Stupid Electrical Question
Thread Starter
Instructor
Joined: Sep 1999
Posts: 197
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From: Ridgefield CT
Stupid Electrical Question
Car is a 99 convertible, automatic with 37,000 miles. Car sat for 3 days and I forgot to disconnect my radar detector. When I opened the driver's door I heard a buzz or humming sound from around the underhood fuse box and the interior lights did not go on. I checked the volts with my mickey mouse digital meter and it read 8.5. I didn't try to start it, I just hooked up my Battery Tender and it took 2 days to get a fully charged battery (an Optima Red Top but I don't know how old it is). In the past I always got a fully charged battery in a matter of hours.
After charging it read 12.8 so I took it out for a ride and the DIC shows 14.4 to 14.6 with the heater, radio and detector on. My stupid question is this; does the 14.4-14.6 tell me anything about the condition of the battery or is it just telling me that the alternator is doing its job? I plan to let it sit for a day and see what voltgage I get without starting it up. Thank you in advance.
After charging it read 12.8 so I took it out for a ride and the DIC shows 14.4 to 14.6 with the heater, radio and detector on. My stupid question is this; does the 14.4-14.6 tell me anything about the condition of the battery or is it just telling me that the alternator is doing its job? I plan to let it sit for a day and see what voltgage I get without starting it up. Thank you in advance.
Tech Contributor
Joined: Jan 2007
Posts: 19,360
Likes: 1,127
From: Dyer, IN
Car is a 99 convertible, automatic with 37,000 miles. Car sat for 3 days and I forgot to disconnect my radar detector. When I opened the driver's door I heard a buzz or humming sound from around the underhood fuse box and the interior lights did not go on. I checked the volts with my mickey mouse digital meter and it read 8.5. I didn't try to start it, I just hooked up my Battery Tender and it took 2 days to get a fully charged battery (an Optima Red Top but I don't know how old it is). In the past I always got a fully charged battery in a matter of hours.
After charging it read 12.8 so I took it out for a ride and the DIC shows 14.4 to 14.6 with the heater, radio and detector on. My stupid question is this; does the 14.4-14.6 tell me anything about the condition of the battery or is it just telling me that the alternator is doing its job? I plan to let it sit for a day and see what voltgage I get without starting it up. Thank you in advance.
After charging it read 12.8 so I took it out for a ride and the DIC shows 14.4 to 14.6 with the heater, radio and detector on. My stupid question is this; does the 14.4-14.6 tell me anything about the condition of the battery or is it just telling me that the alternator is doing its job? I plan to let it sit for a day and see what voltgage I get without starting it up. Thank you in advance.
ok, try a little experiment. What is the battery voltage with the ignition on, and the engine off?
Le Mans Master
Joined: Feb 2002
Posts: 6,937
Likes: 21
From: Waldorf MD
12.8 is a GOOD reading for your battery. You should be okay, but these batteries can't take many full discharge episodes. Your running voltage is okay also, although after running a while it should come down to about 13.6 volts.
Thread Starter
Instructor
Joined: Sep 1999
Posts: 197
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From: Ridgefield CT
To me, the engine off voltage was 12.8 per the meter and the engine on voltgage was 14.4 per the DIC. If I use the meter while the engine is running should I expect something other than 14.4? I have had this Vet for 6 months now and although I normaly run with either water or oil temp on the DIC, when I do page through the guage functions I can't remember seeing anything below 14.1. I thought that was good. My problem (question) is I just don't know what the DIC voltgage is trying to tell me, healthy battery, healthy alternator, both or neither.
Le Mans Master
Joined: Nov 2005
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IN the "old" days, they use AMMETER's in the dash. The voltmeter you see today mostly measures the output of the voltage regulator. If the system is "NORMAL", you should see mid/high 13's to low 14 V on the meter. If It's overcharging (all the time), the battery is usually on it's way out, if it's undercharging one (or more) of the diodes in the regulator is usually going bye-bye. If you jumped it to get it started, it would probably have been overcharging for some time.
Thread Starter
Instructor
Joined: Sep 1999
Posts: 197
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From: Ridgefield CT
My understanding of the voltgage reg. is it will supply enough to whatever accessories need power and enough to the battery to get it fully charged, After the battery is fully charged it drops down to the output needed by the accessories only. If I'm correct it sounds like the battery is asking for more than the NORMAL current if the regulator is always putting out over 14 volts. Sounds like I need a new battery.
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Le Mans Master
Joined: Nov 2005
Posts: 6,993
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True, what's on the guage is the output of the alternator when the car is running. A 12 V battery should measure around 12V with the car not running.
Thread Starter
Instructor
Joined: Sep 1999
Posts: 197
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From: Ridgefield CT
Well I bought an AC Delco battery just to ease my mind and now I will know the age of the battery if I have problems in the future. Nothing much has changed with the new battery as follows:
Voltgage not running per multimeter 12.1
Voltgage not running per DIC 11.4
Voltgage running per multimeter 14.5
Voltgage running per DIC 14.6
Just for the hell of it I checked the Red Top and got the following:
Voltgage not running per multimeter 12.2
Voltgage not running per DIC 11.5
Voltgage running per multimeter 14.6
Voltgage running per DIC 14.8
It sure looks like the entire problem was caused by the radar detector and the Red Top did not need to be replaced. I didn't turn the Red Top in so I guess I'll throw a charge on it every so often and keep it as a spare unless someone out there has a need for it. By the way, the only "data" that got lost when I removed the battery was the fob learning and the time, all my memory settings and radio stations remained. Thanks to everyone for all the help.
Voltgage not running per multimeter 12.1
Voltgage not running per DIC 11.4
Voltgage running per multimeter 14.5
Voltgage running per DIC 14.6
Just for the hell of it I checked the Red Top and got the following:
Voltgage not running per multimeter 12.2
Voltgage not running per DIC 11.5
Voltgage running per multimeter 14.6
Voltgage running per DIC 14.8
It sure looks like the entire problem was caused by the radar detector and the Red Top did not need to be replaced. I didn't turn the Red Top in so I guess I'll throw a charge on it every so often and keep it as a spare unless someone out there has a need for it. By the way, the only "data" that got lost when I removed the battery was the fob learning and the time, all my memory settings and radio stations remained. Thanks to everyone for all the help.
Thread Starter
Instructor
Joined: Sep 1999
Posts: 197
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From: Ridgefield CT
Thanks Chuck S., it's on the battery tender right now. I have to go to the local tavern (I can walk) so I won't be able to tell when it goes green but I'll take another reading in the am. If I try anything later tonight I might burn the garage down.