Low power from 12 volt outlets

[jayspi]

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!

[mchero]

do those cigarette lighter sockets get hot ??

[jayspi]

Thanks everyone, I appreciate the help. I learned a lot!

[wa8yxm]

At Power on the inverter likes to pull max load for a brief period but yes it pulls about 10 amps for every 100 watts of load. But you are looking at an outlet with at the most 10 amps capacity even if it is fused for 20.

I used to run a 450 off a dash outlet or a compressor outlet on a Chevy Lumina but those were full 20 amp outlets. And even it complained on the compressor outlet (reare of ride) ..

You can install heaver wireing (I have some 20 amp outlets 10ga wire feeds them) but your best bet is to hard wire the inverter to the batteries via a fuse and extend the 120 volt.

[SailingOn]

The power lost through a wire is much less at high voltage than at 12 volts. That's why the city supply lines on utility poles run 20,000 volts or so and need those big canister transformers.
IF you connect your inverter directly to the battery, with several feet or less of thick cable, then run an extension cord (120V) over the longer path from the inverter to your appliances, you'll have no trouble.
In a similar situation, I added a 120V outlet wired only to the inverter, for a cleaner looking setup.

[MrWizard]

jayspi wrote:
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.

totally confusing, what do you mean, the inverter voltage ?
you don't measure 120v on 12v outlets

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?

NO.. your on inverter, plugged into 12v socket ?, with the generator on you should get steady 13v power for the inverter, but that won't help bad wiring, bad batteries etc..
and yes Bad batteries can mess with your 12v power, even with converter on, and will damage the converter
BTW; you don't pull volts, the inverter will USE DC amps to create 115v AC output power , volts is more analogous to water pressure

Thanks!

[Sandia_Man]

I did the same thing and tried to use a small 350 watt pure sine wave inverter in our rigs entertainment center where a DC socket was located. No dice as the inverter squealed mightily due to the small diameter wiring used by the manufacturer. I was not surprised by this knowing how RV manufacturers cheap out wherever they can, I still use the DC socket for a plug in DC voltmeter.

My choice was to either locate inverter close to battery and then run extension from inverter to entertainment center, or run a much larger diameter wire directly from battery bank to feed inverter in entertainment center, chose the latter and now PSW inverter easily runs our HDTV, HD satellite, soundbar & subwoofer, HD gaming system, and for charging portable electronic items.

[jayspi]

wa8yxm wrote:
400 Watts means the inverter needs a 40 amp Feed
Those outlets are rated at 10 amps. (Generally) perhaps 20 but no way can they run 40 amps. The inverter is simply too big for that type of connection.

I believe you guys but I am trying to learn more about electrical systems, so bear with me.

Wouldn't the inverter only pull as much power as it needed to power devices connected to it?

Either way, I think I see the mistake I made when purchasing these. I was calculating my power needs with 120 volts, but I should have been doing it with 14. So if the outlet is rated for 10 amps the I could get 120 watts max out of it (10 * 14).

Is that right?

[wa8yxm]

400 Watts means the inverter needs a 40 amp Feed
Those outlets are rated at 10 amps. (Generally) perhaps 20 but no way can they run 40 amps. The inverter is simply too big for that type of connection.

[jayspi]

SoundGuy wrote:

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.

Yes that is what I meant. I agree the way I was doing it wasn't the best; I'm way out in the mountains in Colorado so resources are limited 🙂

Fortunately I found a battery for my voltmeter. I checked the batteries and I'm getting 13.28 volts with the converter running. That seems about right.

I still have my 1500 Watt pure sine inverter from the last rig. I guess I'll connect that and just run an extension cord inside. I'll see about getting a transfer switch when I get back to civilization.

Thanks to all of you for your help!

[Mandalay_Parr]

Batteries should read about 12.6 and 13.4 if the converter is on.
Jerry Parr

[SoundGuy]

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.

[jayspi]

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.

[time2roll]

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.

[Mandalay_Parr]

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.