Do Dual 220 Amp Alternators Lessen Fuel Economy?

[Goose55]

From what I’ve been told, every 25 amps consumes 1 hp. The extra 220 amps is like running a 9 hp motor wide open the whole time you’re driving. If you don’t need it, don’t order it on the truck.

This is the common sense I've been looking for in this thread. Thanks!

 

[lpennock]

Good common sense there. I am ordering the truck with the 2nd owner in mind. They might want to haul a 5th wheel, so I got the 5th wheel prep package. But with the standard output CTD, and the 68RFE, it couldn't be a giant 5th wheel with full a/c, so just one alt should do for them. They guess they could also add the 2nd afterwards. The order is being confirmed later this morning and I will delete the dual alts. Thanks!

Second ALT wouldn't help with a 5er unless they added new wiring. The stock 7way connector wiring is too small to pull more than about 7amps before the voltage drop is to much to charge a Lead Acid battery. On my 18 with the truck running with 14.0 volts at the battery the 7 way was only able to pull 7.5 amps before the voltage was down to 10.5v. Unless you run a dedicated 2ga or larger wire to the 5er or truck camper you aren't going to be able to use any of the extra capacity a second alternator would give.

FYI I ran dedicated parallel 10Ga to my in bed 7way to allow my truck camper to charge the LiFEPo4 batteries at 13V and 20+ amps. Parallel 10ga is the same current capacity/Voltage drop as a single 8ga.

Bottom line is unless you have heavy wiring directly to the battery a second alt is a waste of money.

 

[leroys73]

I am sure it could be measured.
If buying a 2500 or 3500 don't worry about the drain of an extra alternator. Your foot and load will make the biggest difference.
I own a 2500 with them, not because I need them but because there was that option, they are there if I need them, and I wanted all the options available on my Longhorn except sunroof. First new truck or car that is mine in 50 years and it may be my last.

 

[Deeuubee]

Unless you are actually drawing the additional amperage from the second alternator, there is no practical additional load on the engine. Just minor additional pulley friction. If your load requirements don't require the additional alternator, don't waste your money. If you have a Limited or Laramie Longhorn blasting all four heated seats, steering wheel heat, high wattage light bars, snow plow all while listening to your 5000 Watt stereo, then maybe

 

[Choupique]

No, the alternators won't directly affect anything. The total amperage on the system will be the same for a given set of accessories and therefor the engine load will be the same. If you use the capability of the dual alternators by adding 400 amps of electrical stuff that you're going to use all the time than you might make enough load to measure it in fuel consumption, but it would take a lot of use for that to happen.

 

[TorqueWagon]

Totally agree with Deeuubee and Choupique above. The extra load of dual alternators (with ordinary/little-to-no load on them) is negligible. The more current they put out, the more load on the engine. The worst mileage case would be if you ran so many accessories at once that the alternators were at their highest load, 200-ish amps ( times 2), ALL the time. I am wondering what your use case is. Are you really running 440 amps of accessories for any significant percentage of the time the truck is running? I did some quick calculations and while at max electrical load it'd be around 10-12hp even considering the inefficiency of the alternators.

 

[BossHogg]

I am ordering the truck with the 2nd owner in mind. They might want to haul a 5th wheel, so I got the 5th wheel prep package. But with the standard output CTD, and the 68RFE, it couldn't be a giant 5th wheel with full a/c, so just one alt should do for them. They guess they could also add the 2nd afterwards. The order is being confirmed later this morning and I will delete the dual alts. Thanks!

5th wheel prep package is good.

So is the optional rear air suspension system.

A dually is over the top for most fivers and makes a horrible vehicle for parking at sightseeing venues, the big-hipped gal is hard to find parking for.

Dual alternators, wow, that is over 5,200 watts of power. Did you know that most over-the-road truckers run a 180-amp alternator?

If you are going to order for the next owner and are set on a dually, then add the HO Cummins, rear air suspension, and Longhorn trim. Please let me know when you are ready to sell.

 

[Goose55]

5th wheel prep package is good.

So is the optional rear air suspension system.

A dually is over the top for most fivers and makes a horrible vehicle for parking at sightseeing venues, the big-hipped gal is hard to find parking for.

Dual alternators, wow, that is over 5,200 watts of power. Did you know that most over-the-road truckers run a 180-amp alternator?

If you are going to order for the next owner and are set on a dually, then add the HO Cummins, rear air suspension, and Longhorn trim. Please let me know when you are ready to sell.

The 2023 I factory ordered is a Flame Red 4WD 8 Foot Box 3500 DRW, Longhorn SO CTD, w/ Towing Tech Group, 50 gal Tank, rear air suspension, 5th Wheel prep, Cold Weather Group, Safety Group, Black & Cattle Brown Interior...

 

[Docwagon1776]

From what I’ve been told, every 25 amps consumes 1 hp. The extra 220 amps is like running a 9 hp motor wide open the whole time you’re driving. If you don’t need it, don’t order it on the truck.

Except the alternator isn't actually making 220 amps the whole time you are driving unless you have a huge electrical load. If there's no demand, it's not under load.

The dual alternator will affect gas milage regardless, because physics is a thing and any extra parasitic loss sucks up more energy...but generally it's in the same proportion as dropping a cup of water in a bathtub raises the water level. Technically true, largely irrelevant.

 

[BossHogg]

The 2023 I factory ordered is a Flame Red 4WD 8 Foot Box 3500 DRW, Longhorn SO CTD, w/ Towing Tech Group, 50 gal Tank, rear air suspension, 5th Wheel prep, Cold Weather Group, Safety Group, Black & Cattle Brown Interior...

View attachment 517469

Simply STUNNING but the picture is of a 1500 interior. The newer Gen 5 interiors have only in part made it to the HD line or did they for the 2023s? The biggest giveaway is the steering wheel controls. None the less, stunning.