Low voltage issues

[JHZR2]

My 98 Chevy S-10 ZR2 (4.3L V6) sits a lot. I keep a battery charger on it for good measure, but it can be more than that - it can be a necessity. For some reason the voltage after sitting can go to be quite low - say, low 12's, though it will never go below that that I have observed (perhaps because I always have put a charger on there to be careful).

Recently I was concerned that it appeared that the headlights would vary in brightness when at idle. Of course I knew of the voltage issue, but my past tries at isolating that have not been successful. So I figured Id go to Autozone and AAP to get the free checks and see what they could tell me. The first AAP botched the free test because he didn't put the amp clamp on correctly, the second place said nothing wrong. The Autozone said all was well but at the initial startup said there was too much ripple. FYI, I have an Autozone reman in there because at one point I thought my idle shake was coming from a noisy bearing in the alternator (stupid me I guess).

So since I was getting a new free alternator, I wanted to do some checking... When the door is opened or the vehicle recently turned off, the draw is quite high... 0.8-0.9A for I'd say 15-30 seconds.

Then it drops to about 0.1A

After a minute or so, I can sometimes hear a faint click, but one way or another, it drops to 0.03A

Id think that 0.03A is sufficiently low enough to not create issues, at least over short time periods which is when I see voltages drop low, no?

So I replaced the alternator with an AZ rebuild. I noticed a lot of black dirt on the old alternator all in one spot. Not sure if it is related to the belt, pulley, or something inside... Thoughts?

Also, I noticed that the existing alternator and the replacement (which had a Remy marking on it, not Delphi) has four pins in the alternator, while my harness has only one. Any ideas why there are four pins in both of these? I assume the single pin in my harness is the exciter?

When I installed the new alternator, I checked out the AC ripple on the volt meter. I got 34.9mVAC, certainly very low. Any idea what the acceptable range is for reference?

The other odd thing I am seeing is that the reading from my scan gauge is different from the actual reading of a DVM. I verified that the cigarette lighter voltmeter I have in one of the power ports reads spot on with my Fluke... and when I put the Fluke in the OBD port, it reads the same as the other voltmeter in the cigarette port.

So either the scan gauge is improperly calibrated, or perhaps it gets a reading from the ECU, which is getting an improper value? Anyone know if the SG pulls a voltage reading from the OBD pins or from a data signal? I guess Ill have to check that out.

So, now a number of hours after I completed the alternator install, and with a brand new battery installed today, Im seeing 12.69V on the battery... Not bad. I suppose that the old alternator had something wrong in one of the diodes that was intermittent... Since the AP stores didn't pick it up with their equipment (as good or bad as it may be), something else may also be off or odd... But time will tell.

Will be interesting to track over the next few days and see if the alternator did fix things or not... Something was/is not right, and if the ECU is reporting an incorrect voltage, that is another issue... But time will tell.

 

[Merkava_4]

JHZR2, which camera did you use for those shots ?

 

[George7941]

The voltage displayed on my ScanGauge is off by 0.4V from the actual battery voltage.

 

[JHZR2]

Originally Posted By: Merkava_4
JHZR2, which camera did you use for those shots ?


iPhone 5s

Originally Posted By: George7941
The voltage displayed on my ScanGauge is off by 0.4V from the actual battery voltage.


Good to know. Do you know if it reads obdii data or actual voltage?

 

[Vikas]

What really shocked me that the el cheapo Innova plug-in gave the exact same reading as your Fluke!

Unless the ScanGauge is connected to 2008+ model vehicle, it is definitely reading its own voltage and displaying it and perhaps quite inaccurately. Older vehicles do not have the battery voltage as OBD data.

 

[JHZR2]

Originally Posted By: Vikas
What really shocked me that the el cheapo Innova plug-in gave the exact same reading as your Fluke!

Unless the ScanGauge is connected to 2008+ model vehicle, it is definitely reading its own voltage and displaying it and perhaps quite inaccurately. Older vehicles do not have the battery voltage as OBD data.


I was too. Of course it was like $14 vs free or $2.99 with coupon for the HF multi (emphasis multi) meters. So perhaps innova could do a little better with a single function?

Is it definite that voltage is only after 2008? No vehicles had it as part of their proprietary or enhanced obd set?

 

[Merkava_4]

Originally Posted By: JHZR2
iPhone 5s


Thanks. That's the phone I'll get.

 

[JHZR2]

This morning after sitting all night the battery was down to 12.56 V. I just don't get it. I've validated everything goes to sleep in that parasitic draw is minimal. It was only one night, and not that cold. The battery is brand-new so it's not internally discharging, unless some aspect of the internal design of the group 75 battery just does that by itself.

As a comparison my new BMW which has a fairly small battery and a lot more electronics still sits at full charge over 12.7 V after a few days. All the connections are actually clean and bright so I did verify that as well.

 

[Vikas]

This is very strange. Is it possible that you have got a bad new battery? A weak cell may do something like this. Since this is a older vehicle, the chances of any devices coming out of sleep in the middle of night on that vehicle are very remote. If you want to be 100% sure, disconnect the negative cable for 24 hour period and see if the voltage is dropping.

I am almost certain that ScanGauge only displays standard OBD parameters. I know one can hand program it to display specific PID but as far the battery voltage is concerned, no way it is getting it from ECM on a pre-2000 vehicle.

 

[JHZR2]

This woukd be the third battery exhibiting this if that's the case.

I recall reading that gm historically used a slightly different chemistry than other makers, which also drove the alternator output to be a bit higher. If the group 75 battery is gm specific, it could have different Ca/Sb alloy ratios in the lead, which could cause variations in the ocv I suppose.

http://jgdarden.com/batteryfaq/SoC.xls

 

[supton]

Can't see your pictures (at work) but are you measuring at the battery? I'm wondering if some line resistance is somehow preventing full charge. Where is the regulator? I wonder if it thinks the ambient temperature is different than what it really is.

Speaking of things coming awake: when does the gas tank venting get checked? IIRC my Toyota's check some time long after shutdown. I wonder if a solenoid is bad and it draws heavily, but only during that test.

 

[JHZR2]

This thread has a variety of pics, but I verified voltage at the battery, charger port, cigarette lighter and obd2 connector. All the same.

Alternator output is great. It's the battery voltage at rest. Thought it was a diode or other short but seems not.

 

[supton]

Sent link to my iPad and looked at the photos.

Don't know enough about battery chemistry. I do wonder about series resistance. I found this link: http://www.pirate4x4.com/tech/billavista/Wiring/Part2/ and 3/4 of the way down is a wiring chart. I think your single wire is the fault lamp wire, mostly by default.

I suspect the black crud on the old case was from the brushes, but it looks like those are on the back.

 

[wrcsixeight]

Fully charged OCV varies from battery to battery, I know a lot of people have a set opinion ( fact in their mind) as to what voltage signifies a fully charged battery, but this varies battery to battery, brand to brand and even among those batteries coming off the same line.

The group 34 and 75 and 31 batteries are kind of weird battery group sizes that suffer from wonky plate to acid ratios, If a respected former battery engineer I trust is correct.

I've seen a range of 12.62 to 13.07 fully charged resting OCV, and it can take 2 days with no load for the voltage to stabilize there. So when I see someone saying matter of factly that 12.78v or some other number is definitively a fully charged battery for every battery, I feel I must say/type something.

So I'd start by figuring out where that open circuit voltage rests at full charge on that specific battery, and this might require a manual charger, voltage into the mid to upper 15's for an equalization charge and A hydrometer to see when the SG no longer rises or battery temp exceeds 120f, and then waiting 2 days for surface charge to naturally deplete itself.

Disconnected from vehicle of course.

It might also require a partial discharge beforehand to trick the charger into the "bulk current" phase, if an automatic charger.

Automatic chargers, despite the flashing green light, stop short of a full charge, because it is safer, and all batteries vary slightly as to what is needed to reach a true 100% SOC.

The Glass float turkey baster type Hydrometer is the non sealed battery's best friend. The voltmeter a distant second. The plastic hydrometers tend to have far too many bubbles stick to the float throwing off readings into the favorable side of things.

In my experience the newer the battery the longer the Surface charge sticks around, and surface charge is the great fooler that leads many to believe that alternators are magical near instant battery chargers. The fact is they are actually one of the poorest and slowest methods to fully 100% recharge a battery, especially when the battery has been drawn below 80% State of Charge.

I wonder too if your vehicle also has a cycling parasitic load every so often that you have not yet noticed.

 

[meep]

I'd trust the fluke over any other voltage measurement.

In line with what Vikas has said, in general 12.6V is considered fully charged after the surface charge has worn down. However there can be some variation. I've never seen it said though that full charge can be had LOWER than 12.6V. Back in the day when I was in school, cell voltage IIRC was said to be 2.12 or 2.15, which is 12.72 or 12.9. But that was based on details in the chemstry that I just can't remember. I generally just stick with 12.6 for full for normal troubleshooting.

your ripple voltage is only accurate if the meter is true RMS. most are A/C RMS only at 60hz.

A bad diode in an alternator could cause the v-reg to get frustrated and exhibit some flickering, especially at lower rpms. A bad diode could also discharge the batt while sitting.

0.03A resting current is 30mA, which is acceptable "off" draw. Some may say it's a little high. All depends on how much gear has "memory" in the vehicle. At 0.03A, you lose 0.7Ah charge per 24 hours. Average auto battery is 50AH.

The ~1A draw before you close the door is likely the dome light.

Gut thought is you have a bad diode.

Some ECUs don't sleep for 20 minutes or so. some stay awake and do self-tests during that time. A 98 may pre-date that silliness.

just various thoughts responding to various other thoughts...

 

[hattaresguy]

Here is a quick fix.

We have a couple pieces of equipment with mystery parasitic draws that will drain the batteries right down if they sit. Can't figure it out, HO Penn can't figure it out, they said most guys just run them every day so its not a problem. We solved it by just wiring in a battery shut off switch, problem solved.

Since you don't use the truck very often just wire up a kill switch and call it good.

 

[JHZR2]

Originally Posted By: wrcsixeight

I've seen a range of 12.62 to 13.07 fully charged resting OCV, and it can take 2 days with no load for the voltage to stabilize there. So when I see someone saying matter of factly that 12.78v or some other number is definitively a fully charged battery for every battery, I feel I must say/type something.


Well for each chemistry there is an actual value, temperature dependent for when it is at full SOC. And it varies by chemistry and temperature... Yes, lots of variables still in play here, but its lower than my other vehicles after being fully charged and then rested under no load. Temperature may have some to do with that, and the chemistry and characteristics of the Grp 75 may also...

 

[JHZR2]

All seems well again. When I returned the core to autozone we bench tested it on their machine and found no issues. The aap tester didn't either. Only the AZ handheld ever indicated a ripple issue. But obviously the cause of that was enough to cause my battery to drain and now all seems well.

Knock on wood...

 

[chrome]

A friend with a 2002 Civic had a case of mysterious battery drain, it will be ok for days or even weeks, then suddenly a dead flat battery in the morning.

I checked the parasitic draw with a clamp, and it was less than 0.1A with the car off, which is ok.

Turned out, it was a rogue A/C clutch relay. It will behave itself most of the time, but sometimes when the car is off, it will energize the A/C clutch and drain the battery.