From: John De Armond Newsgroups: rec.outdoors.rv-travel Subject: Re: Generator output - was Meanwhile-Back to RV's Date: Fri, 01 Dec 2000 02:37:45 -0500 Stanley Miller wrote: > On Thu, 30 Nov 2000 12:58:32 GMT, W F Sill <will@epix.net> wrote: > > >Not long ago, Stanley Miller <skp51443@tds.net> wrote: > > >>I think that if you put many rv generators on a scope you will see a > >>distorted waveform with lower peak voltages than power company power. > >>Better quality generators have less of a problem with this than do the > >>cheapies and smaller units. Lightly loaded units display less sag than > >>heavily loaded units. > > > >Stan, you said "I think". OK, that's fine, but IMO you are dead > >wrong. I got rid of my scope many years ago but have never seen a > >difference in output beween a properly running genset and grid power. > >Unless you are using some kind of square wave generator (not the norm) > >you cannot get 120vac RMS without getting 170v peak values at 60 Hz. > >We have a 7kw standby genset & 200a transfer switch here in out home > >and can run anything in the house with no detectable difference except > >for the noise of the gen. > > Please note I said better quality generators and that lightly loaded > ones have less problems. Yours sounds both high quality and not loaded > to it's limit. Grab a cheap one that is being taxed near it's maximum > power and you might notice the problem I was referring to. > > I did not say that the output voltage didn't show as lower on an RMS > meter. It does show as lower on my cheapie but it isn't RMS... > > I never had a problem with my 30 KW unit but when I retired Uncle Sam > wanted to keep it and I had to downsize. [snippity] > Took a quick look online to see if I could find someone sharing my > opinion with little luck. I did a quick catalog search in my shopping > pile and did find find several RE dealers selling 10% voltage boost > transformers for correcting sagging voltage from generators to restore > full performance to your charger. If you have a Backwoods Solar > catalog it is discussed in it. > > Since I can't find indisputable evidence to prove my point I will > leave the field of battle. No need to do that, Stan. Certainly no use in letting Bozo beat you down with his usual ignorant posturing. Ur hmbl svt is ever ready to hang a scope on something interesting and toss the results up on the net. Look here:
What we have here is a series of scope shots of the output of my Onan AJ genny under different conditions. A couple of notes before I explain. The AJ is a self-regulating or as some refer to it, a saturated field generator. That is, the generator is designed to be inherently voltage regulating. The field is driven at a fixed level sufficient to saturate the magnetic circuit. There is no external voltage regulator. These generators generally (but not always) have better waveforms than actively regulated generators. I know from examining other generators that this is a better-than-average case. I would have done this procedure on my Yamaha but it's in winter lay-up mode. Photo 1 (onan_1.jpg) is the generator running unloaded. Photo 2 is the generator running fully loaded. The generator has slowed a bit and the frequency has dropped. And one can see the beginning of some distortion on the waveform right before the center graticule. Photo 3 is the generator overloaded (with this generator, the engine overloads far before the alternator.) Both the voltage and frequency have dropped and the distortion is noticeable. Photo 4 (onan_2.jpg) shows the 3 waveforms overlaid. This shows the differences in the waveforms very graphically. Where small generators get really hinky is when they drive non-linear loads. A typical non-linear load will have a rectifier (bridge) downstream of a transformer with the rectifier feeding an energy storage device (capacitor, battery, etc.) A couple of examples are the microwave oven and the battery charger. Photo 6 shows the generator waveform when running a small microwave oven. Though this oven is only a small load on the generator, it causes significant distortion. The distortion occurs when the diode rectifier in the microwave suddenly conducts when it becomes forward biased. This is almost identical to the waveform one would see when driving a battery charger. In general, generators with active regulators and lesser amounts of iron and copper exhibit poorer waveforms. Again, my AJ is better than most that I've observed. Photo 5 shows the no-load waveform with the microwave oven waveform overlaid. Stan, I imagine what's happening with your battery charger and generator is that the charger is causing distortion similar to Photo 5 and possibly affecting the active regulator if your genny has one. On my genny without a regulator, my battery charger behaves essentially the same as on shore power. I have a simple way of addressing poor waveform, low voltage and any desire I might have for a higher charging voltage/current. That is to hook my battery charger through a variac. The variac lets me run the voltage up as high as I need to get the charging current I want. When I have to REALLY cram a charge in the batteries on my rig, I roll out my 15 volt, 250 amp DC power supply and power it through a variac. I can run the current all the way up to the limits of the power supply if I want to. You might consider getting a small variac. There are always some for sale on Ebay as well as the various electronic surplus houses. Very handy gadget to have around. If you get a high powered charger like mine, it is important to disconnect the batteries from the rig so that the high voltage necessary to force that kind of current won't affect anything in the rig. John