Your alternator is the electricity power plant in all internal combustion engines. It produces the power you need to recharge your car’s battery to create a stable power bank.
However, most of the power generated when the car is running goes into powering crucial electronics like:
- The car’s ECU
- The fuel pump
- Electric power steering and vacuum pumps
- Electric hydraulic pumps
- Fuel ignition (in spark plug engines)
- Infotainment system
- Lights in and outside the vehicle
With so much demand on the modern alternator, getting an undercharging alternator is more common than finding one that’s overcharging. Luckily, we have already addressed that.
What Does it Mean When an Alternator is Overcharging?
An overcharging alternator provides a consistent voltage above the standard operating Voltage for your car’s electronic system. Most alternators in 12V systems produce between 13.5 and 14.5V with the engine running.
This is enough to provide a steady 12V to car electronics and fully charge a Lead Acid battery.
The ideal float voltage for a lead-acid battery is around 13.6V. When the battery consistently sits at the level, a smart alternator or charging system should reduce the current it sends to the battery or produce to avoid overcharging.
If it doesn’t drop the current, it will cram more into the battery forcing its Voltage to go up hence the spike beyond the ideal 14.5V max.
ProTip: Different cars have different voltage ranges. Consult your user manual to find out the ideal figures and maximum Voltage the alternator should produce when working perfectly.
Signs that Your Alternator is Overcharging the Battery
Even though modern vehicles have regulators to protect your electronics and battery from a rogue alternator, overcharging can still happen. If it goes unattended, it could damage the regulators and take out other electronics in your vehicles.
High Voltage Reading on Your Dash Voltmeter
Some older cars had dedicated voltmeters that actively monitored your electronic system’s voltages. They were a great way to tell the status of your electric system at a glance.
If you have one, your alternator will be overcharging if the Voltage constantly sits above 14.5V (or the maximum specified for your vehicle.)
Check Engine Light With Charging System Error Code
Many modern vehicles skip the voltmeter and opt to monitor voltages via the ECU. They will only notify you if a problem arises.
The ECU actively monitors and regulates how much power the alternator produces especially a smart alternator. This ensures that the alternator doesn’t unnecessarily load the engine to produce power that isn’t otherwise needed.
If the ECU constantly detects high charging voltage that it can’t regulate, it will throw the Charging System Voltage High P2504 error code.
While the error code mostly hints at an overcharging alternator, it could also mean:
- You have a bad voltage regulator
- The battery wiring is faulty
- You have corroded or dirty battery terminals
- Your battery is worn out and can’t hold charge
You will need an OBDII diagnostic tool to read the error codes. Some cars have a dedicated battery light that will pop up when you have battery charging system problems. The error code will help you narrow down the problem.
Blown Bulbs (and Sometimes Fuses)
The fuses, bulbs, and other electronics running straight from the 12V system without a power regulator take the full grunt of the power from your electric system.
For instance, the bulbs will dim when cranking the car or if your system voltage is low.
They will glow brighter when the Voltage goes up. If the Voltage keeps going up, they will eventually draw more power than they can handle and blow.
Bulbs get more power with higher Voltage because while their resistivity is fixed, they have no way to clamp the voltage across them.
Since Power = Voltage x Current, and their fixed resistivity keeps their current draw almost Constance, an increase in Voltage will lead to more power hence brighter bulbs.
While high Voltage shouldn’t damage fuses unless it spikes beyond the fuses’ maximum voltage rating, the damaged bulbs or electronics could cause a current spike that will damage the fuses.
Your Battery is Losing Electrolyte
When a battery overcharges, the electrolyte bubbles as it converts into hydrogen gas and other constituents.
Lead batteries have vent holes to get rid of a small amount of the gas. However, since the hydrogen is part of the electrolyte, every amount that escapes or gets trapped as gas means your electrolyte levels are dropping.
When the electrolyte drops and can no longer cover the lead plates or lattices, your battery’s capacity drops. Sulphation will be more rampant, and the battery will deteriorate quickly, forcing you to replace it.
A Bloated or Leaking Battery
If the hydrogen generated during overcharging can’t escape through provided vents, the battery will become pressurized and start swelling.
This is common in AGM, and other maintenance freed battery designs. If the pressure builds beyond what the battery structure can support, a leak will develop somewhere in the system cause more of your electrolyte to escape. Eventually, the battery will be damaged. No reconditioning will fix it and you will need a replacement.
Your Replacement Batteries Keep Failing Fast
All these damaging impacts of overcharging take a toll on your car’s battery. You will have to replace batteries more often. Even if your batteries aren’t bloating or leaking, the hydrogenation impact of overcharging is definitely there.
Your battery will no longer hold a charge for a couple of days (or overnight), leaving you stranded more often.
Why Is My Car’s Alternator Overcharging?
A couple of things could make your vehicle’s charging system pass more power than it should to the battery. Here are the top reasons why your system could be overcharging.
A Wrong or Damaged Battery
A car’s battery does more than give you cranking power and juice for electronics with the engine off.
It is a power-soaking device that helps even out the power fluctuations in the system since alternators can’t ramp up or down production in an instant.
If the battery is too small or damaged to the extent that it can’t take up the spikes and dips, then your charging system will fluctuate between low and high status too often.
Modern cars actively monitor how much current the battery is taking in. They then use this information to regulate how much the alternator produces.
A damaged battery can accept current inrush creating unexpected voltage runaway. Since the battery can’t deal with these brief surges, they will translate to overcharging that will also show in your vehicle’s electric system.
The Wrong Alternator Size or Output
Aftermarket replacement alternators rarely have the exact specifications as the stock alternator. While an alternator with an internal regulator could fit in perfectly, problems arise if your ECU is the one that controls the alternator.
The unexpected specifications will cause incompatibilities that will result in overcharging as the alternator produces more than it should or undercharging when the alternator can’t keep up.
Disclaimer: Alternator output is only a problem if it creates a voltage higher than your system’s nominal. The amperage shouldn’t bother you. The lead-acid battery will actually charge slightly faster. Getting a bigger battery with more reserve capacity can help you capitalize on this.
Check this too: How To Test An Alternator Diode
Using the Wrong Pulley on the Alternator
Another common problem with alternator repairs or replacement is throwing in something with a smaller pulley than expected. A smaller pulley will always keep the alternator rotating faster than expected.
More RPM means more power than translates to more Amps or more Voltage than your car can handle.
ProTip: Only do an alternator upgrade if the electricity requirements of your vehicles go up to match the extra production. Upgrades are common in camper settings with a house battery or a car with a powerful aftermarket sound system.
A Damaged Voltage Regulator
Since it is hard to keep an alternator spinning at a constant RPM as it relies on engine RPM, voltage regulators are used to ironing out any spikes in the system.
It could be an internal regulator or an external regulator.
Either way, a voltage regulator ensures that the alternator never sends out Voltage beyond the acceptable system limit. This could be anywhere between 13.6V and 14.5V, depending on your vehicle’s specifications.
If the regulator is damaged or shorted out, your electric system will receive all the spikes. You could get anything to the north of 16V from the alternator without a voltage regulator.
Sustained high voltages will definitely overcharge your battery and even damage some of your electronic components.
ProTip: Modern vehicles with intelligent alternators and multiple sensors have a lot of power conditioners and regulators. Changes in voltage levels could damage expensive car computers, and manufacturers don’t want that to happen.
A Damaged Charge Control System
Instead of connecting the battery straight to the alternator, newer alternators send their power to the battery through an intelligent charge controller.
The system regulates how much Voltage goes into the battery depending on temperature, charge level, and other factors. Overcharging a battery on such a system is impossible as the regulator sends just as much Voltage as the battery needs to top up.
However, if the charge controller is damaged, it could remain open or send the wrong voltage feedback, causing the battery to overcharge.
Can I Drive With an Overcharing Alternator?
Technically yes. Most modern vehicles have a couple of safety features to ensure that alternator voltage spikes don’t harm the electronics right away.
While such circuits will keep your car moving until you get it fixed, it could have long-term repercussions other than just ruining your battery.
Have your charging system checked and fixed as soon as you see the error codes or notice any of the overcharging signs and symptoms.
Can a Bad Battery Cause an Alternator to Overcharge?
A bad battery with one or more compromised cells will definitely overcharge. A normal charging voltage can’t be attained. The alternator will keep pushing the battery but will instead overcharge the remaining cells.
What Stops an Alternator From Overcharging
Alternators don’t overcharge your battery because of the voltage regulator. It could be the regulator in the alternator or another smart one that works as a charge controller. If it goes bad, it will let the voltage spike above the acceptable nominal Voltage.