Disconnecting panels under load

[rha9]

Thanks for all the replies. Sounds like the consensus is that disconnecting a panel from the controller should not be a problem.

To the extent there might be (any) problem, an on/off switch in the positive feed between the panel and the controller would eliminate any concern?

[team karst]

Originally Posted by rha9

Thanks for all the replies. Sounds like the consensus is that disconnecting a panel from the controller should not be a problem.

To the extent there might be (any) problem, an on/off switch in the positive feed between the panel and the controller would eliminate any concern?

THe one caveat to watch for, is that the open circuit voltage tends to run at 20 to 30 Volts, per panel. So, if you had two or three in series, that's now hazardous voltage. So, use care. Or, a blanket

[rha9]

Originally Posted by team karst

THe one caveat to watch for, is that the open circuit voltage tends to run at 20 to 30 Volts, per panel. So, if you had two or three in series, that's now hazardous voltage. So, use care. Or, a blanket

Thank you for that observation. I do have multiple panels, but they are connected in parallel.

[colinalleck]

As electrons scare the “s—t” out of me, ⚡️����
Why not disconnect yr panels at night.

��

[Jim Cate]

Originally Posted by colinalleck

As electrons scare the “s—t” out of me, ⚡️����
Why not disconnect yr panels at night.

��

What is the point of doing that? At night the panels don't produce the electrons that you fear.

But really, you should educate yourself to the point that you loose your irrational fear and replace it with informed respect... and leave your panels hooked up 24/7.

Jim

[flightlead404]

Originally Posted by HeywoodJ

To Boatpoker’s comment, the risk of disconnecting at the battery side is similar to the risk to alternators - the collapsing field in the controller power electronics might cause damage when their output is disconnected under load.

The problem with disconnecting an alternator is that the collapsing magnetic field induces a current. This is why quenching diodes are used.

An MPPT controller is a solid state device afaik (have not actually opened one up) so would not have the same problem.

Or am I completely off base here?

[team karst]

Originally Posted by flightlead404

The problem with disconnecting an alternator is that the collapsing magnetic field induces a current. This is why quenching diodes are used.



An MPPT controller is a solid state device afaik (have not actually opened one up) so would not have the same problem.



Or am I completely off base here?

Very close. V= L dI/dt

L is your winding inductance. So the equation calls for increasing large V as the current changes. Therefore a sudden disconnect of a inductive output shoots the voltage to very high levels.
That high voltage is what threatens the alternator diodes.

[tanglewood]

Originally Posted by rha9

Thanks for all the replies. Sounds like the consensus is that disconnecting a panel from the controller should not be a problem.

To the extent there might be (any) problem, an on/off switch in the positive feed between the panel and the controller would eliminate any concern?

Not really. You need to look at what you are disconnecting and be sure it's rated to disconnect under load. MC4 connectors found on most panels are NOT designed to disconnect under load and you will almost certainly damage them. I think a warning is embossed right on them. On the other hand if you have disconnect switches installed that are rated for their use, then switching off the panels that way would be fine. Disconnecting a wire from a screw terminal is also problematic. I tried that once and the wire arc welded itself to the terminal as I was pulling it off. I had to break it off after that.