Electrical question - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

Fairlane Boy · 06-02-2002, 05:08

How do you tell if your alternator is shagged or your battery?

my "other" car just wont even try turning over by the power of its own battery, it needs jumping everytime now.

at idle the voltage is @ 12.5 but at about 100rpms higher than idle or more its up at 13.5-14V at the battery.

the alternator is 31 years old and is OEM, never rebuilt.

lsd0 · 06-02-2002, 05:19

Your alternator must be working O.K. if you have about 14 volts output. Looks like you need a new battery.

Fairlane Boy · 06-02-2002, 05:24

thanks

svo347 · 06-02-2002, 22:19

I think you'll find it should be around 14v at any RPM... Try turning your headlights on 7 see if its still 14v If its not its cactus mate as it should still pump out 14v+ under any load..
Cheers

dcstraight · 06-03-2002, 00:46

Quote:

Originally posted by svo302
I think you'll find it should be around 14v at any RPM... Try turning your headlights on 7 see if its still 14v If its not its cactus mate as it should still pump out 14v+ under any load..
Cheers

All things being equal - yeah it should pump out 14V, unless you've got an audio system which can also cause voltage drops. Either way, it sounds damn old - might perhaps pay to have it rewound, if you have further problems. If it is a battery, and you don't mind spending a bit (and if you're pedantic like me) look at a dry cell like an Optima yellow top or Odysey (SP?). Anywho, just my 2c.

Cheers,
Steve

Fairlane Boy · 06-03-2002, 03:50

Quote:

Originally posted by dcstraight

All things being equal - yeah it should pump out 14V, unless you've got an audio system which can also cause voltage drops. Either way, it sounds damn old - might perhaps pay to have it rewound, if you have further problems. If it is a battery, and you don't mind spending a bit (and if you're pedantic like me) look at a dry cell like an Optima yellow top or Odysey (SP?). Anywho, just my 2c.

Cheers,
Steve

the engines running like shyte at the moment, idling so slow its barley even running. it gets to 14v when its at the speed its ment to be idling at. Its not going anywhere till its got its new floor, new paint & new leather. I wonder how to rebuild a twin carby setup.....

LTD4Me · 06-03-2002, 15:12

Alternators need the motor to be running at about 1000 RPM for their maximum (best & efficiet) output, & it shouyld be around the 14V mark (13.8V is optimal). It sounds like your alternator is working fine.

To check the battery, put it on a charger over night. Then check each cell with an acid level meter (I don't know it's correct name. Its a glass tube with a float inside it with a rubber bulb on the top). Each cell of the bettery should come up to the same float level, ideally in the green band on the float.

svo347 · 06-03-2002, 17:22

Hydrometer... measures the specific gravity of each cell