Charging System Chronic Undercharging

[SubLGT]

My Subaru OE battery lasted 6 years. The replacement Duralast battery lasted 2.5 years before sulphation weakened it, due to chronic undercharging. Therefore I have been monitoring the state of charge (SOC) of my new Everstart Maxx battery on a regular basis by measuring its CCV (closed circuit voltage). After fully charging the battery with a CTEK charger, its CCV is 12.65V. After a month of driving the CCV is down to 12.30V, which is about a 70% SOC. I reconnect the CTEK charger, and it requires about 1.5 hours to recharge (in absorption phase) the battery to 100% SOC.

My charging system voltage is usually at 13.8 - 14.8 V, and even with a 75A load on my 110A alternator, the voltage only goes down to 14.0V. Voltage drop tests did not turn up any bad cables or connections. Measurement of AC ripple did not turn up a smoking gun.

The only suspect issue is that immediately after starting the engine with a fully charged battery, the charging current going through the battery (as measured at the battery negative cable at 14.4V) is only 0.8A, which strikes me as a bit on the low side. The current measured at the alternator B+ output cable is 11.5A with all accessories off.

My guess is that the voltage regulator is running a few tenths too low, and this is leading to chronic undercharging of the battery.

What do you think?

 

[wrcsixeight]

When my engine battery is fully charged, the amps quickly taper into the 1 to 3 amp range after starting.

I think batteries of today have been cost and corner cut so much due to consumers expecting free replacement, that one cannot expect the longevity of the past.

12.65 is low for a battery just removed from a charging source. The surface charge should hold a reading well above that for several hours until it diminishes.

 

[JHZR2]

Sounds like a soft internal short. Something like a few hundred to a few thousand ohms does not effect much of anything in the charging system, yet it causes the battery to drain quick. Add just a little extra phantom load to the car and the battery will do just that.

What you describe is exactly what Ive seen on the two Wal-Mart Maxx batteries Ive put into my 98 S10.

What is the final charge voltage on the ctek?

 

[jrustles]

Everything appears to be in spec TBH. 0.3V diff in float is really just noise from batteries of various quality, especially going from a smart charger to the vehicle's alternator.

 

[JHZR2]

Originally Posted By: jrustles
Everything appears to be in spec TBH. 0.3V diff in float is really just noise from batteries of various quality, especially going from a smart charger to the vehicle's alternator.


Float perhaps, it is highly temperature dependent. But he is reading voltage in a static state, just connected normally. The battery is not charging properly, or is bleeding energy via soft short, which is my guess. Chronically low float voltages can induce sulfation.

 

[SubLGT]

Originally Posted By: wrcsixeight
When my engine battery is fully charged, the amps quickly taper into the 1 to 3 amp range after starting.
................


I was expecting to see that after my engine start also, for at least several minutes. After all, the starter motor does pull around 150A for a few seconds, and that energy should be returned to the battery by the alternator.

 

[SubLGT]

Originally Posted By: JHZR2
Sounds like a soft internal short. Something like a few hundred to a few thousand ohms does not effect much of anything in the charging system, yet it causes the battery to drain quick. Add just a little extra phantom load to the car and the battery will do just that.

What you describe is exactly what Ive seen on the two Wal-Mart Maxx batteries Ive put into my 98 S10.

What is the final charge voltage on the ctek?


My battery only drains when the vehicle is being driven. If I leave the vehicle parked, the drop in CCV over time is much slower, due to 45mA of parasitic current. My theory is, the battery gets drained by use of the starter motor, but is not being sufficiently recharged by the alternator. The voltage regulator is supposed to sense battery voltage, and adjust alternator current output accordingly, but that does not seem to be happening.

After charging with the CTEK, the open circuit voltage (OCV) is around 12.70 - 12.75V, after allowing surface charge to dissipate. If I then connect the battery cable, and wait a half hour, I measure a CCV of 12.65V

 

[wrcsixeight]

Can you monitor voltages when actually driving? You seem to be charging when idling with the hood up.

My vehicle uses a fusible link that once, would only pass alternator current for the first few minutes before it got hot enough to pass nothing. It was difficult to find as the insulation looked fine and it tested fine, and it wasn't until I felt it get super hot trying to charge a healthy but depleted battery, and wiggling the fusible link was changing the engine tone slightly as it provided 25+ amps to the battery then nothing with subsequent changes in battery voltage.

I don't imagine your vehicle uses a fusible link, but perhaps you have a highly resistant connection somewhere that is only apparent sometimes

 

[SubLGT]

Originally Posted By: wrcsixeight
Can you monitor voltages when actually driving? .........


Yes, I have a voltmeter in the dash, and it has been showing nothing abnormal. I don't have any other odd symptoms such as lights dimming or flickering. Just the battery losing charge when the car is driven, but not when parked.

 

[SubLGT]

Originally Posted By: wrcsixeight
..............My vehicle uses a fusible link that once, would only pass alternator current for the first few minutes before it got hot enough to pass nothing. .......................I don't imagine your vehicle uses a fusible link, but perhaps you have a highly resistant connection somewhere that is only apparent sometimes


Yes, my car has an 120A fusible link, bolted to the bottom of the fuse box. It looked fine to me, no corrosion or evidence of over heating. A voltage drop test for that part of the circuit revealed no problems.

 

[wrcsixeight]

This voltmeter in the dash, is it stock, or aftermarket? Can you actually see the difference between 12.6 and 14.x via the gauge? I have wired a ciggy plug to my DMM.

If not a maintenance free battery, Have you stuck a hydrometer in the cells? Stir up the electrolyte with the bulb, Does it get super cloudy and have grey matter swirling around in it? Does one cell read far different from the others?

How is the alternator grounded, through its case, or does it have a separate cable?

 

[jrustles]

Originally Posted By: JHZR2
Originally Posted By: jrustles
Everything appears to be in spec TBH. 0.3V diff in float is really just noise from batteries of various quality, especially going from a smart charger to the vehicle's alternator.


Float perhaps, it is highly temperature dependent. But he is reading voltage in a static state, just connected normally. The battery is not charging properly, or is bleeding energy via soft short, which is my guess. Chronically low float voltages can induce sulfation.


You're onto something with the soft short. It's gotta be the sulfation.
With these newer batteries, the plates are getting thinner and thinner, with more and more surface area. This is how they can achieve higher CA ratings with less lead. The problem is, that you cycle it once, or semi cycle it a handful of times, those bristly preforated plates ares gonna get deep fried in sulfates. Once that happens, no 14.8 DC float charge will ever achieve the original SOC. Only special PWM/high voltage chargers will bring it close, and even then it would probably be a phantom 100% SOC.

Sub, check the resistance of the battery. If the voltage is there, but the current isn't flowing, there's only one explanation..

 

[The_Jeff]

The new cars have computer controlled alts and won't shove tons of amps at a battery right after starting. They're trying to make things "soft" so the car can get a nice idle without a ton of load right off the bat.

For that matter, the battery will only take so many. If system voltage rises to 14-ish and the internal resistance of the battery is up, it might only charge at 20-30 amps, if that, and only for a few seconds before it drops even more.

 

[SubLGT]

Originally Posted By: SubLGT
..............The only suspect issue is that immediately after starting the engine with a fully charged battery, the charging current going through the battery (as measured at the battery negative cable at 14.4V) is only 0.8A, which strikes me as a bit on the low side. The current measured at the alternator B+ output cable is 11.5A with all accessories off..............


This morning immediately after starting the car (at 48 degF) I measured the current through the battery, and it was 6A, and it slowly tapered down to 0.8A after 10 minutes of idling. There is always a little bit of current going into the battery, even with a 50A load at idle. The charging system seems to be operating normally. At first I thought it was the culprit, but maybe the battery is at fault. [censored] those mysterious electrons.

 

[SubLGT]

Originally Posted By: JHZR2
Sounds like a soft internal short. Something like a few hundred to a few thousand ohms does not effect much of anything in the charging system, yet it causes the battery to drain quick. Add just a little extra phantom load to the car and the battery will do just that.

What you describe is exactly what Ive seen on the two Wal-Mart Maxx batteries Ive put into my 98 S10.................


I assume you are talking about a "soft short" inside the battery??? Is there a specification for "normal" battery resistance in ohms? I can't remember ever seeing one.

My OE battery that lasted 6 years was a group 85 Johnson Controls (JC). The Duralast Gold and Walmart Maxx are also from JC, but are larger Group 35 batteries.

 

[SubLGT]

Originally Posted By: wrcsixeight
.............. Can you actually see the difference between 12.6 and 14.x via the gauge?


Yes I can.

Quote:
Does it get super cloudy and have grey matter swirling around in it? Does one cell read far different from the others?


No and no.

Quote:
How is the alternator grounded, through its case, or does it have a separate cable?


Through the case

 

[SubLGT]

Originally Posted By: jrustles
..........Sub, check the resistance of the battery. If the voltage is there, but the current isn't flowing, there's only one explanation..


Is there a specification for "normal" battery resistance?

 

[jrustles]

Originally Posted By: SubLGT
Originally Posted By: jrustles
..........Sub, check the resistance of the battery. If the voltage is there, but the current isn't flowing, there's only one explanation..


Is there a specification for "normal" battery resistance?


It varies by the battery. You would need to find the manufacturer's resistance vallue for your specific battery.

 

[meep]

the measurements and observations don't add up yet.

1. initial post: car is 13.8-14.8 volts. this suggests not a problem with the alternator or regulator.

2. battery reads 12.65V immediately after coming off a charger. A wet cel gets float charged to stay between 13-14 volts typical. 12.65 is indeed full SOC but there should be a surface charge hanging on-- a regulated charger must output more than just 12.65V to motivate the battery to accept a charge at any decent rate. this suggests a weak cell in the battery. what is V measured while on the charger??

the only thing that doesn't add up is that the batt ends up at a lower SOC after driving. Are you monitoring vehicle V the whole time? If this is the case, then I'd wager you need to check for V-drop again.

idle car. turn on a good bit of accessories. high-beams, heater blower, defrost grid.

start with the ground paths between /specifically/ the ALT frame and battery post.
then /specifically/ the alt + to batt + post.
no shortcuts

 

[SubLGT]

Originally Posted By: meep


2. battery reads 12.65V immediately after coming off a charger...............


No, all my voltage measurements are after allowing surface charge to dissipate for at least 6 hours

Quote:
the only thing that doesn't add up is that the batt ends up at a lower SOC after driving. Are you monitoring vehicle V the whole time? If this is the case, then I'd wager you need to check for V-drop again.


My theory is that operation of the starter motor uses up (as an example) 1000W of power, but the charging system only replenishes 975W. While driving, there is at a minimum a trickle charge of around 0.8A going into the battery, even at 650 rpm idle with a 50A load. The voltage regulator seems biased towards undercharging rather then overcharging. I wish I could tweak this electronic regulator a few tenths of a volt higher, like I used to be able to do with the older mechanical regulators.

Voltage drop (alt > battery) on the alternator positive side is 0.016V, and on the negative side it is 0.006V, at idle speed and 11A load.