Lister Engine Forum
Slow Speed Diesel Engines => Changfa Engines => Topic started by: Veggiefuel on March 25, 2009, 09:00:09 PM
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Hi Guys,
Experiment # 16662G2TT34990 Earth ;)
First an explanation, then a question.....
In an effort to reduce noise, vibration, and increase lifespan, I tried slowing down the Changfa engine to 1000 rpm.
The noise reduction was dramatic. One can stand right beside it and talk normally. No earplugs needed.
Noise recordings dropped from 95 dba to 85 dba.
According to the power curve, at 1000 rpm I can expect 5.4 HP or 4.02 kw.
Being coupled to an ST-5 head, I think I could expect a reliable 3.5 kw from the machine on a continuous basis.
Question:
Does anyone see a problem with running the engine at 1000 rpm for the rest of it's life ?
The neighbors won't even know it exists !!!
I really like the idea of having this slow speed Changfa putting away for a long time and I don't want to damage it prematurely.
You can see and hear the engine running here....
(Note the starter wires hanging from the engine, virtually no vibration at all.)
http://www.youtube.com/watch?v=l-AhoFWn4VA
Cheers,
Veggie
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Me? I would think that your expectation of a reliable 3.5kW continuous is the thing that would kill the engine in a very short time. :-\
Unless one third of that is thermal, of course.
According to the power curve, at 1000 rpm I can expect 5.4 HP or 4.02 kw.
If that is an extrapolation of the power curve, beware. Things can drop off the curve very quickly. I like your precision, btw. 4kW (1 sig fig is the best, I would suggest). If it is an interpolation of the manufacturer's spec sheet it should be perfectly operational at that speed, unless they actually quote those figures but warn of possible problems....
Regards, RAB
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The power curve chart does go as low as 1200 rpm so I suppose I could speed up the engine by a couple hundred in order to get into the "safe zone".
How does one know if the lower RPM is causing any problems? Are there some telltale signs that could be inspected from time to time ?
Also, at 1200 rpm, I would get 6.530034335 HP ;) enabling me to pull about 4 kw from the ST5. Still low speed for a Changfa.
Veggie
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Also, at 1200 rpm, I would get 6.530034335???
there is something bad wrong with your engine!!!
i am getting 6.530034336!!!
geesh!!!
:)
bob g
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Hey Bob,
You have done a lot of playing around with your Changfa. What do you think about running them between 1000 rpm and 1200 rpm at say 90% load. ?
PS: The 0.000000001 BHP difference between mine and yours is probably due to elevation differences :D
Veggie
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enabling me to pull about 4 kw from the ST5.
If you mean about 4kW continuous electrical it will still kill the engine in short time.
Try using the well tried and trusted formula of 2HP per kW electrical. Of course, there is always an exception to the rule :)
Regards, RAB
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Hi Veggiefuel, One point to check is the governor response at the low end of the RPM range. Most governor specs only apply from about max. torque speed to max. governed RPM. Below that range,speed droop under load will increase, along with response time. When driving an alternator under these conditions your voltage and frequency can be quite unstable. You may have to try various drive ratios to find a speed where governing is acceptable. Regards, Combustor.
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at 1000rpm you will be doing well to get reasonably stable operation with a 2.5kwatt load
at 1200rpm about 3 kwatt load
these are at around sea level, and 70 degree's ambient
in reality i would not expect more than 2 kwatt at 1000 and 2.5 at 1200rpm in practice.
the engine does not have enough flywheel mass to run stable hz over these load levels in my opinion
and governor work is not going to help much, because flicker is going to be bad if you push it much above these levels
i don't think 4kwatt at either 1000 or 1200 will be a reality on a 195 changfa, making AC power via belt driven genhead.
ymmv
bob g
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I spent a bunch of time in China. I don't ever remember a Changfa type engine running at high speed. Most often, the farmers would keep the RPM low. Very much in the range of what you are running yours at.
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Thanks for the comments everyone.
I suppose the next thing to do is set the sheaves at 1200 rpm, load her up, and actually try it out.
Veggie
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next thing to do is set the sheaves at 1200 rpm,
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.
Regards, RAB
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RAB, (and others)
I took your advice and slowed her down. Then added some resistive loads.
The head started smoking and my appliance wires melted !
Just kidding ;)
Here's the results of a quick test I did today. I'm not sure what can be concluded from this, but maybe one of you guys can help.
First at full speed:
NO LOAD:
Engine @ 1763 rpm
Head @ 1820 rpm (belt driven)
LOADED to 3.6kW/120VAC:
Engine @ 1705 rpm
Head @ 1760 rpm
That got her nice and hot.
(Governor did not hold the engine to the original speed, but that's another issue.)
Then a slower speed test:
LOADED: ( by plugging in two element heaters which draw 1300 watts each @120vac )
Engine @ 1284 rpm (the speed I intend to run when sheaves are changed)
Head @ 1332 rpm
When I turned on the loads (2.6kw total) she grunted a bit but handled the load nicely.
Here's where I need some help. I'm not sure what I accomplished by running the 1800 rpm head at 1332 with the resistive loads.
My estimated max. available power at this speed was between 2.6kW and 3kW.
Did the loads I added actually demand 2.6 kW of power from the head? and did they get it?
Does this test confirm that I can provide 2.6kW of power from the system once I change the sheaves to allow the engine to run at 1280 rpm while the head runs at 1800rpm ?
Thanks,
Veggie
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When you say 2.6kW, are you actually getting 120V? For a trick like this you need a voltmeter and an ammeter to work out the power. Preferably use analogue meters (or check to make sure your DMM is true when way off normal frequency).
If you have an AVR, the voltage may have been controlled well, but I am suspecting that may not the case.
You are certainly moving in the right direction. The 4kW seems to have evaporated, so we are talking sensible practical figures here. You will be close to the correct result if the voltage has held up or close to the reult you find using Ohms Law etc.
Regards, RAB
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another concern if i read your report right
"Then a slower speed test:
LOADED: ( by plugging in two element heaters which draw 1300 watts each @120vac )
Engine @ 1284 rpm (the speed I intend to run when sheaves are changed)
Head @ 1332 rpm"
if the genhead speed is truely 1332 and not a misprint, as RAB points out, you need to know if you are truely getting 120vac
and find it acceptable to have ~44 hz, and most important you will want to measure the rotor current and make sure the AVR
is not over driving the field current above nameplate rating.
some st heads apparently are very unforgiving of over current to the field with burnouts the reality.
this of course only if the head is turning at 1332 and not 1832rpm.
can you clarify?
another concern i would have is,
what if you are correct and you are getting 2.6kwatt at 1332 gen speed,
if you now change the drive ratio to get to 1800, it is doubtful you will have the 2.6kwatt capability.
also remember, in any case the 2.6 kwatt is at unity pf, which is ok with purely resistive loads, but
if you are trying to drive a mix of loads your pf is likely going to be well below unity, which means
the amount of power available to do actual work goes down.
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.
bob g
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Redo this test with redstone at 1330ish rpm with head at 1800 once have correct pulley?
Cheers, Wizard
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Wizard,
Not sure I understand you. What does Redstone have to do with this subject ?
Veggie
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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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...
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]
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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
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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
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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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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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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
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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
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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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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
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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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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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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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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
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Redo this test with redstone at 1330ish rpm with head at 1800 once have correct pulley?
Cheers, Wizard
OOPS!
Change Redstone for changfa and my question applies, been awake too long overnight twice. :)
Cheers, Wizard
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Wizard,
Aaaahhhh!
Now it makes sense.
Easy to get the two mixed up. Both are excellent powerhouses ;D
Veggie
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harvesting and putting to use low value heat is certainly a challenge
radiant heat from the engine, genhead, piping etc, add up to significant btu's, but
not generally high enough in temp to do much real work, except for space heating.
the smell of diesel and oil limit that use though, wives and kids don't seem to have the same
appreciation for either :)
have you considered a compressor/freon heat pump system
iirc you have a fully enclosed genset, maybe an evap in there could take our the low value heat, move it
where it is usefull and leave the smell behind?
in any event it will certainly improve the quality of the heat, so it could also be used to preheat domestic water
in times where domestic space heating is unneeded?
i am using a sanden rotary compressor and plan on driving r22 to do just that, i figure why not take all the waste heat
and put it to use?
i wanna try and grab all the waste heat normally left to flitter away.
anyone else going that route?
bob g
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we need a totally new forum dedicated to micro co/trigerneration
there are lots of forums for the big boys, that build cogens in the megawatt class
and there are forums for commercial manufactures of mid and small size units, but
to my knowlege there is no such thing for micro units designed and built by individuals
at least that i am aware of, at least none that are serious about doing so.
there are literally dozens of approaches to this subject, everything from heat pumps, exchangers
and heat pipes
all which are within the ability of a relatively sharp guy in a home shop in my opinion.
and there is literally tons of parts, bits, and pieces ready made and ready to be adapted for our uses.
as well as many good how to books written to make these technologies a reality.
one can certainly buy all the parts, assemble, and fit a heat pump system, and if forced to hire an hvac guy to
come out and evac/charge the system.
for that matter a complete system can be removed from a car at a wrecking yard, without the loss of refrigerant
all in one piece given enough time and some persistance, i know because i have done it.
an old ford wagon with an r12 system can produce about 20-25kbtu without much problem
and about 50 percent more if it is recovered, flushed and the oil changed, and r22 used instead or r12.
anyway i digress :)
still looking for a micro cogen forum for the home built guys
bob g
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Guys,
Have look at this Yahoo group dedicated to home CHP systems.
It has a very small membership, but if enough of us interested users signed up, it might liven things up !
http://tech.groups.yahoo.com/group/HomeCHP/
Veggie
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Jens,
Re: "Don't forget that it's easy to draw heat from a 185F tank but a lot more difficult when you are down to 80F"
I too have been thinking about that lately.
Heat transfer in a fan coil is closely related to CFM passing through the coils.
One solution I thought of was to put a 3 speed fan on the fan-coil unit.
At first, when there is a high temperature delta, the fan comes on at low speed, then when the temp drops to 130f it speeds up to medium speed. When the temp reaches 100f is shifts to high speed. Effectively giving the same BTU's throughout the run.
Would not be very hard to rig up.
Veggie
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You might find this post interesting.
The Volvox exhaust gas heat exchanger.
have a look....
http://tech.groups.yahoo.com/group/HomeCHP/message/22
Here's the Volvox/Listeroid CHP website...
http://www.volvoxengineering.com/
Veggie
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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
Yeah, that isn't much square footage ... but it does get a bit chilly out your way :)
Don't forget that it's easy to draw heat from a 185F tank but a lot more difficult when you are down to 80F ..... but you are right, it all depends on what you are after.
One thing I am trying to figure out (and maybe it's not cost effective) is how to utilize the available heat better. For example, you can use 80F water for heating but that same 80F water poses a problem for domestic hot water. If one could somehow set up to utilize the colder water where it can still do the job and reserve the hotter water where it is needed then efficiency could improve. Oh well, just rambling on .....
Re heat exchanger .... Bob will have some plans for us real soon now (I hope). His design promises a self cleaning action which seems to be much more important than I had realized. Those are just the plans and not the full unit though .....
Jens
About the best use for 80F water is for radiant heating. You don't want the loops that hot, as it is a gentle wide area heat. Have you seen the solar shed article? Here is a link. http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm
Interesting and very descriptive setup by the author, including BTU calcs. In his system, he used a thermal regulating valve that only mixed in enough hot water from the storage tank to maintain his desired radiant loop temperature. Eventually as the tank temp dropped with the heat being put into the house, the thermal reg valve would mix in greater and greater qantities of storage tank water. Once the tank reached a set low temperature, it would shutdown for he night, and his other domestic heat source would take over to maintain house temps. With a heat storage tanks natural tendency to separate by temperature, a small loop and heat exchanger could be used to keep a domestic hot water tank "topped off" untill it's temperature dropped below 120F. But with a thermal reg valve, the entire tank volume would be available for radiant heat untill say 80F was reached.
We are in the process of planing our new home, and a very large thermal storage tank(750-1000 Gal) is in the basement area plan. Ideally, if I can collect enough solar, this will meet the heat loads of the house(should be low with super insulated 15" thick walls), and maintain the domestic water temp. I have a plan for a very low cost solar collector in my head that I am going to prototype this summer. Maybe $3 per sq/ft, VERY efficient, and very easy to produce at home... Ideally, I hope to be able to collect enough solar on a sunny day, for that days needs, and perhaps 2 days after that. I am cooking up a chip wood fired boiler using a heat exchanger design I have had bouncing around in my head for the past year or so, as a cloudy backup for the solar system. The fallback will be electric, but only as a last resort if something in the system fails, as electric is the least cost effective option. The real key is the house insulation envelope, and to just plain need less from the beginning...
Thanks for the link Veggie, I will have to check it out. I think a CHP forum or section is an excellent idea.
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ronmar,
Don't forget to tap your Lister(oid) into that system somehow.
You can make a lot of heat when charging a battery bank at 3kw/hr or during a power outage on a cloudy day. 8)
I signed up at that Yahoo CHP site. Lets get it rockin' !!
Veggie
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what i would be most interested in, in a forum is "quality" not "quantity"
one post that clearly presents for instance a test protocol, that was clearly illustrated, closely adheared too
and which results were laid out in an understandable format, that is credible and reproduceable by others
is worth far more than 500 posts that go all over the place, with faulty, false or inflated claims.
personally i just find it hard to believe that we need to accept less, or rather why we do?
for instance, test equipment
most everyone accepts the killawatt meter as being adequately accurate for test purposes, a pair of which can
handle everything the typical 6/1 can throw at them, and they are low cost.
a decent surplus gram scale is pretty cheap as well, leaving maybe a 10 dollar stop watch to time events?
electric kitchen cooktop elements are dirt cheap from the bone yard and make for easy load bank parts,
all one needs then is to agree to a test protocol, then we got "apples to apples" and can make sense of what works
and what don't, and perhaps more important why it works or why it don't?
so maybe a scratch built low volume forum fixated on serious testing and results might be useful? i have to belive it would slowly
attract those that are trying to exact the best out of what they have?
just a thought
it might even be better to link up a set of websites with a common theme or goal, and allow each the ability to develop in their
specific area of interest or expertise.
it just seems like maybe there are a few folks that are about tired of reading yet another account of "how the lifter turns"
or "like sand through my crankcase, so are the days of our lives"
and are ready to take the next step?
whatever that is?
:)
bob g
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Jens,
That's quite a "system". Be careful it doesn't start thinking on it's own !! ;D
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Maybe we should be asking for a new section to this forum for CHP ideas?
Scott R
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most likely posted before, but here's a couple of Listeroid CHP systems....
http://www.youtube.com/watch?v=YArccvSb9s8&feature=channel_page
http://www.youtube.com/watch?v=UAZKxYZ3QH0
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ronmar,
Don't forget to tap your Lister(oid) into that system somehow.
You can make a lot of heat when charging a battery bank at 3kw/hr or during a power outage on a cloudy day. 8)
I signed up at that Yahoo CHP site. Lets get it rockin' !!
Veggie
Yep, just shy of 18,000 BTU/HR at a 3KW electrical load(from the cooling system):) The exhaust should also yield just about as much heat at that load...
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Hi Bob,
I stand by my post, but I’ll take a shot at clarifying. And concede that I did make an approximation…
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
Agreed.
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
Ummm… Sort of. Here’s the area where precise language is really beneficial. The thing is that, yes there is extra current flowing (circulating as you say) but it doesn’t equate to heat in the magnitude you might be thinking. Some heat, to be sure, but I’ll leave it to you as to whether its significant…
Here’s an example that may help put it into perspective.
Let’s say he needs 2.6 kW, but he has a 0.7 PF, as you say.
At 120V, this means his line current is 31A. (If he had a perfect 1.0 PF, his line current would be 22A)
So, clearly, the line current is higher with the low PF. But how big of a problem is this?
The 31A is still within the rating of his 5kW ST head, so no problem there.
Now, If you’ll allow me to pull a number out of my ass, I’d like to estimate the resistance in the ST head stator windings and wiring to the load. And I’m going to estimate it at 0.3 ohms. (Actually this is not a total rectal extraction – My 12 kW head is 0.1 ohms if wired for 120V, which I doubled to 0.2 ohms for this case, plus I added 0.1 ohms for an assumed 100 feet of 10AWG copper wire to the load)
Thus, in the 0.7PF case, the total power lost as heat in the ST head winding, and copper wire due to I2R loss is 31^2 * 0.3 = 290 Watts
Now, in the 1.0PF case, we have 22^2 * 0.3 = 150 Watts
So, yes, some power is being lost due to the poor power factor. (290-150 = 140 extra Watts lost)
This 140 Watts of loss, compared to the 2600W being delivered represents about 5% of the engine’s output power.
Significant? You decide.
BTW, your first post said this
at .7 pf you might only be able to cover about 1.8kwatt of loading
Which is way out of whack, based on the analysis I show above. And it indicated to me a misunderstanding where you multiplied 2600W by the 0.7 PF. This is irrelevant, and not the correct approach to this problem.
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thanks Jim:
always good to have input from the guru"s
another question if i might
i get the resistance of the st head, ~.1 ohm, another .1 for the wire run, but
are we not neglecting the resistance of the load?
ih any event the losses as you surmise at around 140 watts of 5% doesn't seem like much to be worried
about unless one is running long hours? and is worried about eeking out efficiencies?
the reason i ask is based on the cumulative effects, if we discount a percent here, a couple there, another over
there,, pretty soon we have some losses that begin to cost fuel to cover?
anyway thanks a lot for the explanation, and forgive me for being a bit thick between the ears
i am under the weather pretty bad for the last week with the flu,, thankfully the garden variety type
and not the pig kind!
if you don't mind i might (probably) will have other followup questions, later when i feel better.
thanks
bob g
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another question if i might
i get the resistance of the st head, ~.1 ohm, another .1 for the wire run, but
are we not neglecting the resistance of the load?
Right, it's neglected. The load resistance does not enter into the calculation of the power loss due to a low PF. The load gets 2.6kW in either case.
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not wanting to argue a point i am unsure of, i need to dig back into the text again
iirc from a few days ago my reference's state that the resistance of the alternator, wiring (along with all interconnects, breakers,
twiston's etc) and the resistance of the load (reference was to motor loads and maybe different for others?) all must be include in
figuring losses. i gotta confirm that for sure.
i don't know if it is worth fighting over or not, striving to capture but
i do know i can measure the difference in fuel consumption a 50watt difference in load fairly easily in fuel consumption.
i think the only way i will ever have a difinitive answer is to do some actual fuel consumption tests with a fixed load at X pf
, then correct to unity and retest again to see what the results might actually amount to, and whether of not the difference's are
significant enough to go after?
going back to the OP i would toss this out
at 2.6 kwatt load (whatever the powerfactor) and at low speed
the fuel consumption in grams/kwatt/hr will be higher than if
the engine was allowed to run at 1800 rpm and produce~7kwatt
in all my tests the 195 changfa driving an st head just can't compete favorably at this low a loading
with a 6/1 according to my results.
now a 195 driving a specially prepared 110-555 into a 24volt nom battery bank can compete very well with a 6/1
at ~2.9kwatt output (being dc pf is not an issue) at lower engine rpm.
so i guess it really depends on what the end use or goal is for this 195 low speed project?
(i gotta go back and reread to find out what the original plan was)
:)
bob g
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i almost forgot one of the most important aspects of trying to get max output from the changfa
and this will be aggravated at lower speeds.
if the engine is a idi changfa it will have 20:1 comp ratio
at max loading of around 7.3 kwatt at 1800rpm you will start to have head gskt fire ring failures
with the oem gasket, the fire ring is too thin and too hard at the fold line. it will crack and fail, leaking
compression into the coolant which will show up upon the next cold startup.
if you calculate 2.6 to 2.8kwatt as max loading for ~1000rpm you may be in this stress region for this gskt
one has to remember the injection timeing is optimized for 2000rpm at full rated load
half that speed and the timing might be a couple degree's too fast, this adds siginificantly to the cylinder pressures
and likely will lead to gskt failures.
all is not lost though, there is a better gskt available :)
just wanted you to be aware of the risks
i have cracked several oem changfa fire rings, doing hard run's (equivalent to dyno torture tests) on my changfa
of note, the rest of the engine could care the less how hard i beat on it
it appears the head gskt is the weak link, and maybe a nice sacraficial one at that?
cheaper to kill a gskt than beat a rod to death i suppose?
(although i think it would take a lot more to kill any hard part in a changfa)
just wanted to pass that along
bob g
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Bob,
Thanks for bringing up those important points.
If I am going to design a system built around a slow running Changfa, then those points must be addressed.
My engine is a direct injection version. The manual states a 20:1 ratio.
Would you still expect the same problems with a DI engine ?
1] You noted that a better head gasket is available. Can you advise where this can be purchased?
2] Injector timing: I looked in my Changfa manual on this subject but the translation from Chinese to English became enough of an issue to make it dangerous. ;)
Have you played around with your timing?, if so, what's the best method of adjustment.
3] How do you know when a fire ring cracks??
Thanks for your comments,
Veggie
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iirc the DI changfa engines are ~18:1 or lower comp ratio (the exact i don't remember but lower than the idi engines)
a better gskt is available from gasket to go, ask for the changfa 1100 gskts "if" you engine is truely an idi and not a di engine.
the DI engines use a different head gskt that looks to be heavier built to start with
injection timing is altered by changing gskt shims under the injection pump, iirc it take .004" to alter 2 degree's
i have not tried to alter the timeing for running at slow rpm, my primary use is at 1800rpm at heavy loading and
at 1200 rpm at low loading, so i have not looked into changing the timing.
you won't know when the fire ring cracks unless you are very well instrumented, then you might notice a slight change in power
while running, however
the next time you try a cold start, you will have water forced out the overflow of your cooling system, hard starting if at all
and exhaust vapor clouding.
bob g
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not wanting to argue a point i am unsure of, i need to dig back into the text again
iirc from a few days ago my reference's state that the resistance of the alternator, wiring (along with all interconnects, breakers,
twiston's etc) and the resistance of the load (reference was to motor loads and maybe different for others?) all must be include in
figuring losses. i gotta confirm that for sure.
Those can all cause losses. Some more than others, ie. undersized cables, bad connections.
i don't know if it is worth fighting over or not, striving to capture but
i do know i can measure the difference in fuel consumption a 50watt difference in load fairly easily in fuel consumption.
If you can measure a 50 watt load by fuel consumption, I'm impressed. You would be easily be able to remove 50 watts of load, by correcting the bad PF at the source(s). That is the only way to remove the losses that the excess current is causing in the cabling system. Otherwise you are just removing those loses from the windings, and might not see that much of a difference.
i think the only way i will ever have a difinitive answer is to do some actual fuel consumption tests with a fixed load at X pf
, then correct to unity and retest again to see what the results might actually amount to, and whether of not the difference's are
significant enough to go after?
Do you have equipment to accurately measure PF on bigger loads?? That is to say, something with a higher power rating than a Kill-A-Watt? If so, I'd be interested in hearing about it. Please don't tell me you are going to correct the pf based on the motor nameplate alone. Note that a motor will have a different pf loaded vs. unloaded. So don't measure the pf of your circular saw spinning freely, and then expect the same system to correct the pf if loaded up. On a 2.7kW load, I'd bet you'd easily save the equivalent of 50 watts of fuel by correcting the power factor, unless its already better than 0.95. However, when you correct the pf, you might find the voltage will be higher, so resistive loads might draw more power. So you'd be saving fuel on waste, but the other loads might consume more. As long as they were useful loads, you would be getting it back in appliance performance (example: water heater elements would draw more power, but wouldn't run as long).
Sorry if I was re-iterating something you already knew, but thought I'd also post it for the benefit of the group.
Steve
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You would be easily be able to remove 50 watts of load, by correcting the bad PF at the source(s). That is the only way to remove the losses that the excess current is causing in the cabling system. Otherwise you are just removing those loses from the windings, and might not see that much of a difference.
Ummmm ..... I am not sure if I understood you right but just for the record, the power factor correction should happen at the load and not the source IMHO. The power source will then see a pf of 1.0 and you won't have losses from the source to the load. I would think that the load itself would still have excessive currents circulating. IE the power factor correction will not do anything to help with pf inefficiencies in the motor de to the power factor .
.... at least based on my interpretation and understanding.
Jens
Jens,
Sorry, it made sense in my mind... I meant at the source of the bad pf, ie. at the load with the bad power factor. Not the source as in generator. My apologies for clumsy wording. The inefficiencies would then be limited to that load, as you stated above. Also, I forgot to mention that you'd want to switch the pf correction with the load, so that you don't end up with leading power factor, instead of the lagging power factor you were trying to correct.
Steve
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i can measure pf all the way up to around 200amps, if needed
but of course i can't do anything near that with the st7.5
in other words i can get accurate numbers on any st head i am likely to need to test a load against.
and yes i am aware that pf shifts depending on loading
an unloaded induction motor can have horrible pf, one 1/2hp motor i have registers .26 pf no load
but only improves to about .4 under moderate load,, and haven't checked under heavier load yet.
my 8 inch bench grinder is similar, it starts out at .36 and improves somewhat when grinding
but not nearly what i would expect doing normal grinding.
thanks guys
bob g
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Ok,
Let us know what you find, and any improvements you make.
Steve