Should I worry about amp hours while charging

[TimeMachine]

Little confused. 400 watts of solar (Bluetti panels), Renogy DC to DC mppt controller and 2 BattleBorn 12v 100 aH lithium. Charging with solar or shore, I can get a full charge but the amp hours do not get to maximum. I have a Renogy 500amp battery monitor. Does amp hour rating mean anything and all I should be worried about are volts. Hopefully this makes sense. I have searched this forum and google etc but can’t find the answer. Thanks for the help!!!!

 

[Bluedog225]

I think you can safely measure charge state by voltage. Others will know.

 

[MisterSandals]

I have a few shunt type coulomb counters and at least one Hall effect monitor. I pretty much only watched voltage to casually measure SoC so they all eventually ended up in a box, unused.

There are a couple charts that are “good enough for me” to use as a SoC indicator. This is the easiest to use. Steve_S created a few fancy graph type charts from real data that has finer detail if needed.

 

[RCinFLA]

Most coulumb counting battery monitors use a defined battery voltage (end user settable) near full charge to reset their 100% full reference. Normally you want this reset voltage slightly below your absorb voltage setting on your charger.

If you don't allow charge to reach the reset voltage level, at least periodically, then the monitor will cumulate errors in its AH used number and SOC reading over time.

You also need to provide monitor with AH battery capacity. You can make it anything you want if you want to give yourself some safety margin to avoid over discharge.

Many monitors have a charge efficiency factor that derates charge current. Often default set for lead-acid battery with something like 85% charge efficiency. For LFP this should be changed to 98-99%.

 

[mikefitz]

You reset the monitor when the battery is full or empty,
From the instructions,
First set the usable AH capacity of the battery as the preset AH capacity. For Lithium and Sealed Lead Acid batteries to calibrate to 100% charge the battery fully and hold the "up" key for 3s to set the capacity to 100% For Lithium batteries to calibrate to 0% discharge the battery completely and hold the "down" button key for 3s to set the capacity to zero.
full instructions,

https://uk.renogy.com/content/files/Manuals/RBM500-G2.pdf

Once set up it may/should track. Consider that this is a low cost monitor without the enhancements ( like efficiency setting) that a monitor like the Victron Smart Shunt or Victron BMV712 will have. Over time it will accumulate errors so you may have to carry out the calibration process from time to time.

Mike

 

[TimeMachine]

I may have the Renogy monitor installed incorrectly. When plugged into shore power the monitor is showing amp hour increase, when on solar it is not. I download the Renogy app for the mppt and it shows approx 18amps and the Renogy doesn’t. Appreciate everyone’s helping a newcomer on this so far.

 

[mikefitz]

The shunt should be wired as shown. In your application you have two batteries wired in parallel. Apart from the second battery negative there should no other connection to the battery negative other than the B- of the shunt. all other negatives connect directly or indirectly via a buss bar to P-.

Mike

 

[Ampster]

To answer the specific question in the title about what to worry about, voltage is the thing to worry about. As others have said that will the thing to watch as the pack approaches the knees.
I don't worry about Amphours but my inverter and BMS do track kWhrs and it does give me a frame of reference about how much my pack had discharged.

 

[TimeMachine]

View attachment 69230
The shunt should be wired as shown. In your application you have two batteries wired in parallel. Apart from the second battery negative there should no other connection to the battery negative other than the B- of the shunt. all other negatives connect directly or indirectly via a buss bar to P-.

Mike

Thanks Mike!!!! That was my issue, controller was not connected to P-.