Regulated output generator

[dieselman]

Recently I have been monitoring the ouput of the alternator on my truck while driving to find an elusive charging problem. 

The voltage maintains relatively constant ( between 13.9 and 14.1 Volts).

Why couldn't a generator be made to maintain a certain voltage/Hz with variations in RPM.

Obviously my knowledge of generating elctricity is very limited, so when you stop laughing could someone explain why this couldn't be done?

Thx, Jim

[mkdutchman]

Theoretically you could... ....with an asynchronous generator, i.e. induction motor?

I think there were some posts regarding that topic a while back

[SteveU.]

Hi Jim,
You certainly CAN closely regulate the DIRECT CURRECT output voltage of DC output generator/alternator. Storage Batteries will only accept and store DC energy.

Its ALTERNATING CURRENT voltage control that gets difficult, tricky and expensive. But still not impossible.
However Hz cycles per minute on AC are directly tied to the RPM you drive the AC generator. Many AC designed load devices either wont't work or work poorly if you do not/cannot keep the RPM therfore Hz stable within a narrow range.

Lots of info out there with more detail and good explainations on the internet (wikipedia, ect.) and in books.

Good reading
SteveU.

[dieselman]

Soooo.... If you cannot maintain a certain RPM you cannot maintain Hz?

I hate that "C" word.  I try never to use it. It sounds defeatist.

Jim

[mobile_bob]

without stable rpm you cannot have stable hz, yes that is true in a mechanical sense.

but cannot is a tough word isn't it.

you can do anything with enough time and money.

you can drive generator making dc, or an alternator making ac and rectify it
then feed a battery bank, which feed an inverter and have stable hz and voltage
over a very wide rpm range, so yes in a fashion it can be done,

but it cannot be done using a single stage engine driven generator.
you simply have to have stable rpm at least to set the hz, a voltage regulator can then be
added to get relatively stable voltage.

defeatist? no
realistic? yes

bob g

[Tom]

The Honda inverter generators will run the engine at varying speeds depending on the load. I believe the feed DC to the inverter and it fixes the voltage and HZ issues.

[dieselman]

What about a mechanical clutch device that would maintain a constant RPM as long as the driving head/engine was maintained above the needed RPM.  Then when the load changed the engine would have a lag time for response.  Probably not practical. 

Jim

[AdeV73]

What about a mechanical clutch device that would maintain a constant RPM as long as the driving head/engine was maintained above the needed RPM.  Then when the load changed the engine would have a lag time for response.  Probably not practical. 

It sounds like you want a DAF Variomatic, but running "backwards" somehow (instead of constant engine velocity = increasing output speed; you want varying engine input = constant output speed). It may be possible, but I'm not sure how.

[ZackaryMac]

The Honda inverter generators will run the engine at varying speeds depending on the load. I believe the feed DC to the inverter and it fixes the voltage and HZ issues.

You're right. The Honda's alternator is converted to DC, then back to AC/60hz. There is a computer-controlled stepper motor on the throttle shaft, and the throttle may open up without increasing revs, to compensate for increased load. In other words, increase the load somewhat, and it gets a bit louder as the throttle opens, yet the engine doesn't rev higher. Weird, when compared to a conventional generator, as this may happen at a lower rpm. Or, if you start with the auto throttle off, turn your load on, then flick the auto throttle on, the revs keep dropping till the computer finds an equilibrium. Honda also claims their AC is clean and pure, not a modified sine wave.

[SteveU.]

Yes, yes. Of course you guys are right. I can could list at least three manufactuers web sites: UK, US, and China that with more electronics than it took to take Appolo to the moon and back that can take varing wind power AC production and give you a clean stable AC Hz and voltage. And all done with rapid switching electronics, not slow responding mechanical.

But as Mobile Bob and I are tring to do before you take a fellow and throw him off a cliff and hope he can fly how about we get him up to walking speed first.
Direct Current; what, how and why.
Alternating Current: what, how and why.
Commutator Rectification: old school yes, but still a building block knowledge.
Electronic Rectification: just the basics.
Ohms Law: A-B-C, 1-2-3, just like the song.
"Conservation of Energy" meaning "There ain't no free lunch" meaning: every time you convert energy from one form to another you WILL lose a little to Mr Heat. Convert enough times and you will have nothing useable left except a lot of heat. Enough heat that the insulation will burn and let the magic electrical smoke out and it go by, by and everything quit.
Sorry, if you really want to understand the dues to pay is a liitle reading.
Then get a young adult science kit and make a little elctricity, light, motor/generator and hopfully a little smoke even.

Try it it's fun
SteveU.

[dieselman]

The problem, as I see it,  is these engines do not respond fast enough under large load changes.  They work great for a constant load, like a pump, but the govenor is just too crude too maintain a constant RPM for generating electricity under constantly varying load conditions.

Just trying to use some of the brain trust in this forum for a solution.

Jim

[GuyFawkes]

One should easily be able to stay within a tiny frequency range - maybe 1/4 hz plus or minus. Of course this figure is grabbed totally out of the air but I don't see any reason why this wold not be achievable.

Jens

Apart from basic physics maybe.

That's the trouble with these places, those who do know eventually get bored of repeating the same lessons and go away, and all of a sudden the only voices left are the blind leading the blind.

So some VERY basic physics.

1500 RPM / 60 = 25 revs per second.

If you want 50 Hz (UK) out of a 1500 RPM gen head it *has* to be 4 pole, if it is a 2 pole you have to spin it at 3000 RPM

Listeroid at 650 RPM, 2 pole head at 3000 RPM = a 4.62:1 ratio.

4 stroke combustion cycle is 720 crankshaft degrees, 2 turns, or  9.24 head turns.

Actual power stroke is about 100 degrees of crank rotation, or 100 * 4.62 = 462 head degrees, or 1.28 revolutions.

1.28 revolutions, for a 2 pole head is 1.28 AC cycles, during which the RPM is increasing under the power stroke, the remaining (9.24 - 1.28) 7.96 cycles the RPM is decreasing under the exhaust, induction and compression strokes.

So we're talking 13% of the time accelerating, and 87% of the time decellerating.

AC electrical loads also decellerate.

Opening the rack during our 13% can ONLY counter this by INCREASING acceleration.

In physics, there are only three ways to even this out.

1/ throw away the one lung 4 stroke, say a straight six with 120 degree crank.

2/ use a 4 pole head at 1500 RPM in preference to a 2 pole head at 3000

3/ add inertia, massive flywheels.

My start-o-matic, 600+ lbs of motor flywheel mass, concentrated at the rim, nearly 75 lbs extra head flywheel mass, concentrated at the rim, 4 pole head for 2.30:1 ratio (ratios get a lot worse as soon as you go from 50 hz to 60 hz)

Holding listeroid w spoke flywheels + chinese 2 pole head to plus or minus 0.25 Hz, not a snowballs chance in hell, not with an AC load bigger than a clock radio plugged in.

[dieselman]

I didn't put any limitations or requirements when I proposed the original question.

If you are going to take a shot at someone, at least try not to generate positions for the argument that were never introduced.

Jens, I thought your post was at least thought provoking.

Jim

[1958steveflying]

Hi All,
  Could anyone explain in layman terms the importance of holding the 50 Hz Uk and 60Hz Us frequency so close with generated electricity. Whilst i am a mechanically minded person i have no idea of the importance of this factor. i feel as there is so much reference to different ways of keeping it so close i need to know the reasons why. Apologies if i shouldn't have posted the question here.
Cheers Steve

[oliver90owner]

Where is this thread going?

Just trying to use some of the brain trust in this forum for a solution.

You get a perfectly good apraisal of the situaation and then say:If you are going to take a shot at someone

Without doing any maths I doubt you will get within 0.25 Hz even with only clock,lt alone a radio. There are physical limits to what can be done with a CS.  I thought GF made that fairly plain for any reader.

Mains frequency is probably plus or minus 3% (not checked, but easy enough to check if you are that interested) but utilities will do much better than that.  They will allow for worst possible case before disconnecting from that source - or simply disconnecting the load.   You have that same choice. Most accept a reasonable quality, especially for stand-by.  Alternative, as I see it is the battery/inverter route or the Honda technology to invert without batteries.  KISS is my principle with a Lister.

The problem, as I see it,  is these engines do not respond fast enough under large load changes.

Absolutely correct.  If you want fast reponse you have multicylinder and no flywheel weight.  What you are wanting is no change in the first place.  Case of chicken and egg, I think.

Regards, RAB