? size solar panel

[dtappy3353]

Folks:

We would like to use a 12v deep cycle battery for topping off our 2 laptops, 2 kindles and cell phones.

What size solar panel would be needed to keep the 12v battery charged/topped off.

Thanks much!

[Harvey51]

I like to ease into these things. I first tried a 100 watt panel. It turned out that was sufficient to keep the two batteries over 80% charge all the time. We need a little furnace time even in summer at 58 degrees latitude, freely use the lights, two phones and two iPads.

[MEXICOWANDERER]

You have to satisfy the chemical demands of your battery, not a calculator. This is where E=MC2 meets reality. Unless you put Velcro tabs and wing nuts on your battery hold down.

When a charging protocol just meets the sanctification of battery chemistry is the real world goal. And only a hydrometer can determine this with a flooded battery after a month or six weeks of service. AGM capacity tests or the half-percent rule has to be met.

The above rules for extended boondocking. The 3 days to a week usage then suckle at a power post can get away with murdering the extended boondocking/E=MC2 reality.

[scrubjaysnest]

dtappy3353 wrote:
WOW....

I have 120 watts of solar feeding 2 12v deep cycle batteries on the fifth wheel which seem to maintain a 55-60%. We only use LED light bulbs with only one light on for the entire evening till we go to bed.

I'm hoping I'm clear and forgive me if I'm not.

We ONLY wish to recharge laptop battery with a 12v that has a trickle charge on it. How many watt solar panel would it take? We spend most of the time in AZ. Oregon doesn't factor in on this equation.

We did 2 laptops, cell phone and tablets with two 105 aH 12 volt batteries and 400 watt inverter. The solar for that and LEDs and conservative pump or heater usage was 360 watts in full sun.

[red31]

battery saver took over on battery, 60% @ sun up, took a few hrs this morning to get down to 6%/9minutes per battery icon info. 1 yr old Dell inspirin laptop, 40wh li batt, its first deep discharge.

Start 45w charger, display = 20w, pf .5, .32A, 39 VA
20w steady for 70 mins then 21w with taper.
Kill-a-watt changed from 0.03 to 0.04KWH @ 7w - 2 hrs 7 mins
0w @ 3 hrs 43 min, no data between!


previous 110w was never in sleep on ac power.

With solar as the maintainer it is hard for me to not go with PT and 100w needed / 100ah for top charge/equalize.

A 12v cig lighter charger is available.

[MEXICOWANDERER]

Figure 10 ampere hours day per laptop net. Need to bump the voltage up. How are you going to do that? A DC/DC converter?

I was averaging 5.13 hours daily same latitude. Blue skies computed against max kWh potential of panels. January. With a tracker.

But a nasty skew was taking place. Losses and degradation. Just throws all the set calculations out the back window to the pig. There is solar watts inch2 differential. Summer is light years from winter - solstice. Inverter, converter, regulator, power transmission efficiency deductions.

Experiencing the error between stubby pencil with worn eraser, thoroughly crunched calculator and wadded up sheets of paper, versus reality is a very rude school of hard knocks. I used to have a motto: Do it right for 100% of the cost or do a retrofit at 130% of the cost.

[red31]

so 25 hrs yields 0.11 KWh of my daily laptop use Dell inspirin 3000 series.

tomorrow I'll see what the 40wh batt needs to recharge. over/under 50wh?

One recharge a day would be plenty for me and to make it simple, in AZ where on ave a properly tilted panel collects 5000 wh/m2/day on average, ya take the 40wh battery and double that to 80 wh / 5 and need a 16w panel to keep up. The 10wh cell phone batt would need another 4w panel, that's 20w for a laptop and phone. That explains the WOW! a 80ah batt would have a few poor solar days of capacity.

[MEXICOWANDERER]

I love it when people ask to learn something new. An enlightened disciple of electrical reality spreads wisdom. Hard to argue with that.

[2oldman]

dtappy3353 wrote:
I have 120 watts of solar feeding 2 12v deep cycle batteries on the fifth wheel which seem to maintain a 55-60%.

Then I can safely say you need 240 watts.

[red31]

MEXICOWANDERER wrote:

One device at a time or all ganged together. This will give you watt hour total and absolutely nail your energy usage hard and fast

I'm doing this as suggested with one laptop. At this point disregarding using '12v' charger, inverter losses, panel production, time of year angle and the rest.

Tomorrow I'll discharge to 10% and measure recharge power. Cell phone also, at that time I should know the size of both batteries.


1230 HRS CST "0.08 KWH" BATTERY, PRIMARY, 40WHR, 4C, LITHIUM, SIMPLO

[MEXICOWANDERER]

Then keeping the battery shiny side up enters the picture

Calculated discharge

X

120% to account for CEF charge efficiency factor + controller vigorish

A test replicates reality

An experiment is "Shake The Jar Dewey And See If They Fight"

Try for accurate numbers. And remember, solar panels ONLY give rated wattage when solar axis A and axis B equal 90 degrees. The dreaded BELL CURVE*

*Actually, a pyramid

[red31]

pianotuna wrote:
red31,

Please do share the data!

sure, the OPs trickle comment leads me to believe he wants a 5 or 10w panel and no controller to run his laptops, readers and phones.

If that is the case I believe he's mistaken, also assume his 5er has co/propane detectors and a fridge brain using 12v.


0.07wh @ 10:40 am cst, surfing, paying bills, transferring $$, selling stock, ... Firing up youtube peaks at 20w and settles to ~11w.

[time2roll]

dtappy3353 wrote:
WOW....

I have 120 watts of solar feeding 2 12v deep cycle batteries on the fifth wheel which seem to maintain a 55-60%. We only use LED light bulbs with only one light on for the entire evening till we go to bed.

I'm hoping I'm clear and forgive me if I'm not.

We ONLY wish to recharge laptop battery with a 12v that has a trickle charge on it. How many watt solar panel would it take? We spend most of the time in AZ. Oregon doesn't factor in on this equation.

What's wow?

If you are already getting down to 50 percent charge you already need more power. At least one more panel at 120 watts and probably two to make life easier and to include the laptop.

Too many variables on power usage and solar production to give a precise calculation. Typical laptop is 75 watts and solar is about 5 hours per day. So if you run the laptop 5 hours and have a 100 watt panel it will be close to even.

If you pass through So Cal on the way to AZ you can stop in Norco and pick up some panels at a good price. Call ahead to verify inventory.

https://www.solarblvd.com/product-category/solar-panels-systems/12-volt-solar-panels/

[pianotuna]

red31,

Please do share the data!

[red31]

pianotuna wrote:
Hi

Run the entire RV via the kill-a-watt. Do not exceed 1800 watts. Measure for 24 hours.

I agree but for 'fun' am measuring just one laptop to see what it might use over one day for a dedicated 12v with solar/controller.

Tomorrow I;ll exercise it to determine what one recharge is worth.