Solar Car Battery Charger DIY

Here's how to charge your lead-acid car battery with a solar panel.

The simplest way:
Get a voltmeter and a solar panel. Connect the panel to your battery and watch the voltage rise. When it gets near 14 volts your battery is charged. Disconnect your solar panel to keep it from overcharging your battery.

Your battery can be damaged if you charge it too fast, so don't get a panel that's too big for your battery. Consult the battery manufacturer's data to see how many amps it can handle, both while charging and discharging. If you happen to have a big panel and a little battery, there are tricks further along in this instructable.

Some solar panels are made just for the purpose of maintaining batteries in vehicles that are parked a long time. They don't go over 13.5 or 14 volts and don't ever produce enough current to damage the battery. These you can just hook to your battery and forget.

If you want to use more power you'll want to get a bigger, higher voltage panel than that.
Here I am running my truck's electrical system off a solar panel wedged in the windshield.
My alternater fell off the engine and the belt broke. I'm driving south so I just set up the panel and drove into the sun, peeking over the panel. Read more of that Haywire Mechanic Story or click on "step two" to read more battery/solar tricks.

Step 1: Voltmeter Human Supervision

Here's the setup in the cab. I watch the voltmeter to see how things are going. If the voltage goes to zero I know something has gotten disconnected or shorted out. I then sniff to see if there's a burning smell, which means I need to pull over quick, open the hood, and put out an electrical fire.
If the voltage suddenly jumps to 17volts I suspect the jumper cables that carry the solar panel current to the battery have gotten disconnected.

The panel output voltage rises to 17 volts or so when it's not connected to a load. When current flows the voltage drops due to internal resistance in the panel.

If your battery voltage gets to 14 volts or if you hear a bubbling sound when you put your ear to your battery it means you're overcharging your battery. Disconnect your panel. You'll get to know your panel, battery, and loads, and maybe you'll disconnect at a lower voltage, like 13.5 volts.

This method works fine when camping and you can lay around watching to see how your battery is doing, or if your panels can't keep up with demand so you don't have to worry about overcharging.

Comments

[auhs1]

hye..
how are u??
what equipment thaht we need 2 do this thing..

[strangegg]

I want to charge an extra battery in my van, so I can run a car heater or cooler in my cab at night while the engine is off. I would also like to use my computer and light if possible at night. I want to charge the extra battery while i drive during the day from solar panels. I was thinking of mounting the solar cells on my side windows. Do you think this is possible or wise? I also wondered if i could hook two batteries into my alternator and charge both while driving.

[Yerboogieman]

whats the peanut butter for?

[Paulie151]

That was his lunch when he threw this thing together. ;)

[ReCreate]

I think attracting bears? id put a big electric current through the car so that when a bear comes ZZAAPP and leaves

[ssisssy19]

hi everyone.i am new to this solar stuff.i have a 12v die hard battery i want to use.i would like to charge it using solar panels but i dont have any idea on how to hook it up and what i need to do this.do i need a battery charger to hook up to the solar panels or do i hook the battery right to the panel and how do i do that.i told you i am new to all this sorry everyone.if somone can help a dummie i thank you lol

[thorpenny]

A good idea would be to invest in a charge controller which would keep your batteries from getting overcharged. Do some research!

[pennsteve]

Why would you need this to charge your battery if you are driving?  Thats what your alternator does.

[juicepig21]

Or you could just read the text and it would tell you that his alternator broke.

[Badlad220]

mayb his altonator broke or summin so he has to charge it manuly

[Entropy512]

Do you really think he's driving with a panel propped up against his windshield?

This approach is usually used for keeping the batteries of rarely driven vehicles float charged - I use a 5W panel on my convertible with great results.

[pennsteve]

He says if he smells a burning smell he has to pull over quick..........etc.......

Yes, I think he is driving with it.

[abadfart]

maby his died  

[knektek]

Get a 15v solar cell,
Get 10 of them in parralel,
Check the output,
Regulate it,
And your now happy with a quick reboot of power in your 12v battery.

[jimmy dean]

How many amp-hours does your typical car battery put out. I can onlyfind cold crank amps. Is that the same thing? Also, I'm not really sureon what wattage panel I should get if I just want to charge one battery.Could someone plese explain to me what a good wattage would be and why.

[tammasus]

shouldn't there be a diode between the panel and the battery to prevent the battery from discharging into the panel?

[ElectricMan1]

No the charge controler does that for you.

[Ausi319]

reverse diode to be exact but yes the charge controller does that for you

[Heliosphan]

Hi all.
This is a helpful instructable for me as I'm interested in buying this -
http://www.maplin.co.uk/Module.aspx?ModuleNo=99760&C=Newsletter&U=09P05-2&T=666389
I already have a 1Watt solar cell which is doing a nice job of powering a salvaged PC Fan to do a reasonable effort of cooling my dining room as the sun shines! The amount of time the fan is on as the sun shines does bring the whole room temp down a good few degrees, esp if you're close to the fan.
Now I'm interested in doing a little more - ie getting hold of a big car battery and charging it up for duties such as charging my mobile phone, laptop, etc.
I have done quite a bit of circuit design in the past, including programming microcontrollers for controlling motors etc.
I'm somewhat unfamiliar though with the concept of charging a battery at the same time as using it. Sure cars do it all the time with the alternator, but if you think of it from the classic electronics and electrics standpoint its a little confusing - how can you power a battery, and at the very same time, take power from it, its akin to connecting two landline power sources up to each other, you'd never do that with traditional mains power supplies!
Any ideas on how/why this works, what caveats are there, eg is power from the battery actually going TO the solar cells too and potentially damaging them?
Thanks all.

[deerfeeder]

Can someone give me a recommendation on a solar charger controller combination that will keep a 12 volt car battery charged when used to run a deer feeder once a day. I have a small panel (8" X 8") on the battery right now but it is not keeping the battery charged. Any help would be welcomed. Thanks

[netbuddy]

Unless you know what current it outputs you won't know how many hours light is needed to charge it. If you took a discharged 12 volt car battery and hooked it up to a single solar panel like the ones on offer in maplins, it would take about 6 months to fully charge the battery to a usable capacity. I know because I have put it to the test, one 12 volt 1.5watt cell charged a total of about 0.5 volts a month. So the higher the wattage of the panel the quicker it will charge. Your cell voltage potential needs to be significantly higher, typically a solar cell needs to out put at least 15 volts to charge a battery. If that is not happening then your not charging just maintaining a trickle charge. If you have a 15 volt output from your cell and it outputs 15 watts, your current output is 1 Amp per hour, on a small cell like a 7 Amp cell will take about 7 hours to charge assuming that your cell gets adequate light.

[greatscotmagic]

Hi, I use a handicapped scooter at festivals and I can't always charge up my batteries. is there a way for me to rig up a solar panel to run the motor during the day while i am using it? Could I charge the batteries while I was using it and charge the batteries while the scooter was not being used? I do like these ideas as I get to events that I can't get access to power but I would still like to use my laptop. Thanks.

[netbuddy]

I would say that you are a candidate for the next generation of solar PV. Amorphic cells give more output at lower light levels monocrystaline gives higher output per cm² polycrystaline is a mix to produce a cell that gives good output at all light levels. You are best off investing in several cells over one large cell. reason being that if the big boy gets damaged or is obscured, the overall output is lower or non existent.

[TimAnderson]

Just follow the same steps in this instructable. It doesn't matter if you use your scooter while charging it. Probably you'll want the panel overhead as an awning. You probably want lightweight panels. Look for weight vs. power rather than wieght vs. size.

[greatscotmagic]

Tim Thank you. I was planning to use the panel like an awning, not only will I be able to run my cart, but I can keep the sun and the rain off too! Another question: when you are using your laptop with the solar panel and the batteries, do you use the power inverter and the laptop's AC Adapter to power the laptop? Thanks again.

[GadgetGuru01]

Good question...my girlfriend just got me Solar Gorilla Solar Laptop Charger. I was able to run my MacBook with solar panels

[ReCreate]

oh wow

[TimAnderson]

yep, I used an inverter to regular powersupply. one advantage is that inverters usually have a low-voltage cutoff so save your batteries from getting totally drained.

[netbuddy]

That is wasteful way of powering a device designed for low voltage. I am aware that not all laptops use 12 volt DC input but you can get DC to DC converters that output 24volts which then can be regulated to the laptops preferred voltage requirements. The upshot it that you get more than a few hours worth of operation over an inverter method. It is pointless to take 12 volts and have it converted up to 110 / 240 volts only to be converted back to 12 to 18volts. The losses in such a circuit are huge and your battery's will serve you better.

[ac-dc]

Actually the losses are not huge as a switching circuit, and the distinct advantage is you have 110/220VAC available should you ever need to power something else. You cannot expect to boost 12V to 24V then reregulate again and have it be much better efficiency. The high efficiency option would be a purpose specific laptop car adapter that goes straight from the 12V-13.8V DC to the laptops required input voltage.

[static]

I understand that some laptop battery chargers don't like modified sine wave inverters and one may be better off use an auto power cable to run the laptop. YMMV

[greatscotmagic]

Is an auto power cable a cable that will run a laptop directly from a car's battery? can all laptops do that? Thanks.

[greatscotmagic]

Thanks again, Tim.

[explosivemaker]

"I then sniff to see if there's a burning smell, which means I need to pull over quick, open the hood, and put out an electrical fire." ....that just made me laugh....though I hope you haven't actually had it catch on fire....

[Unit042]

Whoa! It looks like an army of bears and gramlins ate the insides of your car, then got themselves eaten by a dragon that was too fat to fit into a black hole, then shifted through time and interdimensional space to barf it back up, minus the fuzzy stuff that goes on the floors. Anyway, cool 'ible!

[Unit042]

Whoops, they are gremlins, not gramlins.

[SuperJesus]

there gramlins if your from the south lol.

[sabarblatoe]

From texas and felt the need to say "Gramlins" out loud just to see......and your right. Laughed my assoff.....and still laughing.

[Unit042]

Yeah. Half gremlin, half gram cracker with cinnamon.
Thus, gramlin.

Heehee.

[TANZMEISTER]

They're only gramlins if they call you gramma or grampa