Hooking 4 15-Watt Panels Into a Controller For Camping?

[KenRyan]

Hi. I'm brand new to the forum, so please forgive a little (or more) ignorance on this topic. I did try to look at the stickies and other posts, but my eyes started to glaze over with all the stuff I didn't understand. But hopefully, my question is simple.

I'll be camping for 10 days. I have four 15-watt solar panels and two 115 ah 12-volt deep-cycle marine batteries. And I actually have two charge controllers a 7 watt charge controllers. One is small 7 amp "Battery Charge Controller" I got from Northern Tools. The other controller is the one that came with a "45 Watt Solar Kit." It is a box with several cool adapter outlets and a voltage meter display on it. The kit had 3 panels, this controller and some accessories.

I know I'm supposed to connect these panels together somehow and then run the combined wires to a controller, which is then hooked up to the battery bank (my "bank" of 2). But I'm not sure how to do the "connecting-the-panels-together-and-then-to-the controller" part.

Part of the question is whether I can connect all 4 panels to one of these controllers. The box that came with the 45 Watt kit has screw posts on the back, and the instructions said just to run each of the 3 panels directly to the screw-posts. So in that case, I'm not combining the wires of the panels. But I don't know if this box can accept a fourth panel (my assumption was that it was designed for three since the kit is called the "45 Watt Solar Kit." But if I can only hook up three panels to this controller, what do I do with the 4th one?

Or would it be better just to hook all 4 panels to the 7 amp controller? Since I have 4 panels, each sending 1 amp and 15 watts, it would seem that the 7 amp controller would be able to accept 4 panels. But in that instance, I don't know what to do with the wires from the solar panels. This controller just has 2 wires (+ and -) coming out of the "Solar Panel" side. So do I combine the + wires from the 4 panels and twist them together, doing the same with the - wires? Or is there a common way to combine the panel wires so that I end up with 1 - and 1 + wire to connect to the controller wires?

Can someone explain this or direct me to a post or tutorial (one aimed at pretty new solar folks)?

Thanks!

Ken

[PNjunction]

We can cut directly to the chase here.

Yes, those 4 panels could merely be paralleled with each other to the plus and minus of the controller. But there are bigger issues, and it is pretty common.

Your battery bank is too large for the panel to support, aka "deficit charge". Unless of course all you are doing is charging cellphones and laptops but you are humping 230ah worth of lead through the forest. If you can return the batteries, do so. A 45w panel actually provides about 2.5A of charge current under the BEST of conditions. Because you have chosen huge batteries, you must be expecting gigantic loads. Let's say you draw your paralelled 230ah bank down to half capacity of about 115ah.

With 2.5a of charge current, at about 6 hours in texas solar-insolation, you are looking at

115 / 2.5 * 1.78 compensation, that's about 82 hours to recharge.
82 / 6 = 13.6, so about two weeks of nothing but charging under perfect conditions with no load. This would be like putting just two little battery-tenders on your bank only 6 hours per day.

Most of those kits contain a splitter / combiner for the panels. You must be missing those. And some of the places sell little AGM's more appropriate to the panel size, like little 35ah agm's.

There is a lot more to it, like what exactly are you running, and for how long each day? A Kill-A-Watt meter can help you determing that for ac loads. A multimeter for your dc loads. THAT determines your panel and battery size, along with geographic solar-insolation hours.

Without knowing your loads, we are just winging it. However, if you can return those 115ah batteries, and get something smaller, like an 18-35ah general purpose agm - but that is a far cry from your initial desire to go with 230ah of storage - so what you are trying to power might kill it right off.

And the 7ah charge controller is junk. It is the old and inefficient ping-pong type from the 1970's that really doesn't get the job done. So other than buying a very small battery just to play around with, stop spending any money until you know your loads.

In reality, what you are looking at is a total redesign, but you can goof on this stuff for now.

[Sunking]

You ar enot going to like any of the answers you receive here, and all of us regulars know exactly what you have; a Harbor Fright kit that cost you some $200. Unfortunately the box is worth more than what came in it.

Those 4-15 watt panels cannot even charge one of the batteries you have, more like a 12 volt 30 AH battery at best and that is stretching it a bit. What you basically have is a cell phone and tablet charger. To charge the two batteries you have wil take on the order of 250 to 400 watts of panels, and a real charge controller.

A decent camping kit would be a 150 watt panel, 10 amp charge controller, and a 12 volt 80 AH AGM battery. May not generate the energy you want but is a good starting point and would provide roughly 300 watt hours per day of usable energy.

[KenRyan]

Wow! I knew I was lacking in knowledge in this area, but I didn't think it was that bad. thanks so much for the information. Yeah, that kit I bought was from Harbor Freight. And the other panel seems to be similar - same specs.

Acting out of ignorance, I bought those batteries thinking "the more AH capacity I had, the better." It wasn't based on calculation.

I was asked for my load. It works out to appoximately:

- CPAP: 18 ah per night (rated by the manufacturer as over an 8 hour period)
- LED Rope Light for the perimeter of a 20'x12' tent (made from a King Canopy Portable Garage frame): 12 ah per night
- LED Rope Light for perimeter of common area shelter: 14 ah per night
- Charging a MacBook Air: not sure, but the battery lasts about 6 or 7 hours, so only every couple of days will I need to recharge it.
- Charging a portable DVD player (not sure)
- Charging a couple of cell phones (not sure)

Assuming I did the calculations correctly on the LED lights (.8 watts per foot), I think I'm looking at about 60 to 70 ah per day. I know I should try to be more exact.

So as you can probably tell, this isn't your typical camping trip. It's a sort of festival in Pennsylvania (north or Pittsburgh). And our "tent" is surely not like what most people use. One of the laptops and the DVD player is for my autistic son.

So given all that, and given that my current (ha!, no pun...) plan is deeply flawed. My plan is to return the batteries and hope to exchange them. Given my estimate of, say, 70 ah per day, and that both replies suggested AGMs, would it be better to get two 80 ah AGMs, a 150 watt solar panel and a 10 amp charge controller? If so, what sort of charge controller (brand? model? type?) would be recommended?

Thanks again!

Ken

[Sunking]

Ken let's try to save you some heartache here OK?

How many days will you need to operate? 1, 2, 3? Be reasonable in your expectations. What I am thinking is you may not even need any solar. Just a battery of proper capacity charged up at home, then take with you.

Ken how are you calculating the rope lights? For example the one for the tent is 64 linear feet? 64 x .8 watts = 52 watts roughly. at 12 AH/night is only running them 2.8 hours. That does not sound right. What you really want to work with is watt hours, not amp hours as that can generate errors from multiple conversions.

Example lets say that same LED rope uses 52 watts and you run it 5 hours per night = 52 watts x 5 hours = 260 watt hours. That alone translates to about 22 AH on a 12 volt battery. Bad news is your panels cannot generate that much power.

If you calculations are corrent you are looking at a 300 watt panel and a fairly expensive battery and charge controller.

[mapmaker]

- CPAP: 18 ah per night (rated by the manufacturer as over an 8 hour period)

Is that 18 ah from a 12 volt battery? If so, that means the cpap draws 27 watts. That sounds a bit optimistic... it probably draws more than that. You better figure that out before your trip.

Head over to your local honda generator dealer and take a look and listen to the eu1000 inverter generator. Run that for an hour per day with a battery charger and your problems will be solved.

You cannot get the battery to 100% state of charge in only an hour, but it won't hurt to be undercharged for only a few days and you can charge it all the way to 100% when you get home. An AGM battery would be a good choice for you because they can take higher charge rates... you can get it most of the way charged up in an hour.

--mapmaker

[KenRyan]

Thanks Sunking,

We will be there for 10 days. So it won't quite be as easy as that, sadly. I was using amp-hours only because the site where I (ahem) "learned" the stuff I thought I knew simplified things as basically amps used need to be put back into the battery each day. OK, so watt-hours? Yeah, for the main tent, in early August in Pennsylvania, I'm thinking only about 3 hours per night, which is (64 * .8 = 52 watts) * 3 = 156 watt-hours per night, which is about 13 ah. And that's just for that one room.

So if I were to do the 300 watt panel, battery and charge controller, do you have any suggestions as to sourcing and type of battery and controller?

Thanks!

Ken

[paulcheung]

Can you use generator on the camp? If yes, I would get a cheap 1000 watts small portable generator and a 40 amps battery charger, Run the generator for two hours each day to charge the batteries.

[KenRyan]

Is that 18 ah from a 12 volt battery? If so, that means the cpap draws 27 watts. That sounds a bit optimistic... it probably draws more than that. You better figure that out before your trip.
--mapmaker

Mapmaker - I got the info here: http://www.resmed.com/assets/documen...de_glo_eng.pdf - for AutoSet Spirit II: "Current draw at 12 V DC (amps) - Battery size for 8 hours use (amp-hours) (includes 50% safety margin) = 13 (for pressure setting of 10)." Am I reading that right then? 13 ah over 8 hours?

Also, I will be sharing camp space with other people in very close proximity (like literally 5 feet on either side), so we're not allowed to use fuel-based generators.

So I guess my "simple" question turns out to be not so simple. Ain't that always the way?

Thanks for the reply. I wonder how quiet the "Super Quiet" EU1000 really is?

Cheers,

Ken

[mapmaker]

Battery size for 8 hours use (amp-hours) (includes 50% safety margin) = 13 (for pressure setting of 10)." Am I reading that right then? 13 ah over 8 hours?

that's also what I read. I take it you don't have a humidifier... they use a lot more power.

I wonder how quiet the "Super Quiet" EU1000 really is?

Depends on the load. With a modest load they sound like a car idling. Aren't there any events, mealtimes, etc when nobody is in the sleeping tent and you could run the generator for an hour or two?

--mapmaker

[Wy_White_Wolf]

...Thanks for the reply. I wonder how quiet the "Super Quiet" EU1000 really is?

Cheers,

Ken

I use one to run the wife's Oxygen Concentrator and CPAP at night when we are at the ranch. It is real quiet and beats packing bottles for the O2 when there.

WWW

[KenRyan]

Thanks again for all the help!

The generator idea is out. There are no scheduled times for people to be away or anything. I have to do this via solar with batteries. So the only real changes I can make are to either go without some of the things I was hoping for (the lighting, primarily), or make the change to the 300 watt panel, different battery(ies) and "good" charge controller.

If I go the latter route, does anyone have any recommendations on where/how to get a 300 watt solar panel for the best price? I'd also be interested to know what is considered a good charge controller (10 amp was recommended), since the small 7 amp one I have seems to not be very good.

Thanks!

Ken

[mapmaker]

does anyone have any recommendations on where/how to get a 300 watt solar panel for the best price? I'd also be interested to know what is considered a good charge controller (10 amp was recommended), since the small 7 amp one I have seems to not be very good.

You will need at least a 30 amp controller if you use a 12 volt battery and a 300 watt panel. btw, 300 watt panels are not very portable... you might be better off with a couple of smaller panels.

--mapmaker

[KenRyan]

Thanks Mapmaker!

Ken

[Sunking]

OK Let's get you fixed up. First and this is extremely important. The solar panel has to have clear horizon view east to west ot this is not going to work. It has to be full sun from sunrise to sunset with NO SHADE whatsoever. Understand?

You need roughly 900 watt hours per day and August in Pennsylvania gets decent Sun Hour in August of about 5.2 Sun Hours so that is good news. You want to orient with a slight tilt to solar south in August. Best way to set it up is at around noon when the sun is directly over head at solar noon, point the panel directly at the sun and leave it there. That will give you maximum harvest.

OK to do this you want to buy a Grid tied panel, NOT A BATTERY PANEL. Grid tied panels are higher voltage, higher wattage, and much less expensive or about half the cost of battery panels. Shop for a Grid Tied panel of 220 watt minimum and up to no more than 300 watts. You should be able to find one loose stock, over stock, or cosmetic defect for less than $200. There are a lot of 220 watt panels out there up to 300. With a 220 watt panel will generate up to 19 amps

By using a Grid Tied panel means you have to use a MPPT controller. Two come to mind that should work really well for you;

1. Morningstar TS-MPPT-30 is a 30 amp MPPT controller and @ 12 volt battery can handle up to 400 watts @ 30 amps of charge current.
2. Midnite Solar Kid 30 amp controller and @ 12 volts battery can handle up to 400 watt input @ 30 amps charge current.

There is a third one I am hesitant to suggest but will save you some cash is Tracer 20 amp MPPT.

For a battery you want a total of 12 volt 200 to 250 AH battery. This will require you to buy 2-6 volt 200 to 250 AH golf cart batteries and wire them in series for 12 volts. If you think you can handle flooded without spilling them go to a Sams, Walmart, or Costco and get you two 6 volt golf cart batteries. Normally I would not recommend a Wally World battery, bu tsince this is a 1-time application no reason to buy a premium battery. These will last about 2 years. Another inexpensive brand is US Battery. Or you could use the batteries you have now.