Author Topic: Experimental 48VDC Generator  (Read 14075 times)

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ChrisOlson

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Experimental 48VDC Generator
« on: October 18, 2014, 10:16:22 PM »
Not a lot of exciting off-grid stuff going on here as of late.  So I made a little video of my experimental 48VDC genset.

I've been trying to figure out what sort of head to use for a 48VDC genset, as I've wanted one for a long time.  Then the lightbulb came on over my head today - use a little Honda conventional generator and rectify it.  The AVR that Honda uses in their gensets will maintain 110VAC no-load output with the engine even at dead idle.  I tried it with a MidNite Classic 150 and it did not work because it puts out 165VDC.  It works beautiful with the 2:1 step-down transformers on our Bergey wind turbine, simply hooking the single phase output from the generator to the wye primary neutral of the transformers, and the hot to the primary on one transformer.  It steps the AC voltage down to 55-60VAC and then rectifies it to 77-84VDC open circuit before being "clamped" by battery voltage.

I was surprised how well it works - actually beyond anything I imagined:

http://youtu.be/DEXEtjjiu20

gww

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Re: Experimental 48VDC Generator
« Reply #1 on: October 18, 2014, 11:08:58 PM »
I haven't watched the vidio yet but am going to.  Oztules tried to explain how I might rectify my cheep 5000 watt generator to charge my bank but I am not up on circuits.  Hopefully a picture will be worth a thousand words.
Thanks fo doing it.
gww

ChrisOlson

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Re: Experimental 48VDC Generator
« Reply #2 on: October 18, 2014, 11:53:38 PM »
Many conventional generators will drop to 80 volts or so if you idle them down to 2,000 rpm.  If you can get the voltage down I think it would work with a MidNite Classic 150 in Hydro Mode.  The voltage has to be below 150VDC in order to get the Classic to come online.  If you can get it online, then you should be able to add throttle and bring it up to whatever speed you want and the Classic will keep it "clamped" below 150VDC.

When I tried it with just a block rectifier feeding the DC output to the Classic the DC voltage would only go down to 165 with this Honda and the Classic just said "Hyper VOC" on the screen.  It refused to come online.

These wound field generators with a AVR are a bit different than a permanent magnet generator.  Depending on how strong your exciter winding is in the gen head, and how aggressive the AVR is at increasing voltage to the field, you may not be able to get the voltage low enough for a Classic to work.  In that case you'd need a 2:1 step-down transformer like I used.  You could still use the Classic 150 on the secondary rectified output of the transformer if you wanted, but it didn't seem to need it here as I could get very close to the rated continuous power of the generator to the battery even slightly below 3600 rpm.

The nice thing about using a Classic 150 is that it would handle absorbing the battery for you at the correct voltage.  The setup I got to work was direct hooked so there is no voltage regulation at all once the battery reaches Absorb V.  In theory a guy could rig up some sort of voltage sensing servo to control the throttle on the generator so when the battery reaches Absorb V it would start to idle the generator down and reduce it's output.

gww

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Re: Experimental 48VDC Generator
« Reply #3 on: October 19, 2014, 12:01:16 AM »
I was thinking of unregulated to the battery cause I thought I might be able to use stuff I already have with out having to buy a battery charger. like maby if the power was out for a week and their was no sun.

I also though I might try to run a smaller old gen I had on wood gas.

We were talking about just rectifying the generator and letting the battery clamp it and maby adding caps with the correct rf value to clamp the volts.
Your thoughts?
gww

ChrisOlson

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Re: Experimental 48VDC Generator
« Reply #4 on: October 19, 2014, 12:15:16 AM »
We were talking about just rectifying the generator and letting the battery clamp it and maby adding caps with the correct rf value to clamp the volts.

I don't think it would work to try to clamp 165VDC open circuit down to 48V battery voltage.  Too much "clamp" and it would blow the breaker on the generator.  With the 2:1 transformer I was getting 84VDC at rated engine speed.  With the engine idling there seems to be very little load on it and it was putting out about 200-300 watts.  As I open the throttle the load on the engine increases very rapidly as the AVR is able to send more current to the field.  At wide open throttle, clamping from 84V open circuit to 56 or 57V at the battery was stressing it pretty hard because the throttle was right against the stop.  I'm sure it would've popped the breaker on the generator if I didn't back it down a bit.

Like I said, a wound field generator with an electronic AVR is a different animal than a permanent magnet generator.  The wound field unit is designed to maintain 120V output no matter what the load, as long as it has a strong enough current and voltage from the exciter winding to do it.  So "clamping" it too far results in overloading the stator winding on the generator, which will pop the breaker on it.

Frank S

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Re: Experimental 48VDC Generator
« Reply #5 on: October 19, 2014, 12:23:12 AM »
I'm not sure how the exciter winding's would be tapped into but I am wondering if a small veriac or possibly a simple pot could be placed inline to limit the exciting voltage probably right between the AVR and the exciter leads to limit the output voltage.
 Or maybe a 1 to 2 step up in the AVR input lead that way the AVR would think the generator was putting out 1 voltage while the actual voltage to the sockets would be something else which could then be rectified to DC.
 Probably not feasible but it was just a thought.
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Frank S

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Re: Experimental 48VDC Generator
« Reply #6 on: October 19, 2014, 12:27:49 AM »
I have 3 or 4 older Onan gensets that have manual voltage regulators some day I might try to get 1 of them running to try my theory
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ChrisOlson

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Re: Experimental 48VDC Generator
« Reply #7 on: October 19, 2014, 12:35:58 AM »
I'm not sure how the exciter winding's would be tapped into but I am wondering if a small veriac or possibly a simple pot could be placed inline to limit the exciting voltage probably right between the AVR and the exciter leads to limit the output voltage.

Well, there's a diode on the exciter that rectifies the exciter output to DC and then the AVR regulates the DC current to the field thru the brushes and slip rings.  With these electronic AVR generators the AVR and brush holder is all one unit.  And the diode in the exciter winding is integral with the winding and buried someplace inside it.  You'd have to somehow step up the AC output voltage that the AVR senses in order for it to cut the current to the field and reduce the AC output voltage of the main winding.

It's way simpler to just put a 2:1 stepdown transformer on the generator output than it is to mess with the AVR.

Frank S

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Re: Experimental 48VDC Generator
« Reply #8 on: October 19, 2014, 12:54:42 AM »

Well, there's a diode on the exciter that rectifies the exciter output to DC and then the AVR regulates the DC current to the field thru the brushes and slip rings.  With these electronic AVR generators the AVR and brush holder is all one unit.  And the diode in the exciter winding is integral with the winding and buried someplace inside it.  You'd have to somehow step up the AC output voltage that the AVR senses in order for it to cut the current to the field and reduce the AC output voltage of the main winding.

It's way simpler to just put a 2:1 stepdown transformer on the generator output than it is to mess with the AVR.
OH well like I said I am not familiar with the electrinic AVRs or how they are connected to the exciter circuit
old relays with hard wiring   are easier to coin a phrase muck around with
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ChrisOlson

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Re: Experimental 48VDC Generator
« Reply #9 on: October 19, 2014, 01:18:38 AM »
What I was looking for was something that's not finicky or hard to adjust, and is simple and "Just Works".  I was pleasantly surprised to find out all I have to do is plug in the cord, start the generator at idle, flip the breaker on and set the throttle to whatever power output I want.

That generator has a GX160 engine.  I know it runs 16 hours on a tank at 1,200 watt load because I've run it at that output many, many times on gen support.  It beats our Robin diesel for efficiency.   If I can run it at lower rpm and get a full 24 hours out of a tank of fuel, getting somewhere between 20-22 kWh from it, it will serve its purpose well.

gww

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Re: Experimental 48VDC Generator
« Reply #10 on: October 19, 2014, 09:22:19 AM »
Chris
Maby something like this.


Quote
chrisIts abit dangerus since its tied directly to the ac line. I can't post the diagram but I'll try to disrib it. It is very simple and It works very well.
One side of the ac line is conected to one terminal of the capacitor. The other terminal of the capacitor is conected to one of the "AC" terminals of the fullwave bridge. The other "AC" terminal of the fullwave bridge is conected to the other ac line. The dc outputs of the fullwave bridge are conected to the battery.
If you made this setup without the cap the bridge would expolde. The cap provides the pulseing.
For 12 volt charging 24UF delivers 1 amp of chargeing. Nice thing about these chargers is they don't care if the battery bank is 2 volts or 120. The battery bank voltage will vary the amperage.
The caps are motor run NOT start. Start caps will get very hot and self distructed.
I'm using 900 UF of caps. At charge start up I see about 15 amps of inrush tapering fast to 12 amps and after an HR or so levels of to 8 amps.
I'm using a group of missmached batteries. Some with pore SG are starting to get much better SG and catch up to the better batteries.
As far as safty conected directly to the AC line. A large enogh line isolation transformer can help this situation. Sofar I've had no ill effects with direct line conection.
I'll post upgrades as they happen.
                          JK TAS Jerry


Your thoughts
gww



ChrisOlson

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Re: Experimental 48VDC Generator
« Reply #11 on: October 19, 2014, 10:03:58 AM »
gww - I guess I don't know enough about what the capacitors do in that situation.  I'm not much on electronic circuits.  The way I looked at it is that an AC 120V generator is really no different than a wind turbine generator - or any other DC generator.  All generators produce AC current, including DC ones and the alternator in your car.  The DC ones just have a rectifier - either a mechanical rectifier in the form of brushes and commutator, or a solid state rectifier in the form of a diode bridge.  The only difference with the genset is that it is wound field instead of permanent magnet and you have to find a way to get the voltage down to more normal levels for a battery bank so it doesn't "clamp' it too far and overload the generator stator winding.

The little generator I used with a 2:1 stepdown transformer normally puts out 20 amps.  The 2:1 stepdown transformer reduces the voltage by half and doubles the amps so I get 60VAC and 40A from it.  That just happened to work perfectly on a 48V battery bank.  The rectifier, I suspect, makes the sine wave look more square instead of a normal sine wave, so the DC ripple seems to be pretty minimal.  If I reduce the throttle setting the exciter has less power available, it reduces the field flux in the gen head, and the voltage can "sag" more in the winding which reduces the power output of the generator.

I'm not exactly sure how the capacitors in  your example could reduce the voltage enough to prevent the generator winding from overloading.  And, in fact, I think I can get this work with a Classic 150 controller, without using the transformer, by plugging in some sort of resistive load to the generator with it idling to get the voltage to "sag" so the Classic will come online.  Then use Hydro Mode in the Classic with the Vmp set at 140V max, 120V min.  Once the Classic comes online in Hydro Mode it SHOULD keep it clamped below 140VDC and I should get better performance from it.

I think the key is a way to reduce the voltage and have a way to track the generator's power curve, and a Classic 150 should work perfectly for that.  The only problem I had yesterday was the fact that I had 165VDC with the engine idling so the Classic wouldn't "kick in" as it was stuck in HyperVOC.  Once I get it to "kick in" I'm pretty sure it will work and then the generator can run at its normal voltage with very little "clamp" and let the Classic do it's thing on the DC->DC conversion from 140V to 48-62VDC.  If the Classic unloads the generator due to the battery getting to Absorb V I can have its AUX turn on a AC SSR and add a resistive load to its AC output to keep the voltage down so it the Classic stays online and the DC voltage doesn't exceed 150V.

That's the "vision" that I woke up with this morning, and is my next stage of the experiment for today.  If it works, I've got success with a MPPT engine-driven DC generator, and at that point you could even get it to work on a 24V system.  It is no different than what I've done with wind turbines with a Classic 150.

I think the other key is to use a very small generator.  A 5,000 watt generator will put out ridiculous amps, approaching over 100A with the battery at 48V or lower.  It's going to take some big stuff to handle 100A of DC current.  Where with the little 2300 watt generator I'm using I only have to deal with 40-42A, which is plenty for what I need it for.  Even a tiny engine-driven generator can rival a huge wind turbine, or thousands of dollars worth of solar panels, with ease for power output.  If I can keep the amperage down to 20A thru the full-wave bridge, then the bridge won't get hot, it'll be more efficient, and the Classic 150 is the only way to do that.

ChrisOlson

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Re: Experimental 48VDC Generator
« Reply #12 on: October 19, 2014, 10:36:00 AM »
Even a tiny engine-driven generator can rival a huge wind turbine, or thousands of dollars worth of solar panels, with ease for power output.

I'd like to add for this thread, that this is the reason I have gone to more interest in combustion engine driven power for off-grid power vs solar and wind.  If you look at the total generating capacity on this planet in coal, natural gas and nuclear power plants, it is a pipe dream to think that you could replace that capacity with solar panels and wind turbines.  A little engine driven generator that you can almost carry around under one arm will produce more energy in a day, without even breaking a sweat, than a $40,000 wind turbine will.  We put in a Bergey Excel-R turbine thinking it would be the answer to our energy needs.  Nope.  It doesn't produce any more power on an average day than my three home-brew turbines used to - most of the time, less.

For my large shop I needed 50 kW of power and we put in a Cummins 4BT diesel cogeneration set.  We initially ran it on it on petroleum diesel fuel, but have since found a supplier of B50 off-road fuel at a little cost savings over what we were paying for #2 petroleum fuel.  So now our shop runs on 50% of its power that comes from America's farms and is grown every year by farmers.  Eventually we're putting in our own biodiesel plant and hope to run the generator on B100 year 'round.  We put in the grain facility this year to handle the soybeans that we're going to squeeze for oil, and sell the soymeal to food processors.

But the point is, we put in a $40,000 cogeneration set that fits in the back of a pickup truck and it will produce 960 kWh/day in electricity and another 320 kWh in heating and air conditioning.  Do you have any idea how many solar panels and wind turbines it would take to match that little unit that fits in the back of a pickup truck?  And how much it would cost?

That's why I'm going to develop an efficient engine-driven peaking plant for our house.  We want 30 kWh/day no matter what the weather conditions.  And $100,000 worth of solar panels and wind turbines can't produce it, day in and day out, with 100% reliability.  Engine driven generators do.

joestue

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Re: Experimental 48VDC Generator
« Reply #13 on: October 19, 2014, 11:03:12 AM »
Chris, the single phase two pole, 5kw generator heads have two coils, wound together in series, each for 120volts, they are connected in series for 120/240vac.
In this manner, you can pull 20 amps from each wire, or you can pull 29 amps from one wire and zero for the other.
( This is how they have a 30 amp breaker on a 120 outlet, but only a 20 amp breaker on the 4 pin 120/240 outlet; the wires, wound together, share the thermal load)

Well there's two poles and they are both in series. So if you break the two wires where they cross over to the other side of the machine, and bring those 4 wires out, you'll have half the voltage, four 60vac coils. you'll have to break the series connection as well and will end up with 4 separate coils
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ChrisOlson

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Re: Experimental 48VDC Generator
« Reply #14 on: October 19, 2014, 12:55:21 PM »
Chris, the single phase two pole, 5kw generator heads have two coils, wound together in series, each for 120volts, they are connected in series for 120/240vac.

Actually, they are center-tapped for the neutral with each coil still at 120V amplitude, but producing a sine wave 180° out of phase with the other one.  It's not a true series coil group.

I need to add a disclaimer here also - if folks read this and think it's an idea to try, remember that you are dealing with lethal voltages and current, and the DC side especially is very dangerous.  A 165V DC arc will jump a 2" air gap and you can weld with it with the types of current produced by an engine driven generator.  So don't do anything that might compromise the well-being of your life.  LOL!

ChrisO modifying this important part :-)
« Last Edit: October 20, 2014, 04:06:14 PM by Bruce S »

bart

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Re: Experimental 48VDC Generator
« Reply #15 on: October 19, 2014, 02:00:32 PM »
I have 3 or 4 older Onan gensets that have manual voltage regulators some day I might try to get 1 of them running to try my theory


   Ran my old Onan to see. On the regular rheostat +/- 30v and on the combination field rheostat from 50v to well over 300v, where it starts sounding funny. 

gww

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Re: Experimental 48VDC Generator
« Reply #16 on: October 19, 2014, 02:37:16 PM »
Chris
Thanks for the update.
gww

ChrisOlson

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Re: Experimental 48VDC Generator
« Reply #17 on: October 19, 2014, 05:39:47 PM »
Ran my old Onan to see. On the regular rheostat +/- 30v and on the combination field rheostat from 50v to well over 300v, where it starts sounding funny.

Them old Onan generators are one hell of a unit.  You can't break one.  I've seen 'em with 30,000 hours and they still ain't wore out.  They put out clean, stable power with the best of 'em and got incredible surge capacity.  David Onan founded the company in 1927 and sold his first generator - the company was bought by Cummins in 1986 and they got product support that is rivaled by nobody - anyplace on earth.

The cons are that you have to replace the fuel pump diaphragm and spark plugs, points and condenser every 30 years or so.  And since David Onan built his first genset engineers have yet to devise a smaller machine that can suck in more gas than an Onan generator engine.  So that requires that you plumb one into your own pipeline that runs direct to OPEC to ensure that you got a good enough fuel supply to run it.

joestue

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Re: Experimental 48VDC Generator
« Reply #18 on: October 19, 2014, 05:50:49 PM »
Chris, the single phase two pole, 5kw generator heads have two coils, wound together in series, each for 120volts, they are connected in series for 120/240vac.

Actually, they are center-tapped for the neutral with each coil still at 120V amplitude, but producing a sine wave 180° out of phase with the other one.  It's not a true series coil group.

just a different way of saying the same thing.

If you can find the midpoint of the two coils, clip those two wires, bring out four leads, then you'll have 60vac single phase.
this is only true for a 3600 rpm gen head.
1800 rpm 4 pole units are more likely to be wound with concentric coils that cannot easily be split in half. the mid point will be found in the middle of the coil stack and it will be a laborious attempt to even find it. not to mention you can't parallel the coils because the circulating currents will be signifiant.

in fact, i just might do this mod so i can weld from the generator directly (60vac open circuit at 100 amps should be plenty)
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ChrisOlson

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Re: Experimental 48VDC Generator
« Reply #19 on: October 19, 2014, 08:38:02 PM »
just a different way of saying the same thing.

I should've said that differently.  Yes, they are in series but each coil is excited with an opposite generator pole.  So the single-phase voltage is not additive.  It is split-phase, which is still single-phase, but the amplitude of the sine waves is not 230 or 240V like it is with European power.

bart

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Re: Experimental 48VDC Generator
« Reply #20 on: October 19, 2014, 09:17:26 PM »
   Hey, then at 2600+ hours, it's just broke in!
And it do like it's petroleum products.

ChrisOlson

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Re: Experimental 48VDC Generator
« Reply #21 on: October 20, 2014, 12:31:32 AM »
I got it to work with a Classic 150 with no step-down transformer.  Hydro Mode didn't work all that well.  I am using a power curve for a wind turbine and it works beautifully.  Although it's not really much of a power curve because it's pretty flat.  But it works.  With the engine at 1600 rpm idle it puts out about 100 watts.  At rated speed it gets to about 2250 watts.  And the Classic compensates for the battery voltage automatically so if the voltage is 60 then it puts out about 38 amps.  If the Batt V is 48 then it puts out about 47 amps.

It works much better with the Classic 150 than it did with the transformer and hooked direct.  I tweaked the curve a bit either way with the generator running and this is the curve that gives me the most power at any throttle setting:



The only caveat is that the Voc is 171 with the genset cold and idling.  I have to plug in a 1500 watt space heater to one of the plugs on the generator with it idling.  That makes the voltage "sag", the Classic then "kicks in" and once it has the generator "clamped" it don't let go of it.  So I can unplug the space heater once the Classic is online and she's good to go.

kitestrings

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Re: Experimental 48VDC Generator
« Reply #22 on: October 21, 2014, 10:12:56 AM »
Quote
they are in series but each coil is excited with an opposite generator pole.  So the single-phase voltage is not additive.  It is split-phase, which is still single-phase

Chris can you explain this, because I'd thought if they were 180 out of phase you essentially had the same thing, unless it is say a network connection (2-legs of a wye) where now things are 120 deg apart.

Regarding the Bergey.  I've seen more than a few folks disappointed with the production, relative to the investment.  Usually it is where there sold on a site they shouldn't have been - and I know that's not your case.  The state monitored a number of them a few years back at various sites.  Two of them were real good; excellent sites, most of the rest were a waste.  Now these are the grid-ties, and I believe Bergey de-rates the battery versions considerably.

In the case of meeting the demand of your shop your point is well taken.  And, if you can use the heat, better still.  Still for a lot of more modest uses, I'm still amazed at how much you can squirrel away with wind & sun.  When you've generators a bit - we've got an Onan - you develop an appreciation for what 3 or 4 kW of solar is doing silently in your yard.

Anyhow, good luck with this.  Looks like your having some fun.

~ks


kitestrings

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Re: Experimental 48VDC Generator
« Reply #23 on: October 21, 2014, 10:13:50 AM »
Quote
they are in series but each coil is excited with an opposite generator pole.  So the single-phase voltage is not additive.  It is split-phase, which is still single-phase

Chris can you explain this, because I'd thought if they were 180 out of phase you essentially had the same thing, unless it is say a network connection (2-legs of a wye) where now things are 120 deg apart.

Regarding the Bergey.  I've seen more than a few folks disappointed with the production, relative to the investment.  Usually it is where there sold on a site they shouldn't have been - and I know that's not your case.  The state monitored a number of them a few years back at various sites.  Two of them were real good; excellent sites, most of the rest were a waste.  Now these are the grid-ties, and I believe Bergey de-rates the battery versions considerably.

In the case of meeting the demand of your shop your point is well taken.  And, if you can use the heat, better still.  Still for a lot of more modest uses, I'm still amazed at how much you can squirrel away with wind & sun.  When you've generators a bit - we've got an Onan - you develop an appreciation for what 3 or 4 kW of solar is doing silently in your yard.

Anyhow, good luck with this.  Looks like your having some fun.

~ks


ChrisOlson

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Re: Experimental 48VDC Generator
« Reply #24 on: October 21, 2014, 08:46:50 PM »
Chris can you explain this, because I'd thought if they were 180 out of phase you essentially had the same thing, unless it is say a network connection (2-legs of a wye) where now things are 120 deg apart.

If you look at European 230V power you have a single sine wave that is 230V amplitude and it is 230V to neutral.  US split phase power is different.  It is 240V but consists of two sine waves that are 120V each to neutral, but because they are 180 deg out of phase with one another the difference between the two is 240V.  A US 240V appliance will operate on the two hot legs with no ground or neutral whatsoever.  A European 230V appliance must have a (grounded) neutral to it in order to work.  In a two-pole generator one of the series coils is being excited by the north pole of the generator while the other is being excited by the south pole, and both stator coils are the same polarity.  This creates two sine waves that are a mirror image of each other when you compare from the start lead of one coil to the center tap, or the end lead of the other coil to the center tap.  It is still single-phase power and not polyphase because both L1 and L2 sine waves reach their maximum amplitude at the same time, and also zero at the same time.

kitestrings

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Re: Experimental 48VDC Generator
« Reply #25 on: October 22, 2014, 01:09:52 PM »
Thanks.  I learned something - always a good start to the day.