older Trace/Xantrex acting up?

[domeguy]

My wife and I have been living off-grid for a while now.  We have a fairly normal house with the normal electicral appliances, such as an electric fridge, small deep freeze, etc.  We run things with a couple of Trace/Xantrex 4024SW inverters, about 2000W of solar, a 12' Dan-built wind turbine and a Kohler 12KV propane generator.  The system has been really amazingly reliable, but lately not 100% reliable.  While my wife and I were out of town, we had a severe cold snap AND my daughter w/ friends had decided to come up to our place for a fun weekend.  Luckily they were on hand when the power when out!

It seems as if the autostart circuit in the older Trace inverter wasn't happy with the quality of the power from the generator, or something; the generator would start and run for almost a minute and then quit.  We resolved this issue (via cell phone with my daughter's engineer boyfriend) by bypassing the autostart feature in the inverter and setting the generator to "RUN".  This all happened at about 9:00 at night; so I told them to just let it run all night and then set the generator back to "AUTO" in the morning.  The batteries charged just fine, but now that I'm home I don't have the confidence in my system that I did just last week.

A couple of things have occurred to me - the problem could be in the voltage regulation system in the generator, which I don't understand at all.  It seems unlikely that the inverter would have such a subtle failure and keep working otherwise.

Any thoughts?

[ChrisOlson]

Something was out of spec - either voltage or frequency - so the inverter failed to sync with the generator, so it shut it down.  It should've tried five more times to restart the generator and sync with it again.

Are the inverters series stacked with the ISC-S cable, or parallel stacked?  How they are stacked can affect syncing both inverters with the generator, especially in cold weather if the generator output isn't "clean" or on-spec.  I'd see that problem with our dual SW+4024's with the EcoGen when the voltage was below 220.  And sometimes the master inverter would try it three times before it would finally sync with it and put the generator to work.

I finally "fixed" that by yanking the Generac out and replacing it with a new Honda generator.
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Chris

[domeguy]

Thanks for your comments, Chris.

In this case the inverter may well have tried five time to get a good start from the generator.  One thing I've noticed is that I can hear an undulation in the sound of the generator when there is no load on it.  This doesn't seem to be a problem when the batteries are charging at low current (float charging) - the inverter doesn't shut it down then.  As I mentioned, this system has been working almost flawlessly for over five years, including some very cold (sub-zero) weather.

But to answer your question, the inverters are stacked with an auto-transformer* between them and the control cable is connected between them.  I use the generator start feature on the older Trace unit.  The generator makes split-phase power, with a 120VAC cable going to each inverter.

If you're correct about the generator being out of spec at startup, then I suppose some adjustment to the regulator is required.  I'll see if there is an adjustment there.

*I still have the autotransformer that I used to make 240VAC with only one inverter.  I rewire it, of course, but I think it sometimes evens out the power load when it's all coming from one of the legs.

[ChrisOlson]

Identical to our setup.  We have a T240 between the inverters to leg balance the 120 volt loads.  Ours are new SW+ inverters so we have the external Trace GSM for auto gen start.

I'd take a look at the governor on the generator.  If it's surging a bit under no load, it could be sticky and cause a sync problem due to either high or load freq or voltage.  The inverter requires 57-63 Hz and it has to be stable for at least 20 seconds before it considers it OK.  The voltage range the inverter will accept is adjustable in the gen menu.  But if it's cold out, making the governor less stable yet, and that generator is surging the inverter will tell it to go to hell and come back when you can supply me with stable power.   
--
Chris

[domeguy]

I just talked to the service guy at Colorado Standby.  His suggestion that the linkage rod that connects the governor to the throttle might have too much play appears to be true when I checked it out.  I'll be getting a new part soon.  Of course I won't really know until the part has been replaced...

I'll get back when I've put the new part in.

-Lee

[ChrisOlson]

That could possibly do it.  One thing that's different about Trace/Xantrex inverters is that they actually synchronize both voltage and frequency with the generator, and that gives them the capability to do generator support.  Meaning they can use a generator to take over heavy loads and if the generator can't supply all the power for the load the inverter will supply what the generator can't.  This allows us off-grid folks to use much smaller and more fuel efficient generators.  Outback and Magnum inverters don't have this capability, however, Magnum is coming out with one in a few weeks that does have generator support.

So, because of this, the Trace/Xantrex requires stable power from the generator.  If the gen is surging (or undulating as you call it), that means the frequency is constantly varying and the inverter won't sync with it.

During the final stages of absorb charging, the Trace/Xantrex does load and unload the generator to "test" how well the bank voltage holds up during the unloading part - this is how it determines if the bank is nearing the charging end amps.  If the bank drops too much in voltage when it unloads the generator (and reduces the charging amps to below the ending amps setting), then the inverter goes back to absorb charging for a bit more time until it decides that the bank voltage is holding up when it drops the amps below ending amps.

This "pulse" type charging is actually great for the batteries - they love it.  But again it requires a generator with a stable governor because if it starts to surge when the inverter does this, the inverter will spit it off and see if it evens out and becomes stable.

Edit:
The new inverter Magnum Energy is coming out with is called the MSH4024RE.  It has dual 60 amp AC inputs, and generator support.  The first ones will be 120V only and are non-stackable.  It is in beta testing yet, but very close to production release.  It will be Magnum's version of the venerable Trace SW.
--
Chris

[domeguy]

I never posted the outcome of my inverter/generator travails:

In the process of installing the new governor linkage rod in the generator (Kohler 12kW) I realized that it wasn't the problem.  BOTH bolts holding the carburetor to the engine block had backed most of the way out and the carburetor could wobble; which it did when the engine was running - hence the "undulation" in engine RPM.  I should note in my own defense at this point that the carburetor itself is not visible at all unless the generator is partially disassembled.  In the process of correcting this, I somehow managed to lose a washer (or something similar) and when I started the generator for testing it only got about one revolution before clanking to a stop.  I then bought a new generator - a Kohler 14 KW unit - and everything worked well again.  This all happened around the end of 2012.

This newer Kohler has an unfortunate intermittent problem of throwing an error (something like "main power overload") and not starting.  This has now happened three times since I bought the generator in January of 2013.  Last night this error prevented the generator from starting and, naturally, the power was shut down by the inverter.  So last night, after clearing the error at the generator I allowed the inverters to again start the generator.  The master inverter (Trace 4024 bought in 2003) was never happy with the power output, although the slave inverter (Xantrex 4024 bought in 2007) accepted it quickly.  However, when I set the generator function to "ON" (rather than "AUTO") at the master inverter, the power was accepted rather quickly.  I let the generator run the rest of the night and set it back to "auto" this morning.

Since the new generator was installed about 18 months ago the generator has auto-started many times - about 1 to 5 times a month - and failed to start only two times.  The weather last night was foggy.  I should also note that I cannot hear any variation in RPM with this generator.

I'm getting pressure on the home front to hook up grid power, which is possible but quite expensive (about $50K).  On whole, I'm very pleased with the up-time I've been getting from this system and I'm not familiar with the reliability I might expect from a newer inverter system.

If you've managed to read this far, maybe you have a suggestion about my inverter situation?

Thanks for your time,

Lee

[ChrisOlson]

If you've managed to read this far, maybe you have a suggestion about my inverter situation?

Lee, we upgraded our SW Plus system to a new Schneider Conext/Xantrex XW6048 and have never looked back.  Your pressure to spend $50 Grand to get grid power will be gone after you install one of these because they're more reliable than the grid and put out cleaner power:



And the controls for the power system on our kitchen wall, with an Android tablet computer that connects to the Conext ComBox for system logging functions, and control over wireless network: