Solar panel/dual battery concerns

[Landay]

Hello all,

I am thinking about purchasing a solar panel and mounting it to the roof. Looking at a 60-100W panel to keep the secondary battery charged and allow for year-round fridge usage.

I don't have an easy way to plug into a battery charger every night, so this seems to be the best option.

I know I need a charge controller, and I know that controller simply goes between the panel and the battery.

Does anyone have a recommendation for a controller? I'd like something easy to mount, and while we are at it a recommended mounting location.

My other question is how to wire it up taking into consideration I also have the dirty parts dual battery kit. I don't want to fry the controller when the battery is being charged by the alternator.

What say you, electrical gurus? Thanks in advance for your help.

 

[CaliMobber]

sorry looks like we all left you hanging.

I have this charge controller

http://www.amazon.com/SunGuard-SG-4...985&sr=1-1-catcorr&keywords=morningstar+solar

But its only good for 4.5 amps maybe 60w panel at the very max.

This guy is prob more what your looking for

http://www.amazon.com/Morningstar-S...067&sr=1-2-catcorr&keywords=morningstar+solar

Im a fan of morningstar because they make good quality stuff a decent price.

I just have my 30w panel wired into the rear 12v plug since I ran a 6 gauge wire to it for my fridge. You can run the charge controller anywhere as long as the wire is hot always. Dont worry about being connected to the main line, I havent seen any ill effects from the alternator at all.



Oh and my 30w panel does not handle the fridge load, car battery drop into the sub 12v range after a few days. So 60W + is a smart choice, always check solarblvd.com for best solar panel prices.

 

[lysol]

Just an FYI... I just bought the controller in your second link a couple of weeks ago. I had to send it in to get a new one directly from Monringstar as there are a bunch of the "SS-10-12V" controllers that have bad firmware and would error out each morning. The new one works fine though.

Back on topic, how many amps do you draw in a given 24-hour period?

Lets say you have a consistant draw of 1 amp per hour (1Ah), then in 24 hours, you will have used 24Ah's. You will want to make at a minum that if you want to run it solely off solar power. (If you drive the vehicle everyday, you could get away with less, but understand that if it sits for too long, the secondary battery will die).

On average, it is a good rule of thumb to make all your daily power needs in just 4 hours. That is because the 4 hour window when the sun is highest will net you the most power. You will get some power before and after this window, but it won't be as much. So in order to harvest 24Ah's on a 12V system, you would need at minimum a 72 Watt panel. That is to say that you live in a "perfect world with no inefficiencies" and will have the Sun out during this whole time as well.

I got this number by doing this:

W=A x V
(Watts = Amps x Volts)

24 amp hours total needed to be generated

With a 4 hour window for harvesting, I will need to consistently generate 6 amp's per hour (6Ah).

In order to generate 6Ah on a 12V system, (W = 6 x 12). 72 Watts. Now, the solar panel will put out power at a slightly higher voltage, but with the degradation through the wire, sticking to this formula using just 12V is your best bet.

If you want to run your fridge indefinitely, a 100W panel would do you good. It would give you a charge cushion in case some cloud cover is overhead. I would stick with a Monocrystaline panel so you get the most power per space real-estate. Another thing to take into account is that although according to the equation (W=A x V), it leads you to believe that a 100W panel would put out 8.333 amps... Good luck ever seeing those numbers. I usually expect 75% of the power. With a 100W panel on a 12V system, you will actually probably see around 6-7 amps output on a perfect day, at high sun, at the equator... lol.

 

[Landay]

Thank you so much for the helpful answers! I'll post up when I get my parts gathered and installed.

 

[lysol]

Thank you so much for the helpful answers! I'll post up when I get my parts gathered and installed.

How many amps does your fridge pull?

 

[Wicked 2007]

Here's a write up on my 100w panel to keep my AUX battery topped off:

http://www.expeditionportal.com/forum/showthread.php?t=101799

 

[Google it Research]

+1 for solarblvd. I bought two Kyocera 100 watt 12v panels for $190.

 

[RangerXLT]

Quick question if someone could help me out. Does it matter how far away my charge controller is from my battery? Basically it would be about 6 feet or so away. Panel would be mounted on top at the rear of the cab.

 

[goodtimes]

Quick question if someone could help me out. Does it matter how far away my charge controller is from my battery? Basically it would be about 6 feet or so away. Panel would be mounted on top at the rear of the cab.

No problem, assuming the wire used is sized appropriately.

My panel is on the roof of my camper (about 20 "cable-feet" from the controller, then another 5 "cable feet" to the battery).

 

[Dan Grec]

One more quick question - I noticed those morningstar controllers have wiring for "load +/-"

Do you have to wire everything you want loaded through there?
Or is it OK just to wire everything straight off the battery?

The wiring diagram in the How-to-make-a-cheap-isolated-dual-battery-setup-for-$50 thread doesn't say anything about where to wire up the load (fridge, lights, water pump, etc. etc.)

Thanks,

-Dan

 

[goodtimes]

The only wires coming off of output side of the charge controller should be to the battery.

Run all of your utilities (fridge, lights, etc) off of the battery.

 

[RangerXLT]

No problem, assuming the wire used is sized appropriately.

My panel is on the roof of my camper (about 20 "cable-feet" from the controller, then another 5 "cable feet" to the battery).

Awesome, thanks! So much good info on this forum. Always appreciated!

 

[Dan Grec]

The only wires coming off of output side of the charge controller should be to the battery.

Run all of your utilities (fridge, lights, etc) off of the battery.

Wicked, thanks

-Dan

 

[lysol]

One more quick question - I noticed those morningstar controllers have wiring for "load +/-"

Do you have to wire everything you want loaded through there?
Or is it OK just to wire everything straight off the battery?

The wiring diagram in the How-to-make-a-cheap-isolated-dual-battery-setup-for-$50 thread doesn't say anything about where to wire up the load (fridge, lights, water pump, etc. etc.)

Thanks,

-Dan

The "LOAD" side offers you a LVD (Low Voltage Disconnect) option. It's output is usually rated at the same as the input. For example, a 10 amp controller usually will allow you to run 10 amps off the LVD load. 20 amps would be 20 amps.

This is really good for not killing your battery for the devices that will run regardless of your ignition (i.e. fridge). It will disconnect the battery if it becomes dangerously low. Now, for the higher amp devices such as off road lights, Just wire the power side of the relays directly to the second battery and the switch portion to an ignition powered switch. That way, they will shut off with the key. That's the way I like it at least.

I usually wire in a switch that will override the ignition hot line for my switches for when I absolutely want to run the lights and junk without the key.