Solar up and running

Very nice install! Did you wire the panels in series or parallel? If parallel, you're losing some of the befits of the MPPT charge controller, since when the sun gets low the voltage will dip below 12 volts. No biggie either way, its a slick and beautiful installation, just mentioning. And there's disadvantages to series too, like if one panel gets shaded it has the effect of shading both panels.

I'm in the process of doing a very similar install. Picked up a 320 watt 72 cell panel (about 48 volts) off Craigslist for $150, basically brand new. Its amazing how cheap these have gotten. I mounted it with beefy aluminum angle iron, which works nicely. I may install a second 300+ watt panel for goofs, since I have the roof space and they're basically free, and the controller can accept it.

I have 4 Trojan T105 6-volt batteries in my rig, and proudly don't have a generator. My generator compartment fits the 4 batteries beautifully, with room to spare for tools and extension chords. I don't need air conditioning where I live (coastal northern california), so the closest I ever come to needing aux power is when I run my furnace with that obnoxiously inefficient blower (80 watts!). But that'll be replaced soon enough with a catalytic heater.

I previously had two 100 watt panels going through an old style PWM charge controller, and I'm absolutely blown away by how much better this new system works. I thought I needed new batteries since every night my inverter would be whistling by about midnight, even if I only ran some music and LED lights. But with the new system I'm still at 12.2 volts even after very heavy use (including that **** furnace!).

Anyway, for folks still using their generator just to watch TV, there is a choice and its very cheap and easy. Not to mention infinitely nicer to your neighbors than running a generator aimed right at them.

The charge controller (this is the 30 amp version):

https://www.amazon.com/TRACER-3215RN-Solar-Charge-Controller/dp/B008KWPGAE

Or get the 40a version if you plan to add more panels:

https://www.amazon.com/Renogy-Tracer-Charge-Controller-100VDC/dp/B00E7NI9PE/ref=sr_1_1?ie=UTF8&qid=1475637903&sr=8-1

Optional but recommended remote monitoring:


https://www.amazon.com/gp/product/B008KWPGLI/ref=pd_bxgy_86_img_2?ie=UTF8&psc=1&refRID=XNCRHVPRYFFWB5ZAH6AT

Don't scrimp on the wire:

https://www.amazon.com/gp/product/B01D7VBLME/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1

Make the wire run as short as possible since that's where your loss will be (though that's much less if you run 48 volt+ solar panels).

And go on Craigslist and get the largest solar panel you can fit. Search for 300 watt solar panels, which will usually be around 48 volts, and don't get an old style 12 volt panel since they're relatively ineffecient and don't take full advantage of MPPT technology. Mine is flat mounted on my roof and even during a rain storm the other day I was getting 3 amps of output! Try that with a 100 watt @ 12 volt panel.

Aluminum angle iron does a good job of mounting it for cheap without any disadvantage that I can see, and you can just cut one length to 6" sections and make 4 brackets.

And if you don't have an inverter yet, I heart Xantrex:


https://www.amazon.com/Xantrex-806-1210-PROwatt-1000-Inverter/dp/B002I04A74/ref=sr_1_2?s=automotive&ie=UTF8&qid=1475636093&sr=1-2&keywords=xantrex+inverter

Note the link to get the remote on/off switch, which is nice. Mount the inverter as close as possible to the batteries.

I have the 600 watt version of that inverter and have never needed more. One down and dirty way to connect the inverter to your RV's power so you can use the outlets, you can just make an extension chord with male plugs on both ends and connect your inverter to any power jack. But remember to remove the fuse from your battery charger when you use it or you'll be running your battery charger off your inverter.

I mounted the charge controller to the outside of the generator box (which is inside my camper, under the couch), and the remote monitoring box means I can still control it.

Mine is an older RV (a good ol 1989 Class C) and I removed the built in battery charger since it was oversized and noisy and replaced it with this:

https://www.amazon.com/Powermax-Supply-Converter-Charger-Pm3-55/dp/B00F8MC440/ref=sr_1_1?ie=UTF8&qid=1475637308

Mounts nicely right in the battery box (previously the generator box). If I'm near power I plug it in, which powers my inverter. So my outlets are actually powered by my inverter, as opposed to by the outside power. If that bugs you, you could conceivably get fancy and rig up a transfer switch, but I can't imagine a reason to do that.

I made a few observations of my battery voltage in the 24 hours after the solar charging was switched off. I didn't notice that the propane detector was on until the 5 hour point, probably slightly hastening the decline and causing the little rise to 12.83 when I turned it off. The battery monitor was on throughout, drawing about 20 mA. The monitor said 100% charged for the whole 24 hours.


It appears to suggest it takes 24 hours of waiting before the state of charge/voltage chart works.

Well, voltage is accurate enough for operating an RV.
The above article criticizes voltage, but doesn't offer what IS a more accurate method. Hydrometer readings are another way, but a pita.


Also, the resting voltage will tend to drop over time.

Ah, that could be useful for sure. I guess you would record a series of voltages as a battery is under load, graph it. Then do it again in a month or year and see if there is a change.

I tried to find a graph of voltage vs time on a resting battery but haven't found one. I know, I should do it myself with my batteries.

I did find this comment at battery university:

http wrote:
Voltage Method

Measuring state-of-charge by voltage is simple, but it can be inaccurate because cell materials and temperature affect the voltage. The most blatant error of the voltage-based SoC occurs when disturbing a battery with a charge or discharge. The resulting agitation distorts the voltage and it no longer represents a correct SoC reference. To get accurate readings, the battery needs to rest in the open circuit state for at least four hours; battery manufacturers recommend 24 hours for lead acid. This makes the voltage-based SoC method impractical for a battery in active duty.

Battery university

Batteries lose ah capacity over time, and that can be seen by a more rapid decline in voltage. Works for me.

You bet I have LEDs! My first mod.

"How does it 'maintain' amp hours?"
I meant it just stores the count in memory, adding or deducting when sensing charging or discharging. I don't know if it is a digital circuit or clever use of analog devices. There was an Arduino micro controller project going on one of the hobby forums to make a digital battery monitor but I took the lazy way out and bought the finished product for $25 from China. So sad.

Harvey51 wrote:
If DW leaves the bathroom light on all night it doesn't bother me at all.

If you have LEDs she could leave it on for months.

Harvey51 wrote:
The monitor counts (integrates) the amp hours going in and out to maintain a number of amp hours in the battery at all times.

How does it 'maintain' amp-hours?

Thanks, Mike. I wish I had seen your post a few years ago. i relied on the voltage chart and killed the batteries half way through our first long trip. No solar. We drove every day and engine charging kept the voltage well above the dreaded 12.0 (half discharged; damage begins) but soon the heater wouldn't work in the morning. Only cost $200 to learn the lesson. After that, I never relaxed until I got the monitor.

Someone asked how a battery monitor works. Good question.
The monitor reads the voltage and the current and has a timer. Current multiplied by time is charge, in units of amp hours. The monitor counts (integrates) the amp hours going in and out to maintain a number of amp hours in the battery at all times. It compares that to the number entered for a full charge to get % of full charge. My cheapo monitor ignores charging over 100% so it is self calibrating.

Now I'm REALLY relaxed with solar. If DW leaves the bathroom light on all night it doesn't bother me at all.

"MOST resting batteries will stay around 12.7 or so just a few minutes after charging, and will stay there if no loads."
I've seen my van engine battery over 13 in the morning after no charging for 12 hours. It doesn't get driven far enough to make up for engine starting so I have to use a trickle in winter or I soon find it won't start - and that probably means it is "chronically" undercharged and damaging the battery. I would like to have a battery monitor on it but the starting current is probably too much for an inexpensive monitor.

Any decent solar controller will absorption charge the batteries at a voltage in the mid 14 volt range (e.g. 14.4 V). The absorption charge usually takes an hour more or less. After the current drops (or after a maximum time at absorption voltage), the battery is full and it will drop to a float voltage in the mid 13 volt range. If you keep an eye on the voltmeter occasionally, you'll see it go above 14 V. If it later drops to the mid 13's, you're full. You do have to be aware that you're not using something which is drawing the battery down. But if you have enough solar power, you would probably be both powering and charging from solar anyway.

Harvey51 wrote:
how you can tell if the batteries are fully charged with a voltmeter?... can't know the state of charge until at least 8 hours after you want to know. With solar, it's always over 12.6 volts unless I disconnect the panels for 12 hours.

MOST resting batteries will stay around 12.7 or so just a few minutes after charging, and will stay there if no loads.

Voltage as SOC is just fine, unless you want to know exactly how many ah you've consumed. To me, voltage is a very good indication of the SOC. I really don't know how it could be shown by any electrical device any other way.

rkentzel wrote:
We have so high winds here from time to time I had them I used them (brackets)

The standard 4 corner brackets stand up to driving down the road at 60+ mph.