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Victron 100/20 sizing questions

That thread talks about short-circuiting the input. Other threads on the Victron Community site say the same thing. What no one has been able (or willing?) to explain is why a controller would ever short-circuit the input. It seems to me that if they want to protect from over-charging, they could just turn off the inputs.
My best-uneducated guess is that it's probably down to the inner circuitry or electrical components of the SCC. Maybe it's the only way the SCC can stop the panels from frying the SCC when the BMS cuts off the battery from the SCC or similar events.

Would love it if someone that perhaps has a deeper understanding of these things would shed some light on this.
 
The temperature messing with the voltage current is in the spec of the solar panel. It's not voodoo. Just think of it like tire pressure. If the MPPT says the most pressure it can handle is 100 and the fastest you can drive is 20, then you know pressure changes with temperature. In the case of solar, voltage pressure goes up when the temperature goes down. So, the spec will tell you by how much with each degree change from 21C (about 72F).

If you don't want to run the numbers, there are solar calculators online (free). Or you can swag it like the 99% of us by oversizing the MPPT.
 
I put 800 watts of panels through my 100/20 for a couple of months on a 24volt system. 200 watts were mostly wasted so I went back down to 600 watts. Then I bought more panels and a bigger controller.
 
Please be sure to check your system and ensure that your 24V in alignment with what Victron calls 24V. If you check their spec for wattage, you will notice that 24V is actually 29V. Unless you hit 29V, for example, 100/20 will not give you the rated 580W. The math wouldn't work. 24V*20A is 480W -- not 580. You have to use 29V to get the rated 580 (again 29V * 20A).
 
Please be sure to check your system and ensure that your 24V in alignment with what Victron calls 24V. If you check their spec for wattage, you will notice that 24V is actually 29V. Unless you hit 29V, for example, 100/20 will not give you the rated 580W. The math wouldn't work. 24V*20A is 480W -- not 580. You have to use 29V to get the rated 580 (again 29V * 20A).
I actually see the 580w rating as the maximum that the charge controller can output. Not necessarily that it will output 580w at any given voltage.

you will however get the 20amps that the unit is rated at.
 
I actually see the 580w rating as the maximum that the charge controller can output. Not necessarily that it will output 580w at any given voltage.

you will however get the 20amps that the unit is rated at.
That is the way I view it as well. You have to view any comment about MPPT wattage as a marketing statement. The Vin and Iout are the key parameters to work with.

A couple of observations.

1) This only comes into play if the array is large enough to push enough watts to hit the controller's current output limit.
2) Sadly, if you can hit the limit, it impacts you the most when the batteries are at a low state of charge (Low Voltage) and you need all the energy you can get.

Like anything else in engineering, you must know what the specs mean to design a system properly.
 
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