5 Reasons Why Your Power Inverter is Squealing and Screaming at You!

When I was looking at inverters a while back, I noticed that one of the most common questions regarded the squealing noise coming from the inverter during operation.  I personally haven’t experienced this problem with either of my inverters, but I was curious and did some research to find out why this occurs since there’s no guarantee that I’ll never run into this issue.

Why is my Inverter Screaming?

Inverters can scream or squeal for many reasons which may stem from 1.) Overheating, 2.) Fan Obstruction, 3.) Low Voltage (discharged battery, loose cables/connections, the starting of a car battery), 4.) Exceeding the inverter’s continuous power output rating, or 5.) a Faulty or Dying Inverter.

That’s the short and sweet answer but there’s a bit to unpack in it to make sure you keep your inverter in tip-top shape.  I’ll share the things I’ve picked up through a few hours of research to save you a bit of time or hopefully point you in the right direction if you’re experiencing this problem.

1.) Your inverter is Overheating

Many warning labels warn not to operate an inverter in temperatures exceeding 100 degrees.  So, above a car engine while it is running might not be the best idea. To counter this, I always recommend mounting your inverter to a wooden board (you can check out how I do mine with Velcro at this link) and to keep the board at the edge of the car. 

The board gives the inverter a buffer from the direct heat from the engine, gives it something more stable to rest on, and also keeps a buffer between the engine block and the inverter cable posts.  You don’t want to cross the posts with metal or you’ll fry the inverter.

Regardless of where you operate your inverter, always make sure it has proper ventilation and isn’t in direct sunlight.

Another reason for overheating might be due to the fan and we’ll cover that next.

2.) Your Inverter has a Fan Obstruction

Carefully inspect your inverter for anything that may have gotten past the cage that guards the fan.  Use a flashlight if necessary for a better view. Is there a loose sticker in the inside that’s catching the blades?  Is there a piece of paper? Did you leave the inverter mounted in an area that has low human traffic and maybe a mouse built a nest behind it and it now has debris/feces inside?

If your inverter isn’t used regularly, it’s a wise idea to do a quick inspection before you put it to use.

If the problem is literally a squealing from a fan that is experiencing friction, I’ve read about people using a small amount of machine oil to lubricate the fan with success.  I’ve never tried it, but it might be worth a shot if your alternative is a dead inverter and you’re past the warranty.

3.) Your Inverter is Experiencing Low Voltage

This is probably the most common cause of all of my research and it comes in many forms. Simply starting a car while the inverter is hooked to the battery is enough to send the inverter screaming in some cases due to the instantaneous voltage dump to get the car powered up.

You might also have loose cables where the cords attach to the back of the inverter or where they connect to the battery terminals or cigarette lighter socket.  Make sure they aren’t over tightened, but they should definitely be snug.

If your cables are loose and your inverter is vibrating in the car or under the hood of a car with the engine, the cables are for fractions of a second not getting the proper current through them due to gaps and interruptions and this will cause your unit to squeal.

Another problem might simply be where you plug your inverter into. If you plug it into the cigarette lighter socket, but the wiring to that socket within the car is faulty, then your inverter will squeal.  You might mistakenly blame the inverter, but it is actually the fault of the car.

A low battery is often the biggest culprits for a squealing inverter.  Once the battery starts its drop from 12.7 downwards, many inverters will start to squeal when the battery approaches 11 volts of charge (about 5% of the batteries remaining life just before complete discharge).  

Unfortunately, this is not enough to start over a car, so if you’re relying on that squeal as a warning to crank your engine, you’ll be out of luck.  When your battery starts getting to 12.1 volts you’re starting to get to a coin toss about whether or not it will turn over the engine.

4.) You’re Exceeding the Inverter’s Continuous Power Rating

Your inverter will come with its advertised number on it, like the Duracell 800 watt inverter.  What it really is capable of is a peak surge rating of 1280 watts, a maximum output power rating of 800 watts and a continuous output power rating of 640 watts.  It can do 1280 watts for a few seconds to help start up an appliance that requires a surge to start, and it can sustain 800 watts for a short (but unspecified) amount of time to cope with temporary surges in power during normal operation.  However, it is only designed to run at 640 watts to remain a happy inverter.

If you push it past 640 for long enough, it will start to squeal since you’ve pushed it past its tolerances. You will need to lighten the load on the inverter or scale up to the next inverter size to continue doing what you want.

5.) You’ve got a Faulty or Dying Inverter

If all of your cables are snug, your battery is charged, you’re well below the continuous output rating for the inverter, there’s nothing obstructing the fan, and the temperature around the unit is reasonable — well, then you might just have yourself a defective or dying unit.

If it’s under warranty make sure to return it.  If you suspect that it’s going to die anyway and you want to tinker with it, you might be able to take it apart and work some magic.  For the price of a modified sine wave inverter, I’d just buy a new one before I’d tinker with it, but that’s just me. Your mileage may vary.

The best takeaway from my research is that nearly every inverter (if not all) are made in China and they are cranked out of the factories en masse.  There are going to be duds, and even the ones that work will have their built-in tolerances for how long they’ll function before joining the junkyard.  

If you’re relying on your inverter for home backup power, there’s no reason to not have at least two of them for your setup.  I carry both the Duracell 800 and 400-watt inverters and they have performed flawlessly for me over the last 4 years. I don’t abuse them or push them to their limits, and they have saved my bacon in a pinch many times.  You can check out my review of these cool and affordable units here.

Remember, “two is one, and one is none” when you’re really relying on something.

Robert Van Nuck

Robert lives in central Michigan and enjoys running, woodworking, and fixing up small engines.

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