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polly-nowak avatar image
polly-nowak asked

SmartSolar 75/15 Load output stays "on" even if the app says "off"

I bought a 75/15 SmartSolar (24V). I wanted to use the Streetlight function and I tested it a few times without any load connected, and it worked just fine. I attached a 24V- Relais to the load, the relais turned on, and now the load output won't turn off anymore.


The App says the load outlet is switched off, but it isn't. I still have 24V there. I disconnected the batteries and the PV, I reset the device to factory defaults, and while I can configure the load output in the app to turn on and off, the hardware is not following suit, even without any load connected to the outlet.


According to the Load Trend, the Relais sucked 4A of current while the Voltage remained unaffected. Considering the load output is supposed to be short circuit proof I don't want to believe a mere 24V DC Relais managed to kill the load switch on a 15A device. If anyone has an idea, I'd be grateful.

smart solar charging behaviour
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wkirby answered ·

How did you connect the relay coil to the load output? What other components did you include in the circuit between the relay coil and the load output?

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polly-nowak answered ·

A1 to + and A2 to -. I added a Voltmeter and a 2-pole circuit breaker between the load and the relais.

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wkirby avatar image wkirby ♦♦ commented ·
OK, so you did not mention the flyback diode to clamp the coil back EMF Voltage.

Without that diode, hundreds of Volts would be sent up the MPPT's load output terminals when the coil is de-energised, which is hundereds of Volts outside of the specifications that you mention.

In standard circuit design, whenever powering a coil, a flyback diode is essential to prevent the back EMF that a coil releases when it is de-energised.

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polly-nowak avatar image polly-nowak wkirby ♦♦ commented ·

I'll book that as non industrial DC learning experience. Thanks.

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