fan in circuit-breaker box is cycling every 10 seconds

Question...Are you parked, plugged into shore power and disconnected from the tow rig when you noticed this? If so.. Have you moved the TT since? IF you are parked with shore power make sure you didn't accidently engage the electric brakes. If you moved you obviously could feel the brakes drag but check the pin on the emergency switch. This happened to me. The pin got pulled out slightly, didn't notice until the extra load caused the fan to run to cool the converter. Seems unlikely but something to look for.

In the past n TT’s I found that of the battery is weak or getting weak the converter/charger runs more.

Check the battery voltage, check for excessive battery gassing and heat.

Disconnect the battery and see if the fan issue stops.

Post the results. Also post the breaker panel make and model number.

All the above is on target. Also, not trying to be "uppity" here, but if it has a WFCO brand converter, it could just be giving up on you. My WFCO brand lasted about 7 years, then one night it just sorta freaked out, fan running on and off and the power was visibly going up and down as the lighting fluctuated bright and dim(well...not so bright). My batteries were perfect, the converter just up and croaked. I got a Progressive Dynamice retro-fit to replace it.....easy peasy, if that turns out to be the issue.

As above, unless you have a large 12v draw that is cycling on and off, likely a bad battery or charger issue.

Yep, they normally run on a longer cycle, like for minutes at a time, or stay on if the electrical load is high. You're probably going to have to contact the panel mfgr. to do a troubleshoot. I'm going to make a WAG that its location below the fridge has something to do with it.

The cooling fan runs, when the converter/charger is under heavy load. If it runs on/off continuous, I would check battery condition. May need new battery, or water added to battery. Water way too low, likely need new battery.

The converter itself could be failing, some are better than others. What model do you have?

Are you running any device, that may cause converter to overwork?

Jerry

I don't know if it is normal behavior for your RV or not, but I can tell you what it is. It is the cooling fan for the converter that provides 12v power to power your RV's 12v system, and to recharge the battery bank. Mine runs whenever the converter is under a heavy load, like recharging depleted batteries.