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jayspi's avatar
jayspi
Explorer
Jun 19, 2018

Low power from 12 volt outlets

Hi everyone, I'm having an issue with the 12 volt outlets (cigarette lighters) in my RV. It's a new-to-us 2004 Colorado 5th wheel, but we haven't used the 12 volt outlets until today.

In our last rig I had an inverter that powered the whole rig, but with this one I wanted to save money so I got two Bestek 400 watt inverters.

The problem is that devices powered off the inverter are getting intermittent power. The TV is 85 watts and keeps powering off. My wife's laptop is like 75 watts and it charges on and off. I can hear the inverters revving up and down, and occasionally the power/fault light turns red then immediately recovers.

I checked the voltage from both 12 volt outlets and they are fluctuating between 107 and 115 volts.

The fluctuating voltage is obviously the problem, but I'm not sure why. We have four 6 volt GC batteries and AFAIK they are fine. I check them regularly. All other 12 volt systems in the rig work properly.

We have friends using this same 400 watt inverter and they do not have this problem.

Could it be that the fuses are too old? Or the outlets are just bad? Any feedback is appreciated.

Edit: I fired up the generator and the problem persists. With the gen going the 12 volt systems should be pulling from the shore power through the converter, right?

Thanks!
  • jayspi wrote:
    I checked the voltage from both 12 volt outlets and they are fluctuating between 107 and 115 volts.


    Presumably what you really mean is you checked the output voltage of these inverters with a voltmeter ... problem is, these readings are erroneous because these Bestek inverters you have are MSW - modified sine wave - rather than PSW - pure sine wave. You can't compare these readings to those you may get when you measure a 120 vac receptacle that's powered by your generator or campsite power post. Your problem is you're trying to draw too much power from cigarette lighter outlets that are only rated to perhaps 5 to 7 amps at best. The solution is to locate the inverters closer to the batteries and use heavy gauge cable to wire to those batteries.
  • Thanks guys. I just checked at the batteries and I'm pulling 113-115 volts. Is that normal, or should I get a steady reading of 120 volts?

    Also, there was a small spark when I connected the inverter to the ground. I'm going to go check all the connections.
  • Low voltage issue due to long thin wire. 75 watts is about max and with 10% overhead you are just pulling too much. A small transfer switch $50 and you can wire that 400 watts direct to the branch circuit and power the regular outlets. Much better system.

    Those 12v connectors are good for USB charging only.
  • With the generator running the converter runs off the generator.
    You need to start at the nbatteries with your meter and see where you are loosing voltage.
    Poor connections will cause voltage drop with current flowing.
    Call me if you wish. I am an experienced troubleshooter.