MPPT 75/10 Not using full solar power ?

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urs-hofer asked Jul 10, '19

MPPT 75/10 Not using full solar power ?

Hello -

I'm using a MPPT 75/10 with a 100 W Panel and a 45AH Exide Solar Battery. Short Circuit Current of the Panel is now about 4 Amperes on about 20 Volt.

The Controller never loads the Battery with more than 1.8A - max load current is set to 15 A.

Which means, a Load consuming 3.5 Amperes always uses the Battery, even if the Solar Panel is producing more Power.

I'm a newbie - so there's probably something to configure I don't know?

The Load is attached to the controller, not to the battery.

Thanks for any advice

Urs Hofer

Solar Panel

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Answer 1 · 2019-07-10T11:01:15Z

Mark answered · Jul 10, 2019 at 11:01 AM

If you can possibly provide some screen images from VictronConnect it may help to diagnose.

But in general if it's an overcast day you may only get about ~10%-25% of your panels max power output which is ~10-25W for a 100W solar panel.

So assuming your running a 12v battery and charging at ~14.4v, then the MPPT charge current @25% panel output would only be 25W/14.4V = 1.7A.

So unless it's a bright summers day and your solar panel is facing directly at the sun, then there may be nothing wrong - you may just need more solar power/panels...

Even at the full 100W of solar power (that needs near perfect conditions and would rarely occur) the max MPPT charge current output is still only ~6.9A (100W / 14.4V).

The max charge current limit set in your MPPT is purely a limit and can only be achieved if you have enough solar power to do so.

Lastly, if the MPPT is towards the end of the absorption phase or float with no or little load connected, then the MPPT will automatically reduce the charge current to maintain the voltage setpoint. In your case it sounds like your having this issue with the charger in bulk phase while running a load - so probably not the explanation.

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urs-hofer commented · Jul 10, 2019 at 04:00 PM

Thanks for your detailed explanation. I was just wondering why the battery is still decharged with -1.8 A if I am consuming 3.8 A load and the input from the solar panel is only 2 A even if my panel is delivering 3.8 A short circuit power (measured it the very same moment with the same sunny situation). The math makes total sense (2 - 3.8 = -1.8), only the difference between 2A on VictronConnect and 3.8A short circuit power not for the solar panel.

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