At long last I'm putting up photos of our Generac Guardian EmergencyStandby Generator
. This thing is extremely cool. It monitors incomingutility power and if there is an interruption automatically firesitself up and switches over loads you designate the generator power.While running it's about as loud as a lawn mower and from inside thehouse you can't tell you're on generator power.
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Strangely, I ended up purchasing the thing through Home Depot
.They had by far the best price. They sell both consumer grade stand-byunits and the water cooled industrial ones up to 45Kw. They take careof the installation, hooking it up to both power and gas, etc.
In my research on standby generators a couple of issues came up that were hard to track down:
- gas supply line issues
- UPS issues
I have natural gas supplied to the house which I had originally wantedto use for the generator. I couldn't get a clear answer as to whetheror not the gas supply to the house would be sufficient to run thegenerator. Apparently the generator pulls alot more than averageconsumer appliances and its possible that the gas service might need tobe upgraded in order to support the generator. Since I already had twopropane tanks in the yard, I decided to avoid the whole mess and runthe generator off propane. This has the added advantage that it putsout more power on propane and I'm completely off the grid.
The second issue has to do with an interplay between generators andtypical line-interactive UPS's you can buy at consumer electronicsstores. These line-interactive UPSs pass through AC voltage and monitorit. If they notice a certain variance they switch over to the internalbattery. Once voltage comes back to within specs they switch back. Fromwhat I've been told the tolerance that these UPS can deal with arefairly narrow in terms of voltage and frequency.
Since the generator is a relatively weak source of power in comparisonto utility power, each time a new load is switched on the generatorwill react slightly. The closer the generator is to it's max load, themore it will tend to react to additional loads (at least if theWesterbeake 5K generator on my boat is any indication). What peoplewill tell you is to have a generator that is at least 5X the capacityof all the UPSs you have. This way when the UPSs switch on and offthere's less likelihood that they will affect the output of thegenerator.
If your UPS load is some significant fraction of the output of the generator what can happens is as follows:
- UPS notices slight variance in power due to some load coming on, so switches to battery.
- The generator stabilizes and power comes back into the green.
- The UPS notices power is back in the green, so switches off battery onto generator.
- The generator output momentarily dips as it adjusts to the new load
- The UPS notices the dip in power and switches to battery
- etc. eventually burning out your UPSs.
The solution to this problem is to replace your cheap consumer gradeUPSs with "real" ones. These "real" ones are what are known as "fullyonline" UPSs. They actually convert incoming AC power into DC and thenback into AC to power the loads. As a result it's always "converting"power making certain that the output voltage is solid. A side-effect ofthese UPSs is that they can stand a much wider variance in incomingvoltage and frequency than consumer grades UPSs. They are much lesslikely to exhibit the switching on/off feedback loop and I've been toldyou only need to have about 2X the generator vs the UPS load when usingfully online UPSs.
I ended up replacing all my cheap APC and Cyberpower UPSs with aPowerWare 9210 which is something I should have done ages ago. ThePowerWare is a very good UPS.