Log In | Register
Skip to main content
Topic: Wiring solar into power panel? (Read 357 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.
Wiring solar into power panel?
I got a great deal on a 125 watt panel and a charge controller. Going into a 1989 MP. Given that the amperage is small (5A ish), is there any issue with tapping the power converter charge wiring back to the batteries instead of running new wiring to the battery? Thanks!
1989 MP
Re: Wiring solar into power panel?
Reply #1 –
Jeff,
With 125 watts you should be installing about 15 amp circuit with 14 gauge wire, full power plus 20%.
I installed a 30 amp in line ATO fuse holder with 10 gauge wire to the solar charge controller directly to the B+ lug on the fuse board of the original Magnate 6336 power center. I also put a second in line fuse at the solar charge controller since it was more than 18 "  of wire to the power center.  This was because either device could be a source of power if the 10 gauge wire was to be over loaded or shorted.  You can adjust your wire sizes a fusing to the solar charge controller manufacturer recommended sizing, but do not exceed sizing and ampacity of the wire coming from the batteries to the fuse board. 

As an example, My 1988 MB has a 6 gauge battery wire which is good for about 50 amps. The controller is rated for 30 amps, and my solar panels provide a maximum of 14 amps and are in line fused at 15 amps.  All of my solar wiring is 10 gauge.
Rodney
1988 Mid Bath
Re: Wiring solar into power panel?
Reply #2 –
    Hi Jeff; If that is one panel, it depends on it's nominal voltage out. Peak voltage is kind of a dream, you'll never get that high. It would help if you included the type of solar controller. Wiring from the panel to the controller is separate, isolated from anything else, not even ground. Depending on the controller, the PV leads might be, or not, grounded.  The controller lead out to the battery is ground. The controller should be near the power distribution box (12 v fuse panel). You could wire directly into the ground and +12v. lead going to the battery from the power panel, but most people here would prefer to go directly to the batteries. 125 watts divided by 13.6 or so from your controller is more like nine amps than five amps. #10 wire is good. #8 might be better.  A fuse, or two as Rodney suggested is a good idea in series with the positive lead. The fuses aren't to protect the electronics, it is to prevent hot wiring from starting a fire.   RonB
RonB (Bostick) living in San Diego
Original owner of "Bluebelle" a '99 TKB
Re: Wiring solar into power panel?
Reply #3 –
Because voltage drop is inversely proportional to wire size, the thicker the wiring, the more current will be delivered to charge the batteries. The issue is not sizing the wiring for safety, but for performance. Attach inside the converter to the battery buss, via a 15A ATO-style fuse. Note if your charge controller is a MPPT model, it will extract the maximum possible from your single panel.

Steve
2004 FL
2013 Honda Fit
Re: Wiring solar into power panel?
Reply #4 –
This is how I fused the solar with an old magnatek  6336.
In the first picture: The yellow in line fuse holder under the red battery wire goes to sub fuse panel.
In the second picture :
1st left fuse is main fuse for the sub panel from the yellow fuse wire and 10 gauge buss wire.  Hence protection for the 10 gauge wire.
2nd left fuse is to the Solar controller.
3rd left fuse is for the CO Propane detector
4th left is open for future use.
5th left fuse is for blue tooth battery monitor.

1st right fuse is solar panels to solar panels in to the solar controller.  It also can function  as a solar panel switch.
Rodney
1988 Mid Bath
Re: Wiring solar into power panel?
Reply #5 –
Thanks for this. I'm using 10 gauge wire, the charge controller states to fuse both the panel side and the charging side.

My fusebox has an open slot from the factory. Any issue with running the positive wire from the charge controller to the open slot and adding a fuse? There isn't anything like a diode that would prevent current from flowing "backwards" into the rest of the system, right?
1989 MP
Re: Wiring solar into power panel?
Reply #6 –
There could be a 12 volt transfer relay that would interfere with proper charging in the older converters. In my picture, reply #4, only #7 & 8 are always connected  to the battery.  1 through 6 are connected only to the converter, when on shore power.  You need to check for this situation, assuming you have not already done so.  With no openings, I chose to go straight  to the battery through the B+ and ground lines and avoid additional loads on the circuit board traces.
Rodney
1988 Mid Bath
Re: Wiring solar into power panel?
Reply #7 –
I will tap the main line, thanks!

I got the panel mounted and all the wiring run, using the Fridge vent to run wiring. I needed to take my water heater out to fix a leaking line (no other access), which was good because access to the back of the converter is awful otherwise.

Final step is to mount and connect in the charge conrtroller.

I can call my motorhome "green" now, right? :)
1989 MP
Re: Wiring solar into power panel?
Reply #8 –
Everything is wired in and the system is working. Yay!

One further question I have is how concerned I should actually be about a fairly long run (maybe 8-10' of wire) from the charge controller to the batteries. Originally I understood that the recommendation to place the controller close to the batteries was for charging efficiency, but only AFTER I installed everything did I read that being further away can cause issues with the controller incorrectly reading battery voltage and overcharging. Of course it seems to me that if voltage drop on the line was causing the controller to read voltage lower than actual, that voltage drop would also limit overcharging.

In any case, I get a whopping 3 ohms of resistance in the wiring from the controller to the battery lug on the power converter (10 gauge wire), so I don't feel I should be exceptionally concerned. Right?

The controller is a Gen-2 Morningstar Sunsaver 10L, which is a PWM charger. I'm into this whole system for about $75 and it is exceptionally rare that we boondock for more than 3 days- my primary motivation is keeping the batteries topped off (AND NOT BOILING) when it is parked and keeping the batteries from being totally flat on day 3 as they tend to be pretty spent.
 
1989 MP
Re: Wiring solar into power panel?
Reply #9 –
Quote from: Jeff Newman  - 
Everything is wired in and the system is working. Yay!

One further question I have is how concerned I should actually be about a fairly long run (maybe 8-10' of wire) from the charge controller to the batteries. Originally I understood that the recommendation to place the controller close to the batteries was for charging efficiency, but only AFTER I installed everything did I read that being further away can cause issues with the controller incorrectly reading battery voltage and overcharging. Of course it seems to me that if voltage drop on the line was causing the controller to read voltage lower than actual, that voltage drop would also limit overcharging.

In any case, I get a whopping 3 ohms of resistance in the wiring from the controller to the battery lug on the power converter (10 gauge wire), so I don't feel I should be exceptionally concerned. Right?

Any resistance in a charge circuit is charging power lost. 3-ohms is a lot of resistance.
I wouldn't use a small wire as current limiter, rather I would depend on the controller to do its job.
When it comes to charge circuits, bigger wire is never a problem since it reduces resistance . When designing charge circuits, I try to keep the voltage drop in the 1-2% range .

Larry
Larry
2003 23.5' Front Lounge, since new.  Previously 1983 22' Front Lounge.
Tow vehicles  2020 Jeep Wrangler Rubicon, 2001 Jeep Cherokee
Photo Collection: Lazy Daze
Re: Wiring solar into power panel?
Reply #10 –
As Larry said, 3 Ohms is a lot - matter of fact, hard to see how that much resistance could be real - from the cabling alone. I would check all the connections. One way you can check is by calculating. Measure the voltage at the battery, and at the output of the charge controller. Divide the difference by the current output shown on the controller, and that is your cabling resistance in Ohms.

Steve
2004 FL
2013 Honda Fit
 
Re: Wiring solar into power panel?
Reply #11 –
Three ohm can be a lot of resistance.  How much is due to the inline fuses?  I installed solar with the sub panel to B+ to stay off the grid while it was stored in the yard at home.  I show a .4 volt difference between the controller and the battery.  When RV Ing I tend to drive every day or two. Solar is not critical until the adult kids have to charge a laptop pc. I decided I could live with the losses compared to the additional labor and costs.
Rodney
1988 Mid Bath