I am chasing a charging problem on a 1990 240. My stupid question is this: If the battery is bad (7 year old Volvo battery that passes a load test)will you still have 14v at the battery post with the car running?

I am having another charging problem with this car, after thinking I had it fixed two months ago.

At that time, I had some bulbs missing in the dash (PO)and a questionable alternator. It charged at 14v at the Batt.post with the car running. Thanks!

First of all, you probably (unless it freezing temperatures) should not see 14 volts at the battery terminals with the engine running. Usually, it means that the battery is toast (or heavily drained, and will be toast soon - see below) and the alternator is putting out a sizeable amount of current that the battery cannot absorb.

That aside, you should know these things, assuming a healthy battery and alternator:

1) Before starting the engine, with a cold engine compartment (has been sitting overnight), the voltage at the battery should ideally be about 12.65 v.
At 12.2 v, the battery is already half discharged -- and any lower means that the battery is ruined unless it's a "deep-discharge" or "deep-cycle" type.

2) Upon starting the engine, the battery voltage should rise briefly to about 14 v give or take, but that also depends on temperature (higher voltage in the cold, i.e., winter, and lower voltage when warm, i.e., summer), and the condition of the battery just before engine start (fully charged, lower voltage, depleted charge, higher voltage).
[Your alternator's voltage regulator has a built in temperature compensation for this -- not as good as some yacht's temperature sensors at the battery, but then a yacht's battery bank costs thousands of dollars and deserves better monitoring.]

3) After starting the engine, the voltage (in any case) should quickly drop, and level off gradually to about 13.3 v (again, higher in cold weather and lower in hot weather).

4) Any sustained voltage closer to 14 v than to 13.3 v means that electrolyte is boiling off in the battery and the fluid level is dropping (unless you have a non-conventional wet-cell battery, such as a low-maintenance, or newer types) -- you need to check the fluid level (and add distilled water if necessary).

All of the above voltages assume it was made at the battery terminals, not at some dashboard gauge whose connections might have some voltage drop.

Hello,

Yes its possible.
You need to give more info on whats happening.
Is the battery not charging, or is it losing the charge over time.
What is battery voltage after running the car(engine off), vs voltage in the morning before starting. You could have something draining the battery.
Post as much information concerning your situation as you have, in order to get a proper response.


Larue

Regardless of any other conditions, a 7 year old battery should be a candidate for replacement.
Bob
66S

Larue,
Sorry for the lack of details. As mentioned, I am on my back after knee surgery, or I would give more details. I probably spent 20 +or- hours searching on the BB and the TB on my charging problem with this car two months ago, thought I had it fixed, and now it is not charging again. I will provide more info. on Sunday when I have someone to work on the car. I will then report voltages under various conditions.

The main reason for my post was to see if a bad battery will show 14v at the post while running. I guess I just kind of highjacked my own thread by adding the reasons for my inquiry.

Mr. Bob,
Yeah, a battery is definitely in the cards, especially with winter coming on. Money is a problem for him right now, or I would have told him to just replace it to eliminate that as a possible problem.

Sorry for no correspondence on this post for a couple of months. Basically, I replaced any burnt/missing bulbs in the dash, and remounted the alternator, making sure that the ground was solid, and all connections were tight, and it has been charging for the last two months. Then, my stepson (his car)screwed up his wiper motor, changed it out, and accidentally left the key on for about 15 minutes, ran the battery down, and now it is dead in the water again. I put a known good battery in the car and it was charging at 14.15vdc. He drove it 25 miles, parked it and it wouldn't start again. It had ran the battery down in 25 miles, even though when it left here, it was charging at 14.15!! How can this be??

Let me back up a little. I had knee surgery as noted in the orig. post. Then, one month later, I had emergency exploratory surgery for a perforated bowl. So, I have been through hell, and am still beat up. I cannot work on cars right now (have to have another major surgery to reconnect intestine) or in the near future, so I am having to try to tell my stepson what to do. Very frustrating.

Could bad battery cables be the problem? They are kind of green looking......

Hey Jeff,

How did the knee surgery go? "On your back" sounds like it did not work out like most I know. Funny, I am trying to picture your monitor and keyboard setup, or is your neck bent sharply forward with a laptop where it was designed to be?

Anyhow, the alternator doesn't have to put out much current at all to raise the system to 14.0V, especially if the battery fluid has a low specific gravity or the plates are heavily sulphated. The Bosch system regulates at a nominal 14V but it is temperature dependent and the regulators vary one to the next, when you're into 3 significant digits.

I suggest your measurement is not catching the demon in the act, if the load test was done correctly. It is very common to open the hood and see things check out nicely, only to crap out down the road a piece. Like loose belts.
--
Art Benstein near Baltimore

GREAT TRUTHS THAT LITTLE CHILDREN HAVE LEARNED:

If your sister hits you, don't hit her back. They always catch
the second person.

"The main reason for my post was to see if a bad battery will show 14v at the post while running."

When you see 14V at the battery (or basically anything above 12V) it's coming from the alternator to do two things:
1) Charge the battery
2) Be propagated to the rest of the car's electrical system as needed.

With the car running, the voltage at the battery has little to do with the battery, except to charge it.

--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Sorry, let me clarify my original post a little. Two months ago, I was having a no charge problem with this car. After trying multiple things, like different (used) alternators, voltage regulators, and making sure that all of the dash light bulbs worked, I was finally able to get 14v at the battery post, car running, headlights on. My stepson drove it for about 2 months, and now it is not charging again. Approx. 12.5 at the post, engine running, nothing turned on. like lights, fan, etc.

I just had knee surgery, so I am not able at this time to answer any of the other questions yet, like what is the cranking voltage, and running voltage at the battery post, with everything turned on. I am going to have someone help me this Sunday with the car, and at that time, I will report back with the requested info. and more. Thanks!

First off....What problem are you having?

If you have a good battery and your alternator is charging 14V at idle, you may have a problem with the voltage regulator.

What is the battery voltage with everything turned off?

If you turn everything on....lights, Max. A/C, etc. what is the charge voltage with the engine idling? At 2000 RPM?

steve

You can get 14+V at the battery posts with a good alternator and a marginal battery. What do you get an hour after the car has sat idle? What do you get when cranking?

Your alternator can charge even without the exciter wire being hooked up (the little red wire at the alt that is ultimately connected to the bulb in the dash). There is residual magnetism in the alternator that once it reaches X speed will self-excite (I always feel dirty typing that) the field coil and once it is excited it stays that way (again, I feel like a Viagra commercial).

You can read all about my soapbox item, the alternator ground wire, but I will just say that it is the most often overlooked cause of intermittent charging issues. There is not reasonable way to inspect it on the car but if you must, pull hard on the wire as if you are trying to pull the end off. Do it in both directions so that you test both ends. Then insure a clean tight grounding point where the chassis-side eyelet connector is bolted. By that point you might as well have removed it and inspected it off the car.

Mike