power inverter installation

[Artstang]

???I just bought a power inverter 3000w cont./6000 surge (MAXX SST). Got it hooked up from a 12v power, but I don't know whether to connect it to the coach transfer switch or to the main panel. Any suggestion is appreciated. I understand it can power the TV, Microwave or A/C. Thanks Art

 

[King]

Vector manufacturing, who makes inverters, recommends #4/0 cable.  It must be connected directly to the battery bank.  Remember, the 6000 W surge requires 500 Amps (2 to 3 times what a car starter draws).  Car starter cables usually are #4 or #2.

 

[John From Detroit]

I will second that connect direct to the battery bank and with the shortest and most direct cable possible.  At 1000 watt the inverter is drawing approximately 100 amps, and even a fraction of an ohm resistance at that current means a BIG voltage drop to the inverter (.1 ohm just a tenth, would drop it 10 volts and disable the inverter)

So invest in good cables with well crimped ends

 

[Tom]

If I read your question correctly, you're asking about the AC wires to/from the inverter. You should make the AC connection between the transfer switch and the power distribution panel.

In addition to the suggestions to use large gauge wire from the batteriy, you need a fuse between the battery and the inverter.

A more detailed explanation is available in our library. Click the Library button above, select Tech topics and click Installing an inverter.

 

[Gary RV_Wizard]

Got it hooked up from a 12v power, but I don't know whether to connect it to the coach transfer switch or to the main panel.

The inverter output could go to either place, but if you do you must observe some very critical rules of use. It is imperative that you never allow inverter power to be on and supplying power at the same time that either the generator or shore power is also suppling power to the same circuits. Failure to do so will almost surely result in major damage to inverter, the devices on those circuits, and possibly even the generator and/or shore power wiring. Connecting the inverter directly to the load panel or transfer switch makes it easy to make a mistake and the results will almost surely be costly. As a minimum, install a switch (50A, double pole, double throw variety) so that simultaneous power can never happen.  Wire the center termoinals of the switch to the main panel feed. Wire the inverter output to one side and the wire from the shore/genset transfer switch to the other. That way the switch controls the power source to the main panel and you can never have multiple sources live simultaneously.

Doing it this way, be sure that you  turn off loads you do not want to run on the inverter. As a minimum, make sure the a/c units are off - you don't have enough batteries to supply inverter power for them. I also suggest making sure the refrigerator is locked on to LPG mode and the water heater is also in LPG mode rather than electric. Most everything else should run OK on the inverter, though a large microwave will drain the batteries in a very short time as well.

How many batteries do you have? Many people do not realize how much 12 volt DC power is needed to provide even a modest amount of 120 volt AC.  Every 100 watts of AC load will draw 8-9 amps from a 12 volt battery, so a typical  85-100 amp-hour battery doesn't last too long if you run large loads for very long.

 

[Tom]

Art,

I just looked at the Vector MAXX SST online. Is this the inverter you have? If so, it doesn't appear to be intended for permanent installation; More for plugging stuff into.

 

[Artstang]

Thanks for all your responses and suggestions. The inverter in question is a Vector MAXX SST 3000W which is mounted less than 3' from the batteries (2- 6 volt series) with #2 battery cables. The front panel of the inverter has 3-115v receptacles and a terminal for direct connection or hard wire to 115v source. The intent is to power only two TVs, DVD and occasional microwaving which is 900W. I understand the batteries will not last long if A/C (13,500 BTU) is used. I like the idea of providing a 50amp DPDT switch to isolate any simultaneous power. Thanks a bunch....Art

 

[Gary RV_Wizard]

Your 900 watt microwave generates 900W of cooking power. It will actually draw more like 1500 watts to do so. Check its rating plate.

A pair of 6V golf cart batteries has a capacity of 220 amp-hours when new and fully charged. Somewhat less after a year of use. That rating is based on a 20-25 amp rate of consumption - it will be less if the amp rate is higher, which it definitely will be when running the inverter with any load over 400 watts.  The load the 900W microwave will put on the inverter will most likely quickly drop the battery voltage below the inverter's minimum voltage threshold, which is typically somewhere in the 11.0-11.5 volt range. It will shut itself off if that happens.

Don't even think about running the a/c.