Battery charger with solar panel

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Hi to all.

Did someone try this approach:
http://cds.linear.com/image/314_circuit_1.jpg

when designing solar charger ?
Power consumption will be under 75Wh per day..

Other infos:
- solar panel 15W
- battery 12V / 7Ah

GM

Re: Battery charger with solar panel

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Easy enough to do with a comparator, see

"OverAndReverseVoltageProtection.pdf"

on the S.E.D/Schematics page of my website.
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: Battery charger with solar panel
gm prodded the keyboard with:

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I've done exactly that using an LT8490 and the circuit on the data
sheet. My panel is a 300W 42V 8.5A. feeding two 110 Ah wet cell
leisure batteries.

--  
Best Regards:
                      Baron.

Re: Battery charger with solar panel
On 2/4/2017 3:41 PM, gm wrote:
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Wouldn't that be a pretty inefficient design?  The panel output voltage  
is dragged down by the shunt regulator wasting power both in the solar  
panel and the shunt regulator.  You can find any number of converter  
circuits on eBay and elsewhere for cheap.  Or you can build your own  
like Baron.  The LT8490 looks like a pretty Cadillac chip at over $15.

I found one guy who is already making boards and sharing the design.

http://www.mictronics.de/tag/lt8490/

--  

Rick C

Re: Battery charger with solar panel
On 2/4/2017 12:41 PM, gm wrote:
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The devil is in the details.

You seem to be focused on the isolation diode loss.

Are you in a location where you can reliably
get 75Wh/day out of a 15W panel in winter?

Depending on the time of load, you may be running
the battery flat every day.  Not a good idea.

Charge efficiency is not 100%.

Overdischarge management?

Overcharge management?

Depending on available insolation, time of load
and the characteristics of your panel,
you may be better off with a way bigger battery,
way bigger panel and a MPPT controller.
The MPPT is quite simple to build with a
microcontroller.  It also solves all your
charge management issues.


Re: Battery charger with solar panel

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Looks like the ideal solution to keeping my pick-em-up truck battery
charged, since I drive it only every few weeks.

And in Arizona we certainly don't lack for sunshine ;-)
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: Battery charger with solar panel
On 2/4/2017 3:00 PM, Jim Thompson wrote:
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Do you really need 75Wh/day?
http://www.harborfreight.com/15-watt-solar-battery-charger-68692.html
For $12, it's hardly worth walking all the way to the lab to
turn on a soldering iron so you can spend way more than that
making one.
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Re: Battery charger with solar panel

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I was talking of others... I plan to buy that the next time I'm near
the Mesa Harbor Freight store.
        
                                        ...Jim Thompson
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| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: Battery charger with solar panel
On 2/4/2017 7:35 PM, mike wrote:
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I believe that is only 1.5 watts.  That's barely enough to trickle  
charge a car battery.  I've used a 2 watt, 15 volt wall wart to trickle  
charge a car battery and that's just barely enough running 24/7.

--  

Rick C

Re: Battery charger with solar panel
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How can you tell it's just barely enough?

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Re: Battery charger with solar panel
On 2/4/2017 8:22 PM, Jasen Betts wrote:
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My truck draws 9mA.  As I recall 6mA is the radio.
All I need is that plus whatever self-discharge is going on.

Re: Battery charger with solar panel
On 2/5/2017 2:26 AM, mike wrote:
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The self discharge is not trivial.  Or I should say the trickle current  
to maintain a car battery.  Without rereading all the post to find what  
size battery you are charging, it *is* a regular car battery, right?  Or  
do you have one of those sealed gel cells?

--  

Rick C

Re: Battery charger with solar panel
On 2/4/2017 11:22 PM, Jasen Betts wrote:
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You clipped my example.  It would take a full day to charge a slightly  
run down battery.  If it was fully down it would take three days.  I've  
measured the current it supplies and I see very little difference when  
it is run down or fully topped off.

--  

Rick C

Re: Battery charger with solar panel
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Huh? I quoted all that arrived here.

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"barely enough" is, to my mind less than twice the self discharge rate.

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If the vehicle can sit for 4 weeks (without the battery being fully depleted)  
and then recover on that charger in only 3 days, I'd say it's got
at-least 8 times excess capacity (for for the task of preventing unattended
discharge)

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That is not unusual in a constant-current charger.

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Re: Battery charger with solar panel
On 2/6/2017 10:55 PM, Jasen Betts wrote:
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Yeah, well I'm not sure there is any meaning to that calculation.  This  
unit barely will put current into the battery.


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Who said it was a constant current charger?  It's a tiny wall wart that  
barely charges the battery.  Even a 2 amp charger will fully charge a  
battery overnight.  This thing takes days because there is very little  
excess capacity compared to the minimum current required to keep the  
thing up.  But then again, I guess it is constant current considering  
that the battery always draws the full load it is capable of delivering.  
  It's a 15 volt power pack and once attached to the battery it never  
gets above 13.5 volts.  So it does put out a constant current under  
those conditions.

I don't think charging a lead acid battery is a zero sum game.

--  

Rick C

Re: Battery charger with solar panel

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Argh.  That's an amorphous silicon solar panel.  Low efficiency (about
7%) but cheap to produce and works in low light and shade:
<http://www.solar-facts-and-advice.com/amorphous-silicon.html
<http://energyinformative.org/amorphous-silicon-solar-panels/
In full sunlight, open circuit voltage = 20v and short circuit current
= 0.1A or 2 watts.

I have two solar panels similar to the Harbor Freight model.  I used
them in the distant past to keep the battery charged when I had a
collection of dead vehicles parked in front of my house.  
<http://802.11junk.com/jeffl/pics/home/slides/cars.html
A dead car in front is considered a status symbol and indication that
I own the house as no landlord would let a tenant collect dead cars.
During the winter, I had to top off the batteries every week with a
boost from a conventional battery charger:
<http://802.11junk.com/jeffl/pics/drivel/slides/dead-battery-chargers.html
as the solar panels were insufficient.  I eventually went to a 12v
1.5A "battery maintainer" powered by the AC line.  They worked quite
well until someone stole both of them.

I also have an ICP Solar 04021 Battery Saver Plus 5w, which is about
twice the size of the Harbor Freight model, and allegedly delivers
twice the power:
<https://www.amazon.com/ICP-Solar-04021-BatterySaver-Plus/dp/B00008IHTV/>
Oddly, I've never tried to use it.

Incidentally, you can purchase a ready made solar powered battery
maintainer.  Just add a solar panel:
<http://products.batterytender.com/Accessories/Battery-Tender-Solar-Controller.html
<http://products.batterytender.com/021-1162-man.pdf
Or, get it with a 5w, 10w, or 15w panel built in:
<http://products.batterytender.com/Chargers/ (near bottom of page).



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Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Battery charger with solar panel
On 2/4/2017 9:17 PM, Jeff Liebermann wrote:
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Not sure why you are multiplying these numbers, but assuming this is the  
potential power output from the panel is a faulty deduction.  Is this  
just a convention for rating a panel?

--  

Rick C

Re: Battery charger with solar panel

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Nope.  You're correct but I didn't want to get into the details.  The
data sheets sometimes use the simple arithmetic I used.  However, the
real power output is about 20% less.  The difference is called the
fill factor.  Measure Voc (Voltage open circuit) and Isc (Current
short circuit) and plug it into the calculator below.  Multiply and
you get Pt (theoretical power), the maximum power that an ideal solar
panel can deliver.  Multiply again by the approximate fill factor and
you get a more realistic value for Pmax (maximum power):
<http://www.ni.com/white-paper/7230/en/
<http://www.pveducation.org/pvcdrom/solar-cell-efficiency
<http://www.pveducation.org/pvcdrom/fill-factor-0
<http://www.pveducation.org/pvcdrom/short-circuit-current
<http://www.pveducation.org/pvcdrom/open-circuit-voltage
Everything else causes the power output to decrease.  Output drops
when the panel gets hot, the angle of the sun is less than
perpendicular, dirt on the glass, voltage drop from series diodes,
reflections, weather, clouds, panel aging, etc.



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Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Battery charger with solar panel
On 2/4/2017 1:41 PM, gm wrote:
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Google "MPPT"


Re: Battery charger with solar panel
On Saturday, February 4, 2017 at 3:41:40 PM UTC-5, gm wrote:
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A very simple charger can be constructed with
a few current limiting resistors and forward
biased diodes. The reverse breakdown voltage
of the diodes must be larger than the maximum
battery voltage so that the battery does not reverse discharge into the solar panel, after  
sundown.  

Ideally, the maximum charging current should
be 700 mA, i.e., (battery AH rating)/10.0 --
current limiting resistors ensure this, as
well as ensuring that the maximum forward  
current of the diodes is not exceded. Also
note that the solar panel power output rating  
is what has been measured under ideal testing conditions of the manufacturer -- on site  
daily power output will vary will depend on  
that day's weather conditions.  

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