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15-11-2021, 07:14
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#16
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Registered User
Join Date: Nov 2014
Posts: 31
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Re: Disconnecting panels under load
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?
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15-11-2021, 09:51
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#17
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Registered User
Join Date: Mar 2021
Location: Flagler County, FL, USA, Earth
Boat: Lagoon 380
Posts: 1,514
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Re: Disconnecting panels under load
Quote:
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?
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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
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15-11-2021, 10:02
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#18
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Registered User
Join Date: Nov 2014
Posts: 31
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Re: Disconnecting panels under load
Quote:
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
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Thank you for that observation. I do have multiple panels, but they are connected in parallel.
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15-11-2021, 11:13
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#19
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Registered User
Join Date: Oct 2018
Location: Lake Macquarie NSW Australia
Boat: Jeanneau Sun Odessey 45.2
Posts: 66
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Re: Disconnecting panels under load
As electrons scare the “s—t” out of me, ⚡️
Why not disconnect yr panels at night.
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15-11-2021, 15:34
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#20
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Moderator
Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 21,283
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Re: Disconnecting panels under load
Quote:
Originally Posted by colinalleck
As electrons scare the “s—t” out of me, ⚡️����
Why not disconnect yr panels at night.
��
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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
__________________
Jim and Ann s/v Insatiable II, lying Port Cygnet Tasmania once again.
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17-11-2021, 07:20
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#21
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Registered User
Join Date: Oct 2020
Location: SE USA
Boat: Hunter 38
Posts: 1,469
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Re: Disconnecting panels under load
Quote:
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.
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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?
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17-11-2021, 15:22
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#22
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Registered User
Join Date: Mar 2021
Location: Flagler County, FL, USA, Earth
Boat: Lagoon 380
Posts: 1,514
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Re: Disconnecting panels under load
Quote:
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?
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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.
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26-11-2021, 11:09
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#23
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Registered User
Join Date: Feb 2015
Posts: 1,235
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Re: Disconnecting panels under load
Quote:
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?
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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.
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