Charge current

[Yoshimura]

I just bought a DC current clamp and decided to log the charge current of my 105 Ah AGM battery. Before charging it, I applied a 5A load during 12h (60 Ah). Before that, the battery was on the charger for numerous days.

If I understand correctly, the battery was in bulk charging for the first 1.5 hour and went to float after 4h? After that, I don't know how to interpret the current.

Your comments are welcome!

[booster]

Originally Posted by Yoshimura

I just bought a DC current clamp and decided to log the charge current of my 105 Ah AGM battery. Before charging it, I applied a 5A load during 12h (60 Ah). Before that, the battery was on the charger for numerous days.

If I understand correctly, the battery was in bulk charging for the first 1.5 hour and went to float after 4h? After that, I don't know how to interpret the current.

Your comments are welcome!

How are you measuring the state of charge?

[Yoshimura]

Originally Posted by booster

How are you measuring the state of charge?

"Total charge" in my graph is integration of current over time. However, I don't know if this represent state of charge.

[booster]

If you could hold the charger in absorption for longer, then your amps readings would give you a much better idea of where you are, where you were for SOC after the discharge, and how full you got the battery on recharge. Without that, it gets really tough on an AGM where you can't directly check SOC with specific gravity like you can on wet cells. Knowing the system voltage would also have made it more useful to determine what stage the charger was in.



The amps curve is what I would expect to see for the most part.


Charger was in bulk at constant current for 1.5 hours and then dropped current quite quickly may have gone to float and maybe not. If it was holding voltage at 14.4v or so it was in absorption and just tapering the current as SOC came up. My guess it was in absorption until 4 hours and then went to float.


After 4 hours did you notice, or even does it show, which direction the current was going until it bottomed out at zero at 5.5 hours? My guess is that the current might be negative at that point as the surface charge came off, but without direction can't be certain. It is very normal to see negative current for a while right after going to float. If it was negative, it didn't do a bounce like is shown in the graph, it would have just gone through zero and back to positive and started the slow positive current in float.


All speculation, but without more data pretty tough to get more.

[GeorgeRa]

In 1.5 hrs there is a sharp drop in current but Ah is steady, is it a margin of error in your calculation.

[Yoshimura]

Originally Posted by booster

After 4 hours did you notice, or even does it show, which direction the current was going until it bottomed out at zero at 5.5 hours? My guess is that the current might be negative at that point as the surface charge came off, but without direction can't be certain. It is very normal to see negative current for a while right after going to float. If it was negative, it didn't do a bounce like is shown in the graph, it would have just gone through zero and back to positive and started the slow positive current in float.

The meter displays positive and negative current so I would expect it to also log negative current. But I will need to check.

I just remembered that the inverter manual explains the charge stages...

So the first 1.5 hour was Boost CC, then Boost CV for 2.5 hours. But after 4 hours, it doesn't seem to match documentation.

Bulk charging is CC and Absorption would be CV?

[Yoshimura]

Originally Posted by GeorgeRa

In 1.5 hrs there is a sharp drop in current but Ah is steady, is it a margin of error in your calculation.

To me, the slope of Ah seems to correctly matches the current level.

[Yoshimura]

Originally Posted by booster

If you could hold the charger in absorption for longer, then your amps readings would give you a much better idea of where you are, where you were for SOC after the discharge, and how full you got the battery on recharge.

So I should have logged current longer?

[booster]

We can't really tell what the timer would calculate because we don't know how long it took to get to the second stage, boost CV. All we see is the constant current, so it likely the voltage was rising over that time until it got to CV stage start point. 3% voltage rise before that point X 10 would be how long the CV stage would run and would be different on every charge cycle.