Dimming lights

[Alan Wilson]

Have a 2001 38' Holiday Rambler Scepter that is mostly stock. We recently purchased the motorhome and having never owned a Class A we don't know what is normal and what is not. The lights would dim when the furnace came on but the furnace motor soon showed signs of a bad bearing. The dealer replaced the motor. We are now in Texas enjoying the 'Polar Vortex' and again running our furnace. The lights still dim when the furnace comes on. We are hooked up to 50 amp shore power with fairly new batteries so I am a surprised the lights still dim momentarily. Is this normal? If it isn't, what could be the problem? I would think with new batteries installed just before I purchased the motorhome the terminals would not need cleaned again already. Looking for some people with experience.

Thanks,

Alan

[wildmandmc]

power surge, what else is plugged in using current,

[Alan Wilson]

Originally Posted by wildmandmc

power surge, what else is plugged in using current,

The lights only dim when the furnace comes on so I am not inclined to believe it is a power surge or they would be getting brighter at some arbitrary time. I am trying to figure out if the furnace motor really pulls enough power to dim the single light or lights that are on when the furnace comes on and if that is normal.

Alan

[wildmandmc]

sorry my mis use of term, what i actually meant is, possible the furnace motor pulling more power, im not too sure, but my guess probably normal. as in a auto if u have lights on then turn key, lights will dim a sec or so as u start it.

[94-Newmar]

You will need a voltmeter. You will need to check voltage at those light(s) when the furnace fan is both stopped and running. Please post your voltage findings. I suspect you will find a substantial voltage drop. Now check the voltage at other lights that aren't dimming or being affected when the furnace is running. Do you see the same voltage drop? If so then I would remove the house battery terminals - clean them well with a wire brush including any grounds that you can easily get to. If no other lights are affected then it's entirely possible that someone previously has wired that particular string of 12v lights to the furnace 12v circuit. Since you are not the previous owner it's difficult to figure out what previous owners have done in the past.

[Alan Wilson]

Originally Posted by 94-Newmar

You will need a voltmeter. You will need to check voltage at those light(s) when the furnace fan is both stopped and running. Please post your voltage findings. I suspect you will find a substantial voltage drop. Now check the voltage at other lights that aren't dimming or being affected when the furnace is running. Do you see the same voltage drop? If so then I would remove the house battery terminals - clean them well with a wire brush including any grounds that you can easily get to. If no other lights are affected then it's entirely possible that someone previously has wired that particular string of 12v lights to the furnace 12v circuit. Since you are not the previous owner it's difficult to figure out what previous owners have done in the past.

Let me clarify that all lights dim no matter if it is one or many so I would expect the voltage to be the same on all of them. You also mention the battery terminals which was my first thought but the dealer put in new Interstate batteries so I made the assumption they would have cleaned the terminals so I dismissed that as the source of the problem. I take it that the lights dimming is NOT normal. Is that correct?

Alan

[Alan Wilson]

Originally Posted by wildmandmc

sorry my mis use of term, what i actually meant is, possible the furnace motor pulling more power, im not too sure, but my guess probably normal. as in a auto if u have lights on then turn key, lights will dim a sec or so as u start it.

I have no idea how much power the furnace motor should draw. So the lights dimming when the furnace comes on is not normal?

Alan

[94-Newmar]

Yes that is correct. A brief flash or dimming while the fan motor first turns on, then returning to normal brightness is not abnormal - lights staying substantially dimmed while it's running is not normal. I still would like to know your voltages on the 12vdc side of things while plugged into shore power, both with the furnace running and not running. It is very possible your converter is the problem, but voltage readings will determine that.

[Pepper2]

The cables to the batteries may have been cleaned. How about the ground to the chassis?

[Alan Wilson]

Originally Posted by 94-Newmar

Yes that is correct. A brief flash or dimming while the fan motor first turns on, then returning to normal brightness is not abnormal - lights staying substantially dimmed while it's running is not normal. I still would like to know your voltages on the 12vdc side of things while plugged into shore power, both with the furnace running and not running. It is very possible your converter is the problem, but voltage readings will determine that.

I will check the voltage later when I get a little time. Exactly where do I take the reading?

Alan

[Alan Wilson]

Originally Posted by Pepper2

The cables to the batteries may have been cleaned. How about the ground to the chassis?

You may have something there. The terminals appear clean on the outside but of course that has nothing to do with what is at the terminal. I seriously doubt the ground has been cleaned. I am going to check the voltage drop when I find out where to check and it is daylight.

Alan

[94-Newmar]

You can take the reading from any 12v source for now. Once we see the voltages there I suggest you pull a voltage reading right from the converter itself. This will determine how much further in depth you need to go. As suggested, it could possibly be a bad ground, but rather than go thru all that hassle right now we can determine whether or not the converter is failing - if it's not then it's time to break apart grounds and clean them all.

[Brockx]

The furnace is a 12 volt system??
Learned something there / today. I have only used mine a couple of times, thought it was 120 volt, shore or Gen powered.

[Alan Wilson]

Originally Posted by 94-Newmar

You can take the reading from any 12v source for now. Once we see the voltages there I suggest you pull a voltage reading right from the converter itself. This will determine how much further in depth you need to go. As suggested, it could possibly be a bad ground, but rather than go thru all that hassle right now we can determine whether or not the converter is failing - if it's not then it's time to break apart grounds and clean them all.

My converter is not on as far as I can see unless it comes on to charge the batteries. I don't know.

Alan