Solar CC going from Bulk to Absorb with a load on battery?

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Solar CC going from Bulk to Absorb with a load on battery?

Postby Jman » Tue Sep 18, 2018 6:13 pm

Hello.

How does this work with solar controllers? Because with my AC 3 stage smart charger right in the end of bulk stage at 14.3V I turn a load on from battery terminals & it will stay stuck in bulk & won't go into absorption until the load is off, and it's not even a big load. As I understand this sag is just the nature of constant current mode.

Do solar controllers recognise a sudden load in late bulk & just switch to absorb? What happens with a constant load throughout bulk?

If the controller holds the constant current until the voltage eventually rises to 14.4V does this mean the battery will overcharge?

I can't test this out as I have only have a tiny solar panel atm, so wanted to ask, Thanks
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Re: Solar CC going from Bulk to Absorb with a load on batter

Postby Gordon-Loomberah » Tue Sep 18, 2018 7:42 pm

The load you turned on will have kept battery voltage below Vabsorb, meaning the charger will continue in bulk charging. It doesn't have to be a big load, just sufficient that the charger doesn't have enough output to supply the load plus the necessary current for the battery to reach Vabsorb.

The staying in bulk charging mode is generally determined by the battery voltage (although some chargers may use a timer, which wont give as good a result), and how the charger interprets that, IE it might switch directly to absorb when Vabsorb is reached, or it might wait, for example, until it has been maintained for 30 sec. In the latter case, if the voltage drops below Vabsorb after 20 secs at that voltage, the 30 sec timer will start again once it reaches Vabsorb.

Any overcharging is likely to occur in the absorb (constant voltage) stage, rather than the bulk (max current) stage, since a battery will never be at 100% SOC after bulk charging (to the correct end voltage where absorb starts).

Having too small a panel, ie very low current charging, may cause sulphation in some batteries.
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Re: Solar CC going from Bulk to Absorb with a load on batter

Postby australsolarier » Wed Sep 19, 2018 6:44 am

jman,
you really have to tell us what the charger is delivering and what your load was drawing.
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Re: Solar CC going from Bulk to Absorb with a load on batter

Postby davidg » Wed Sep 19, 2018 7:36 pm

What Gordon says is exactly how any decent charger/system should work.
The timings depend on the charging design though some are programmable some are not.
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Re: Solar CC going from Bulk to Absorb with a load on batter

Postby Jman » Thu Sep 20, 2018 6:20 pm

australsolarier wrote:jman,
you really have to tell us what the charger is delivering and what your load was drawing.

Hi,
Well I think I figured out what is going on, the extra load just delayed the absorb set point.

The charger was delivering 35A & the load was constant 15A, so does this mean the battery gets only 20A or does it vary alot?

cheers
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Re: Solar CC going from Bulk to Absorb with a load on batter

Postby Gordon-Loomberah » Thu Sep 20, 2018 6:34 pm

The net charge or discharging rate of the battery is whatever the charger is delivering less any loads. If one or both of those vary, then the net charging, or discharging (when loads exceed output of charger), will vary.
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