Solar on the cheap?

hpcmbw said:

Any idea what size/gauge wire to use? I wouldn't think it would need to be very heavy gauge wire, since I doubt there is a lot of electricity going thru the wire, but I wonder if I need a heavier gauge wire so i don't lose alot of power between the panels and the controller. I'll probably have about a 15' run from the panels on the roof to the controller which I'll probably place in the battery compartment (large compartment in the 5th wheel overhang, under the bed). Any ideas re: the correct gauge wire?

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It's about four amps max under best of possible conditions after all three panels are wired in parallel.

See the chart (in the link below)  and use five amps at 15 feet and get 16 gauge for your answer:

http://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html

I hooked up the solar panels last Sunday. When i hooked them up, my Trojan 6v battery set was reading 11.6 v. By the end of the day, the battery set was reading 12.1 volts, so I'm hoping this is going to work out well. I'll see what the batts are reading when I get up there this weekend.

Thanks for all the advice!

hpcmbw said:

I hooked up the solar panels last Sunday. When i hooked them up, my Trojan 6v battery set was reading 11.6 v. By the end of the day, the battery set was reading 12.1 volts, so I'm hoping this is going to work out well. I'll see what the batts are reading when I get up there this weekend.

Thanks for all the advice!

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It sounds like they are working fine, but I am wondering if you have your disconnect switch on disconnect with the solar controller output bypassing that switch, as you should. 11.6 VDC just seems low when there's nothing connected. But perhaps you're just starting with a well discharged battery.

After a few sunny days I would expect during the day for your battery voltage to be right at 14.5 VDC (exactly where the solar controller stops charging) and around 12.7 during each night.

My battery was at 11.6 before I hooked up the solar, hence the need for the solar. When you refer to the disconnect switch, are your referring to the little button that turns off the display or something else? I only recall having two switches, the display on/off little button and the "on/off" rocker switch.

Don, I found that if I had the rocker switch to "off" the charger didn't send any juice to the batteries. I have the on/off rocker switch on "on" and the display button pushed so that I don't have a display showing. Is there a third switch I'm missing?

I've run a set of wires directly from the solar charger controller neg and pos battery outputs on the back of the controller, to the pos and neg battery posts.

Can you clarify what disconnect switch you are referring to?

Trailer is in a partially sunny spot at Donner Lake, gets full sun maybe 4 hours/day, and partial sun the rest of the day. It's been hot and clear up there the last week, so there should be plenty of solar power.

I'll be at the trailer tomorrow (fri) nite, and am hoping to find my batteries at full charge and the beers in the fridge nice and cold!

hpcmbw said:

I only recall having two switches, the display on/off little button and the "on/off" rocker switch.

Don, I found that if I had the rocker switch to "off" the charger didn't send any juice to the batteries. I have the on/off rocker switch on "on" and the display button pushed so that I don't have a display showing. Is there a third switch I'm missing?

I've run a set of wires directly from the solar charger controller neg and pos battery outputs on the back of the controller, to the pos and neg battery posts.

Can you clarify what disconnect switch you are referring to?

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Is your trailer battery disconnected from everything else except for the solar controller? You will get better charging that way because there will be no parasitic loads on the battery to drop down the solar charging voltage.

Most RV's (not sure about trailers) have a switch to turn off all 12 volt stuff while in storage. And I mean all the way off, just as if there's nothing connected to the battery. Many individual items draw a little current even when off. The disconnect switch turns all that stuff completely off, just as if the battery is disconnected from it all.

But if your battery voltage is 14.5VDC during the day and around 12.7VDC at night, just don't worry about any of this. Then just leave everything as is.

Yes, always keep the solar controller on (rocker switch) at all times, except for when connecting it up or disconnecting.  I keep the voltmeter (small round button) off unless I am checking the voltage, but it should not  make much of a difference if left on.

hpcmbw said:

I'll be at the trailer tomorrow (fri) nite, and am hoping to find my batteries at full charge and the beers in the fridge nice and cold!

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Oh, I didn't realize that you wanted to leave the fridge on. Even if it runs on mainly propane, it needs to draw some 12 volt current while on. Your voltages may not be as high, especially during the night, but it should still work fine. The solar will still  help a lot.

Let me know what your day time and late night time voltages are. It might be a few tenths lower than I mentioned in my previous post, which will still be fine.

-Don-

I'm resurrecting my old post with some questions re: battery charging. As I recall, last summer the solar kept the batteries about 12.6v after a day of charging, and down to about 12.1v in the morning, before the sun hit the solar panels. Everything worked (except for some fridge problems) and I don't think I ever had to use the generator last summer. I was able to run fridge, use lights, radio and run heater and water pump without ever running out of electricity. When the batteries got down to 12.1 or 12.2 in the evening, I'd run some jumper cables from the two 6v batteries to a backup 12v RV battery for peace of mind.

I hooked up the RV to shore power in an RV park for the winter, but now I'm back to boondocking for the summer.  During the winter, I removed the two 6v batteries, took them home, fully charged them, then put on a trickle charger. The trickle charger was a small one for motorcycles, and never turned "green" (meaning fully charged).

Now I've put the batteries back in the RV and have the 45w solar panels hooked up. I run the fridge all week, but otherwise turn everything else on the trailer off from mon to friday. Saturday I show up and stay in the rv for the weekend.

Now for my question - after a full week of solar charge, the batteries were at about 12.6v when I arrived Fri night. By sat morning (after running heater for an hour), the batteries were at 12.1v, which quickly went up to about 12.5 v once the sun came up and hit the solar panels. I don't think the batteries ever get to 13v, let alone the 14.5v that Don had mentioned in an earlier response (not this summer or last summer).  The volt readings are all off the charge controller that came with the harbor freight solar panels. I haven't checked with a multimeter to verify the charge controller reading.

I purchased the batteries early last summer from a shady battery shop near a bunch of auto dismantlers. Of course, I was told they were brand new, overstocks, but I think I only paid about $125.00 for both trojan 6v batteries, so who knows the true story.  Then I let them get pretty discharged the first couple of weeks before I got the solar panels. Maybe my batteries aren't holding a charge?

I guess I'll try turning off the fridge and disconnecting everything from the batteries except the solar chargers this Sunday, and see if maybe there is a significant parasitic load. I'll see if next week the batteries at above 13v.

Should my batteries get up to 14.5v during the week? How low is "low" for discharge? I don't think I've seen below 12.1v since I've been boondocking this summer.  The solar charge controller is wired directly to the + on one 6v batt and - on the other (with the other + and - connected to make it 12v).

Sorry for the long rant. I really appreciate all the help I've gotten so far.

The expected voltage has to be viewed in the context of whatever charging may be taking place and the load (amp draw) at the time.You may see 14+ when the battery is actively being charged by the solar panel, but 13.3-13.6 is the resting voltage for a fully charged battery with little or no load. That same battery would probably show 12.6v under a moderate-to-heavy load but would soon drop down if the load lasted very long.  The fridge circuit board does not draw much power at all, so I would expect the battery to still show more than 12.6v once the solar charger is inactive. Maybe not 13v, but probably somewhere between 12.6 and 13.0.

Have you checked the water in the battery cells and replenished as needed? Use distilled water.

I'm surprised your trickle charger was not able to get the batteries into the green zone after an extended period of charging. Makes me suspicious. On the other hand, if your batteries aren't getting any lower than 12.1v after a night's usage, I would not be too concerned. 12.1v with a light load is about 50% charge.

Note that the gauge of wire running from the solar panels to the charge controller and on to the batteries can make a big difference if they are sized too small for the length of the run.

I got to the rv after dark on Sat nite and the batt voltage read 12.6. The solar chargers (15w x 3 harbor freight solar panels with HF charge controller) had been hooked up all week. I get partial sun most of the day, full sun probably 2 hours per day. Only thing left on was the fridge.

That night I ran 12v light for an hour, water pump for 10 minutes, phone charger in cigarrette lighter outlet overnight, and fridge. At 7 am next morning, I ran heater for 15 minutes and checkd batteries- batt voltage was 12.2. I ran heater for another 30 minutes and plugged in 175w inverter to charge laptop and battery read 12.0 (solar panels in partial sun by now).

The voltage seems a little low to me. I checked battery water and it was good. The solar panels are hooked up with the wire that came with them - bigger then speaker wire, but not much bigger. The wire run from solar to charge controller is about 12 feet. The charger controller to battery wire is same as other wire (came with the kit), probably 3' run. The charge wires are connected to the batteries with alligator clips.

I'm planning on turning off fridge when I leave today, disconnecting all power from batteries, then see what charge I've got next weekend when I come back up.

Any addtl ideas or input appreciated!

Well, I guess my batteries aren't up to snuff. I turned off the fridge and disconnected all hot wires between battery and RV. I left the 45W solar panels hooked up for a week of sunshine. I checked last night in partial sun, about 6:00 pm, and the charge controller was only showing 12.8v. I checked the water level in the batteries last week and it was good. I guess my batts won't charge beyond about 12.8v. Fortunately, my weekend usage seems to be light enough that I haven't run out of power yet. Maybe when I pull the batteries for the winter I'll have them hooked up to one of those desulfiting battery chargers and see if that will bring them back.


Thanks for all the help.

You should do an energy budget.  Figure out how much each of your devices, including inverter and laptop charger, consume while running and how long each run for.    Note that an inverter consumes some milliamps even when nothing is plugged in and it's turned on.

Now figure out how much energy you calculate is coming in via the solar panels.  You will need to know the length of time you get reasonable strength of sunlight for your latitude.  Also realizing that cloudy days mean about 15% of the energy.  You should also calculate the angle of the solar panels to the sun.  You may be getting as little as 50% efficiency given that they will never be directly pointing to the sun.