Poor Man's Guides


Do it Yourself

Grid Tie


Do it yourself Grid Tie.  Homemade AC Grid Tie made easily!

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 When it comes to reducing your power bill, some people just are not interested in big bulky battery banks and battery maintenance.  They want to take their windmill or solar panels and just hook them up to their grid.  Even if their power meter doesn't turn backwards, they can offset the power that they use.  This book shows how to take a simple AC induction motor and use it to pump power back into the grid.  It is a lot easier than people think.  These motors are everywhere.  

You can find small ones in:

  • weed eaters
  • blow dryers
  • vacuum cleaners
  • blenders
  • ceiling fans
  • dish washers
  • fans
You can find medium size(1/4 to 1/2 HP) ones in:
  • clothes washer
  • clothes dryer
You can find larger ones in:
  • air conditioning fan motors
  • electric lawnmowers
  • attic fan motors
A lot of these motors you can get for free or cheap

I know what you are thinking.  Why can't you use a regular grid tie inverter like the "Windy Boy"?  Well, there are a few reasons.  The first major reason is simple.  Because my homemade grid tie inverter is either free or very cheap.  The Windy Boy inverter is $2,000 to $3500 depending on what you get.

For the other reasons, I'll have to risk boring you a moment while we look at the specs of some Windy Boy inverters:
WB1800U -  Price $2,180

Maximum DC Input Voltage 400Vdc
DC Operating Range 139*-400Vdc (*line voltage dependent,
see SB2500U Technical Description)
Maximum DC Operating Current 12Adc
Maximum DC Short Circuit Current 18Adc
Nominal AC Output Voltage 120Vac
AC Operating Voltage Range 106-132Vac
Nominal AC Frequency 60Hz
Maximum AC Output Current 17Aac
Maximum AC Output Power 1800Wac
AC Output Overcurrent Protection 20A
Power Factor Fixed, Unity
WB6000U -  Price $3,390

Maximum DC Input Voltage 600Vdc
DC Operating Range 250-550Vdc
(line voltage dependent, see SB6000U
Operators Manual)
VdcWindStart Programmable Range 250-550Vdc
VdcWindMax Programmable Range 250-550Vdc
Vpv-Start 250-550Vdc
Maximum DC Operating Current 25Adc
Maximum DC Short Circuit Current 25Adc
Maximum AC Current 25Aac
Nominal AC Output Voltage 208/240/277Vac (configurable)
AC Operating Voltage Range 183-229Vac (208V Nominal)
211-264Vac (240V Nominal)
244-305Vac (277V Nominal)
Nominal AC Frequency 60Hz
Maximum AC Output Power 6000Wac (240 or 277Vac)
5100Wac (208Vac)
AC Output Overcurrent Protection 40A
Power Factor Fixed, Unity

The average small home windmill (800 - 1000 watts and 7 foot diameter blades) that hooks to a 12 volt battery bank starts charging at about 200 rpms and tops out power at about 600 rpms.  That is about 15 rpms per volt.  At 25 mph wind and 600 rpms, you would be producing about 40 volts at up to 50 amps or so.

If you look up in the yellow section above, notice the WB1800U inverter doesn't even start working until it has 139 volts or more going into it.  So, having 3 regular wind turbines running "full tilt boogie" wouldn't even start the grid feed process.

Let's say you have a 48 volt wind turbine and it is 4 rpms per volt.  And in 10 mph wind you normally start charging a battery bank.  So you hook up a Windy Boy and see what happens.  It is producing 50 volts..oops, not enough.  So, you go out and buy another turbine or build one.  Still not enough.  So, now you are feeding the grid at 12 mph wind instead of charging a battery at 10 mph.  Don't even look at the WB6000U.  It takes 250 volts to start grid feeding.  Which is fine if you already have a small wind farm.  I know, you could use a transformer to step up the voltage, but only if you have a permanent magnet AC generator.  And if you have a 3 phase PM generator (as is my modifiec car alternator) then you would need a 3 phase transformer as well.

But, if you make your own inverter using a DC motor that turns an AC motor, then you can size the pulleys appropriately to start charging whenever you like.  You can also add more windmills and make a new wooden pulley to go with it.

Now, let's look at efficiency.  I know that a DC motor coupled with an AC motor isn't that efficient.  It looks like about 60% on average.  But the Windy Boy and others say that their "peak efficiency" (whatever that means) is 90% or more.  But, let's look at the numbers.  We'll take the max power out and divide by max power in to get efficiency.  The WB1800U has max input of 12 amps DC at 400 VDC.  That is 4800 watts input.  The max output is 1800 watts.  So 1800 / 4800 is 37.5% efficient at max power.

The WB6000U has 550 VDC at 25 amps DC for max input of 13,750 watts.  The output is limited to 6,000 watts.  That makes it 43.6% efficient at max power.

But imagine 10,000 watts of input into a 15 hp DC motor that turns a 15 hp 3 phase motor (wired up according to the grid tie ebook).  You would be feeding 6,000 watts into the grid at 240 VAC at 25 amps.  Or you could get the exact same output by using the $3,400 Windy Boy.  In this case, they would both be running at 60% efficiency.

But you can also use this book to find out how to hook up an AC induction motor to a windmill to feed the grid directly without an inverter.  And just use a homemade grid tie inverter to connect the solar panels to the grid.

Let's look at a Sunny Boy 700.  It takes 75 to 150 VDC input at max 6.8 amps DC. But I have 3 Sharp panels at 120 watts each.  They put out about 21 VDC at up to 7.8 amps.  So, three of them in series would be 63 volts, but I need 75 just to start charging, so 4 panels would be the minimum.  And even if I had a 4th panel, the amps are too high.  I could go to the next bigger Sunny Boy and that would handle 8 amps input, but it needs 125 volts DC minimum.  That means I would need 6 panels minimum.  So, using the Sunny Boy means I need to purchase another $2,500 worth of panels plus an expensive inverter.

Or, I could use a cheap $50 DC motor from ebay.com, a free washing machine motor , and a homemade plywood pulley or pulleys to match the two up.  And I can just keep my 3 solar panels and not have to spend a bunch of money.  Sounds like the way to go to me.

This e-book will show you the following:

 How  asynchronous  grid tie works

Make pulleys, any size you want out of plywood, super easy

Make an automated Poor Man's Power Point Tracker (solar or wind)

Homemade grid tie inverter - solar can grid tie with this!

Use your windmill with an AC motor to "backfeed" the grid

Charging batteries using grid tie (for emergency backup)

Make a simple wind speed sensor to engage the grid tie at the right time

This e-book is in full color.  It is just less than 3 MB in size and you will need a PDF viewer to view it.  Upon ordering, you will be shown a download link for instant download .

$19.95 USD

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