Battery Level - Charging

[jelag]

I'm driving my 04, its got 132K miles..... I've got an electric cooler plugged in that runs 24/7 and draws 3. 5 amps... . I've used ohms law and have decided that if the truck doesn't sit for more than 24 hours it will start during the summer and its been fine for 60 days since I put the cooler in the back seat... .



But I've noticed that some of the time the volt meter is not as high sometimes as it is at other times... . Sometimes it just a bit below the 14. 0 mark and sometimes it just above... . this is after the truck has been running for more than an hour..... and the batteries should be charged up..... going down the road at say 2000 rpm's... .....



I know this is just a simple gauge that is fed information from the ECM..... is there any real concern here... . is this a valid gauge... . I'd hate to come out some morning and find the batteries dead... .



BTW my 05 with just 22K miles does the same thing... . without the cooler...



Jim

 

[klenger]

You might want to consider installing a 12 volt deep cycle battery with an RV battery isolator to power the beer cooler. Then if the battery goes dead, you will have warm beer, but you'll still be able to drive to the store to get ice. :-laf

 

[rbattelle]

3. 5 amp is a lot of current draw!



Anyway, I think your charging system and batteries are okay. My voltage gauge does move around a bit whilst driving. It's never left of the center mark (remember visual parallax - be sure to look at the gauge straight on, which requires you to lean over far to the left from the normal driving position), but it will generally act like this:



1. Right after a cold startup (not so cold as to activate the grid heaters) the needle sits clearly to the right of 14v.

2. After driving for awhile it gradually drops down to right about 14v and stays there.



What I'm about to say is an assumption, as I don't have my service manuals in front of me, so if I'm wrong someone please correct me.



Engine startup draws a ton of current, so the alternator (which I am assuming uses an ECM-controlled voltage regulator) is commanded to provide extra charging power to the batteries to bring them up to full charge as quickly as possible. Once they have reached full charge (not sure how the ECM defines "full charge"), the voltage regulator is commanded to step down the charging power to a lower-current (lower voltage) maintenance mode; hence the drop in voltage registered at the gauge.



I believe the voltmeter is a "real" gauge, mostly. I say "mostly" because I know the PCM modulates the needle movement when the grid heaters are on so you can't see the voltage jumping all over the place as the grids cycle.



-Ryan

 

[K5IP]

I think you are OK too. Even if you leave your cooler on overnight, for say 10 hours, 3. 5 A times 10 hours results in a 35 Amp Hour load. Our batteries are good for about 70AH each at that load rate. As long as you don't do this several days in a row without charging your fine. The Alternators are rated at 120AH so they can bring the batteries up fairly quickly.

Battery charge voltage levels (what you observe on the voltmeter) are not constant. They have a negative voltage coeffiecient (about -100mv/degC). At your truck gets warmer, a sensor tells the pcm to lower the voltage. So, you will see a slightly higher battery voltage on a cool morning then you will during the hear of the day (assuming a fullly charged set of batteries). I say, you are quite observant!

Rog

 

[DBond]

starting battery's like to be kept at full charge, so by having them partially discharged will reduce the battery life some.



I'm not a fan of those thermoelectric coolers, they can only cool 40F below ambient, and to get there very slowly. My experience was that frozen items melt faster with the cooler running than with it off on a warm day.

 

[p-Bar]

Two enemys of a battery heat and a constant discharge.

 

[MNielsen]

Klenger,

I like the way you think about warm beer and getting ice, It made me smile, thanks for it has been a helacious noght here at work!!!