Furnace fan surges causing LED lights to flicker.

Fast Lane

New Member
Joined
Nov 2, 2024
Messages
4
Location
Sonora
LED lights flicker and dim when furnace fan engages. Furnace fan surges too drawing power from lights.

I noticed this last season a few times but this year it's constant. Also, when the converter fan goes on for about 5 seconds every 1-2 minutes it makes lights flicker too.

Refrigerator and microwave have no effect of lights.

On shore power. Battery connect is on. Batteries read 10v when furnace fan is on, 12v when it goes off.
 
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Well, the fan is drawing too much current. Could be from failing bearings or poor connections so the fan motor is not getting the full voltage it needs to run properly.... could also be a faulty motor but less probability imo.
 
Well, the fan is drawing too much current. Could be from failing bearings or poor connections so the fan motor is not getting the full voltage it needs to run properly.... could also be a faulty motor but less probability imo.
Fan spins freely no noise or binding. could be worn out I guess. I was thinking connections too but couldn't find a problem. Then I noticed the lights flickering when converter fan goes on briefly. Checked fuses on converter and furnace.
 
Well, the fan is drawing too much current. Could be from failing bearings or poor connections so the fan motor is not getting the full voltage it needs to run properly.... could also be a faulty motor but less probability imo.
I just turned the breaker to the converter off and the lights dimmed quite a bit but the flickering stopped.
 
While there are a number of other possibilities, the first one, with many times the probability, is the battery is bad. Try a different, fully charged one to see if the issue continues. You may be able to even swap in one from one of your vehicles temporarily. Or use jumper cables. If the problem does not happen then - you have the guilty party.
While the converter does supply 12v to the trailer, it is not high amps, and depends on the battery as an assist for higher draw periods. While less usual of an issue when on shore power, not unknown. Usually the first symptom is when the water pump goes on, the lights flicker, when not on shore power.
 
While there are a number of other possibilities, the first one, with many times the probability, is the battery is bad. Try a different, fully charged one to see if the issue continues. You may be able to even swap in one from one of your vehicles temporarily. Or use jumper cables. If the problem does not happen then - you have the guilty party.
While the converter does supply 12v to the trailer, it is not high amps, and depends on the battery as an assist for higher draw periods. While less usual of an issue when on shore power, not unknown. Usually the first symptom is when the water pump goes on, the lights flicker, when not on shore power.
Thanks for you input:

I have 5 batteries.
they now read 13.6v but slowly drop to 11.9v with furnace on.
 
You may want to get out the meter and check the amp draw for the furnace fan. Google says 5-7 in general, but you really need to check with the manufacturer of the furnace, as they can be much better or worse. The converter fan itself is a really small load - but it is running because the converter is getting warm due to working hard, hence too hard to supply the lights fully also. Perhaps trying to charge a weak battery, and can't do both that and the fan/lights.

You have access to 5 batteries? Or you have 5 batteries in parallel in your rig?

13.6v is way too high- you are measuring the input from the converter as it is trying to charge the batteries. Ideally, after being fully charged, they should be disconnected and rested for 24 hrs. Then your 100% charge reading will be 12.7-12.8. It is fully discharged at 11.9-12 volts (at which the battery is being damaged).
 
LED lights flicker and dim when furnace fan engages. Furnace fan surges too drawing power from lights.

I noticed this last season a few times but this year it's constant. Also, when the converter fan goes on for about 5 seconds every 1-2 minutes it makes lights flicker too.

Refrigerator and microwave have no effect of lights.

On shore power. Battery connect is on. Batteries read 10v when furnace fan is on, 12v when it goes off.
Are you on shore power when this happens?
 
You may a 1 of the 5 batteries with a short in it. You need to load test all the batteries with them disconnected and fully charged.
 
Google 'Voltage Drop Test'.

Once you know what the test results are, you can make a decision on what the possibilities are. Stop guessing. Build a good foundation with testing to determine what the problem really is.

Or you can load the parts cannon like most people. Sometimes it works.

Assuming the batteries are good, I would assume your connections are not, somewhere in the circuit.

We all know what assuming does, but remember, we are talking about RV's on this forum so it's safe to say, nothing was right when it left the factory.
 
While I agree with the high loads like jacks and slides...a furnace fan in good working order is not a high load
By itself it shouldn't be. But if he is running a few other 12v items (sound system, 12v fridge, something off an inverter, etc.) it may be enough to exceed what the converter alone can supply. Hence checking the amp draw of the fan itself against mfg spec.

@Fast Lane - tell us what model you have, and more about those 5 batteries.
 
FYI measuring voltages with a load is nearly useless. It's also fairly useless on LFP batteries.

A 12VDC amperage meter is a very handy tool.

Most auto parts stores will test a lead acid/AGM battery for you, for free!
 
Any load will drop the down, but how far? For a single load it seems the full voltage should fall across the load. But you almost never have a single load. Also "smart" supplies like converters may increase their output. Worse, inductive loads like motors behave differently. (That's more of an AC issue but weird stuff can happen.)

In short, unless you know the load, the voltage is pointless.
 
For the heck of it,,,, check for a bad capacitor.
The fridge motor might have one somewhere and its bad, so drawing more power to start and or run.
Sometimes its a visual blow, other times it needs to be tested.
 
"they now read 13.6v but slowly drop to 11.9v with furnace on."
What does that tell you?
It tells you something ain't right. Investigate. Excessive load? Bad battery? Bad or corroded connections. Bad converter? It tells you that you need to investigate and find the cause of thee issue.
 

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