If you have a performance car, you may need to run two batteries? You may be asking yourself:
Can my alternator charge two batteries? The answer is yes!
Your alternator can handle two batteries at the same time. This is due to special safety features that help it self-regulate.
Let’s look at the different ways that alternators operate two-battery setups.
Can You Run Two Batteries on One Alternator?
As I mentioned in the introduction that the short answer is Yes. You can run two batteries on the same alternator.
Alternators protect against excessive current drain and aren’t affected by multiple batteries. When you connect the batteries, the voltage equalizes. This means that the lower voltage battery sucks power from the other. In the process, the power level in both batteries remains equal.
The alternator registers these two batteries as a single large battery and charges them the same. The batteries self-regulate the amount of current they take as they charge. This means that a single alternator is effective for multiple batteries.
What is a Battery Isolator? Do I Need an Isolator for a Second Battery?
A battery isolator is a device that disconnects the batteries from each other while the alternator isn’t charging. This is required so that the separate battery systems don’t pull from each other and discharge.
Different conditions inside of each battery may allow one to drain the other. Even when using the same size and age, the batteries will sometimes drain each other. Different discharge rates create different conditions. The level of discharge of the battery also creates an opportunity to drain from each other.
This is why you need an isolator between the batteries. Using an isolator helps lengthen the lifespan of both batteries. It doesn’t draw from the main battery by isolating the idle or ‘leisure’ battery if it’s overused. An isolator helps ensure that both batteries work as they’re supposed to.
What Size Battery Isolator Do I Need?
Choose a larger battery isolator than the size of your alternator allows the isolator to work optimally without harming your alternator.
However, you want to keep an eye on the cost. Larger battery isolators are costly. You also need to make sure that you have the mounting space for a large battery isolator.
There are two types of battery isolators:
- Diode Battery Isolators use two high-current diodes. They direct the current away from the battery. Diode battery isolators are easy to maintain, last a long time, and are simple to repair when something goes wrong.
- Solenoid Battery Isolators, on the other hand, use multiple relays to direct current. This type of isolator also monitors the batteries’ power level. It is more effective than a diode battery isolator. However, it is more complicated and often much more expensive.
Find purchasing options for Battery Isolator online:
Victron Diode Battery Isolator
Stinger SGP38
Solenoid Battery Isolator
KeyLine Pro
Dual Battery Isolator
Do Dual Batteries Have to Be the Same?
Will dual batteries hurt your alternator? No, but that isn’t where the discussion stops. When you use a dual-battery setup, you must follow some rules to make sure everything runs optimally.
Dual batteries should always be the same type and age. Why? There are a few reasons that this is optimal.
First, resistant differences are essential for your alternator. Batteries of the same age and type have similar resistances, which can help them charge equally.
If two batteries are a different type, they may discharge each other over time. Batteries that are not the same type or age have different properties. The risk associated with the batteries discharging each other is much greater.
It’s also essential to run the same batteries in parallel if you aren’t using an isolator. Without an isolator, there’s a chance that batteries of different types and ages will catch fire under load.
Wires and Fuses
Wiring can make all the difference when connecting two batteries to a single alternator. Fuses can also be extremely helpful. Together, wires and fuses play a huge role in how safe and effective your system is.
The larger the current is, the bigger the wire must be. That’s because electrical current works a lot like water. If you want to move more water, you need a bigger hose. If you’re going to move more current, you need a bigger wire.
Buy Big Wires for charging system here:
Spartan Power Battery Cable
TEMCo WC0180 Battery Cable
In case you wire batteries together across a long distance, you need an even larger cable. The problem is that larger cables quickly become dangerous. When the wires rub, become damaged, or if you are ever in an accident, these cables can easily catch fire.
To protect these cables, you need to install fuses. Since each battery is connected to a single cable, you need to install at least two 100 amp fuses. You should install these at each of the batteries individually to offer maximum protection. These fuses melt under heavy load. Make sure to get very sturdy, high-performance fuses to help with electrical resistance.
Once you have the fuses installed, it’s much safer to run the car. The risk of the cables catching fire is greatly reduced. Overall, installing dual batteries for one alternator is challenging. It’s well worth it for performance vehicles and stereo systems.
Buy 100 Amp Fuses online:
Renogy 100A ANL Fuse
RKURCK 100A Fuse
Tips to Avoid Damaging the Alternator with a Second Battery
Heat is the major problem when you’re running an alternator with two batteries. Alternators charge all day long. That’s going to build up plenty of heat when you are using it continuously.
To avoid damaging your alternator, make sure that your batteries are not frequently in a state of low charge. Also, make sure that you are not always running the devices that use the batteries.
Using a battery isolator can help keep the alternator stable. Additionally, you should avoid running the alternator for hours and hours at a time. Giving the batteries time to cycle can reduce the chance of damage to the alternator.
Alternatively, you could install a high-powered alternator as a replacement for the one that is already in your car. This can help distribute high-powered charge more evenly without the risk of damage.
Conclusion
You can run two batteries on a single alternator. Consider different factors before you try. Using a battery isolator can help a battery live longer. Making sure to use the correct cables and wiring is key to a successful dual-battery setup.
