Author Topic: SIZING A GENERATOR FOR HOME USE  (Read 21907 times)

oliver90owner

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Re: SIZING A GENERATOR FOR HOME USE
« Reply #15 on: December 14, 2007, 04:49:19 PM »
Jens,
Precison is the name of the game.  Precise readings which are reproducible is better than trying to get absolutely accurate results.  Fuel consumption is easily addressed by setting up a separate tube as a U tube to the main tank.  Mark off two points and you simply allow fuel to be metered from that standard volume and measure the time to fall past the two marks.  Do it several times to get a narrow spread of times to average out.  Do it at different loads, different temperatures, etc, etc.  As long as that volume can be measured accurately, by whatever means you have available (gravimetric or volumetric), you can compare your results with others.  Graphical results can be analysed using a computer prog such as Excel.  In the chemists armoury is a volumetric tool called a burette.  There is also a dispenser called a pipette.  Either of these can make things soooo much easier.  Only one mark is required using a pipette, of course, as a dispenser.  You do need a couple ofgood fuel shut-off valves, probably not  Indian ones!!

hope this helps.

Regards, RAB

Timing?  First check they are both the same.  Adjust both together.  Tough if you have two to do but think of a guy with 6! Changing one of six would show nothing, would it? Same applies to a twin.

diesel guy

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Re: SIZING A GENERATOR FOR HOME USE
« Reply #16 on: December 14, 2007, 04:56:30 PM »
Jens,

You should set both cylinders at the same timing, then perform you evaluation. You also need an infrared heat detection gun to fine tune the fuel delivery and match the exhaust temperatures in both cylinders when under load.

In the past I designed many high performance engines (diesel and gas), first I figured out what the application was and then I design my own cam grind (lift, duration, valve overlap, ramp speeds, ect.) to meet the set requirements, then have it cut to specs. Camshafts are like pump injection timing on diesels, they only operate at optimum efficiency in a very small rpm range. This optimum range works great when working on generators with their fixed operating speed. As to an automotive engine that needs to operate efficiently at a wide range of operating speeds.  

If a diesel  engine has an useful operational speed  between 1,500 RPM and 3,000 RPM for instance, the proper pump setting would be configured to 2,250 RPM. Anything above or below this operating speed is a “compromising” pump timing setting. Maximum cylinder pressure has to be set at 5 and up to 7 degrees ATDC for maximum power and fuel economy. This enables the proper rod to crank angles for maximum burn rate and mechanical leverage. The further down the pistons travels the greater the mechanical leverage but at a much reduced downward force from the thermal expansion. This brings me back to the heavy flywheels on the engine and on the generator.

You can retard the timing more on an engine with heavy flywheels than on an engine with lighter flywheels. Case point, when an engine with heavy flywheels approach TDC the fuel is injected 2 degrees (approx.) later than an engine with light flywheels. This would display a smaller deceleration effect on the crank due to it is compressing a smaller thermal expansion effect than on an engine that is injected 2 degrees sooner. Now, after TDC the heavy flywheeled engine would stay closer to TDC longer (so it could still achieve proper burn rates) than the light weight flywheeled engine because of the stored kinetic energy potential is higher. The light weight fly wheeled engine would “crack” ATDC and the piston would move further down the cylinder per given time frame.

Your valve train would receive reduced sudden shock loads as well with mild timing, which is a problem in these engines. The reason behind all this is that even the slightest reduction in pump timing can dramatically increase the engine operational life and provide better quality electrical output.

To achieve optimum pump timing at a certain engine speed, load, fuel ect. , I’m afraid you are going to need to take the heads off periodically to see if you are producing too much carbon buildup. If this happens you should slightly advance to achieve a suitable amount, or add a constant DC load to keep the combustion temperatures in a suitable range. The key is to have the engine still perform as it should with minimum pump timing to achieve your goals. It sounds like a lot of work but it is time well spent, you will have a smooth long lived engine.

This is what an engine sounds like with conservative pump timing and it could be close the same timing as conventional 6/1 but has heavy flywheels, you would need to know altitude and BTU content of the fuel to directly compare this to other engines:

http://video.google.co.uk/videoplay?docid=-5803127844512609207&q=lister+start-o-matic&total=2&start=0&num=10&so=0&type=search&plindex=0

If the belt chirping still persist, I would opt to a double belt system to increase traction on the flywheel without over straining the bearings with a single belt system. As BruceM mentioned, Lister had it right over a half a century ago with its dual v belt design, which sunk into the groves when the piston past TDC and then released.

Oliver90owner mentioned that you don’t need to be so precise and he is correct you can just mark where you are now and retard or advance from there. I’m a motor head and would pursue the exact timing but that’s just me.

Diesel Guy

BruceM

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Re: SIZING A GENERATOR FOR HOME USE
« Reply #17 on: December 14, 2007, 06:07:42 PM »
Anther way of getting TDC without pulling the head is to use a piece of music wire down the the injector hole, then dial indicate off of the angled music wire. 

Very interesting posts, Diesel Guy!

Procrustes

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Re: SIZING A GENERATOR FOR HOME USE
« Reply #18 on: December 14, 2007, 07:27:15 PM »
My biggest problem now is the inability to find a reasonably priced air cleaner for the compressed air system - my only source was Fremont Industrial Supply but ever since I asked them for shipping costs they have stopped replying to emails. No idea if they are buried in snow, flooded out, don't ship to Canada and too lazy to say so or if they closed their doors. VERY frustrating.

I have been trying to get in touch with Fremont for a week.  Bill sent me a 4.6" sheave instead of the 6.4" one I ordered.  It's evidently got nothing to do with Canada though as I'm in the states.

oliver90owner

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Re: SIZING A GENERATOR FOR HOME USE
« Reply #19 on: December 14, 2007, 10:01:37 PM »
Jens,
Yep, don't even think about it until it is run in properly.  Other things to think about are injector spray pattern , injector pop pressure, your compression ratios, valve clearances, injection volumes.  They are all likely to be only about right from what I have gleaned about 'oids' and possibly streets apart, cylinder to cylinder.
In my opinion don't bother with the piano wire to find actual TDC - the piston doesn't move very far as it approaches and pasees TDC.  A bit like timing a pendulum swing accurately but guessing when it actually stops moving!  (you always time it when it is moving fastest). Checking identical positions before and before in both directions is the better method  You could use wire hitting the piston for a common dial guage deflection, but a wire stop in both diections keeps it simple - no dial guage needed!

Diesel Guy,

Don't mix up precision and accuracy, they are different and I did say he could measure it accurately afterwards.  All good tests are made fair.  Placebos are often used as base monitoring.  Pre-conceived ideas should be avoided, so not knowing the actual absolute setting is a good baseline from where to start to get a fair result.

Regards, RAB

buickanddeere

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Re: SIZING A GENERATOR FOR HOME USE
« Reply #20 on: December 14, 2007, 11:21:52 PM »
 If the generator head used permanent magnets in the rotor rather than DC power your burn fuel to make.  That larger and partly "unused"magnetic field in the 15KW is costing you more I2R losses than the smaller magnetic field in a smaller machine that is loaded to 80%. But it's your fuel bill.
    A wildly oversize generator will cost due to other efficiency losses. You will still be paying for extra windage, hystericous and losses in the magnetic flux path.
  As far as storing extra rotating energy in a 5KW rotor vs. a 15KW rotor. You can't see the difference.
  In fact your 5KW generator will happily make 15KW for a minute or two if the engine has the guts to turn it. 
  If you want to oversize for high inrush starting loads, then spin several hundred pounds of metal at 1800rpm on the generator shaft.
  Why the obsession with  starting capacity? Do you have a 5HP single phase deep well pump or are you starting and running a 100ton punch press in a stamping plant?

diesel guy

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Re: SIZING A GENERATOR FOR HOME USE
« Reply #21 on: December 15, 2007, 03:25:38 AM »
oliver90owner,

Your absolutely correct and I didn't mean to be degrading at all, I just sent the post without viewing your last post. But doing a full test as you and I mentioned would allow the engine to operate not only at peak efficiency but reliably. I’m a true die hard testing person on my other projects and technologies besides the Listers, so I know where your coming from. Thanks for your input.

Diesel Guy


cujet

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Re: SIZING A GENERATOR FOR HOME USE
« Reply #22 on: December 16, 2007, 01:23:19 AM »
cujet,
 There is one thing you missed and it is the most important. The stored kinetic energy "within" the flywheel on the generator "exceeds the stored kinetic energy on the heavy flywheels 
Diesel Guy



Did not miss that one, as I have exactly the same pulley, and I took that into account. Also, my ammeter shows nowhere near 5X normal load during starting of a 5 ton AC. Simply put, there is not enough stored energy to drive the 15KW ST head to capacity. Nor is there enough HP.

Chris
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diesel guy

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Re: SIZING A GENERATOR FOR HOME USE
« Reply #23 on: December 16, 2007, 11:00:44 PM »
Chris,

The information in your last post is exactly correct, we are looking at "sizing a generator for home use" in different ways, you were looking at the generator head working at full load and we both know this would be more than enough to "stop" my engine, never mind slow it down. As I mentioned previously, there are two reasons for such a large generator head.

First, it can easily handle high initial spikes and then the 2-3 second surge for starting motors and the other is that the bearings are larger than a properly sized generators, which can support such a large mass on the shaft (120+ lbs.) without over working the bearings. This setup is my alternative backup system and produces 4,250 watts continuous. My primary power system is a large 4,000 amp/hr. 12 volt battery bank with large inverters with wind turbines as an energy input. If this primary system goes down, I need a system that can operate 24/7 without battery/inverters/wind and provide reasonable fuel economy due to a long term operation if necessary and still enable the high surges as mentioned.

I have a large family with 2 large freezers, a large refrigerator and a 3/4 hp well pump (high surge loads). The oversized generator head and heavy pulley allows me to operate lights, computer and screen television set without worrying about unacceptable frequency variations and voltage droop without the need for any vulnerable electronic voltage regulator and electronic governor systems. My backup setup consumes slightly more fuel than a properly sized generator head design. This setup still provides lower fuel consumption than operating a IDI 12/2 to handle the required surges, 24/7.

This DI system is designed to offer the fuel economy of slightly more than a IDI 6/1 with a properly sized head and then enable a surge capability approaching or matching a 12/2 with light flywheels for 2-3 seconds with a properly sized head without additional flywheel mass on the rotor. Also, it is fully mechanical and basic without any sensitive electronic systems to fail. As I mentioned in other post, I design my systems fully redundant and I can fix the power system with just a rectifier, brushes, belt, ect. I'm in the process of designing a high powered motor/generator system that has no electronics as well to add to this backup system, therefore I can still convert the produced electrical power from the wind turbines to usable electrical power. It will operate at a lower efficiency level than inverters but will operate in the most extreme circumstance and can be fixed in minutes if required. Putting all the eggs in one basket is not part of my plan, I'll rather have the additional operating cost of fuel as an insurance policy to meet my set requirements on my backup system that stays operational, this is a well thought out system that meets my needs with a full understanding of it's mentioned shortfalls.

Like how Doug said previously, everyone's needs are different, not saying who is right or wrong here just this is how I do it with the engine timing/generator design and each persons needs are different. I started this post just to show how starting motors consumes a large amount of electrical power that should be in the set design. Chris also, some motors have higher starting requirements than others, your fortunate by the lower readings. I appreciate everyone's input, it helps everyone design their own special system to meets their needs by looking at the advantages/disadvantages of each system, one shoe don't fit everyone's foot.

Diesel Guy

jzeeff

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Re: SIZING A GENERATOR FOR HOME USE
« Reply #24 on: December 16, 2007, 11:23:28 PM »

Someday, when grid-tie inverters get inexpensive, you will be able to maintain a 12V battery and when a big starting surge occurs, the inverter will kick in and add the necessary power.  This would allow sizing the generator for the normal load, not the instantaneous peak load.

Or just use a big flywheel and a larger generator head....


buickanddeere

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Re: SIZING A GENERATOR FOR HOME USE
« Reply #25 on: December 16, 2007, 11:36:46 PM »
   5X, 10X what ever spike refers to the current only in the 1st cycle or two when the motor's contacts are initially closed before back EMF is induced by the rotating rotor.
   If you save a trace of starting current. Depending on the rotor's resistance and if it's a single,double or triple bar design. After the initial current spike in the 1st cycle or two. Inrush current drops to locked rotor current until rpm builds to at least 30-60% of rated speed. The locked rotor current LRC can be in the 3X to 6X range depending.......When the rpms rise enough to open the starting winding's centrifugal switch. Current will drop to less than 2X rated FLA on the way up to rated speed. 
  So if you look at the "area under the curve", starting inrush current is really only 3X or 4X FLA.
  If your power supply can supply that LRC  for a couple of seconds, you are away and running.
  As for starting requirements of fridge or freezer compressors. The smaller compressors per cubic ft used in modern freezers/fridges start very easily compared to the "bad old days".
  The well pump being a centrifugal load rather than reciprocating  load to start. All it needs is 2X to 3X FLA to wind up to speed. Not a hard starter either.
   So unless you are doing a dead cold start with all three motors starting at once. Sizing both the generator and engine for continuous use at 80% of max rated capacity should suffice.   

Doug

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Re: SIZING A GENERATOR FOR HOME USE
« Reply #26 on: December 17, 2007, 12:46:58 AM »
Where are you running not triple bar rotors?
I've never even seen that......

Quote Diesel guy:

"Like how Doug said previously, everyone's needs are different, not saying who is right or wrong here just this is how I do it with the engine timing/generator design and each persons needs are different. "

Yes everyones needs are different but I still don't agree with using too big a generator head. These generators we a using are not very efficient from an electrical standpoint to begin with so I don't think you will realy see the difference in fuel burn from a2.5 to 5 kW head on a 6/1. You might notice it on a 7.5 but some people prefer that size becuase they want to be able to draw the full rating of 3500 watts threw one leg only if they need too. 

More fly wheel mass would be better than a bigger head of you want surge power and smoother opperation.
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buickanddeere

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Re: SIZING A GENERATOR FOR HOME USE
« Reply #27 on: December 17, 2007, 02:54:53 AM »
   I forgot all about that one. To be able to draw the engine's full rated while only using 1/2 of the alternator. Keeping loads balanced is well nigh impossible.
   I'm cheating like crazy with my current 5500W standby generator. It's wired for only L1, L2 and chassis ground from the alternator to a 7.5KVA single phase transformer. From the transfer switch comes the L1,L2, Neutral and ground to the transformer.  There is a 4.0Amp power factor correction capacitor in there too.
  Don't worry now about having only 3000W load only on one line of the generator and having the breaker trip. The transformer takes the 240 and handles the 120/120 imbalances.

diesel guy

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Re: SIZING A GENERATOR FOR HOME USE
« Reply #28 on: December 17, 2007, 05:32:57 AM »
All of you bring up great points and that's what makes this forum such an asset to allow minds to look at something and we all see through a slightly different prism, which is fine.

jzeeff,

You got it, just the way I see it. Years ago when Trace came out with the 5548 inverters I purchased two. They did not last long at all, so I sent them back and got two more. Some time later the same problems occurred. The automatic transfer switch, digital display and battery charging problems, they are over rated inverters. This is why I went the other route with the "big flywheel and a larger generator head" you mentioned because durability and reliability are everything and I would not want to count on those advanced controls and options on these inverters, I couldn't sleep right at night knowing this is all I had for my back up system for my family, forget it.

buickanddeere,

If everything was just for a backup system your design would be fine, but as I mentioned in earlier post I designed this generator to handle all the motors starting at once and still have acceptable frequency and voltage so my sensitive equipment computer, screen tv don't get destroyed. The military wouldn't design a system without taking into account the highest surge rating and so won't I either. If my daughter cooks popcorn in the microwave then my son flushes the toilet at the same time, also my refrigerator and freezers start, my system I designed is not over sized, it is barely powerful enough to pull those surges combined. As far as the transformer goes, I used a 8 kw step down 240/120 volt on my 10 kw marathon/Isuzu LB1 generator, allowing me to put 120 volts in each of my 5548 inverters and your right they are very efficient. I didn't need to do that but if on inverter went down I had another exact 8 kw step up transformer 120/240, allowing me to power the home with limited power.

Doug,

I know you don't like over sized generator heads  ;) but if I just placed a heavyweight on a properly sized generator head I could have a shortened operational life of the small bearings which is unacceptable for me. The big generator head provide durability due to the heavy flywheel mass (120 lbs.) don't bother it much.

So overall I agree with all of you, but like I said reliability and durability first and fuel efficiency second. If anyone could show me a more durable and reliable route (any Lister type engine/generator/rpm/configuration) that burns less fuel (for 24/7 operation) than my DI 14/1 operating at 600 RPM and still be able to handle the high surges stated with no electronics to fail, then I'm all ears.

Until then I stick to the basics 'all mechanical system' with heavy engine and generator flywheels and built it heavier than I need (including my H beam frame), also set it up to operate 24/7 indefinitely if required. When the large surges hit, the heavy generator flywheel and large bearings absorbs a lot of the sudden shock. Enabling a somewhat buffering effect to the belt and engine internals, that's where my lazy timing also comes in, allowing the engine to pull smooth and steady for extended time with minimum engine wear.

Diesel Guy


Doug

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Re: SIZING A GENERATOR FOR HOME USE
« Reply #29 on: December 17, 2007, 05:42:43 AM »
Well Diesel guy, you can always cut a steel plate down and add that for fly wheel mass.....

More eficient?
Well, here's somemthing I have been thinking about. I have a 13 and 18 Hp gas engines and I have been thinking about adding stand by asyncronous generation on demand.

Its realy a freaking nightmare to try and bring additonal units online as required and keep the system stable. But on the upside can you amagin how much noise I could make with 3 engines runninng?

I  love the idea of the 14/1 with for my taste a 8,000 watt head. I realy would engine taking on a second project with that or even a large GM 90 20/1. Big singles are the best choice I belive
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