12V mystery

[narcodog]

Here's one I cannot figure out. I have two AGM group 31 battery's that are about four years old. They stay plugged in when at home and I have a 2020 Trimetric monitor which I monitor often whether on the road or here at home to see if there is any change.
Now the mystery, last week I drove eleven hours with a stop over night after seven hours. The monitor was reading 12.6v when I hit the road. I arrived at my destination and spent the night where I was going to be parked for three nights. Wed. night I used LED lights, pump a little and the fridge was on 12v. Thursday morning the reading was 12.5 and the monitor stated I was at 99%. At noon I came back to the rig and the volts were at 12.5 and 95%. At 5pm I returned and my reading was 11.2v. Now nothing was on, no lights, no pump no furnace just the fridge and CO/LP detector.

I ran the genset for three hours knowing it was not going to recharge the batterys in that amount of time. At 0500 I got up and the fridge was flashing and the batterys were dead again, which was expected.

I hit the main switch and used my third battery a group 27 which is on a separate circuit. That battery lasted through Friday and Saturday.

On Saturday night I was at a State Park and plugged in. The batteries took the charge and I kept them charging until Sunday evening. I hit the main switch because I wanted to see if they would now hold the charge, and they did straight through Tuesday morning when I hit the road. Drove two days home and did not plug in until Thursday, again to see if the would hold the charge, and they did.

So, here what do you 12v guru's think might have happened as this has never occurred in the 13 years that I have had the rig.

[NRALIFR]

That’s correct Robert, the DC-DC charger should be placed as close to the battery or batteries it’s charging as possible. After boosting the voltage to the optimum level for charging, you wouldn’t want to introduce voltage drop from too long a circuit.

There are at least three brands you can consider for a DC-DC charger: Redarc, CTEK, and Renogy. I’m only personally familiar with Redarc, and can recommend them. I think you’ll find the best price is at etrailer. Don’t undersize the wires between the truck batteries and the DC-DC charger or you’ll be disappointed with the performance.

:):)

[adamis]

Camper_Jeff_&_Kelli wrote:

NRALIFR wrote:

Camper_Jeff_&_Kelli wrote:
..........
Just another point. If you have 2 AGM batteries rated at 12.8 volts in the TC and a regular lead acid battery rated at 12.6 volts in the truck. It is possible that the AGM's may be fooling your voltage regulator with the different voltage rated batteries. I have all AGM batteries in the TC and the truck, trying to better match the whole electrical system for 12.8 volts.

Another good reason to have a DC-DC charger in the camper. You get the right charging voltage for your camper battery chemistry, and it acts as a battery separator between the truck and camper batteries. The truck charging system doesn’t know its there.

:):)

I need to look into the DC to DC Charging System.
One quick question, Is it typically mounted in the truck camper near the batteries or in the engine compartment?

You may get a few opinions on this so don't quote my answer as gospel but in my own case, I have the DC to DC charger in the camper. My reason for doing this is that I knew I would experience a voltage drop from the truck to the camper. By placing the DC to DC charger in the camper I am counting on the charger being smart enough to pull more current from the truck in order to boost the voltage being used to charge the batteries. If you put the charger on the truck, the charger will have higher input voltage but it still has to deal with the line loss from truck to camper.

[Camper_Jeff___K]

NRALIFR wrote:

Camper_Jeff_&_Kelli wrote:
..........
Just another point. If you have 2 AGM batteries rated at 12.8 volts in the TC and a regular lead acid battery rated at 12.6 volts in the truck. It is possible that the AGM's may be fooling your voltage regulator with the different voltage rated batteries. I have all AGM batteries in the TC and the truck, trying to better match the whole electrical system for 12.8 volts.

Another good reason to have a DC-DC charger in the camper. You get the right charging voltage for your camper battery chemistry, and it acts as a battery separator between the truck and camper batteries. The truck charging system doesn’t know its there.

:):)

I need to look into the DC to DC Charging System.
One quick question, Is it typically mounted in the truck camper near the batteries or in the engine compartment?

[NRALIFR]

Camper_Jeff_&_Kelli wrote:
..........
Just another point. If you have 2 AGM batteries rated at 12.8 volts in the TC and a regular lead acid battery rated at 12.6 volts in the truck. It is possible that the AGM's may be fooling your voltage regulator with the different voltage rated batteries. I have all AGM batteries in the TC and the truck, trying to better match the whole electrical system for 12.8 volts.

Another good reason to have a DC-DC charger in the camper. You get the right charging voltage for your camper battery chemistry, and it acts as a battery separator between the truck and camper batteries. The truck charging system doesn’t know its there.

:):)

[Camper_Jeff___K]

I had an odd occurrence one time. I was driving several hours at night. It was cold outside, raining hard, fogging and cold inside the truck. I had the headlights on, AC defrost on, Fan on high, All the running lights blaring. I had a full battery when I started and ended up with 2 AGM group 31's at 12.2 volts. I'm guessing my alternator could not meet the demand. I have a new alternator now and have not had the problem happen since.

Just another point. If you have 2 AGM batteries rated at 12.8 volts in the TC and a regular lead acid battery rated at 12.6 volts in the truck. It is possible that the AGM's may be fooling your voltage regulator with the different voltage rated batteries. I have all AGM batteries in the TC and the truck, trying to better match the whole electrical system for 12.8 volts.

[narcodog]

Well, after having the battery's plugged in and then unplugged the battery's are dead. I called Randy at Best Converter today and bought two Full River group 31's. Oh everything checks out, so it still remains a mystery.
Thanks for all of the suggestions.

[narcodog]

pianotuna wrote:
Hi deltabravo,

Because at 85% state of charge, a bank can only accept 12.5 amps per 100 amp-hours of storage. As the bank gets closer and closer to 100% that number drops off--so it may be only 4 amps at 92% state of charge.

That is why no one in their right mind attempts to fully charge a bank from a generator--the run times become huge.

It is true that tapering on charging happens later with AGM jars.

The best thing to do is find an inexpensive campground. Try freecampsites.net

PT you are correct. Today is Sunday and it has taken since Thursday morning to get the battery's fully charged. If one does not have Trimetric or another high tech monitor you will not know when they are fully charged. When fully charged the Trimeteric will read 0.00 which means no more amps are needed to charge the battery's. Now it will be on maintance, float whatever you want to call it.

Those plug in and a multimeter will not show when the bank is fully saturated.

deltabravo wrote:
Why would it take more than 3 hours to charge that size battery bank?

[pianotuna]

Hi deltabravo,

Because at 85% state of charge, a bank can only accept 12.5 amps per 100 amp-hours of storage. As the bank gets closer and closer to 100% that number drops off--so it may be only 4 amps at 92% state of charge.

That is why no one in their right mind attempts to fully charge a bank from a generator--the run times become huge.

It is true that tapering on charging happens later with AGM jars.

The best thing to do is find an inexpensive campground. Try freecampsites.net

deltabravo wrote:
Why would it take more than 3 hours to charge that size battery bank?

[Grit_dog]

Well narcodog, it’s your mystery maybe that’s why. Just sayin.....

[deltabravo]

narcodog wrote:
I ran the genset for three hours knowing it was not going to recharge the batterys in that amount of time.

Why would it take more than 3 hours to charge that size battery bank?

[narcodog]

Thanks for all the good commentary but I don't think anyone has hit on what occurred.

The fridg was on LP, the fans were off, had that happen in WY one time. I was not charging any electronics and the mattress pads were not plugged in.

According to the Trimetric the batterys are fully charged now. so I'm going to disconnect from shore power and see what happens.

[Camp_woof]

Are your batteries in series, if so perhaps there is an intermittent short in one of the cells. Shorts can heal with charging, especially faster charging. But they can also come back ...

Measure each battery separately if you can.

Dave

[Flapper]

And don't forget - hot of a charger, it can take as long as a day for the charge level to read accurately. And for batteries that have been in service, one should wait at least 1/2 hr with no use before taking a volt reading.
I'm thinking you were seeing a lot of "surface charge" numbers, that reverted to real lower ones after they had rested unused for a while.....

[AnEv942]

Our fridge has 4 positions, DC, AC, Gas and Auto. If option other than auto selected its not supposed to switch -but has twice (over18 years) switching from gas to DC while away. One time did run out of gas but it still should not have switched, batteries flat. Second time still had gas but coming back to camper hour later it was on DC, maybe brushed the panel while throwing on coat.
Its something I have never been able to duplicate short of manually switching -so how or why I've no clue.
That said if refer switched to 12v it would show on control panel.
That batteries were only 11.2v, over 5 hours well at least on ours fridge was not on 12v very long.

Other sources of draw, vent that has auto temp, or refer fans?
Too many electronics charging or on standby, or something self awakening becoming active.