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panther3505's avatar
panther3505
Explorer
May 05, 2015

Batteyr charging in an RV

Here's my rant for the day.

I have heard so much outright misinformation, misnomers, and just flat out uninformed individuals passing off their opinions as gospel regarding maintaining their batteries in their RV's. Hear are some cold hard facts from an electrical engineer.

1. RV’s do not have battery chargers; they have converters, which are nothing more than power supplies.

2. An RV converter does not know what a battery is. The batteries; when installed in an RV’s electrical system are in parallel with the electrical system and, therefore, are nothing more than an additional load on the system.


3. Regardless of current marketing ploys or manufacturer claims, no converter manufactured today by anyone can charge a battery separately from the 12v system, again the battery is in parallel.

4. There are no components in a converter that isolate the charging function separate to supplying voltage and current to the entire 12v system.


5. Current converter “multi-stage” technology offers no real benefit over a single stage converter. When viewing the charge curve of a single-stage versus a multi-stage converter, the charging is nearly identical. The only thing that stands out is the fixed points in which the output voltages drop, however, time and current are constant regardless of single or multi-stage. Even with more popular 4 stage converters on the market, the misnomers that abound in the RV world are frightening. According to major battery manufacturers, the voltages that are required to desulfate or equalize a battery need to be a minimum of 15.4VDC. Due to the limitations of an RV’s electrical system that is 13-14.4vdc, the voltages required to desulfate a battery would be detrimental the sensitive low voltage systems now inside modern RV’s.

47 Replies

  • panther3505 wrote:
    5. Current converter “multi-stage” technology offers no real benefit over a single stage converter. When viewing the charge curve of a single-stage versus a multi-stage converter, the charging is nearly identical. The only thing that stands out is the fixed points in which the output voltages drop, however, time and current are constant regardless of single or multi-stage. Even with more popular 4 stage converters on the market, the misnomers that abound in the RV world are frightening. According to major battery manufacturers, the voltages that are required to desulfate or equalize a battery need to be a minimum of 15.4VDC. Due to the limitations of an RV’s electrical system that is 13-14.4vdc, the voltages required to desulfate a battery would be detrimental the sensitive low voltage systems now inside modern RV’s.
    So if I have a 70% depleted battery and a 90 minute window to run my generator you are saying a fixed voltage of 13.6 volts is the same as a multistage charging at 14.4 volts?

    This graph must be flat out wrong?



    http://www.progressivedyn.com/charge_wizard.html
  • Your wrong of course - and I'm a retired EE as well. But that degree certainly doesn't make one an expert on RV converters.
    If one has a modern 3 stage converter, it charges the battery(s) just fine. It makes no difference that there are more than one or that a few accessories are on the same circuit. This is in part because the battery takes what it needs.
    The proof is in the fact that these converter/chargers are working just fine for hundreds of thousands of RV's. If you want to get more technical, further proof is in the measurement of said batterys specific gravity.
  • Uh partner, me hates to tell you this but an electrical engineering degree is a mere single component needed to make an individual an authority on batteries. A chemical engineering degrer is also mandatory then the two disciplines have to be melded with oh, say, several decades of practical experience actually working with genuine live batteries. It also helps to have some decades of experience working around yachts, RVs and alternative energy.

    An ability to shovel coal does not make one a locomotive engineer.
  • RoyB's avatar
    RoyB
    Explorer III
    I think he got up on the wrong side of the bed and fell out of his 5th wheel window...

    Must be a Sears and Roebuck engineer or maybe a Georgia Tech.. We was working with one of them ther types and he would always say them ther electrons would jump the open relay contacts and do you sum harm...
  • LOL!

    **The basic RV charging system is called a Converter-Charger. Its primary function is to convert 120v shore power to 12V DC power so that your battery does not need to provide DC while you are plugged in. Its SECONDARY FUNCTION is to charge the battery(s) when and if it has excess capacity. It is rated in Amps, e.g. it can produce ~55 amps of DC (for example), which will supply the RVs lighting and appliance circuit boards with power and probably have enough to do some charging as well. **

    Totally copied and pasted that. I have sen some rather expensive converters that claim they are true chargers, but it always goes back to the power out is SHARED with the power the camper uses.

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