12 Volt Battery Generator





Introduction: 12 Volt Battery Generator

Inexpensive 12 volt back-up battery generator that is not hard to make. It will power what counts if the power goes out! Note:

You must have a working knowledge of electricity and electrical circuits to do this project otherwise you could really hurt yourself.

I've powered space heaters, refrigerators, televisions, fans, washing machines, lights. You name it and this will most likely power it including small ac units. The small mini fridge seen here has been running for 25 hours now with plenty of battery power remaining to run more stuff. You can take this to your remote cabin and be completely off grid. See my other instuctables for the foldable lightweight solar panels that compliment this generator nicely!


1. 60 ft of 3-1/2 in by 1-3/4 in board.

2. Box of wood screws 1-1/2 inches long

3. 1500 watt power inverter (pure sine wave inverter recommended)

4. Solar charge controller

5. Battery meter (I have two on this)

6. Toggle switch

7. DC power outlet

8. Two hinges

9. Two clasps

10 Four battery cables

11. Plenty of wiring and a handful of alligator clamps big enough to clamp to batteries. Also other wire connectors and electrical tape. Amounts will vary depending on how you set it all up.

12. Four heavy duty castor wheels

13. Drill with up to a half inch drill bit. You'll probably want some smaller ones to.

14 Door knob drill kit (2 inch) for the round battery meter. Yours may be a different size?

Step 1: Wood Needed

1. You'll need 60 feet of cheap wood that is 3-1/2 in by 1-3/4 in.

2. Cut 9 pieces 26 inches long

3. Cut 7 pieces 17-1/2 inches long

4. Cut 22 pieces 12 inches long

5. Cut 4 pieces 16 inches long

6. Cut 2 pieces 15 inches long

7. Extra pieces of any kind of wood like (2x4) to brace the batteries inside the box.

Step 2: Constructing the Box

Hopefully this picture explains how the box goes together (at least the end result)

1. Start with building the four sides.

a. connect seven 12 inch boards (no space in between) with a 26 inch top and bottom piece. Center the 26 inch boards which should leave roughly 3/4 of an inch on both ends. Repeat this step again. Use the screws but pre-drill all your holes first.

b. connect 4, 12 inch boards with the 16 inch top and bottom pieces. Repeat this again. Again make sure the top and bottom pieces are centered which will leave you with roughly 3/4 inches on both ends. Remember to pre-drill all your holes first.

c. Connect all four sides now.

2. Use all seven of the 17-1/2 inch boards and screw them in the bottom of the box. Space them out so they go from end to end with no left over space.

3. Use the remaining 5, 26 inch pieces to build the top. Lay them flat with no space in between the boards and screw the two 15 inch pieces down opposite direction on top of the boards.

4. Hinge the top to the box.

5. attach clasps to the front to lock the lid down.

6. Flip the box over and screw the castor wheels to the bottom of the box.

Box is done. (Tires were a later addition).

Step 3: Connect the Power Inverter

1. Chose the exact location where you want your inverter to be and leave enough room to drill holes for the positive and negative cables behind the inverter.

2. Drill two holes behind the inverter using the 1/2 inch drill bit.

3. screw the inverter to the top, connect the cables to the inverter and run the cables down through the two holes.

4. Once batteries are in the box you can connect the cables to the batteries.

Step 4: Connecting the Solar Charge Controller

1. Choose the exact placement of your charge controller and again screw it down and drill holes behind it to run the wires down through the top. When the batteries are in the box, you can connect the battery wires from the charge controller to the batteries.

Step 5: Adding the Battery Meter and Toggle Switch

1. Again, find a good convenient spot to attach the toggle switch, some place close to where the battery meter will be. Drill a small hole next to where the toggle switch will be to run the wires down through.

2. Attach your battery meter where you want and then connect it to the toggle switch and battery. You have to have a basic knowledge of electrical to accomplish this. Mine is set up so that I have to switch on the battery meter to see the battery level. I can turn it off or leave it on.

3. If you use a round battery meter like I have on mine, you'll need to drill a hole with the 2 inch door knob drill bit like I did in order to seat it down nicely in the wood. Looks really cool to do it.

Step 6: Adding the LED Light

This is completely up to you what you use but I recycled some fish tank led lights and an old ipod case to create this light. It's taped to an old GPS suction cup holder with directional capability. It's really bright!

Step 7: Adding the Batteries

I used two MK 74 AH Wheelchair batteries. Found a heck of a deal on Craigs List. Just make sure you use 12 volt deep cycle batteries. There's room for one more in there I think but for now this will do. Connect them in parallel. Attach all your gadgets to the batteries via alligator clamps or how ever you do it.

Brace the batteries in place with extra wood so they don't slide around when you move the box.

I use the homemade solar panels and extension cord you see to charge the generator when I can but I also have a 12 volt battery charger that I use when the sun doesn't shine. The panels I have here equal roughly 100+ watts of charging power on a sunny day. I get about 5-6 amps out of the panels.

I hope you like this instructable. Let me know what you think.

Step 8:



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    59 Discussions


    6 months ago

    VMAX Solar batteries are great for this, they are sealed and do not release harmful gasses. Check out my similar instructable here which goes into more detail regarding how to select an inverter and batteries:


    1 reply

    Thanks for the comments and link to your instructable! It's been a few years since I posted mine and I have since upgraded a little. I have included a few pictures of my new battery back-up/solar generator. Hope you like it. It features 6 deep cycle MK wheelchair batteries at 76 amps each in parallel . The box is vented in the rear and the lid allows for ventilation as well, although there is very little gassing that occurs with MK batteries. I have attached a 2000 watt pure sine wave inverter to the rear that powers most everything I'd need incase of a power outage. I've had this for a couple years now and have only used it to see what it'll do, never for a power outage. It is wired for a small solar panel/array in the 12 amp range which I intend to increase someday but for now that would simply keep the batteries topped off. My wiring job is not pretty but it works.

    battery backup.jpgBattery backup 2.jpgBattery backup 3.jpgBattery backup 4.jpg


    all the ingredients

    hello, The idea is great, however the way you carried it out needs a lot of improvement...1 put the batteries in separate battery boxes. 2 you need an internal sealed fan to blow in fresh air and additional vent holes to remove any gases generated from charging. This is a safety issue as the gas is explosive. 3 The wiring harness needs much improvement. 4 Never Ever charge large batteries like the ones you are using indoors sealed or not.....Walter Hynson

    8 replies

    I take it you have never worked on large battery powered machines Walter Hynson, I have worked on battery powered cherry pickers along with many other battery powered machines and none of them tell you to take them outdoors to charge them the amount of gas output from sealed lead acid batteries is almost nothing there is a little from standard lead acid batteries if you charge them fast but as long as you follow the makers specifications for charging then you will have little problems with the gas if you tried it in a small sealed cupboard then if you tried lighting a match next to the floor then you may have a problem.

    In all my years (38) of working with battery powered machines I have never heard of any problem with charging them indoors unless some one tries over charging them then it is their own fault.

    regards Poppy Ann.

    oops, "lighting a match next to the floor then you may have a problem". Hydrogen goes up, Poppy - you knew that.

    Shame about your body going south, mine's headed that way as well. Not holding my breath for Obama health care.

    Large enough alternator can be used as a stick or TIG welder with a few modifications. Repaired lots of SS stanchions and rigging 'in the wild'.

    Am thinking back to when I was in submarines - do they qualify as "indoors"?

    Med can get cold but doesn't have tropical storms! Red Sea was difficult to navigate celestially because haze obscured the horizon and it was before GPS. Had Walker sat nav in Med but kinda useless - took HOURS to compute and sometimes would only get one fix per day AND was a serious drain on battery.

    My boat (long story) was confiscated by Cypriot government and sold at "auction" when I came back to the states for a bit. $150,000 boat flogged for $2,500 and I was PNG. Sigh

    Hi again,

    don't know what I was thinking about re gas but I blame it on my brain slowing down with age(62 now) I was lucky with gps when i started out cruising I fitted a nice 10" plotter on the boat it was only black and white as I could not afford a colour one at the time at the moment it has a 10" colour one along with a 15" combination plotter and radar which is connected up to my autopilot if I had had a self tending head sail I could sail without doing anything once the sails were set but even the way I had it all I had to do was get ready to tack when the plotter bleeped and as the auto pilot turned the boat I just released the head sail when it started flapping and pulled it in on the other side as tight as I could then once the boat was all the way through just a slight trim and I was set until the next tack I can set the plotter to sail within set lines so I knew I could just lay back and let it sail itself when I had a long way to go which was great as I was single handing for most of my time out there, its a pity I came back but it is too late to do anything about it now, all I can do is think of the good times I had which were 10 years on board.

    regards Poppy Ann.

    I liked it. As an experienced seaman I can tell you, you need not concern yourself too much using this indoors (as long as it's a fresh, well ventilated area. Those are sealed gel batteries as well, so, they are very safe, can be used in any position. They should have a valve for hidrogen/acid discharge, which if it ever happens, it should be minimal. Yes, orderly routing the cables looks better, but who am I to criticize. Safety first, always. Fuse your connections. When you see things like this: http://www.ercshowcase.com/wp-content/uploads/2013/02/cables.jpg you know it took a long time and effort to make it so.

    I liked it. As an experienced seaman I can tell you, you need not concern yourself too much using this indoors (as long as it's a fresh, well ventilated area. Those are sealed gel batteries as well, so, they are very safe, can be used in any position. They should have a valve for hidrogen/acid discharge, which if it ever happens, it should be minimal. Yes, orderly routing the cables looks better, but who am I to criticize. Safety first, always. Fuse your connections. When you see things like this: http://www.ercshowcase.com/wp-content/uploads/2013/02/cables.jpg you know it took a long time and effort to make it so.

    If you where using conventional lead acid batterys yes you would need a vent, however since he is using sealed gell cell batterys from a wheelchair, or if they where any type of sealed non lead acid battery you are fine, hence why you you can recharge your wheelchair in the house. Otherwise hydrogen is released when a heavy charge is put on lead acid batterys. Also no need for battey boxes for the batterys he is useing.

    Much appreciated information. thank you.

    did you forget to include Batteries in your supplies list? (lol)

    this is just the same as I have on my sail boat except for the batteries as I went for 6 x 6 volt golf cart batteries wired as 2 series 3 parallel which gave me 750 amp hours in total but as I never drag my batteries down below half discharge to protect the batteries also I have 2 x 300 watt solar panels plus one wind generator and with these whilst living full time on the boat I only had to run my generator once a week to give it the batteries a top up and I run a desk top computer 24/7 plus a large fridge/freezer plus lights and fans as required (the fans run around 12 hours a day (boat is in the Caribbean)) but with the way some places get stuck with loss of power this is a good instructable, well done.

    5 replies

    similar to the setup I had on my sailboat but with only two banks. Have you considered battery isolation switches or diodes to protect the batteries from themselves? Should a battery go bad it can drag all the other batteries with it - happened to me. I dispensed with the wind generator, too bulky, too much vibration and I didn't like the swiveling propeller on a 12m boat.

    Hi there, my boat is 12 meter as well it is a ketch rigged Hughs North Star the wind generator is up the mizzen mast around 30 foot so not safety problems also I balanced the blades before I fitted it and the only time I had any vibration is if it gets above 30 knots I get a small amount of vibration which I like as I use it as a warning when I am in bed to get up and check the anchor.

    I have 2 battery banks but one of them is just for engine starting I have a parallel switch for when I make a mistake and I need a extra boost for starting I fitted the engine with a 60 amp alternator for when everything else fails then I can still charge from my engine.

    regards Poppy Ann.

    Caio Poppy

    Mine was a cold molded schooner. Wasn't all that keen about elevating the wg. Sailed Indian Ocean, East Africa , Red Sea and Med. 80 amp on engine but 4l/hour was spendy so I mounted a 60 amp alternator onto a 2hp engine. Ran for hours on a liter at idle and did a wonderful job charging - simply rev up engine until the alternator is excited and drop to idle. Quiet, compact and efficient. Didn't have economical photocells in the 80s and I had forever sun.

    Hi Scotty, my boat is still in Puerto Rico where I left it 3 years ago I was hoping to return to it after 6 months when I returned to England as I was hoping that the local hospital would be fixing my knees and right hip which they had told me several years earlier that they were worn out and needed replacing but when I went back they now do not want to do the work as they do not want to give me a general anaesthetic and can not give me a epidural due to the damage in my back so I am stuck as when I left the boat I was having trouble living on the boat and now I have deteriorated further so most likely I will have to sell it off but with the way the market is I would get nothing back on what I paid for it.

    I forgot to add that I had had 2 of the Honda 2000 watt generators which I bought when I was building solid hand rails and davits to the rear out of 2" aluminium tube I needed two of them to power the welder as one was to small but the beauty with the Honda silent generators is that you can plug them into each other to get a higher output and they use almost no fuel when I ran them to charge the batteries they just reduce the rev's to balance the output to what is needed so no messing about by me. it sounds like you had a nice area to sail I had first planed to go to the Med until I found out that it got cold in winter so quickly changed to the Caribbean.

    regards Poppy Ann.

    I have amp envy! Sounds like you have plenty of power to do with what you need. I hope to have more batteries someday soon. The Caribbean huh!, some people have all the fun and thanks for liking my generator.

    Awesome, the solar panels..

    Looks alot like the setup I have in the van.

    of mono christaline solar cells into 2 deep cycle wheelchair batteries
    and a block of 20 7ah SLA cells keep my computer going most days and all
    through the night.

    Batteries are second hand and one is officially 'dud' but im not to concerned.

    provides more power than I can use in good sun and the Steca controller
    cant cut them off properly so I have manual switches on them also.I
    need more batteries. In NZ these 25w panels are $20 each, I have 8 of

    A suggestion is to double the number of solar you think you
    need to cope for winter days and double the batteries also. Three
    batteries is a good size for me.

    Go MPPT controller and off days will be better.

    enough the Solar panels I have work better on cloudy days, with the
    wispy white clouds the sun is diffused and 'blooms', my panels love it.
    12-14a max charge I have seen on 200w, 8a plus on 100w into 13v, thats
    more than rated output. This was is during winter, at 42 south latitude.

    Power output increases if they point (near) directly at the sun, think of this and optimize placement for winter time.

    1 reply

    Hey thanks for the reply. NZ? Wow! Yep, I got an MPPT controller just the other day to put on "Wattsun", that's the wooden box, I named it :). So, did you have an interest in solar and batteries before outfitting your van or did it come about through necessity? Just curious because my interest sparked from me needing lights in my tool shed almost four years ago.

    As far as solar panels go, I'm about to post a new Ible on how to make a tri-fold 120 watt gun case solar panel so look for it here in the next few days. Basically, I recycled an old rifle case into an amazing solar panel that is very portable and weather proof. I really just want to show it off but there may be someone out there that can use the idea, who knows.

    I actually have many solar panel projects lying around the house that I just don't use, no need really, but I can't stop making different style ones. Sounds like you're doing missionary work over there? Keep up the good work.