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Remember the 1984 original release of the movie “Gremlins”? If not, according to Wikipedia:

“The term “gremlin”, denoting a mischievous creature that sabotages aircraft, originates in Royal Air Force (RAF) slang among the British pilots stationed in Malta, the Middle East, and India in the 1920s.”

I like to use the term “gremlin” to describe an intermittent incident, failure, or event that is difficult to explain.

There are several areas gremlins hide in an RV, the 12-volt electrical system, appliances, 120-volt electrical system, and even in roofs. And how about those annoying refrigerators that won’t cool efficiently only to hit 34 degrees sitting in the service bay! We’ve all experienced some type of gremlin in our RVs and it can be not only frustrating, but expensive. For this blog, we are going to focus on the gremlins that can plague our 12-volt electrical systems.

12-volt DC Deep Cycle Lead Acid Batteries

Lead acid batteries have been a frustration for years for RV owners and typically last about 2 years, however they should last 5-6 years. The deep cycle batteries in your house system are designed to be drained down to approximately 50% of their amp hour or power storage capacity and recharged either by a converter, inverter, or solar panels many times, or “cycles”. They are measured in amp hours which means the approximate amount of time they can provide power to 12-volt systems such as the lights, roof vents, water pump, and any appliance running on LP. Lead acid batteries can only be drawn down about 50% of their capacity so a Group 27 battery with 100 amp hours can only provide about 50 amp hours.

Lead acid batteries are simply storage devices for power and as that power is drawn out of the battery, sulfur attacks the lead plates and coats them. If this coating is not removed during the recharging process, it gets thicker and eventually limits the storage capacity.

Traditional converters that are part of the distribution center simply start the charging state at 13.6 volts and then reduce to 13.2 volts when the battery reaches 12.6 volts. This is the voltage that the battery will no longer accept a charge so it is a maintain state. 

This is a typical distribution center with the circuit breakers for 120-volt applications and the converter behind the grill at the right. This type of charge will not break up the sulfation and will limit the batteries chemical to electrical conversion. Sulfation can also occur when a battery is stored without a full charge during the winter as all batteries will experience a slight drain if not connected to a charging or maintenance system.

To properly charge a lead acid battery, your system needs a multistage charger that starts with a bulk or de-sulfation stage which is a high voltage charge that literally boils the acid and breaks up the sulfur. This also causes excess gassing and acid depletion. This means more maintenance is required on each cell. Chargers like the Progressive Dynamics models with Charge Wizard, inverters with chargers, and solar panels with charge controllers all have the multi-stage chargers that will properly charge and maintain a lead acid battery.

You can get more information on the Progressive Dynamics products here: www.progressivedyn.com/rv/charge-wizard

The gremlin in this case is in the actual condition of the lead acid battery. If the battery is sulfated, it can be charged to 12.6 volts which is a fully charged lead acid battery, however it will drop fast and not provide the amp hours it was originally designed for. And it can not be accurately tested by local auto shop and service center equipment. According to my sources at Lifeline Battery, Trojan, and US Battery, the only way to truly test a batteries condition is to properly charge the battery and place it on a 25 amp load machine and verify how many hours it provides power which almost never happens! And I get this all the time, “I had the batteries checked by a technician and they are fine”, “The batteries are 12.6 volts so I know it’s not the battery”, “The batteries are only 6 months old and register 12.6 Volts so I know they are good”.

If an appliance such as the refrigerator or air conditioner has intermittent performance, the first gremlin I look for is 12-volt power. Yes, even though both of these run on 120-volt AC power, they require 12-volt DC power to run the control module, thermostat, and other components. If your batteries are sulfated, they can draw down fast and limit the DC supply to those components before the converter kicks in and starts to charge. The first thing I recommend when there is intermittent functions is to connect a portable charger to the house batteries to see if that eliminates the situation. Then you know it’s not the batteries and can dig deeper into the system.

I get many questions from readers that the system did not work while out camping only to bring it to a dealership and it works fine! What typically happens in this situation is while you are camping, there are several variables that affect the operation such as higher ambient temperatures that would make the roof air conditioner and refrigerator run more often drawing more power and sometimes at the same time. Other components will be used such as the interior lights, water pump, water heater, all of which come on at times you are not aware of and draw power. Then you take it to the dealer and they plug it into a good 30 amp service with nothing else on and the appliance works great. Next time you take it out, it doesn’t work again! One reader indicated they had an issue with a furnace and the service center actually pulled the unit out and bench tested it three times and it worked every time! This tells me that the unit is working fine and there is an issue with air flow restriction, temperature, or the house battery since the furnace was isolated on the bench?

That is why it is important to test in real world situations and always document everything being used.

About the author: Dave Solberg: Managing Editor, RV Repair Club

For the last 25 years, Dave has conducted RV maintenance and safety seminars, developed dealer and owner training programs, written RV safety and handyman articles, authored an RV handbook reference guide and logged over 100,000 miles on the road in an RV.

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