Mounting solar panel on the coach roof

Sep 24, 2008
346
Groundhog

The panel looks good but the controller should not really be mounted on the
panel. Not only are the connections exposed to the weather but the
controller is best mounted close to the batteries to minimize loss. I don't
know how long the wire run to the batteries is but there will be a
noticeable loss - especially with the small wires you used.

Last week I installed a 90 watt BP panel on an arch similar to yours. The
mount was made by bolting 2 aluminum bars (1/4 x 2) across the panel in the
short dimension and the 2 clamps were bolted to them.
I used 10 awg wire to the controller which was installed less than 15" from
the batteries - also 10 awg. I used the same Morningstar controller as you
did.
 
May 30, 2006
1,075
Yes, I noticed too much voltage drop on my first set of wires and changed them out yesterday for AWG 10 solid copper.

Can you explain further the nature of the loss you describe? I dont understand.
gh
 
Oct 30, 2019
1,459
Solid, not stranded? I have been told solid wire is dangerous for marine use.



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Feb 12, 2008
337
I've heard solid is not allowed for marine use because of the expected flexing will fatigue and break the wire. I typically use tinned stranded wire. Tim
________________________________
From: groundhog groundhogyh@...
To: AlbinVega@yahoogroups.com
Sent: Wednesday, April 18, 2012 2:55 PM
Subject: RE: [AlbinVega] Re: Mounting solar panel on the coach roof



Not sure why solid would be dangerous, but solid has less loss than stranded ... I think.
groundhog
 
Feb 12, 2008
337
That's a pretty clever idea, using the shakespeare mounts. I'll have to try to remember that one... -Tim
________________________________
From: groundhog groundhogyh@...
To: AlbinVega@yahoogroups.com
Sent: Wednesday, April 18, 2012 2:55 PM
Subject: RE: [AlbinVega] Re: Mounting solar panel on the coach roof



Not sure why solid would be dangerous, but solid has less loss than stranded ... I think.
groundhog
 
Sep 24, 2008
346
The controller is set at 14.4 volts at its output terminals. On a long run
the battery never sees that high a voltage and either takes a lot longer to
fully charge or never charges fully if the loss is large enough.

The panel will output 17+ volts to the controller but after the controller
it is a specific charging voltage.

Solid copper? Wiring should be stranded copper and tinned for corrosion
protection.
 
Oct 31, 2019
303
You are right. Since there is constant movement on a boat, solid wire
doesn't flex, and in time could break. It is best to use tinned wire such
as Anchor brand. (I have seen wire corroded well away from the end of the
vinyl in old boats). The reason for this is that it will not corrode is the
vinyl is broken somehow. The original wiring in the Vega isn't tinned, at
least that I have replaced isn't. The ABYC only allows stranded as does the
military.

There was another question about voltage drop. There are dozens of tables
on the internet giving the drop/foot of various size wire (wire does have
resistance, thus there will be drop). There are two levels of drop: 3% and
10%. 3% percent is usually required for sensitive items such as
instruments. The 10% for things like lights. If you have too much voltage
drop just go to a larger gauge wire. Remember when figuring drop that the
wire length has to be calculated to the item and the return to the source
-- basically doubling the length of the run.

One other comment about wire. With the new LED lights the current is
ridiculously low. Thus one can use wire that is considerably smaller in
section, such as 18 or even 20 gauge. One has to be a little careful since
some folks consider anything under 18 gauge to not have the physical
strength for a boat. I have used 18 gauge duplex when wiring in difficult
runs, but usually try to use at least a 16 gauge.
 
May 30, 2006
1,075
Yes, I understand now.
The PWM controller is watching its output terminals to see if the battery is charged, and if the wire is too long, it will get faked out that the battery is more charged than it really is and turn itself down.
Thanks.
groundhog
 
Sep 24, 2008
346
Loss due to distance has to do with wire gauge, not whether it is solid or
stranded. I use 16 awg minimum on a boat. ABYC also calls for 16 awg to be
the smallest current carrying wire on a boat. While led lights use very
little current ABYC hasn't made any changes yet. As said the thinner the
wire the more fragile it is.

I am not sure what the distance from the controller on the panel to the
batteries is but lets say you wire for 3% voltage drop. The controller
outputs 14.4 volts for charging. Minus the 3% the batteries only see 13.97
volts, greatly reducing their charging ability. If a standard alternator
only sent 13.97 volts to the battery I would replace it as it isn't very
effective.

The run from the panel to the controller should also be sized for minimum
loss. In bright sun the panel outputs about 17.5 volts, but in the morning
or late afternoon this will drop. If it drops enough the batteries will not
receive any charge.

The controller you used - the same Morningstar I used - has fixed output.
More expensive controllers allow full output voltage adjustment which for
someone that depends on solar is important. The fixed output is too low for
some batteries anyway. For example Trojan calls for a charge of 14.8 volts
or higher for their batteries.

Everything you can do to keep the voltage at the batteries as high as it
should be will help.
 
May 12, 2009
57
Hi there John,
I've been considering the NOA mounting system as well, but I might just buy some parts of it, and get the rest as generic parts.

Mikko
 
Oct 30, 2011
221
Hi Miko, you will not be disappointed with the NOA stuff.... I was
reluctant to spend so much money on a mounting system but I am now
glad I did. Hopefully it will make the most of the solar panel's
output and it will be easy enough to remove when I need to do so. I
guess it is the old adage - you get what you pay for!
My only complaint is that the instructions are in Swedish ( I think) -
you really would think they would take ten minutes to get them
translated into English!
 
May 30, 2006
1,075
You guys have scared me....
I have been watching my solid no. 10 wire for the last few days very carefully.
Im waiting for it to move. It hasnt yet, but I think it wants to.
gh
 
Sep 24, 2008
346
Last month I was working on a 36' Islander sorting out a few wiring
problems, charging circuitry mostly. I noticed that the output wire from
the 2000 watt inverter to the breaker panel was solid core copper. I
mentioned it to the owner and suggested it be changed. When i removed it 2
of the 3 connectors came off in my hand as you can't crimp onto a wire that
will not compress. When I bent it one of the 3 strands broke right across.
That is why you don't use solid core copper.

Groundhog - how have you terminated the ends?
 
May 30, 2006
1,075
Just bent them and put them under the screws. No crimp connectors.
I moved the charge controller to the battery and it seems to be working better. Thanks for the tip.
THe resistance of the wire is 0.078 ohms.
THe solar panel is rated at 85 watts. So I am expecting to see somewhere around 5 amps with perpendicular sun. But so far the max current I have observed is 2.5 amps and about 35 watts from the panel.

When they test and rate the panel, do they use some optimum resistance as a load?

groundhog
 
Sep 24, 2008
346
Groundhog

I am not sure exactly how they rate a panel but you can be sure they do it
in a way to show the best results.

How many feet of wire is between the panel and the controller, and how far
from the controller to the batteries?

I have to do some other work on the boat I most recently installed the
panel on. If it is sunny I will measure the output.