Just because you're in your car doesn't mean you will not need 120VAC power. So many gadgets we use nowadays! I prefer to hide the power unit in the trunk and have a diecretely placed outlet in the front.
For more Technical Information, scroll to the bottom.
The upper of the 2 round switches to the right of the HVAC controls is the inverter switch. It has a green LED to let me know when it is on. The outlet is mounted in the passengers side sound insulator panel. Things used in an automotove environment need to be robust. Always use the best grade of outlet you can get!
Here is the actual power inverter in the trunk, nicely hidden and out-of-the-way!
For my Nova, the outlet is mounted in the console. The lower of the 2 round red switches operates it. The inverter its self is mounted in the trunk.
Technical Details.
Most of the small, inexpensive inverters that are for sale at department stores or uuto parts places are not equipped for remote control. They have a small switch on one end of the unit. With a remote mounted inverter, you need to be able to control it from the passenger compartment. Modifying these units to be remotely turned on and off is not difficult at all!
First off, why not just run the battery power into the inverter through a switch on the dash? Well - most inverters must be connected to battery power with the inverter's built-in power switch "off" or they will not operate. Maybe a safety feature I don't know. Even if that wasn't the case, this would still be a bad idea. Power = voltage X current. The inverter pictured above is rated at 750 watts. Fully loaded, this unit pulls over 62 amps from the 12 volt battery! It takes a very large wire to support that, and FORGET about a toggle switch handling this power. An inverter follows a similar set of rules to an AC power transformer, with respect to power, voltage, and current. Since it is multiplying voltage by (roughly) 10 from battery towards load, it is also multiplying current by (roughly) 10 going from load twards battery. In other words, look at the nameplate "amps" rating on your appliance, and multiply it by 10 to get an estimate of the load it will place on your battery or alternator. You get the point - a toggle switch in the dash, breaking the battery cable to the inverter is not an option.
So why not remove the inverter's power switch and run 2 wires to the dash of the car? That's also a bad idea because the power switch on many inverters is not connected to 12V or to ground on either side. The switch is in a low-voltage portion of the inverter's control circuitry and it could destroy the inverter if power or ground were applied to any part of the internal wiring. If it didn't destroy the inverter, it could at the very least cause a malfunction in the safety overload circuit. I don't recommend routing the built-in power switch wires outside of the inverter housing.
The secret is to install a miniature relay inside the inverter, which completes the inverter's built-in power switch circuit. The contacts of this relay complete the exact same power path as the original switch. I used the Radio Shack 275-241 12Vcoil, 1A SPDT relay, pictured below.
This item is glued to the inside of the inverter's front panel (avoiding blocking air vents) and connected so it's "C" (Common) and "NO" (NormallyOpen) contacts are wired in parallel with the original built-in power switch terminals. Use as small and flexible wire as possible, #18AWG or smaller wire will work. Then it is a simple matter of supplying 12V and ground to the relay coil to actuate the inverter.
The inverter manual will specify the size of input wiring, but I recommend bigger - the biggest you can use that will route where it is needed. In my car the battery and inverter are in the trunk so wire length is not a problem. However if you have a trunk-mount inverter and conventional underhood battery, you will need to massively oversize the wiring to avoid low voltage trip-out of the inverter from voltage drop in the power feed wiring.
Many inverters require 11V minimum at the input terminals under full load. If you have trip-out problems, test with your meter at the inverter's terminals with the inverter at full load and compare with your inverter instruction manual. Mainteining 11V with a 60 amp draw when your VBatt is 12V requires some very well designed and constructed wiring. This is especially important if you plan to use the inverter without the engine running. Don't skimp on the input wiring!
The 110V output wiring can be considerably smaller, because it is only carrying 10% of the currant of the input side. For anything under 1000W a #14AWG wire is fine. However for safety's sake make sure all the connections are sealed so moisture can't cause a short and so that exposed wiring will not shock someone.
The control wiring, from the new relay you added to the inverter can be very small. I recommend #18AWG for ease of routing and convenience.
The power electronics in the inverter do produce heat, but only when it is under a load. If you are running a phone charger (less than 1 watt) from a 750W inverter, it will not even get warm. But if you plan to really load it, there must be some air circulation. My inverter pictured above is really too close to the battery box- it is blocking the air vents. However it's never tripped out, even in the heat of summer.
Here's a few words of warning. These units are powered by a lead-acid battery capable of thousands of watts of power, and/ or a 500 to 2000W alternator. The stepped-up voltage is more than adequate to shock and kill. Treat the output side of the inverter as you would a live household outlet. It is just as dangerous. Inside the inverter, there are high voltage DC capacitors charged to 140VDC or better. These may or may not discharge automatically after the inverter is turned off. If you take apart your inverter, don't touch the bottom of the circuit board until you have tested the HV capacitors with a meter and verified they are not live.
How does an inverter work? There are basically 2 types. The older, more expesive and heavier type has a low-frequency power transformer. It has a heavy iron laminated core and looks like a conventional transformer. The DC comes into the unit and is converted to 12VAC, 60 HZ by the power electronics. This low-voltage AC is then fed into the power transformer and steped-up to 120VAC. These are heavy but take longer to overheat and tripout if overloaded. For a picture click here.
Most of the smaller, lighter, high-power units have a DC-to-DC converter instead of a power transformer. In these units, the DC comes into the unit and is chopped into a string of high-frequency pulses by the first stage power electronics. These are fed to a "flyback transformer," which works like an ignition coil. These look like small power transformers with a solid core, there are usually 2 or more ones in an inverter. The high-voltage DC pulses are stored in a capacitor at about 140 VDC. This completes the DC-DC converter stage. A second stage of high-voltage powere elctronics take this high voltage DC, and switch it back and forth to create the 60 HZ AC output. This type inverter is very small for its power rating, however will trip out quickly if overloaded. For a picture click here.
