solar panal... do not connect under load?

[centerline]

I have all the wires connected from the 130w solar panel to the MPPT controller and have the wires ran from the controller to the battery with a fuse inline, but not yet connected....

the sticker on the panel and on the wires say "DO NOT CONNECT UNDER LOAD".... there needs to be better clarification as to how we are supposed to do this witout any load being present.
I can only think that maybe im supposed to throw a blanket over the panel to keep it from producing while I make the connection... or connect it at night.

so I have 2 questions,

can someone who has experiance with solar panels explain this warning to me so that i can connect it properly?...

and what size of fuse should I use in the line from the controller to the battery? I am thinking 20 or 25 amp, but as I dont know too much about how the controller actually works or its actual output, im at a loss as to what I really need... thank you

 

[Hartley]

I have more experience with land-based solar, but AFAIK, it works the same..

I believe what they want you to do is connect the panel to the controller first, then connect the controller to the load (battery). This will keep the amount of sparking to a minimum, and will be friendlier to the controller electronics.

As far as a fuse/breaker between the controller and battery, you have two considerations - first, the max output current of your panel - and you should go up to at least the next increment in size - you have a "130 watt" panel, so at max, it might source 10-11 amps (not likely, but we want to be conservative) - which implies a 15 or 20 amp fuse/breaker. Either would work, (as will the 25 amp size you mention) though if you are thinking of adding more panel in the future, you may want to think ahead as far as wire size and fuse/breaker, and save work later.. )
Second, if this goes direct to the battery without any other fuses, you want to make sure the fuse/breaker is rated at a sufficiently high Interruption rating (I know Maine Sail has some good articles on this elsewhere). If you already have a suitable main fuse at the battery, this is not a worry.

Hartley
S/V Atsa

 

[centerline]

I have more experience with land-based solar, but AFAIK, it works the same..

if you are thinking of adding more panel in the future, you may want to think ahead as far as wire size and fuse/breaker, and save work later.. )

Second, if this goes direct to the battery without any other fuses, you want to make sure the fuse/breaker is rated at a sufficiently high Interruption rating (I know Maine Sail has some good articles on this elsewhere).

If you already have a suitable main fuse at the battery, this is not a worry.

Hartley
S/V Atsa

Hartley, thank you for the information...

I have already sized the wire in the system accordingly to handle a future installation of another 130w panel....

at this time with one panel, a 20A fuse sounds like it should work fine.... it will run directly to the battery

with all the work i put into the boat this past winter, I did nothing with the electrical system except change all the nav lights to LED...
the main panel has 4 circuits on it (3 lights & 1 accy). all are fused thru the panel. the panel has an unfused hot wire running to it from the battery. length of run, 20 inches....

all componment wires run to either of 2 different common hot leads that are fused at the battery with their own fuses.... all components each have their own fuses as well at the device.... ALL GROUNDS go directly to the battery.

i will be adding a larger main panel to handle the loads and to clean up the battery area, as with all the wires either being connected there or passing thru, it looks like a mess....

 

[Hartley]

Hi Again,

The article about battery fuses (with an excellent explanation of "why?") is here:

http://forums.sbo.sailboatowners.com/showthread.php?t=130775

It sounds like you are heading in the right direction already. One really great reason for having your common junction points away from the battery itself is that every wire connected to the battery may/will eventually corrode - so having a short/heavy jumper to a buss bar (fused for safety on the positive side) means less work down the road..

Hartley
S/V Atsa

 

[Stu Jackson]

If you read Maine Sail's excellent tutuorials, you'll find that you fuse for the wire size and not the load.

And, sure, why not throw a blanket over the panel? That'll assure no load, either way, right? What do you have to lose?

 

[centerline]

as I was going to connect the wires from the controller to the battery, i tested the voltage at the wire ends.... i have no voltage there.
so im wondering if the controller is sensing a lack of battery and preventing any measurable amount of voltage thru it....
or else why would there be no voltage?...

 

[Hartley]

So you have hooked up the panel to the controller, and the panel is in the sun? Is there voltage on the panel leads?

The controller may be shutting down the output because it sensed no load, but I don't know what your particular controller is doing. If you hook up the battery and charge current flows, all is OK..

Hartley

 

[walt]

Controller itself likely "runs" on the 12 volt from the battery. Ie, all the electronics in that box doing all the monitoring and conversion probably need the 12 volt hooked up to turn on. The controller is not likely powered from the panel. It of course also happens to pump current back out the same line to the battery - but it still has to turn on.


Dont worry.. likely works fine.

 

[centerline]

I have 21 volts at the incoming leads to the controller from the panel.....
im sure you are correct that it needs to sense a load before it will output to the batt leads... but i wanted a second opinion

 

[rgranger]

I think Hartley is correct and Stu's suggestion seems reasonable.

 

[Sumner]

I guess we are just guessing without knowing exactly which controller is being used and how it works. Based on the controllers we have Walt is right in that it needs elect. from the battery to work.

On the Mac I use a double pole switch that connects the panel side and the battery side at the same time from controller. If you wire to a switch between the controller and the battery then you can wire everything and then throw the switch. On the Endeavour with a larger array I have separate switches on both sides of the controller.

I think they are worried about connecting the negative and positive one at a time under load. If you don't want to put in the switch/switches then unhook the battery while wiring.

The fuse should be sized according to the wiring size as suggested and placed at the battery end of the run or wherever the controller output is going like say a common post before the battery from which a larger wire goes to the battery where there is a fuse for that wire.

There is no reason to have a fuse between the controller and the panels since that wire is sized for the panel output and elect. coming from the battery is handled by the fuse on the other side of the controller.

Now saying that we have six 80 watt panels on the Endeavour and they are fused separately before ...

http://purplesagetradingpost.com/sumner/endeavour-electrical/electrical-index.html

...the run to the controller since the individual wires to the panels and the panels them selves need protection from the output of the other 5 panels. I see no need to do this unless you start getting more than two panels or if say one of the two panels was 15 watts with a small wire going to it and the other panel was 100+ watts with a larger wire. Then possible put a fuse on the small wire to the small panel or easier use the same size wire to it as the larger panel,

Sum

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[Squidd]

On my solar system I was told to hook the batterys up first (to controler and monitor) and "then" hook up the solar panal... they were very specific about this...

It also makes sence as I will be disconnecting and removeing the panal when not in use and the batterys and controler will remain hooked up, till the next time I plug in the panal...