Wednesday, October 13, 2010

Selection,Preparation, and Installation of a Power Inverter for an Automotive Application

Selection,Preparation, and Installation of a Power Inverter for an Automotive Application
By. Jon Hardwick


In this article we will discuss how to select the appropriate power inverter for your application and your vehicle. We will also provide an overview on preparing for an installation, actual installation of the inverter, and what situations warrant the use of additional accessories such as battery isolators, fuses, and DC breakers.


When selecting a power inverter for use in your vehicle you must have an idea of what you are trying to operate in your car or truck. Are you trying to provide power for a mobile office, a gaming system, tools, or just to have some emergency power. The process is pretty much the same in all applications with one exception; whether or not to choose a pure sine wave inverter or a modified sine inverter. This can be tricky if you don’t know what kind of loads you will be running. That is why planning is crucial to selecting the right inverter. For example, let’s say for the sake of argument that you will be sizing this system for a mobile office. You are looking to run a laptop computer, all-in-one laser printer, wireless router, modem, and some miscellaneous rechargeable devices. Refer to the list below for specifications:

· Lenovo ThinkPad – 2.0A
· Brother All-In One Laser Printer/Fax/Copier/Scanner – 8.8A
· Linksys Wireless Router – 1.0A
· ClearWire WIMAX modem – 1.0A
· Smartphone - .02A

Total requirement for all of the devices running at the same time is 12.82A or 1474.3 Watts. It is recommended to size the unit 25% above the actual requirement, bringing the total to 1842 Watts. Since you won’t find a power inverter rated exactly at 1842W you will need to find the closest unit by rounding to the total to the nearest thousand; which would be a 2000W. Now that we have determined what size we will need to power all of the devices we need to decide what output waveform we will need for this application. Since we will be dealing with a laser printer we need to select a pure sine wave.

(Note: We arrive at this conclusion based on my experience and the research I have conducted on this type of application. For most, this would take some research or simply trial and error. But there you go, I have cut out the time it would have taken you to research the waveform required for the laser printer. FYI, if you want to know why they don’t work on modified sine it has to do with the fuser and laser unit.)

Pure sine wave is a guarantee that you will not have any problems down the road with any device. Modified sine wave will work with most everything except sensitive electronics, medical devices, and variable speed motors.

Additionally, selecting a pure sine wave will not interfere with the radio in either the wireless router or WiMax modem. This is important if you want to get Internet in your vehicle. We have heard reports that if you use a wireless router on modified sine wave it significantly slows the speed of data transfer. However, with the exception of the laser printer all of the remaining devices would work on modified sine wave it’s just not recommended. Pure sine wave should be used on all battery integrated devices as it will not affect the battery life of the devices.

Now that we know what size inverter is required and what type we need. We can move forward with what will be required for planning the installation and moving toward the actual installation.
Vehicle Assessment

Before installation we need to ask a few questions about the vehicle the inverter will be installed in. For this example we will use a Ford F-150. The information we need off the vehicle is alternator size, location where the inverter will be installed, and whether or not we need to upgrade or add additional batteries.

First, let’s take a look at our alternator and figure out what size we have. For the 2004 Ford F150 there is a 130A alternator. Not bad, this alternator should not have a problem keeping up with the continuous loads we have. Now let’s look at the battery. In most cases you will find a heavy duty starting battery under the hood of a stock Ford F-150. This is a problem. We have a couple of choices pertaining to replacing this battery. Since the battery is in decent condition one could simply leave the battery alone and not replace it until it has been cycled past the threshold. Or, replace it now with a dual purpose deep cycle battery. The choice is ultimately yours. My opinion is to do it right, and do it once. A single battery configuration for this application would be all you would need to get rolling if you plan on using the system mostly while the vehicle is running and with minimal printing. However, for this example, let’s say that we are going to use the equipment a lot while the vehicle is not running and with some moderate printing and scanning. This would require the addition of a second “Auxiliary” battery. We will address this in just a moment. Since we have decided to install a second battery, and will upgrade the starting battery we need to determine the best place for the inverter to be installed. In this case, under the rear seat is the best place to locate the inverter. This provides the best central location to both the starting battery and the auxiliary battery which will be located in the bed.

Auxiliary Battery Installation

Choosing to install a second battery for this application is the best choice for a couple of reasons. It will help to absorb the surge from the printer, be closer to the inverter, and provide a longer run time for the mobile office equipment. Now we must decide whether or not to install a battery isolator. For this application one is not required since the starting battery will be replaced with a dual purpose deep cycle battery. For installations where replacing the starting battery is not an option an isolator would be required. If you wanted to add an isolator to this system you would simply size it around the size of the alternator and use this chart to determine which one is required for the vehicle.

Installation & Running cables

Now for the fun part, running the cables to the inverter. For the example we have outlined in this article we will need to run a cable from the battery under the hood to the auxiliary battery in the bed. We would choose to run the cable from the starting battery to the bed by running along the frame of the vehicle and drilling through the bottom of the bed, then running another cable to the inverter by drilling a hole in the back or bottom of the cab (whichever option you choose). Once the cables have been run they will need to be secured tight to the frame and away from any exhaust components as this could melt the coating on the cables or create a potentially dangerous situation later as you’re vehicle is in motion.

Fuses & Safety

Quick note about fuses and DC breakers, it is good practice to install a fuse or breaker in every inverter installation on a vehicle. However, there are some installations that don’t absolutely require a fuse. One example is; installation inside a van where the inverter is installed right next to the sealed AGM battery. This is fine as long as there is no possibility of the battery cables being damaged. My personal opinion on fusing is to install a fuse just in case. It is really good insurance and they are relatively cheap.

Sweet! We now have power in our truck. We can run our mobile office and help our clients while on the road. By installing this inverter and adding power we have accomplished adding a computer, printer, and a wireless Internet hot spot. The possibilities are absolutely endless.

If you have any questions about this article or you would like to learn more feel free to shoot me an e-mail at: