Tweaking Your Power Inverter, Get More Bang for the Buck

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About: Im a Student at RPI in Troy NY. The best part of college is most definatley 'Spelunking' or dumpster diving for parts in the elctrical engineering dumpster.

Intro: 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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    44 Discussions

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    JustinR164

    Question 5 months ago on Introduction

    I have a POTEK 750w power inverter that I just blew up. 2 if not all 4 mosfets were damaged (physically burned and split apart) as my wife tried to use the blow dryer with it...Problem is is that I need this ASAP and do not have time to order parts and wait. So my question is is what kind of electronics devices can I salvage from to get these kinds of mosfets? I have boxes of scrap circuit boards and a million mosfets but I don't even know where to start. Most of my boards are from Tv's and whatever else around the house has broke. Will I have any luck on these kinds of boards or should I be looking specifically for power inverter boards which means I have none.. the particular mosfet I need in this case is a MXP4004BTS YOL2 L4659H.

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    zogworthWildBill76

    Reply 5 years ago on Introduction

    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.

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    Gliwa01zogworth

    Reply 10 months ago

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

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    bodoWildBill76

    Reply 2 years ago

    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

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    wikitjuggla

    3 years ago on Introduction

    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?

    2 replies
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    psronwikitjuggla

    Reply 1 year ago

    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.

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    kool_kruzer

    3 years ago on Introduction

    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.

    1 reply
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    psronkool_kruzer

    Reply 1 year ago

    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.

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    Nick_Zouein

    9 years ago on Introduction

    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.

    1 reply
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    WileyS1

    3 years ago on Step 3

    I wonder if anyone trying this has found an adjustment inside for lowering the allowed input voltage before the inverter faults out? I have the exact same Whistler model and it drops out at about 11.5 volts. It would be nice to be able to run it down to 11.0 or so. (It's set at 11.5 so joe six pack doesn't ruin his car battery by running the voltage down. A lead acid battery can be permanently damaged by taking it down below 11 volts.)

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    BoogWar

    7 years ago on Introduction

    Hi all,
    I have a WAGAN Slimline 1500 watt Inverter. I ran the output through the breaker box in the house, which is grounded. I used my car to run the system, but had another, larger battery in parallel with the car battery. The unit ran everything in the house. Microwave, fridge, lights and TVs. Had the unit going for about eight hours, then decided to give it a break and turned it off. I then experienced a very dramatic fireworks / light / smoke show. I was most upset. I know enough about electronics to figure that the inverter was toast.

    I put it down and forgot about it. Two years later I broke out the electronics gear and decided that I would try and fix it (the fact that another storm had passed through leaving us without light again probably had something to o with it!) I found that the MOSFET's on one side of the circuit board, all eight of them, were completely gutted. Talk about your catastrophic faliure. The MOSFETS are Fairchild FDP8770 N-Channel. There are eight other MOSFET's on the opposite side of the board, LVP640's (N Channel also). They look fine. The fans were working at the time of the fireworks.

    My questions are:
    1) Why did it blow up when the unit was being turned off?
    2) If I start the car with the Inverter connected will it do any harm to it, and why?
    3) I see three pots on the board, and am decent with a soldering iron. I want to fix it myself. Assuming I can get the parts I think it needs, Do I need to match the MOSFETs, which would mean I might have to throw away some good looking LVP640's, and how do I go about doing this?

    The board is set up with four transformers, and each is in series with a fuse. None of the fuses blew. I know that I'm kinda above my head in this, but I wanna try. Thanks for any help I can get!

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    qwerty156BoogWar

    Reply 7 years ago on Introduction

    1)No idea
    2)The starter motor of a car draws LARGE amounts of currents from the battery ( read 150 Amps) and placing do much load on the battery (inverter +car) will probably cause fireworks
    3) I do not get the three pots thingy but if you wish to fix it you should replace all the blown components with new ones!

    Best of luck :)

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    wlucas1

    7 years ago on Step 3

    Most inverters today have good mosfets already mounted, (1000W inverter uses 4x100A mosfets). Its usually the small transformers that take the beating. (Source: Experience). Anyone done a transformer hack? :+)

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    microxy

    7 years ago on Introduction

    Hi guys,
    i am a new person here,can somebody help me explain how these modern inverters work without large transformers please?.

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    revjimjones

    9 years ago on Introduction

    Hi, I'm trying to repair a blown 400W (continuous 300W) inverter. I see one thing that puzzles me - your DC-DC FETs are only rated 5.6A, this unit I have uses IRF1404 rated at 220A, 40V, 2 pieces. The H bridge is 4 pieces IRF630, 200V, 9A. Am I getting the 2 stages confused? The 220A FETs exploded, are they the DC-DC converter section? If your DC-DC FETs are 5.6A x 12V, that's only 67W each? My FETs are coming from HK, China, so it will be a while before I try them. Thanks! Rob

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    Hey Den , Do you have the Circuit Diagram or a brief block diagram of this inverter? I'm trying to make one for my home.... -Shashank

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    omnibot

    9 years ago on Introduction

    Any info on the oscillator? A thought I've had a while runs like this; Power inverters transform 12vDC to 110-230vAC An oscillator applies a frequency to the current Transistors in a push-pull configuration reverses the output according to the frequency. Result is 110-230vAC at 30-60hz If the oscillators frequency can be varied you have a PWM speedcontrol for a regular AC-motor. Result is shortcut to an electric vehicle. What do you think? Any ideas on what the oscillator is or how it can be made to be variable?