voltage monitoring relay - what works on an ST head?

[BruceM]

I tried a Schneider 831VS-240A voltage sensing relay.  It is very unhappy with the no-load ST-3 waveform, even when I added some filtering before the relay.  The no load waveform is close to a triangle wave, a bit ragged.  Massively filtered, to a more curved form, this VS relay is still unhappy, even with a load.  With a 1/2 HP motor on and no or modest filtering  it is happy and works properly.  So it is just not going to work for my application.

I wonder if anyone has found a voltage sensing relay (high, low, time delay trip) that seems to work well on an ST type waveform. 

I have my own voltage range sensing circuitry on my ST-3 AVR but was hoping to just buy something off the shelf for my neighbor's DES propane conversion project. 

[buickanddeere]

The only way to obtain a "smooth " output . Is to forget about those funky harmonic windings. And use one of those output terminal sensed and supplied rectifier/regulator units to power the brushes .

[mike90045]

Maybe power the relay from the rectified DC bias winding ?  Should not be much of an extra load on it.  Add a DC cap if needed (heard a cap helps the waveform anyway)

[BruceM]

 I tested the Schneidetr/Magnecraft 831VS-240A on my own ST-3 with my own AVR, which is not using the harmonic at all.   Still no joy without a load, and didn't like a filtered input either.  The ST head's output is a bit rough, some spikes on the top/bottom of the sine, and some "ratcheting" even without the harmonic.  I fiddled with variations of RC and LC filtering for a couple hours and nothing seemed to make the damn thing happy, even though the spikes were diminished greatly, and the waveform was fattened up. (Seemed better than with load to me.)  This unit is an AC line voltage monitor, and is not rated for a DC input.

Anyone tried one of the ICM 491 line voltage monitors?

[EdDee]

Hi Bruce,

A small trick I have used before to smooth out/condition a crappy waveform - Step down to 12vac, ac cap across the 12v and then step up to input voltage using a transformer identical to the stepdown... Play with the cap to try and hit a close to resonance on the low voltage side (ferrite beads also help a bit with the little nasties too, sometimes a toroidal ferrite filter from a PC power supply also works wonders, but of course, they only trap the really hi frequency stuff).... Sometimes this crude and inefficient RLC circuit cleans things up enough for sensing circuits... Just a thought...

Cheers
Ed

[BruceM]

Thanks Ed, good idea. Transformers are one way to add some serious filtering inductance.  I do have a pair of tiny toroidal transformers I could use back to back and will see if that makes the damn thing happier.  I'll solder that up this AM and give it a go.

It's very strange that when I filter the AC waveform of higher frequency distortions so it's looking much smoother on my 'scope the 831VS then indicates out of range, even though my RMS voltmeter says 240VAC on the filtered waveform.  It's out of range indication stays lit no matter what the voltage setting on the 831VS, with my 1/2 hp motor load or without.  I suspect that like everything else, they have gone to an embedded microcontroller and their software is computing AC voltage in a shortcut manner (not true RMS) that is resulting in some pretty strange behavior.  In part, they may not like the frequency variation my Listeroid 5 Hz power stroke causes.

[EdDee]

I think you may have hit it on the head with the 5hz power stroke.... lemme know how it pans out.....

[BruceM]

A tech support guy at ICM did some good checking for me.  Their products are also microprocessor, sampling based, and not designed for generator output.  Spikes and such, waveform irregularity and the frequency variation from our low speed engines are going to be problematic for their ICM491 and 492 products.  They say they are dong essentially the same thing as the Magnecraft 831VS type units. 

So it appears that unless I can experimentally find filtration (on it's input only) that keeps the 831VS unit happy, I will have to roll my own voltage monitor.  Sheesh. 

[buickanddeere]

Still an advocate of hanging a big fat DC capacitor on the excitation circuit. And an AC oil filled power factor "Run" capacitor on the output. Not perfect but good return on the time and investment.

[BruceM]

I found a Siemens voltage monitor that does both AC and DC input monitoring, which should be more likely to give true RMS regardless of frequency and waveform irregularities.  If it works on my neighbor's ST-3 output.  I'll post it. 

I had no luck with filtering the input to the Magnecraft/Schneider 831VS unit.  There seem to be lots of copy cat units similar to that, no doubt also made identically in the same factory in China with the same crappy firmware. 

[BruceM]

The Siemens voltage monitor works fine, relatively easy to program to exactly what voltage range and delay you want.  The one I got is the SIEMENS 3UG4632-1AA30.  It requires a tiny bit of 24V (AC or DC) for operating power, but I couldn't complain at the $39 price it was being sold for on ebay.  I think the 3UG4633 does not need 24V. 

This unit doesn't care about frequency up to about 600Hz, and will monitor DC voltages just as well.