Charging
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Laughing Gas
Joined: May 2007
Posts: 1,100
Likes: 0
From: Davis, Ca.
Charging
Battery light came on today, I figured were in need of replacement so I got new ones. Light is still on, until I reach about 1800 rpm. It goes out until truck idles down. Can an alternator do this? I always thought when they went, they went.
Token Redneck
Joined: Jun 2007
Posts: 9,339
Likes: 350
From: Breckenridge, TX
If voltage is dropping (that's what the light means) then alternator output can't meet demand until the alternator spins up. You probably need a new alternator, but there could be other problems.
Watch voltage across a battery with a DVM at idle, then have someone slowly idle the truck up until the light goes off and see what the reading does. Pull the alt and get it bench tested at a parts store. While it's out check and clean all your battery cable connections, especially the lower ends of the grounds on the frame.
Any belt squeal? If the belt is old or the tenionser is weak, the belt could be slipping on the alt. That should have the exact opposite symptoms of this situation because the belt drive is going the slowest at idle, but might as well cover that base anyways.
My alt died somewhat slowly. Over about a month it went from 13.2Vs to 12.8Vs consistently while running. I replaced it before it completely went out. When the alt in our other '07 went it died pretty darn suddenly. I guess it's a matter of if it's the brushes, the diodes, or what component in the alt is going out.
Watch voltage across a battery with a DVM at idle, then have someone slowly idle the truck up until the light goes off and see what the reading does. Pull the alt and get it bench tested at a parts store. While it's out check and clean all your battery cable connections, especially the lower ends of the grounds on the frame.
Any belt squeal? If the belt is old or the tenionser is weak, the belt could be slipping on the alt. That should have the exact opposite symptoms of this situation because the belt drive is going the slowest at idle, but might as well cover that base anyways.
My alt died somewhat slowly. Over about a month it went from 13.2Vs to 12.8Vs consistently while running. I replaced it before it completely went out. When the alt in our other '07 went it died pretty darn suddenly. I guess it's a matter of if it's the brushes, the diodes, or what component in the alt is going out.
Elder User
Joined: Dec 2004
Posts: 819
Likes: 3
From: Putnam Valley, New York
Light on
New what ??? Batteries, Alternators (some trucks have 2 of both) ??? When the battery(alternator) light comes on, it usually indicates that the alternator is not charging properly. Sounds like you need a new alternator.
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Laughing Gas
Joined: May 2007
Posts: 1,100
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From: Davis, Ca.
There is no belt squeal. The batteries are 9 year old Optimas. I replaced those though. I've had the old ones on a trickle charger but they got to where they seemed weak even with that. Then today the light came on but as I stated before goes out out with higher rpm. Same thing with new batteries installed.
Elder User
Joined: Dec 2004
Posts: 819
Likes: 3
From: Putnam Valley, New York
It sounds like your alternator bit the dust, possibly from trying to fully charge those 9 year old batteries. People don't realize it, but when your battery starts to go downhill, the alternator sees it as an undercharged battery and it then tries to charge it, and charge it, and charge it, until it charges itself to death.
Lead Driver
Joined: May 2003
Posts: 9,303
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From: Lyndonville, Vermont
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Laughing Gas
Joined: May 2007
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From: Davis, Ca.
Rongold, I was concerned about that but I was being cheap. I don't drive it much anymore, about 9k in 4years
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Postmaster
Joined: Jul 2015
Posts: 4,392
Likes: 22
From: very South Texas
YES, alternator killed itself .. trying to Charge BAD batteries...
future.. have batteries LOAD tested every year... do not need to remove them..
but get a 100 amp load test.. most auto parts stores do this for FREE.
if you do not Drive it much.. keep a maintainer type of charger on them... "Battery Tender" is one.
NOT a battery charger... they will over charge, dry out a battery and kill it.
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future.. have batteries LOAD tested every year... do not need to remove them..
but get a 100 amp load test.. most auto parts stores do this for FREE.
if you do not Drive it much.. keep a maintainer type of charger on them... "Battery Tender" is one.
NOT a battery charger... they will over charge, dry out a battery and kill it.
.
.
Fleet Mechanic
Joined: Nov 2011
Posts: 1,825
Likes: 43
From: Land of Taxes
Also when servicing the charging/battery/starting system, clean ALL the connections/grounds from the battery's down to the starter. Not preforming this when installing any new components will cause the new parts to work a little harder to do the same job due to higher system resistance which will decrease the life on the new parts. Clean connections will make everything happy.
Fleet Mechanic
Joined: Dec 2015
Posts: 1,521
Likes: 412
From: Washington Coast
Spent a few years doing truck service for UHaul, lot of guys try to do electrical cheap and end up getting stranded at the most inopertune times.
Spend the couple extra dollars in the long run and you'll be much happier. Lot of good recommends here, clean everything even the mounting points for the alternator, a little vasalene or wheel bearing grease on the battery post when they're reconnected helps reduce the corrosion, you can check voltage after it's running 14 to 14.5 at idle. Battery voltage shut off 13 to 13.5
Spend the couple extra dollars in the long run and you'll be much happier. Lot of good recommends here, clean everything even the mounting points for the alternator, a little vasalene or wheel bearing grease on the battery post when they're reconnected helps reduce the corrosion, you can check voltage after it's running 14 to 14.5 at idle. Battery voltage shut off 13 to 13.5
Laughing Gas
Joined: Jan 2005
Posts: 1,142
Likes: 25
Sounds like you definitely need a new alternator. Many on here are using DC Power or Mechman replacements for more power, but if you don't use your truck that much at least make sure that if you have the 110amp OEM alt, that you replace it with the 140 amp OEM replacement, they are a much better alternator and a direct bolt in, for about the same price. It is also a good idea to up grade the battery wiring from the alternator to the battery and from battery to battery, there are many write ups on the forums.
