any input would be great. we are using a 5000 watt generator, (7hp i think) to do some tests. is the input to turn this or any generator linear?? meaning, this generator says max output at 3500 rpm, what i am wondering is, at 3500 rpm, the motor needs to be at least 7 hp to turm it, is this right, and does this mean a 3.5 hp motor would only turn this generator to only 1750 rpm??? or is there a "spike" in input needed to turn it at higher rpms verses lower or vice versa?
what i am trying to get at is, is there any way to figure out how much hp i am using to turn the generator at a lower rpm than the max of 3500???
If I understood you correctly what you are asking ... then all dependes are upon about the generator,
loosely speaking:
When permanent magnet generator then all is in linear addiction to RPM (up to max power ( depends about copper wire, iron core, magnets ...)) voltage as well as power,
When wound rotor then linear dependency, when independently stabilized excitation (for example 12V direct to rotor coil) then output voltage changes linear to RPM - exact like PM Gen.
When to use step-down voltage regulator, then output power will depend about RPM up to max perf. (of course you have to reckon with minimum RPM too ...)
When wound rotor connected with output without any stabilizing circuits then output voltage will be very-very non-linear to RPM ...
When wound rotor and voltage stabilizer (like car alternator) - then output voltage is stabil - max power depends about RPM (op till declared max power).
means
When you driving your gen (voltage stabilisator through rotor coil) 5000W / 3500 RPM then with 1750 rpm you can get only half of output power.
Possible it was not what you asked,
my English is true DIY (selfmade ;-)
Cheers,
khabe
kind of answers me, i am not sure what type of generator this is, it was a standard gas generator we purchased, removed that gas motor and we are using the actual electric generator. what i am trying to figure out is can i use a simple graph to estimate the input power required to turn the generator from 0 rpm to 3500.
example, if i can turn the generator at rpm of 500, 750, 1000, 1500, can i deduce that it requires X Horsepower to do this??? based on the graph ?
I take it that this is a generator used to replace 50Hz utility power?
If it is, the answer would have to be generally "No". All generators that
are meant to service demand electrical load need to have a regulator
that dictates how much current is allowed to flow through to it's field coils.
So the generator will adapt to electrical load resistance demand by altering
it's field strength, trying to keep it's output voltage constant. Then it expects
the prime mover to change it's output torque via a throttle governor to keep
the RPM's constants.
An AC generator needs to have a precise RPM to have it's n* magnetic poles
hit per second to generate the correct Hz frequency for the AC output. This
controller could very well be resonant. So drifting off the correct RPM and not having
the prime mover torque be controlled by a governor sounds like a recipe for system
instability. Most likely the regulator won't even enable the electrical output until RPM's
are within 10% bounds of those required to prevent from damaging the load electrically
as it first comes up or engine shuts down.
There is also something called a "digital" generator that do things somewhat
differently, using an alternator and an electronic DC to AC inverter, though I
doubt that they are in that 5Kwatt power range at this time.
What you need is a dynamo generator meant for a "Brake Horsepower Dynamometer".
That would be expected to run at different RPM's and generate calibrated DC power output.
It may have the same mechanicals as any other generator but the field current regulator
will be very different. Alternatively one could see what is required and redesign the
utility power generator regulator to perform like one in a dynamometer and get rid of
any resonant aspect of the utility generator. Also, most AC stand-alone generators
have an "exciter" which is a small permanent magnet magneto for generating the
field-current initially while the generator section comes on-line.
:S:MarkSCoffman
the generator isnt being used for its power output, yet, we are only using it as a "load" on our motor and what we do know is if we can turn it , the generator at 3500 rpm, put a load on it, by plugging components in to it, and are able to continue turning it at the rpm needed, we can make our evaluations.
Gen needs to run at 3500rpm to maintain the set voltage. The HP is needed for amps. 700watts=1hp. 7hp x 700=4900watts
i am not really concerned about the output, what i am looking for is basically can i look at a generator like a generic dyno up to the 3500 rpm. i know that if i turn it at 3500 rpm, i am using the required hp to do that, but can i guage how much power is being used at any rpm lower than 3500?
How much power you need to spin it up to 3600 rpm?
My God!
It depends about load of generator and about losses.
When nothing switched to output of generator then the power you need to spin it is equal to losses like bearings friction and magnetic games included drag and even cogging between stator and rotor what highly depends about design - total efficiency of your generator depends about design and used materials, when generator loaded then few more losses will come on like eddy losses, iron losses copper losses ... Good generators has at least 90% of efficiency. Most of
companies declares even higher - in reallity its mostly like bluff.
When you want to load this generator with 1kW - then also your engine must to be able at least for 1 kW + losses ...+ reserve ...
And ... you have never told us what kind of generator - is it DC or AC ...when dc output then will you need fixed frequency or not ...
cheers,
khabe
regular store ac generator.
here is where this is pointing.
if i can make my motor turn a this generator at its 3500 rpm, and the generator has load on it, ie accessories plugged into it, and i am using less than 5000 watts to run my motor....... we are in the green.
what i would like to know is if i can turn the generator at any rpm lower than 3500, can i deduce how much hp i am using..??
You did not tell us - frequency important or not - when inductive load then it plays not small role ...
And I dont know is it PM (permanent magnet) generator?
but ok,
when you are able to measure output voltage and current (Amper clamp and Voltmeter ;-) and if you know true efficiency of actual generator - then its simple to calculate the power you using from Engine using for example simple ohm law where P= I x U ... you have only add the losses ... I offer 20%
And when you turn the generator at any rpm lower than 3500 - you also can see wat will happen with voltage and current ... and then to tell us ::)
Regards,
khabe
Do you use just an electric motor to spin it (Gen)?
Are you trying OU Motor-Generator :o
Do you use just an electric motor to spin it (Gen)?
Are you trying OU Motor-Generator
yes.
Then I dont understand at all ... why you do not measure what you spending and what getting. The only things you need are pair of clamp -and voltmeters ... not any needs to ask from anothers how the changing of rpm acts to power ::)
cheers
Hereby my bet:
P_out = P_in - (subtract) motor losses - (subtract) generator losses >:(
Quote from: cameron sydenham on September 17, 2008, 04:49:07 PM
regular store ac generator.
here is where this is pointing.
if i can make my motor turn a this generator at its 3500 rpm, and the generator has load on it, ie accessories plugged into it, and i am using less than 5000 watts to run my motor....... we are in the green.
what i would like to know is if i can turn the generator at any rpm lower than 3500, can i deduce how much hp i am using..??
I don't believe you can because I don't think that particular generator was designed to run more than 10% away from correct RPM.
It certainly should not hurt to try as the generator probably won't be damaged. The 5KW is the *maximum* power the generator
could possibly put out. You may want a bank of incandesent lamps where the (100W) bulbs are indiviually switchable to act
as a dynamic load. To know the power output at an particular time you will *need* to calculate it based on the current voltage
times the current amperage output of the generator. A 100Watt bulb then is not 100Watts if the input voltage is half.
So you are going to *have* to be calculating the power output mathematically anyway at less then 100% voltage.
So for the test it would make more sense to run the input generator at 3500Rpm with no load. Then begin to switch in lamp loads
while trying to adjust your prime mover to supply 3500RPM. When you can no longer hold 3500RPM. then the lamp setting
is the maximum power you prime mover can supply.
You should look up CVT continous variable transmission. There is a CVT gearing unit that has a manual dial disk. As the prime
mover begins to slow down under load you could use the CVT to reestablish 3500 RPM output for the generator.
You should also google "syncronous generator" or "syncronous alternator" These are genreators that idle as motors.
Then you use the CVT to "overrun" them. The more torque you put in the more you overrun the motor idle RPM
the more power goes out on the line. The line already needs to be powered by utility current. This is used for
wind generators and water generators.
:S:MarkSCoffman
yea, i have considered a cluthch or tranny style like you spoke about. as far as banking lights, we have that. i kind of figured that a generator can not be used as a rude dyno, all is fine though, as long as i can turn the generator at a certain rpm and put load, 5000 watts on it, and continue to turn at desired rpm, all is good.