Camper batteries drop when truck is running

[FoxenTec]

I recently noticed the following. Ram Truck and 2018 Grandby camper sits in fog, gray skies and rain for a number of days. The solar panels (2 x 100 watt) don't quite keep the two AGM batteries floated in this weather.

I take the truck out for a long drive, expecting the FWC installed wiring to my truck battery/alternator and separator to bring up the batteries but when I return home they are lower then when I left.

Once the engine of the truck is shut off, I observe my Overland Solar MPPT display unit. I see they are in BULK and as I watch the voltage display, I see the display then slowly climb from say 13.2 volts to the normal 13.8 float.

I noticed this has happened on 4 hour drives also. When we arrive at the campground, the AGM batteries have gone from 13.8 volts in float when we left to 12.9 volts and BULK when we arrive. Once the camper sits for a while in partial sun, the batteries start coming back up. All this info occurs when the battery disconnect is active meaning nothing should be drawing power from the AGM batteries.

My question is whether or not something is drawing power away from the AGM batteries when my truck is running instead of the opposite, actually charging the batteries. Not sure yet how to diagnosis but will start looking into. The first 6 months of ownership this did not happen but the last 4 months it has.

Thank you,

 

[Vic Harder]

Jon, Do you have a volt/ohm meter? Check the truck and camper battery voltages before starting the truck. Start the truck and let the isolator connect and measure both again. Drive for a bit, repeat the measurement, then shut down the truck and measure again.

I'm thinking the truck batteries must have a lower "resting" rate than the camper, maybe because a cell has gone bad sometime in the last few months. The truck's batteries will then drag down the camper batteries.

 

[DYNOBOB]

Not sure if this is your problem but If the house batteries drop below a certain voltage the FWC isolator will not connect to the trucks charging system when you start the truck. This has caught a few folk out. You have to bring them up with solar or shore power to get them to reconnect. I wired a manual 60a switch around the isolator so I can get them charging if they're not connecting automatically.

.

 

[FoxenTec]

Thank you Vic and Bob for your help. I do have a VOM and will follow what you said to do. Always appreciate the great input!

 

[Pax2525]

May be a silly question but want to ask regardless...

Do you have the master kill switch pulled out during these drives and such or is it pushed in?

 

[FoxenTec]

Sorry for not getting back to the forum on this. Regarding the master kill switch. Answer is twofold.

When going camping, it is pushed in because our ARB fridge is then running off the batteries.

When we just take it out for an hours drive, (aka not camping) then it is always pulled out.

When it sits in my driveway during the day, it is also pulled out.

Once this rain stops, I will get in there with my VOM and check what Vic mentioned.

Thank you!

 

[veryactivelife]

When charging from either the truck or solar the switch position does not matter. To change from shore power it must be out. To utilize the 12 volt camper system, as in running the fridge, it needs to be out not in. Unless your ARB is wired straight to the batteries.

Dean

 

[FoxenTec]

We took our first extended trip with the Grandby this July for 10 days. Before we left I checked a few of the recommendatinons that others have listed above. I found that our trucks charging system was providing the correct voltage to our FWC batteries (2 - 12V AGM 70ah) when the engine was running. Our Volt meter as well as the Overland Solar MPPT controller was showing about 14.2V - 14.4 V to the batteries with the engine running.

I did find that when we would pull into a place to camp for the night, the battery voltage read 13.8V and the solar controller showed we were in FLOAT. However, once the engine was shut off and I was able to pull only about 55 - 77 watts off of two 100 watt solar panels due to cloud cover, the 13.8 would drop immediatlely to 13.2 and within an hour 13.0 and finally down to 12.7 and by late evening 12.5. At this point I would shut down our ARB fridge for the night until I could use solar or our generator the next morning to bring the batteries back up to 13.8. (our only DC draw in the camper during this time was the intermitt. running of the ARB fridge which was around 1.5 - 4 amps and of course the carbon monoxide alarm. We use a LED lantern for light in the camper at night)

The batteries were installed 3/2018 by FWC so they are not that old. It seems as soon as a "load" is placed on the batteries, they kinda just start dropping fast. Could it be that I have not properly kept them charged during the gray skies and rain of this past Nov - Mar.? With the 200 watts of solar on the roof, I kinda just let them keep the batteries up during our Central California winter and when I checked the camper they always were between 13.6 and 13.8 with just the solar keeping them charged, so I didn't think to put a charger on them.

One other thing I noticed is that when they would get to say 12.9 volts, I would run my 12 amp charger on shore power for a while and could never get my CTEK AGM battery charger to show "float", they would only show "absorption" BUT the Overland Solar controller would show them in "float". Not sure if that means anything.

I guess I should pull the batteries out of the camper and take and have them tested. Part of my job at work is testing our -48V DC battery plant in our Data Center with a Midtronics tester. Maybe as a first step I will try the Midtronics and see what it comes back with.

Thank you as always for you time and input everyone.

 

[PaulT]

Get a battery monitor like the Victron units. Voltage is a necessary but insufficient measure of battery State Of Charge (SOC).
A battery monitor measures the energy pulled from the battery and/or pushed into the battery so you will know the actual SOC even while under load or charging.

As you have noticed, voltage drops under load. Even if you see 12.5 volts under load, you may be closer to fully charged than you think. Turn off all loads at 12.5 volts, and let it rest for several hours & the voltage may recover to 12.7 or 12.8 volts. This is expected with lead acid batteries. LiFePO4 batteries show much less of this effect.

A fully charged AGM in good condition will show about 12.7-13.0 volts in a resting state while one at 50% charge will show about 12.2 volts. 12.5 resting volts indicates about 70% charge.

Anyway, a battery monitor will give you piece of mind about your batteries. AGM’s will charge quickly to about 80% in bulk mode. They then enter absorption mode and it takes hours to get them high enough to enter float mode about 95% SOC. It may take several days to get them to 100% with your solar.

When adding a battery monitor, it will be necessary to also add a shunt so that the monitor can calculate amp Hours out of and into the batteries.

Have fun and ease your mind.

Paul

 

[rando]

I am not sure I am seeing an issue here. The 'fully charged' voltage of an AGM battery is somewhere between 12.6 - 12.8V depending on the manufacturer, with the caveat that you can only get an accurate idea of the state of charge from the voltage when the battery is neither being charged or has any loads.

What you appear to be seeing is the battery being fully charged (charger in float) then the surface charge bleeding off in the evening as the fridge runs. The late evening measurement is still an 80% charged battery, and probably even higher if the fridge is running or has run recently when you take the measurement. I wouldn't start to worry about charging until the battery is down around 12.0V when not loaded - which would be around 50% SOC.

 

[FoxenTec]

Thank you Rando and PaulT for the comments. I guess I do need to understand the difference between the voltages when under load and resting. I am just so used to always seeing that 13.8 on my display.

I thought my MPPT Controller display was my battery monitor but it sounds like I either I need to better understand the unit and how to use it or use a different monitor.

The instructions for this unit that came from Overland Solar are beyond minimal help.

 

[Lineman]

I second Rando's statements.

I would recommend spending a few days running everything you want to run, including the fridge all night. If the battery voltage is above 12.0v in the mornings, before your solar comes on, you're good to go.

 

[Vic Harder]

I second Rando's statements.

Ditto

 

[veryactivelife]

Rando and iowahiker make good points. I would add that SOC open circuit voltages will vary by battery make and model. My 2015 FWC came equipped with Exide Edge batteries and Exide’s specs state that 12.0 volts is 20% SOC. 12.4=50% and 12.5=60% so everyone’s SOC may vary depending on your battery manufacturer’s specs. Just another reason why a battery monitor with a shunt to measure Ah draws is a good investment in maintaining healthy batteries.

 

[FoxenTec]

Once again thank you all for your input. I am still learning.


I noticed Iowahiker mentioned the following:

- Full voltage not at rest (charging stopped), 13.0-13.3
- Full voltage at rest (no discharge), 12.8-13.0


I would have thought that a battery NOT at rest (meaning it's under load) and no charging would have a lower voltage then a battery that is at rest (no load). Maybe at rest just means it is not being charged?

Thank you,

 

[klahanie]

After charging has stopped or been removed the battery measured voltage will show a surface charge (temporary elevated voltage). After this surface charge is removed and/or the battery is rested - per the mfr-, the voltage will measure lower. And then a more accurate measure of SOC using the battery voltage - per the mfr - can be determined - if that is desired.

I don't know much about solar or MPPT chargers but I would treat the meter display you posted as a voltage meter, continuously showing camper system voltage.

With variables like battery temperature and condition; system loads; the fridge cycling; and multiple source charging etc, it's a dynamic system. ON EDIT: unfortunately I don't think you can't look at the system voltage display and know exactly where everything is at, all the time.

IDK why before the display was showing 13.8v often enough that you got used to it but some of those variables must have different values now. That's not necessarily a bad thing though, IMO, if the system is still providing your power needs.

 

[FoxenTec]

Thank you Klahanie, great info and that does make sense.

Many years ago we had a 24 battery string at work and they asked me to check the batteries voltages with a VOM weekly. I always checked the batteries and they read 2.25 volts which was perfect for this -48V plant. However when we had a power outage, the batteries died quickly before our generator started. I learned then there is a lot more then just reading the voltage across the posts.

Just for fun, I put a Midtronics battery tester on the batteries tonight. They were perfect. The fail message is just a temperature fail due to the min/max settings in the tester. It was 103 today and our camper was closed up. Felt like a 150 inside the camper sitting in the sun. I didn't have an exact reference value for this brand and model but based on past experience they look good.