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 Series Wiring

This is my 4th post in a series about RV electrical set-ups. Although the information is is fairly basic it will help if you read the entire series.

Post #1 Deep cycle batteries

Post #2 Ratings and sizes

Post #3 Parallel wiring

In my previous post I talked about the most common way RV batteries are wired when there are multiple batteries being used for electrical power in your RV. In this post I will describe series wiring. To wire two batteries in a series you connect the negative lead to the positive lead of the second battery. The open posts of each battery are connected to the load. Keep in mind each battery increases the voltage. In the example below two 6 volt batteries connected in a series create a 12 volt output.

Likewise if two 12 volt batteries were wired together in a series you would have a 24 volt output. Most autos, motor-homes, and travel trailers operate with 12 volts.

So why would you use two 6 volt batteries wired in a series to run a 12 volt system? I’ve heard competing opinions on this topic. There is one school of thought that says 6 volt golf cart batteries have higher reserve capacity and are constructed better for deep cycle discharges than a 12 volt deep cycle battery. There is another school of thought that says today’s 12 volt deep cycle batteries are constructed just as well as golf cart batteries.

What set-up do you use?

Batteries Parallel Wiring

This is my third post in a series about RV electrical set-ups. Although the information is fairly basic it will help if you read the entire series.
Post #1 Deep cycle batteries
Post #2 Ratings and sizes

Batteries Parallel Wiring

There are two ways that batteries are typically wired, when there are multiple batteries being used for electrical power in your RV, that is either parallel or in a series. Parallel wiring is the most common. In this post I will describe parallel wiring. Parallel wiring does not increase the voltage, so when two 12 volt batteries are wired in this way it remains a 12 volt system. here is an example:

the effects can be seen when jump starting a car. The battery in the dead car remains 12-volts, and will still turn the starter, but only very slowly. Parallel wire a charged up 12-volt battery to the weak battery, and the dead car turns the starter at the required speed and the car starts immediately. Parallel wiring the charged battery to the weak battery did not alter the voltage – it remained a 12-volt system. The car’s system is 12-volt, and running greater voltages through that system would be destructive to it. To avoid increasing the voltage and damaging the vehicle, the batteries are simply parallel wired.

Two 12 volt batteries wired in parallel means that the positive post of each battery is connected to each other, and the negative posts are also connected together. Connecting the lead of the positive side of one battery to the load, and the lead of the other battery’s negative side to the load is the best practice. In parallel the voltage remains the same, but the amount of current available increases. Batteries connected in parallel should be the same brand, type, size, and age. Otherwise long-term capacity could be reduced. It is possible to connect more than two batteries together in parallel, but space is a major hindrance in a RV setting.

It is recommended that if you are going to wire more than two batteries together in a parallel system that they share a common positive connection, and a common negative connection. This will best allow each battery to be charged correctly. Again using the same brand, type, size, and age are important factors for the life of the batteries.

How many batteries do you use in your set-up (motor home, or travel trailer)? How long are you off the grid usually?

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”

Batteries Deep Cycle

I was talking with a friend about his RV set-up that allows him to go hunting and stay off the grid for weeks at a time. I thought this info might be helpful to RV’ers of all kinds so I’m going to do a series on batteries, which will lead into solar set-ups too. Just so you know I’ll be using references from the “RV Repair & Maintenance Manual” by Bob Livingston Trailer life books 1998.

The electrical system in your RV runs on two types of current; AC (alternating current) the same as your house, and DC (direct current) the same as your car. The stronger your DC system, the longer you can remain off the grid. The terms you need to understand are amps, watts, and volts. Most RV’s run on a 12 volt system, but did you know 2 – 6 volt batteries wired in a series will run your lights and appliances longer than 1 – 12 volt battery? Before you go and replace your batteries lets look at some basic information in this post, and the pros and cons along with the requirements of each set-up in posts to follow.

Batteries are not created equal

• A car’s battery is designed to provide a very large amount of current for a short period of time. This surge of current is needed to turn the engine over during starting. Once the engine starts, the alternator provides all the power that the car needs, so a car battery may go through its entire life without ever being drained more than 20 percent of its total capacity.

• A deep cycle battery is designed to provide a steady amount of current over a long period of time. A deep cycle battery is also designed to be deeply discharged over and over again, something that would ruin a car battery very quickly. To accomplish this, a deep cycle battery uses fewer, but thicker lead plates often coated with antimony or calcium, which increases the hardness of the plate.

Deep cycle batteries tend to cost more than the average car battery, but buying a regular car battery for your RV will only save you a few dollars on the short run. It will wear out quicker making it necessary to replace sooner.