Any EE types out there?

[Steve GF]

I've been conjecturating on reliability issues for inverter modules, leading to possible repair stategies when facing a "engine runs, but no power output" case.

I'm not a school trained EE, just an electronics hobbyist. My strongest area is probably old vacuum tube audio amps; I've re-capped a half dozen or so, set output tube bias, and replaced a few other components.

From my work with 'large' electrolytic caps, they seem like they might be the Achille's heel of genset inverter modules. I haven't seen detailed descriptions of generator inverter circuits, but in DC to AC inverters, there's a similar set of large electrolytics, the "DC link" capacitors. They seem to serve at least one function that would presumably be needed in generator modules: acting as a 'quick response' reservoir for fast load increases.

In a genset inverter module, I'd reckon the large electrolytics are called on (discharged!) by the module, to meet instantaneous load increases, to cover the demand as the module also adjusts the carb throttle stepper motor, to increase engine RPMS and generator head revolutions.

With electrolytics tendency to lose capacitance when sitting unpowered (i.e. "in storage"), I'd think that portable generators would (compared to a DC-AC inverter, that's energized and running daily, if not 24/7) typically present a worst-case scenario, for many generator owners---caps that have lost capacitance "on the shelf", suddenly pressed into service with high demands, with no chance to re-form.

Mashing all that around, leaves me with the concept that replacing the electrolytics would be the place to start, with a failed inverter module. The DC-AC inverter literature suggests cap quality is important, not just for heat rating, but frequency of duty cycle capability.


Any thoughts? Am I out to lunch?

 

[MorePower]

I totally get it. I've played around with a few old UPS inverters too and have run into some similar problems, those bad electrolytics always seem to be the first culprit. Your intuition is spot on. In generator inverter modules, those large DC-link capacitors are there to manage surge loads while the engine is getting up to speed. If they've been sitting idle for a while, they can lose capacitance and their ESR (equivalent series resistance) can spike, which might result in a lack of output even if the engine is running smoothly.

If you're facing a no-power issue, the first thing I'd suggest is to replace those capacitors with good quality, high-temp, low-ESR ones. It's affordable, straightforward, and it often does the trick. You're definitely on the right track.

 

[Steve GF]

Hey MoPo, thanks for the response. Good to hear I'm not out to lunch, lol!

I've decided for future home outages, I'll set generator out (in yard--after checking oil inside), level it, and power it on.

Then, I'll arrange the power transfer cable to house, and distribution inside...which should give me almost ten minutes of "unloaded" running on generator. I think 15 minutes is probably a tolerable 'wait time', to give link caps a chance to come up to snuff. An hour would be better, but who's gonna wait THAT long in an outage ))

Seems like many generator op manuals advise to "not load generator more than 30%" in first XX hours of use. Along with engine mechanical break-in (which really shouldn't take more than an hour, I'd think), I wonder if some of that "low load" break-in time is giving the link caps a chance to reform to their full potential capacity--since mfr has no idea how many months a generator might sit unused, in shipping, and in a warehouse somewhere, before getting in a consumer's hands.

 

[chescake_]

@Steve GF, you know, replacing the electrolytics is often an excellent first step for a 'runs but no power' inverter. They're usually less expensive than other power components and relatively easy to swap if you're comfortable with soldering. It's a high-probability fix

 

[Steve GF]

I won't say I know, but I've conjectured on it and saw maybe three vids---after a LOT of searching--where guys claimed success. Have you re-capped a failed module and got it going again?