By Chris Dougherty
Chris Dougherty is a certified RV technician. Here is a letter he received from a reader while he was serving as RVtravel.com’s technical editor.
Dear Chris,
I have a 50-amp transfer switch. My question is if the power from the converter/charger goes through the transfer switch? I’m boiling batteries and trying to determine if the converter or transfer switch is bad, or none of the above? —James
Dear James,
I have good news and bad news. The good news is that the transfer switch is not involved. The transfer switch selects incoming AC power from the generator or shore power.
The bad news is this is a normal condition for basic AC/DC converters. Simply put, the purpose of a converter is to take AC power from an external source (electric utility or genset) and convert it down to DC. These will frequently apply 13-14 volts to the system continuously, which can lead to boiling the batteries.
The best fix would be to replace that converter with a smart converter system. There are several on the market, including the Xantrex TrueCharge2, the Iota IQ4, and the Progressive Dynamics Intelli-power system. They range in price depending on the size and options of the unit, but installation is usually pretty straightforward.
In any case, until you resolve the issue, make sure you keep the batteries topped off with distilled water!
##RVT836
Follow up question on 50 Amp transfer switch. I leave my motorhome plugged into 115V shore power at my storage facility to keep the batteries charged. Recently I went to my storage facility and heard the transfer switch “thumping”. It turned out the transfer switch was bad and the thumping I heard was the switch, switching from generator mode to shore power mode. My question, could this problem have caused a fire had I not caught it in time?
Perhaps. What’s the make and model of the transfer switch? I’m getting a lot of emails about them failing.
To James-
If you’re not camping and you’re not a full timer, are you leaving the rig plugged in all the time? If the answer is yes than you’ll boil out the electrolyte and leave the cells dry in just a matter of time. Much depends on the type of charging your converter does and when. If you store your rig between trips you should be able to completely disconnect your batteries and have them fresh enough to work for you when you’re ready to go again. We leave our rig sitting and unplugged for 60 to 70 days between trips and the batteries are always ok. Our rv has a simple single stage charging circuit. Unless you leave your rig stored for months you should be fine with this way of doing things. If you feel compelled to keep your rig plugged in- I’d suggest using a device like the “Battery Minder”. It will keep the batteries safely charged and will also help de sulvate the plates if you get the correct model. In any case, my last resort would be to depend on the on board converter/charger.
I have another question. I just installed 2 6v batteries and I had perfect power going to the trailer. 2 days ago I plugged into shore power to dewinterize my trailer and I guess I messed up and out of habit I turned the battery disconnect switch to on and it was charging the full batteries. Now there is 0 volts in both batteries, nothing. I guess I fried the batteries? They look totally new with no sign of stress. I guess I need new batteries, again?? I don’t have a charge controller to stop charging in my unit I am assuming.
Don’t panic yet. If these batteries have only been flat for two days, you can probably still save them. Get an external charger that includes a battery tender function. Something like this should work or anything with that has 1.5 to 2 amps normal 6/12-volt charging plus a minder function:https://www.amazon.com/BLACK-DECKER-BM3B-Automatic-Maintainer/dp/B0051D3MP6/ref=sr_1_4?ie=UTF8&qid=1526504357&sr=8-4&keywords=battery+charger+tender&dpID=41OD04up5CL&preST=_SY300_QL70_&dpSrc=srch I would disconnect the batteries from each other and charge one 6-volt battery at a time. And watch to make sure the water level stays up. This will take a day or more to charge each battery. But then you can hook them back together and use the float charger function to normalize all the cells over the next few days. Good luck and let us know how this works.