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Disconnecting MPPT Controller


BlueStringPudding

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I vaguely recall that there is a preferred order in which to disconnect (or indeed, connect) the cables when working with a MPPT controller. For example:

A. If I want to disconnect the MPPT controller from the system do I detach the battery from it first, or the solar panels?

B. And do I disconnect the positive or the negative cable first, for each? 

 

Please can someone list the order of what to disconnect? And then argue amongst yourselves till there's a bit of a consensus so that I don't blow any fuses, baffle the controller (or myself) or damage owt. ?? I want to work on the batteries without having voltages skewed by solar input. 

I'll assume that reconnecting it all will be the same thing but in reverse order, unless anyone tells me otherwise.

 

Thanks. ?

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I understand that the panels should be disconnected first and  battery connections second  and then re  reconnect in the reverse order .

as a precaution i cover my panels so that they are not producing any  charge to protect the MPPT unit  when i disconnect the system 

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When changing batteries , I was told by the electrician that installed ours to disconnect the solar first, by preferably pulling the inline connector that sits under one of the panels.  Alternatively, but not as good, to cover the panels so they produce no output.  Then swap the batteries, and reconnect/uncover the solar.  The controller needs to be connected to the batteries first as it senses the battery voltage.

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Thanks. I was aiming to disconnect at night so there's no charge. And to simply pull out the wires from the MPPT controller as it has screw connectors.

 

Is there any preference with the battery connection whether the positive or the negative is detached first?

Edited by BlueStringPudding
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1 hour ago, BlueStringPudding said:

Is there any preference with the battery connection whether the positive or the negative is detached first?

Nope :)


The reasoning behind connecting the controller to the batteries first is two-fold.

 

1. The controller senses the battery voltage so it knows if it’s a 12V or 24V system. 
 

2. If the battery charge is low and the sun is shining then connecting the controller after the panels can cause sparks and can damage the controller. 

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10 minutes ago, BEngo said:

Technically, disconnect battery negative first, because that separates the battery from the hull and you cannot then get a positive to hull short.

 

N

Actually... technically, disconnect the positive first and then the unit can’t find a possible spurious negative return via the exhaust/aerial braid/anything else that shouldn’t be connected to the hull. 

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1 hour ago, BlueStringPudding said:

Thanks. I was aiming to disconnect at night so there's no charge. And to simply pull out the wires from the MPPT controller as it has screw connectors.

 

Is there any preference with the battery connection whether the positive or the negative is detached first?

I actually have a switch/breaker in the supply from the panels to the controller. This means I can just switch them of rather than faffing about with covers, or waiting for dark.

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3 minutes ago, Richard10002 said:

I actually have a switch/breaker in the supply from the panels to the controller. This means I can just switch them of rather than faffing about with covers, or waiting for dark.

So have we, but I prefer to wait until there is not a full load of sun on the panels before activating the switch.

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10 minutes ago, rusty69 said:

So have we, but I prefer to wait until there is not a full load of sun on the panels before activating the switch.

Why is that?

 

Not suggesting you are wrong... just interested in the reason. When I was talking about fitting a switch, nobody mentioned being careful as to when you switch it off. There was a bit of talk about it being a DC switch capable of handling whatever might be going through it, so I assume some were considering it would be switched off when subject to a reasonable amount of power.

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4 minutes ago, Richard10002 said:

Why is that?

 

Not suggesting you are wrong... just interested in the reason. When I was talking about fitting a switch, nobody mentioned being careful as to when you switch it off. There was a bit of talk about it being a DC switch capable of handling whatever might be going through it, so I assume some were considering it would be switched off when subject to a reasonable amount of power.

I think it stems from the days I used circuit breakers (Schneider) suited for ac use to isolate the panels. I have since changed them, but as I was unsure if they were suitable for dc, even though it was suggested they were,I would leave it until dark, or a low load on the panels to switch off. My reasoning, rightly or wrongly, was that if they weren't dc rated, switching the panels off under load may cause an arc across the switch contacts, and eventually cause it to fail.

 

I guess I just got into the habit, and it has stuck.

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21 minutes ago, rusty69 said:

My reasoning, rightly or wrongly, was that if they weren't dc rated, switching the panels off under load may cause an arc across the switch contacts, and eventually cause it to fail.

 

I guess I just got into the habit, and it has stuck.

Hard to break habits of a long time.

 

There was definitely a lot of talk about not using an AC switch because of the arcing and burning out of contacts. I couldn't find a DC with a rating of more than 50V, (roughly), so I paralleled my panels to minimise the voltage.

 

Unless you or I find anything different, or anyone suggests anything different, I think it will be safe to break your habit from time to time, if necessary :)

 

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5 minutes ago, Richard10002 said:

Unless you or I find anything different, or anyone suggests anything different, I think it will be safe to break your habit from time to time, if necessary :)

Probably right, and I do sometimes forget. The trouble is, at the time I had 3 x panels in series, giving something like 120V. I have since changed that to 2 in series, so a bit better.

 

I think there are a lot more DC rated switches available than there were a few years ago at a reasonable cost, so that is the obvious solution, and a good opportunity for the OP to install one.

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4 hours ago, BEngo said:

Technically, disconnect battery negative first, because that separates the battery from the hull and you cannot then get a positive to hull short.

 

N

Unless I am misunderstanding the question, this was about the connections on the solar charge controller, not the main battery connections.  Therefore disconnecting them would not change the way the batteries are connected to the hull.  I can’t see that it matters which you disconnect from the charge controller first, just don’t let them touch each other or anything else metal.

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1 hour ago, john6767 said:

Unless I am misunderstanding the question, this was about the connections on the solar charge controller, not the main battery connections.  Therefore disconnecting them would not change the way the batteries are connected to the hull.  I can’t see that it matters which you disconnect from the charge controller first, just don’t let them touch each other or anything else metal.

If the panels are disconnected from the controller then it doesn’t actually matter which wire you disconnect first because there won’t be any voltage on them. 

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20 hours ago, WotEver said:

If the panels are disconnected from the controller then it doesn’t actually matter which wire you disconnect first because there won’t be any voltage on them. 

The other side of the controller is connected to the batteries, so whilst I would agree it does not matter which you disconnect first, there is a voltage between the two wires and you certainly don’t want to let them touch or else you are going to blow the fuse that is hopefully at the battery end of the connections.

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21 minutes ago, john6767 said:

The other side of the controller is connected to the batteries, so whilst I would agree it does not matter which you disconnect first, there is a voltage between the two wires and you certainly don’t want to let them touch or else you are going to blow the fuse that is hopefully at the battery end of the connections.

I was assuming in my post that it was the battery end of the cables that was being removed. If it’s the controller end then the order of disconnection still doesn’t matter but before disconnecting them you should pull the relevant fuse. 

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On 04/02/2020 at 11:33, Richard10002 said:

I actually have a switch/breaker in the supply from the panels to the controller. This means I can just switch them of rather than faffing about with covers, or waiting for dark.

Sounds handy. But rewiring them isn't something I plan to do often ?

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