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Old 05-18-2012, 01:14 PM   #1
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Practical ways to protect appliances against unstable power


Recently, our power in the neighborhood for whatever reason has not been stable. It would go out for a split second and then come back. It doesn't happen all the time, but did happen a few times recently. My computers and routers are protected by an APC, which worked out beautifully.

I already installed a surge protector at the 200Amp panel, but apparently, it does nothing in this situation. I wonder what's the best code compliant way of protecting expensive appliances against such frequent fast power outage especially now that I'm in the last stage of wiring for the kitchen remodel.

Code requires dedicated circuits, so I have a home run 240V/50W for cooktop, 240V/30W for oven, both of which require direct connection (via wire nuts instead of plugs) and a 120V/20W for MW Oven, etc. I'm hoping to have a way to sustain the appliances for a few seconds to bridge the <1 second of power outage or can have time to shut them down normally if the power outage stays. But I should point out that having a generator does not seem to be an option for us (no room).

Any pointers for me to research into? Thank you!

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Old 05-18-2012, 01:48 PM   #2
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Practical ways to protect appliances against unstable power


Do you have any data that shows that short voltage sags or short voltage dropouts shortens the life of appliances?
Things with switch-mode power supplies (computers, CFLs) probably will not even see this transient since they have large capacitors inside. Motors may not care either.

Overvoltages for sure will chip away at the lifetime of an appliance.

Is your PoCo liable for appliance damage?

I once saw a graph of NYC power and it was pretty flaky. I'm not sure what kind of crap state power commissions allow PoCos to ship to your house.

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Old 05-18-2012, 02:58 PM   #3
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Practical ways to protect appliances against unstable power


Quote:
Originally Posted by mudworm View Post
Code requires dedicated circuits, so I have a home run 240V/50W for cooktop, 240V/30W for oven, both of which require direct connection (via wire nuts instead of plugs) and a 120V/20W for MW Oven, etc.
The stove and oven are resistive appliance so they are immune to dirty power. The digital components would be like a computer and will be protected by the power supply. The early microwave oven tubes could be susceptable to dirty power, but modern ovens power glitches will shutdown the digital controls before harm will come to the tube. Basically, I am saying that staying up or shutting down normally is already built into the design.

There are voltage conditioners available, but they can be expensive when dealing with high amperage.

Time for a related story:
Back in the 70 the company I worked for had a 20 platter 600 MB disk drive. It was bigger than a 2 drawer file cabinet, weighed 200 ibs and cost about $50,000. One day I was in the technicians room adjacent to the glass house, when the lights start going on-off-on-off. I look in the computer room and the disk drive is bouncing across the floor in sync with the lights. By the time it stopped the drive had moved 3 feet. On power off 20 heads would retract to home and power on they would seek to the zero ring. Later we found out that the city was installing a traffic light and the PoCo man was entertaining himself waiting for the city crew by switching the main power on and off for the street.

The fix was 1) call the manufacture, 2) call the lawyers 3) install high speed crowbar circuit on all the disk and tape drives. There is a thread on this forum on how to build a circuit that shuts off when it loses power. We took the stepper motors and made a really strong computer operated rockum-sockum robots.

Last edited by goosebarry; 05-18-2012 at 03:07 PM. Reason: rephrazed sentence on MW
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Old 05-19-2012, 10:48 AM   #4
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Practical ways to protect appliances against unstable power


Even if you had one, a generator would not solve your problem, they come on line in minutes not fractions of a second. A system of energy storage would be needed (like your APCs) but they become large, bulky, and expensive if high amperage is required. There is also an efficiency hit.
Also some parts of the world have truly abyssmal power quality. Modern electronics and appliances are mostly designed to work anywhere in the world, so their design takes this into account.
Good luck.
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Old 05-19-2012, 12:24 PM   #5
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Practical ways to protect appliances against unstable power


You need to find out if the power is just going on and off or if something else is wrong and causing significant voltage swings.

For the most part, all you sensitive stuff can handle simple on's and off's.....otherwise, you would be at risk the first time you turned the device on. What hurts them is spikes.

One of the more common issues in a neighborhood is the transformer going out and causing an issue with your neutral or one of the hots. A few years ago I was in the garage doing some woodworking. My wife came out and told me that every time I turned on the saw, the computer would reboot. Ok...so I go over to my main panel and stick my meter on the buss lugs and tell my wife to turn on the saw.....one side drops down to about 90Vac...the other up to about 135Vac.

I called the PoCo that night...the next day they came out....a few min later they knock on the door and inform her our transformer is going....they will replace it....3 days later they installed a new one....0 problems since.

Take a meter and see if your getting voltage swings. If not...then call the PoCo and ask them what is up?

To be honest....I wouldn't be surprised if someone in your neighborhood has a growing operation going on....
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Old 05-19-2012, 12:30 PM   #6
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Practical ways to protect appliances against unstable power


What are you using to monitor the voltage? A whole panel surge is there to protect against any spikes, not for brownout situations. There are battery bank type UPS setups that you can install, that will keep stuff online, until the genset kicks on. I use a Ted5000 to monitor the incoming power.

Now of course the best thing to do, is to have the POCO check to make sure that the connections are tight at the meter base, and no problems in the meter head, before venturing that there is transient problems with the power distribution.
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Old 05-29-2012, 03:40 PM   #7
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Practical ways to protect appliances against unstable power


I was searching on a different issue but found this post helpful.

Question. I've read that newer inverter generators are better for electronics than the usual rotating armature or field generators. Is this true?

I have a 7500 watt 240v non-inverter generator for power outages. It connects to a 200 amp manual transfer switch. If power fails (has not just yet), I could power any house electrical circuit. The plan is to switch off circuit breakers for the high demand items such as the water heater, HVAC, clothes dryer and a few others.

My concern is how clean the power is for digital electronics in the refrigerator, washer, tv, sat dish, computer, etc.

The only high amperage item will be the well pump. So, should I be ok with this generator since it has a good bit of wattage to spare?
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Old 05-29-2012, 06:43 PM   #8
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Practical ways to protect appliances against unstable power


I guess in NY and CA the expectation of reliable power is not an option. Only (mostly) those things running are subject to problems. If the stove is off, the microwave is not cooking, the desktop (laptops immune) is not computing, the big screen is off, or in "sleep" mode, I think no problem. Bigger concerns are A/C units, well pumps, etc. It sounds like you have a house, if you want spend alot of money, generators, transfer switches, UPS, are a good options. In my area, I had crappy power for a year, I shut off A/c or furnaces, tv and cable boxes and desktops, shut off by themselves, just don't have them set to "reboot" on power return. I lost a power supply on a desktop that was old and "going to fail anyway" according to the internet chatter. Just my opinion, not fact
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Old 05-29-2012, 07:12 PM   #9
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Practical ways to protect appliances against unstable power


The only reasonably inexpensive way to almost protect equipment is to have surge suppressors together with an electronically controlled switch that cuts the power if there are severe enough irregularities. It would be turned back on manually.

Automatic turn on would depend on some way of analyzing the power to see that any group of irregularities has passed.
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Last edited by AllanJ; 05-29-2012 at 07:14 PM.
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Old 05-29-2012, 08:03 PM   #10
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Practical ways to protect appliances against unstable power


Laptops-immune, desktops have settings, F8 or something, where you can select what it does in the event of a power failure, the TV and cable boxes have similar settings. The biggest problem is if you lose 1/2 of your incoming, ie. 120 gone on one side, ok on the other, only 240v devices will be in trouble, if its out, its bad, if it "flickers" its worse.
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Old 05-29-2012, 08:19 PM   #11
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Practical ways to protect appliances against unstable power


Quote:
Originally Posted by Yoyizit View Post
Do you have any data that shows that short voltage sags or short voltage dropouts shortens the life of appliances?
Things with switch-mode power supplies (computers, CFLs) probably will not even see this transient since they have large capacitors inside. Motors may not care either.

Overvoltages for sure will chip away at the lifetime of an appliance.

Is your PoCo liable for appliance damage?

I once saw a graph of NYC power and it was pretty flaky. I'm not sure what kind of crap state power commissions allow PoCos to ship to your house.
Yoyizit,
I like your book style, Its refreshing to find another, however, if you take a 120ac motor and power it with 75ac, do you think it will run slower and draw less current, no, that's dc, on ac it will start on fire

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