Wednesday, May 14, 2014

Thoughts on inverter and generator sales pitches

So, when you're shopping for inverters or generators, they make a big deal about the power being "clean sine wave" because "then you can power sensitive electronics like computers"

I think these days (IE last 5 to 10 years) that's exactly opposite of true.  Computers and really any electronics are pretty much required to be energy star compliant, which means they're all running off switching supplies, and most of them are universal, usually 85 to 250 volts.  The very first thing that a switching supply does is rectify the inbound power to pulsating DC - it would actually run BETTER off a square wave than off a sine wave.

So you could run most modern electronics off the nastiest-ass power, varying wildly from 100 to 200 volts, frequency all over the shop, square wave, triangle wave, sine wave, wavy wave, and it probably wouldn't give a toss about it and it would run just fine.

It's motorized appliances and power tools that would probably be most affected - using a non-sine wave will affect the efficiency and power output of a synchronous motor and probably would irritate even brushed motors.  It'd be really irritating to something like a refrigerator.


Karl Loeffler said...

Neighbor lost their Denon receiver, Samsung TV, and Cable box while running off their "non-clean" generator. I'm not "real" concerned since I run all power through a APC Power Conditioner for my home stereo/TV and my PC setup. Only two things I'm really worried about.

Karl Loeffler said... this stupid "Please prove you're not a robot" is a real P.O.S...

Anyway, my neighbor lost their new Denon Amplifier + New Samsung D8000 series TV, and Cable box while running on a generator that was not "approved for electronics use" believing the same thing you state. I personally run all my stuff through a power conditioner because I'm paranoid about having good power. My old house would experience power drops when the A/C kicked on down to 84V, and at that point I bought APC Power Conditioners for the electronics. Never ran better! YMMV.

John Ridley said...

Probably the voltage variations are more problematic, especially if they're caused by sudden large inductive loads on a substandard service.

Interesting info about the neighbor. It would be interesting to do an autopsy on that equipment. Just looking at the schematics for switching supplies I can't imagine why they would care at all what the input waveform looked like.

However, I can easily believe that a purely inductive generator might be putting out some very weird stuff.

I'm primarily thinking of inverters here - the cheap ones put out square waves rather than sines, and ISTM that a switching supply should actually be happier about a square wave than a sine.

Actually I think I might know what the problem is - most good power supplies have an input filter, usually a common mode choke. If you feed that something much different than a sine wave, it's going to start trying to clamp it, and it could easily overheat and burn up. It's possible that the only thing wrong with them is the simple choke right where the power goes on.

That's ironic if the thing that went wrong was the input filtering when in fact input filtering isn't even needed anymore. Though it probably is needed to some extent, just to keep out HF noise, but the low pass could be boosted to 1000 hz without trouble, instead of 100hz or whatever it is now.