Lead Carbon - Current slowly rising while charging during CV phase

[rbs]

I have a brand new 100Ah Lead Carbon 12v battery. Which I will be using in my boat as a deep cycle for the instruments.

OCV was 12.74V when unboxed.

Manufacturer specs state 14.7V @ 0.1C recommended (0.3C maximum initial) for cyclic use.

So I attached my battery charger set the voltage to 14.7V, and set a maximum current of 10A with a cut off at 1A.

As I expected, the current tapered off very quickly to 1.7A and of course the voltage rose very quickly and stabilized at 14.7V.

But the behavior I did not expect is that the current is slowly rising. Over the last 60 - 90 minutes, the current has gone from 1.7A to 2.21A and appears to be continually climbing.

I had fully expected the current to continue to drop down to 1A which is what I see with my other non-carbon SLA/FLA and AGM batteries.

Can anyone explain what is happening here please?

 

[sunshine_eggo]

Is the battery temperature rising? This typically accounts for the current rise. As temperature increases, voltage decreases, thus more current is required to maintain the same voltage. This is very common when equalizing batteries as their temperature increases in response to the over-charge.

Is the battery compartment well ventilated, or can heat accumulate?

Is your charger temperature compensated?

Were you charging at exactly 25°C/77°C?

 

[wholybee]

I'm not experienced with Lead Carbon, but if the tail current is down to 1.7% of capacity, shouldn't you drop to float voltage? If you are still applying 14.7 volts is the battery warming up? The temp increase could explain the slight increase in current.

 

[rbs]

Is the battery temperature rising? This typically accounts for the current rise. As temperature increases, voltage decreases, thus more current is required to maintain the same voltage. This is very common when equalizing batteries as their temperature increases in response to the over-charge.

Is the battery compartment well ventilated, or can heat accumulate?

Is your charger temperature compensated?

Were you charging at exactly 25°C/77°C?

The battery is in my living room. The AC is set to 24degC, A laser temp sensor pointed at it reads 25deg and the temp sensor on the charger is showing 25C

The current climbed steadily to 2.32A and has been dropping ever since, down to 1.8A now...

Maybe it is as simple as I didn't give the battery time to warm up after unboxing it...

 

[rbs]

I'm not experienced with Lead Carbon, but if the tail current is down to 1.7% of capacity, shouldn't you drop to float voltage? If you are still applying 14.7 volts is the battery warming up? The temp increase could explain the slight increase in current.

The I-terminate is 0.01C so at 1A the CV phase should be terminated.

 

[sunshine_eggo]

The battery is in my living room. The AC is set to 24degC, A laser temp sensor pointed at it reads 25deg and the temp sensor on the charger is showing 25C

The current climbed steadily to 2.32A and has been dropping ever since, down to 1.8A now...

Maybe it is as simple as I didn't give the battery time to warm up after unboxing it...

if the battery started cold and warmed to room temp, that's it.

 

[OzSolar]

The battery warming up is all I can attribute it to as well. It's such a small delta I'm not sure I personally would have thought anything was out of the ordinary but perhaps I should have.

If it was a flooded battery and the delta in amps was much higher I'd say you were starting the knock the sulphation off.