Charging system question
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Joined: Jul 2009
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Charging system question
I'm looking for the alternator output specs for a 1999 F-250 Super Duty with the 6.8L engine. I'm pulling a 12,000# fifth wheel camper and am wondering what the OEM amp output of the alternator is supposed to be, what is the best way to test the alternators present capability,
and what is the best way to check the amp draw. I have a clamp type amp meter that can measure DC amps if that helps.
Thanks
and what is the best way to check the amp draw. I have a clamp type amp meter that can measure DC amps if that helps.
Thanks
Cargo Master
Joined: Apr 2007
Posts: 2,659
Likes: 2
The process that most OEM's use is to make sure the alternator charges the batteries 99% of the time. This basically means all the time with the exception of intermittent loads such as windows, seats, etc...
You are interested to measure the difference between alternator output current and all current going in/out of batteries. As long as the alternator can cover electrical loads at idle with the trailer hooked up, lights on, A/C blasting, and any other accessories you use for long periods then the alternator is sized properly. Alternator output will improve when the engine speeds up so you will charge batteries well when driving. SAE specifications recommend 10A charging capacity per parallel set of batteries.
You are interested to measure the difference between alternator output current and all current going in/out of batteries. As long as the alternator can cover electrical loads at idle with the trailer hooked up, lights on, A/C blasting, and any other accessories you use for long periods then the alternator is sized properly. Alternator output will improve when the engine speeds up so you will charge batteries well when driving. SAE specifications recommend 10A charging capacity per parallel set of batteries.
Post Fiend
Joined: May 2006
Posts: 10,007
Likes: 4
From: Central Florida
Here's what I've learned about them. OE's give you about 10% headspace, meaning if the stock alt can produce 130amps, the truck needs ~117A with most of the accessories running. This gives you ~13A to recharge the battery under the worst conditions (lights, heaters, AC compressor, wipers, ect running.) It also means if you go much over 13A, you run a good chance of not charging or draining the battery if you have all of those accessories on and additional (aftermarket) 13A loads.
The OE spec's I found were 130A, but all of the remans I could put my hands on at the time were only 110A. For measuring output, you have two options, you can use your inductive clamp or put in a shunt on the charge wire and watch the voltage drop across it. Shunts for 150A are expensive to buy, and probably dangerous (to your alt and possibly yourself) to home build if you don't know what your doing.
Also, Welcome.
The OE spec's I found were 130A, but all of the remans I could put my hands on at the time were only 110A. For measuring output, you have two options, you can use your inductive clamp or put in a shunt on the charge wire and watch the voltage drop across it. Shunts for 150A are expensive to buy, and probably dangerous (to your alt and possibly yourself) to home build if you don't know what your doing.
Also, Welcome.
