mppt solar charge controller does the current draw affect how it regulates the charge?

gkny

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I have a Victron MPPT charge controller and a Victron battery monitor.  I have noticed that the current readings of the battery monitor are generally less than what I have seen as measured at the panel.  I assume that this is because the batteries are close to fully charged.  What I am curious about is what happens when there is current draw such as the refrigerator kicking on.  Does the solar charge controller just regulate based on the state of the charge on the battery or does it regulate based on the additional draw on the batteries from something like the refrigerator?

 

longy

Overlord of Anarchy
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Charger just works off of voltage readings - so it will respond to a draw as soon as batt voltage drops enuff to trigger it's set points. 

I have a Victron MPPT charge controller and a Victron battery monitor.  I have noticed that the current readings of the battery monitor are generally less than what I have seen as measured at the panel. 
Batt monitor reads net current into/out of batts. Panel display (usually) only measures what flows thru panel. So if you have 20 amps charge from solar, and concurrently a pump consuming 15 amps thru panel, batt mon will read 5 amps positive, panel will read 15 amp negative

 

IStream

Super Anarchist
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Also, make sure you're comparing apples to apples. The power from the panels equals the power to the batteries (less charge controller efficiency) but P = V * A so if you're measuring panel output, V will be higher and A will be lower than what comes out of the controller.

 
Your panel will output whatever current it is capable of for the conditions, the MPPT "should" send the optimal current to the battery based on the charge state of the battery and the capability of the panel when it needs it (this includes harvesting if needed), many MPPT output in bursts that are fast enough to appear as DC.

Most battery chemistries have lower top up charging requirements when they get somewhere over 80-90% and most chemistries require a lower maintenance current/resistance to get to full.  Yours may also be able to compensate the current for battery temperature if you have the sensor. 

Then you have losses in the cables, connectors, and all that other stuff.

As for: 

Does the solar charge controller just regulate based on the state of the charge on the battery or does it regulate based on the additional draw on the batteries from something like the refrigerator?
Depends how fancy your charge controller is if that is an option. It is not on mine, however that is a function of my inverter which controls and monitors my battery bank.

 

weightless

Super Anarchist
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Does the solar charge controller just regulate based on the state of the charge on the battery or does it regulate based on the additional draw on the batteries from something like the refrigerator?
If by state of charge you're thinking about the states of the charging algorithm (eg. bulk, absorption, float) then I think it might be complicated and the programmer will have made some choices. 

If you're just wondering if the controller reacts to changes in loading then I think longy covered it; those loads are reflected in the battery voltage and the controller reacts to changes in voltage.

A smart controller/charger has to decided when to change states. I believe the main input is usually battery voltage and to allow it to make "smart" decisions there will be some kind of time keeping and/or current monitoring. So, ideally the bulk state might end at some voltage, the absorption state at some acceptance current and the float state might last for some indefinite period. Since loads will change the battery voltage and the current that the controller sees and because it's a solar controller and sunshine is unreliable the states may not proceed nicely. I'm sure the folks who designed the controller will have considered the edge cases.   

 
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