TrailManor Owner's Forum - View Single Post

**Bill** · 09-05-2002, 10:18 AM

Bill / Happy -

I hate to be a wet blanket, but yes, you are headed for trouble.

The function of an inverter is to take current in from a 12 volt source, and send it out at 120 volts. Your refrigerator needs 185 watts, so the inverter must provide about 1.55 amps at its output [120 volts x 1.55 amps = 185 wattts]. Since watts is watts, the converter will need to take in 15.5 amps at 12 volts (12 volts x 15.5 amps = 185 watts]. But this is true ONLY if your inverter is 100% efficient, meaning IF it could do the conversion perfectly. Unfortunately, NOTHING is 100% efficient - the inverter will waste some power, so it needs to take in a little extra to make up for this waste. If we assume it is 90% efficient (a very optimistic number), then only 90% of the input current gets changed to 120 volts. So it really needs 17 amps, not the 15.5 amps we calculated earlier. The extra 1.5 amps is what is wasted.

Now consider this. At the TM converter, the wires to the refrigerator are protected by a 15 amp fuse. When you plug in your inverter and turn on the refrigerator, this fuse will probably blow. It is tempting to put in a bigger fuse, but you can't do this because the wiring can handle only 15 amps. If you increase the fuse, it will overload the wires.

And we haven't even talked about the turn-on transient yet.

My suggestion is that you set up your refrigerator, your inverter, and a spare battery on the floor of the garage or someplace, get an accurate ammeter, and MEASURE the current going from the battery to the inverter. Measure both the starting current and the running current. This should tell you what is going to happen in the final installation.

My guess is that you will see an overload, and the only answer is to run a new pair of wires to the refrigerator cubby - not a big deal for someone of your skills and intimate (!) knowledge of your TM. Let us know how it comes out. But please, don't try to cheat on this. Fried wires and a trailer fire are not something any of us wants to experience.

Bill

09-05-2002, 10:18 AM	#9
Bill Site Team Join Date: Feb 2003 Location: The mountains of Scottsdale, AZ, and the beaches of Maine Posts: 10,105	Re: Replacement Refrigerator Bill / Happy - I hate to be a wet blanket, but yes, you are headed for trouble. The function of an inverter is to take current in from a 12 volt source, and send it out at 120 volts. Your refrigerator needs 185 watts, so the inverter must provide about 1.55 amps at its output [120 volts x 1.55 amps = 185 wattts]. Since watts is watts, the converter will need to take in 15.5 amps at 12 volts (12 volts x 15.5 amps = 185 watts]. But this is true ONLY if your inverter is 100% efficient, meaning IF it could do the conversion perfectly. Unfortunately, NOTHING is 100% efficient - the inverter will waste some power, so it needs to take in a little extra to make up for this waste. If we assume it is 90% efficient (a very optimistic number), then only 90% of the input current gets changed to 120 volts. So it really needs 17 amps, not the 15.5 amps we calculated earlier. The extra 1.5 amps is what is wasted. Now consider this. At the TM converter, the wires to the refrigerator are protected by a 15 amp fuse. When you plug in your inverter and turn on the refrigerator, this fuse will probably blow. It is tempting to put in a bigger fuse, but you can't do this because the wiring can handle only 15 amps. If you increase the fuse, it will overload the wires. And we haven't even talked about the turn-on transient yet. My suggestion is that you set up your refrigerator, your inverter, and a spare battery on the floor of the garage or someplace, get an accurate ammeter, and MEASURE the current going from the battery to the inverter. Measure both the starting current and the running current. This should tell you what is going to happen in the final installation. My guess is that you will see an overload, and the only answer is to run a new pair of wires to the refrigerator cubby - not a big deal for someone of your skills and intimate (!) knowledge of your TM. Let us know how it comes out. But please, don't try to cheat on this. Fried wires and a trailer fire are not something any of us wants to experience. Bill