Solar Power (part 1) Battery Bank

My previous series was on understanding batteries and different ways to connect them. This series is a continuation, but moves into solar power set ups.

How do you know how much power you will need to generate and store for your RV needs? All appliances are rated in AC watts or amps. You can use the following formula to determine the DC amp hour draw for a 12 volt DC system:

(AC amps X 10) X 1.1 X hours of operation = DC amp-hours
(AC watts / 12) X 1.1 X hours of operation = DC amp-hours

This formula should be used to calculate the number of amp hours used between recharges for each appliance. Although a deep cycle can be discharged 80% without permanent damage it is best practice to allow for 50% cycling to improve battery longevity.  Do this by calculating the amp hour usage between charging cycles and then use a battery bank twice that capacity.

 

Sample Power Consumption in 12 volt DC Amp hours

Appliance Wattage 15min 30min 1hr 3hrs
light 100   2 4 8 24
blender 300 6 12 . .
coffeemaker 1000 20 40 80 .
Refrigerator 750 . 21 42 126
microwave 1500 30 60 120 360
vacuum 1100 22 44 88 264

How many batteries do you have in your battery bank?

 

 

 

Some of the information contained in this post is from the Bob Livingston RV Repair & Maintenance Manual 1998

Batteries-Ratings & Size

This is part two in my series on batteries. In part one I explored the different types of batteries used for RV’s. In this post I will do an overview of batteries-ratings and size.


Batteries are rated in one of two ways Amp Hours or Reserve Capacity. RC is the most common rating today.

  • Amp Hours (AH) .The amp hour rating is basically, how many amps the battery can deliver for how many hours before the battery is discharged. Amps times hours. 5 Amps X 20 Hours = 100Amp Hours or 20 Amps X 5 Hours = 100 Amp Hours.
  • Reserve Capacity (RC). Reserve Capacity rating is the number of minutes at 80 degrees F that the battery can deliver 25 amps until it drops below 10.5 volts. If you want to figure the amp hour rating you can multiply the RC rating by 60 percent. RC X 60 percent.

RC rating is established by the Battery Council International (BCI). Some manufacturers use a 15 or 22-amp discharge rate rather than 25-amp discharge. The lower discharge level allows a higher number of minutes to be displayed on the battery label which does not reflect the true RC minutes at a 25-amp discharge. According to interstate batteries

 

BATTERY CHART CHEAT SHEET The battery group size number listed for each battery in our chart represents the maximum dimensions of the battery and they are as follows: Maximum LENGTH x WIDTH x HEIGHT

  • Group 24: 10.75” x 6.82” x 9.4”
  • Group 27: 12.1” x 6.82” x 9.25”
  • Group 29: 13.2” x 6.75” x 9.2”
  • Group 30: 13.5” x 6.82” x 9.25”
  • Group 31: 13” x 6.82” x 9.44”
  • Group 34: 10.25” x 6.82” x 7.88”