Fact or fiction? You shouldn't disconnect individual solar panels during the day.

[Deleted member 165]

The title kind of says it. It's time to add a couple panels; do I really have to do it in the dark, or is that an old wives tale?

 

[TCgreg]

Between midnight and 3am is the best. Have fun!

 

[gnubie]

It depends on the configuration. The issue is DC arcing. Once you strike an arc with DC it can be hard to quench. Anything above about 80v will sustain an arc for as long as you like. The higher the voltage the bigger the gap the arc will span. The temperature at the point the arc lands is more than hot enough to melt most metals.

 

[Deleted member 165]

I'm at 12 volts with 100w mono panels (parallel). Going from 2 to 4 panels. Sounds like I'll do it at night. I want to use my system to do some welding someday, but not as a surprise.

 

[gnubie]

Your VoC is probably 22v, nothing to worry about there really.

 

[Deleted member 165]

Good guess-it's 22.5. That seems high. Are there really enough losses there to be an appropriate input for that controller(12v input)? They sell them as a set, so I assume so, but almost 50% loss??

 

[gnubie]

The MPP point for most '12volt' panels is around 18v. A cheapie PWM controller throws away a significant percentage of the power in producing the 12-14v on the output. This is why one of the important points when using a PWM controller is to keep the panel's output close to the voltage the battery is charging at. If you have 44v input on a PWM controller charging a 12v battery the losses would be large.

If you do want to work on the system during the day and are still concerned about unplugging, throw a sheet of cardboard or a thick blanket over the panels. Better yet, just open that isolator switch you have inline with the panels...

 

[Deleted member 165]

Good ideas. I'll be upgrading to MPPT at the same time I add the panels. Currently, everything is 12 volts, and I'll be keeping it at 12 volts with the additions, but am getting ready to go to 24.