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bjornm avatar image
bjornm asked

SmartSolar 250/100: What is the max array voltage that will give 100 A charge current?

This is with regards to the SmartSolar MPPT 250/100 controller. The higher the difference is between the array voltage and the battery voltage, the more power loss there will be in the controller, which will generate heat. I assume that there is only so much heat the controller can take, so there will be a practical limit to how many volts the array can be at for a 100 A charge current. Anyone with practical experience in this? Any official charts I can look at? In my case my array is 125 V and my battery 24 V.

battery chargingMPPT SmartSolar
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Alexandra avatar image
Alexandra answered ·

@BjornM

It's not a PWM and shorting to battery voltage. It tracking voltage and amps from the array.

The controller will get hotter the more wattage it is processing more than the battery voltage vs the array voltage.

The controllers have overheating protection.

The practical limit is the 250v input and 70A max short circuit input of the controller.

Derating is in the manual.

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bjornm avatar image bjornm commented ·

An MPPT charge controller is basically a sophisticated buck DC-DC converter. Those are the most efficient when the input voltage is only slightly higher than the output voltage. See below chart that illustrates this for a Morningstar MPPT charge controller. The higher the array voltage goes the higher the losses are.

efficiency.jpg

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efficiency.jpg (85.8 KiB)
Matthias Lange - DE avatar image Matthias Lange - DE ♦ bjornm commented ·

But with a lower PV voltage you have more losses across the wire from the panels to the MPPT or you need to use thicker wires.

The difference in that diagram is just around 3% IMO neglectable.

With the Victron MPPTs the PV voltage needs to be at last 5V above the battery voltage before the MPPT can start. After that the voltage difference can go down to 1V.

(The RS 450 needs a starting voltage of 120V and than can go down to a minimum of 80V)

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