Tweaking Your Power Inverter, Get More Bang for the Buck





Introduction: Tweaking Your Power Inverter, Get More Bang for the Buck

Using less than 12 dollars worth of parts, get more power / fix your broken power inverter

Step 1: Diagnosing the Problem

This instructable is a guide for repairing/increasing the output power of a simple dc-AC power converter (this instructable address the boost dc-dc converter based power inverter). For the record, a power inverter converts ~ 12V dc--> ~120 AC (normally non-sinusoidal). to increase the power output, the amount of output current the device can source is increased, whereas its output voltage remains the same.

Below is an MS Paint rendition of the first stage of a boot dc-dc. the boost stage amplifies the current from a lower voltage to a higher voltage, all in a DC environment. Read about dc-dc inverters on wikipedia.dc-dc converter (boost)

The boost topology can be made smaller and lighter than huge transformer systems, like an APC or UPS power supply.

At the heart of this system is two N channel MOSFETS. (your inverters configuration could have anywhere from 1 to 4 based upon design)

For those who dont know what a mosfet is, its simple enough to say its a kinda like a really fast switch.
The characteristics of this switch are what determines how much current the dc side of the device can source.

Step 2: Digging Deeper

Below displays the power inverter used in this modification. it was a cheap ~200 W inverter and i had blown it apart on an electric bike project electric bike project. So obviously i needed more power and a working inverter.

inside the inverter are the some of the DC-DC converter's main fet's. They are normally clamped to the heatsink.

The first step is to identify them, so grab your spectacle and find a part number. MOSFET'S have many characteristics aside from current and voltage rating. RDS on for example, is the resistance while the fet is enabled. this value should be as low as possible. the higher the RDS on, the more heat is dissapated at the junction, and the more chance for overheating. The gate threshold range is also important. your replacement fet should have about the same range.

Finally, make sure the pinout of your fet is the same and in the same package (EX. mine is a TO-220) dont order the wrong package size! for your replacement fet's

Step 3: Making the Modification

Using a solder sucker / copper braid / a brillo pad (whatever works for you) remove the existing mosfets for the DC-DC converter. Try not to destroy the pads on the board!

carefully reinstall you new fet's. re-solder back in and reattach to any heatsink.

at this point (when everything is disassembled) its a good idea to give it a trial run.

1. make sure the surface your working on is free of conductive debris.
2. attempt to power up the inverter. (use a current limited source like a power supply/ wall wart if possible, not a car battery)
3. carefully check the output voltage (set meter to vac and check the output side)
4. if the output is 100VAC, try a simple 100W lamp.

5. note, i take no responsibility if you blow up you laptop/ house/ solar-system by following this instructable. prolly not a good idea to plug in an expensive laptop, but a blender / lamp / electric pencil sharpener / your 386 can take a beating and are less finicky to odd power supplies.



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    How can I combine my 750 watt and my 400 watt inverters to make it an 1150 inverter? 

    replying for future readers.

    If you try to run your inverters in parallel you're going to have a bad time.

    They will fight each other and at best you get less power and less efficiency and at worse you get inverter death and a fire.

    If you french fry when you should pizza’d. You're gonna have a bad time!!!


    try to use one to one transformers 750 w and 400w aand use the out puts paralel perhaps so you can save yoru power suplyes

    I don't know if anyone is still paying attention to this, but could you take two exactly identical in brand and wattage power inverters and parallel the 120v outputs w/o incident?

    NO... never, it will release the "magic smoke" from them... once that is released, they will not work any more.

    Here's why...
    Inexpensive inverters are what's called "asynchronous"... meaning that the AC output waveform is not "in-sync" with anything else... and they usually are not even exactly 60Hz (or 50Hz for non-North Americans). So when one inverters output is going up, the other may be going down... they will fight each other and... as mentioned, cause the release of abundant smoke.

    Only "grid-tie" inverters can be operated in parallel, because they "look at" the AC Mains signal phase, and synchronize their own output to be exactly in-phase (in step) with the AC Mains.

    No, there will be no synchronization of ouput AC.

    hi. I just bought a 1000w omega dc-ac op-w1kc invertor with charger, connected 2 x 12v batteries. using a mulitmeter set to ac i get a reading of 316 vac. is this normal as the vac output supposed to be 220vac.

    AC Mains line voltage is specified as RMS... Root Mean Square... it's a Sine Wave function. Most inexpensive multimeters will read P-P, or Peak-to-Peak... the highest and lowest points of the AC waveform. The math to convert RMS to P-P is RMS x 1.414 (square root of 2); which results in 311V P-P for a 220V RMS sine wave.

    Hello, I'm sorry to tell u that u can't increase power of an inverter by just replacing/increasing the FET's (the power stage) and neglecting the output transformer, the transformer should be replaced with a bigger one too to deliver the increased wattage. This is not to mention if the inverter has protection a built in overload cutt off system that is regulated to cutt off power on the old configuration, so whatever increase u make still it shut's off at the load that it was designed for.