How to adjust PCM alternator charge voltage

CharlesHS said:
Disconnect the negative cable from the battery, place a VOM between the battery cable and the negative battery terminal and set on mA to test for a parasitic draw on the battery.
Anything more than a few hundred milliamps is too much.
Remove fuses one by one and retest to see which fuse removes the draw.
You can download the PDF for your year FSM and use the electrical schematics in section 8W to further trouble shoot the source.

https://wranglertjforum.com/threads...ice-manuals-fsm-technical-documentation.4618/
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Thanks.

I just did a drain (IOD) check as suggested using my Fluke multimeter. At first connection, something kept kicking in that drove it up to around 125mA intermittent (I didn't set peak hold), but after a while, it settled to a constant 37mA, which I tested for about 10 minutes. If the battery were to have the AH it says, that is over 60 days capacity.

The sparking when reconnecting sure seemed a lot more. I have a recording meter that can go inline and possibly measure it over days if it sits that long.

I guess either I have to do longer drives or somehow top up the battery regularly. This shelter in place stuff is creating havoc. On the other hand, it has been a long time since I went so long on a tank of fuel!
 
just uploaded the modified voltages posted in this thread to my 06 LJ 4.0 auto. voltages were around 13.6-13.7 prior to modifying the table. Now I am getting 14.45-14.5 at cold idle. Much better for the AGM battery I am running. I was wondering why it was still taking a long absorption charge on my plug in charger. 13.6v charging is a float charge voltage not an absorption voltage for AGM. A fully charged AGM battery should be 13v. I was only seeing around 12.5v regularly.
 
Regular change voltages for AGM batteries terminate when the set voltage is reached. Float charge voltages are lower. Interesting consideration for this particular venture, the higher voltages must be terminated when the battery is charged and our systems can't really do that. A long drive will essentially kill an AGM at these higher voltages because it doesn't know when to terminate the change.
 
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I really enjoyed this thread, I enjoyed the science of it too. But at the end of the day our systems are float chargers and not peak chargers. The charge voltage on an AGM battery must be terminated when it is reached or you have to use a float charge value which is extremely close to the factory setting. Unless you can rig a charger that terminates you can't get around this little detail. Charging with a good AGM charger before a trip will do it, our charging system can't without long term damage to the battery.
 
As you delve into manufacturer sites, the different information for even different batteries from the same manufacturer get confusing. For instance, right from the Optima Q+A for their Yellowtop AGM:
"
Recommended charging information:

  • Alternator:
    • 13.65 to 15.0 volts, no amperage limit.
  • Battery Charger:
    • 13.8 to 15.0 volts, 10 amps maximum, for approximately six to twelve hours.
  • Cyclic Applications:
    • 14.7 volts, no current limit as long as battery temperature remains below 125°F (51.7°C). When current falls below one amp, finish with two-amp constant current for one hour.
  • Rapid Recharge:
    • Maximum voltage 15.6 volts (regulated), no current limit as long as battery temperature remains below 125°F (51.7°C). Charge until current drops below one amp.
  • Float Charge:
    • 13.2 to 13.8 volts, one amp maximum current, time indefinite (at lower voltage).
    • Strictly adhere to all limits."
They also say about resting voltage:
"Fully charged, engine not running, starting batteries (all REDTOP® or BLUETOP® 34M) should measure about 12.6 volts to 12.8 volts. Deep-cycle batteries, including all YELLOWTOP® and dual-purpose BLUETOP batteries, should measure approximately 13.0 to13.2 volts. "
Then in other sections, Optima says to use the regular charge profile / setting, not the AGM one for their batteries too.
 
pagrey said:
Regular change voltages for AGM batteries terminate when the set voltage is reached. Float charge voltages are lower. Interesting consideration for this particular venture, the higher voltages must be terminated when the battery is charged and our systems can't really do that. A long drive will essentially kill an AGM at these higher voltages because it doesn't know when to terminate the change.
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Maybe but my previous AGM battery was just over 10 years old when it died. My present AGM is just over 5 years old. Optima AGM batteries are lucky to make it to 4-5 years. I had 3 Optima AGM batteries die within 5 years total. 2 Yellow Tops and 1 Blue Top which are identical internally.
 
AGM batteries like the Northstar and Odyssey batteries are built to tolerate the higher alternator charge voltages for hours after charging has completed.

Most older cars, including the TJ, do not have any means of reducing the charge voltage after a set charge state is reached. Some modern vehicles (like the newest F150, for example) actually do measure the charge state of the battery and adjust voltage accordingly, but this is still not yet the norm.

Northstar itself recommends a charge voltage of anywhere between 14.1 and 14.8 volts when a single voltage alternator system is used. Others may recommend a service voltage of 14.4 to 14.8 volts. I have never seen any AGM manufacturer recommend charging below 14.0 volts; in fact, most caution against it as it can accelerate decay of the battery. Note in the link below, Northstar actually suggests that 14.6 to 14.8 is actually optimal.

For anyone interested in the more technical details, I strongly recommend reading through this thread. It's 45 pages, but has a lot of useful information and discussions:
https://www.tacomaworld.com/threads/the-northstar-agm-battery-voltage-booster-upgrade.604478/
 
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Jerry Bransford said:
Maybe but my previous AGM battery was just over 10 years old when it died. My present AGM is just over 5 years old. Optima AGM batteries are lucky to make it to 4-5 years. I had 3 Optima AGM batteries die within 5 years total. 2 Yellow Tops and 1 Blue Top which are identical internally.
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Yes, my first Optima lasted probably 10 years, but more recent ones much less it seems. Something isn't the same.

I would need something with the same case dimensions to fit the dual.battery setup. Any recommendations?
 
Tinkerer said:
Yes, my first Optima lasted probably 10 years, but more recent ones much less it seems. Something isn't the same.

I would need something with the same case dimensions to fit the dual.battery setup. Any recommendations?
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Is this a bracket designed for Odyssey batteries? If so I doubt anything else will fit without significant modification. No other battery company uses the round cell design, as it is a quite inefficient use of space.

A Group 34 Optima provides 55Ah and 750 CCA. Two of those would double that specification. A single Group 24 Northstar or top line Odyssey provides 76 Ah and 840 CCA, and should last 3x as long. So a single NSB Group 24 (which bolts in with either no modifications or a modification to the hold-down) might still do the required work of the dual battery, unless the battery is run below 50% charge on a continual basis.

If you have money to burn, you can get a lithium Group 24 with 120Ah and 1200 CCA:
https://www.lithiumion-batteries.co...teries/group-24-12v-120ah-lithium-ion-battery
 
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Tinkerer said:
Yes, my first Optima lasted probably 10 years, but more recent ones much less it seems. Something isn't the same.
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You're right, Johnson Controls purchased Optima and moved the entire manufacturing line to Mexico and stopped using quality components like pure lead. That's when Optima's quality and longevity took a giant nose-dive.
 
Steel City 06 said:
Is this a bracket designed for Odyssey batteries? If so I doubt anything else will fit without significant modification. No other battery company uses the round cell design, as it is a quite inefficient use of space.

A Group 34 Optima provides 55Ah and 750 CCA. Two of those would double that specification. A single Group 24 Northstar or top line Odyssey provides 76 Ah and 840 CCA, and should last 3x as long. So a single NSB Group 24 (which bolts in with either no modifications or a modification to the hold-down) might still do the required work of the dual battery, unless the battery is run below 50% charge on a continual basis.

If you have money to burn, you can get a lithium Group 24 with 120Ah and 1200 CCA:
https://www.lithiumion-batteries.co...teries/group-24-12v-120ah-lithium-ion-battery
Click to expand...
Thanks. I will measure, but I expect that any group 34 should fit and that is the size and terminal layout I am using now. Odyssey is more available where I am in Canada. From what I read so far, lithium isn't very tolerant of cold. One Canadian manufacturer even builds one with self heating!

At the moment, I am running single battery, as I am not running key-off accessory loads, Amateur radio mostly, or key-on like my winch.
 
Our alternators float charge the battery because they have no way to terminate charge so manufacturer charge voltage or cycle voltage doesn't apply. That's why @Jerry Bransford has had such good luck with his stock setup, it float charges his AGM batteries right about where it says to on the battery. I think the concept of charger and float charger are really what's lost here.

charge.jpg
 
Jerry Bransford said:
The dual Optima battery holders I've seen were too small to fit conventional square Group 34 battery cases.
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It seems so, around ½" too narrow based on specs. No dimension drawings though. Two options, modify the brackets I have or relocate second battery to the rear. For now, not an issue. For newer models after the TJ, there are brackets out there for dual odyssey etc.
 
As stated, this is a compromise between not over charging a battery by applying and absorption charge for too long and under charging a battery by only applying a float charge. From what I am reading, normal driving with a float charge is likely to do more harm than not properly charging a battery with an absorption charge. I just installed a Victron smart solar charge and 100w solar panel on my roof rack so I will let that take care of daily absorption charging and may dial the alternator output back down. I need to see who is making the current Advance Auto Diehard AGM battery and see if I can get specs. I think it is Clarios
 
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mfilippello said:
As stated, this is a compromise between not over charging a battery by applying and absorption charge for too long and under charging a battery by only applying a float charge. From what I am reading, normal driving with a float charge is likely to do more harm than not properly charging a battery with an absorption charge. I just installed a Victron smart solar charge and 100w solar panel on my roof rack so I will let that take care of daily absorption charging and may dial the alternator output back down. I need to see who is making the current Advance Auto Diehard AGM battery and see if I can get specs. I think it is Clarios
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My Odyssey-made Diehard Platinum and Northstar AGM batteries have done perfectly well using the stock TJ charging system. The previous Odyssey lasted over ten years and my current Northstar is over 5 years old.
 
Jerry Bransford said:
My Odyssey-made Diehard Platinum and Northstar AGM batteries have done perfectly well using the stock TJ charging system. The previous Odyssey lasted over ten years and my current Northstar is over 5 years old.
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What voltage does your TJ normally charge at? If you have the battery temperature sensor it may be setting a higher voltage than those TJs without one. It seems that TJs without one default to the lowest voltage.
 
Steel City 06 said:
What voltage does your TJ normally charge at? If you have the battery temperature sensor it may be setting a higher voltage than those TJs without one. It seems that TJs without one default to the lowest voltage.
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An an electrical guy who doesn't mind getting into circuits, I have never bothered checking since mine works well as the factory designed it. I never had a problem with how it charged my batteries in either of my two TJs. I believe this worry causing much hand-wringing for some to be completely unnecessary. If I had a problem with battery life I would have looked into that.
 
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