am I missing something? Solar

[felixx]

Hi team
I will be running 12V only I will have at most 3x 2W LED lights on in my teardrop at night. (and possibly charging a set of bluetooth speakers)

During the day I may be charging my phone or the speakers

6W = 0.5A @12V?

(P= VxI)

So will a 25W panel suffice? or am I missing something?

A 25W should put out a little over 2A
(even if only 50% efficient I am still getting double what I take out?)

Thanks in advance for helping me with this

[daveesl77]

When we had our little truck camper I got a 50 watt (still have it) and it kept our battery fully charged with no problem. We were running a small fan, a laptop at times, multiple LED strips, a water pump and several charging station thingies. In addition, we would sometimes run our inverter/refrigerator or icemaker. I have a group 27 LA battery. For what you describe, the 25 would probably be fine, but you might want to look at something slightly larger, just in case you do more stuff.

dave

[GuitarPhotog]

Will you be charging the battery from the vehicle while towing? And, how big (in AH) is your battery?

If you have a small (~25AH) battery that you charge while towing, a small panel like that should be OK, until you run into a string of cloudy, or worse rainy, days. At which time you'll need more power.....

My last two extended trips with my trailers both encountered extended rainy spells. In '13 on the Oregon and Washington coast, I had rain 4 whole days and 8 partial days, out of a 21 day trip. In '14 on a 30 day trip through B.C. and down to Yellowstone, I had 11 consecutive rainy days ;-(

Expect the best but plan for the worst.

<Chas>

[felixx]

I was going to get a 90AH battery
I wont be charging as I tow, purely because most of my towing will be done via work vehicle and they wont let me change wiring to do that.
(I can however fire up car and charge via jumper leads I guess (work pay for fuel)

By my reckoning a 90AH battery will give 90 hours of 0.5A current before it is 50% flat.

Most of my trips will be 2-3 days but just trying to get it right

[GuitarPhotog]

Your 25W solar panel will take forever to charge a 90 AH battery run down to 50%. Do the math. A 25 W panel can put out, optimistically, 2 A at 12 V (less at the 13.2 necessary to charge a battery) in full sun. At a 2A charge rate, it will take 24 hours or more to deliver 45 AH of power.

Get a bigger panel. 75-100 W would be fine, I think.

<Chas>

[MtnDon]

Lead acid batteries, and that includes AGM batteries, do not like to be left in a partial state of charge for too long. If run down to 50 - 75% of charge and left for several days the sulfur crystals that form on the plates can harden. That makes it difficult to impossible to fully recharge the battery. The formation of the sulfur crystals is natural, a part of the chemical reaction that produces the electricity. Charging the battery reverses the chemical reaction, but only when the sulfur crystals are soft or recently formed. It's the in and out of solution that makes the battery electrolyte specific gravity change. Remove the sulfur and the Sp Gr falls, put the sulfur back into the acid solution and the Sp Gr rises.

With that in mind it is best to plan a PV system to be able to fully recharge the battery every normal day of use. That needs larger PV panel capacity.


We can avoid the worry and potential problems of sitting in a partial state of charge by using an LFP battery. Cost is the main drawback. One way to look at it is to use an LFP battery and don't bother with any solar. LFP can run down to 10 - 20% and sit there and not be damaged. Recharge with shore power or a generator.

[felixx]

Your 25W solar panel will take forever to charge a 90 AH battery run down to 50%. Do the math. A 25 W panel can put out, optimistically, 2 A at 12 V (less at the 13.2 necessary to charge a battery) in full sun. At a 2A charge rate, it will take 24 hours or more to deliver 45 AH of power.

Get a bigger panel. 75-100 W would be fine, I think.

<Chas>

Thing is even with 4 hours use , it has only drawn 2AH (2/90 or 1/45 ) the charge (just over 2%)
If the panel is out every day of use (usually a 3-4 day trip) and it is cloudy all 4 days and no charge is produced by the sun I am sure I will still only use 10% of the 90AH


Or am I stupid

I might see what price I can get a 50 for

[daveesl77]

This is the 50 watt we have. We have had 2 of them and they both work great. One went with a trailer I sold. Even on an overcast day my little panel still pumps out some power. On a full sun day, it is cranking.

http://www.amazon.com/RENOGY%C2%AE-Mono ... olar+panel

I have a fairly inexpensive, but highly rated charge controller, mine was a different name than this one, but it looks the same

http://www.amazon.com/Docooler-Controll ... AD4AZ9Q15P

I also got a 25' link line extension wire and a few of the connectors. I got one of the freebie HF VOM to act as a voltage display. I doubt I have $130 tied up in the whole rig.

dave

[Shadow Catcher]

My suggestion, plan for more than you think you need. You will be surprised. While ours is on the far side of elaborate, we charge cell phones, laptop, iPad, weather warn radio, XM radio, battery charger for flashlights, DVD/TV lots of lights... Once you figure out how convenient it is...

[daveesl77]

Shadow Catcher is dead on right...it doesn't cost much to upgrade to a bigger system and in my case I'm probably going to double up mine to 100w. Nice to have it if you need it and it doesn't hurt to have it if you don't.

dave

[GuitarPhotog]

Shadow Catcher is dead on right...it doesn't cost much to upgrade to a bigger system and in my case I'm probably going to double up mine to 100w. Nice to have it if you need it and it doesn't hurt to have it if you don't.

dave

And the money you spend now will be insignificant later on when you are enjoying (or not) the fruits of your labor.

<Chas>

[MtnDon]

Wise move IMO. Many times if one tries to expand a PV system they run into something that ends up costing more than if it had been built larger in the first place.

[felixx]

It appears I may have scammed a free 60W system!
WOW! (2nd Hand but free)

[dales133]

Good score felix

[daveesl77]

Free is what we like! Way to Go!

dave