MC4 solar connectors convention?

[Tracy D'arth]

Is there a standard or convention regarding the fitting of MC4 connectors?  Do you use the male plug part on the positive panel lead or the negative?

The reason I ask is that I have seen either way connected on professionally installed panels.

My own opinion is that the plug part should be on the panel positive lead so that the positive lead from the controller/battery is in the shielded socket part and will not short to the roof when disconnected.

 

Agree or disagree?

Edited September 15, 2023 by Tracy D'arth

[MtB]

20 minutes ago, Tracy D'arth said:

My own opinion is that the plug part should be on the panel positive lead so that the positive lead from the controller/battery is in the shielded socket part and will not short to the roof when disconnected.

 

Well looking at a pair of MC4 connectors, both of mine here have shielded conductors that wouldn't short if left lying on the roof. The solar panel I have here has the male part on the positive lead. I'll bung up a photo in a sec.

 

On my last boat I had six panels bought as three pairs from three different suppliers a year or more apart for each purchase and all three pairs had the same polarity connectors so they could all be plugged together in series for example (not that this is a good idea with six!) so there seems to be a convention across suppliers.

 

 

 

Connector on the +ve lead. 

 

 

 

[Tracy D'arth]

2 minutes ago, MtB said:

 

Well looking at a pair of MC4 connectors, both of mine here have shielded conductors that wouldn't short if left lying on the roof. The solar panel I have here has the male part on the positive lead. I'll bung up a photo in a sec.

 

 

 

That is the same way I would connect them, male part on the panel positive lead and the socket part on the controller lead,  heck, we agree.

[blackrose]

2 hours ago, Tracy D'arth said:

My own opinion is that the plug part should be on the panel positive lead so that the positive lead from the controller/battery is in the shielded socket part and will not short to the roof when disconnected.

 

I may have misunderstood but I thought MC4 connectors weren't supposed to be disconnected unless the panels were covered first because they're not rated for making/breaking in any sort of sunshine? And if they're covered there would be no short would there?

[magnetman]

Worth bearing in mind that these connectors are nothing to do with boats. They are for house roof installations fit and forget.

 

I can't remember which way round I did mine (3 large house panels on each of my boats) but either way I don't intend to be unplugging them so its not going to cause me a loss of sleep. If I do unplug I will be disconnecting from the battery first.

 

 

 

All of my panels came with wires already connected. I did obviously check polarity the time but don't recall what it was.

 

It will be a standard I think.

 

[Tracy D'arth]

8 minutes ago, magnetman said:

Worth bearing in mind that these connectors are nothing to do with boats. They are for house roof installations fit and forget.

 

I can't remember which way round I did mine (3 large house panels on each of my boats) but either way I don't intend to be unplugging them so its not going to cause me a loss of sleep. If I do unplug I will be disconnecting from the battery first.

 

 

 

All of my panels came with wires already connected. I did obviously check polarity the time but don't recall what it was.

 

It will be a standard I think.

 

But, but, if you disconnect the battery, the controller may well blow. If the sun is shining!

[blackrose]

33 minutes ago, magnetman said:

 If I do unplug I will be disconnecting from the battery first.

 

Bad idea. Your first and last connection in a solar system on a boat should always be from controller to batteries.

[beerbeerbeerbeerbeer]

24 minutes ago, Tracy D'arth said:

But, but, if you disconnect the battery, the controller may well blow. If the sun is shining!

Why?

3 minutes ago, blackrose said:

 

Bad idea. Your first and last connection in a solar system on a boat should always be from controller to batteries.

Why?

Genuine question

[MtB]

29 minutes ago, Tracy D'arth said:

But, but, if you disconnect the battery, the controller may well blow. If the sun is shining!

 

 

Not only that, but the wires from the panels will still be live!! 

[Tracy D'arth]

Disconnected the panel open circuit voltage can go over the controllers limit without a battery to absorb the current.

[DShK]

31 minutes ago, Tracy D'arth said:

But, but, if you disconnect the battery, the controller may well blow. If the sun is shining!

 

I think this is a myth. I disconnect mine within it's software all the time and it's caused no issue. Might vary with the make though! Didn't have an issue with the battery BMS disconnecting itself either.

Edited September 15, 2023 by DShK

[GUMPY]

Depends on the controller.

If the controller is set to auto it takes its working voltage from the battery.

If you have 36v panels, connect them to the controller and then the batteries the controller will often default to 24v output.

Won't do 12v batteries much good.

[magnetman]

I have Victron MPPTs and regularly disconnect batteries as I use them in the floating electric beer drinking platform. 

 

Never causes a problem whether it is sunny or not. 

 

batteries connected downstream of the controller with Anderson SB50 connectors. Whip it orf no problem the only thing is the controller still thinks it is in absorb or float so you have to switch it on and orf again with the bluetooth app. 

 

No worries but maybe with other controllers there would be issues. 

 

 

My batteries are LTO 6s2p set to 15.2v float. 

[MtB]

20 minutes ago, DShK said:

I think this is a myth. I disconnect mine within it's software all the time and it's caused no issue.

 

So far. 

 

If your controller leaks out the magic smoke one day when you do it, will you be onto the manu looking for a fix under warranty?

 

Does the manual say you can do it? Or does it say not to? If the latter then I'm inclined to predict the manu will reject your claim. 

[magnetman]

3 minutes ago, MtB said:

 

So far. 

 

If your controller leaks out the magic smoke one day when you do it, will you be onto the manu looking for a fix under warranty?

 

Does the manual say you can do it? Or does it say not to? If the latter then I'm inclined to predict the manu will reject your claim. 

 

The Victron app has a feature to turn the panels orf. No mention of throwing a tarp over them or doing it in the evening. 

 

You just tap the thing and it stops the charge flowing. 

 

I think if this was dangerous and the panels were producing some sort of pent-up energy it would not be an option but it is an option. 

 

 

Edited September 15, 2023 by magnetman

[beerbeerbeerbeerbeer]

27 minutes ago, Tracy D'arth said:

Disconnected the panel open circuit voltage can go over the controllers limit without a battery to absorb the current.

ok,

know I can understand that,

 

but…given solar panels never perform to there best, isn’t that unlikely?

[MtB]

7 minutes ago, magnetman said:

The Victron app has a feature to turn the panels orf.

 

Ah right. That is a different kettle of poissons to physically disconnecting the battery terminals whilst solar charging. 

 

 

Edited September 15, 2023 by MtB
Clarify.

[magnetman]

I'm unsure how the solar panel would be supplying current if there is no circuit. 

 

Obviously one would always specify a controller according to the open circuit voltage of the solar panel(s). 

 

 

[beerbeerbeerbeerbeer]

So where can one put an isolation switch somewhere amongst the solar wiring?

 

[magnetman]

Just now, MtB said:

 

Ah right. That is a different kettle of poissions to disconnecting the battery while solar charging. 

 

I do both. Unplug directly and switch orf via the app. 

 

Never had any issues. 

 

Maybe I am just lucky. It could be a personal energy thing as I have narrowly avoided nasty deaths quite a number of times. 

 

 

 

 

[MtB]

1 minute ago, magnetman said:

I do both. Unplug directly and switch orf via the app. 

 

I deffly think u should do it the other way around. Turn it off in the app then disconnect the batts.

 

I agree about the personal energy. I too should have died on several occasions. 

 

 

[magnetman]

I don''t reckon it makes any difference unless you have installed a controller the maximum voltage of which is lower than the ocv of the solar panel combination. 

If the controller burns one just gets another controller. 

 

If the boat burns one gets another boat. 

 

Such is life. 

 

 

[beerbeerbeerbeerbeer]

So it matters not a jot  ??

 

I disconnect by pulling out the battery neg from the controller. 
 

 

 

[magnetman]

 

I reckon it is fine but if you end up on fire and while trying to get away you trip over a cyclist and break your leg don't come running to me to complain about it. 

 

 

 

[rusty69]

1 hour ago, magnetman said:

My batteries are LTO 6s2p set to 15.2v float. 

LTO=Lithium thrown overboard.

Whether they float depends on the current