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Iron Genny update
By phil b, Section Wind Posted on Thu Jun 07, 2007 at 06:17:36 PM MST
Here's some data I collected yesterday from the iron genny.

35 mph winds and 45mph gusts

I had the iron genny hooked to a fully charged 48 volt battery bank being controlled
by a Trace C-40. It didn't take long to determine when the C-40
is bypassing power to the dump load at 9.3kHz, which caused the values to
change rapidly.
I used my digital camera to snap pics of all 3 electronic meters at the same time.
When graphed,it's easy to see the values are not as good as they should be.
The wattage ranged from 0.5 kW @ 60 Hz to about 3.3 kW @ 104 Hz.
I used (Hz*120)/24poles to get the RPM values. The wind averaged 20 mph
for the hour I took the readings below.
Hz    Vac    RPM

1    34.48    285
12    36.02    295
73    39.71    329
28    42.9    366
67    41.37    368
89    43.3    369
15    41.51    371
32    42.01    402
01    44.4    415
35    42.67    437
    43.9    465
34    44    487
    45    520
Next, I hooked up a scope to the genny. At about 70 Hz or less, I got a pretty good
sine wave.

Higher Hz chopped the top and made it look more like a PWM trace.
Any ideas what caused that?

Here's a pic of the dump load.It needs to be resized.
The battery voltage was still higher than 48 volts after 2 hours.

A pic of my new and soon to be returned multimeter. It's supposed to do ac&dc watts, ac&dc volts, amps, everything but ohms.
Most of the time, it does what IT wants. I only got a few good watt readings.
Expensive toy. Here, it is registering the dump load kW correctly.

I have a 50mV, 100 amp shunt. Can someone tell me how to use it with my Fluke DMM multimeter correctly?
Constructive comments are always welcome!

Iron Genny update | 6 comments (6 topical)

Re: Iron Genny update (3.00 / 0) (#1)
by Flux on Thu Jun 07, 2007 at 12:38:52 PM MST

I can't make any sense of your figures, I haven't much idea what you have or are trying to measure, but with the dump load chopping at 9kHz I think you have to think long and hard whether your results are meaningful.

Frequency meters are a pig in the presence of fast switching waveforms and need careful filtering. For power measurements again you probably need a lot of filtering and careful connection of leads particularly ground.

The modern digital meters are more inclined to lead you astray than their ancient analogue counterparts. Measurements under these conditions is a bit of a specialist job and requires a bit of instinct that you acquire over time, what you see may not be what you get.

The red hot resistor is a good rms indicator, you are producing something useful.

I wouldn't trust anything other than a coaxial shunt at that frequency with chopped square waves a conventional shunt will be an inductor.

Flux

Re: Iron Genny update (3.00 / 0) (#2)
by TomW on Thu Jun 07, 2007 at 12:42:14 PM MST

phil;

Reading the shunt current is simply a matter of connecting the fluke across the shunt "meter" terminals and reading millivolts on whatever range you need [AC / DC]. The 100 amp, 50 mv shunt should drop [show] 1 millivolt [mv] for each 2 amps. So if it is passing 100 amps the meter will show 50 mv. The rest is just math. Check my math, cuz I suck at math.

Good luck.

Cheers.

TomW

The Truth is the Truth, even if no one believes it; and a lie is a lie even if everyone believes it

Re: Iron Genny update (3.00 / 0) (#3)
by Ungrounded Lightning Rod on Thu Jun 07, 2007 at 12:59:12 PM MST

Next, I hooked up a scope to the genny. At about 70 Hz or less, I got a pretty good
sine wave. ... Higher Hz chopped the top and made it look more like a PWM trace.
Any ideas what caused that?

Yep.

Cutin was about 70 Hz. Above that the battery was clamping the output voltage. The generated voltage was still climbing with RPM but the observed output voltage is that minus the resistive drop of the current through the coil and wiring resistance.

The series resistance of the battery and the local wiring is very small and the diode voltage drop varies only a little with current, so the middle of your observed waveform just upstream of the diodes is almost completely flat-topped at the battery chemistry voltage plus two diode drops.

Re: Iron Genny update (3.00 / 0) (#4)
by Flux on Thu Jun 07, 2007 at 01:16:45 PM MST

Yes that's right about the waveform. Up to cut in you will see the open circuit waveform of the alternator, usually fairly near a sine wave.

Beyond cut in the rectifier and the battery will chop the peak to near constant volts.

The dog leg as it crosses zero is caused by the commutation of the rectifiers on the other phases. That waveform is perfectly normal that is why I keep saying you can't use the normal sine wave based equations for these alternators on load.

If you want to measure power into the battery from the rectifier you can probably get away with the shunt without too much trouble.

If you are using that shunt in the chopped waveform of the charge control then I wouldn't believe one bit of it.

I would measure all your power into the battery that is what you are looking at. Even then you will need to be sure that the chopped mess from the dump is not messing the results. The battery will filter most of it out but a few wrong ground connections may swamp the meters.

Probably if the dump load is reasonably chosen you may be better off connecting it directly to the battery and taking your measurements, things will then work normally.

Flux

[ Parent ]

Re: Iron Genny update (3.00 / 0) (#5)
by phil b on Thu Jun 07, 2007 at 02:40:14 PM MST

Thanks Flux and ULR,
I didn't remember seeing anything close to that warped sine wave form without iron. I thought it might have been adding it's contribution. You guys are great!

I will repeat the tests by using a known resistive load coupled to the generator to get accurate numbers without the high kHz stuff. This data set is bad.

Since this is a new mill, I did check for 3 phase short circuit shutdown. Did fine.I also ran it with an open circuit, no load speed on the oscope pic. It pegged out on 184Hz and 120 Vac, if the interference didn't adjust the numbers.

Also, thanks to TomW for relieving the mental block of an old brain cell. Sort of a duh! thing.

Re: Iron Genny update (3.00 / 0) (#6)
by vawtman on Thu Jun 07, 2007 at 06:09:26 PM MST

Nice Work Phil
HAVE FUN :>}}}}
Mark

Iron Genny update | 6 comments (6 topical)

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