Battery Charging Voltage

Hi Doug, I have a digital volt guage in my 355 so I am able to follow the voltage readings. When I first start the engine it reads at 14 volts and settles out at about 13.4-6 volts. Even when the fans kick on the regulator keeps it about 13.3. Get a battery tender if you are only driving it once a month, it would not be uncommon for the battery to lose a charge in that time. Also its very hard on the alt. to have it always bringing the battery back to full charge. Hope that helps. Regards, Vern

 

Doug,
My GTSI was pulling that too. I came to find out by accident one night when I was walking by it that the red light on the door had a mind of its own and was turning itself on by itself with the door closed causing a slow drain. I lubed it and it never did it again. I chased this little gremlin thinking I had a voltage problem too. 1 alternator and 1 battery later I learned that the when in doubt rip it out theory may have not been the best solution to my problem.
Mine was holding in about two weeks at a time before it dis-charged enough to kill the battery.
Hope this helps...........

 

As long as your Voltage is in between 13.5 to 15.0 volts you are OK.

 

Guy at Napa checked mine a few months ago and it read 13.5

 

My 308 runs at 13.5-6 at 1000 rpms or better. I believe the alt is designed to run at that voltage. Most GM/Ford will run at 14.2V. It's normal

 

You might want to check the parasitic (off) current draw from the battery just to make sure it isn't too unreasonable. Sitting for a month might be trouble if you had a ~250 mA draw from a lot of added electronics so maybe no choice but to use a tender, but added things don't always get added correctly either -- just a thought...

 

Lead acid chemistry at normal temperatures dictates that maintaining a voltage of 13.6 will ensure 100% full charge. If the battery is less than 100%, the alternator internal regulator goes up to 14.4v to quickly get the battery capacity back. With charging and loads removed, steady state voltage of a fully charged battery is 12.6. Those 3 numbers change slightly with temperatures out of the normal 10-30 Celsius range, and also change slightly with strange lead alloys is specialty battery...both not a concern here.

The reason charging voltage is kept at 14.4v is because a higher voltage will boil the electrolyte and a lower voltage will never get the battery to 100%. Incidentally, numbers for 100% charge in AmpHours is dictated by the plate area. Adding more plates yields a heftier capacity but in a given space, plates are thinner to make more of them, and dependability may suffer. Using non-distilled tap water containing mineral deposits will do just that...deposit on the plates and reduce plate area and capacity.

Aside about tenders: Marketing a unit using the title 'tender' instead of charger, is worth additional $10 right there. In order to extract the maximum dollars and produce a 'buy-me' product, manufacturers will also include automatically switchable features. A simple shoebox sized garage charger which is capable of regulated voltage output of 13.6v and is current limited to 1-3 amps, will work as well if not better than any 'full featured' tender. High current auto-switching is great in commercial fleet applications if you can't wait overnight to recharge a depleted battery but they aren't available under 30-40# and 300+ dollars regardless what the 'tender' box says.

I use primarily open frame supplies with screwdriver potentiometers to fine turn the output to exactly 13.6v. Bought at hamfests or Mouser type stores in the $10-20 range, one has been in reliable daily use for 30+ years now, and I use a separate in-line meter unit as everything I own such as the car pigtails are 20A polarized nylon Molex sockets for quick connect and interchangeability. The only failures have been human such as leaving car lights on and my batteries routinely outlive warranties by 1-2 years.

 

What's the best way to do that?

 

Remove one of the battery terminals from its battery post, and then connect one lead from an ammeter to the loose battery terminal on the cable and the other lead to the bare battery post. If you've got added electronics (and the current reading seems high), leave it connected for a few minutes -- sometimes these added gizmos do a short self-test at start-up.

 

Thanks. Very helpful. One more question. What is the acceptable draw on the average battery?

I have a problem with passive drain on my Rx-7. I had a "professional" do a 134a conversion. Then it kept blowing seals. Finally, the Mr. Pro talked me into putting another fan in front of the condenser, thinking heat was creating pressure and blowing seals. He wired it to come on when the a/c was on and the clutch was engaged. Now, my battery keeps running down. The car often sits for a week or so. I pulled the fuse for that contraption so I know that's the culprit. With the fuse out the battery doesn't run down. Only other component running while it sits is a little OEM digital clock.

Current draw without new fan contraption fuse: 00.00mA

Current draw with new fan contraption fuse in place: 140.0mA

Seamus

P.S. The new fan contraption fan blades are not turning when the car is sitting and off, but some part of how it is wired up is pulling juice. I will be taking it back to Mr. Pro soon.

 

Anything less than ~100 mA is usually OKish (for a large battery):

50 mA or less -- typical for a car with only a clock and maybe a radio, battery can go more than a couple of months before not being able to start the car, maybe even a few months.

50 mA to 100 mA -- might need a recharge for starting after a couple months. My own TR is 65 mA with clock, radio, CD changer, alarm, and radar detector, and, although it will start OK after ~1 month, I still put a charger on the battery first if it sits that long.

~150 mA -- about the max limit that can be masked by quasi-regular use without hassle. Might need recharge after a couple~few weeks and the frequent deep cycling won't help the battery life (as you've already found ).

250 mA or more -- really unacceptable, maybe a week and the deep cycling is a killer.

Have you been able to have the issue with your added AC condensor fan corrected?

 

Yes, and no. The *excessive* parasitic drain was corrected.

The underlying a/c issue was never resolved until the so called "master technician" and owner of this independent shop claimed the compressor he sold me was "faulty" but out of warranty despite it never having worked reliably, though returned repeatedly -12 times- for not working. I decided some battles are not worth continuing to wage when you are dealing with a drooling moron.

 

I installed a voltage meter in the location of the clock on my ex 308. While driving/running it always showed about 13.5v