alternator problems
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
15.48? That's pretty high but maybe in the ballpark depending on state of charge and, temperature especially. Is it zero degrees F where you're at? And does it come back down in a few minutes? You want to see it hold 14.5ish and not start to sag too much under load.
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Cross-Country
Joined: Jun 2012
Posts: 85
Likes: 0
hey guys the temp was around 27 f it wont die with the terminals on the battery,,,,now it seems to be doing fine i ccleaned the terminals on the starter seloinoid they were very rusted i worked it all day today and it never failed to start ill check the voltage again tomorow and let you know whats going on...
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
It's important that there are no high resistance connectors or grounds in the charging system, the regulator will "see" that extra resistance as a battery that needs charging even when it's charged.
The proper charging voltage is dependent on temperature, load, battery state of charge, RPM, etc. it can be as high as 16 volts. Usually though, about two volts above the base voltage at 70F, is what you're going to see. A fully charged "maintenance free" battery is 12.8 volts, etc; you need to make sure the battery is accepting the charge and the charge voltage is correct for the temp and load.
It sounds like you have the "charging dead battery" part under control. This is very hard on alternators and can kill them. Always charge up the battery overnight on an outboard charger before spooling up a new alternator. It's important to not force an alternator to charge up a dead one if it can be helped. Test alternator output at idle, 1500 RPM, and then again with headlights and heater on and whatever else, also at idle and 1500 RPM. it will sag but should still be around 14 volts depending.
http://www.aa1car.com/library/charging_checks.htm
The proper charging voltage is dependent on temperature, load, battery state of charge, RPM, etc. it can be as high as 16 volts. Usually though, about two volts above the base voltage at 70F, is what you're going to see. A fully charged "maintenance free" battery is 12.8 volts, etc; you need to make sure the battery is accepting the charge and the charge voltage is correct for the temp and load.
It sounds like you have the "charging dead battery" part under control. This is very hard on alternators and can kill them. Always charge up the battery overnight on an outboard charger before spooling up a new alternator. It's important to not force an alternator to charge up a dead one if it can be helped. Test alternator output at idle, 1500 RPM, and then again with headlights and heater on and whatever else, also at idle and 1500 RPM. it will sag but should still be around 14 volts depending.
http://www.aa1car.com/library/charging_checks.htm
pedant
Joined: Jan 2008
Posts: 23,576
Likes: 40
From: EXTREME southwest CT
Seems to me if he is putting out 15 1/2V but doesn't produce enough amperage to keep the ignition and lights alive at the same time there is a problem with that alternator or a MAJOR load unaccounted for.
Lights and ignition should only be about 20A.
Lights and ignition should only be about 20A.
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Cross-Country
Joined: Jun 2012
Posts: 85
Likes: 0
Sorry about not ritin good words I never had the skoolin for dat.....Lol...Ok...I'll try again...when I said the headlight kills the engine I mean without the terminals on..I thought if the truck ran with the hot terminal off it meant it was charging that was just my way of checking the alt...which now I know is bad.......the truck is starting fine now but I haven't checked the voltage again I will in a few hours...I cleaned all the terminals and connectors and its staying charged now but maybe over charging???I'll post what numbers I find today...thanks guys for all the info it has been very helpful......
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Cross-Country
Joined: Jun 2012
Posts: 85
Likes: 0
Ok guy I checked today truck off it had 13.48''''''running it had 14. 48''''how much voltage should be in the battery after its turned off
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Sounds about right. There is a link above that will walk you through alternator testing. It's comprehensive. Did you use it?
A battery that's just been charged has a "surface charge" that is a little higher than the base voltage. That's what you are seeing.
A battery that's just been charged has a "surface charge" that is a little higher than the base voltage. That's what you are seeing.
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