Overloaded my inverter -now only works when hooked to car battery

In order to produce 100 watts at 120 volts, the current will be 1.2 amps. But if you are producing that power from 12 volts input, the current will be at least 10 times the output current, and that would be at 100% efficiency, which is impossible to achieve, The efficiency could be assumed to be around 70% though, meaning that the current input required to produce 100 watts at the output would be somewhere around 13 amps. That's a lot of continuous power drawn from a cig. lighter, and the load might blow the fuse or breaker for that circuit.

The lighter socket power cord has a 15 amp fuse. The cable with the battery clamps do not have fuse protection.

Power inverters can do this if they are internally shorted or they are being over loaded. If you are just using it to charge a phone or a computer it should not be over loaded. Now if you are charging a computer and running a small cooler at the same time, that may be real close to max which may blow a fuse. Have you tried hooking it straight to the battery to see if it will run what ever you are running. It has it's own fuse so if it has an internal short it will blow that fuse. It if works hooked to the battery and is just blowing the cig lighter or acc. fuse it can be a weak socket. If the socket is hot it may have a loose wire on the back side causing low voltage which can blow a fuse. So hook it to the battery direct, if it works ok there, reconnect it to your acc port and if it is getting hot it may be the weak socket. If it will not run hooked to the battery, it has an internal short and it would be better to buy new than try and fix. Sorry.

If the inverter is blowing your vehicle's lighter socket fuse, does it do it immedately or only when you try and operate a device? If its when you operate your device, it may draw more than 100-150 watts. This wattage is the limit for most lighter sockets. Double check the devices power requirement.

Hi Gena, the inverter is a 400 watt unit. This is not a rating for a continuous load. You do not mention which fuse is blowing. This could be the fuse in the inverter or the cigarette lighter (power source) fuse. In either case, a fuse blowing could be a short circuit, something in the inverter shorted, or too much load. I am going to look at the too much load side of things. Not knowing how many laptops are being used, with the inverter if you have a 20 amp fuse in the cig lighter, this will allow you 20 amps X 12 volts = 240 watts. I would not run the inverter over 240 watts because of overheating issues. So, 240 watts will run 3 laptops. Just the laptops. Most laptops draw around 70 watts. check your power supplies on them to find their rating. If you exceed the 240 watts by combining the ratings, then you can expect trouble with your inverter. It will give 400 watts, but this is a temporary condition only. Another inverter will be needed or a larger one installed and it being connected directly to the battery (with a fuse of sufficient size installed). You could also (let us say there are 6 computers) charge and run 3, and the other 3 are running on their batteries. After an hour, switch so that the 3 running on batteries now are charging as well as running. The other 3 are now charging.
I hope this helps. If you have any other questions please provide additional information. Such as the size and location of the fuse blowing. The laptop power supply ratings.
thank you

There are two possibilites: the first is the over 400W power draw, the other is how you have the inverter connected. Do you have the inverter connected directly to the battery terminals (the clips) not the outlet plug (cigaretter lighter)? This is needed for any load over 80W and under 400W. (the inverter can handle a load demand over the 400W limit but only for short periods (800W).)

What is the load that your PC pulls (Is it a laptop or a desktop)? The laptop in my home has either a 65W or a 90W load (depending on the battery and the AC adapter we are using). Desktops take much more power (usually).

I hope this helps.

Cindy Wells

Low input voltage or current.
Bad input voltage sensor.
Test by connecting directly to battery (with jumpers or make an adapter). The wiring or connection to your power port (cigar lighter) may be bad.

If it works at the battery, it is the car wiring. If not, it will cost more than the 25 dollar price tag to have it repaired. Just replace it (try http://search.harborfreight.com/cpisearch/web/search.do?keyword=inverter )

i would say inverter scewed//oz

Your connection willl be governed by the size of the inverter. Some smaller units plug into a vehcile's "power outlet." This used to be called the cigarette lighter. This is usually true for inverters up to about 400 watts.

For larger inverters, you should have received a set of cables, one with a red clamp and one with a black clamp. The black clamp gets attached the vehicle baterry's negative terminal and the red clamp goes to the vehicle's postive terminal.

If you plan to use the inverter for any length of time, the vehicle should be runnig to prevent the battery from going dead.

sounds like your inverter has died :)