Tiny House DC system Overview

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In this video, I discuss our off grid capable electrical system as well as how we run our lighting and other electrical gadgets on DC power.

This video is an adjunct to the article Tiny House: Episode Nineteen

I also go into a brief discussion of amps, amp hours, watts and volts. This subject can seem very complicated, and it probably is if you want to know all the minutia, but it is actually quite simple when planning a basic 12v electrical system. For our needs, we ultimately wanted to know how many batteries we would need to run our house if we went off grid.

A single battery, like ours, has 100 amp hours of power. An amp hour is 1 amp of power draw for 1 hour. For example, our furnace uses approximately 3 amps to run the fan which means we could run our furnace fan off of our battery for 33.3 hours. Pretty simple right? Once you figure out which electrical appliances you use on a day-to-day basis, and for how long, you can determine how many amp hours of battery power you need daily.

Sometimes, the electrical device you want to use doesn't list the amps required. Looking at the packaging in the picture below, you can see that this bulb we used is 2.5 watts. So exactly how many amps does that translate into? Time for some math.

12v DC LED bulbs are extremely efficient. This 2.5w bulb is probably equivalent to a 30-40w incandescent bulb.

The formula for amps is watts/volts. Using the bulb above:

2.5W/12V=0.208A

 
In other words, five of these bulbs would be just a hair over 1 amp. You could run five of these bulbs for 100 hours off of one 100AH battery!

Unfortunately, you wouldn't ever want to do that by choice since draining a lead acid battery 100% will cause damage. If you want to get the maximum life out of lead acid battery, the key is to only drain them no more than 30-50%. So being conservative, a 100AH battery has 30AH of useable power on a daily basis. Once you know how many amps you need on a daily basis then you can divide that number to get the number of batteries you need.

In our case, four 100AH batteries would give us 3-4 days of power. Four batteries also provides enough of a buffer to run the house using solar panels in the winter so long as we have a back up generator we can rely on for appliances that draw substantial power, like the dryer, and to top up the batteries if the sun doesn't shine for a few days.

The fuse block covered and with labels. Note that the numbers in the top left corner of those stickers is the size of fuse we need if we ever need to replace one.

Thanks for reading/watching everyone! Please upvote, follow and resteem to support this work. As always, comments are welcome and I would be more than happy to answer any questions you may have about tiny houses.

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