Truck alternators

The need for extra alternator output comes with people who run snow plows that have extra lights to run as well as power the electric over hydraulic lift for the plow. Overlanders use the extra alternator output to run electric air compressors, winches, and other electrical accessories. The thing to remember is that the battery in the car is a power reservoir used to start the car not run other electronics. The alternator is what runs the electrical components in any vehicle, and top of the battery after it has been used to start the engine. When you start running aftermarket accessories you can easily use all the alternator’s capacity and drain the battery, hence the need for an alternator with a larger output.

Another need for high amp is electric cabin heater some vehicles have.
In my Ford Truck the option forced me to get dual alternators.
In my Sprinter van I have single 250 amp alternator.
I still remember older diesel pusher with 60 amp alternators doing just fine.

Also, some trucks have an optional built in inverter to power a 120 volt a/c power outlet. I would assume that option would require the higher amp alternators.

Well said bwlyon. Very accurate response.

“Also, some trucks have an optional built in inverter to power a 120 volt a/c power outlet.“

Two are standard on my new Silverado LTZ, Optomistic.

At first glance the concept of replacing the OEM alternator with a large, high output unit would seem like a good idea...........at first, at least with my particular truck. I have added a large (17,500#) winch and did a lot of research on the topic. As it turns out, if you own a 7.3L PSD, adding a high output alternator could actually shorten the life of your glow plugs which are designed for 11 volts. You can do a search as there has been a lot written on the subject. Secondly, most of the manufacturers who make or sell the h.o. alternators recommend upgrading to larger cable from the alternator to the battery(s). As it turns out, with my diesel having dual batteries, I simply set my tuner to high idle (which also gives you more amps as output is based on rpm’s) rather than idle and have not had an issue with enough reserve power to run the winch at it’s rated duty cycle. Same thing with my inverter for camping- I simply set the tune to high idle if I’m running a heavy load. Obviously, everyone has a different rig / motor, but there’s more to consider when significantly increasing amperage output well over the manufactures specs. Good Luck!

To the OP, I see and understand your original post was “options from the manufacturer” which in that case, engineering has been done. But there are an awful lot of people throwing h.o. alternators on older trucks—- I guess my comments are just precautionary for those thinking about aftermarket products :)

mt-ed wrote:
Can anyone please explain to me why a truck owner might want, or have the need, for an alternator that has these higher outputs? I'm assuming there is some need for it, but exactly what might these needs be?

Higher output = more charging amperage.

There's also trucks with DUAL alternators, which my truck has

Per my experience no winches and no inverters will run on alternator power alone.
They have high spikes and when alternator helps in recharging the battery, the power for high draw device has to come from battery.
Heck even my camper jacks will not operate on alternator. That's due the 30 amp charging wire, but still I need battery in camper to raise or lower 4 jacks.
Bottom line, it takes some calculation to make right call.
I was using 1500 W inverter for oven power -with single battery on my boat having 30 amp alternator. But boat did not have any other power draw, so the 30 amp was used for recharging in 99% and boat run at high rpm most of the trip.
Now if you have battery bank to power your AC and want to recharge it in 20 minutes, you need 200 amp alternator.
Actually I am thinking about doing such setup on my Sprinter.
120V AC on the roof, 2 house batteries with 1800 W inverter and the van 250 A alternator should keep the system running.
The 4-cylinder diesel in van probably sips less fuel than most RV generators.

Get the optional large or dual alternator if you are an outfitter building ambulances, tow trucks, Fire or police support vehicles, or some other commercial application.

Put 200 watts solar on your truck camper and any base OEM alternator is fine.