Re: Emergency generators [TELECOM]

The Telecom Digest
> Volume 30 : Issue 283 : "text" Format > > Messages in this Issue: > Emergency generators. (David Chessler) > > ---------------------------------------------------------------------- > > Date: Sat, 05 Nov 2011 15:57:34 -0400 > From: David Chessler > To: snipped-for-privacy@and-this-too.telecom-digest.org. > Subject: Emergency generators. > Message-ID: > > Some years ago we had a windstorm (or hurricane) that knocked out > power for days--a week for some people. This is not an uncommon > problem in Maryland and the Eastern shore. Summer thunderstorms can > knock out power for days. > > Anyhow, the problem was getting power into the house to run the > computer (I was on deadline at the time), the refrigerator, and maybe > a light or two. I don't own a generator, and for events that happen > only once or twice a decade, that seems an excessive expense. Then I > remembered: I had two cars, each of which had a generator with > battery backup. A quick trip to a nearby truckstop (if two counties > away is nearby) and I owned two inverters. These cost about $100-125 > each. (Truckstops are the most likely local sources, but Wal-Mart > sometimes has them. Or, there is the internet.) > > I connected the one with the nominal rating of 1000 watts > (continuous) to the battery of my Ford, which had the larger battery > and generator, using large crocodile clips (like jumper cable > clamps), and ran an extension cord into the house. I plugged in the > refrigerator and "POWER". The one with the nominal rating of 750 > Watts could not run the refrigerator, but attached to the battery of > the Honda it did just fine on the computer and printer. I had the > cars idling, so the batteries had a chance to recharge (IIRC, modern > alternators deliver full power even at idle). There is no way this > arrangement could supply full power to the house. I think the Ford > had a 65 AMP alternator, which means 780 Watts at 12 volts, less the > losses. However, the battery supplied any surge that the alternator > could not. (When an electric motor, like the one in the refrigerator, > starts, it draws perhaps double its usual load for a fraction of a > second.) Electric stoves, air conditioners, electric heat just won't > work with such small alternators, though you could probably run the > fan in a forced-hot air furnace. > > This arrangement would also work for camping at events [or > evacuations] where you can leave your vehicle reasonably close to your > tent. >

You do NOT get your full car alternator output at idle, it's spinning barely fast enough to keep up with engine running loads of the EFI computer and injectors, fuel pump, electric cooling fan, etc. You need to get the engine over about 1800 - 2000 RPM for maximum alternator output.

Cars are not designed to sit there for hours unattended in one spot (no cooling airflow underneath for the exhaust system) and run with a brick on the gas pedal. Cars don't have any automatic shutdown safeties, if it overheats or runs low on oil you can wreck an expensive engine that way. And car batteries are designed for a burst of starting power and immediate recharge, they will only last a half-dozen or so deep discharges from running an inverter - just like leaving the headlights on overnight.

Which is why it's far better to have a purpose built gasoline engine generator set for running larger household loads like refrigerators, well pumps, furnace blowers. And a genset will last a long time with just a little maintenance - add gasoline stabilizer to the fuel, start them for an hour's workout every few months, and rotate out your emergency gasoline supply once or twice a year - dump it in your car's tank and fill the can with fresh gas (and another dose of stabilizer) and put it away next to the generator.

If your main needs are for 12V power like for camping and for recharging dead car batteries and Ham Field Day operations, you can build yourself a Mule - you couple a large lawnmower engine and a large car alternator.

***** Moderator's Note *****

> I don't know how to calculate the startup load of a refrigerator: you > are right, of course, that the starting demand is much higher than the > running power that's needed, but I'm not sure how to calculate it. I'm > told that the worst case power-demand is from an air conditioning > system, but I don't know why. > >

The usual rule of thumb for figuring motor starting surge is 10X the running full load amps for that first fraction of a second as it's not moving yet, and current ramps down as the motor spins up to speed. Or look at the motor nameplate for "Locked Rotor Amps", and there it is. Other than that, it varies (a LOT) depending on the motor design and the control system - there are "Soft Start" motors and drives for when you don't have the available current or don't want to pay the utility rates for it.

That said, inverters need to be massively oversized for starting and running motor loads - the bare minimum is a "2000W Continuous 4000W Surge" rated unit to start a 500W motor. And the inverter really should be running off a second dedicated "Deep Cycle Battery" in the car or truck to supply those big current surges, and charged from an oversized alternator (100A to 225A, biggest one you can stuff into the space available) through a diode charge isolator.

When camping you can run small energy uses like a TV Computer or Radio from the inverter or directly off the Deep Cycle battery with the engine off, and it will recharge in the morning when you start driving to your next stop. And you *can* start the car in the morning because you didn't run anything off the starting battery.

If anyone has a pointer to an EPA or other site that gives the

procedure, please send it in. I'm very interested in getting > information about the running costs of various fuels, as well: I read > that Natural Gas is much more expensive than gasoline. TIA. >

For raw BTUs per dollar, Natural Gas is far cheaper than gasoline - no international tanker shipping, no complex refining, no adding MTBE or Ethanol oxygenates, no tank trucks or home delivery charges. They take it out of the well, clean it up a little (extract "sour" sulfur compounds and the Helium if there's enough to bother), add a little Methyl Mercaptan stink, and stuff it into the pipeline.

Propane is a byproduct of oil refining, but it's good point is local storage where you can have a week or more of fuel on hand for emergencies. One caveat, if your tank location goes way below zero have a safe way of warming the storage tank or you can lose pressure - there's gas in the tank but it won't vaporize when it gets below ~ -30F in the tank. Running hot water over the tank works in a pinch. This makes Propane bad for unattended Telecom backup generators in Snow Belt states, you have to put heaters and thermostats on the fuel tank and monitor them for operation.

And both Natural Gas and Propane are a lot cleaner than Gasoline to run your permanent installed generator on, the engines last a lot longer - Propane is 108 Octane, NG almost as good. Several companies make easily convertible residential sized backup generator sets that can switch from NG to Propane (and back) with a few minutes work. If the disaster disrupts your NG supply, you switch over to Propane.

Price wise, it's probably NG cheapest, then Propane and Red-Dye Diesel (no road taxes) neck and neck, Road Diesel a bit more because of the taxes, then Gasoline trailing in the rear, but local markets fluctuate.

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PS: Mr. Moderator, I've made a few submissions through Usenet that never hit the queue - they might not have had the Keyword though. Check the filters at your end of the Interweb Pipes, please.