of three 120 VAC legs at rated output current as you would have with a 120 / 208 3-phase connection.

Best regards,
Andy Hall
JKSon 6/1, 5 kW ST Head, 1992 Dodge RAM Cummins 5.9L Turbodiesel, 2001 VW TDI 1.9L Turbodiesel, 2006 Jeep CRD Turbodiesel, Yanmar FX22D Diesel Tractor

mobile_bob

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Re: Difference between 3 phase STC and Stamford heads???
« Reply #5 on: August 13, 2009, 05:01:51 AM »
its my understanding that all 12wire "world" heads can be connected as single phase
but at reduced capacity,, i don't recall what the reduction is but i am thinking it is around 58% of the full 3phase rating

they have to be configured in star/wye connection so that you have a centerpoint for 120 siingle phase
and across two leads for 208vac

i am thinking that the stc are 230/400vac, so maybe you get 277volts when connected in star/wye across two leads

just not sure

as for efficiency

i would expect a well built brush type head should be a bit more efficient than a head built to the same standards but brushless
most brushless have double the airgaps to cross or have to induce current across an airgap to provide excitation current.
but that is an opinion, and there may very well be other designs where this is not the case.

the stc 3phase heads would make a superior alternator for battery charging in my opinion, getting in to split the poles is going to result
in a bunch of extra leads to keep track of, but it should make one hell of a nice charger for a 48volt system with low ripple and
a bunch of amps.

i have an stc12 and am planning on doing just such a conversion, now that i am cast in stone with 48volt exeltech mx series inverter system.

getting down now to zero'ing in on batteries, the last major investment to complete the sytem

figured i would save them till last because of shelf life issues, and the hope of better technologies, and lower prices
but looks like pricing isn't going to get any better and maybe even higher over time.

bob g

otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

Doug

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Re: Difference between 3 phase STC and Stamford heads???
« Reply #6 on: August 13, 2009, 09:57:12 PM »
Not sure now....

Been a very long time.

Its reconnected and not single phased so my gut feeling is its going to produce more than 58%....

Way back in the day I did an Internal scot T to a real old timer than ran it full voltage and power. Maybe I am am confusing the two.
It's a Good Life, If You Don't Weaken

jzeeff

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Re: Difference between 3 phase STC and Stamford heads???
« Reply #7 on: August 14, 2009, 01:52:18 AM »
I can't follow this without a wiring diagram, but it would seem that if you took every winding individually (none in series)  and rectified it separately, you would get the smoothest waveform and the lowest voltage.




trigzy

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Re: Difference between 3 phase STC and Stamford heads???
« Reply #8 on: August 15, 2009, 05:12:04 AM »
12 Wire heads are rated for 2/3s of rated power when in single phase mode.
The current and voltage remain the same at each winding, but because of the double-delta connection, or the zig-zag connection, you only get 2/3rds of the power.  (Of course the gen only takes 2/3s of the power to drive)  I never explored the idea of using that "wasted" capability for a heater load or other isolated system..... I just thought of that and will have to consider it in the morning when my brain is on.

IE  If it was rated for 120/208, 3PH, 100A (36kW)  The single phase rating would be 120/240 @ 100A (24kw)   

24/36=   2/3!!!

The supplier that I have been dealing with, the STCs were just a reworked ST head, and the geniune Stamford clones had a different designation like WTW etc.

Steve
Power Anand 24/2, Brushless 20kW, some other antique iron.
Vendor of AVR's, Small Clones of Yanmar Diesel and Honda Gasoline Engines

mobile_bob

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Re: Difference between 3 phase STC and Stamford heads???
« Reply #9 on: August 15, 2009, 05:32:27 AM »
did a bit more research,

typically the 2/3 rule applies, but

in a wye configuration where you are taking 208 you got only 57% or so

in wye and if you configure to take 120 off each and every leg to neutral you can get full capacity
but this will require a 3/phase panel.

delta, wye/star, and zigzag connected give you all sorts of ampacities and various voltages.

as a battery charger, where you split each pole set and rectify all and then parallel connect them for final output
you can get to near full capacity.

your still limited to the windings ampacity no matter what the voltage is, whether 120 or 48volts nominal

then there is the 1.414 thing when you rectify, so you get approx 84volts off each rectified pole, and to then drop
it to ~57.6 one will need to reduce either excitation current and/or rpm,,, and both have drawbacks in my opinion

reduce the already relatively small amount of excitation, one will need a purpose built regulator, and if you are going to
do that you may as well add the 3 stage control, temp sensor for battery temp compensation and and temp sensor
to cut back the field should the alternator get to hot.

also reduction in rpm leads to reduction in cooling fan airflow,

either way, perhaps an altered stc head for dc charging should be derated to 70-75% of nameplate kwatts?

a 12kva head would still be around 9kwatts as a battery charger, that is a huge amount of charge capability
about 156amps at 57.6vdc, hmmmm not bad?

sure would make short work of charging a battery bank, at least one sized to take that amount of current
seems appropriate for a 600-800amp/hour 48volt bank.

would be nice to see someone tackle this project even if not as large an stc head to start with?

bob g
otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

jzeeff

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Re: Difference between 3 phase STC and Stamford heads???
« Reply #10 on: August 15, 2009, 02:03:28 PM »

Could one use a higher DC voltage to charge two strings of batteries in series - say 8 batteries in series for 96V and then have two inverters - each one using 1/2 of the string (48V to each stackable inverter)?     This doesn't require so much reduction in voltage - say 75V RMS,  105V peak, not too far from the design voltage of 120V RMS.






europachris

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Re: Difference between 3 phase STC and Stamford heads???
« Reply #11 on: August 15, 2009, 03:32:26 PM »

i have an stc12 and am planning on doing just such a conversion, now that i am cast in stone with 48volt exeltech mx series inverter system.

getting down now to zero'ing in on batteries, the last major investment to complete the sytem

figured i would save them till last because of shelf life issues, and the hope of better technologies, and lower prices
but looks like pricing isn't going to get any better and maybe even higher over time.

bob g

I find the more I fiddle with DC to AC conversion, the more I want to set up some sort of off-grid power just to reduce dependence on The Man.  I think 48V is the way to go, and I would look into VRLA forklift batteries for my storage.  I build forklifts for a living, and industrial motive batteries are darn near indestructible if maintained properly.  Only problem is moving them around.... ::)

But our electric forklifts are all AC powered using two three-phase motors - one for traction, and one for hydraulics (steering and lift).  IIRC, the 'nominal' voltage from one phase to ground is around 10 to 12 volts at the motor, and currents can be up to 600 amps.  Nominal ratings are I believe 10 to 11kW output.  All of this is done in a single integrated motor controller that converts the DC to 3-phase AC as well as handling all of the other forklift specific functions and telling the meter panel what to display (speed, trouble codes, battery level, interlock functions, etc.) and the entire controller weighs about 45 lbs. and smaller than the average mini-tower PC.  Compared to the previous generations of DC trucks (even with chopper electronic controls), these newer trucks are amazingly simple and reliable.  But, I don't know that they are any more efficient....

Back on topic - I would call around to forklift distributors and see what is available for batteries.  Many times reconditioned batteries are available.  Rather than get a single 48V battery which can be had up to 1000Ah or so and weigh 4000#, a pair of 24V pallet jack batteries would work really well and 450Ah is a nice size.  You can get them with a nice steel lid and they will have lift hooks to move them around with an engine hoist or winch.  I'd do a bit of solar here, but wind would be our panacea, especially in the winter - here in N.Central IL, the wind NEVER seems to stop blowing.  Unfortunately, the homeowners assoc. where we live would likely frown upon a wind turbine, even though they are not called out in the CC&R specifically.  But I could easily generate all my power needs between a small solar array and a turbine.

Chris

jzeeff

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Re: Difference between 3 phase STC and Stamford heads???
« Reply #12 on: August 17, 2009, 01:48:40 AM »
From what I have read, DC is only slightly more dangerous than AC of the same voltage.

Doug

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Re: Difference between 3 phase STC and Stamford heads???
« Reply #13 on: August 17, 2009, 02:55:11 AM »
It all burns.
It all makes the same smell.
Its all makes your heart stop.......
It's a Good Life, If You Don't Weaken

oliver90owner

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Re: Difference between 3 phase STC and Stamford heads???
« Reply #14 on: August 17, 2009, 04:50:17 PM »
It all burns.
It all makes the same smell.
Its all makes your heart stop.......



But DC can make you hold on tight to it rather than throw you across the room?

Regards, RAB