Hey guys I have a 3500watt power inverter in my work truck that stopped working. It runs off a second battery wired in parallel with my trucks engine compartment battery to keep it charged. I am getting 12 volts from the battery and determined the battery is good. The inverter itself turns on beeps and gives me a red light. When I metered the inverters output I get 120vac for the first 2 seconds it’s turned on then the beep happends and it drops to 0v. I plugged a normal receptacle plug tester into the output as well and my plug tester tells me there’s an open ground. I heard mosfets are quick to go on these things anyone know what the problem could be? It’s a power bright 3500watt power inverter

 

Don't worry about the open ground indication from the plug tester. In a normal distribution system one leg of the supply is connected to ground at the last transformer in the distribution system. Your inverter will probably have a floating output so this is the reason for the ground fault indication. Connect your voltmeter to the 12 volt input terminals on the inverter. Note is the voltage drops when the inverter is switched on. If it does drop then either the battery voltage is dropping under load or there is a high resistance connection somewhere between the battery and the inverter.

Les.

 

I looked it up and saw where is is designed and made.

 

Don't worry about the open ground indication from the plug tester. In a normal distribution system one leg of the supply is connected to ground at the last transformer in the distribution system. Your inverter will probably have a floating output so this is the reason for the ground fault indication. Connect your voltmeter to the 12 volt input terminals on the inverter. Note is the voltage drops when the inverter is switched on. If it does drop then either the battery voltage is dropping under load or there is a high resistance connection somewhere between the battery and the inverter.

Les.

Yes actually when switched on the line input terminals of the inverter read 10vdc, is it possible this under voltage is causing the inverter to shut itself off? Also I noticed who ever installed this second battery happened to Ground it out to the bed frame of the truck which in my experience has lead to a high resistance ground connection rather than going straight to the negative terminal on the battery in my engine compartment. Do you think the bed side ground connection offers a resistance too high or do you think the secondary battery is shot considering it’s voltage also drops to 10vdc under load.

 

If the voltage directly at the battery terminals drops to 10 volts when the inverted is switched on then the battery is the problem. When the inverter is providing 3500 watts output the current on the 12 volt input will be over 300 amps. For this current you would require VERY heavy gauge cable between the battery and the inverter.

Les.

 

If the voltage directly at the battery terminals drops to 10 volts when the inverted is switched on then the battery is the problem. When the inverter is providing 3500 watts output the current on the 12 volt input will be over 300 amps. For this current you would require VERY heavy gauge cable between the battery and the inverter.

Les.

They ran what looks like 2awg between the battery and the inverter which seems small for 300amps. When I metered the battery nothing was plugged into the inverter meaning the inverter wasn’t under much load and yet the battery still dropped to 10vdc so it seems that must be the problem. Also this was while the truck was running so shouldn’t I have been getting 14vdc if the battery was good? I know that usually car battery’s will put out 14vdc with the motor running.

 

Also if the secondary battery is connected in parallel with my trucks engine compartment battery which is functioning properly how am I getting 10vdc at the terminals? Wouldn’t I still be reading 12vdc because it’s still connected to my main battery? I did not isolate them before taking the reading.

 

Your inverter at full power can severely overload an ordinary car or truck battery if it supplied 3500W(!) for more than 5 seconds. The overload might boil away some of the water in the battery.
A car battery that is over 5 years old is not good anymore.
A car battery stored without being charged for longer than 2 months is ruined.
A car battery discharged to less than 12.0V is ruined.
A car battery that is vibrated has bits inside that fall and partially short the battery.

Did the inverter ever produce smoke? Do the truck lights dim when engine is not running and the inverter is turned on with no load?