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Old 03-15-2012, 08:50 AM   #1
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new solar install

I decided to install a new battery tongue box and mount my 30 watt solar on it vs on the roof. No holes, no leaks. I installed marine 12v outlets and plugs.
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Old 03-15-2012, 08:51 AM   #2
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Old 03-15-2012, 08:53 AM   #3
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Very nice, nice job!
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Old 03-15-2012, 11:06 AM   #4
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i think i will get a solar panel. i plan on having it loose and set it up with adjustable legs sort of like a tilted table. it will have an outlet to plug into to charge the battery when we are boondocking. since we don't use much power, mostly a light for a little in the evening. it should be able to recharge during the day . or at least extend the charge.
being able to move it to take advantage of clearings in the leaves and a better angle towards the sun should help. and when we don't need it it can stay at home.
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Old 03-15-2012, 01:23 PM   #5
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Simple and relatively inexpensive install. Great job. I am getting supplies together ATM to solar charge my boler. Your installation highlights a simple way to keep wire runs short. Losses from panel to controller, inverter and battery can be high if the wires are too long or too small a guage. At least 10 gauge wire is required for most installations and wire runs should be in the 6-12 foot range. Check out a table on recommended wire sizes and lengths.
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Old 03-15-2012, 02:41 PM   #6
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I'm not too sure that these huge wire gauges are needed for short runs like 10 feet.

16 gauge wire has a resistance of about 0.05 ohms per 10 feet. A 30 watt solar panel produces no more than 3 amps. That represents a voltage drop of 0.15 volts.

Is this correct?
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Old 03-15-2012, 02:59 PM   #7
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I honestly don't know how to do the calculation. I use the tables which call for 2% or less voltage drop. I am using 10 gauge wire. My controller recommends up to 6 gauge and runs of no more than 6 feet between the battery and controller. Lots of systems perform poorly due to small wire. The bigger the better when it comes to 12 volt wiring although there are real limits when it comes to practical application.
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Old 03-15-2012, 05:20 PM   #8
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The Powerstream site has a good calculator for voltage drop. Scroll to the bottom of the page, stick in your information & it does all the work.
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Old 03-15-2012, 05:57 PM   #9
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Solar Panel Wiring

The thread got my curiosity up since I've never measured the voltage drop.

There's certainly nothing wrong with using 6 or 10 gauge wire though I expect it's not necessary for a 30 watt solar panel. Though I must admit it would minimize the voltage drop.

I have two 40 watt panels. I wired them with 16 gauge wire. From my solar controler to my battery is in the 8-10 foot range. The drop is 0.2 volts measured with a digital volt meter. This takes into account all contact resistance between wires and terminals.

As an interesting side bar, a 10 amp auto fuse has a 0.1 volt drop at 10 amps.

To insure a realistic reading I took measurements while drawing between 3 and 4 amps from the solar panel/battery.

One interesting aspect of at least of my solar panels is that the wire size is substantially less than 10 gauge coming from the panels.

We have been running almost wholely off our panels and they seem to easily meet our needs with the battery fully charged by noon. The biggest continuous current draw, particularly in the west, is the two fans that blow air over the fridge's coils. With these fans we are capable of keeping our temps in the high 30s F.

The solar panels are humming in the AZ sunshine. Totally unlike New England. Here no matter the temperature the Sun shines brightly virtually every day.
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Old 03-15-2012, 08:45 PM   #10
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Nice calculator, Jon. When I ran my numbers it all came down to the amperage for sure. Using the amperage specs from my panels, they will be putting out about 4.5 amps each. Depending on whether I use 1 or 2. Will probably use both if I can fit them on properly. Using a 10 amp load, 10 guage wire can run 12 feet one way and just come in at about 2% drop. Then you have to consider the load of the inverter, again short and large wires are the key.
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Old 03-15-2012, 08:58 PM   #11
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Originally Posted by honda03842 View Post
The thread got my curiosity up since I've never measured the voltage drop.

There's certainly nothing wrong with using 6 or 10 gauge wire though I expect it's not necessary for a 30 watt solar panel. Though I must admit it would minimize the voltage drop.

I have two 40 watt panels. I wired them with 16 gauge wire. From my solar controler to my battery is in the 8-10 foot range. The drop is 0.2 volts measured with a digital volt meter. This takes into account all contact resistance between wires and terminals.

As an interesting side bar, a 10 amp auto fuse has a 0.1 volt drop at 10 amps.

To insure a realistic reading I took measurements while drawing between 3 and 4 amps from the solar panel/battery.

One interesting aspect of at least of my solar panels is that the wire size is substantially less than 10 gauge coming from the panels.

We have been running almost wholely off our panels and they seem to easily meet our needs with the battery fully charged by noon. The biggest continuous current draw, particularly in the west, is the two fans that blow air over the fridge's coils. With these fans we are capable of keeping our temps in the high 30s F.

The solar panels are humming in the AZ sunshine. Totally unlike New England. Here no matter the temperature the Sun shines brightly virtually every day.
Between the abundant sun shine and your conservative needs, it is obviously working for you Norm! I don't know the exact output of your panels in amps so I have no idea if your wire is within 2% voltage drop. In your case it may not matter.
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Old 03-15-2012, 09:10 PM   #12
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I feel it is wise to think about voltage drop differently when looking at recharging batteries, particularly from solar. The acceptable 3% for home & industrial wiring means the incandescent lamps will be a bit dimmer if they are on a fully loaded circuit (something that is rare). Under most actual conditions home wiring (as well as the 12v wiring in your trailer) are not loaded anywhere near capacity, so the real voltage drop will be far less than the calculated.

The exceptions? Because of the cost & efficiency, inverters are often sized as small as possible so they very often closer to maximum load for wiring capacity. Since many have built in electronics to disconnect them when the battery voltage drops below a set point, oversized wiring is necessary to prevent voltage drop in the wire from looking like a depleted battery and shutting down the inverter before the battery is really down.

The other exception is the wiring from a solar panel. At the time you need it most (bright sun) you will be drawing continuous calculated amperage. If you use the standard tables to determine wire size you will be losing unacceptable amounts of the panel output to heating the wiring.

In the case of a solar charging system every amp hour you put back into the battery is less time you need to run a generator, or the lower wattage solar panel you need to replenish your batteries. While you can certainly go overboard with wire size, every percentage of voltage drop is costing you amp hours getting back into the battery. You only have so much sunlight...

Panels are getting more efficient and less expensive, so I suspect it won't be all that long until just putting a higher wattage panel will be less expensive than going to oversized wire, but I would shoot for less than 1% for a current installation.

Although he does go on, if you want some interesting opinions on RV solar installations, try reading Handy Bob's Blog. A bit of overkill for the shorter wiring distances in our smaller trailers and lower power systems, but good stuff.
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Old 03-15-2012, 09:28 PM   #13
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Originally Posted by honda03842 View Post
The thread got my curiosity up since I've never measured the voltage drop.

There's certainly nothing wrong with using 6 or 10 gauge wire though I expect it's not necessary for a 30 watt solar panel. Though I must admit it would minimize the voltage drop.

I have two 40 watt panels. I wired them with 16 gauge wire. From my solar controler to my battery is in the 8-10 foot range. The drop is 0.2 volts measured with a digital volt meter. This takes into account all contact resistance between wires and terminals.

As an interesting side bar, a 10 amp auto fuse has a 0.1 volt drop at 10 amps.

To insure a realistic reading I took measurements while drawing between 3 and 4 amps from the solar panel/battery.

One interesting aspect of at least of my solar panels is that the wire size is substantially less than 10 gauge coming from the panels.

We have been running almost wholely off our panels and they seem to easily meet our needs with the battery fully charged by noon. The biggest continuous current draw, particularly in the west, is the two fans that blow air over the fridge's coils. With these fans we are capable of keeping our temps in the high 30s F.

The solar panels are humming in the AZ sunshine. Totally unlike New England. Here no matter the temperature the Sun shines brightly virtually every day.
Hi Norm,

Did you connect your panels in series or parallel?; you had that option with MPPT controller. Connection in series increases voltage but reduces current consequently reduces demand on wiring. This benefits wiring between solar panels and charge controller only.

George.
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Old 03-15-2012, 09:35 PM   #14
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Yeah thats the guy I read already. Handy BOB (angry Bob?) So good I think I will read it again. It may be overkill for some more casual RVers but if you are off the grid or a hardcore boondocker or wannabe like me it makes a lot of sense. Thanks again Jon.
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Old 03-16-2012, 04:58 AM   #15
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Originally Posted by Jon Vermilye View Post
I feel it is wise to think about voltage drop differently when looking at recharging batteries, particularly from solar. ...........
Right. It took me a while to wrap my head around this, as we spend most of our lives thinking about sizing wires such that they don't overheat and start a fire. It really comes down to the voltage that the battery sees and how that voltage correlates to the battery charging rate.

I've mentioned this before, but I buy heavy wiring at my local metal recyclers (aka junk yard). Electricians sell the "short" ends off huge rolls for scrap, so the wire is new and may be 10 or 20 feet long. You can find any gauge you want within reason - I picked up some #6 to wire my TV for charging the trailer battery. The price by the pound is a fraction of retail.
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Old 03-16-2012, 05:18 AM   #16
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Jim,
Nice neat install.

Norm, John,
Wire size is less critical when connecting panels in series and using an MPPT charge controller. The series connection means that you're feeding the charge controller with a higher voltage and lower current for a given wattage (power = voltage x current). Panels connected in parallel should use larger wire to the charge controller.

The wire size for the connections between the charge controller is very important. These wires should be as large and short as possible to minimize voltage drop. Many solar charge controllers provide staged charging for your battery bank, which extends the life of your batteries. The controller determines the state of the charge by reading the battery voltage and the difference between fully charged and 50% discharged is only about 0.5 volts. A tenth of a volt drop can easily affect when your charge controller switches to a float charge rate. Overcharging will boil away electrolite and destroy a battery just as easily as overly discharging.

Ron
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Old 03-16-2012, 08:26 AM   #17
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Interesting

Ron,

I carry distilled water on our trips, check my battery water monthly and see very little loss of battery water. I assume this means I'm not over charging.

Yesterday I measured the controler's input voltage, it was near 18 volts; the controller's output voltage was 13.4 volts (about the same as the battery) indicating no current flow.

This suggests that as the controller sees a high voltage at the battery, current flow is reduced, further suggesting that wire size is not important (to a limit) because when there's no current flow there's no significant voltage drop.

It seems the controler charges to 13 plus volts, not unlike my intelligent Converter. In the morning after running off the battery the battery voltage is typically around 12.6 volts.

I hope this makes sense and further hope it indicates that the panels and controller are working correctly.

I have my panels wired in parallel. When I started I had a non-MPPT controler.
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Old 03-16-2012, 03:23 PM   #18
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Jon, thats a great tip about going to a scrap yard to get cheap large gauge wire. Even at retail prices though large wire is the best investment you can make in your system. It also makes adding panels or batteries in the future much easier.

Norm, I highly recommend reading the link for Handy Bob that Jon posted in this thread. The Battery Charging Puzzle does a great job at explaining how less than half a volt can make a tremendous difference in system efficiency and how wire size plays a role.
Bob also shows how MPPT charge controllers are not cost effective on small systems because the controller costs much more than adding a panel and the boost that MPPT controllers can provide is only available under certain conditions.
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Old 03-16-2012, 07:17 PM   #19
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Handy Bob

Rene,

I did read all of Handy Bob's post on Solar Panels and RV electronics.

I definitely agree that Trojan 105s are great batteries. My motorhomes 105's were 15 years old when I sold the rig and still going strong and, though he suggests other wise, were charged by an inverter with a charge wizard on it that only produced 14.1 volts.

My solar controller never outputs over 14 volts as far as I've seen but the battery, even after being used all night for lights and so on are still near 12.6 volts in the morning. I think they fully charge but I don't have a hydrometer to really check.

Though I don't have super large wire for the panels everything seems OK. Of course, our panels are a lot smaller than his by more than a factor of four.
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Old 03-16-2012, 09:51 PM   #20
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The peak voltage depends on your controller. My Go Power PWM-25 controller can be set for battery type. If it is set for flooded, it will produce 14.1V absorption charge when the batteries are low, 13.7V as a float charge once the batteries are fully charged, and go to 14.8V for a couple of hours every 28 days to equalize & desulfate the batteries.

Oh, by the way, getting cable from a scrap yard (as long as the insulation is in good shape) is a great idea, but it was Thomas G's idea, not mine...
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