Fan-like noise from fuse box on shore power

[LRL]

Today when I connected to shore power and opened the electrical system bypass switch (so that the battery is NOT being bypassed), I noticed a fan-like noise coming from the fuse box. I note there are vent holes below the fuse panel, and I can feel a bit of cool air coming through these, so I presume it's a fan? The owners manual mentions nothing about this, however, and I've never heard this noise before (with or without my hearing aids!). It has been going continuously for the past two hours.



The battery was low (11.9 V), so is being charged. Electrical system appears to be working perfectly well.



When I close the bypass switch (to bypass batteries) while still connected to shore power, the fan noise stops.


Appreciate any insight as to what is going on.

[Mark B1]

I think that is happening when you are converting the AC to DC which likely creates heat so the fan runs. The fan should cut out when the battery is charged. I also think that while plugged into AC, if you switch your fridge to DC or have other high DC loads which results in results in the converter working the fan will again be running to dissipate heat.

[Eggscape]

All working normal…the charging system was working hard to top up your battery which makes the fan come on to keep it cool.

[LRL]

Originally Posted by Eggscape

All working normal…the charging system was working hard to top up your battery which makes the fan come on to keep it cool.

Thank you! I was hoping that would be the answer, but as I said, had never heard the noise before and was concerned that I’d done something wrong.

[Eggscape]

Originally Posted by LRL

Thank you! I was hoping that would be the answer, but as I said, had never heard the noise before and was concerned that I’d done something wrong.

Almost…keep in mind that you should not run your standard lead-acid battery below 12 volts if you want it to last for many years.

[LRL]

Originally Posted by Eggscape

Almost…keep in mind that you should not run your standard lead-acid battery below 12 volts if you want it to last for many years.

Yeah, I know that. They're AGM's but your point is well taken. Trailer is parked at home under a roof, so solar does not good. Generally the battery holds really well, so I was surprised and chagrined to see it so low!