Question Marks

Will Power Inverters Kill my Alternator?

Power inverters are a great tool to have installed on your vehicle rather it be for your car, truck, motorhome, or even your boat. These tools convert the direct current (DC) energy that is produced from your alternator and stored in your battery over to what’s known as alternating current (AC). AC electricity is what all of our homes, offices, and buildings use to power our electronics and appliances. By installing a power inverter you will be able to plugin any of these appliances or electronics right into your car. This allows you to hook up a crock pot, coffee maker, television, laptop, refrigerator, or even power tools. Whatever your need is power inverters can provide you with the electricity!

Over the past few months here at we have been writing article after article on the topic of these power inverters. The goal here is to provide a comprehensive listing of any and all questions related to these tools. In today’s topic we are going to look at the role alternators play when using a power inverter. Let’s take a look:

Power Inverters & Alternators

Before I answer your question lets first go over how your alternators and batteries interact with each other. Most vehicles are outfitted with a standard twelve volt cranking battery. This battery is used to for short bursts of energy and it is what provides the initial power to start your vehicle. When the vehicle has started the alternator takes over for your cranking battery. All electrical needs are now powered directly from your alternator. At the same time your alternator is also charging your battery to ensure that you have plenty of charge for the next time that you start your vehicle.

Now most standard alternators range from sixty-five to one-hundred amps of power. This is a measurement of how much power the alternator can produce. They also typically have wiggle room between ten to fifteen percent. What I mean by this is that you can add additional power demands to your vehicle without impacting your alternator. An example of this would be using a power inverter with an appliance plugged in.

This is where it can get a bit tricky. If you use a large sized power inverter then you could up exceeding that ten to fifteen percent window. This will result in the overloading of your alternator. When this occurs the alternator will do its best to keep up with the demand. When no more power can be produced it will look for alternative sources, such as your battery. We now end up with the reverse of what should be happening. Instead of your battery being charged while the vehicle is running the battery is being drained in an effort to meet your high power demands. This can result in your battery dying on you even while you are driving down the road. This is NOT a good position to be in as you will end up stranded with no way to start your vehicle. Along with being stranded overloading your alternator can also result in shortening its lifespan as well as wasting energy and fuel.

The good news here is that there are alternative solutions. I mentioned earlier that alternators typically range from sixty-five to one-hundred amps of power. If you plan on using a significant amount of power then I would highly suggest that you look at purchasing a high output alternator. This is an aftermarket upgrade to your current alternator. These high output alternators can produce as high as two-hundred and fifty amps of power. In some cases that is two or three times more power then your standard alternator. You also do not need to worry about going TOO high in the alternator size. Alternators only produce the power that is NEEDED. So, if you get a two-hundred and fifty amp model and only need two-hundred amps you will not be waiting energy or fuel by having the two-hundred and fifty model.  These are also not that expensive to purchase. Just make sure to buy one that is compatible with your vehicle. If you are not much of a do-it-yourselfer then I would recommend taking your vehicle to the dealership or a local mechanic and telling them you need a high output alternator installed.

So, when should you consider purchasing a high output alternator? As you know, each vehicle and each application is different so I cannot give you a definite answer here but I can give you a guideline. In my opinion if you are going to be using a power inverter that is at one-thousand watts or over then it will make sense to purchase a high output alternator. If you are under that one-thousand marker then chances are you will fall within that ten to fifteen percent window and will be fine to run whatever it is that you are intending to power.

Power inverters range from just a few hundred watts all the way up to four or even five-thousand watts. The size of inverter is going to depend on exactly what you intend to power with it. Before plugging something into your inverter you should determine exactly how many watts it will use. In some cases the label of the appliance/electronic has a wattage label. In other cases they do not, BUT if you find the total amps or amperage number you can calculate the watts yourself. As an example say you have a coffee machine that takes five amps. All you have to do is take that five amps and multiply it by the total volts. Volts are HOW the appliance is plugged-in. If it uses a standard outlet like most everything does then it uses one-hundred and twenty volts. So, the math becomes five amps times one-hundred and twenty volts equals six-hundred watts. I also recommend exceeding the calculated wattage by twenty or thirty percent to ensure you have some wiggle room.

Another point here is that the more complex the machine the more power it will require. Anything that moves, produces heat, or produces cold will require a lot of wattage. That coffee machine we mentioned earlier uses six-hundred watts. That is quite a bit but that is because of the heater element within the machine. A fifty inch television would only use about two-hundred watts. That is a significant difference and it is because of that heating feature of the coffee machine. Keep this in mind when looking at power inverter sizes. What do you want to power?


To answer the initial question in this article a power inverter that outsizes your alternator can end up draining your battery even while your vehicle is running. If left unchecked you could end up damaging your alternator as well. If you are in these situations the best course of action is to purchase and install a high output alternator. This will take care of you power problems and allow you to continue using the power inverter and whatever appliances or electronics that you have plugged into it.

Thanks for reading,

Alec Johnson

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