Photon to calculate Float Mode of a deep cycle battery charger

I was wondering if it is possible to monitor a deep cycle battery charger with a Photon.
I need to know a charger has reached float stage.
Perhaps by using a current sensor and voltage divider, take measurements of current drop vs voltage over time as it tapers off after absorbtion ? Does this seem like a correct approach?

You can use INA219 Voltage sensor to send back the battery voltage and then graph it out to see the different stages of the charging process over time.

You can also use the Float Indicator on the charger as an indicator by measuring the light it gives off if it’s a LED or the voltage to that LED when it’s ON.

The led is a great idea, but in cases where indicating lights dont exist I would need the graph.

Anybody to assist with this issue?

Have you considered the suggestion of @RWB about INA219?
Or if you can state what cell chemistry you’re intending to use a dedicated charge controller could be found - @RWB has quite some experience with rechargables.

I do have an Allegro ACS758 Series Hall Current Sensor 150amps max.
What I thought of doing was measuring the voltage of a 12v deep cycle battery as an example, while being charged. If the voltage was less or equal to 13.3v and charging current was less or equal 1amp then to trigger an action.
I dont know how to take these measurements over a period of time(lets say 1 minute), then execute the trigger.
Does this make sense?

What do you mean by a dedicated charge controller?

You just set up some timer that fires in regular intervals and triggers the reading of voltage and current, and store these readings in some array to collect the history of the readings and perform the analysis on that array.
Circular or ring buffers are quite useful for such things.
You may also want to make your buffer retained in case you want to use deep sleep or a reset might happen, to prevent losing past readings.

It depends on how quickly you want/need to identify the Float Stage has started.
With a 3 Stage Charger, Stage 3 (Float) would be identified as soon as the Voltage starts to drop off, since Stage 2 has ended the Constant Voltage portion of the charge profile. Depending on the battery, it could take several hours for the voltage to drop to the “resting” voltage.

The Float Stage is the only time the Voltage should decrease. The Amps could theoretically increase over short periods in the initial Float Stage.

If you want/need to know asap that Float Stage has started, you will need to watch for the voltage drop.
If the timing isn’t critical, then you could watch for the Voltage & Current Threshold values.

I would like to try this approach. Can you guide me towards a tutorial or example code of this?

The dillema I am facing is this…
When the charger is turned on, voltage rises slowly during bulk stage. During Absorbtion amps drop slowly over time.
I want to know roughly when absorbtion has almost finished.
The reason I need to know, is to kill a backup generator that is charging a battery bank. As this charging process can go on for hours, its essential to know when batteries are at least 85% charged rather than having the generator run for extended periods until they reach 100% SOC.

No Worries… recognizing ~85% of Stage 2 shouldn’t be any harder to accomplish.
If you were able to have the Electron log the Voltage & Current for a few Charge Cycles, you could remove some logic from the CODE for a particular installation.

You may need to also measure the Current leaving the battery bank (Load) and subtract this from your Charging Current.

Do you by any chance have a sample code of this?
How to log these measurements.

If you have internet access or if your using an Electron with cellular access I would just post the battery voltage to a dashboard service like Ubidots or Losant and push the voltage of the battery to that service for databasing and graphing.

Then you can create a dashboard to show the battery voltage over time and create alerts via SMS or email when the battery voltage goes over certain thresholds like the voltage you hit at the end of the charge cycle before going into float mode.

I will check that out, thanks!
But will also need a solution if no internet is available.

Why do you want to monitor it?

I dont want to monitor it. I just want to know when that point in charging process happens to kill generator through code. With or without internet connection.

OK, just use the INA219 to measure the voltage of the battery and trigger the generator to stop one the photon sees the battery voltage at the peak charging voltage and then add a 20min to 1-hour delay to the generator turn off action.

Graphing the charging voltage slopes will give you a better idea of when to trigger the gen to shut off.