16 replies to this topic

[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.

Edited by veryactivelife, 07 August 2019 - 12:28 PM.

[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.

Edited by klahanie, 07 August 2019 - 04:49 AM.

[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.