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Old 01-27-2014, 09:02 AM   #21
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Tom and Phyllis,
V=IR (amperage times resistance equals voltage), the reason using higher voltages can use a smaller wire is there is less amperage to flow through them for the same amount of "power" or wattage (power equals amperage times voltage).
The problem with that on an RV is when 2 or more panes are in series, if one gets any shade on it at all, it reduces the output of ALL the panels drastically. A parallel hookup is much more efficient on RVs as they are often times partially shaded.
If you want to run higher voltages, get panels that put out that voltage and connect them in parallel, but you still have to calculate the proper wire size for the AMPERAGE, as Lewster pointed out.
What I can't believe is no one has mentioned doing a usage analysis on his estimated wattage per day and then sized the system to that. Without that it is like picking out a tow vehicle based on color.
I'll also bet that the RV dealer won't put protection fuses on each panel on a multi-panel system, a very essential requirement.
Another rough guide is for every amp hour the battery bank is rated at, figure the same amount of panel wattage. Thus a 200 amp hour battery pack needs around 200 watts of solar panels to keep it charged and give enough headroom to equalize regularly.
Make sure the batteries the dealer installs are true deep cycle and not boat type starter-trolling motor batteries. They have a much shorter life span when used as deep cycle, and don't last at all if ran down further than the recommended 50% SOC a few times.
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Old 01-27-2014, 09:14 AM   #22
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Originally Posted by workerdrone View Post
This is sort of counterintuitive, but it's my understanding that more solar panels will not necessarily require or even benefit from larger wire - the wire running from the panels to the charge controller, that is. If the additional panels are wired in series, resulting in higher voltage output from the panels, the same wire may be just fine. You'd just definitely need an MPPT controller then to deal with high panel voltage.

This assumes that it's quality wire and sufficient for the initial smaller panel not to lose any power on the way to the controller. The problem with many dealer or 'pro' installs that don't work well is cheap flimsy wire from the panels to the controller, inverters and controllers located too far from the batteries, and insufficient gauge wire for the inverter to give its full output or the controller to deliver all amps to the batteries. But the path from panels to controller to batteries is really critical to get your money's worth out of your panels to charge those batteries.

You might also save some money by going with quality deep cycle lead acids over AGM batteries, not sure what your install looks like. The AGM's are lower maintenance, can often take a very high charge rate from shore power, and can be mounted in awkward locations. Lead acids are still great batteries but must be upright and you must check the water levels regularly.
A few comments if I may.

I happen to be one of those 'professionals' that install solar charging systems PROPERLY! Series connections for solar panels will reduce the required wire size by increasing the voltage being sent to the controller, but as with any series connection, a small shadow on just one of the panels will drastically reduce the charge voltage coming from the series connection. This is why we use larger cabling and parallel connections exclusively.

I certainly would not consider the 6AWG thru 2AWG class K welding cable that we use in our installations to be 'cheap or flimsy'. I do consider it necessary and rather expensive as well.

Also, we will install systems with existing liquid lead acid batteries, but prefer and strongly recommend Lifeline AGM batteries for a number of reasons. Start with their super low internal resistance, which allows for the full utilization of all of the charging amperage to be sent to the batteries to be utilized for charging and not overcoming the 10-12% internal resistance of a liquid cell before the actual charging begins.

Add to this the total lack of maintenance, versatility of placement of Lifelines, their 5 year warranty and their great track record for extended longevity and they make a lot of sense. Expensive on the initial installation....yes. Worth the investment.....DEFINITELY!

The bottom line...............buy components from a trusted company and/or have your system installed by professionals that know what they are doing, follow NEC and component manufacturer guidelines and have a track record of great work.
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Victron Solar Components and Inverters, Zamp Solar Panels, LiFeBlue and Battle Born Lithium Batteries, Lifeline AGM Batteries
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Old 01-27-2014, 10:00 AM   #23
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Lewster, sounds great! Looking at your location, I'm not sure if you work out of Florida or Oregon, but either way, I'm sure I'll be in both of those state sometime in the next year. Maybe we can meet up and I'll hire you to look over my solar power system and improve it by adding and/or replacing some components. For now, I need something to get started, and it's a bit overwhelming taking it all in at once. I'll do my best to explain what I want to the Airstream dealer and hopefully it will be done the best way. If not, I'm sure it will work in the interim, and can be improved later.
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Old 01-28-2014, 03:48 PM   #24
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Lewster, you sound like a knowledgeable fellow - my comments about 'pros' were in no way directed towards ya, I've just heard a few horror stories about high dollar installations at dealers and such that didn't work worth a darn.
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Old 01-28-2014, 08:22 PM   #25
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Originally Posted by workerdrone View Post
Lewster, you sound like a knowledgeable fellow - my comments about 'pros' were in no way directed towards ya, I've just heard a few horror stories about high dollar installations at dealers and such that didn't work worth a darn.
No worries! NO offense taken………..
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