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building a generator help

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building a generator help

Unread postAuthor: jsefcik » Sun Aug 28, 2011 1:25 am

me and my neighbor are trying to build a generator, using an 8hp engine which will turn a dc motor , which creates electric when turned, but we want ac power , so i have a little bit of a background on elctronics, and figured we need a inverter,

so i was wondering if a have a step down transformer, ( from an old charger) it takes in 120volts and puts out 12v, now my main question is if i connect my dc motor wires to the wires on the step down transformer, and then crack open the case and connect a wall socket to it, when i turn my engine on will it give me 120volts?( not usin the prongs putting in a male part,

more less using the step down transformer back words , like putting power into the wires and coming out out the part that goes into the wallsocket,


somebody help!!!!!!
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Unread postAuthor: jackssmirkingrevenge » Sun Aug 28, 2011 1:34 am

Buy one cheap.

Depends what you want to run, if it's something substantial you'll need something more heavy duty.

edit: still cheaper than $15 posted and good for 75 watts
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Unread postAuthor: jsefcik » Sun Aug 28, 2011 1:39 am

jackssmirkingrevenge wrote:Buy one cheap.

Depends what you want to run, if it's something substantial you'll need something more heavy duty.

edit: still cheaper than $15 posted and good for 75 watts



ive seen those b4 but i wanna run my air compressor, will that lil gadet do it? or burn it up


but if i get one of those and hook wires to the nipple looking end, then turn on my engine which will turn my motor which will give me 12 volts the then plug my compressor into the wall socket on that gadget will that work?



this is the generator i have right now http://www.google.com/imgres?q=campbell ... 80&bih=625
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Unread postAuthor: jackssmirkingrevenge » Sun Aug 28, 2011 1:47 am

I cannot say how well this will work, but for $15, no big loss if it doesn't :)

What sort of wattage is your compressor rated to?

You can get a 300W fan cooled and protected inverter for less than 35 bucks posted.

The above lets you connect the wire directly.

For those with a cigarette lighter plug, you can get a female socket cheap too.
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Unread postAuthor: jsefcik » Sun Aug 28, 2011 1:51 am

jackssmirkingrevenge wrote:I cannot say how well this will work, but for $15, no big loss if it doesn't :)

What sort of wattage is your compressor rated to?

You can get a 300W fan cooled and protected inverter for less than 35 bucks posted.

The above lets you connect the wire directly.

For those with a cigarette lighter plug, you can get a female socket cheap too.



im not sure, hopefully that car thing might work!!!
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Unread postAuthor: jackssmirkingrevenge » Sun Aug 28, 2011 2:00 am

jsefcik wrote:im not sure, hopefully that car thing might work!!!


I couldn't find a watt rating for that compressor, but this page puts it at 2 amps, which at 120 volts is over 300 watts.

In short, you'll need this one.

If this only for your compressor, have you thought about removing the compressor motor and running it directly off the generator engine?

It would certainly be more efficient and avoid all the power lost through energy conversion.

You'd go from chemical energy -> kinetic energy -> electrical energy -> kinetic energy -> air compression to kinetic energy -> air compression ;)
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Unread postAuthor: jsefcik » Sun Aug 28, 2011 2:18 am

jackssmirkingrevenge wrote:
jsefcik wrote:im not sure, hopefully that car thing might work!!!


I couldn't find a watt rating for that compressor, but this page puts it at 2 amps, which at 120 volts is over 300 watts.

In short, you'll need this one.

If this only for your compressor, have you thought about removing the compressor motor and running it directly off the generator engine?

It would certainly be more efficient and avoid all the power lost through energy conversion.

You'd go from chemical energy -> kinetic energy -> electrical energy -> kinetic energy -> air compression to kinetic energy -> air compression ;)



ill have to take a took tomorrow, mainly just wanna power my compressor in a field, im not using a bike pump to sit there for a half hour trying to get 1 shot off lol
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Re: building a generator help

Unread postAuthor: Crna Legija » Sun Aug 28, 2011 2:24 am

jsefcik wrote:more less using the step down transformer back words , like putting power into the wires and coming out out the part that goes into the wallsocket.


that wont work, what you should do is have the motor turn a cars alternator then run it into a car battery then run the battery power into apower Inverter
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Re: building a generator help

Unread postAuthor: jsefcik » Sun Aug 28, 2011 2:27 am

Crna Legija wrote:
jsefcik wrote:more less using the step down transformer back words , like putting power into the wires and coming out out the part that goes into the wallsocket.


that wont work, what you should do is have the motor turn a cars alternator then run it into a car battery then run the battery power into apower Inverter



will that car inverter work? or not enough power?
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Re: building a generator help

Unread postAuthor: Crna Legija » Sun Aug 28, 2011 2:44 am

jsefcik wrote:will that car inverter work? or not enough power?


That one wont because its for 240VAC but it should be in the watt range.
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Re: building a generator help

Unread postAuthor: jackssmirkingrevenge » Sun Aug 28, 2011 2:54 am

Crna Legija wrote:That one wont because its for 240VAC but it should be in the watt range.


Which is why I linked to a 120V one earlier ;)
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Unread postAuthor: POLAND_SPUD » Sun Aug 28, 2011 5:00 am

but i wanna run my air compressor
They use a lot of power - forget about it is not practical

as JSR has suggested get a gas driven air compressor. You might build one but I am guessing it would be cheaper for you to get a new one (or even better a second hand one)
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Unread postAuthor: Technician1002 » Sun Aug 28, 2011 10:22 am

An issue with air compressors of the home variety and inverters is the issue with start current. AC induction motors will use about 3 to 5 times the run current to start. Many small compressors don't list the start current. Most larger motors and some fridge compressors will list this value. It is the value marked LRA which stands for Locked Rotor Amps. It is the current drawn when the rotor is not turning, which is the condition when the power is turned on and the compressor is not running.

Many inverters will shut down on this overload before the compressor will start. To start a compressor, the inverter must be larger than the compressor and able to provide the start current. Look for an inverter that has an Overload Capacity or the ability to power a temporary overload such as a motor starting.

This Overload current must come from somewhere. If the gas engine and alternator, or wire, can't supply the surge, the inverter won't put it out.

In my car, I use the car battery for the surge capacity and a 1,000 watt inverter to start and run the 1/3HP compressor for field power. The DC cable is arc welder leads.


Image
Using this inverter

In use filling my cannon. Light is for night ops.
Image

A quick note on the wall wart transformer. The power the transformer can handle does not change if it is used to make 110 volts. It it is rated for 5 watts, it is still a 5 watt transformer. Connecting a 300 watt compressor is like using a hamster wheel to power your car. It's not going anywhere.

A quick comment on power.. Volts Times Amps in the DC circuit = Watts.
A two amp compressor at 120 volts will need 20 Amps at 12 volts if your conversion is 100% efficient. It will need more to cover the conversion loss.. The wall wart transformer did not put out 20 amps.. It won't handle 20 amps in to drive the compressor.
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