CGG AVR- not so hot for non-linear loads

[BruceM]

Hi Guys,
We're using the CGG AVR on my neighbor's ST-3 with propane converted DES 8/1.  It is using the Harmonic winding as the excitation source, since it just doesn't work at all using one leg of the line voltage (can't start even a 1/2 hp motor).  Tom lists that configuration, but frankly, he should not.

On the harmonic the CGG AVR works fine on induction motor loads, but on non-linear loads like a small wire feed welder, or a Vitamix on (electronic controlled) low speed,  it regulates the voltage so low our RMS voltage monitor trips. (regulates to 170V RMS instead of 240, and 85V on the stepped down 120V supply).  On straight harmonic the ST-3 does fine on these same loads.

So alas, while Tom's price is appealing, the AVR being sold by CGG has some serious limitations:

1. You can use it only with the harmonic winding for excitation.  
2. It regulates only to peak AC voltage levels, not RMS,  and will down regulate to grossly low voltage for some non-linear loads.

Can anyone suggest a 240V AVR that does a decent job of regulation?  Something that says "RMS" voltage in the specs perhaps?

[carlb23]

bruce,

I am using one of tom's st115 avr's on an rigid 10kw generator that has a bad harmonic winding connected to one of the 120 vac legs and it is working fine.

[BruceM]

Thanks for the info Tom.   What is your engine on that 10KW head?  What kind of load?  I suspect that much of the problem with this CGG AVR without the harmonic is that the ST-3 is intolerant of imbalanced loads.  A 240 to 120 step down transformer (instead of harmonic)  is what I use on my own ST-3 to drive my homebrew AVR. 

The CGG AVR we have does seem to regulate well on the harmonic- except for larger non-linear loads. My homebrew AVR has the same problem, since I could not use an analog RMS computing IC and still correct for flicker. 

We don't need flicker correction on my neighbor's system, so I'm looking for a true RMS voltage regulating AVR. 

[carlb23]

The engine is a 14hp 3600rpm Subaru engine and the load was my normal house load maybe 1500 watts plus a 3.5 ton Central ac unit with air handler.    I also have tested it with a resistive load up to about 7kw.  This avr is connected to L1 since the genhead has a bad harmonic winding.  This is only used as a backup generator when i need air conditioning during a power outage, but, for most power outage issues my 6/1 is fine. 

[BruceM]

Thanks Carl. Your 10kW head can handle load imbalances way better than our ST-3; it can handle none at all.  I'm glad that works well for you. I think I was the one who recommended CGG's AVR  as a way to get around your bad harmonic issue.

I think our AVR problem is more specific to the ST-3, and relatively (to the total capacity) large non-linear loads.  It does work fine on the harmonic for motor and resistive loads. The surprise was the response to a Vitamix set to the lowest speed... our our 120V down to 85V, enough to trip our voltage monitor.  It's a universal (brush) motor fed by a triac based (wave form chopping) speed controller. A smaller capacity generator head has a lot more waveform distortion when presented with large low PF, non-linear loads.

All the low cost AVRs I've found so far use the rectified AC average voltage for regulation, not RMS voltage.  RMS voltage regulation would add about $10 in parts cost so it gets left out.  I'm still searching for an affordable true RMS voltage regulating AVR.  Mostly, there are no engineering specs to speak of on the AVRs I"ve found, all from China.  The sellers are sales/marketing and have no idea what they are selling.  I'd make my own, again, but don't need another project.

It makes me appreciate the stock harmonic excitation, which actually does a fairly good job for nasty non-linear loads.

[BruceM]

The CGG AVR has become very erratic, not regulating intermittently and sometimes with load changes.  I wonder of some of the non-linear load problem was in fact the early stages of this failure, at about 60 hours.  I took it out for Jeff today, going back the the straight harmonic until it can be replaced.