Lights going bright & then going dim

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danthegunman

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Joined
Nov 12, 2018
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This weekend we were camping & hooked up to shore power, 30 amp service. Every 5 minutes or so the lights would all of a sudden go bright with the fan running on the converter then after about 5 minutes or so they would go dim & when the lights went dim the fan would shut off. This continued for four days. When the lights were bright my battery showed fully charged on my monitor panel, but when they were dim the battery only showed 1/3 charged.  Like I said this continued for all four days. I also have a Camco Power Defender 30 amp that showed no problem at the power source. I stood out side of my RV while the lights went from bright to dim & there was no change in the lights on the Camco Power Defender. What could the problem be??? Dan
 
si camper, I thought an "inverter" took DC power & made AC power, whereas a "converter" takes AC power & makes DC power? Am I wrong? Dan
 
Test your battery.

It sounds like what mine did when it was dying.

You can lug it to a car parts store and they will test it for free.

Once I replaced mine my lights worked fine.
 
You're correct about inverters and converters, Dan.

I'd get a multimeter and measure voltages at the batteries and converter, at least, when this is happening. I'd also check the 120V at the pedestal, as well as after the "Defender." Depending on whether the "bright" or the "dim" was the normal state, you probably had either a high or a low voltage. The converter fan running probably indicated that it had warmed up and needed cooling, thus was probably working harder.

Certainly it could be a bad converter, but I'd do a little more troubleshooting before replacement, to identify the problem source for sure.

I suspect others will be along shortly with more thoughts.
 
danthegunman said:
si camper, I thought an "inverter" took DC power & made AC power, whereas a "converter" takes AC power & makes DC power? Am I wrong? Dan
Click to expand...

This is one of those "Yes, But . . ." situations.

Usually, you are correct.  However some of the LARGER inverters are combination inverter/chargers, with BOTH functions, and usually the transfer switch also, built in, and RVs that have those don't have a separate converter.  I'm guessing si camper was thinking of those.  See:

https://theinverterstore.com/product-category/pi/psic/12-volt-dc-pure-sine-power-inverter-chargers/
 
Welcome to the Forum.

Back to your original question.  When the batteries get a bit low, the converter kicks on to charge them.  When this happens, you have 13.4V from the converter also feeding the lights, and they shine brightly.  Once the batteries appear charged, the converter goes off, and the batteries now feed the lights with no help from the converter.  If the batteries are weak or going bad, they will produce only 12. 4 V or less, and quickly be drawn down lower, and lights dim.  When battery voltage hits the set point, converter comes back on and lights brighten.

I suspect the converter is fine (the lights DO brighten!) and you have a weak battery.  If so, make sure the replacement is a true deep cycle battery.  Ask more questions about this if needed.
 
danthegunman said:
si camper, I thought an "inverter" took DC power & made AC power, whereas a "converter" takes AC power & makes DC power? Am I wrong? Dan
Click to expand...

Sorry, wrong term. My bad.  But my reason for believing in may be your converter is that a buddy had a similar problem.  We were camping together one weekend and we thought we noticed the lights on his camper appeared dimmer at times.  I admit we were having a couple of beers around the fire but we were sure of what we had noticed.  His wife inside the camper also stated she thought she had noticed the lights dim occasionally.  We could find no problem with the power source.  Once at home and doing more testing and having the converter rewired, the problem was fixed.
 
grashley said:
Back to your original question.  When the batteries get a bit low, the converter kicks on to charge them.  When this happens, you have 13.4V from the converter also feeding the lights, and they shine brightly.  Once the batteries appear charged, the converter goes off, and the batteries now feed the lights with no help from the converter.  If the batteries are weak or going bad, they will produce only 12. 4 V or less, and quickly be drawn down lower, and lights dim.  When battery voltage hits the set point, converter comes back on and lights brighten.
Click to expand...

I'm sorry, but converters don't work this way unless they are broken.  They may shut down from overheating or another problem, but they do not turn on and off by design.

13.4 volts is the float voltage.  It's high enough to slowly charge the batteries but low enough that it can be left on the batteries indefinitely without causing water loss.  The battery "floats" on this voltage without harm. A single stage converter puts out this voltage continuously.

Some converters have a boost setting that raises the voltage to 14.1 volts or so the batteries charge faster.  They return to 13.5 volts either after a fixed time or when they sense the battery is nearly full. 

When the converter switches from one voltage to the other you may see incandescent lights dim or brighten but this should only happen once each time you plug into power, not on a recurring basis.

You should never see the battery output voltage of 12.6 volts or less when hooked up to power unless your converter has failed.

P.S.  Welcome to The RV Forum, Dan.  Glad you are here!
 
So Lou Schneider, You are saying that I've got a bad converter & not bad battery or should I replace both?  Dan
 
Think of it this way, if Lou is right one problem has most likely lead to the other.  If the converter is bad or failing it needs replaced.  If it needs replaced it most likely is not doing it's job and that means the batteries need replaced. 

How old are the batteries?  Anything over 3-4 years I would be suspect, considering a failing converter.
 
danthegunman said:
So Lou Schneider, You are saying that I've got a bad converter & not bad battery or should I replace both?  Dan
Click to expand...

What is your battery voltage after it sits disconnected for a half hour or so?  If you have more than one battery disconnect them from each other so you can measure their voltages individually.

Each cell contributes about 2 volts to the 12 volt total.  If your battery stays at 12 volts or more when it's disconnected all of it's cells are OK and it's not drawing current from the converter once it's fully charged.  But if the battery drops to 10 volts one cell is shorted and the battery needs to be replaced.

If you have a shorted cell, the battery will continue to draw current after it's charged and this can overheat the converter, making it cycle on and off.

So I'd test the batteries first, then look at the converter.
 
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