Power In A Storm

Dan Miller
By  Dan Miller , Progressive Farmer Senior Editor
A backup generator can keep your shop, livestock facility and home running even when something knocks out the grid. (DTN/The Progressive Farmer photo by Jim Patrico)

With winter on the way -- snow in the North, the "second" tornado season in the South, and ice all around -- it's a good time to take a look at the capacity and condition of your standby electric power system. If you don't have one, it's an insurance investment you'll appreciate when a power outage would otherwise deliver a serious beat down to your bottom line.

There are three types of standby electrical power systems -- permanent standby generators, portable, engine-driven generators and manual generators driven by a PTO.

Pay for a reliable backup system with the generating power to protect the most critical functions of your farm. An underpowered backup system is not much better than no system at all -- either you have the power to do the work, or you don't.

Generators are sized by the wattage and voltage they produce. There are a wide range of generators that produce as few as 1,000 watts of power and generators 100 times larger and more -- big enough to operate large livestock operations.

The power required to run a piece of machinery is calculated in watts (amps x volts). By adding up the watts to run each piece of equipment, you'll determine the minimum supply of power needed to keep critical circuits energized.

You also want to consider the electricity needed to power the "nice to runs" or those functions that would be useful to have in operation but not critical to the farm's ongoing function.

Think of an additional bank of outlets to power a big screen on a football Saturday or lights to find the nacho tray.

Even without lights, we are not savages after all.

Here are power requirements for common pieces of equipment.

Milking machine: 800-5,000 watts

Milk cooler: 1,500-12,000 watts

Water pump: 500 to 2,500 watts

Water heater: 4,500 watts

Space heater: 1,000 to 5,000 watts

Ventilation fan: 300 to 1,000 watts

Silo unloader: 2,000 to 7,500 watts

Electric fencer: 7 to 10 watts

Feed grinding: 1,000 to 7,000 watts

Feed mixing: 800 to 2,000 watts

Feed conveyor: 800 to 5,000 watts

Security lights: 100 to 500 watts

Shop tools: 300 to 1,500 watts

Electric motors require special consideration. An electric motor requires three to seven times the current needed by the motor when it is fully operating.

Here's how to calculate your backup power needs.

-- The starting wattage of largest motor. If there are two or more motors of the same size, list the starting wattage of only one.


-- The running wattage of all other motors.


-- The nameplate wattage of appliances and equipment.


-- The wattage of lights.

Overloading a generator because of a poorly executed backup plan causes poor power quality that damages both the generator and critical equipment systems. On the other hand, it is not a good idea to purchase a generator with an electrical capacity well beyond your power needs. If, during its operation your generator is under only a partial load, the engine may not reach full operating temperature. Over time, that can damage the engine.

A backup generator, whether portable or permanently installed, requires a double throw, or isolation switch. The switch serves several functions, and one critical safety function.

Connecting a generator directly into any point of electrical wiring without a transfer switch is illegal and dangerous because it may cause back feeding.

Back feeding is the result of sending electricity from your backup system out onto commercial power lines. It energizes the transformer serving your farm and could cause the death of anyone working to restore power to your home and farm.

Electrical transformers work the same in either direction. The transformer reduces the 14,000 volts of power on an electrical line to the 240-volt service delivered to your operation. Putting power onto the line from your backup generator through the transformer energizes the line to 14,000 volts.

The switch is installed to isolate a handful of critical electrical circuits from incoming electrical service. If the generator is powering those circuits and regular power is restored, that electricity will not flow to those isolated circuits until the generator is shut down and the transfer switch is set to receive commercial electrical service.

Finally, the switch prevents power from your generator and the power company from energizing your electrical system at the same time, which risks the catastrophic failure of your generator and equipment.

Installation of the switch and wiring of the critical circuits is a job for a qualified electrician. This is not a job for shortcuts.

Regular maintenance of all three is critical to their performance.

Permanent, standby generators, generally feature an automatic, self-checking function that runs once a week, or so. These self-checks indicate maintenance that needs to be performed.

Portable, engine-driven generators and manual generators (those operated with a power take off) require periodic maintenance.

On a regular schedule:

-- Check both the oil and fuel levels.

-- Change the fuel stored in the generator every six months.

-- Check the units for animal and insect infestations. Mice may build nests inside the protective casing, even around the electrical windings. They may also eat into the windings.

-- Check exhaust systems for nests and other obstructions.

-- Portable generators should be run every month. Manual generators should be exercised every quarter. In both cases, run the generators for about an hour under load.

If you looking for more information, here's a pretty good tutorial on standby electric power systems from the University of Georgia. Go to:…

Dan Miller can be reached at



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