# Car Battery Powered House Ideas, Questions

Discussion in 'Power Electronics' started by kamilavalamp, Aug 4, 2015.

1. ### kamilavalamp

4
1
Aug 4, 2015
Hi, everyone.
I am a hobbyist with expert computer and mechanical skills, but I only have basic skills with general electronics
so I have a few questions about an idea of mine.

My Idea is to power a house year round using only car batteries and 12V Power Inverters. This house would have a TV, Computer, Lights, all the comforts of home. I would like to give each room it's own dedicated power supply using this method. Is this Idea feasible? My main concern is how long each battery would last before It had to be recharged\replaced? I plan on using the heavy duty 4000 amp car batteries that people use to power their sound systems and I wouldn't want to be recharging\replacing batteries every day. My second question is how much juice things around the house use up? Would 1 or 2 of these batteries per room be enough to do the job. Like I said I only have very basic skill with general electronics so any advice would be appreciated especially if there's some variable here I don't know about. -Thanks in Advance.

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2. ### Gryd3

4,098
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Jun 25, 2014
Something to keep in mind, is that those car audio guys usually upgrade their alternator to put out more current.
This means that the battery in the car is *not* used as the primary power supply. The battery is only used during peak power draws, and is often supplemented with large capacitor.
Now that you know that, it's time to go into more details:

Do an audit and determine how much 'power' each of your devices use. Add these values together for a 'peak' draw.
Once you have this information, determine how many devices will be on at any given time. Add these values together for a 'sustained' draw.

Now.. the next step is determining how long you want the batteries to last between charges.
You can also use the 'peak' draw value to determine the size of the inverters you need to use.

If you are unsure of the power draw of a device, there are a couple places to look.
Usually by the power input on the device, there will be a rating showing current draw in Amps, or an Energy use in Watts.

To give you a bit of an example...
I leave my desktop computer on 24/7 which draws around 200 Watts.
I have a small backup battery that can hold it up for about 25 minutes. It's a 12V, 7.2Amp-Hour Sealed Lead Acid Battery.

If I wanted to power my computer for a full day, I would need batteries totalling over 400 Amp-Hours.
Note that this would be pretty close to leaving 3, 60-watt incandescent light bulbs of for 24 hours.

Of course, your situation will be different, you need to know the draw, and on average how many hours a day it will be running.
From there, I'm sure you will give yourself sticker shock at the cost of batteries.

* How will you charge these things? That will be another challenge in itself.

3. ### Tha fios agaibh

2,107
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Aug 11, 2014
And the life of lead acid batteries is only about 5 or 6 years.
Also, it would cost a small fortune wiring heavy gauge wire from all the batteries.
Also, need to add roughly 20% extra to account for heavy inductive loads. Inductive loads can draw >8 times their normal current draw at start up.
Example; the power required to start an air conditioner (LRA) can be well over 100amps.

Good luck.

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4. ### AnalogKid

2,393
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Jun 10, 2015
Given that you have to charge up the batteries somehow, and then convert the DC back to AC to run the household devices, the overall energy efficiency will be about 50% of just using an AC outlet directly. What is the point of the project?

ak

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5. ### hevans1944Hop - AC8NS

4,536
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Jun 21, 2012
I think perhaps your are ignoring the cost of energy, measured and billed in kilowatt-hours. For example, I have a fairly typical house that uses on average about 1200 kWh of electricity every month. Some months it is more (summer with air conditioners running) and some months it is less (winter with natural gas providing heat), but the lighting and appliance load is pretty much the same all year long.

So, if I had ten 12 V batteries providing all my electricity, then you tell me how much current I would have to draw on a continuous basis to use up 1200 kWh every month. Hmmm. Lessee... we have 120 V (10 batteries x 12 V per battery) and if we were to draw ten amperes from those batteries, it would provide 1200 watts or 1.2 kW of power. There are roughly 720 hours in a month, so that load would require 1.2 kW x 720 hours = 864 kWh of energy every month. That's a bit shy of the 1200 kWh my house actually uses, so clearly I would need to draw more current from those ten batteries. But never mind that detail. How am I going to make up for ten amperes of continuous current drain from my batteries? Bear in mind that is the average current I need. At night, when most of the lights are off, the current will be less, but it goes back up during the day and into the evening, so I also have to consider peak current demand when I size my inverter.

The important variable, if you "wouldn't want to be recharging/replacing batteries every day" is the ampere-hour capacity of your batteries, because that will determine how often you need to re-charge them. Generally, if a battery has a 1000 AH capacity (which is a large battery), you never want to use more than half of that capacity before re-charging. Deep discharge cycles are not good for lead-acid battery chemistry unless they are specifically designed for it, as some marine batteries are. So let's assume you will use 500 ampere-hours of your battery capacity, and that the load is a measly 10 amperes as before. So, you will be able to run continuously for 50 hours before re-charging. That's a little more than two days. You will either have to find another electrical power source from which to re-charge your batteries every two days, or go back on the grid and purchase the energy from your friendly electric utility. Or I suppose you could swap out for ten freshly-charged batteries every other day, as some proponents of electrically powered automobiles have suggested.

Some people attempt to solve this energy problem of going "off the grid" by substituting solar photovoltaic panels, or windmill-driven alternators, or low-head hydroelectric generators placed in a local stream of water, or even steam-driven alternators using alternative fuels such as methane or alcohol which can be derived from biomass. At the present time, none of these alternative energy resources can even begin to compete with commercially generated electricity in terms of cost, reliability, and convenience. But these alternative energy sources may be the only electricity available if a catastrophe occurs that prevents commercial electricity generation and distribution. So your idea of being prepared by converting your house to run off of batteries makes a lot of sense if you see it likely that electricity will not be commercially available, and you are preparing alternative electrical energy sources to replace it. But be prepared to spend a LOT of money preparing for the collapse of civilization. And even more defending against the zombie hoards who will try to take it away from you.

And one other thing I almost forgot: a battery vault. It is both unsafe and illegal to charge a lead-acid battery bank inside a residence. You need to build a well-ventilated concrete-block vault to house your battery bank. Because of the risk of hydrogen explosion if over-charging occurs, this vault should be located some distance from the house. Check your local electrical codes for details.

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6. ### kamilavalamp

4
1
Aug 4, 2015
I guess you figured me out. This really isn't for a house it's for an underground fallout shelter. (I figured if i mentioned that right off I would be laughed at.) I don't want the tv and computer for staying in touch with the outside world. I have a CB for that. I know about how the satellites and all that will be down. The Tv and computer are simply for storing and enjoying my collection of music and videos. I want to ride out the apocalypse in style in an hidden underground shelter. I already learned about underground construction and how to build my shelter and I've drawn up the blueprints. Now I'm just trying to figure out how to provide off the grid power. I don't want to use solar power since the place will be completely hidden underground and I want to keep things set up simple so they will be simple to repair. I've been suggested to use deep cycle batteries because they can be recharged repeatably by a generator and they sound like a good idea especially if I can tune that generator to run off of E90. Will deep cycle batteries with a generator to charge them be a better solution for off the grid power? I don't know much about them. Will they pose the same risks of exploding as regular batteries?

Last edited: Aug 4, 2015
7. ### BobK

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1,686
Jan 5, 2010
If you have a generator, why waste power by charging batteries instead of running directly off the generator?

Humoring your fantasy for now, the best place to put your effort would be in getting the most efficient devices possible.

And don't forget the ventilation fans!

Bob

8. ### kamilavalamp

4
1
Aug 4, 2015
I didn't want to have a huge generator that would be hard to repair and would need tons of fuel. I just wanted to use some sort of battery or batteries that would last and that I could recharge with a small generator.

9. ### Gryd3

4,098
875
Jun 25, 2014
Well... you 'need' a generator... and food for thought:
If you, on average use about 1000WattHours / day, you will end up needing to run a small 100Watt generator for over 10 hours /day to charge the battery bank.

If you only want to charge once a week, you will end up using 7000WattHours, requiring a small 100Watt generator to run for 70hours!

I realize you want to rely on the batteries, and only charge momentarily, but you will end up in one of two situations... running a small generator for a very long time... or running a big generator for a shorter period of time.

I also understand your desire to avoid solar panels to avoid being seen... but how do you plan to hide the noise a generator makes? You can setup and remove solar panels easily enough for short charge periods... you can run and hide a small hydro-electric generator in nearby water.

I honestly think your best option for any long-term storage or use of electricity is to buy a bicycle generator and a set of small lead acid batteries to power some small amount of lighting like LED.

Any other generator solution will require you to go out to find fuel (which decays over time) or to make your own fuel. At this point, you might as well look as solutions that do not rely on the storage of volatile chemicals.

10. ### Gryd3

4,098
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Jun 25, 2014
Actually... more realistic number would be using a 3000Watt generator for 'small'
But it still comes down to the need to replenish how much power you take from the batteries. The more power you take, the longer you need to run this thing every night / week.

11. ### hevans1944Hop - AC8NS

4,536
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Jun 21, 2012
There are several scenarios that could by regarded as apocalyptic. One of the most plausable is a high altitude nuclear detonation (one or more) whose resulting ground-level EMP would disable the power grid and anything else electrical or electronic not hiding behind a Faraday shield. I think the likelihood of such an event increases as nuclear weapons and rocket delivery systems become available to unstable or rogue nations. Homeland Security takes this problem seriously and is working to harden critical facilities, but they cannot in the near future protect the national power grid, which is falling apart anyway. And who knows what protective measures are being taken elsewhere in the world?

The question for the long term, is what do you do if civilization as we know it collapses? Some people of similar minds are joining forces to create fortified compounds and underground shelters to preserve at least a few people "until things get back to normal." But in a true apocalypse things never get back to normal. The rapidly mutating and invariably deadly pathogen sweeps across continents killing everything in its path. Or the blight that destroys all vegetation leaves the world starving to death. Or the asteroid that appears out of nowhere, crossing the ecliptic and hitting Earth head-on, throws up enough dust worldwide to block out the sun for months or even years killing all the crops and creating "winter" conditions world wide. The question you have to ask yourself is, "Do I feel lucky?" I am old enough to think I will be dead before an apocalypse occurs, or certainly shortly thereafter. It is one of those things I can do nothing about, either to avoid or survive it. That doesn't mean I wouldn't go down fighting, but I do think resistance is futile, to borrow a phrase from the Borg of Star Trek fiction. I prefer to work to maintain civilization, rather than prepare to hide if it fails.

A lot of people from my generation did build so-called "fallout shelters" and some were quite elaborate. I am certain the government has built shelters to preserve the lives of "essential personnel" in the event of a global or national catastrophe. Guess what? In another hundred years it will turn out that it didn't make any difference, certainly not to me. But good luck with your preparations. There will always be a demand for anyone who can find and harness energy resources after the SHTF event.

12. ### kamilavalamp

4
1
Aug 4, 2015
I don't really expect the world to end any time soon but I do expect a civil war in the next decade or 2. I will be coming into some money for the first time in my life and I want to make the most of it by building a nice secure off the grid hidden underground compound for myself and my family to live comfortably in and wait it out. And if there's no war I can still pass the place on to future generations so they will always have a place to live without having to worry about crumbling infrastructure, economic failure, inflated mortgages, and etc, etc, etc. The only thing they will have to worry about is fuel.

So in reality I'm gonna need a big generator no matter what.
Is it gonna end up being more economical to just run the whole place directly off a large generator and forget about the batteries?

13. ### Alec_t

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Jul 7, 2015
... and lack of fresh food, and going stir-crazy, and ...

14. ### Tha fios agaibh

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Aug 11, 2014
To me the underground shelter and battery idea are not feasible.
The ventilation fans alone would be a huge draw of power.
What do you do when it rains for 3 days and your shelter starts to flood?

If you want to go off the grid, buy yourself a farm and live like the Amish.
It would be a great exercise plan.

John

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15. ### Tinker Unique

22
2
Dec 1, 2014
There are quite a few options and companies available for what you are looking for. Example = LARGE motorhomes are run on 12v power WITH an inverter to supply the range and other items. One of the companies that can give you answers is "Seimens". They make the supplies to build a complete system for a solar/wind powered home. I would recommend the newer "6=pak" style batteries. They are more expensive, but last longer and need no maintenance. There are also other companies that sell surplus equipment that is in good working order. MY first 12v "project" was a car battery in the garage, heavy speaker wiring and a stop light bulb in the end of a soda can (top end cut off) to be used as a reading light by the bed. Auto door/dome light switches can be used for lights turned on when a door, or gate is opened. Currently, I have two car batteries in my shop with a single solar cell on the roof, and 3 automotive break lights on the ceiling, and a fog light, lights up my back yard. (small yard). Many sources on the internet for "Alternative Energy", Solar Power", and "Wind Energy". An auto alternator can be used as a wind generator when linked to a "fan" It all depends on your research and creativity, or imagination.

16. ### BGB

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11
Nov 30, 2014

it would be nice to be able to live somewhere rural, but then there is a lot of hassles:
no grid power or internet;
need to drill a well;
need to haul out/set-up a mobile-home or similar;
...

or even just living slightly out of town, where one still has a drive over dirt roads and any internet connectivity generally sucks pretty hard (or one has to get satellite internet), and still has neighbors around (though usually one already has power and a well available if they buy a house), but people don't really care what you are doing (and it was a land where fences were often made of things like barb wire and corrugated sheet steel).

one might live in the city, where despite is drawbacks, and probably being screwed if SHTF, it is convenience in the name of grid-power, decent internet, and convenient access to paved roads (and being able to get places with short drives), and the post-office and UPS bring packages right to ones' house, ... though, it still isn't quite so urban that there aren't people around with horses or CAT tractors or similar in their back yards. but annoyingly, it is sufficiently urban that people will complain about little things (like parking cars in the front yard or similar).

elsewhere, people won't notice/care if cars are parked in the yard or similar (or have a big pile of scrap metal or whatever), and one is free to let their lawn return back to how nature intended it.

though, one factor is one still needs to live somewhere where they can easily get to/from their job and similar.

but, yeah if living somewhere good, it might be nice to have a battery back-up system and maybe some solar panels. maybe a mostly concrete house with Faraday shielding. ...

or such...

17. ### Tha fios agaibh

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Aug 11, 2014
Yes, I understand your dilemma, but one also needs to be realistic. Say the grid shuts down two years from now; Do you really think you can rely on your batteries to be charged and ready? Especially lead acid batteries. They need to be charged to keep voltage up and the cells need to be watered likely monthly. I think the problem with our generation is we cant imagine our lives without electricity or internet. In reality most would adapt and survive without this modern luxury.

My Dad went thru the great depression. He said they did not even notice there was one, because they lived on a farm where they were self reliant. Conversely, the people in the big cities were starving to death. Many returned to the farms to survive. It is likely we will face some hard times ahead, but thinking we need all the modern luxuries is kind of silly.
As far as the lead acid battery, I would not trust it as a reliable back-up for my sump pump.

John

18. ### BGB

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11
Nov 30, 2014
PbAc AGM batteries tend to work reasonably well IME, and seem to have a lifespan somewhere between 5 and 10 years if treated well. adding water shouldn't really be necessary unless you are severely overcharging them.

though, yes, if not actually supplying power to them, they will drain down pretty quickly.

probably an actual means of generating electricity is needed, such as solar or a generator.
better yet if a person has a facility setup so they can produce their own fuel, such as growing a lot of osage orange trees and having a big still. if the still is big enough, a person should hopefully be able to produce enough fuel for them and maybe also their neighbors to use.

for example, stockpiled gasoline will only last so long and gasoline "goes funky" pretty fast.
for anything longer term, facilities are needed to produce ones' own fuel and make/replace things that break (such as a well-stocked machine shop, ...).

longer term? who knows...