Greetings,

The Battery System is one of the most important sub-systems in your RV.  Virtually every device in the RV uses the Battery System for its power.  Yet, most RVers have little or no knowledge of how the Battery does it job in the RV.

Recently, a reader sent this interesting Email. 

“I have a situation that is going on in my RV that I need expert assistance with. I have noticed over that past several months that the lights in camper will periodically go dim and then bright again. It doesn't do this all the time but more than not. Also, since the weather has turned cold I have begun to use my central heat. I noticed the other day that the fan motor would sound like it was losing power but then it would speed up after a few seconds. This would go on 2 or 3 times during the cycle the furnace is on. I installed a new battery about 3 weeks ago thinking that this would solve the dimming lights but that wasn't the case. Now the furnace blower issue has come up over the past 2 weeks.”

Now I am sure that all RVers, at some time or other, have experienced this problem.  It usually becomes more prominent in the Fall and Winter months when we have less daylight and begin to rely on the RV’s lighting system.  Also, as the reader noticed, when the weather cools we come to rely on the RV’s furnace and it’s circulating blower for warmth.  Before moving on, we must realize that the lighting and furnace blower are two significant users of Battery power.

First, the variations in lighting intensity and blower sound that the reader observed does not indicate a serious problem.  The change in light output and the change in sound of the blower are the result of a change in battery voltage.  The light output increases and the blower fan speeds up at the point when the Power Converter begins the battery charging process.  This difference will be explained.  So read on….

Let’s look at some of the causes and possible solutions of the Reader’s problems.

• Battery Voltage is strongly influenced by temperature changes.  In other words, hot batteries have lower voltages than do cold batteries.  This change, which can be in the range of 1.0 volt, is due to the basic chemistry of the battery and has nothing to do with the RV.
•  The RV’s Power Converter charges the battery when the RV is connected to the Campground Power Post.  Generally, the Power Converter’s output voltage is set at a specific level that will allow the Battery to charge while simultaneously providing power for the RV’s lighting and furnace blower.
• There is a narrow range of voltage at which the battery can be safely applied.  Typically, this voltage is between the highest and the lowest expected operating temperature.  Typically, this voltage is between 13.5 to 13.8 volts, but in very cold conditions, the battery voltage may be as high as 14.0 to 14.2 volts.
• Power Converters are set to allow recharge of the RV battery until the battery’s voltage reaches 14.35- 14.4 volts.  This voltage is near the voltage at which the efficiency of the battery charging process becomes critical and begins to decrease quite rapidly.  If the voltage is set at a level higher than 14.4 volts, the battery will begin to “boil off” water from the battery cells.  Continuing this process for long periods will harm the battery.
•  When the battery is cold (i.e – less than 40 degrees F), its terminal voltage will be greater than the desired 13.5 to 13.8 volts.  Thus, when the lights are turned ON in the RV, the lights will slowly drain off the battery voltage (i.e – the battery is being discharged) until the voltage decreases to the 13.2 to 13.5 volt level.  At this point, the Power Converter will kick in and begin to recharge the battery.  When this happens, the lights will regain their brightness and the furnace blower will regain its operating speed.  This process repeats as long as the battery is being used. 
•  This process is similar for a hot battery except that the battery voltage is typically closer to the 13.2 to 13.5 volt range.  Thus, when the lights are turned on, the Power Converter does not have to wait as long before it starts to recharge the battery.  That is why there is no noticeable change in the brightness of the lights.

 While the chemistry of batteries usable in RVs has not seriously changed for many years, the same does not hold true for RV Power Converters.  The Power Converters used in late model RVs generally have excellent regulation characteristics while the Power Converters in older model RVs do not have the same regulation.  The degree of regulation is a key feature of modern Power Converters.  More information on Power Converters can be found at www.progressivedyn.com.    

A final word regarding battery performance and selection. 

• Battery performance depends upon the size/rating, age, temperature, and battery construction.  Always select a deep cycle battery when replacing the battery in your RV.  Deep-cycle batteries usually are more expensive than automotive types, but are well worth the additional cost.
• Never use a battery rated for automotive use for your RV as they will soon fail.
• At least once a year, and more frequently if you have your RV connected to a Park Power Post continually, shut off the power to the battery and remove it from its location on the RV.  Make sure that it is clean (use a mild soap and water solution) and check the liquid level in each of the cells.  If you have problems performing these tasks, take the battery to a competent automotive service station.  

If you are experiencing an electrical problem with your RV, please send me a message.  I’ll get back to you with an answer.  For more information on low voltage problems, click on www.dynamorv.com or send an Email to info@dynamorv.com.

Respectfully,

Tech Support