John Summerfield wrote: > Mikkel L. Ellertson wrote: >> John Summerfield wrote: >>> Mikkel L. Ellertson wrote: >>>> John Summerfield wrote: >>>>> In the event of a quake, it seems to me prudent to cut HT and >>>>> mains, but >>>>> then generator sets automatically starting up would tend to negate the >>>>> action. >>>>> >>>> Not really - before you cut the mains, you switch the generator set >>>> control to off instead of auto. >>> And if the power goes when nobody's home? >>> >> The same thing as happens if the power does not go out. Unless your >> generator runs out of fuel before the power comes back on. After >> all, if nobody is home, you are not going to cut the mains either. > > If the mains is down, the power's off. > Your point? You were talking about pulling the mains, and having a generator does not change that. Not being home is home means the mains do not get pulled in any case. On the other hand, if you have an auto-start generator, the mains "get pulled" because the transfer switch disconnects them, protecting you from power fluctuations. > >> On the other hand, if you do not want the generator to run while you >> are gone, then turn the selector to off as part of the normal >> preparation for being gone for 2 weeks. You do do things like turn >> off the water heater, put the thermostat in the away setting, and >> things of that nature, right? > > Being away does not mean I don't want the computers running. I used them > daily while away, it's how I knew one didn't come back up. > So? If you have the generator in the off position, then it functions the same way as if you did not have the generator. The Auto-Off-On switch just controls the generator starting or stopping. The transfer switch uses generator power to switch the connection, so it would not change. >>> I was away two weeks recently, and the power went while I was away. One >>> of the systems didn't come up, and when I got back a week later the >>> office had an evil smell, the smoke got out of a switch. >>> >> About the only change having an auto-start generator would be that >> your power would have been out for a shorter period of time, > > Without an autostart generator, the system would run for a > strictly-limited, short time. > > With one, it could run for days. > Yes - this is why you have a generator. So the system stays up longer then the UPS alone will manage. The UPS then only has to provide power long enough for the power loss timeout before the generator start sequence kicks in, plus the time the generator takes to start and its output stabilize. The the generator takes over, powering the system(s), and recharging the UPS. Now, if you do not need the system to be up and running longer then the UPS will provide power for, that is another story. But that was not what we were talking about. > >> >> I fail to see how a properly installed auto-start generator would >> increase your risk. The transfer switch isolates the generator from >> the outside power - there is never a connection between the >> generator and outside power. The only place they should meet is in >> the transfer switch, and that is configured so that only one can be >> connected to the load at a time, and the two sources can never be >> connected to each other. I can see how an improperly connected >> generator can cause problems, but that is a problem in any case. > > > Most power failures are a few seconds, sometimes some electrical > appliances don't even seem to notice. Fairly recently, the clock on one > oven kept running, the other didn't. Sometimes, some but not all > unprotected computers restart. > In that case, the generator would not start up either. That is not how an auto-start generator works. There is a power loss timeout that is necessary before the generator start sequence kicks in. How long the timeout is depends on your needs. I know places that have it set for 2 minutes, and places that have it set for 2 hours. The controls run off the same battery that normally starts the generator, and also function to keep the battery at full charge when there is power. There is a separate timer setting that controls how long the normal power must be on, and in the proper range, before the change is made back to normal power. Power loss, or excessive voltage fluctuations reset the timer. > Once one needs better protection than that, then one increases the time > power may be on when it should not. > Well, if it is a house, then I would want things like the refrigerator powered until power was restored, but that is just me. On the other hand, if you want the backup generator to run for 4 hours, and then shut down if power has not been restored, this is also an option. It is not a commonly used option, but it is not hard to implement. I would have to look, but I believe there are transfer switch/generator control systems that offer computer interfaces similar to what is offered for a UPS. You are talking a lot more then a couple of time delay relays and a latching contractor in a modern backup generator system. (A smart controller is cheaper then a couple of time delay relays now days.) > If it's a UPS protecting a computer or two, it's only covering a small > area, it doesn't matter so much, but when you go to backup power > supplies powering a house or more (until the 60s we had no mains power, > it was all 32-volt DC) then the likelihood increases quite a bit. > The thing is, you size the backup power for what you need to keep running. Keeping the entire house powered up is not how most home systems are configured. You configure things so that just the necessary circuits are powered. I prefer powering the entire house, because usage changes, and the circuits you need powered changes with it. But it also means that you need a larger generator, because people will use more power. The thing is, you have the option of using a generator as a UPS extender, to keep the entire place building powered, or something in between. But the risk of powering things from a generator are not greater then powering them from normal power, as long as you are using a proper generator. The risk is much greater if you are using a generator that is not designed for the job, but that is not what we are talking about here. A proper auto-start generator will shutdown if the output goes out of specifications, if the motor starts to over heat, lose oil pressure, etc. It will not try to crank too long and burn out the starter, or burn up the battery cables. It will also shut down if you try and draw too much power. (It will handle brief peek loads such as a motor starting, as long as you are not fully loaded otherwise.) As for not having mains, and running on 32-volt DC, that was a greater risk. Because of the lower voltage, you required higher amperage. Because of this, mains capable of interrupting DC current at this current level tend to be expensive, and require a fair amount of maintenance. (AC current is much easier to interrupt.) Disconnecting anything under load is much harder on DC power. The exception to this is pulsating DC, where you have 0 voltage points as you do with AC, but that has its own problems, and few, if any advantages over using AC. Mikkel -- Do not meddle in the affairs of dragons, for thou art crunchy and taste good with Ketchup!
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