Lights flicker when furnace is on - Fiberglass RV


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Old 04-27-2011, 04:47 PM   #1
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Lights flicker when furnace is on

Was out camping last weekend and noticed my interior lights dim and brighten rapidly whenever the furnace was running. Has anyone else experienced this? Not sure if it's a bad connection issue, or if the furnace blower is causing the flicker.
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Old 04-27-2011, 06:32 PM   #2
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Does the same thing happen when you run the water pump?

Norm
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Old 04-28-2011, 02:26 AM   #3
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Does the same thing happen when you run the water pump?

Norm
The lights dim substantially whenever the water pump is on and cycles, which I attribute to the higher current draw. But the furnace blower, an Atwood 8012, draws little current.
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Old 04-28-2011, 09:46 AM   #4
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How is your battery voltage reading, at rest, with nothing on or running? If your battery is old, it may not be carrying a full charge anymore. If the battery is ok, then I would suspect undersized wiring, or corroded/dirty terminals/connections. Worth checking anyway, as these are "no-cost" things. Let us know what you can find out.
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Old 04-28-2011, 11:14 AM   #5
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Greg is right on.

Check all connections starting with the battery connections, then ground connections, then the rest of the connections.

Here's another thought: I had a Miata with an older battery in it and it would do the same sort of thing then one day it (Exploded). It appeared there was an intermittent problem inside the battery and when the gas built up inside the battery, it sparked and Boom, all over the trunk where the battery was connected.

I could have avoided this by doing a LOAD test on the battery. A load test might have reveled a problem. It may be possible to get the battery load tested by taking it to Advance Auto (For Free).
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Old 04-28-2011, 12:38 PM   #6
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I suspect it's the connections more than the battery, which is relatively new. All the wiring connections are made with crimp connectors or scotch locks, which seem to corrode over time or vibrate loose. I'll probably go in and do some jiggling of the connections, and solder every connection I can get at. My brakes went out on a 7000 mile Alaska trip, which I temporarily repaired it by adding another scotch-lock. When I got home I cut off every crimp / scotch lock, and soldered every connection for the brakes.
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Old 04-28-2011, 12:41 PM   #7
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Also what gauge wire runs from your batteries to the power supply? Mine looks to be 14GA.
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Old 04-28-2011, 12:48 PM   #8
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On our Scamp, the battery had a wire to the frame as did the converter, brakes and other DC items.

Once in a house that we lived in, the deck lite would go off and I found that the AC wire in the Pannel had never been tightened down so when it got hot, it moved and the lite went off and after it cooled, it went back on.
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Old 04-28-2011, 03:02 PM   #9
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On our Scamp, the battery had a wire to the frame as did the converter, brakes and other DC items.

Once in a house that we lived in, the deck lite would go off and I found that the AC wire in the Pannel had never been tightened down so when it got hot, it moved and the lite went off and after it cooled, it went back on.
OK, Your Scamp was altered by somebody then. Mine only has one connection to the frame, it's where the 120V comes in and it's the green "safety ground" as required by the National Electric Code. That's it, nothing else is connected to the frame.
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Old 04-28-2011, 05:30 PM   #10
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Unplug the shore power then take the ground lead from the battery and then do an ohm check from the ground lead to the frame, is there connectivity?

Mine was wired this way at the factory. It also used the frame as the return for the electric brakes.
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Old 04-30-2011, 09:19 AM   #11
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Neither AC nor DC wiring should be using the frame for a return path for any branch circuits. Yes, it will "work" after a fashion, in so much that it will conduct electricity, but it is a "lazy man's way" of doing things, can be potentially dangerous, and is totally wrong from a circuit design standpoint. It will only lead to electrical problems down the road, such as backfeed on other circuits, "ghost power vampires" that can drain your battery when you think everything is turned off, electolytic component corrosion, increased radio interference (static), etc. In short, a whole panoply of self-inflicted bugaboos can arise from this style of circuit design. All DC wiring circuits should be TWO wire, and ALL ground wires should come together (terminate) on ONE common ground bus bar or ground strip. This ground bus is then connected to the frame AT ONLY ONE POINT! This is also the same connection point used for any trailer bonding wire. Multiple circuit grounds made to the frame are a big no no, but it is more common than not. Many "home electricians" do not understand the relationship between a "grounding system" and a "bonding system". Although they both (ideally) terminate at ONE COMMON POINT on the chassis (frame), they are NOT INTERCHANGEABLE in their use or function. In summary, NEVER use the trailer frame as a return leg in any circuit.

Bonding systems are meant to provide a low-resistance path to ground for any heavy overcurrent loads, such as a lightning strike or a direct short in any bonded system component's casing or enclosure to prevent electrocution. Using the frame as a return path is not what a bonding system is designed to do.

Your AC wiring should be grounded to the frame at the same ground point as your DC wiring and your frame/electrical component bonding connection. Again, this should be the same point as your DC and bonding grounds (1 ground point only).
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Old 05-01-2011, 05:24 AM   #12
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ThomasE, my guess is you are seeing battery loading, a reduction in battery voltage due to higher current demand. Any increase in circuit current will cause a drop in battery voltage. Put a voltmeter on the battery and take note of the voltage as various things are turned on and off. Loading effect is more pronounced with an aging battery. Bad connections tend to draw less current not more so I don't see how a bad connection anywhere other than the light circuit itself causing the lights to dim. Please let us know what you find, Raz
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Old 05-01-2011, 09:41 AM   #13
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ThomasE, my guess is you are seeing battery loading, a reduction in battery voltage due to higher current demand. Any increase in circuit current will cause a drop in battery voltage. Put a voltmeter on the battery and take note of the voltage as various things are turned on and off. Loading effect is more pronounced with an aging battery. Bad connections tend to draw less current not more so I don't see how a bad connection anywhere other than the light circuit itself causing the lights to dim. Please let us know what you find, Raz
Let me see if I can explain how this works. A bad connection reduces the amount of current that can flow. This creates a voltage drop across the bad connection. When the something like the fan in furnace comes on it draws what is called "in rush" current which is higher than running current. That higher current through a defective connection causes a voltage drop across the defective connection which reduces the voltage available to very thing beyond the connection.
If the fuse or other connection at or near the battery are defective the lights will dim every time the furnace comes on. If the connection is bad enough the light will dim and the furnace will not come on.


One of the concerns of a defective connection is that they can heat up. In extreme cases a defective connection can actually cause a fire.
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Old 05-01-2011, 11:54 AM   #14
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Let me see if I can explain how this works. A bad connection reduces the amount of current that can flow. This creates a voltage drop across the bad connection. When the something like the fan in furnace comes on it draws what is called "in rush" current which is higher than running current. That higher current through a defective connection causes a voltage drop across the defective connection which reduces the voltage available to very thing beyond the connection. If the fuse or other connection at or near the battery are defective the lights will dim every time the furnace comes on. If the connection is bad enough the light will dim and the furnace will not come on. One of the concerns of a defective connection is that they can heat up. In extreme cases a defective connection can actually cause a fire.
My assumption is that the lights and the furnace are separate independent circuits although I suppose they could share a common return wire. If they are independent parallel circuits then the only way the lights can be effected is if the supply voltage drops. While I agree a bad connection in the furnace circuit will could cause a voltage divider between the connection and the furnace motor (there's your Kirchhoff's voltage law), it's not going to cause loading of the source as it will reduce the current not increase it.

The place where a bad connection would be an issue is between the battery and the distribution panel as that is common to both circuits. I'd start with a voltmeter at the battery. Raz
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