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Consumer A buys Generator B. ;)

1.Generator is rated at 10Kw at 88 amps (60 Hz) spinning at 1800 rpm.
Power One-Phase
Load Amperage at 120 volts ---
Maximum Load 88 Amps
Continous Load 83 Amps
Load Amperage at 240 volts ---
Maximum Load 44 Amps
Continous Load 42 Amps

Fuel used
Consumption at 0 load .35 gallons/hour
Consumption at 1/2 load 0.55 gallons/hour
Consumption at 3/4 load 0.76 gallons/hour
Consumption at full load load 0.94 gallons/hour

Customer A finds that the Generator is generally under no load most of the time, therefore decides to lower the rpm to 800.

Fuel used at this rpm at almost 0 load = .08 gallons per hour.

Problem is that at 800 rpm, voltage drops to about 32 volts at 27 Hz.

Goal: maintain 120 volts and 60 Hz if possible at 800 rpm under no load. As rpms increase I want to maintain voltage until its reaches its rated 1800 rpm where everything is gravy.

Ideas? Suggestiongs?

Last edited Mon, 31 Oct 2011, 3:38pm by Duff

Lots of suggestions in chat but you refused to listen, Surprise Surprise!!

hbert, I dont think you actually read the problem. There is nothing here in my proposed goal which will be violating the laws of thermodynamic efficiencies. All I am doing is saving fuel.

Heres one idea.
http://www.otherpower.com/pmgreg.html

doofy wrote:

Consumption at 0 load .035 gallons/hour
Consumption at 1/2 load 0.55 gallons/hour
Consumption at 3/4 load 0.76 gallons/hour
Consumption at full load load 0.94 gallons/hour

Customer A finds that the Generator is generally under no load most of the time, therefore decides to lower the rpm to 800. [...]

matt wrote:

doofy wrote:

Consumption at 0 load .035 gallons/hour
Consumption at 1/2 load 0.55 gallons/hour
Consumption at 3/4 load 0.76 gallons/hour
Consumption at full load load 0.94 gallons/hour

Customer A finds that the Generator is generally under no load most of the time, therefore decides to lower the rpm to 800. [...]

Customer A should recognize from the above data that he isn't going to save any money that way, and leave the generator as it is.

Actually there is a typo
Well I save money by lowering the rpms to 800 during no load. At 800 rpms with 0 load I only burn .08 gallons per hour. AT 1800 it burns .35 gallons per hour. Roughly 4 times the fuel saved.

Why do you conclude that you will save gas by lowering the generator rpm?
Lowering the motor rpm will possibly make it more efficient at low loads but incapable of handling high loads so to lower the motor rpm you need an automatic gearbox and something clever to control the gearbox.

Output frequency of simple generator like that is always dependent on rpm, so you have to rectify the output to dc and then use inverter to form suitable voltage/frequency ac. Additionally you'll need control logic to rev it up when load increases. Not simple or cheap.

Wouldn't you be better off with a UPS to give a 240 volt supply at 44 Amps for a short period (minutes) and leave the generator switched off unless current was actually being drawn. That way there is almost no energy consumed unless there is real load.

Actually, an EESU would do this very nicely..... But in the meantime lead-acid batteries are pretty cheap (and nasty).

You would still need the control equipment though.

Regards,
Peter

Technopete wrote:

Wouldn't you be better off with a UPS to give a 240 volt supply at 44 Amps for a short period (minutes) and leave the generator switched off unless current was actually being drawn. That way there is almost no energy consumed unless there is real load.

Actually, an EESU would do this very nicely..... But in the meantime lead-acid batteries are pretty cheap (and nasty).

You would still need the control equipment though.

Regards,
Peter

Well I did consider this and I can automatically start it given the current depth of charge of a simple deep cycle battery and an inverter which would supply the immediate energy needed and the start up energy for the generator. My only issue then is switching from the inverter power which only handles 3000 watts of "Modified sine wave" performance to the 10000 watts of pure sine wave performance. Seems like it would be a more complicated system that way.

Seakell wrote:

Why do you conclude that you will save gas by lowering the generator rpm?
Lowering the motor rpm will possibly make it more efficient at low loads but incapable of handling high loads so to lower the motor rpm you need an automatic gearbox and something clever to control the gearbox.

Because I fracking measured it.

As load increases I automatially increase rpms up to its most efficient 1800. My issue is leveling the 120 volts at a variable rpm.

Bone wrote:

Output frequency of simple generator like that is always dependent on rpm, so you have to rectify the output to dc and then use inverter to form suitable voltage/frequency ac. Additionally you'll need control logic to rev it up when load increases. Not simple or cheap.

Yes you are correct. This is similar to what I wrote techno. Id rather not convert to DC if I can avoid it.

The rpm controller is just a simple arduino mega programmed to a stepper motor which monitors the voltage drop and keeps it from going down. The stepper motor is linked to the throttle control. I already had the auduino and the programming was on me, so all in all, that was about 30 bucks. Anyways.....

You should look into wind power inverters. They are typically capapble of handling wide input voltage range, and models with adequate output power and pure sine wave output are available. Expensive solution, but if there really was cheaper and easier way to do it, then nobody would buy those inverters.

Last edited Tue, 01 Nov 2011, 2:27pm by Bone

Bone wrote:

You should look into wind power inverters. They are typically capapble of handling wide input voltage range, and models with adequate output power and pure sinne wave output are available. Expensive solution, but if there really was cheaper and easier way to do it, then nobody would by those inverters.

hbert wrote:

Lots of suggestions in chat but you refused to listen, Surprise Surprise!!

Hint: it wasnt you.

If you want to avoid TP's UPS approach how about having two generators, one small (say 2-3 kW) runs all the time then the 10KW one is only started when large loads are needed.
Could you give some more information on your installation, such as a typical daily/weekly load profile and what the major loads are ?
Do you know in advance (even a few seconds) when the large loads are needed ?
Even more left field would be to use two ICE motors and a pair of mechanical clutches to swap over but I prefer the two generator approach as it doesn't require custom mechanical engineering.

SimonB wrote:

If you want to avoid TP's UPS approach how about having two generators, one small (say 2-3 kW) runs all the time then the 10KW one is only started when large loads are needed.
Could you give some more information on your installation, such as a typical daily/weekly load profile and what the major loads are ?
Do you know in advance (even a few seconds) when the large loads are needed ?
Even more left field would be to use two ICE motors and a pair of mechanical clutches to swap over but I prefer the two generator approach as it doesn't require custom mechanical engineering.

Yes a smaller generator was suggested but again that doubles the potential maintenance and everything else related. I have not done a load timeline as it would be very unpredictable. but I always need 120 volts for some monitoring equipment that only takes 100 watts or so.

Thanks for the extra detail, couple more questions though ;-)
1) Could you split the supplies to the monitoring system from the large loads ?
2) Does it matter if the output takes a few seconds to recover once the large loads are applied ?

SimonB wrote:

Thanks for the extra detail, couple more questions though ;-)
1) Could you split the supplies to the monitoring system from the large loads ?
2) Does it matter if the output takes a few seconds to recover once the large loads are applied ?

1. sure as long as source energy is derived from 1 generator.

2. Yes it would matter, I was thinking a medium duty Capacitor could be used to provide energy while Genny spins up to speed (Takes about a second to go from 800 to 1800 rpms). The hard part would be getting it (cap) not to discharge while ideling.

Use active inverter with some supercaps.

Doofy, I see you're bound and determined :)

Ok, so you aren't interested in making a decision based on Fully Burdened Cost and thermodynamic metrics like hbert suggested. He's right you know.

But I get the sense that cost, effort and time out of your life do not tally in the minus column as it would with most people - ie, you like the challenge and enjoy the prospect (among a myriad of other considerations). That in itself is worth something. I think I get it.

I'm thinking your aptitude leans more towards mechanical than electrical. Here's a suggestion: if the engine and generator assemblies in your 10kW unit aren't too difficult to separate, then separate them and mount them on a steel jig. Find an old POS beater Civic or Micra at a junkyard or on Craigslist, and rip out the CVT and link it between the ICE and the gen.

Rig up a centrifugal speed controller that uses the generator RPMs as input, and whose push plate output drives a lever that varies the CVT ratio. Adjust the lever arm and the orbit radius / mass of the centrifugal controller so that the gen RPMs is always 1,800 regardless of the RPMs of the ICE (is it diesel? Are you making your own fuel? I think I understand what you're trying to do here).

You could create an electronic/electromechanical circuit that does the same thing, but the fundamental physics (and therefore the equations that describe them) will be exactly the same. Doesn't really matter. Whatever medium you're most comfortable with. Watch for slack (low impedance hysteresis) that produces backlash (long time constants) that can result in pogo-ing (oscillations).

If you do decide to go this route, back-channel me and let me know how it goes. It strangely sounds kind of fun. I haven't been able to get my hands dirty for over 30 years. I think I miss the tactile stuff. My grand dad owned a taxi company and a service station. I can still smell the grease and gasoline. I think I'm of two minds about the death of the ICE. Oh well :)

spaceballs_3000 wrote:

Use active inverter with some supercaps.

I like the Caps idea, can you give me some more detail?
thanks sb

Daniel R Plante wrote:

Doofy, I see you're bound and determined :)

Ok, so you aren't interested in making a decision based on Fully Burdened Cost and thermodynamic metrics like hbert suggested. He's right you know.

But I get the sense that cost, effort and time out of your life do not tally in the minus column as it would with most people - ie, you like the challenge and enjoy the prospect (among a myriad of other considerations). That in itself is worth something. I think I get it.

I'm thinking your aptitude leans more towards mechanical than electrical. Here's a suggestion: if the engine and generator assemblies in your 10kW unit aren't too difficult to separate, then separate them and mount them on a steel jig. Find an old POS beater Civic or Micra at a junkyard or on Craigslist, and rip out the CVT and link it between the ICE and the gen.

Rig up a centrifugal speed controller that uses the generator RPMs as input, and whose push plate output drives a lever that varies the CVT ratio. Adjust the lever arm and the orbit radius / mass of the centrifugal controller so that the gen RPMs is always 1,800 regardless of the RPMs of the ICE (is it diesel? Are you making your own fuel? I think I understand what you're trying to do here).

You could create an electronic/electromechanical circuit that does the same thing, but the fundamental physics (and therefore the equations that describe them) will be exactly the same. Doesn't really matter. Whatever medium you're most comfortable with. Watch for slack (low impedance hysteresis) that produces backlash (long time constants) that can result in pogo-ing (oscillations).

If you do decide to go this route, back-channel me and let me know how it goes. It strangely sounds kind of fun. I haven't been able to get my hands dirty for over 30 years. I think I miss the tactile stuff. My grand dad owned a taxi company and a service station. I can still smell the grease and gasoline. I think I'm of two minds about the death of the ICE. Oh well :)

The cvt idea is good. always turning the genny at 1800. Suprisingly I had not thought of that. I dont want to seperate the 2 right now, but it is a rather genius sugestion and I suspect I could build one easier than I could try and retrofit something else. CVT transmissions are suprisingly simple when you break it down.

I still want to forge ahead with the electrical options first. When those are all exausted, I may try this.

fyi, yes its a diesel. and yes I can get my fuel for free. 400 gallons at a time. ;)

doofy wrote:

1. sure as long as source energy is derived from 1 generator.

2. Yes it would matter, I was thinking a medium duty Capacitor could be used to provide energy while Genny spins up to speed (Takes about a second to go from 800 to 1800 rpms). The hard part would be getting it (cap) not to discharge while ideling.

I Assume the "medium duty capacitor" would only provide "ride through" for the monitoring system not the full 10KW, let me know if I've misunderstood.
My suggestion is:
1) Split the low power stuff from the high power loads.
2) Use a wide input range AC-DC supply to convert the generator output to DC, at say 24 or 12 volts DC. You may not be able to slow the generator all the way to idle as most DC-DC convertors only work over the range 85 to 250 Vac.
3) If you want decent ride-through use an old car / tractor / boat battery to hold up the 12/24 volts while the generator spins up, it won't need to be in great condition.
4) Feed DC output into a small invertor (100W inverters are only $50).
5) Take output from inverter to run the monitoring system.

Is this anything like you need ?

One final suggestion, If the ICE drives a traditional auto alternator, this would provide 12 volts DC to run the invertor and hence the monitoring system without having to do anything on the high voltage side.

Thanks all, something to chew on. The thing I dont understand is why cant a big enough linear or switching regulator be used? Anybody have experience with these types of voltage regulators? and where to aquire?

Thanks

doofy wrote:

Thanks all, something to chew on. The thing I dont understand is why cant a big enough linear or switching regulator be used? Anybody have experience with these types of voltage regulators? and where to aquire?

Thanks

By the way I like the CVT approach too, bear in mind you will be putting around 20 HP through it at full output, so it will need half decent engineering. I'll suggest looking for a CVT box that was mechanically controlled so you don't have to reverse engineer the electronics.
Finally, try and find one that has a similar rated power to minimise losses in the gearbox itself.
Anyone got a DAF variomatic gearbox in their shed ?

Last edited Wed, 02 Nov 2011, 4:06pm by SimonB

doofy wrote:

spaceballs_3000 wrote:

Use active inverter with some supercaps.

I like the Caps idea, can you give me some more detail?
thanks sb

Place an active inverter between the generator and your equipment. i.e. AC to DC to AC. Active inverters are used in hi end stuff, seen a few labs setup like this.

Then place the caps at the DC point, or batteries if you want.

The trick that sophisticated wind generators use is to
either have two sets of windings or to dynamically change
the configuration of the windings based on RPM and load
requirements...

doofy wrote:

Thanks all, something to chew on. The thing I dont understand is why cant a big enough linear or switching regulator be used? Anybody have experience with these types of voltage regulators? and where to aquire?

Thanks

They can be used, and devices like this already exist, just depends on how much you can afford.

If cost if a problem for you, and want to go with something you want to build. Just find some Grid Tie Inverter for Solar and Wind that are compatible to run in parallel. Then connect up ucaps/batteries.