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12 to 120 Inverter ?

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RayJ

New Member
While you are on the subject. I copied the inverter schmatic from the free site. The 2 PNP transistors listed don't exist. does anyone know what Radio Shack 276-2025 cross over to? and what watts do the resistors need to be?
 

Roff

Well-Known Member
RayJ said:
While you are on the subject. I copied the inverter schmatic from the free site. The 2 PNP transistors listed don't exist. does anyone know what Radio Shack 276-2025 cross over to? and what watts do the resistors need to be?
Ray, what free site are you talking about? We can't read your mind. How about posting a link to the schematic?
 

audioguru

Well-Known Member
Most Helpful Member
This 500W square-wave inverter has been reported to work well:
 

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Oznog

Active Member
Even that is not a great inverter design. Nowadays an inverter uses low loss MOSFET transistors to switch transformers at high freq to generate a 220v rail (or a pair of +/- 220v rail) through filter caps and switch between them at 50Hz/60Hz.

I thought about building an inverter once but no longer see it as a good project. If you can, just buy an inverter. They're quite cheap and effective, much safer too.
 

audioguru

Well-Known Member
Most Helpful Member
Oznog said:
Even that is not a great inverter design.
Yeah, I just fixed that fairly simple inverter project that was full of shorts and wrong values on its original schematic, and added enough cheap 2N3055 transistors to keep the few original ones from melting.
It was 1st made in the Phillipines where Mosfets couldn't be found.

Remember milk delivery and empties pickup in North America and Europe? In the Philippines they have charged battery delivery and pickup of discharged ones to allow their many inverters to keep their TVs and fluorescent lights working.

If you can, just buy an inverter. They're quite cheap and effective, much safer too.
Yeah, the cheap Chinese inverters are tiny, lightweight, have a built-in fan and a display of battery voltage, power output and other stuff. :lol:
 

audioguru

Well-Known Member
Most Helpful Member
akg said:
except for purely resistive loads , is there any other use for the sq: wave inv: ?
Most cheap inverters have a square-wave output.
In the Philippines they are used to power TVs and fluorescent lights that certainly aren't a resistive load.
Also they are used to power power-tools with motors that are inductive, not resistive.
The only thing that might be in trouble with a square-wave inverter is something electronic with a power transformer that charges its main filter cap to the peak voltage of a sine-wave mains. In a square-wave inverter, the average voltage and the peak voltage are the same, and the peak voltage is much less than the peak voltage of a sine-wave.
 

Overclocked

Member
Im sorry to bump this but Ive been thinking..

The main purpose of an inverter is to invert 12v into 120V Right? So you can run 120V things from 12V....well Lets for say you wanted to run a microwave off of a car...Why go spend the money on an inverter when you can just remove the Diodes and Regulators from a Alternator? Theorectically you will have 120V (but at some frequency...I dont know what freq a alternator runs at..)
 

audioguru

Well-Known Member
Most Helpful Member
I didn't know that a car's alternator can supply 1kW. If you remove its diodes and regulator then your car won't go very far. You might as well remove the diodes and regulator from the microwave oven also, because its power transformer certainly won't work at the high frequencies of the alternator. :wink:
 

Overclocked

Member
Well I was using the microwave as an example..lol

I know they can supply around 65Amps or so..which would be..7800W...

(Im using 65 as a theortical number since batterys can hold that much...)

In which...the only use it would have is powering lamps in case of a power outage....heh power your house with your car!

EDIT: well you can always hook up a gas engine from a lawn mower, and use some weird gear ratio to get 60Hz.

Unless it already runs at 60Hz in a car.
 

audioguru

Well-Known Member
Most Helpful Member
65A at 14V isn't 120V is it? It might be 120V at a high RPM and without a load.
 

Overclocked

Member
I think we have a misunderstanding here. If we were to remove the diodes and regulator from an alternator, you would have pure unregulated AC Voltage. Theoretically it should be 120V.
 

Oznog

Active Member
Overclocked said:
I think we have a misunderstanding here. If we were to remove the diodes and regulator from an alternator, you would have pure unregulated AC Voltage. Theoretically it should be 120V.

Ain't no theory that says that. First off an alt generally makes 3-phase as far as I understand which a regular transformed cannot take, at best you could tap 1 phase. The reg could in theory be hacked so that it adjusts the field to make a 120v output but I'm not sure how much current it would make like this. And you have to remove the connection between the alt and battery and be running the vehicle with no alt charging it, which can kill the battery pretty fast.

The alt output is several times the engine RPM, which may cause trouble with many devices.

In short, just get an inverter. They're not expensive anymore.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Overclocked said:
I think we have a misunderstanding here. If we were to remove the diodes and regulator from an alternator, you would have pure unregulated AC Voltage. Theoretically it should be 120V.

Sorry, but you're talking rubbish!.

You could rewind an alternator to provide a higher voltage, as it is they are wound for low voltage and high current.
 

jrz126

Active Member
Overclocked said:
EDIT: well you can always hook up a gas engine from a lawn mower, and use some weird gear ratio to get 60Hz.

I think most lawnmowers are designed to run at 3600 RPM, (which is equal to 60 rev. per second. or 60 Hz).
I know the HP rating on most motors is at 3600 RPM.

So if they do run at 3600 RPM, then it would be a direct connection to your generating source.
 

chemelec

Well-Known Member
Nigel Goodwin said:
Overclocked said:
I think we have a misunderstanding here. If we were to remove the diodes and regulator from an alternator, you would have pure unregulated AC Voltage. Theoretically it should be 120V.

Sorry, but you're talking rubbish!.

You could rewind an alternator to provide a higher voltage, as it is they are wound for low voltage and high current.

Nigel, If you Remove the Regulator, the output voltage of a car alternator goes Up as the RPM increases.
Back around the 1970's, some companies were selling a "Black Box Device" to convert alternators for 120 Volts. It was just a Switch in a box for $30.00.

At about 2000 RPM, (Motor RPM) the output of the alternator is about 120 Volts DC. (Alternator RPM is Much Higher)
At about 4000 RPM, (Motor RPM) the output is about 220 volts DC.

Usually the Alternator Diodes will handle the 120 volts and can easily power an electric stove. **At Least for awhile.
It did work well for running Power Tools, Electric Drill and Skill Saws.

Removing the Diodes causes a Problem. Both for frequency and phase.
You could just use one phase, but not sure how it will affect Power.
And the frequency goes up with RPM. Can get Very High, definately not 60Hz.
 
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