Square Wave Inerters

[RICK NAPIER]

I am a new member and I was hoping someone may have some experience with my problem. Reading the installation guide for Kidde 120 volt smoke detectors I discovered a warning that their detectors cannot be used with square wave or modified square wave inverters. These inverters are popular on solar photovoltaic systems and I have a number of these supplimentary power systems installed in homes.

I have since contacted Firex and BRK about this issue. Firex was unable to tell me if it was safe but initiated testing of their devices and will contact me in a month or two with the results. A BRK engineer informed me that their detecters cannot be used with these inverters. I have yet to contact any manufacturers of low voltage systems.

So if anyone out there has any information I would apprreciate it.

 

[zbang]

I'll go out on a limb and say that in general, square-wave inverters are evil and should be dumped in the river (or other suitable wet location). Stepped-square inverters can be OK if they use more than one step and have proper output filtering.

 

[George Stolz]

I do know that a customer of mine had a modified square wave inverter from outback, and he ran his PC on it with pride. I have a hard time understanding why a smoke detector would not be able to tolerate it.

I'd never considered the possibility of prohibition on the instructions, so I installed whatever brand smokes we were using at the time without a second thought.

 

[ptonsparky]

I do know that a customer of mine had a modified square wave inverter from outback, and he ran his PC on it with pride. I have a hard time understanding why a smoke detector would not be able to tolerate it.

I'd never considered the possibility of prohibition on the instructions, so I installed whatever brand smokes we were using at the time without a second thought.

George, I am appalled. First I find out you don't secure your wires in the attic and now to find out you don't read every set of installation instructions, my image has been shattered.

 

[kc8dxx]

Terra Firma

Terra Firma

I'll go out on a limb and say that in general, square-wave inverters are evil.

I'll stand on terra firma and say that square-wave inverters are evil.

And vendors that hide the fact that their inverter is a square-wave type are to be drawn and quartered.

 

[tallgirl]

And I'll add that inverter and UPS makers who don't admit that they aren't actually outputting 120vac are the spawn of Satan. I use small Intermatic UPSes for small loads (switches, NAS boxen, WAPs) and they output about 90vac. I just now checked one of the many Intermatics I have and with just a cable modem for a load, the output was 88vac. Of course, I'd have to put it on a scope to see what that waveform looks like, but I'm guessing it's a really BAD looking waveform.

That's something else to consider when hooking devices up to inverters -- the output voltage might not be high enough, when stepped down through the device's internal transformer, to power the device properly.

 

[zbang]

I'll stand on terra firma and say that square-wave inverters are evil.

Hmm, yes, that's a bit better.

And vendors that hide the fact that their inverter is a square-wave type are to be drawn and quartered.

The Fluke 41 power analyser is more than just a friend (although at almost $2k new, it had better be). A few years ago I was eval-ing small UPS for a project. Small in this case is <6kva. With the Fluke and a 1500w load bank (three 500w QH work lights), was was able to capture all sorts of interesting data.... APC SmartUPS and Liebert were great (hardly any harmonics at all). Brand O, which, I think has vanished from the market, had >0.5% harmonics past the 20th. Their marketing folks were not too happy when I faxed them the plots and charts. :grin:

 

[robbietan]

square wave inverters are fine for photovoltaic systems, maybe because most of the time these systems power heaters (who dont care whether they receive sine waves or not).

the manufacturer probably needs the peak of a sine wave to generate a signal to activate the thing.