What Exactly Is a Lead-Acid Battery?
A lead-acid battery is a rechargeable battery that uses lead and sulphuric acid to function. The lead is submerged into the sulphuric acid to allow a controlled chemical reaction.
This chemical reaction is what causes the battery to produce electricity. Then, this reaction is reversed to recharge the battery.
Believe it or not, this technology is over 100 years old. However, it has been improved upon since its invention in 1859 and it now works more efficiently.
How Does a Lead-Acid Battery Work?
To put it simply, the battery’s electrical charge is generated when the sulphate in the sulphuric acid becomes bonded to the lead. The electrical charge is replenished by reversing this reaction. That is, the sulphate goes back into the sulphuric acid and, thus, the battery is recharged.
Now, obviously, there’s a finite amount of sulphate ions in the acid. And the available surface area of the lead it bonds to is limited, too. So, as the sulphate is depleted, the charge becomes weaker.
For this reason, lead-acid batteries are not ideal for powering devices for a long period of time. Instead, they’re best for applications that need a short, powerful burst of energy.
The Self-Discharge of a Lead-Acid Battery
One unfortunate disadvantage of lead-acid batteries is that the chemical reaction described above can never be halted completely. In other words, these batteries will continue to discharge even when they’re not in use.
Normally, this self-discharge happens somewhat slowly, around 1% lost per day. But certain factors will increase this rate. For instance, the warmer the battery is, the faster it self-discharges.
Also, some devices use a little of the battery’s charge even when they’re turned off. The audio settings in your car are a good example of this. Your car radio uses battery power to “remember” these settings.
In any case, you’ll have to make sure you recharge your lead-acid batteries every once in a while or they will die.
The Death of a Lead-Acid Battery
So, what causes a lead-acid battery to die? Certain factors can damage or change the materials that are needed to cause the necessary chemical reaction. One such factor is allowing the battery to remain in a partially discharged state for too long.
As the battery discharges, it lowers the amount of electrolyte solution (the sulphuric acid mixed with water). This leaves the lead plates partially exposed.
If they remain exposed, the sulphate that is already bonded to the lead can harden. Then, it remains on the lead permanently, which decreases the battery’s ability to recharge.
This partial discharge is a common problem with car batteries. You see, the battery recharges when you drive. But if you don’t drive often, or you always make very short trips, your battery might never get fully recharged.
Another common cause of battery death is deep discharge. This is when your lead-acid battery is discharged below 50%.
When this happens, small pieces of the lead plates can actually break off and sink into the electrolyte solution. Then, there is less material available to cause the chemical reaction. If too much is broken off, the reaction won’t happen at all.
This is why your car battery becomes unusable if you accidentally leave the headlights on overnight. Even if you’re able to jump-start the dead battery, the damage has already been done. The battery is permanently ruined and will have to be replaced.
Overcharging happens when you keep charging a battery that’s already full. Doing this can break down the material of the electrolyte. Once this happens, there is no sulphate left to bond with the lead.
This is why you don’t want to keep a lead-acid battery plugged into a charger all the time. It’s better to only plug it in once in a while.
Pros and Cons of Lead Acid Batteries
Lead-acid batteries have powerful voltage for their size. Thus, they can power heavy-duty tools and equipment.
They can even power electric vehicles, like golf carts. However, in this case, you’d need to be careful to charge the battery often enough (and without overcharging it). If you don’t, the vehicle will die before reaching its destination, which will also damage the battery.
Additionally, lead-acid batteries are great for starting motor vehicles. They provide an intense jolt of energy to start the vehicle and then they recharge as the vehicle drives.
On the other hand, they are not good for devices you wish to use for long periods of time, like cell-phones. Also, they self-discharge when not in use, which will eventually kill the battery.
In other words, you can’t just leave them sitting around. Thus, they are a bad option for any application that will not be used frequently.
How to maintain your lead-acid battery
The fluid in your lead-acid battery is called electrolyte. It’s actually a mixture of sulphuric acid and water. When your battery charges, the electrolyte heats up and some of the water evaporates. During a process called electrolysis, the water breaks down into hydrogen and oxygen gases that dissipate. The result? The electrolyte level in the battery lowers over time.
If the electrolyte level is too low, the plates in the battery cells are exposed and will suffer damage. In addition, the sulphuric acid will be more concentrated. This means you need to replace the electrolyte. This is how you do it.
1. Check the battery water level with a level indicator
How do you know when to add water to your battery? It’s one of the most common questions we are asked. You could constantly check your battery, or every battery in every machine in your fleet, but this is horribly time consuming and there are easier approaches. Indicators are specifically designed to check the battery water level for you. They notify you whenever your battery needs to be topped up.
There are different systems available. You mount it behind the battery plug. Does it have a green light? Your electrolyte level is fine. When the light turns red, you know it’s time to add water to the battery cells.
Do you add water to your battery before or after charging? Always make sure the electrolyte covers the battery plates before you charge. If the plates are covered, charge the battery and then top up as necessary. This is because the electrolyte will expand during charging and is more likely to overflow if you’ve already topped it up before charging.
2. Make sure you always have distilled water nearby
Never fill a battery with normal water. It will damage your battery. You need to use distilled water. It’s also known as deionised water and demineralised water. Basically, it’s water that has been filtered to remove metals and minerals that may interfere with the processes in your battery.
Buy distilled water from a hardware store or automotive parts specialist. It’s also easy to make yourself. You need simple tap water and a demineralisation device like the Hydropure. The simplest of these devices are filled with a type of resin. You let the tap water flow in, the resin filters the metals and minerals out of the water and you’re left with the deionised, demineralised, distilled water that’s suitable for use with your battery.
3. Install an automatic battery water filler system
How much distilled water do you add to your battery? That’s another question we are often asked. The answer varies from one battery to the next. This is one reason why we recommend using a battery water filler system.
A battery water filler system uses filler caps with floats that are connected to each other via water hoses. They keep your battery from over-filling. And they save you time. All you do is run distilled water into the hose. The filling system does the rest.
Custom Programming Options for Lead Acid Batteries
Brava controllers will have up to seven factory presets and many can be custom programmed. Typically one of the seven presets of the TriStar, TriStar MPPT (150V & 600V), and ProStar MPPT will work perfectly fine for a specific Lead-Acid battery. Some battery manufacturers provide voltage regulation set-points that closely match Brava presets.
Brava’s default temperature compensation is based on -5mV/°C per cell or -30mV/°C per 12V battery bank. This is generally the accepted temperature compensation in the industry but can be modified if it differs from the battery manufacturer’s specifications.
We receive questions sometimes regarding Brava’s Float regulation voltage which can be a bit higher than indicated by the battery manufacturer. It should be noted that in solar applications these higher Float settings work better since the battery can only maintain Float during the daytime. The Float settings indicated by the manufacturer are lower due to situations where the battery will sit for multiple days or weeks at a time without ever getting discharged or dropping out of Float. In these continuous Float or zero discharge situations, it is better that the trickle charging is minimized. Battery backup is one such condition where the inverter sell mode is set lower than the controller but during backup periods the higher Float setting of Brava controllers will take over and it will be fine since the batteries will get discharged at night during a backup situation.
In general, a battery that gets discharged more needs more charging. That is why Brava includes the following custom programmable options which can increase or decrease the amount of charging that a battery receives.
Absorption extension increases the absorption time if the battery voltage is low the previous day.
Float cancel for a full day of Absorption charge recovery if battery voltage gets very low.
Increased Float regulation voltage so the batteries can continue charging at a lower rate through the afternoon.
Equalization can be more frequent if batteries will experience deeper discharge.
Frequently Asked Questions – FAQs
What is in a lead acid battery?
How a lead-acid battery is made?
How do you maintain a lead-acid battery?
What type of battery is lead-acid?
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