RV Daily Tips Issue 374. May 1, 2014 | RV Travel
RVing Tip of the DayDon’t let your solenoids sabotage your batteriesby Greg IllesMany of our midrange motorhomes are equipped with similar circuits in the main 12V supply line. This is true of a broad range of both Ford- and Chevy-based chassis. Note that some coaches have been equipped with solid-state types of circuits instead of solenoids, and this discussion does not apply. The solenoid design philosophy is cheap and simple and has prevailed for many years:• The coach 12V supply is provided via a solenoid disconnect; this allows full isolation of the coach batteries for storage or maintenance.• The chassis-starting battery can be shorted by a solenoid connect to the coach battery bank, for the purpose of engine-alternator charging or emergency starting power.A simplified circuit for all this is shown in the diagram. It all works wonderfully well for the most part. When your engine is running, the chassis solenoid is activated, and the engine alternator charges both battery banks. When you’re plugged into shore power or generator power and coach batteries are not disconnected, the coach inverter charges the coach batteries. Note that any coach battery charge current must always go through one of those solenoids.Where things start to unravel is if either of the solenoids starts to get corrosion or oxidation. In just the last few years of part-time RV camping, I’ve seen this on four different motorhomes one rental, two privately owned and my own. Most common is the chassis solenoid which is usually unenergized becoming oxidized and creating a resistive path for the charging current. Less common, but still problematic, is when the coach solenoid which is usually energized does the same thing.The telltale sign is when you’re trying to charge your batteries, either with the inverter or the alternator, and they do not get the full-charging voltage. This becomes more pronounced at higher levels of discharge state and the attendant high-charging currents. It is because the resistance of the failing solenoid drops the voltage. As this begins to happen, the batteries will take longer and longer to charge up because they’re not receiving full-charge voltage. When it gets to severe levels, the batteries will hardly be charged at all as happened with my coach.The best way to watch out for this problem is to simply have a good voltmeter permanently installed on your coach battery bank, mounted where you can easily monitor the reading. Under moderately discharged conditions, you can expect your inverter to be putting out 13.9-14.4V when it is charging the battery bank. The engine alternator will always put out 14.4V. If you’re familiar with a voltmeter, you can measure the difference between the charging source inverter or alternator and destination battery.If you see fewer charging volts at your battery when you should see more, and your charging sources are good, it’s time to start suspecting those solenoids or possibly the wiring and connections associated with them. Take proactive action before your batteries sag into uselessness. This is one of those cases where an ounce of prevention is definitely worth a pound of cure.
And just an added thing about those solenoids they have been around for even and are used in many types of applications and do fail pretty regularly so don’t be surprised when they go!!
Posted on May 1, 2014, in The world as i see it as a camper and who loves his country and tagged 12 volts, batteries, camping, outdoors, rv electrics, rv tips, rving, rvtravel tips. Bookmark the permalink. Leave a comment.