RV FEATURE
VOLTAGE ≈ CHARGE STATE |
> 12.6 |
100 |
12.5 |
90 |
12.4 |
80 |
12.3 |
70 |
12.2 |
60 |
12.1 |
50 |
11.9 |
40 |
11.8 |
30 |
11.6 |
20 |
11.3 |
10 |
10.5 |
0 |
State of charge indicator chart for lead acid batteries .
THE SOLAR REVOLUTION
The problem of needing to recharge our batteries while we were camping off-grid was largely solved by the development and increased affordability of solar panels .
You could easily have one or two solar panels installed on the roof of your van or motorhome . Camper trailer owners and 4WDers could purchase portable solutions like solar blankets or folding solar panels to achieve the same result . It was all very exciting .
This constant charging and discharging of our batteries , however , meant that monitoring voltage was not going to be an effective way of determining their SOC . This is where shunts came into play .
Note that these voltages are approximate and are influenced by temperature , etc . Batteries just taken off charge will have a significantly higher voltage until the ‘ surface ’ charge decays over 30 minutes or so .
Repeated discharge to these levels will shorten battery life
Permanent damage will occur
WHAT IS A SHUNT ?
In simple terms , a shunt is a device that connects to the negative terminal of a battery , allowing you to measure the current going in and out . This is measured in amps , which is convenient given batteries are rated in amp hours . You could tell in an instant that if you were drawing 10A from your batteries , a 200Ah battery bank would last approximately 20 hours before going completely flat . You still could measure voltage and also use that to estimate your battery ’ s state of charge .
The problem with using a shunt is not the system itself , but the limitations of lead-acid battery technology and the complications they create for travellers . As I mentioned earlier , lead-acid batteries ’ voltage drops as their SOC decreases . This affects the operation of the appliances connected to them , particularly those that draw a lot of amps .
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