100AH wet deep cycle battery charge rates

[PhilipA]

I have a century wet 100AH battery which is 2 years old and rarely been used . It is often charged with a 20amp 3 stage charger . It is a second batery in my D2 and an Optima blue D34 is the starting battery. The controller is an ABR controller which separtaes at 12.4 volts.

My problem is that when I charge with a 150watt (claimed) solar panel through a GSL MPPT controller directly to the wet battery starting at say 12.1 volts, the charge input is 5 amps. Once the battery charge increases to 12.9-13.0 volts the charge rate reduces to 2 amps or so. This rises to 4-5 amps as the Engel fridge cycles on and remains at 4-5 amps for the entire cycle time. Once the cycle is over the charge rate comes down again to 2amps. This is measured by an inline ABR little volt/amp/watts /time whatever meter.

If I force connect the Optima which is sitting on say 12.5 volts the charge rate will increase to 4 or 5amps until the Optima also shows say 13.0+ volts then it will reduce down.

My theory is that the internal resistance of the wet cell battery is causing the drop off in current.

My problem is that the SOC of the deep cycle battery does not recover the usage of the fridge for a 24 hour period, although it did last 3 days , second day starting at 12.1 volts before solar charging 28AH total and third day 11.9 volts.( which is getting down there) before we came home. This is because the output of the solar panel is reduced by the MPPT controller

I am now thinking to replace the wet deep cycle battery with an AGM as I cannot recall this type of problem when I last had an AGM as their internal resistance is lower.
Comments?
Regards Philip A

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[Aaron IIA]

Are you measuring the voltage at the wet cell battery terminals or at the mppt solar regulator? Is the regulator at the solar panel or the battery?

Aaron

[PhilipA]

I am measuring the amps after the regulator so effectively at the battery while charging.

The MPPT regulator is positioned near the battery and the watt meter is between the regulator and the battery. The cable run is about 300MM. I use a Merit plug near the battery but have checked using clamps on the terminals with same result.
The cable run to the solar panel is 20metres using 8gauge marine tinned cable.
I have used this cable run with a previous 140watt solar panel and AGM battery with same MPPT controller and used to see 6-7 amps.
Connectors are new solar type connectors at the panel and new genuine 40 amp Anderson plugs at the MPPT end.
Regards Philip A

[DiscoMick]

12.9-13.0 is fully charged, so your charger will certainly drop into maintenance mode.

[Aaron IIA]

Voltage, measured in volts, and current, measured in amperes, are two different electrical parameters. The internal resistance of the battery can limit the charge current, but the regulated charge voltage is limited by the regulator. This should rise to around 14.0V for the bulk period of the change, then stay at around 14.0V for the absorption period of the charge. Some regulators will then remain at a float voltage of around 14.0V, while others will drop to around 13.0~13.4V after a set or variable period of time. If a variable period of time, this is usually determined inverse proportionally to the initial starting voltage. For some reason, your regulator seems to be dropping the regulated voltage too soon. We can assume that there is enough sun light hitting the panel, as you stated that the current picks up when the refrigerator cycles on. What would happen if you were to disconnect and then reconnect the solar input to the regulator, tricking it into thinking that it was a new day. This could also be achieved by completely blackening the panel for a few minutes.

I am still interested in what the voltage is directly on the regulator terminals compared to the battery terminals. You don't know if you have voltage drop unless you accurately check.

Aaron

[PhilipA]

What would happen if you were to disconnect and then reconnect the solar input to the regulator, tricking it into thinking that it was a new day. This could also be achieved by completely blackening the panel for a few minutes.


Yes have done that and shows about 5+amps for a few seconds then back to 2 amps when the battery is over 13volts.

If I can leave it long enough it will get to 14.2volts and then go onto float at 13.4,eventually . That is in warmer sunnier weather when I connect solar as soon as setting up camp, with the battery well charged.

I have been reading on this for several hours now and what I think I need is an AGM or better still LifePO4 if only I can afford one. I am suspicious of the cheaper LifePO4s but I notice EV Australia has a Winston 90AH for $720 , which is the gold standard.(Except it is 250MM tall)
WOW I have been reading or watching Betta batteries videos about the latest on Lead Crystal. What a crock.
Having to charge a 100amp battery at minimum 30amps every month or they spring a hissy fit. So you have to buy a 30amp charger . And what about if you purchased them for remote solar where you do not have the opportunity to charge at .3C.
Regards Philip A