Tuesday, February 25, 2014

Generator Transfer Switch (Part 2)

GETTING STARTED - Let's figure a few things out first

1) You understand what the following words mean: Voltage, Current (AC and DC) & Power.
2) You know the items you want to power and the power requirements for each.


I own a Honda EM6500.  (Review to come some day)  

I'll walk through all this giving you the data for my generator.

Voltage - measured in volts.  Determine what voltage your generator is capable of producing.  Mine can provide limited 12 volt DC, 120 volt AC and 240 volt AC power.  

Current - measured in amps.  At 12 volts, I believe it can provide 8amps of current.  At 120 volts... I don't know.  At 240 volts AC, it can provide nearly 30 amps of power.  (I only care about the 240 volts)

Duty - ah, mine is rated for 6500 watts!  So I can run it at 6500 watts 24/7 right?  NO!  While it is rated at 6500 watts, what the marketing people didn't mention is that it is only rated at that amount of power for 30 minutes.  If you are going to leave it running longer than that, it is only rated for 5500 watts.

Surge - How long can it handle a power requirement greater than it's typical power draw?  Slightly different than duty, and still quite similar...  My generator can handle a load of 7000 watts for ten seconds.  This is helpful when you have electric motors starting up.  For more information, read up on current in-rush.


Digging into this a little bit deeper...


VOLTAGE: 120 Volts or 240 Volts? 

It really comes down to what you need to power.  (NOTE: 220V and 240V are interchangeable.  The difference simply allows for voltage drop through a conductor.)  At my house, there is a 240 volt well pump I need to operate in order to do things like take a shower.  Other items that run on 240V will include you Range/Oven, the clothes dryer and possibly a welder or other machine tools.  (I feel like I missed one... if you can think of anything, please chime in!)

HOW MUCH POWER? (Voltage x Current)

I honestly have no idea how much power I will need.  Some people would say I should go get a Kill A Watt electric usage monitor, but I didn't.  I do know my furnace won't start on a 2000 watt generator (also known as 2kW or 2K).  I learned this the frustrating way - I bought a generator and then found out it didn't have the ability to handle the startup current (see below) for the blower motor.  Whatever you plan on doing, you need to make sure your generator can handle the start-up current in addition to whatever else you may have running at that time.  I can speak more on the subject later if there is interest.

A quick note on Start-up Current:
When an electric motor like a compressor for your refrigerator or a fan motor in your furnace kicks on, it uses a lot more current than it does after is up and running.  Or simply put, it takes more power to get it started than it does to keep it running.  For those of you who are of the scientific background, you understand that the static friction is higher than the dynamic - it takes more work to get something rolling than to keep it rolling.

Back to Power and Voltage...
So this time I went with a 6500 watt generator that has the ability to handle surge up to 7,000 watts (7 kilowatts)  It also has the ability to put out either 120volts AC or 240 volts AC.  
Voltage drop - My attempt to explain for those of you who didn't read the Wikipedia article:  When you have power going through a wire, a long one... because of the friction in the wire (also called resistance) you loose some of that power in the form of voltage.  If you plan on running power to something a long way from the generator, you will have a voltage drop!


Wire sizing:  (Don't disregard this one, you can burn your house down!)

So again, power is voltage times current.  For my generator, at 240 volts it is producing 30 amps of current.  Therefore, when picking out the components for your generator hook up, you need to ensure they are all rated for at least that much current!  Doing otherwise can cause the wire to overheat and catch on fire... along with you house, you family, possibly yourself and all things you love!  DOOOOOM TO ALL WHO FAIL TO APPLY THIS!


An Overview on Electrical Wire and Cable

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