Every appliance I have ever just worked on used linecross, not just as a time base, but also as a "power good" signal. At Power On Reset the code looks for linecross and measures a few cycles to see if it's 50 or 60Hz. If it can't find a stable linecross then it keeps cycling around until it does. When linecross is established the control expects to see it at regular intervals. It's normal to miss a few from noise and minor power interruptions, but after a handful the appliance assumes that power has gone away and begins a shut-down sequence.
Normally linecross is very, very accurate and that's why it's relied upon by so many parts of the system. Of course, a gas powered alternator may not provide a stable source, and that can bring the whole system to its knees.
I did a professional instalation of a manual transfer switch, even before I got my residential electrical contrator license. I have a Honda 2500 W generator. To set up a "legal" manual switch-over, you can get various kinds of mechanical interlocks so you don't even need a subpanel. There are interlocks that make the main breaker mutually exclusive with on of the side breakers at the top of the breaker box, where the generator is connected. I used a subpanel (main lugs box) with two interlocked side breakers. Now this does not solve the problem for sophisticated computers and home entertainment.
In my working days, I was a hardware AND software guy building process control interfaces and occasionly fixing minicomputers. It seems like there is a market for this kind of engineering even in the home market, or serious work-at-hme situation. I am making note of this since I am a retired engineer (No PE unfortunately). In many cases, it would appear to need two subpanels--one with an electromechical (manual or automatic) switch-over for the furnace, fridge, and sump pump, with another one connected to the double-conversion UPS, perhaps with extra batteries for computers and serious home entertainment centers.
As y'all have noticed, there are UPS's, Inverters, and crap. Many hardware store Inverters are "Modified Square Wave" which means that the waveform is 0,+,0,-,0,+,0... [only three stair steps] which is OK for motors and resistance heat including incondesant light bulbs. Haven't tried one with CFLs; I use the Honda. BTW my Honda has a voltmeter and a voltage knob--you can set it for 100 volts (Japan Standard) or 120 volts (USA), and it is very quiet. I run the essentials of a four bedroom house with it.
Thank you for the discussion, I have gotten some more ideas for my retirement work as an electrician.
I guess that means another item to add to my test list. I have a Generac generator which I usually run at idle about once month or so, just to make sure it starts in the case of an emergency. I never thought to actually test the output. During the summer, I'll plug the edger into it during the test, just so I can get some useful work out of it. Unfortunately, that might not be enough to find the problem described here, since it is a different plug that goes into the house.
I was afraid someone would tell me that, cvandewater. I mean the fact that we've got to always pay way up at the Rolls Royce end for features that, it seems to me, should be the default in all models and price points, in this case, quiet operation.
The time that a battery backup lasts is a design parameter - reduce your loads and the backup lasts longer (don't light up the whole house, just the rooms that are used) or invest in a larger battery and the backup lasts longer. Or use a genset to recharge the bank and you have virtually unlimited run time. The min 1 hour battery backup is just another choice to minimize generator run time - when it can recharge the battery to >80% in 1/2 hour then it only needs to run 1/3 of the time.
Of course gensets can be made low noise - again another design choice. Most people accept a noisy genset and they are cheap to make, so that is what the majority of the manufacturers deliver, else they are forced in the small niche for expensive high quality, low noise gensets, which typically are only used a few hours or days every couple years.
I'm very curious to see what others think about cvandewater's proposal to help non-specialist people like us not have to go through the piecing together process. However, my concern is that our situation sounds like a pretty different one from the first application. Our outages tend to last 1-3 days.
I do like cvandewater's second application, the grid storage one that isolates us from the grid and pumps power back in. We're not technically on a weak part of the grid, but we're at the end of a section, such that when the power goes out 20 miles away in a totally different community so does ours. But we would need it to potentially last as long as 3 days, possibly 4.
Another thing: One big need we have in the quiet country is quiet generators. That's one of the several reasons we haven't gotten one, aside from 1) expense and 2) stealability in our location. Surely they can be engineered to be quieter?
Ken, thanks for the correx. My electrically-inclined husband is tackling the white papers.
I find it ironic that we are learning more in a few (though highly detailed--thanks again!) posts from the commenters on this article than we ever did reading company literature and/or talking to salespeople of inverters, UPS, etc. We're not just learning about "products," which we don't really care about anyway, but solutions, and even more important, figuring out how to determine what to get for what we need. That initial figuring out is the 101 and pre-101 info we can't seem to find anywhere else.
I installed an natural gas fired generator based on widespread power outage and how are gas stations going to get power to pump fuel out of storage tanks?
After selecting and installing my 12KW natural gas fueled generator, I tested it by loading down with appliances, lighting circuits, and base heaters. It work fine except for the CPU driven gas furnace which I could not get it going at all. The gas meter had reserve capacity when both furnace and generator is going so that was not an issue. (Note: Make sure that your gas meter does not starve your generator & furnace when running at full power. Check specs online.) The CPU board kept on giving me fault codes. I checked the output voltages on it loaded and unloaded as well as frequency, and they were within reason. But why? I decided to put a scope on the output of the genset and saw that there was a considerable amount of hash on the sinewave. I installed a small CVT just for the CPU power supply to clean things up and the furnace started right up. I suspect that the CPU used line frequency for clocking.
Lesson learned: If you decide on getting a nat. gas fired unit, make sure that all desired equipment work before you really need it. If you get a electrical contractor, make sure that he knows with factory training how to properly install generators, transfer switches, size gas meters, load testing, and be able to trouble shoot issues before you realy need it.
I often get frustrated at the clumsiness of the industry, just like Ann indicates - why can't you simply buy a true UPS/backup/genset unit that does exactly what it says and why do you have to piece a system together to do what should be a standard solution?
I have considered for a while now to start a new company to produce a product that I have been toying with for some years. In essence it would be the solution to all these questions: a simple unit that will always generate 100% clean sine-wave power from a large backup battery (at least 1 hour nominal power storage) so there is never a problem with compatibility or glitches on the output power.
This unit is not intended to be installed inside an air conditioned data center, but this unit will include a backup generator, in fact I want to integrate everything in the housing of a backup genset, so that you avoid buying two independent units (generator and UPS) and need to install and maintain all kinds of transfer switches and generator start signaling from grid power failure - everything should be integrated, power can be drawn from the grid when available (double conversion!) to charge the battery bank, but also solar or wind or other locally generated power in addition to the genset, such that the genset only needs to power up if all else fails and the battery energy level gets low - then the batteries can be charged at the optimal load level of the generator so that its efficiency and run time are optimized.
This means that the genset will run as little as possible (Where I spend most my time in India, rotating power outages typically last 1 hour, so the battery pack will carry the UPS through this and the grid will typically come back to recharge the battery bank before it is depleted) and solar or other RE can minimize the use of fuel which reduces pollution, spending on fuel purchase and transport and maintenance of the generator.
Another application of the double conversion with battery backup technology is in grid storage devices, where they can be installed in homes that are on a weak branch of the grid, so when it needs some help (usually in the afternoon) then the grid storage unit will start pumping power back into the grid. The higher sale price of afternoon power versus nightly recharge can easily offset the cost-price of the unit. Large benefit to the home where such a device is installed is that in case of a power outage, the unit can isolate itself from the grid and start power the home as UPS for a very long period (typically a day). In addition to these benefits is the avoided cost for the power company, who does not need to upgrade the transformer(s) and may be willing to pay for the installation of such grid storage devices.
The technology is not essentially different between these two different applications of a double conversion unit and incidentally the same technology can even be found in the electric truck that I have driven for several years, which was equipped with a grid-interactive inverter for both charging and V2G (Vehicle to Grid) capability. Typical power levels of electric vehicles are around 200kW which is also an interesting power level for data centers and a lot of other applications, but the power is easy to scale down (for example 10kW) or up. Battery technology today allows lifecycles of up to 10 years of daily cycling and inverter technology does *not* have a fixed MTBF, in other words: if the product needs to run continuous for 10 years then you can design the electronics to have long life, it is a design trade-off, not a fixed parameter of the equipment! The cost price is typically below $1/W and below $1/Wh. Let me know if you are interested in such products.
Sorry, I gave Ann some bad advice I want to correct. Constant voltage transformers use 'ferroresonent technology', a phrase which nagged at me. In checking it out, they in fact use resonance at exactly 60Hz as part of the control scheme. A generator may vary output frequency significantly for variable loads resulting in poor performance, thus generators are not a good match for these power conditioners.
After confirming this with Sola/Hevi-Duty tech support, they recommended 'double conversion' UPS's for mission critical electronics with standby generators. These, as I understand it, eliminate any 'switch' between line power and battery, instead the output inverter runs continuously on the battery supply voltage, and the incoming power only charges the battery. Somehwere in the description of a UPS you are interested in, you might also look for 'compatible with generators', before purchase.
We also did a bit of experimenting in my plant, and found that sequenced power-ups seem to have eliminated our instability problems. (We tested by hand, and will automate it shortly. We also did everything we could with software in the UPS's to reduce sensitivity to volts and frequency, as cvandewater suggested.
Appended are links to a couple of technical white papers from Cummins. The first may make you despair of ever using a generator with a UPS, but take heart, and go for it with eyes wide open. The second one has some mild contradictions with the first, but both are the best reads I found, if you are trying to spec a back-up generator for electronics.
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