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-   -   Installing serial solar panels (http://www.cruisersforum.com/forums/f14/installing-serial-solar-panels-185245.html)

ErikElmgren 24-05-2017 07:41

Installing serial solar panels
 
When designing my solar panel installation I have a need for advice on disconnecting the solar panels from the charge controllers.

I will have 3 nominally 12V panels in each string, with a Voc of some 20V each the string could have a 60V potential. The MC4 connectors I will use outdoors can not be safely disconnected under those conditions and pulling the wires from the charge controller seems ill-adviced, and I don't want to depend on covering the panels as local weather might not agree.

Thus I need a circuit breaker. But the normal marine circuit breakers are rated at 12 or 24V, and the special solar ones are pricey and rated at 1kV or more. How have you done and does anyone know a suitable product?

Paul Elliott 24-05-2017 07:57

Re: Installing serial solar panels
 
You can find DC-rated breakers with appropriate specs, but they aren't super-cheap. Here's one rated at 30A, 125VDC: https://www.digikey.com/product-deta...1019-ND/483591. Price is about $40 from Digikey, but I see that they aren't stocked and have a six-week leadtime. In any case, high-voltage / high-current breakers are out there.

[edit: Mouser Electronics has a similar breaker in stock for $53]

a64pilot 24-05-2017 07:58

Re: Installing serial solar panels
 
Throw a blanket over the panels and there will be no current, or do it at night.
I used fuses as they were less expensive and I do not expect to interrupt power very often.
I hope the fuses and lightning interrupter I have will help if such an event happens

john61ct 24-05-2017 11:15

Re: Installing serial solar panels
 
An auto battery disconnect, or Anderson plug

Ivansgarage 25-05-2017 08:48

Re: Installing serial solar panels
 
Quote:

Originally Posted by ErikElmgren (Post 2399389)
When designing my solar panel installation I have a need for advice on disconnecting the solar panels from the charge controllers.

I will have 3 nominally 12V panels in each string, with a Voc of some 20V each the string could have a 60V potential. The MC4 connectors I will use outdoors can not be safely disconnected under those conditions and pulling the wires from the charge controller seems ill-adviced, and I don't want to depend on covering the panels as local weather might not agree.

Thus I need a circuit breaker. But the normal marine circuit breakers are rated at 12 or 24V, and the special solar ones are pricey and rated at 1kV or more. How have you done and does anyone know a suitable product?



Check auto parts for these resettable breakers cheap 20 bucks
And 60 volts open circuit voltage solar panels will not shock you
there is no current.

Paul Elliott 25-05-2017 09:00

Re: Installing serial solar panels
 
Quote:

Originally Posted by Ivansgarage (Post 2400170)
http://www.cruisersforum.com/forums/...1&d=1495727149

Check auto parts for these breakers cheap 20 bucks

These look like the same breakers I use. If so, they are only rated for 42V. The OP may have 60V with his string of solar panels.

Given that solar panels aren't inductive and have intrinsic current and voltage limiting, it seems unlikely that there would be a self-sustaining arc and breaker contact erosion. But I would still be reluctant to use those breakers in this application.

ramblinrod 25-05-2017 09:01

Re: Installing serial solar panels
 
Quote:

Originally Posted by ErikElmgren (Post 2399389)
When designing my solar panel installation I have a need for advice on disconnecting the solar panels from the charge controllers.

I will have 3 nominally 12V panels in each string, with a Voc of some 20V each the string could have a 60V potential. The MC4 connectors I will use outdoors can not be safely disconnected under those conditions and pulling the wires from the charge controller seems ill-adviced, and I don't want to depend on covering the panels as local weather might not agree.

Thus I need a circuit breaker. But the normal marine circuit breakers are rated at 12 or 24V, and the special solar ones are pricey and rated at 1kV or more. How have you done and does anyone know a suitable product?

This is the issue with putting panels in series.

What size of panels?

It is not recommended that MC4s be disconnected with current flowing, but it is no big deal for a couple hundred watts.

Even with a huge array, if one starts at the panel level, disconnecting MC4s as they work toward the controller, no issue.

What is the concern with shading a panel to reduce current?

In a series string, one just needs to shade one half of one cell of one panel to bring the current down to near zero.

Which is a major drawback to series connection.

Any shading on any cell of any panel in the string, and output drops to near zero.

Going above 50 Vdc increases risk of shock/electrocution hazard.

So why connect in series?

Saving money on lighter gauge cable only to spend it on other devices, with the shading issue, and shock hazard doesn't seem wise.

Paul Elliott 25-05-2017 09:11

Re: Installing serial solar panels
 
Quote:

Originally Posted by Ivansgarage (Post 2400170)
And 60 volts open circuit voltage solar panels will not shock you
there is no current.

What can you possibly be thinking of here???

Of course there's no current in an open circuit (you could make the same statement about 600V), but 60V is sufficient to get through normal dry skin resistance, and when that happens there will be plenty of current. This is a potentially dangerous voltage.

ramblinrod 25-05-2017 09:16

Re: Installing serial solar panels
 
Quote:

Originally Posted by Ivansgarage (Post 2400170)
77083_primary_225px.jpg


Check auto parts for these resettable breakers cheap 20 bucks
And 60 volts open circuit voltage solar panels will not shock you
there is no current.

Say what?

True, there is no current when open circuit.

But if one puts a load on it, like a soaking wet person, in bare feet, with a nick on their finger (typical boater, most of the time), there most certainly is current.

That's why electrical safety rules generally change as one exceeds 48 Vdc.

Only takes 80 mA to stop your heart.

So if your skin resistance was low, one could receive a fatal shock, by contacting the conductors of an open circuit array.

Sailshabby 25-05-2017 09:29

Re: Installing serial solar panels
 
Quote:

Originally Posted by Ivansgarage (Post 2400170)
Check auto parts for these resettable breakers cheap 20 bucks
And 60 volts open circuit voltage solar panels will not shock you
there is no current.

Thats what we use (if memory serves, we've got a 60a for two 130 panels).

Ivansgarage 25-05-2017 09:31

Re: Installing serial solar panels
 
Quote:

Originally Posted by Paul Elliott (Post 2400190)
What can you possibly be thinking of here???

Of course there's no current in an open circuit (you could make the same statement about 600V), but 60V is sufficient to get through normal dry skin resistance, and when that happens there will be plenty of current. This is a potentially dangerous voltage.

After installing a few hundred panels, know this for a fact.

newhaul 25-05-2017 09:32

Re: Installing serial solar panels
 
My big question is are the panels in each string in series or in paralel and the second is what type controler you are using.

Paul Elliott 25-05-2017 09:38

Re: Installing serial solar panels
 
Quote:

Originally Posted by Sailshabby (Post 2400200)
Thats what we use (if memory serves, we've got a 60a for two 130 panels).

And for two panels, this is a great breaker to be using. It's when you add three panels in series that you exceed the specs on these breakers.

So with three panels you have two choices: wire all three in series, or all three in parallel. I have three 100W panels, and they are wired in parallel for the reasons that ramblinrod mentions -- shading being the big one on a sailboat.

Actually, I am currently rewiring my three panels so that each one gets its own MPPT controller. I expect to get a small increase in power output relative to the previous parallel-panels-to-single-controller setup.

Paul Elliott 25-05-2017 09:53

Re: Installing serial solar panels
 
Quote:

Originally Posted by Ivansgarage (Post 2400203)
Quote:

And 60 volts open circuit voltage solar panels will not shock you
there is no current.
After installing a few hundred panels, know this for a fact.

Meaning what? You grab the bare wires with damp hands and feel nothing?

Well, perhaps you do. But with a typical dry skin resistance of 2000 Ohms, and a voltage of 60V, that's a current of 30mA, which is probably about 1/10 the DC current needed to stop your heart. With damp skin it can be a lot worse.

I used to work on telephone systems that used 48VDC, and yes, I occasionally handled live wires in my bare hands. There's no way I would tell someone that it was safe to do this, especially in a damp environment.

noelex 77 25-05-2017 10:42

Re: Installing serial solar panels
 
I would not connect the panels in series, but if you want to do this you need a breaker rated at 60v +. One of the Din rail MCB is the best choice and they are also good as general purpose circuit breakers with some advantages over traditional "marine' breakers.

As others have said 60v can give you a a serious jolt. Anthing above 50v is potentialy lethal.


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