DC Gen/ Inverter grid tie system for simplicity

[wagspe208]

I could not post in the generator section for some reason.
I currently use grid power. I have 70 acres with no power, so I am doing a test for some day.
I want to grid tie today and avoid batteries. I want clean power though (is this not really necessary with off grid). I need clean power to grid tie and feed back...
So, why not use a DC generator fed into an inverter? This provides clean ac output. Input votage should not be an issue, so I could slow down my engine as needed. I still get "good" AC out, so the power company should be ok with that.
I am new to this stuff, so be easy.
Watt am I missing? 
Wags

[LowGear]

Hi Wags,

What you're missing is the meeting with the local power company to see what their requirements are for their power grid.

An alternative is over spinning an inductive motor but we're back to the first sentence.  You might visit http://www.utterpower.com/

Casey

[wagspe208]

I have talked to them already. They are on board. It is a co op. I have some forms to fill out, but they do not specify how the power gets to their spec, just that the pieces are ? certified, etc.
Meaning ac generated, dc generated/ through inverter/ etc.
Thanks
Wags

[admin]

all the power generated by rotary means is generated as alternating current, even the old
generators common on old cars and trucks,

those old units used the commutator and brushes as a mechanical rectifier,

when alternators came along they did away with the brushes and commutator and went with diodes for rectification.


generally speaking an alternator will always be more efficient and trouble free than a generator

alternators can be smaller, turn faster, cost less, require less maintenance and are more reliable that their older counterpart.

i personally would not use an old style generator for anything unless it was a backup, in very good operable condition, and i wanted
to preserve a collectible.

the only other time i would consider an old generator is if it was part of some older genset, where it would just be wrong to remove
it and replace it with a modern unit, such as the old witte genset we have seen here posted by Flywheel.

bob g

[LowGear]

Hi bob g,

I too have the incredible Witte Power Station only the smaller 4.7 KW unit.  I believe flywheel's is close to 8 KW or 12 HP.  My generator looks like its 60 years old and reportedly doesn't work anyway.  I'd just put it in a good box for storage should the next owner want to be "perfect". 

Where should I go shopping for alternator replacement units that would like to be rectified into DC before fed to my Sunny Boy 6000?  Or where would I find a reliable shopping list?

I've got this recurring dream about three phase giving up a cleaner smoother rectified DC power?  If I got a 15 KW three phase alternator could I use just one leg in case I wanted to go off grid sometime?  How would I limit the output to < 5 KW besides the engine only being capable of 8 HP? 

And Wags.  I'd be pretty surprised if your co op aren't going to want the work done via a permit which demands adherence to code.  Some areas have grants and buy-back programs.  If it weren't for a grant and the energy tax credit programs by the US of A and the State of Hawaii I'd still be complaining about my energy bill.  As I've stated before; we just paid 34 cents a KWH for this last month.

Casey

[wagspe208]

Hi bob g,

Where should I go shopping for alternator replacement units that would like to be rectified into DC before fed to my Sunny Boy 6000?  Or where would I find a reliable shopping list?

x2


And Wags.  I'd be pretty surprised if your co op aren't going to want the work done via a permit which demands adherence to code.  Some areas have grants and buy-back programs.  If it weren't for a grant and the energy tax credit programs by the US of A and the State of Hawaii I'd still be complaining about my energy bill.  As I've stated before; we just paid 34 cents a KWH for this last month. WTF?

Casey

I will stop in and actually talk with them. I had a couple of phone calls and they e-mailed the forms. Permits, shermits. HAHA
I guess I should not be bitching about .12 per KWH then?

I was looking at the sunnyboy also. Do you have solar, or is this whatyou wil use for the alt/ gen to "good" ac?

Wags

[admin]

Casey:

if it were me, i would probably go with a STC genhead which as you know is a three phase unit

i would drive it with two B series belts via a 3 groove pulley,

the extra groove i would use to drive a small 12volt alternator used to provide the field excitation for
the STC head, this would eliminate to a large extent the distortion related to the harmonic excitation of
the oem stc head, however i would keep the harmonic winding and use it for a back up.

i would then rectify the 3 phases to provide high voltage DC for your grid tie inverter.

off of one of the stator legs from the stc head i would take off AC and step it down to ~12volts or so, rectify
and filter this to use as a sense feed for the exciter alternator,

off another phase of the stc i would take another 120vac and use it to power a small charger that would keep
a small car battery properly charged, it would provide power for the exciter field which would remain as a 12volt nominal
unit.

with such a setup, properly setup and tuned in, you could get a very stable DC output voltage, and also be able to have
120/208vac for you AC needs, although not all at the same time, but you could do a split with a little testing and tweaking.

this sort of system although a bit more complex than just simply buying an st head, plugging in a  rectifier, would provide
for a fairly low ripple, low distortion DC power of a high enough voltage to be pretty efficient for grid tie

qualifier here:   this is my opinion only, and should be discussed with others and/or fully understood before you take the
next step which may or may not be NEC code related.

fwiw, i know such a system would work and have tested it myself, however again it takes a bit of understanding by a diy'er
or getting a electrical/electrician/EE or other such guru to help you work out the system.

if you would like a sketch that outlines the components i can provide that, but
you must bare in mind this is for conceptual illustrative purposes only, and i would recommend no one use the sketch as a schematic
to build a working system.

in other words, you will be working with seriously dangerous voltages, that can bite, burn, or worse kill you.

but you already knew that right?



bob g

[wagspe208]

Yes, I would totally need a sketch to understand that. I work with electricity (36DC) daily, so I am not new to schematics. I am new to this stuff, though.
I understand safety, but a picture (or sketch) is worth a thousand words to me.
Thanks
Wags

[LowGear]

Hi bob g.

I have come to accept the famous and most wise words of Dr. Harold Callahan.  "A man's got to know his limitations."  Your system is well outside my limitations.  I, of course, appreciate your effort but its just too complicated for me.  I also have folks on the farm that simply wouldn't turn it on if its much more complicated than a suit-case.  That's the nice thing about solar once you get it installed.  I'm waiting for the electrical inspector right now.  I just remembered a conduit I forgot to strap.  I know there is an end someplace but I don't want to hurry there too fast.

Your warning about high voltage is heard.  I can get a little loose around 240 AC but 300 DC-land demands respect as I've been told by every electrically inclined person I've spoken to about solar or rectified 240 AC.  The Sunny Boy seems to need 350 DC volts for lift off.  The Sunny Boy is the same unit as the Windy Boy so my DC only has to be as nice as that which comes off a wind turbine system.  I've even considered just buying a wind turbine unit, tie-wrapping and belting it to the Witte.  Kind of cheesy and no AC 60 Hz without the inverter but historically that's less than 6 hours a year.  And these SMA grid tie inverters just don't invert if there's no grid signal to sync with.

The fourth question on the Hawaii Electric Company Grid Tie Application was "Approved Permit Number".  I wait to answer that one with baited breath.  But up into the attic and an inter-truss slither to the offending 7' stretch of conduit.  IF it was much further I'd just punch another, yes another, hole in the carport ceiling.

Again, Thanks for your work.

Casey

[admin]

attached is a block diagram and a block schematic illustrating one way to achieve control of the system i alluded to earlier

figure 1 basically shows a drive layout, it could be any engine, any three phase brush type field, and any externally regulated alternator
with its diodes replaced with at least 200piv rated units.

figure 2 illustrates what is needed at a minimum, the output of the bridge rectifier is shown to go to the batteries, but it should have been noted that this output goes to the grid tie inverter system, however some filtering might be in order. because it is 3phase rectified i would expect it to be relatively low ripple to start with, so filtering would not be as difficult as would be with a single phase head.

because the stc field current is supplied by the belt driven exciter, the harmonic z winding is not used, this should produce a lower harmonic content on the output of the stc head, which in turn will make for a cleaner rectified dc current.

the stc stator is connected in wye/star configuration to produce higher output voltage to the bridge, and to produce 120vac to the three legs referenced to the neutral center connection, this provides three legs, each to provide for the three 120vac outputs. one for the  transformer to step down to around 9vac which when rectified and filtered should produce `12.7vdc which will be used for the sense line to the balmar regulator. another leg will provide 120vac for the battery charger which maintains a small battery used to provide the field power to the exciter, this could be a small charger because the field current is ~5amps at 10volts to the exciter.
the last leg could be used to provide 120vac to a duplex socket for power use for any number of appliances within the capability of a single winding of the stc head.

the theory of operation is as follows

the exciter on startup has its field provided by the balmar, the balmar sense no voltage on the sense line so it provides full field to the
exciter from the small battery, as the field to the exciter raises so does its output and it will raise to about 80-90volts dc at 5500rpm
this current is fed into the stc field which energizes the stc head.

the stc head will now produce full rated power as its voltage increases, it feeds the transformer, which is rectified and the sense voltage increases to above the setpoint, wherein the balmar tapers back the excitation current to the exciter, the exciter output reduces and in turn the field to the stc head also reduces.  when the voltage dips under 120volts ac phase to neutral, the sense line
is also reduced and the balmar increases the current to the exciter, and in turn the exciter output increases and in turn so does the stc field and then the stc output increases,

this happens at a few thousand times per second, so the overall effect is a smooth seamless transition, that is too fast to see without
a scope.

bob g

[LowGear]

Thanks bob g.

I know how my associate farmers feel when I start talking irrigation box theory or the programing of a timer in the dark while its raining. 

I think I'm shopping wind turbine units with sufficient bearings to handle a pulley.  Of course, based on the way I got my butt kicked by the county electrical inspector yesterday I may not be in the market for anything except flipping hamburgers if I can get through the extensive training program.  When I said "Plans, I don't need no stinking plans!" and there wasn't even the hint of a grin I knew it was going to be one of those gosh darn days.  Remember the days when we could speak our hearts and it wasn't Terroristic Threatening?

Thanks again Bob,

Casey

[wagspe208]

I had also contemplated the wind generator option.
This above method is a little above my head to comprehend, but I don't have to be an architect to build a house either. Plans are plans.
I wonder what cost vs cost is.
I was working today and glanced at the wiring. I will look some more tonight. The mechanical part is a breeze.
Any estimate of costs for either system?
Thanks
Wags

[mobile_bob]

well lets do a little breakdown of costs

its too expensive for most applications is the short answer, and maybe unnecessarily complex for most folks too.

it really depends on what ones needs are vs what one wants

for a grid tie inverter, you may not need stable dc voltage, just clean current? i don't know

a good stc head is not much more expensive than an st head

a 110-555jho alternator can be had for as little as 115 bucks on sale, but you will need to replace the diodes with
non avalanche units, so one probably would be better off buying a rebuilt alternator spec'd with the require diodes
at 250 bucks or so

the balmar is not necessary, there are other options for regulators with external sense capability that could be had
for 50 bucks or so

the stc output rectifier bridge, will be somewhat expensive new, but maybe 100 bucks or less surplus

the small battery charger and battery, maybe another 50 bucks if you shop it out

with a little careful shopping, perhaps 500 bucks, maybe considerably less depending on how good you are at coming
up with surplus parts, this cost of course in addition to the stc head, and a 3 groove pulley and belt to drive the exciter.

it really depends on what ones needs really are.

bob g

[wagspe208]

Bob... good breakdown.
1) Price-- so, under $1000. (+ inverter) I assume. No huge deal. Not cheap either.

2) Need vs want. I only need what I need. HA Or I need a setup that will grid tie, provide useable power fo me and be ok with the co op.

3) Complex.. well, maybe. It seems well thought out. Are there reliability issues?

I want a "put together once" piece. Serve my needs. Not have to work on it much at all. Reliability.

Thanks
Wags

[LowGear]

Hi bob g. and Wags,

I'm on another thread with rcavictim on this same topic if you'd care to join in. 

http://www.microcogen.info/index.php?topic=1281.0

Casey