Genset voltage reg: capacitor vs. AVR

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Possibly for one fraction of a cycle, but as soon as there is any change, the field coil voltage will be increased to compensate for it. The mechanical feedback loop that controls the engine speed is very very slow, because it is limited by the inertia of the engine an the rotor. The electrical feedback loop that controls the field coil voltage is pretty fast; it is limited mostly by the inductance of the field coil.

And what does he mean by "a cap?" As I said earlier, you have two choices for voltage regulation: a feedback loop controlled by a mechanical buzzer, or a feedback loop controlled by a solid state device. What is this mysterious "capacitor regulation" that he has come up with? Nobody in this thread has yet explained it, described it, or given an example of it. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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On Feb 19, 1:54 pm, snipped-for-privacy@panix.com (Scott Dorsey) wrote:

But what you stated was:
"The engine governor has nothing to do with the output voltage regulation, really. "
Which would mean to me that you could run a generator with a bad or incorrectly adjusted governor running at 3400 RPPM, or 4000 RPM and the only thing that would change is that the frequency would not be 60hz, ie the voltage stays the same. That isn't true, because the voltage is directly proportional to the speed too. I agree that adjusting the field is how the voltage is adjusted without changing the engine speed.
The mechanical

I posted a link to a discussion on the subject previously. Apparently capacitors are used as a cheap voltage regulator. Also, just google and you'll find info.
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But you CAN run the generator at some other speed and the output voltage will be the same. Try it! That's the purpose of the feedback control of the field coil. The faster you run the thing, the more the regulator will drop the voltage of the field coil. It completely decouples the operating speed from the output voltage.

This is just handwaving. What is actually going on? The capacitor can be used to shift the phase of a signal, it can be used as part of a resonant tank. What is the capacitor _doing_ in this magic circuit?
I have googled and I have seen nothing particularly useful, unfortunately. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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On Feb 19, 4:40 pm, snipped-for-privacy@panix.com (Scott Dorsey) wrote:

Yes, IF the speed deviation is within the range of whatever the voltage regulator is capable of maintaining.

I agree that I haven't seen a technical description of how they work. But there is enough info from some google searches that shows that caps are used as voltage regulators in basic generators.
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Okay, here is the story! All of the details can be found in US Patent 4,269,368.
Looking at how this works, it's not a conventional brush-type alternator at all, but an induction device almost like an induction motor in reverse. The patent shows a single pole rotor with a diode across the winding, so the rotor acts as a magnetic short in one direction and a magnetic open in the other. This diode is really the key to the trick.
Now, the stator has two windings, physically 90 degrees apart. One winding is the load winding, the other is the field coil itself, and the field coil has a capacitor across it.
When the first pole of the rotor passes by, it induces a current in the field winding that is proportional to the current passing through the load coil (ie. proportional to the load being drawn). Then that pole continues on and in the next 180 degrees of rotation induces a current proportional in the load winding that is proportional to the current in the field coil across the capacitor.
You can think of this not as an AC generator but as a device that creates pulsed DC... the waveform is going to be very asymmetric. But, the amount of voltage induced in the load coil should stay more or less sort of constant with the current draw on it.
It really is a cheesy kind of trick, and I am not sure I'd want to use a generator like this to run anything more sophisticated than an induction motor, but there are plenty of folks out there who need to run induction motors.
The capacitor isn't doing the regulation, it's just storing energy to keep the field coil running.... the diode isn't doing the regulation, it's just making sure the coils are both excited only in one direction.... it's the design of the whole thing that is doing the regulation. Calling this "capacitor-regulated" is incorrect but "capacitor-excited" is more like it.
I've never actually seen this before and the whole idea is just kind of ingenious. The patent dates back to 1981 so this has clearly been in use for a while. My guess is that in real life there are a bunch of poles on the rotor with an individual diode for each pair, but I've never taken one apart. --scott
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wrote:

http://en.wikipedia.org/wiki/Magnetic_amplifier "A relatively small DC current on the control winding is able to control or switch large AC currents on the AC windings. This results in current amplification."
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No, read the patent! It's not related to magnetic amplifiers at all; nothing is operating in saturation. It is a very cool trick! --scott
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On Feb 19, 1:54 pm, snipped-for-privacy@panix.com (Scott Dorsey) wrote:

>a feedback loop controlled by a solid state device.   What is this mysterious

A cap is a given as a capacitor. You regulate voltage, raising it means you lower its current. Increasing the current means you can run something faster, like a fan, but you lower the voltage, so you are regulating it in that sense. But the power is what always remains the same (assuming reaction in the circuit isn't a factor).
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Sigh.....
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wrote:

Oh, and with a split-phased capacitor, part of one phase can be used to help start a motor before its brought back to normal running the motor.
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Sigh.... None of which has any relevance to how a cap is used to regulate voltage in a cheap generator.
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wrote:

Why expect to regulate voltage if its that cheap?
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Another diversion into lala land. They apparently do it because:
A - If you're not going to use an electonic voltage regulator which costs a bit more, then having SOME voltage regulation on a generator is better than none.
B - Customers want and expect some kind of voltage regulation and the generator would probably be useless for most applications without it.
C - A cap is cheap
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On Sun, 17 Feb 2013 11:23:27 -0500
<snip>

Website, instruction manuals here:
http://www.meccalte.com/index.php?sR&page=0
The model number off your unit would be really helpful :)
Possibly the manual for your generator head:
http://www.meccalte.com/send_file.php?fileid=S20W%20manuale
"S20W Series: 6kVA to 8.5kVA 3000rpm 50Hz or 7.2kVA to 10.2kVA 3600rpm 60Hz"
or it might be this one:
http://www.meccalte.com/send_file.php?fileid=S20F%20manuale
"S20F Series: 8.5kVA to 12kVA 3000rpm 50Hz or 10.5kVA to 14.4kVA 3600rpm 60Hz"
Just guessing, using the output wattage you gave...
--
Leon Fisk
Grand Rapids MI/Zone 5b
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wrote:

Yeah, I'm not sure either, I'll have poke around the generator -- oh, actually, a booklet came with each component, I'll dig it up, post back.
Whatever it is, they'll be sending the AVR sized for that unit.
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EA


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PSI) and sells for $500. The also sell Lincoln electric motors which are owned by Leeson. 7 1/2 HP Lincoln motor is $550. $65 for a pulley. Square D mag starter is $170. Pressure switch is $40. Don't think I'm going to need multiple tanks. What do you see as the benefit to multiple tanks if you have the right compressor to keep up with your needs? ============================================================ True, a good compressor does not require my staged tank strategy, but imo, increasing tank capacity will extend the usable cfm rating of any compressor, AND reduce it's cycling.
This is more important if you are going on the cheap, or have limited power, or space. I got my 26 gal Husky as a floor model for $160 at HD, and just added extra tanks as I stumbled across them -- could even be tall welding tanks! Dat 7.5 hp motor is going to dim the lights! You can also save on the contactor by just using a simple relay, with the coil wired into the pressure switch. For me, space is at a premium, portability is really helpful. And even a 26 gal Husky (vertical) is heav-eeeeee!! Holy shit..... Also make sure it's easy to drain the tanks. I run a long hose from the bottom, with a small ball valve at the end of the hose (1/4" white stuff, like for a fridge's ice-maker), and just empty it into a bucket.
If you are going to mix'n'match, $550 for a motor seems like a lot, I would go to a motor re-winding place, and see what they have on their shelves, for cheap. They often have *hundreds* of spare motors to choose from, I'll bet you could find sumpn suitable for under $100, mebbe way under.
Finagling "small" has its advantages. For example, if you have limited power, and are running cnc, you don't want big-azz motors causing transient voltage drops every time the pressor kicks in. So a smaller motor/pressor is less electrical strain, and larger tank volume creates less cycling, jolts to the electrical service. Which also becomes even more important during outtages, if running off a generator. And also ito moving shit around...
If none of this is a factor, then you can go big and heavy and strong, but if it is a factor, finagling small stuff helps -- a kind of "modularity".
--
EA



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Anybody can make a spelling or grammar mistake or a simple typo in a usenet post, but why would anyone do so intentionally?
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There is always an easy solution to every human problem -- neat,
plausible, and wrong." (H L Mencken)
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My phonetic rebellion..... no more o-u-g-h's for me -- enuf is enuf.

Einstein: Shit should be made a simple as possible.... but no simpler.
Einstein: If you think shit is simple, then you really don't understand shit.
--
EA




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PSI) and sells for $500. The also sell Lincoln electric

"This is more important if you are going on the cheap, or have limited power, or space."
We both have a limited space problem.
Would something like this help you?
https://www.benchsolution.com/products/workbench/ ======================================================= Mebbe in a Leave-It-To-Beaver shop world..... lol In MY world..... lessee, how to describe it....
The only way I can find a pencil in my shop is to buy a gross (or two) and throw all 144 of them up in the air, throughout the shop. THEN mebbe I'll be able to find a pencil somewhere. Ditto flashlights, tape measures, calipers, you name it. I now have OVER 30 small led flashlights ( HD 8-packs, about $10, batts included) throughout the house/shop -- and finding a flashlight is STILL hit and miss!!!
Funny, I built a drop-down welding table almost exactly like that, with shelving on top, when I was still parking <gasp> CARS in the garage -- how silly was DAT??? So I figgered Oh, Gee, I'll just drop down the table to park the cars.... Yeah, right..... Dat drop-down welding table was dropped down exactly ONCE (to show the wife), and was never ever deopped down again!! Cuz, well, dropping down the table would mean..... <GASP> ..... CLEANING UP!!!! LOL 'tis the Nature of the Shop Beast.
Shit like dat is for Tool Time, or This ole House..... or shop teachers in a well-funded school. Noble-ly ideal, but just not in the reality of The Frazzled and The Cramped. Heh, and The Broke.
It DOES look beautiful, tho. But it's sorta like exercise equipment/gadgets that store under yer bed..... Guess what.... they then STAY under the bed. lol
I eventually took my drop down welding table out altogether and made it REALLY useful: I parked it on some milkcrates -- stacked three-high -- which is a li'l tip for Iggy and his ridiculous 30" high welding tables. goodgawd.....
Which I really shouldn't knock...... cuz all those muthafuckas dumb enough to weld on his 30" welding table will be calling Moi up for my apparatus/bars to stretch out/invert their aching mis-aligned backs. Heh, I should send Ig a commission, eh? Well, I will, but AFTER he sends the whole of RCM a commission check for the *unending* (free) business advice he solicits ad nauseum.
--
EA







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On Sat, 16 Feb 2013 10:13:55 -0500, Existential Angst wrote:

Do you have a link to a site that sells the AVR ditty? If it's regulating the field current of the generator in response to the generator voltage, and if all the genset does is rely on the motor's governor for speed regulation, then it should give better regulation.
But I can only speak from a combination of a deep knowledge of control systems theory, a reasonably deep knowledge of how generators work and how Briggs and Stratton engines work, and a near total ignorance of how people actually put these things together in practice.
--
Tim Wescott
Control system and signal processing consulting
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