Changfa Slow Speed Experiment

[Veggiefuel]

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

[oliver90owner]

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

[Veggiefuel]

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

[mobile_bob]

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

[Veggiefuel]

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 

Veggie

[oliver90owner]

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

[Combustor]

         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.

[mobile_bob]

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

[cujet]

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.

[Veggiefuel]

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

[oliver90owner]

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

[Veggiefuel]

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

[oliver90owner]

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

[mobile_bob]

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

[Wizard]

Redo this test with redstone at 1330ish rpm with head at 1800 once have correct pulley?

Cheers, Wizard