Author Topic: 2 gensets on same bus  (Read 24855 times)

creighto

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Re: 2 gensets on same bus
« Reply #30 on: July 19, 2006, 01:42:34 AM »
[

   Disclaimer, I'm not a sparky either.

I *am* a sparky.  I would not consider this.

buickanddeere

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Re: 2 gensets on same bus
« Reply #31 on: September 02, 2006, 12:02:43 AM »
  Guy

  You are thinking of a syncronous motor rather than an induction motor.
  If the four pole induction motor has to slip from 1800 to 1725 rpm to carry it's full rated load. RPM's of 1800 will allow a clean sync with the 60HZ alternator. Winding the rpm's up to about 1875 would bring the induction generator up to full load.
  Voltage regulation can be spooky and using oil filled power factor correction capacitors to supply some reactive power instead of the other generator.
  What kind of voltage regulation is on the two 60 hz alternators you want to sync. If it's just a bridge recitifer and a filter capacitor suppling excitation, no problem.
  If tying two 120V circuits together with a sync lamp between. Use a 240V lamp or get used to a couple of very bright flashes per bulb.
  Disimilar generators/engines/regulators are a swine to sync and share loads.
  I've seen a 7 MW gas turbine fight a 540 MW/650KVA steam turbine generator when synced. While small in size it was throwing harmonics right out into the utility grid. The  excitation on the 540  generator was equiped with but somebody failed to enable the "power system stabilzer"  after running a test. Once switched in the 7MW still hunted but the 540MW would anticipate and correct by varrying it's excitation levels.
  I would say run two identical units about one size larger than you think you need. A cheapo PLC controler and a little soft ware could make starting, stopping, sync and Murphy Switch protection.     

Jim Mc

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Re: 2 gensets on same bus
« Reply #32 on: September 02, 2006, 04:14:34 AM »
  ...I would say run two identical units about one size larger than you think you need...   

Are you talking about two synchronous machines in parallel, or a synchronous machine paralled with an induction generator?

Either approach has problems.  If it's a synchronous and induction operated in parallel, you don't get the reliability through redundancy, since the induction machine can't be operated as the sole source (easily).

If you meant two synchronous machines in parallel, how would you address the issue of the circulating current that flows between the two machines as they drift back and forth in phase due to their low-speed, single-cylinder Diesel engine drive? Despite their big flywheels, their speed does vary throughout the 4 stroke cycle.   Keep in mind we're talking about Listeroid prime movers here, not gas turbines.

Maybe I am over-engineering it, but I wasn't willing to build my power plant in this configuration until I could be 99% sure it would work.

buickanddeere

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Re: 2 gensets on same bus
« Reply #33 on: September 02, 2006, 09:25:41 PM »
  Two synchronous machines in parallel is much preferred. Tieing an induction generator on would only be done as a temporary cobbled up tineration in an emergency. Or with a properly built and controlled water or wind turbine.
  While getting too complex to be practical. If there was a clutch to mechanically link the two gen sets after they are electrically synchronized.
  K.I.S.S. goes a long ways.
  One has to figure the cost of a single medium sized machine often running loaded v.s. two small machines and the complexity.
  The one medium sized generator and two small engines is probably the best solution if you insist. The rotating mass of a large generator and even mass of just one engine  should start induction motors with reciprocating loads.   
  Are you tied to the grid? If so, just net meter. Run the 6/1 and turn the hydro meter backwards during light domestic loads and take supplemental power from the grid when the 6/1 can't keep up.
     

Doug

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Re: 2 gensets on same bus
« Reply #34 on: September 03, 2006, 02:20:09 AM »
Well said....

Doug

Rtqii

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Re: 2 gensets on same bus
« Reply #35 on: September 07, 2006, 09:03:17 PM »
My applications are not exactly normal... But in the end I decided to block mount a 20/2 for pulling the big loads and then a smaller engine, I am looking at a 10/1 for routine power.

When I went out to look at land I was not certain what climate, altitude, etc I would be moving to. Now I know... I am up a few thousand feet and I will lose some efficiency. Also it is very hot in the summer and I will need some form of active cooling for the house and forced ventilation for the shop/lab... So I made the correct engine choices.  I can run the 20/2 to drive my big research loads after shedding everything else, it can also handle all the homestead loads, run shop tools, and small research loads without shedding anything... When the 20/2 needs down time the 10/1 will still provide enough power to run the fountain chiller and cooling loop for the house and ventilate the shop and engine room, plus tools and lights.

I am going to include about $3K in solar to handle the base loads... Chest freezer, reading lights, and hopefully enough left over to pump water for the chiller loop... I may not get all this for $3K in a solar system, but with adequate generator power and sources of free fuel I can afford to take my time and shop for deals on used solar panels.

Engine wise, the larger 20/2 and the smaller 10/1 will be the best solution for my app. I will pony up for some high quality batteries in this system and try to take extreme care I am not taking more than 20% off the top of the bank... I hate overloading battery systems.
« Last Edit: September 07, 2006, 10:02:31 PM by Rtqii »

buickanddeere

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Re: 2 gensets on same bus
« Reply #36 on: September 08, 2006, 02:09:27 AM »
  How effective would a wind turbine perform at your location?

mobile_bob

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Re: 2 gensets on same bus
« Reply #37 on: September 08, 2006, 03:31:52 AM »
"and try to take extreme care I am not taking more than 20% off the top of the bank"

i would like to get a discussion going reguarding this approach

yes your batteries will last longer, but have you done the math to see if having longer lasting batteries outways the amount of fuel and engine time needed to recharge them from 80% SOC to 100%?

this is the area of charging where charge rate has to be reduced and engine run time is dramatically increased, so i wonder if the savings in battery life/ in dollars offsets the amount of extra burned fuel and engine life expended?

i have researched this quite some bit, and from my research and calculations you would be many dollars ahead, running the batteries from 50% SOC to 80% SOC, where the batteries can take a very large charge rate, and dramatically reduce engine run time, by a rather large factor, in some cases more than a factor of 5.

this scheme would require a complete charge from 80% to 100% once a week, and an equalization charge maybe once or twice a month. then the use of a smaller engine and reduced charge rate could be left run at peak fuel efficiency for many hours.

as an example if one has a 1000 amp/hr bank, and cycles from 50-80%, giving an effective useage of 300 amp/hrs a day, then to restore that which was used could be done at 150 amps for 2 hours per day, then at the end of the week fully charging from 80-100% could be done at a reduced rate(which would be needed to keep from gassing) over perhaps 6 to 8 hours.

the bottom line is perhaps run times as high as 42-56 hrs per week charging the example bank from 80-100% as opposed to
20-24 hrs per week cycling from 50-80%.

unless you have use for 42-56 hours of excess heat, which you might in the winter months, you might find it better to go the other route and have a more manageable amount of heat to harvest and use, increasing the overall system efficiency.

to me the fuel savings is more than enough to offset the gains in battery life, by a wide margin, to say nothing about extended engine and generator life as well.

what do you think?
am interested to here opposing views

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

BruceM

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Re: 2 gensets on same bus
« Reply #38 on: September 08, 2006, 02:21:43 PM »
Bob, This is an area I'm also very interested in.  It seems to me that the slow rate and trickle charging should best be handled by the solar system, using the generator for bulk charging only, except for extended sunless periods.

Another area of interest for me is the allegedly higher charge rate and charge effeciency of the AGM batterys; there are some of these now being imported from Vietnam (which are lower priced).  I have been pleased with the AGMs I've used in some applications but not on this scale.  These are apealing to me as my proposed system is 120VDC, (9) 12V batteries in series.  (I'm unable to tolerate fluorescent lights of any kind because of my epilepsy and 12/24V for incandescent/halogen lighting is  bit heavy on copper $.)

I also wonder if there are any important design issues relating to series connection of solar panels to these higher voltages.  Perhaps some external diodes needed to protect the panels from excessive voltages in case of cell shorts/failures? I have read of a few systems like this but they were only "fluff" pieces with no good technical data.

I plan to build my own non-pulsed type solar/generator chargers.

Bruce M
Metro 6/1
Snowflake, AZ








bitsnpieces1

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Re: 2 gensets on same bus
« Reply #39 on: September 09, 2006, 10:37:48 PM »
 BruceM :  Have you considered LEDs?  They make them in a bunch of configurations nowadays.  Even more efficient than
flourescents, HOWEVER:  NOT CHEAP.  Have 'em in 12/120 v.  AC/DC

LYPCB06 CW with 36 Cool White Cree Chip LEDs. Medium house hold base; approx. 3 1/4" tall x 2 3/8" diameter. Clear lens. Great utility LED bulb for those hard to access areas, as porch lights, in sheds and utility buildings. Super outdoor-sign bulb replacement! Estimated life of 60,000 plus hours for Cool White. 3.0 watt consumption - 90 lumen, 40 watt light output at 6500 Kelvin Temp. PCB06 LED Bulbs are UL listed.  $32.00 ea Cool white   $24.00 ea Warm White.  Get cheaper the more you buy. 
http://www.theledlight.com/120-VAC-LEDbulbs.html
Lister Petter AC1, Listeroid 12/1, Briggs & Stratton ZZ, various US Mil. surplus engines. Crosley (American) 4cyl marine engine(26hp).

Jim Mc

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Re: 2 gensets on same bus
« Reply #40 on: September 10, 2006, 02:58:18 AM »
  3.0 watt consumption - 90 lumen...


Common misconception: that LEDs are more efficient than fluorescents.  Generally not true, at least not in the year 2006.  CFL bulbs are typically in the range of 40-60 lumens/watt.  And linear fluorescent (4 footers) run around 70-90 lumens/watt.  The LED bulb you describe was 30.

LEDs are getting more efficient, though.  But today, fluorescents are generally more efficient.

But, Holy Cow,  another thread taken way OT...

DaveW

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Re: 2 gensets on same bus
« Reply #41 on: September 10, 2006, 04:25:12 AM »
mobile-bob -
    I presume you are trying to start a discussion with the question on murdering your batteries to save on fuel.  I have three banks of Absolyte IIP batteries, about 7 years old now, and this is about $10,000 worth of power storage.  With care I should get in excess of 20 years service from these batteries.  The thought of recharging with diesel power alone never would have crossed my mind.  The first thought that came to me when I read your post on trigeneration was wind, solar, and backup power.  My primary source is wind, with solar a distant second.  Only when all else fails do i fire up my generator.  Of course at the moment my backup is an old Wisconsin with a 5.5K Allmand generator, not a diesel.  But I am working on that.  Back to the batteries.  The AGM batteries have several advantages - small footprint via vertical mount racks, no outgassing so they can share space well and don't need an active vent, no messing with water level monitoring, freeze tolerant, and a remarkable tolerance for bulk rate charging.  I have seen them swallow 250 amps without a complaint, of course I do monitor temperature rise just in case.  They also recharge on only about 105% of discharge rate, which is better than my traction batteries which seem to need at least 110%.  If I were to try to recharge via diesel alone, it would be with at least two different setups.  The first for bulk charging should be able to provide a c/5 or c/8 recharge, the second should have about c/20 with a fixed voltage input of about 2.3 volts per cell and let the battery determine the current rate as it finish charges.  I have never had to equalize these batteries.
    Your approach would wreck the battery sets in about two years or less.  This is when I made the assumption that the statement was to start a discussion on the subject.  I can replace any of the rest of the system without too much pain, but I want my batteries to last a good long time

DaveW

mobile_bob

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Re: 2 gensets on same bus
« Reply #42 on: September 10, 2006, 04:35:29 AM »
"Your approach would wreck the battery sets in about two years or less"

interesting your statement, i did say flooded lead acid cells and not sealed lead acid cells.

i am wondering what your reasoning is, behind your statement?

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

mobile_bob

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Re: 2 gensets on same bus
« Reply #43 on: September 10, 2006, 05:15:07 AM »
DaveW:

ok,, it took me a bit to follow where you were going,,, it is late and i am a bit slow

you are in reference to your battery bank, and yes a different approach would be appropriate for sealed batteries or VRLA cells.

the example i was using was for flooded cells, with a sophisticated controller, such as the balmar unit.

in the trigeneration thread when i mention 640 amps charge capacity i should have ellaborated on the point that unless one has a quite large bank it would be crazy to try to pump that much in, that is where the balmar controller takes over. with its temp sensors on the battery it calculates the max charge that can be safely pumped the bank based on SOC, and temperature.

having the 640 amp capacity allows me to not only charge at the max safe level but to continue to use the inverters without lowering the charge rate to the batteries.

incidentally the balmar controller also has a regime for vrla batteries as well.

i would not myself or advise anyone to use such an agressive charge rate by the seat of one pants, but i would do it with a controller.

how do you monitor temperature of your batteries? you mention throwing 250 amps at them, so i am wondering.
how big is your bank in amp/hrs?

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

DaveW

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Re: 2 gensets on same bus
« Reply #44 on: September 11, 2006, 03:59:51 AM »
mobile-bob -
    My largest bat set is 1000 AH, I try to go conservative since many manufacturers suggest 18 to 30 amp recharge rates for each 100AH at 8 hours.  I know this suggests that 300 would be ok, but monitoring the temp rise suggests otherwise.  I use a Betatherm 10K3A thermistor for the front end, through a Burr Brown 1NA118 precision instrumentation amplifier to a PIC 16C74B processor.  I limited myself to 8 sensor inputs cause I'm lazy.  The PIC will input 8 directly, so that became my choice.
     1.  High on the back wall of the battery room.
     2.  Low on the front wall of the battery room.
     3.  High over the battery rack.
     4.  Just above the equipment rack.
     5.  Battery case 4 in from the start of the series.
     6.  Battery case 4 from the end of the series.
     7.  Center battery case.
     8.  And one just outside the door for outside measurement.

   By comparing these inputs I can keep a close tab on what is heating up and how fast.  The center battery case is also used to make voltage adjustments for charge rate, and the average case rise every ten minutes controls the current input. I use 4 360 watt Peltier Effect Devices for both dump load and to either heat or cool the battery room as needed.  They respond very well to PWM control so I can fine tune where the power in from the wind generator goes, either to the batteries or dump load or split operation. 
   A second set of sensors monitors the voltage on every 6th cell. I once thought of monitoring every cell, but the processing time for the PIC would get a little high, and this method seems to work fine.
   An old Compaq Aero laptop runs the system,  does the logging and sends alarms.  If any upper or lower limits are reached in temperature or voltage or current I use contactors to open the inputs to the batteries and the inverters and clamp the generator to full dump load.
   Three good sources for more information would be:
     
     R. Jones, Recharging VRLA Batteries for Maximum Life, Proceedings of Intelec (99) Copenhagen
     S. Despande, Intelligent Monitoring Systems for Continuous Monitoring on VRLA Batteries, (99) Copenhagen
     P. C. Butler, Utility Battery Storage Systems, Sandia Report, SAND92-2272 (1993)
 
  Another good read is the Professional Papers put out by Absolyte, although I realize that they might have a bias on what they print.  However, after about 8 years of monitoring, my numbers match theirs very closely, and I would not hesitate to base a charging system on what they recommend.
    I understand that all this may be just a wee tad overkill for the job at hand, but remember there is no one more anal than a retired engineer with time on his hands, and it does keep me out of the bars.