Help Needed: Aux Battery not Charging (1 Viewer)

[wildpaths]

Hi all. I'd love some assistance on diagnosing my charging problem on my aux battery.

Vehicle: 2001 Land Cruiser with 215k miles, T-Max Dual Battery Management System, Main Battery: Diehard AGM Gold 34R manf Date 2/18, Aux Battery: Diehard AGM Gold 34 manf Date 3/18. You may all know this vehicle as it was previously owned Paul Gardner.

All accessories are wired into the AUX Battery: 3x LED Bars, ARB 47L Fridge, HAM, CB, 1100W Krieger Inverter.

Everything worked okay when driving everyday between camp-sites, and doing little other than sleeping with the fridge running. We just did our first trip where we camped out of the stationary vehicle for 3 nights with no driving, and had heavy use of the electrical system. Inverter was used to charge laptop and drone battery. Fridge/Freezer running. Temps were 77 daytime high and 40 nighttime low.

Inverter started alarming and ARB Fridge would stop cooling indicating low voltage in AUX system. Running vehicle for 30 min to charge would only fix problem for about 4 hours or less. I also connected the main and aux batteries with jumper cables during charging to bypass T-Max and ensure charging, but this produced similar results.

Information so far:

1) Both batteries test ok at local AutoZone. Main battery showed full charge at 12.6v. Aux battery showed only 12.0V charge (about 25%) at AutoZone, and this is after 5 hour drive back from Mammoth (with headlights on and A/C on).

2) Alternator tests ok with in-car test at AutoZone. This was an unloaded test.

3) My voltmeter test of the alternator (with Aux Battery disconnected) showed 13.77v output at 1500RPM unloaded, and 13.61v output at 1500RPM loaded (A/C and high beams). This makes me think alternator is fine, but a little challenged due to age.

4) I have not been able to test the T-Max system yet. Any ideas of how to best do this? Compare charging voltage at the AUX battery with T-Max vs directly connected?

My guess:

Assuming the T-Max is operating correctly, The system isn't broken, just not designed or operating optimally. I am putting a strong demand on the system. The AUX battery is not a true deep cycle. The alternator is likely aging and could have stronger output.

My proposed fix:

A) Clean and reconnect all main electrical connections in the battery and charging circuits.

B) Replace Aux Battery with true deep-cycle. Any recommendations on what would fit in a 100 Land Cruiser? Anybody want to trade batteries? Your good condition deep-cycle for an almost new DieHard Gold AGM?

C) Replace/Upgrade the Alternator. Does this even need to be done based on the voltage data and the good test? Is there a way to get more performance out of the alternator with a better replacement alternator, to better charge a deep-cycle? Or are deep-cycle charging improvements better achieved with some other device dedicated to the aux circuit, so as not to affect the rest of the stock Toyota wiring?

Thanks in advance for any advice, questions, or corrections of my logic. I am not so good with electronics.

 

[J1000]

Voltage is too low to ensure a good charge on a deep cycle battery. You need to be in the 14.4 volt range. 13.6v would be ok for trickle charging or maintenance charge, but in order to bring it back from deep cycle use you need 14.4v minimum, 14.8 preferred.

 

[vman07]

On my dual setup I periodically throw a trickle charger overnight on my second battery, because my 07 LX never puts out 14.4 volts.

My second battery is a deep cycle Optima yellow top.

 

[wildpaths]

Voltage is too low to ensure a good charge on a deep cycle battery. You need to be in the 14.4 volt range. 13.6v would be ok for trickle charging or maintenance charge, but in order to bring it back from deep cycle use you need 14.4v minimum, 14.8 preferred.

Understood. This brings 3 follow-up questions for me.

1) Does this mean my alternator should be replaced in general, because it is only putting out 13.6V under load? What do other LC100 owners typically see for alternator output?

2) Is there a way to get >14.4V out of a LC100 Alternator? Or some aftermarket add-on in the charging circuit to the aux battery to step up the voltage to >14.4V?

3) My DieHard AGM Gold 34 batteries... Are these considered to be "deep-cycle" batteries? I don't think so. Therefore, they probably don't have the same minimum requirement of >14.4V to charge, correct?

 

[wildpaths]

Update: Total Chicken Little moment.

My conclusion: The system is operating exactly as it is supposed to. I just overtaxed the aux battery so deeply it couldn't recharge on its own from the alternator. An alternator is not a charger. Once the aux battery was back up to full charge and the battery terminals cleaned up, the system produced better than nominal numbers for a Toyota of its age. My thanks to Larry of Dirty Parts for walking me through it all in person at his shop.

My solution:
1) Invest in a good charger and make sure the aux battery is 100% before departing on adventures.
2) Get rid of the inverter due to its horrible inefficiencies, especially how I have it installed rather far from the battery. Instead, 12V adapters for items like laptops that previously used the inverter.
3) Install military grade battery terminals.
4) When the time comes and the DieHard is dead, replace it with a nice Odyssey.
5) As a bonus, I bought one of those alternator boost diodes to increase my alternator output by 0.5V for adventures. I'll just slide that in when I know I'm going to be asking a lot from the batteries. Larry sells them for $40 already made.

My apologies for the freak-out. Hopefully my silly story will answer someone's questions in the future.

 

[vman07]

Do you have a link to that diode? Are there risks involved with running it full time?

 

[wildpaths]

Do you have a link to that diode? Are there risks involved with running it full time?

Here is the link: Dirty Parts

The best answers to its functions and risks would be to call the store and talk to Larry the owner at 310-390-9086.

 

[Suprasoup]

Update: Total Chicken Little moment.

My conclusion: The system is operating exactly as it is supposed to. I just overtaxed the aux battery so deeply it couldn't recharge on its own from the alternator. An alternator is not a charger. Once the aux battery was back up to full charge and the battery terminals cleaned up, the system produced better than nominal numbers for a Toyota of its age. My thanks to Larry of Dirty Parts for walking me through it all in person at his shop.

My solution:
1) Invest in a good charger and make sure the aux battery is 100% before departing on adventures.
2) Get rid of the inverter due to its horrible inefficiencies, especially how I have it installed rather far from the battery. Instead, 12V adapters for items like laptops that previously used the inverter.
3) Install military grade battery terminals.
4) When the time comes and the DieHard is dead, replace it with a nice Odyssey.
5) As a bonus, I bought one of those alternator boost diodes to increase my alternator output by 0.5V for adventures. I'll just slide that in when I know I'm going to be asking a lot from the batteries. Larry sells them for $40 already made.

My apologies for the freak-out. Hopefully my silly story will answer someone's questions in the future.

Here’s some thoughts.

1. Lead acid batteries don’t like being under 100% charged. Anything under 100% damages them. This is especially true of AGM batteries. With Flooded batteries you can do a controlled overcharge to recover capacity and just add water. With AGMs that’s not possible so keep them fully charged as often as you can.

2. Turn them off when not needed. Mount them as close to the battery as possible. Make sure you fuse them at the battery.

3. High quality terminals that are cleaned often is king.

4. The best deep cycle batteries are made by Trojan, US battery and Crown. Odyssey doesn’t hold a candle to them nor is it a true deep cycle battery. Flooded last longer than AGM and cost less to boot.

5. Just make sure you are fully charged before and after your adventure. The alternator will keep them at 100%.

Quick and dirty batteries 101.
Batteries go through three stages of charging. Bulk, absorb and float. Bulk recovers 80% of the charge. absorb recovers the last 20%. Float keeps it at 100% indefinitely. Bulk is constant current charging. Absorb and float are constant voltage charging.

During the bulk phase you push current into the battery, typically some percentage of its C rating. In this stage voltage is not limited. When a battery is depleted it limits voltage. As it accepts current the battery voltage rises. Once voltage rises to a certain voltage, the absorb voltage, you switch to constant voltage charging.

The Absorb stage is where most of us have problems as the absorb stage is not a timed event. At the Absorb voltage the battery will continue to accept current slowly tapering off until what it accepts falls to zero (or some value as determined by the battery manufacture. Again some % of the C rating.). This can take up to 24hrs!
Once that current value has been reached the charging switches over to float. Here the voltage is held at some value that is above a batteries resting voltage but not too high as to be above the gassing voltage. This keeps the battery at 100% and accounts for any parasitic loss.

Alternators are typically only single stage chargers. IE float chargers. They are constant voltage 13.6-13.8v. Does some charging and doesn’t boil a battery dry.

Raise the voltage of your alternator and you’ll spend more time in the bulk phase so recover a little more charge faster. The problem is that now you are way above gassing voltage. Drive around like that all the time and expect to add water frequently as well as cleaning your terminals more often.

For fastest charging use a 3 stage charger. For longest life a single stage constant voltage charger set at the float voltage of the battery is king. It just takes longer to get to 100%. But it will get there.

 

[jrmudder92]

Here is the link: Dirty Parts

The best answers to its functions and risks would be to call the store and talk to Larry the owner at 310-390-9086.

Have you Installed it yet? Is it throwing the battery light? Any other problems?

 

[wildpaths]

Have you Installed it yet? Is it throwing the battery light? Any other problems?

Oh, yeah. It throws the battery light. I am betting that this will have no other negative effect. My plan is to keep it uninstalled, living in my ashtray. When I need the boost on an adventure, I'll put it in, and the battery light will remind me to take it out when I am done.

 

[jrmudder92]

Okay thanks for the clarification!

Oh, yeah. It throws the battery light. I am betting that this will have no other negative effect. My plan is to keep it uninstalled, living in my ashtray. When I need the boost on an adventure, I'll put it in, and the battery light will remind me to take it out when I am done.

 

[danthman114]

what did they test the batteries with?

 

[wildpaths]

what did they test the batteries with?

I went to AutoZone because they are right down the street. They slap a combo battery/alternator tester on the terminals. And the device tells you if the battery is good or bad.

 

[danthman114]

I went to AutoZone because they are right down the street. They slap a combo battery/alternator tester on the terminals. And the device tells you if the battery is good or bad.

just curious because a lot of people out there will use a multimeter and test voltage only which doesn't really say if theres a bad cell. a battery with a bad cell can still read normal voltage, but I'm assuming you know that already..

 

[wildpaths]

just curious because a lot of people out there will use a multimeter and test voltage only which doesn't really say if theres a bad cell. a battery with a bad cell can still read normal voltage, but I'm assuming you know that already..

This device does something different. The technician has to enter the CCA of the battery, and the test takes 30 secs or so. I figure the device is somehow drawing charge and adding charge to see how the battery responds...

 

[dogdaysindurham]

So I was reading through my 05 100 series recently and I noticed this (bottom right corner) that the charging rate is 5A max. The fuse for the alternator charging circuit is 7.5 amps if I recall correctly. Or can the alternator exceed this charging rate if there is excess current to supply? Or is that fuse only used to modulate the alternator's voltage and doesn't necessary limit the current passing through to the battery?

However, if the 5 amp rate is correct, I guess this would explain to me the issues with the larger AGM batteries which generally need a higher charge current.

The 31AGMs have typically 105 amp-hour capacity and should be charged at 20-40% of the capacity (when deeply discharged) so 20-40 amps would be required.