How to connect my 20W solar panel?

[cmedsailor]

I am planning to connect a 20W solar panel on my services bank (via a regulator). I have made a little diagram that hopefully will make things easier.
As you can see, I have two separate banks, using a common negative. In the services bank I have a NASA BM1 battery monitor connected. So, to connect now the solar panel, I am correct that the negative goes to the right side of the shunt (as per diagram)?
Also do I need to connect the positive to battery 2 or to either positive of the two domestic batteries? Do I need a fuse for the positive connection and if yes how much amp? What size (diameter) or type of cables do you recommend (the panel does not include anything)? As long as the diameter is fine, does it matter how long the cable to the solar panel is?
Thanks

 

[mattnj]

I am planning to connect a 20W solar panel on my services bank (via a regulator). I have made a little diagram that hopefully will make things easier.
As you can see, I have two separate banks, using a common negative. In the services bank I have a NASA BM1 battery monitor connected. So, to connect now the solar panel, I am correct that the negative goes to the right side of the shunt (as per diagram)?
Also do I need to connect the positive to battery 2 or to either positive of the two domestic batteries? Do I need a fuse for the positive connection and if yes how much amp? What size (diameter) or type of cables do you recommend (the panel does not include anything)? As long as the diameter is fine, does it matter how long the cable to the solar panel is?
Thanks

you want to connect the solar panel to the otherside of the shunt (LH side) otherwise the solar charge will not show up on the BM1

It makes no difference which side of the positive you connect to, yes it should be fused, a 5amp fuse should be fine, any cable that is rated to 5amp (to match fuse) will be fine, and keep all cables carrying power as short as you can.

for a 20w panel, you may not need a regulator if your bank (combined) is over 200ah, they will not overcharge, the regulator will of course loose some of the solar power into heat.

 

[pvb]

As you can see, I have two separate banks, using a common negative. In the services bank I have a NASA BM1 battery monitor connected. So, to connect now the solar panel, I am correct that the negative goes to the right side of the shunt (as per diagram)?

No, the negative should go on the other side of the shunt (with the yellow wire). In this way, the BM-1 will register the input from the solar panel.

Also do I need to connect the positive to battery 2 or to either positive of the two domestic batteries?

You can connect it to either positive terminal.

Do I need a fuse for the positive connection and if yes how much amp?

Yes, I'd use a 5A fuse.

What size (diameter) or type of cables do you recommend (the panel does not include anything)? As long as the diameter is fine, does it matter how long the cable to the solar panel is?

Theoretically depends on how long the cables are, but I'd use 2 sq mm or 3 sq mm wire.

 

[VicS]

2mm² cable would be heavy enough for a battery to panel distance of 14 metres.

1.5mm² might be a more convenient size to use. It will allow a distance of 10.5 metres.

1.0mm² would be fine up to approx 7 metres

As said negative connection to the same terminal as the BM1 yellow wire and positive to either positive terminal of the domestic bank.

The fuse should be in the positive connection and as close as practicable to the battery connection.

 

[pvb]

Agreed, Vic. I tend to over-size cable on the boat for 2 reasons:-

* thicker cable tends to be more robust, and connections are perhaps more reliable

* it allows for the possibility of future upgrading without going to all the trouble of replacing the cable.

 

[VicS]

thicker cable tends to be more robust

Absolutely but you have to remember that as it gets heavier it may get more difficult to route and more importantly won't fit the terminals on things or wont fit through grommets or glands.

 

[pvb]

Absolutely but you have to remember that as it gets heavier it may get more difficult to route and more importantly won't fit the terminals on things or wont fit through grommets or glands.

I don't consider 2 sq mm cable to be particularly heavy - after all, it's only about 3.5mm diameter, including the plastic sheath. As for connections, 2 sq mm cable needs standard blue crimps (exactly as you'd need for 1 sq mm cable), so it shouldn't pose any problems.

 

[VicS]

I don't consider 2 sq mm cable to be particularly heavy

2mm² is not too bad but 3mm² where its not required is a step to far IMHO

According to Merlin the OD of 3mm² round twin is 10.3 mm. That is starting to get awkward I reckon.

2mm² at 8.7mm is bad enough.

If its not required to be any heavier from the volts drops point of view 1mm² at 7.9mm diameter is surely adequately robust for internal wiring.

 

[pvb]

You haven't relocated to Wales, have you Vic?