Question: If I install a high amp alternator to power a bunch of new audio gear, can it damage the rest of the electrical system?
Right now, all the audio gear in my car is stock, and it doesn’t sound very good. I’m in the process of drawing up plans for a complete overhaul, and when I crunch the numbers it seems like I’m going to need to hang a high amp alternator in place of the OEM one. If I slap on an alternator that’s capable of cranking out like 300 amps, is that going to fry the rest of the electrical system? I’m really excited to get all this great new audio gear installed, but I don’t want to take the chance of smoking everything else.
The good news is that no, replacing a factory alternator with a high output alternator, in and of itself, isn’t going to damage the rest of the electronics in your car. I’m not sure that you’re going to be able to find a high amp alternator that’s both capable of putting out 300A and fitting in your engine compartment (unless you’re driving something pretty big), but even if you can, you can rest easy that it won’t damage your electrical system.
There are a few modifications that you’ll want to make if you’re installing a high amp alternator that's really that big, but they’re more to prevent power and ground cables from burning up than to protect the sort of delicate electronics that keep your car going.
High Amp Alternator Supply and Demand
If you’re worried about a high amp alternator providing “too much” power to your ECU, or any other component in your electrical system, you don’t need to. The way that current works is that any given electrical component will only draw as much amperage as it needs to operate. So while a powerful amplifier might suck up 150A, you don’t need to worry about that same 150A going to your headlights and blowing them out.
Since amperage is a function of wattage divided by volts, it essentially works based on supply and demand—the alternator only supplies as much amperage as each component demands. The alternator generates enough amperage to meet the needs of the combined electrical system at any given time, and then each component draws its share.
In order to determine how much amperage a component is going to draw, you can divide its wattage by the voltage of the system. So your 50 watt headlamps are only going to pull maybe 4A (50W / 13.5V), even if your big amp is drawing many times more than that.
Necessary High Amp Alternator Electrical System Modifications
Although the individual electronic components in your car won’t be damaged by a big alternator, there are two things that might be: the alternator power lead and the ground strap (or straps.) Since a high amp alternator will be putting out a lot more juice than the factory unit, and your power and ground cables were chosen with the OEM unit in mind, these cables might not be big enough.
When you install a high amp alternator (or when you have someone else install it), you should consider replacing both the ground straps and the power cable that runs from the alternator to the battery with heavier gauge cables. Although it is possible to calculate roughly the right size based on the maximum amperage you’ll be dealing with, a good rule of thumb is to just go with the thickest gauge that will work in the application.
You can’t really go too big in this case, and the thicker the cables, the better off you’ll be—especially if you do go with that monster of a 300A alternator.