Author Topic: Changfa Slow Speed Experiment  (Read 35447 times)

Veggiefuel

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Re: Changfa Slow Speed Experiment
« Reply #15 on: April 27, 2009, 05:01:25 PM »
Wizard,

Not sure I understand you. What does Redstone have to do with this subject ?


Veggie
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Veggiefuel

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Re: Changfa Slow Speed Experiment
« Reply #16 on: April 27, 2009, 05:04:30 PM »


You guys are right, it's not that simple. I proceeded based on RAB's note
Quote....
"If you have something near to the correct sizes hanging around, use them for testing.  It won't make much difference if you cannot get 60Hz, if you are simply testing for resistive load.

I don't have an ammeter (yet), and without such data I don't think this test revealed anything useful.

I will proceed to change the sheaves and get some REAL data.

Cheers,
Veggie
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Jim Mc

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Re: Changfa Slow Speed Experiment
« Reply #17 on: April 27, 2009, 05:31:24 PM »
...

at .7 pf you might only be able to cover about 1.8kwatt of loading
which if this is used to cover motor loads won't leave enough to do much starting, and might cause problems?

perhaps there are some electric guru's that can confirm or refute this concern.


[guru]

Nonsense. 

He's got a 5kW head.  a 0.7 PF is not going to be a problem.

Remember, in this setup, he's limited by the engine power available, not the generator capacity.  And the engine doesn't care whether the generator is loaded with 2.6 kW at 1.0PF or 0.7PF.

[/guru]




oliver90owner

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Re: Changfa Slow Speed Experiment
« Reply #18 on: April 27, 2009, 05:31:36 PM »
Please don't go round mis-quoting me - or rather quoting me and doing something else.  

I said that meaning exactly that.  60hz plus or minus five would likely make little difference for testing purposes.  You are not anywhere 'near', that is very clear.  Nowhere near 4kW either, so that has at least cleared up one facet of your misconception.

RAB

Veggiefuel

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Re: Changfa Slow Speed Experiment
« Reply #19 on: April 27, 2009, 06:23:40 PM »
Hi RAB,

It's not so much that you were miss quoted, It's more along the lines of me not understanding exactly what I was testing for.
No need to get torqued about it.

Veggie
« Last Edit: April 27, 2009, 06:30:45 PM by Veggiefuel »
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mobile_bob

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Re: Changfa Slow Speed Experiment
« Reply #20 on: April 27, 2009, 06:43:53 PM »
JimMc:

"Remember, in this setup, he's limited by the engine power available, not the generator capacity.  And the engine doesn't care whether the generator is loaded with 2.6 kW at 1.0PF or 0.7PF."

i respectfully disagree, or perhaps i am mistaken?

here is my logic, perhaps you can explain the err?

while i agree he is limited by engine power, the head is not maxed out.
at unity power factor (for the sake of discussion) theoretically all the kva generated go to making useful work, measured in kwatts?

if however the powerfactor of the load drops to .7 there is a significant amount of power kvars? that is doing no useful work?
this power is circulating between the alternator and the load, creating nothing but heat

heat requires power to generate, power requires fuel, and remember he is power limited to start with.

so how does he maintain the ability to produce 2.6kwatts for actual work if the load powerfactor starts to slide off unity.

whatever that heat value is must be removed from the other side of the equation? is this not correct?

perhaps my assessment that the derate might go down to 1.8 kwatt output, but certainly there ought to be some derate
to cover for the kvar heating ?

does that make sense?

the reason i ask, is based on discussion with many electrical engineers over the last 10 years or better, probably 20 odd
books on the subject and there being so much contradictory information when it comes to powerfactor.

enlighten me please,, i am all ears here :)

bob g
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mobile_bob

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Re: Changfa Slow Speed Experiment
« Reply #21 on: April 27, 2009, 07:00:24 PM »
JimMc:

to further illustrate my frustration and confusion, here is a quote from an EE forum

quote

In spite of what others are saying... The better PF will reduce the currents in the generator (and other circuits) and have an effect on the fuel consumption.

1. All electrical circuits have resistance ( including the generator windings)

2. Current through any resistance causes heat. W = I2 R (this is Gods Law)

3. Heat is energy and energy is power. Your Generator is supplying the power.

4. The power comes from the fuel.

Depending on the size and design of the machine, the energy savings may be large or insignificant.

What I am saying is that the RVA (I + jx ) currents are useless for extracting power but Resistance losses (due to reactive currents) must be generated by the generator

end quote


and conversely i can find just the opposite position taken from the same thread by another electrical engineer

now generally speaking guys that promote the quoted position above are generally very capable of explaining the position in
terms that seem to make sense, while on the other hand those that would disagree come off with comments like
"why do you care about pf? you aren't charged for it!" (even though i have explained till i am blue in the face that i am
the power company, power companies charge for poor powerfactor from their industrial customers so there must be a concern
and a cost).

so i am serious, i really would like to hear your take on this subject!

thanks
bob g
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Veggiefuel

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Re: Changfa Slow Speed Experiment
« Reply #22 on: April 27, 2009, 08:26:33 PM »
Hi Bob,

Thanks for your comments and recommendations.
The head is only turning at 1332 in the slow speed test, but as everyone pointed out, without voltage and amperage data, there is not enough info to draw conclusions.

In the end, my intention is to run the Changfa 195 at 1250 rpm and belt drive the head with an efficient poly-vee belt at full generator speed.
The head is a 4kw unit and with an assumed 6 HP@1250 rpm from the Changfa, I was hoping to get 2.5kw to 3 kw from the head.

In any case, I am proceeding with the build of my second Changfa project and will report actual data when done.

The unit will be used for charging a battery bank and when the bank is fully charged, the power will be diverted to a heating element in a water tank.
Part of a CHP system which will also make use of coolant and exhaust heat.

Cheers,
Veggie
« Last Edit: April 27, 2009, 08:28:19 PM by Veggiefuel »
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ronmar

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Re: Changfa Slow Speed Experiment
« Reply #23 on: April 27, 2009, 08:29:27 PM »
At any rate, Veggi, you need an amp meter to get any meaningfull load readings at a reduced voltage output from the generator.  That 2.6KW of load is only valid at 120V input.  A harmonically excited ST head is going to be putting out significantly less voltage at 500 RPM below it's 1800 RPM rateing...  I also don't think you are going to get anywhere near 4KW sustained electrical load at only 6-6.5HP input.  You need to take into account the losses in the "V" belt drive.  They make heat under load, and that costs HP to make that heat.  The generator head itself, depending on load, is only at best about 85% efficient.  That is where the tried and tested rule of 2HP per KW of electrical load comes from.  If you can get 5.4HP out of the engine at 1000 RPM, it is a pretty good bet that you are only going to be able to sustain 2.5KW of electric load after all is said and done.  The low flywheel mass is also going to limit your reserve energy capacity, and increase your flicker at higher loads.

Good Luck
PS 6/1 - ST-5.

mobile_bob

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Re: Changfa Slow Speed Experiment
« Reply #24 on: April 27, 2009, 08:38:20 PM »
Jens:

just to get this clear in my mind :)

at unity and 100% theoretical efficiency he can hold 2.6kwatt, but

would it follow that at lower pf such as .7 lagging he could no longer support that load
based on the fact that the engine was maxed out power wise at unity powerfactor?

is there anyway to calculate the losses? based on what we have to work with? or are other factors needed?

it would seem upon reflection that we don't lose all the power (kvar), some of it circulates back and forth
between the alternator, line, load, and some of it is converted to heat.

is there a way of calculating the heat loss due to low powerfactor?

could one simply do some accurate fuel consumption tests at max loading and unity power factor, and then
rerun the test at max loading at .7 lagging and subtract from the first test.
the result would be the amount of btu's consumed by the engine to cover the heat losses due to low powerfactor?

actually only about 25% of those btu's burned due to efficiencies of the engine converting fuel to mechanical work, transmission
losses of the drive, and alternator efficiency?

if this is so, then it follows that
low powerfactor cost 4 times the fuel to cover the heat losses associated with it!

so even small heat losses due to low powerfactor heating have significant requirements for fuel to cover them,
so maybe one should be taking a good look at the powerfactor of his system, especially if it is a 24/7 operation
and fuel is expensive?

very interesting

btw, veggiefuel this might be offtopic but
with you going the route you look to be going, maybe this is of interest to your project?

bob g
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Veggiefuel

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Re: Changfa Slow Speed Experiment
« Reply #25 on: April 27, 2009, 08:55:21 PM »
Ronmar,

You make some good points. I would be happy with 2.5kw in the end. Let's see how it works out.

I hear of Lister(oid) 6/1 engines generating 3kw (with a belt drive). That follows the rule of 2 kw/HP.
Let's see if my 6HP Changfa can squeek out 2.8 to 3 kw from the head when fully loaded.
One way to find out !

Heck, if the output is not quite what I want, I can speed up the engine in 100rpm increments until I get it.
That's why I choose belt drives. They have their drawbacks, but they really do offer a lot of flexibility.

Thanks
Veggie
« Last Edit: April 27, 2009, 08:57:04 PM by Veggiefuel »
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mobile_bob

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Re: Changfa Slow Speed Experiment
« Reply #26 on: April 27, 2009, 08:59:56 PM »
veggie:

are you using the st predominately to charge batteries?

st > charger > batteries?

what dc voltage are you working with?

just curious

bob g
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Veggiefuel

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Re: Changfa Slow Speed Experiment
« Reply #27 on: April 27, 2009, 09:01:29 PM »
Bob,

I see where you're going with this....
Maybe I should wrap the gen head with 1/2" copper lines and recover some lost heat ?  ;)

Remember guys, my generator will be spinning at full speed and the output will be limited by engine HP.
Power factor should not be a problem as long as I maintain 60 hz, yes??

Veggie
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Veggiefuel

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Re: Changfa Slow Speed Experiment
« Reply #28 on: April 27, 2009, 09:09:02 PM »
Bob,

The head is actually a 4kw voltmaster. (Rated at 5kw intermittent).
The intention is to have the engine charge batteries, heat water, heat elements, and be available for emerg. power.
The system will be 48 volts.
Still looking for a charger / inverter combo, or perhaps separate charger and inverter.

The batteries/inverter will run the shop and the irrigation/heating/pumping system for the greenhouse and gardens.
Engine will run about 4 hours per day to recharge everything.
Waste heat will be stored in an insulated tank.
Evacuated tube solar panel will assist in heating the water.

At night, a fan coil will heat the shop (and or greenhouse) from the hot water tank.

All running on used vegetable oil.

Veggie
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Veggiefuel

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Re: Changfa Slow Speed Experiment
« Reply #29 on: April 27, 2009, 10:44:14 PM »
Jens,

Thanks for the tips.
I currently have a 100 gallon H2O tank. The shop space I am heating is only 625 sq.ft. and based on 185 deg.f water and a 10,000 btu/hr fan coil I suspect I could run the heater for 5 to 6 hrs (through the night) before the water tank temp drops to 80 deg. f.
I'm learning as I go and when it comes to generators and diesels, this forum has been a big help.

PS: My calculations for a 4 hour heat recharge are based on having a fairly efficient exhaust/water heat exchanger. Know where I can get one ??   ???

Veggie
« Last Edit: April 27, 2009, 10:46:08 PM by Veggiefuel »
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