Portable Generators


 Home Portable Generators
Sep 18 '04 (Updated Dec 20 '04)

The Bottom Line How to buy a good quiet OHV home generator lasting for years of service at times you need it most.

There are a couple of issues to consider in choosing a generator:
1. Purpose Have a clear idea as to the purposes you plan to use the generator. A camping generator is a small, quiet portable (meeting national park standards), whereas a home generator must be beefy enough to support a number of loads. Do you need reliable, constant power at a construction worksite (need 240 volts)? Are you running computers that need clean power? The number of types of generators is relatively wide, and diverse.
2. Power as important as purpose is total load, the amount of power needed by the equipment or appliances you plan to run at one time. Do you plan to run contractor equipment or computers? Do you have to have power clean enough for an UPS (Uninterruptible Power Supply)? What are the high surge items?
3. Normal run time and reliability How long do you plan to run the generator at one time? Do you want a generator that requires frequent refilling? Will the generator be an occasional use item or a constant runner?
4. Noise the tolerance you have for the noise created by a generator. A loud generator cannot be used in a national park. Can you stand the noise?
5. Many generators have wheel kits. Portability do you plan to move the generator or is a built-in generator fine?

Power needed

The surge voltage is the startup wattage used by a motor or device to begin movement. A freezer or refrigerator compressor motor will cycle on and off creating a extra demand for power. (Got the amps, but not the watts? Remember: watts = volts times amps, so a 3 amp 120 volt device uses 360 watts).

List of example equipment
A radio uses 50 watts
A light bulb as rated (assume 40-100 watts)
A small fan uses 200, but has a surge of 300 watts
A laptop computer runs at 100-200 watts.
A color television runs at 400 watts and does not surge.
A computer runs between 200-400 watts and has minor surges for watts (depending on the amount of computing being done.
A CRT color monitor runs at 400 watts.
A Deep Freezer runs at 500 and can surge to 750 watts.
A 1/3 HP Motor (like a furnace fan, 1/ 4 inch drill or small sump pump) will use 800-1000 watts with a surge to 1,200-1800 watts.
A camping refrigerator runs at 60 to 200 watts and can surge to 600 (depending on type).
A refrigerator runs at 600-800 watts and can surge to 1,200
A 1/2" Power Drill uses 1,000 and surges 2,000
A 1000 watt Microwave uses 1000 watts
A 1/2 HP Motor uses 1,400 and surges to 4,200
A 7 1/4" Circular Saw runs at 1,500-2000 watts and surges from 3,000-5000 watts
A stove (1500 watt per element) uses 1,500
1 HP Motor will run at 1,500 and surge to 4,500 watts
A Space Heater (works at it’s rated setting so a 1,800 watt heater uses 1,800 watts) Hint: the oil filled radiators have wattage settings and are efficient)
A 5000 BTU Room Air Cond. Uses 1,000 and surges to 1,800 watts
A 10000 BTU Room Air Cond. Uses 2,000 and surges to 6,000 watts (Energy Star appliances make a big difference here, as well as "boost technology" in some Yahama Generators). Some generators (Yamaha) have a boost feature (a battery) for providing surge watts for invertors.

Add up all the rated watts (that’s the normal generator load). This is the rated load. Now take the highest surge rating (or the highest 2 ratings of the surge if you plan to run a long time), and add those surges to the total above (that’s the surge capacity needed).


Example of selecting a generator for Camping.

I am going camping and I need to run a fan, a small radio, a Norcold(TM) camping fridge, two 60 watts lights and a laptop (all at 120 volts). That gives me a rated wattage of 200 for the fan, 50 for the radio, 60 for each light bulb, 60 for the Norcold (surge 200), and 200 for my laptop (or 630 watts). Surge for the fan and the fridge are the highest 2, but since the use is occasional and both won’t start together on a regular basis, I’ll use the fridge rating of 200 surge watts for a surge demand of 830. A certain generator with 120 volts at 1000 watt surge rating and a 900 watt rating will meet my power demand. This generator will run 3.8 hours at it’s rated load (900 watts) or 8.3 hours at 1/4 load (200 watts). (It’ll keep my fan and fridge running for < 8 hours.) Another generator (Ok, a Honda) may run 400 watts (a 1/4 load) for 15 hours on a tank of gas, which also has a rating of 50-60 decibels, so I am well within my noise tolerance.

Example 2 Home Emergency power

I am in need of a emergency generator for storms, and can expect occasionally power outages of 2-3 days. I have a fridge, fan, deep freeze, 4 - 40 watt light bulbs, a TV and a laptop. Wattage needed is 800 + 200 + 500 + 160 + 400 + 200 = 2260 watts. Surge is regular wattage for every thing except that the two largest surge appliances are added in for wattage needed is 1200 + 200 + 750 + 160 + 400 + 200 = 2910 surge watts. Noise is a bit of a factor (under 72 db) as well as refill time, so I'd like something that pushes 2500 watts with a tank lasting at least 8 hours, so I don't have to wake up at 3am for a feeding. I also might like to have 240 volts for some construction work I do, so I get one with 240 plugs.

Expect to buy and use very good larger gauge extension cords, Be safe, keep the generator away from and outside the house.

Noise

A generator can be very noisy. You should not buy a generator whose noise level exceeds 80 db. A camper will want a far quieter generator, and be aware that some parks will not allow generators with more than 70 db. Small Hondas go down to 49 db.

The quieter, the better, as a generator should not be an abusive device. Sound or noise is potentially damaging sound levels range from 85 to 110 decibels, and some generators create this much noise. For every 10 decibels, a sound is half as loud, so a generator at 72 decibels sounds half as loud as a generator running at 82 decibels. Sound like all energy is subject to the law of squares so each doubling of the distance from a generator, the sound drops by about 10 decibels.

A bigger generator is not necessarily always louder, some 3000 watters are as quiet as 49 db at 3 feet (as loud as a quiet air conditioner or washing machine), while smaller ones may be far louder. National park rules say that a generator should be 72 decibels or less at 10 feet. Having gone through Hurricane Isabel in 2003, I have learned a noisy generator annoys a gentle neighbor. Sandbagging a generator can also reduce noise, (surrounding a generator with open walls of sandbags), which a great hint to contractors. Europeans have DIRECTIVE 84/536/EEC, which sets noise limits and requirements for the issue of an EC type-examination certificate for power generators. A camping generator should be below 60 decibels to be tolerable for long periods. Any other generator should be 72 decibels or below at three feet.

Some generators claim US Forestry approved spark arrestors (all generators) check for that feature for camping.


Alternators - A device that converts rotational energy to AC (alternating) electrical current. There are 3 types. Surprisingly the head unit (power generating part) tends to far outlast the engine.

1) Hybrid Generator-driven Invertors (most are small 1000-3000 watts). An inverter converts DC power to AC. They tend to have very clean power. (Some generators are DC-brushed with an invertor).
The best generator is likely the very quiet Yamaha EF3000ISEB 3000 Watt Premium Generator with Yamaha Boost Technology. Seen it, heard it, priced it but haven't used it.
2) Brushless (Longer lasting (good for construction))
3) Brushed (Older generators tend to have these). Brushes are replacement items on generators.

Very important to computers is that they generate "Clean Power" (On phase, and voltage and with few deep surges or spikes). It may be cheaper to have an inverter box for a car and a lowcost generator, than one high quality generator. Pure sine wave generators will use invertor technology for better than utility power.

By the way, strictly speaking, a generator creates DC power, and alternator creates AC. A car alternator has a diode (rectifier) that converts the power to DC.

Many have the ability to provide both 240 (for construction and electric dryers) and 120 volts. Some have 12 VDC battery recharger features.

Types of Engines in generators

Today's small generator engines should have electronic ignition, rather than points and condensers. It's on almost every engine, and isn't a special option of an engine anymore, like it used to be. Electronic ignition gives more accurate engine speed, and should be part of the governor. A governor controls speed and may be mechanical or (better) electronic. A non-generator engine cannot be effectively used for accurate power generation, (except to charge batteries). You may look for an electric starter as a standard item; it’s rare on smaller generators, check if it's already installed. It's a nice feature in cold weather below 20, and should be in a built-in system. Engines in generators are designed for constant speed, but should have an idle control to save fuel by idling engine down when no load is needed. The life of a generator engine is measured in hours, and an hour meter will help determine when repairs or replacement makes sense. Replacing a worn-out engine on a better generator is common, when the service life of the engine is over. Engines that tach at 1,800 rpm, will generally last longer than engines that tach at 3,600 rpm, (an 1,800 rpm generator uses a different head unit (alternator) than a 3600 rpm unit).

Most small engines have an aluminum block, but if the engine has an aluminum block, it should have a cylinder sleeve (usually cast iron). Don't assume that an engine does have this sleeve; many smaller engines do not. The sleeve protects the cylinder from wear, which is pretty quick with an aluminum cylinder. This sleeve is a requirement on any high use generator with an aluminum block.

There are a numerous major engine designs used today in gasoline-powered generators, which are side valve (2 and 4 cycle) and overhead valve. Side valve engines (all 2 cycle engines are side valves) that can produce up to 13 HP; will run harder, hotter, dirtier (EPA rates them up to 30 times more pollution) and a lot louder. Sound is a significant issue with a generator, and depending on your use, you may find it’s impossible to use a selected generator. These designs are named side valve engines because the fuel mixture and exhaust enter and leave the cylinder from the side. Multi-cylinder engines are common in larger generators.

The 2-cycle side valve engines produce power on every other cycle, and so have a smaller cylinder than a 4-cycle engine. They generally don't last as long and are often hard starters, but have few moving parts and are cheap to fix. The 4 cycle side-valve engines are common in larger HP and higher torque applications. While some small generators have a 1-2 HP 2 cycle engine that does not mean that a handy portable can’t be had with a 4 cycle. A 2-cycle engine will require you to mix your gas with oil. (Note: As an exception, Tecumseh makes a 7 horsepower 2-cycle engine with a cast iron sleeve.)

The cycles of an engine in a 2-cycle (or 2 stroke for the English) engine have a power/exhaust stroke and the compression/intake stroke. The 4-cycle engine has separate strokes for the power, exhaust, compression and intake strokes. 4 cycle side-valve engines are common in lower cost, higher horsepower generators. You may hear that a 2 cycle engine has more power for a given displacement than a 4 cycle engine, which is true, but this fact is essentially useless to you. A 2-cycle engine is lighter and smaller by nature, and is primarily used as a trimmer or chainsaw engine. It is built small to carry. Single stage generators use these engines in the lowest cost versions. A 2 cycle can be a hard starter and is especially susceptible to fuel quality. (Note that small Honda generators and all Yamahas are 4 cycle engines.) Side valve engines generally consume more fuel so unless you like to wake up and refuel the generator at night, I'd avoid these.

Pollution in some states is pushing the banning of side valve engines, which generally waste 20-30% of fuel as unburned exhaust.

Overhead valve (OHV) engines have valves like a car engine on top of the cylinder. These engines have valves that open and close in the engine in each stroke. They are more expensive engines, but easier to start and quieter. These are generally 4 cycle (stroke) engines. Torque is improved, and most owners prefer these engines. A 9 HP side valve engine is generally not as good an engine as an 8 HP OHV, based on the torque and reliability. A generator requires horsepower to sustain the power under load.. I switched to an OHV engined Sears model 32360 (Not listed on Epinions) and dropped 20 decibels in sound. My older side-valve engine was deafening, while the 7 HP Gentek OHV Sears hits about 75-80 decibels. Briggs and Stratton calls side valve engines, "L" head engines. Most OHV engines though not all, will have cast iron cylinder sleeves.

Horsepower is different from the torque of an engine. Horsepower is the force applied at speed; Torque is power under load to "turn" the rotating shaft. A higher torque engine with the same horsepower as a lower torque engine will be less likely to bog down under load, a feature of a generator surge watts. OHV engines have higher torque as a result of the design on the engine. The compression cycle is higher for a longer part of the cycle, so more torque (twisting force) is available.

Fuel injection in OHV engines improves the fuel usage and reduces pollution while giving more power to the engine, look for this in the best small gasoline engines. This is better than having a carburetor, which can flood and uses more gas. (This is often designated as "OHVI".) Carburetors and mufflers in generators should have a spark arrestor.

Diesel small engines are available as a replacement engine, and many owners switch to a pull or electric start diesel for high use machines. A diesel engine is not a poor choice in a generator due to the increased reliability and life, which keeps the engine from bogging down. Generally an OHV engine will last much longer, and be more pleasant to run for a large area, while the cost is rarely more than more in price for equivalent gasoline engines under 10hp. Some one in India makes a diesel generator and engine with a 100,000 MBTF based on a 1930’s design.

Governors and generators

All generators must (or should) have a governor (a device that sets the speed accurately.) This can be mechanical (most likely), a flywheel, or electrical (most accurate). Those using UPS may have to adjust the governor for an accurate hertz and phase. This is where clean power is important.


Engine Manufacturer Designations

The designation of some engine manufacturers to have a brand name like Gentek has little to do with the features or type of the engine other than it is designed for constant speed. Read the features of the engine, rather than the brand designation. The word "Gentek" is a marketing designation. The premium engine lines may be designated with specific names like the Briggs and Stratton "Vanguard" or Tecumseh “Premium Line". On Tecumseh engines installed, the "Premium" designation may not be used, so look at the features of the engines. Almost all Tecumseh OHV engines are their "Premium Line" engines. Many manufacturers make extended life engines, which have the better features.
Many manufacturers put in an oil filter for a pressured lubrication system (have an oil pump), this is on the better engines. Most small engines are "splash" lubricated, so parts splash into an oil bath. I don't see a problem with a splash lubrication system for a homeowner who changes the oil every 50 hours, and every season. A constant use generator must have an oil pump and filter to survive long use.

Cost

The features of a generator affect costs as much as power. Don't be surprised that a 2000 watt 49 db Honda costs more than a 5000 watt 85 db generator.

Power without the engine - Invertors

An invertor is a electronic device that creates AC power from straight DC current (like a car battery), and are virtually noiseless. You may wish to consider an inverter (some are 5000 watts) as a alternative or supplement to a generator. While, some generators have an invertor to produce clean power, this section covers invertors only. These can be run off a car's electrical system. A 400 watt invertor can run a laptop and a couple of lights. A battery provides power for (rated amperage / 12) / load amps) hours. Since watts are amps times volts, we know that a 400 watt load is 3.3 amps.

(Note, an average car's alternator, unless "beefed" up creates about 50-75 amps of current at 12 volts (600-900 watts). A stereophile can pay for a 200 amp alternator and double pulley - 2400 watts.) Using a load that pulls a constant 1000 watts from the running car, will in time certainly drain the battery, as it makes up the power shortfall. By the time you beef everything up, you could have bought a unit cheaper as a portable ... It only makes sense on special purpose vehicles (especially diesels). If you must run an invertor from a stationary car, prop the hood open.

An invertor draws power from a battery or dc source rated to it's load + about 120 watts, so a 200 watt laptop can run for 320 watts (power for the invertor) on a 375 amp battery. The time for the battery to discharge (Deep cycle marine battery) is
375/12 = 31.5 amps
320 watts / 120 volts = 2.6
31.5 / 2.6 = 12.11 hours.

Invertors are popular on multi-bank (batteries) boats for that reason. A average car alternator recharges it's battery at 25-50 amps per hour (subtracting the power to run the car).

Making a choice

Choose the generator type with the features you want and then choose one with the engine you can "live with" based on power and sound requirements. You may be able to tolerate a loud generator. A national park needs a quieter engine, by law. One other feature you should look for is a good manual with a parts list. Some manufacturers list every part number in the manual and repairing it is easy. All generators should have a spark-arresting muffler. Using an separate invertor as an adjunct to a generator can save you significant money.

You may have noticed that I consider noise a strong factor, it is very important in most applications.

Some Tips

For many, generators are occasional use items that should have fuel stabilizer added to the gasoline for storage. Change the oil religiously and check lubrication. I keep a can of starter fluid on hand for less reliable engines or really cold weather, but never use starter fluid in a 2-cycle engine.

Heat is the head unit (alternator's) worst enemy followed by bearing failure. Keep the generator in the open (I plug a small outdoor electric fan in.)

Don't use gasoline additives designed for cars in a small engine, the fuel lines in many smaller engines are rubber, not the reinforced neoprene used in cars. Some fuel dryers and carb cleaners eat up (or melt) the hose walls and gum up the engine. (Check the generator manual.)

Run the generator every month for a couple of minutes.

Consider sandbagging (creating an open walled temporary outside housing or a barrier wall) out of sandbags or plywood to reduce noise and effects from weather. Also consider keeping a small 120 volt outside rechargeable emergency light on or near the generator.

(Hint: I use a boater's "Topsider" to change the oil avoiding a lot of mess. A topsider is an oil pump that siphons the warm oil from an engine through an inserted hose.) After the engine break-in period, first 5 hours or so, replace the oil.

Safety

Generator fumes (CO) and electrocution kill many every year, be safe: read the manual, run it on a level surface, away from the house or camp, ground it properly, use very good extension cords of thick gauge, and think.

Make sure that the generators that require grounding (a copper grounding pole is placed in the ground and wired) are grounded. Tip: Put one in ahead of time near where the generator will be used. A booster cable clamp can be used to attach to a ground in a pinch.

Carbon Monoxide (CO) can enter from a cracked door from the extension cords, and kill.

Extension cord Tips

For a generator, the cord you connect with is as important an item as the generator. No cord should ever feel warm or hot.

Consider an automatic or manual "transfer" power switch (consult an electrician) for key circuits in the home to keep from running power cords. This transfer switch changes the key circuits to using the a generator from utility power. Built-in systems (which cost less than you'd think), use these, but a portable can be wired to a ATS (automatic transfer switch).

On the reels, make sure you always unwind full length of the cord before using (keeps the inner loops on the reel from over heating). The shorter cords lose less power, and are less likely to over heat. Do not use extension cords that are cut or damaged. Most people don't have enough cords for the load.

Gauge (size of the wires ) determines what cord you will need as length of the cord. Extension cords (for a given gauge), powers a set of appliance loads to a specific wattage for a given length of distance. Longer cords have a lower wattage (the current carrying capacity at a voltage).

Example, I bought a 16 gauge extension cord of 50 feet in length which will power 1200 watts of appliances. A 16 gauge cord that is longer than 60 feet in length powers appliances to 1000 watts. I could use this cord for a small 1000 watt generator for camping. Store extension cords indoors when not in use, and don't modify a polarized plug.

Below is a listing of 50 foot lengths for extension cord with gauge sizes for 120 based on a surge of 50%. Cords have an amperage, not a wattage rating, which makes it hard to buy for a generator.

Don't expect to use house wire gauge scales for extension cords, a 20 amp house circuit is 12 gauge at less than 50 feet.

I would consider the following safe for 50 feet. For:
8 amperes (normal load 960 watts, surges to 1200 watts), 16-gauge;
12 amperes (normal load 1440 watts, surges to 2200 watts) 14-gauge;
15 amperes (normal load 1800 watts, surges to 2700 watts) 12-gauge; (minimum contractor size)
20 amperes (normal load 2400 watts, surges to 3600 watts) 10-gauge; (contractor size)
30 amperes (normal load 3600 watts, surges to 5400 watts) 6-gauge.

Use two cords for splitting loads (when possible). Two 12 gauge cords (I mean plugged into the generator and not in series) are cheaper than a single heavy 30 amp cord.

Add two gauges for every 50 additional feet, for a 100-foot-long cord, the gauges should be two sizes bigger.

Outdoors, use an extension cord with GFCI (ground fault circuit interrupter) unless you have it plugged into a GFCI outlet.

For home generators, buy contractor's 12 or 10 gauge(look for 12/3 at least or better 10/3) gauge or marine (30 amp) gauge extension cords (very thick) which is required for longer runs of at least 50 feet. Get decent taps. Get the ones with the lighted end. It should weigh a lot. I like the marine (10/3) 120 volt cords that stand up to the sun and weather better.

For any ordinary home generator (as example 2 above), get at least a couple of 10 gauge cords.

Finally, before you buy all those extension cords, many use a transfer switch (automatic or manual) to use the house wiring for the generator circuit, instead of extension cords. This switches off utility power to the generator for your circuits, and can be a cheaper, safer solution.

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