I have the solar system as shown in below diagram. When I connect my battery terminals to the MPPT charge controller, I am observing an arc immediately and due to which I am afraid to connect. Does this arc/spark is expected, is this because of some capacitor present inside the MPPT charge controller?

Also I have doubt on ratings of panel, charge controller and battery too.

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  • Hello, and welcome to Home Improvement. You should contact the manufacturer(s) about this; there's no way we'd know. And, you should probably take our tour so you'll know you'll know the details of contributing here. – Daniel Griscom Sep 6 '20 at 10:41
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    I’m voting to close this question because it isn't about home improvement. – Daniel Griscom Sep 6 '20 at 10:41

Because you're doing it with the power on.

That is to say, during daytime. The arc should go away if you turn off the solar panel. Either throw a tarp over it or wait til night.

Also, try to get out of the inverter business.

Try to arrange things so your loads run directly off 12V instead of off the inverter. The worst sin I see is people running cell phone chargers off inverters. Every gas station, big-box and 7-11 sells cell phone chargers that run on 12 volts.

Certain loads like a refrigerator need to be on inverter. But try to find a way to spin up the inverter only when needed. An ideal setup would be to spin up the inverter hourly, and then have it shut itself down when current draw stops (after the fridge has cycled and quit).


As far as quality ratings, that's on you. You can choose to buy quality stuff or save money, and you endure the result of that. I can tell you "cheap Chinese" isn't anymore; they now charge retail prices as high as 95% of the genuine/quality units. Paying a lot is no longer an assurance of quality.

As far as sizing the system (how big solar vs how big battery vs loads), that is the usual place people go wrong, because they have not bothered to learn the concepts.

It takes some time. Hang out on off-grid solar power forums and such. (SE isn't the right forum; we don't field nearly enough questions about off-grid). You'll get exposed to a lot, such as "don't use more than 1/3 of a lead-acid battery's capacity", what a watt-hour is, how much common loads take (modern refrigerator: 1000 watt-hours per day), how to size solar panels to allow for winter and cloudy days, battery versus your expected draw, etc.

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    Not clear form the question that the panels are connected at all, yet. But it's still utterly normal to get a spark when connecting a battery (MPPT controllers are charge pumps/switching supplies and do indeed have capacitors looking to get charged.) Likewise any UPS I've ever connected a battery to tends to spark unless you precharge with a resistor. – Ecnerwal Sep 7 '20 at 1:02

Utterly normal.

If you want to avoid it you could attach a resistor in series for a minute before connecting directly.

By the way, most UPSes are terrible .vs. a "real" inverter, IME - since you appear to be attempting to use a UPS as an inverter.

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