Solar Car Battery Charger DIY

Step 3 Low Voltage Disconnect and Inverter

Here's my inverter.
It takes in 12 volts DC from the battery and produces 110 volts AC that I can plug my sewing machine, laptop, etc into. You can get them for cheap at any truckstop or discount store now.

This model has a low-voltage disconnect feature which is a big help.
When battery voltage drops below 11 volts it beeps and turns off.
That protects your battery from over-discharging.

Sulfating and De-Sulfating
If you run your battery down further than 10.5 or 11 volts, or if you fail to charge it up again soon enough, sulfate crystals will form on the battery plates.
The sides of your battery will bulge from the crystal deposits on the plates, and your battery won't take a charge anymore. There are tricks to fix this. Look up "desulphate", "desulfate"(both spellings are ok), "pulse charger", "battery edta". According to one vendor of desulfating products, 75% of the lead-acid batteries removed from service can be rejuvenated with these techniques. The others are suffering from shorts, open circuits, and similarly less correctable flaws.

To measure your battery's capacity
Plug in an mechanical electric clock and a known load, like a 5 watt lightbulb. See how long it takes to run down the battery til it shuts off. For example: 5watts/12 volts = 0.42 amps. If it takes three hours to discharge your battery after it's fully charged, your capacity is 3 * 0.42 = 1.26 amp-hours. (not very much) A typical emergency-lighting gel-cell has 7 amp-hours capacity.

Comments

[DaMadProfessor]

So If you were to hook that inverter to a solar panel putting out 15v that u regulate down (instead of the batteries 12v) you could feasibly power a laptop? I am working on a design for a laptop charger/ solar power source

[Tracy]

Uh...no. Not unless you have a battery or a huge capacitor in parallel. Actually, you don't need to worry about regulation; the battery absorbs that. It would take at least a 60 watt panel to power your laptop directly, and even then you would really need a battery.

[naught101]

It's worth pointing out that laptops all have batteries anyway. It could be done, but you wouldn't necessarily need to regulate down, but might need to step up. My laptop's DC in runs at 19.5V, and I've seen ones that run at 14V, which would be perfect. My battery is 80Wh, 11.1V, 7.2 amp hour, and I get about two hours out of it, I think it's a bit rooted though (I'd guess it's equivalent to a 60Wh battery), so it probably chews about 30W (more when really busy+bright, or with USB peripherals). So I guess a 14V panel producing 30W or more would charge the battery and run the computer at the same time, as long as the sun was shining. Keep in mind though, that mine is dell d410, with no CD drive, and a 12" screen. most laptops probably use a bunch more power than this one

[ironsmiter]

have to agree here... For powering a laptop, you're best off matching the output voltage/amperage/regulation of the powersupply. Charge the batteries with the laptop off, and when it's "full" you're set to go. Trying to directly power a laptop from solar is iffy, as voltages(or is it amperage) are NOT steady. changes in sunlight intensity can drastically effect total output.