Stage 0 | Background discussion and research

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Here is some compilation of research brianna did back in October. It's written down in possible lesson-order and missing some things.

Lead Acid Batteries

-Remember, we are using these because they have more capacity.

Let's look at how they work:

  1. two plates, made out of lead and lead oxide (when charged), immersed in an electrolyte that's suspended in some kind of substrate
  1. as the battery charges, the plates become lead and lead oxide, the sulfuric acid going into the electrolyte
  1. discharging, plates turn to to lead sulfate

Different Kinds:

  1. wet cell or flooded, sulfuric acid is dissolved in water. Cheapest. Can be maintenance free or requiring replenishment of water

gel cell , sulfuric acid is held in a gel substrate. Sealed. Limits possibilities of spills.


Starting, crank, automotive, or shallow-cycle batteries – have more, thinner plates can provide higher peak current, but shouldn't be discharged below 80% full as the thin plates will disintegrate more easily

Deep-cycle, or Marine batteries have fewer thicker plates – they can be discharged down to 20%, but cant provide as high current. Should be charged to at least 90%


lead acid batteries contain sulfuric acid. It's dangerous. If the battery overcharges, it is possible for it to explode. You should wear safety goggles when working with them, and protective clothing. Polyester is much more resistant to sulfuric acid than cotton, so it is better to wear polyester clothing if you don't have special protective gear

Proper charging control, covered in the rest of the lesson, is key to preventing overcharging

Proper maintenance will also help it be safe

Monthly: clean terminals, get rid of corrosion, make sure wires are not frayed or melting. If battery cases are cracked, swollen, or otherwise damaged, stop using those batteries. Rotate batteries if you have a bank with multiple batteries, to even the load on them. If you have a non-sealed flooded cell, replenish the water– using distilled water, or rainwater (not reverse-osmosis) to cover the plates, or to be right at the bottom of the input hole. Do this when the battery is fully charged. Having the electrolyte too low allows flammable gasses to collect, which can be ignited with a spark, causing explosion

NEVER use saltwater near them – it can combine with the acid to make chlorine gas –> death

If acid is spilled, neutralize with baking soda (sodium bicarbonate, soda ash, or lime) and rinse with clean water

If there is fire, don't use carbon dioxide directly on the cells. Don't use water if there is molten metal. Use substances appropriate for surrounding materials.

Measuring the charge level

For wet cells, the best way to measure charge level is to measure specific gravity of the electrolyte, because as it discharges the electrolyte solution has a lower concentration of sulfuric acid. However, you might not want to open your batteries to check it, and some batteries you might not be able able to open, so it is useful to have another way. Measuring voltage is a way that we've done this with other kinds of batteries – might we use this here? Unfortunately, temperature can change the voltage, so this has to be taken into account.

(Brief) activity: how charged is your battery?

There is a chart, (an equation). There are different levels for different types of batteries.

OK, now let's charge them.

Lead Acid Batteries should be charged in a similar way to Lion batteries at first. Providing them with a power source until the battery reaches a certain voltage will get most of the charging done. After that, however, things change. For Lead Acid batteries, they also need a “trickle” or “topper” charge. (DEFINE TERMS)

And once the battery is fully charged, it still needs to be kept connected for “float charge” Lead Acid batteries that are left unconnected alone will self-discharge. If it goes too long, they drop below the recommended voltage, and are damaged. To prevent this, there is a 'float charge' stage which provides a small amount of power to push the voltage back up whenever it gets too low. The Float Voltage is lower than the fully charged voltage – Lead Acid batteries should not be left fully-charged for more than 48 hours.

1. power source

2. charge at “constant current” until a high voltage is reached

3. charge at that voltage until the current is really low.

4. Charge at a slightly lower voltage indefinately

There are LOTS of different circuits that you can use.

LM317/L220 The ONE analog design I have…need to edit it to be good for different voltages.

(Random Notes

Maybe use voltage limit like in lamp, current sensing and lowering voltage limit like in this one.

IC's are nice because of temperature feedback

Links to more designs people have used.

Build circuit in these blocks. Connect together. Charge a battery?)


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