Instructables

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
 
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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.
WildBill764 years ago
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.
BoogWar3 years ago
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!
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 :)
wlucas13 years ago
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? :+)
microxy3 years ago
Hi guys,
i am a new person here,can somebody help me explain how these modern inverters work without large transformers please?.
nickk5 years ago
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.
revjimjones5 years ago
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
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
omnibot5 years ago
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?
Emperor Dane (author)  omnibot5 years ago
there's 2 parts of the inverter, one that makes the high voltage dc (140v), and the other that creates the 60hz sinusoid output. the secod part is normally done by a large H-Bridge (check wikipedia) your going to want to bypass the output to the h bridge and drive it from your own system, its a great idea.
Thanks. So that means a 555 or something added at the right place.
bylerfamily5 years ago
Can I turn a 4.7 volt wall transformer into a 12 volt one?
Emperor Dane (author)  bylerfamily5 years ago
not really, does it output 4.7 ac or dc? how many amps do you need it to output? 12v adapters are thrown out all the time, and they are cheap (car battery maintainers / chargers) can do a whole bunch of amps. power wheels chargers are 12v. pc power supplies output 12v. whats your application anywho? -Dane
Well, it is dc current.About 1-2 amps.I suppose you mean what am I using it for?I am using it to make hydrogen.
Emperor Dane (author)  bylerfamily5 years ago
you dont need 12v to break water into hydrogen, it breaks below 2v.. otherwise a 4.7v 1 amp power supply is 4.7 watts, which isnt going to do too much in terms of making alot of hydrogen. its current controlled for the most part
But I want to make a lot of hydrogen.And I want to get it fast.
12V bylerfamily5 years ago
use a 3.2kw arc welder transformer. these are about 15v and up to 170amp. this will produce a lot! be careful not to blowup your garage! and don't allow it to overheat.
Emperor Dane (author) 6 years ago
Its a revived power inverter running on better components!
This is good stuff...but i have a problem that a little bit off. I own a Vector VEC049D 1000 watt inverter. I have it for one year now, i used it up to Sunday morning to charge my laptop battery after the battery was fully charge i switched it off. A moment later i switched it on and noticed the power light and the fault light was on and the power level meter lit up to 500 watts mark and the unit was hot. So i switched off and then on and same problem. Plz tell me what is wrong with this thing. Thanks In advance.
Emperor Dane (author)  docreg6 years ago
howdy, first off, if your unit has a fan (which it probably does) check if it is spinning / if it spins up at all. the problem may be that the source your pulling the power from (12v battery or something was very low) there are 3 types of loads, inductive (motors) capacitive (laptops) and resistive (simple incandescent lightbulb). 1.try plugging in a 100W lightbulb. your inverter should be able to power it without a problem. respond back about what it does / what you observe. 2. if it can power a 100W bulb for over 10 minutes without overheating or causing the problem you mentioned earlier, try something bigger like a hair dryer (on low) they are normally 900W. shoot me an email with whatever happens and i can help diagnose it further. -Dane
Thanks for responding. Really i am using this inverter on a solar system. I am currently in South America vacationing and using it to power a cabin. Here is all i run on it, my laptop,i run 2 20 watts 12volts cf bulbs off the battery directly. I checked the battery which is a 150AH MOURA deep cycle and its good. And one more thing the inverter's fan spins all the time...as the power level meter goes up and down that how its spins; high then low over and over again.
Emperor Dane (author)  docreg6 years ago
ok, its easiest to diagnose if i know everything thats going on. ( i looked up the inverter online, its pretty sweet)

1.are you getting anything from the inverter, like does a cell phone charger, or something small work?
2. what are the exact lights that come on, it looks like there is a 10 bar led display on the front. when you plug it in with no load, what does it say?
3. whats the ethernet port for? (oh its for some kinda remote starter, nevermind)
4. is it doing any thing specific and sequential, like blinking red once ever 2 seconds or some weird pattern?

i looked online for a manual and found it at:
www.donrowe.com/user_guides/vector/vector_d_models.pdfwww.donrowe.com/user_guides/vector/vector_d_models.pdf

oh, is your laptop supposed to take in 50HZ or 60HZ. it appears the inverter is 120 AC, 60HZ. look on the back of your power supply for 50 or 60HZ. is it says both your in the clear. if it says 50 and your inverter does 60, you would have to modify the inverter.

best of luck, send a message back to this list for anything else. send a pic of your solar house if you can, sounds awesome
-Dane
Emperor Dane (author)  Emperor Dane6 years ago
im thinking. i will get back to you asap -Dane
Good afternoon Dane, Its been awhile now are you still thinking about my inverter problem? If you have anymore thoughts on it please let me know early.
Good Night Dane, I have been studying this inverter and i'm thinking maybe i should test the MOSFETS to see if thats causing the problem. What do you think? I will send pics of my Solar setup as soon as i can charge my digital camera's battery again. Until i hear from you... Docreg
docreg docreg6 years ago
Hi, numbered according to your request. 1. There is no output voltage from the Inverter.(i checked it with my Protek 506 meter) 2. the lights that come on are the Green light(power) and the red light(fault). The 10-bar Led display lights up to half; which is the 500 watts mark, but it does not stay at that mark instead it goes up and down continuously.(the inverter get very hot at time point) 3. it is for a remote switch. 4. the red light kinda half blink don't worry about the manual, i read it over and over hoping to find a solution nothing works. My Laptop power supply takes in both 50HZ and 60 Hz.
Are you using the inverter in a car with the engine running or is it running on just a battery ??? because I know several inverters have over voltage protection and this can cause error codes to show up and it also shuts down the inverter ... But this shouldn't make it hot ....
Take pictures, I want to see that electric bike project please! Post that bad boy.
sr1sws6 years ago
How is the power output increased? Just via MOSFETs with better specs?
Emperor Dane (author)  sr1sws6 years ago
the replacement mosfets could handle higher current and had a lower rds_on value than its predecessors. most of the time, small inverter's fail because of overheating. a lower rds_on = lower operating temperature / heat produced during operation.

this hack might be more useful for repairing an inverter, the power gain is on the order of 5 to 10 watts. its limited by the inverter's main inductor after that point.

unfortunately i didn't load cell test the device at the time (a year ago), so no numbers accompany the test. it was however more responsive to inductive loads (motors) after the modification than before.
-if i get a chance to test it i will post any increases. you bring up a good point.
Super, thanks! This is all rather new to me. I understand the general principles but get fuzzy on specifics. Any thoughts on how to mod an ultrasonic cleaner for more power? I have a reasonably nice one from Sharper Image that I'd like to get more "umph" out of. Thanks again, Steve
Emperor Dane (author)  sr1sws6 years ago
if you could send me a link to the "ultrasonic cleaner" description / production site I might be able to help.
smart!