Solar Panels for Trickle Charging 12v lead acid batteries ?

[Old Raft]

Anyone any views on the best type, make, design of PV (or other?) panels for keeping 12v lead acid car batteries topped up? 

With an obvious view to keeping costs down and batteries in good condition. 

[Bob Dunlop]

On Fri, Apr 25 at 06:12, Old Raft wrote:
> Anyone any views on the best type, make, design of PV (or other?) panels
> for keeping 12v lead acid car batteries topped up?

I use a no-name 5W PV panel to maintain the battery on my electric fence.
Makes a nice roof to the battery box. The fence draws about 1W so in the
summer months the panel just about keeps up with it and I don't have to
change the battery to often.

Cost me about 40 pound four years ago, bet they are cheaper now.

Brought a solar regulator [1] as I was a little concerned about over
charging. Basically just a PWM switch that reduces the charge current
when the battery voltage rises. Worked well for several years until
the wind and rain finally got to it. Then I simply put the panel in
parallel with the battery with a Schottky diode to prevent discharge
through the panel overnight. Works just as well for me.


[1] http://midsummerenergy.co.uk/buy/solar-regulators/steca-solsum-6f-6A-solar-controller.html

--
Bob Dunlop

[Eric Rowen]

Thanks...

At present my mate has a £100 panel which provides about 16 to 17 volts, I have no idea what current but will check as panels seem to go from £14 ish for  1.5 W  to between  £50 and £100 for around 15 Watts so keen to know what if anything the £50  difference is.  

At  1.5 W little danger of overcharging (but possibly not enough charging current)  but at 15 W then it's quite likely so some form of controller based say on fully charged voltage would be useful.  I will look at the above to see if it fits the bill.

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[Bob Dunlop]

Hi again,

On Sat, Apr 26 at 03:25, Eric Rowen wrote:
> Thanks...
>

> At present my mate has a ??100 panel which provides about 16 to 17 volts, I

Yep 16-17V open circuit output is fairly typical for a 12V "nominal" panel.
As soon as you draw any current the impedance of the panel will make itself
felt and the voltage will drop to that of the battery etc.

Panels usually produce more power when run at high voltage, low current.
Dragging the output voltage down is not good from an efficiency point of
view, but is okay if you are only interested in trickle charging to
maintain a battery.

If you are interested about extracting the maximum power from your panel
then there are things called Max Power Point Tracking (MPPT) regulators
that allow the panel voltage to remain high and convert this to a lower
voltage, higher current for charging. They are more complex and expensive
than regular regulators and so not normally used for small systems. I
think the smallest I've seen was designed for a 65W system.

The PWM controller I referenced is a simpler device, mainly for battery
safety. It limits the charge current as the battery voltage rises preventing
over charging. That particular model also has an output switch, so it will
turn the load device off should the battery voltage drop too low, preventing
deep discharge.

> have no idea what current but will check as panels seem to go from ??14 ish
> for 1.5 W to between ??50 and ??100 for around 15 Watts so keen to know
> what if anything the ??50 difference is.

I suspect 50 quid could be in quality of the frame, the panel itself in that
you might find the more expensive panel is more efficient and hence smaller,
of of course it could just be marketing/profit.

> At 1.5 W little danger of overcharging (but possibly not enough charging
> current) but at 15 W then it's quite likely so some form of controller
> based say on fully charged voltage would be useful. I will look at the
> above to see if it fits the bill.

You need to know the panels rating. At 1.5W you don't want any additional
load. At 15W a simple regulator makes sense. I'd suggest attach the panel
to a known load on a sunny day and measure the current.

--
Bob Dunlop

[Tom Allen]

Your prices look a bit expensive:

15W panel with diode protection, cables, connectors, postage etc £27

http://www.ebay.co.uk/itm/12v-15w-10w-Solar-Panel-Battery-Charger-3m-Cable-Block-Diode-Alligator-Clips-/221288446017?pt=UK_Gadgets&var=&hash=item3385d1b841


15W panel and more fancy PWM controller with led status lights,
cables, connectors, postage etc £40

http://www.ebay.co.uk/itm/15w-Solar-Panel-with-10A-PWM-Charger-Controller-for-12v-Battery-UK-stock-/221338684477?pt=UK_Gadgets&hash=item3388d04c3d

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[Eric Rowen]

Thanks......... One of the reasons I posted the question was that some prices looked rather high, and prices for 15W ish seemed to be between £50 and £100  and I could not see what the extra was for.   Also these prices appeared to be for just the panel not the regulator. 

[Tom Allen]

It shocks me how much retailers like Maplins seem to think they can
flog them for. I pity anyone who pays those prices without realising.

[Eric Rowen]

The very cheap ones I will give a miss, too many times have been stung by items on eBay, especially when try and comment and eBay does not even recognise the product code.   Also I guess if you buy from a UK retailer, not Maplin who I only use for emergency requirements (plus they are 200 yards away :-)  you get some support. 

I will give the dearer one a try 

[Eric Rowen]

I bought the second items mentioned 15W panel with PWM controller but this does not come with cables connectors etc.

The manual is quite good but the text is so small it takes so much concentration to read that the content is lost.

One question for anyone with knowledge of the controller type.  It has three connections, panel, battery (to be charged) and load.   Having by coincidence on the day my panel arrived been asked to look at a friends setup I found his controller as expected to have the same three connections, but each equipped with cables and connectors except for the load, so contrary to my advice the load remained connected direct to the battery NOT via the controller.

I am about to search for a circuit diagram of this type of controller but just wondered if anyone knows how connecting the load direct may affect the functionality? 

As and when/if I find a copy of the manual on-line I will copy a link here. The manual lists the controller as 

SYC-10L / SYC-20L / SYC-30L   Solar Light Controller 

  

On Mon, Apr 28, 2014 at 2:06 PM, Tom Allen <t...@randominter.net> wrote:

[Barnaby]

Ebay says "Protection from deep-discharging" presumably that only works
if it can switch the load off.

[Eric Rowen]

I suspect you are right, seems daft not to use the separate connections. 

On Wed, May 21, 2014 at 6:01 PM, Barnaby <b...@zi.is> wrote:

Ebay says "Protection from deep-discharging" presumably that only works if it can switch the load off.

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