Picture this, you’ve invested in a new car audio amplifier. You want to know if your car’s stock alternator can keep up with the amp’s power demands.
How do you then decide on whether the alternator has enough capacity to power both the amp and the rest of the car’s accessories?
Is there a general guide to selecting an alternator rating based on an amplifier’s power output?
This post provides some guidelines that can help you work out whether your car’s alternator has enough capacity to power an amplifier, and provides a framework to help you work out what sizes of alternators to consider for a 1,000, 2000, or 3,000-watt amplifier.
Will my Car’s Alternator Handle an Amplifier’s Power Draw?
This really depends on how much of the alternator’s capacity is still available when the car accessories are switched on (aftermarket accessories may have been added) and the amplifier’s power draw.
There are several variables at play and it is therefore difficult to provide a straight-out answer without knowing, for example, the amplifier’s power draw, efficiency, battery, or alternator amperage. Refer to the example below for a 1,000 watt amp.
Worked Example: Can a 110 amp Alternator Handle a 1,000 watt Amplifier’s Current Draw?
To determine this:
STEP 1: Determine how much of the rated alternator capacity is still available with the accessories switched on.
You can do this by taking actual current measurements. With the car engine running, switch ON each of the main car accessories- headlamps, blower fan, heater, and cigarette lighter loads in turn while measuring their current draw (amps) using a multimeter connected in series with the ground terminal of the battery.
Add up all the current draws from the accessories to get an estimate of the current draw by all the connected accessories.
For example, if the power draw by the various accessories is as follows:
- a pair of headlamps, 20 amps
- defrost heater, 10 amps
- cigarette lighter socket, 10 amps
- blower fan, 10 amps
The combined current draw by these appliances is 50 amps.
Assuming the alternator is rated 110 amps, with a current draw from the accessories of 50 amps, the available current supply available is 110-50= 60 amps.
This is a more accurate method than assuming that the connected accessories draw a percentage, say 60% of the alternator’s output as this will likely not factor in aftermarket accessories that you may have added to the car’s electrical system.
STEP 2. Next, work out the estimated current drawn by the amplifier and the rated sound system.
Assume that the 1,000 watt amplifier is working at full power and has an efficiency of 80%, the actual power consumption of the inverter is 1000/80% = 1,250 watts.
To get the current draw, assume the alternator voltage if 13.5 V, current draw = total amplifier output/ alternator votlatge = 1,250/13.5 = 92 amps.
Based on the calculation, at full power, the alternator does not have enough power (recall only 60 amps is available!) to run the amplifier and will rely on the available battery power to make up for the deficit.
Note, in practice though, the amplifier may not be run at full power, and probably not all the accessories may be connected and so you may be able to the 1,000-watt amp off the alternator provided the overall power draw is within what the alternator can handle.
To be on the safe side, you can consider upgrading the alternator to a higher amperage one, say a 200 amp alternator.
How Many Watts from a Car Alternator Handle?
The power output of an alternator depends on its rated current and voltage. To work out the power output of an alternator, multiply it rated current output x the voltage.
Taking a 110 amp alternator as an example, its power output is about 110 amps x 13 V = 1,430 watts.
You should avoid running the alternator at maximum power as it will likely overheat and can fail prematurely. I’d aim for 60-70% of its rated power output maximum, i.e about 1,000 watts or about 74 amps at 13.5V.
What Size of Alternator for a 2,000 or 3,000 watt Car Audio Amplifier?
You’ll need an alternator capable of supplying at least 192 amps and 288 amps for the 2,000 and 3,000-watt amplifier respectively plus the additional power draw by the connected accessories assuming that the amplifiers are operating at peak power.
In practice, they may not be operated at maximum power and fewer accessories may be connected at any one time lowering the overall electrical load and enabling you to use a lower rated alternator.
Can an Audio amp with a High-Rated Current Draw Damage an Alternator?
It depends on the actual current draw of the sound system. There might not be a negative effect on the battery, alternator, or sound quality if the amp is being run at a power output that still works out within what the alternator can handle.
If on the other hand the current draw from the amplifier exceeds that the alternator can supply then:
- The battery will not be charged and will be drained over time as the additional power to meet the amplifier requirements is drawn from the battery.
- In some cases, the alternator may be damaged as a result of being overworked and overheating in the process.
- If the battery voltage is low, at high power levels, the amplifier can draw larger currents than it is rated for to make up for the drop in voltage which can damage the amplifier components.
Closing Thoughts
Unfortunately, there is no straight answer for what capacity of alternator to use for a particular audio amplifier.
Sizing an alternator to power your audio amplifier requires that you take into consideration the amplifier’s power output, efficiency, battery, or alternator amperage.
Workout the current draw of the amplifier and add to it the expected current draw of the connected accessories to be able to determine what capacity of the alternator (amps) to use.
