Quick Alternator size question
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Postmaster
Joined: Oct 2005
Posts: 3,083
Likes: 4
From: Victoria , BC
Quick Alternator size question
What's the amp rating on a 79 f250 camper special 4x4 with a 400?
It's a much larger casing than a stock Fe motor I'm used to. Tested it tonite and it puts out 14.5-14.9 volts which seems real strong. Do the camper specials have larger outputs. Parts store said a stock replacement is only a 70 amp. It's a dual battery setup as well.
It's a much larger casing than a stock Fe motor I'm used to. Tested it tonite and it puts out 14.5-14.9 volts which seems real strong. Do the camper specials have larger outputs. Parts store said a stock replacement is only a 70 amp. It's a dual battery setup as well.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
If you were looking at the voltage with the motor idling and no heavy electrical loads in place, then the voltage you're seeing is really a function of the regulator, not the alternator output strength. The alternator will output whatever the regulator tells it to, as best it can. In other words, the voltage you measure is not a direct representation of the alternator's output if there are no loads in place.
The true test is how well an alternator can meet the regulator's demand under heavy load, for example idling in gear with accessories like the heater and windsheild wipers engaged. The stronger the alternator, the higher voltage it can maintain for a given field current, which is controlled by the regulator.
In other words, it's not like a "strong" alternator will put out almost 15 volts, and a "weak" alternator will put out closer to 13 for a given load condition. They should both put out exactly the same voltage for a given load condition. The difference lies in how well the alternator can maintain the desired voltage as the load increases, and the regulator increases the field current accordingly. A "strong" alternator will be able to maintain the voltage at the regulator's request, while a "weaker" alternator will output as much as it can, which may or may not be enough.
The true test is how well an alternator can meet the regulator's demand under heavy load, for example idling in gear with accessories like the heater and windsheild wipers engaged. The stronger the alternator, the higher voltage it can maintain for a given field current, which is controlled by the regulator.
In other words, it's not like a "strong" alternator will put out almost 15 volts, and a "weak" alternator will put out closer to 13 for a given load condition. They should both put out exactly the same voltage for a given load condition. The difference lies in how well the alternator can maintain the desired voltage as the load increases, and the regulator increases the field current accordingly. A "strong" alternator will be able to maintain the voltage at the regulator's request, while a "weaker" alternator will output as much as it can, which may or may not be enough.
Thread Starter
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Postmaster
Joined: Oct 2005
Posts: 3,083
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From: Victoria , BC
Yeah I understand a higher voltage doesn't mean it's better.
I have a custom built 160 amp alternator in my big truck that was made to do 100 Amps at idle for my electric fan running and while winching and maybe extra lights at night. It always seems to be at just at 14 volts all the time which my electrical shop said is normal.
Basically just curious whats the stock size of this alternator if someone knows don't really need a tech thread I guess.
Thanks for response though
I have a custom built 160 amp alternator in my big truck that was made to do 100 Amps at idle for my electric fan running and while winching and maybe extra lights at night. It always seems to be at just at 14 volts all the time which my electrical shop said is normal.
Basically just curious whats the stock size of this alternator if someone knows don't really need a tech thread I guess.
Thanks for response though
