solar power question

dacflyer · Post by **dacflyer** » Sun Dec 17, 2006 8:29 pm

i have 2 - 12 volt batterys @ 7 amp each in parallel so 12v @ 14ah
with a 40 watt load connected to a motion sensor. and i have
a 40 watt panel to charge them with.

my question is... should i have the charge to the batterys isolated with dioads ? and or the out from the batterys to the lights isolated with dioads?

for prevention of the batterys draining from each other unevenly or unevenly charging ?

also does anyone know if this solar controller is a shunting device ?
this one i have is a

ASC specialty concepts inc. model ASC 12/8

i had this on a test bench with a power supply in place of the solar panel
and when the batterys are charged, the controller here shorts the supply out, popping the breaker.. i put a lamp in series as a ballast load. and as the batterys charge the lamp is very dim,,but as the battery gets full, the lamp light up brightly... once the battery drains some,,the lamp goes dim again indicating a charge.. is this normal...i wouldn't think that a controller would be a shunting device on panels..wouldn't that destroy the panels?

Chris Smith · Post by **Chris Smith** » Mon Dec 18, 2006 8:00 am

I donâ€™t know how your controller works but most run a typical type of regulator.

If yours is simply dumping the extra current to ground via a Zener, [ a waste] I would change that.

All solar panels work like a variable light resistor and they need a diode to stop any flow backwards into them during low light or no light conditions.

Also a separating diode between batteries is a good idea allowing either to work for you and not any imbalance between cells.

Batteries are current filled, and as long as the battery voltage is not too high, the cells wont boil and will self top off with out any problems. My guess is your solar panel may have a high voltage and thus need to be regulated for the out put to not kill any battery?

Buck boost regulators work well, and if the match from the solar and battery arenâ€™t that far apart, a standard linear voltage regulator will do the job as it wont waste too much power.[only if they are matched]

richfloe · Post by **richfloe** » Mon Dec 18, 2006 6:52 pm

Dac,
Assuming the batteries are identical, no problem in putting them in parallel, as you figured, it just gives you 12v @ 14AH, just pretend it is one large battery.

No diode between the battery and the load. A fuse might be nice.

If you were connecting a solar panel directly to the battery without a regulator, you would want a diode. When dark, the panels would draw a small amount of current from the battery. It is most likely that your solar regulator contains the required diode. I have seen some panels that included a diode.

There are three ways that you can regulate charging from a solar panel into a battery:

First, you can do something like a simple series, linear regulator, perhaps an LM-317 or something beefier. The problem here is that aside from generating a some heat, the forward voltage drop will decrease the charge current available slightly.
Second, a linear shunt regulator, something similar to a zener but on a larger scale due to the power it may have to dissipate (like full output from the solar panel, 40 watts). If using a linear shunt regulator, feed from the solar panel to the battery thru a diode and have the shunt regulator shunt the solar panel to waste some of its power when the voltage gets too high.
Third (Often the best option, especially at moderate power levels) is the switching shunt regulator. Feed from the solar panel thru a diode to the battery. When the battery voltage gets up to 14v or whatever, put a Total Dead Short across the solar panel. Wont hurt a thing. After a short delay or after seeing that the battery voltage is sagging, release the short.
The big benefit to the third option is that the power dissipation of the regulator will be smaller (much smaller) than a series pass or linear shunt. When the switching shunt shorts the solar panel, it will drop less than a volt (lots less if you use a mosfet ) times whatever amperage the panel will put out which could vary from about 2.5a to maybe as much as 5a. 5a times 0.6v is a whopping 3w that shunting transistor would have do dissipate, wont take much of a heatsink.
Since you say that the power supply that simulated your solar panel got suddenly shorted when the battery got full, this is what you have.

You said that you have a 40w panel and a 40w load, I assume that the load is controlled by the motion detector and will only operate intermittantly. Else: dead battery.

Have I babbled enough?
Rich

Chris Smith · Post by **Chris Smith** » Mon Dec 18, 2006 9:16 pm

When dark, the panels would draw a small amount of current from the battery.

IF there is no regulator or diode, the draw will be any thing but small.

The cells will become a load in the dark, draining all of yout light time charge efforts.

dacflyer · Post by **dacflyer** » Tue Dec 19, 2006 6:08 am

richfloe >> yes the lights operate intermittently with the motion detector.

the reason i asked about the batterys is...won't 1 battery draw more or less current as they age when charging? or if you are mixing used batterys,,or does that still not matter ?

also is ASC specialty concepts inc. a good type of solar controller to use ?

i thought any short on a solar panel wouldn't be good for it..won't that shorten the life of it ?

Chris Smith · Post by **Chris Smith** » Tue Dec 19, 2006 8:42 am

Zeners and Linearâ€™s are about the same only the Zener is the cheap way to regulate because it dumps all the excess directly to ground in the form of heat as a dead short.

These type of Zeners come with huge heat sinks to disparate all the dumped energy into its fins.

The British bikes used huge Zeners for their voltage regulators simply for cost and the engineering aspects.

The buck boost only spurts on and off the correct amount of energy with little heat loss.

Shunting to ground may be bad for a solar cell but the solar is merely a resistor that produces electricity in the presence of light.

As long as the shunt isnâ€™t too bad [heavy], the cells wont over heat or damage.

Any battery has its own natural resistance and this resistance is the same as a shunt while neither hurt or damage the solar cell as long as it isnâ€™t outrageous.

However I wouldnâ€™t want to dump 100% of the excess of a solar cell to ground once the battery is full.

dacflyer · Post by **dacflyer** » Tue Dec 19, 2006 4:42 pm

this controller i have, has no heat sink...its just a potted circuit in a small aluminum case

Chris Smith · Post by **Chris Smith** » Tue Dec 19, 2006 9:28 pm

Watts = heat.

Potted at your wattage is very little dissipation or heat in the real world, while the bikes used to dump up ward of 20 to 40 amps at their peak.

They could almost glow and burn your fingers if they didnt have a cage around them.

Yours is heat dissipated into the potting probably via a small fin.

You can run a thermometer on the potting with a small value short as a load to see. You dont have to push it to its limits.

dacflyer · Post by **dacflyer** » Wed Dec 20, 2006 10:06 am

i finally found the web site for the controller. and indeed it is a shunting device..
i just cannot understand why the'd short out the panels, i didn't like that idea, so i put an #94 bulb in its place like a ballast resistor..so when the regulator shunts, it will not be a dead short on the panels.
it might be just me,, but i do not like shunting devices when it comes to charging batterys etc.. at least this way i know my panels will not go bad any sooner than necessary,and i am happy now..

thanks

Chris Smith · Post by **Chris Smith** » Wed Dec 20, 2006 10:37 am

What can I say, itâ€™s the cheap and easy way to do things.
Its not the best, but as long as you donâ€™t go overboard it works.

If you want to capture more of the power, buck / boost.

dacflyer · Post by **dacflyer** » Thu Dec 21, 2006 7:23 am

i have heard of buck / boost with transformers, but i am not knowing what this is as far as DC related..

i rember seeing a solar calculator somewhere before also,, cannot find it now

also looking for a solar panel layout chart..for different configurations..
when to series or parallel and when to use dioads etc.
right now i have 2 20 watt panels in parallel...but i have many others that i want to impliment later on...and i want to make the best configuration possible.

Chris Smith · Post by **Chris Smith** » Thu Dec 21, 2006 9:36 am

What you need to do is to find out the actual voltage of your panels. I use six smaller units and tie them all into one strand [series] to achieve around 18 volts total. Always higher than my battery voltage but it has a small trickle charge so it cant burn out my battery packs.

I can multiplex the whole thing with a rotary switch to configure it into different voltage and current values but I donâ€™t and I donâ€™t need to.

Most of my charging is self regulated by the out put load VS the resistance from each battery so plugging in a 18 volt plate will draw down to the desired voltage and fill the individual battery with out damage.

Because I donâ€™t leave it indefinitely it is a self regulating system.

One charge or two a year for my many different value rechargeable flash lights and battery packs.

However in a dedicated system where you charge things a lot heavier or daily the voltage and current rating should be close to your specs and you shouldnâ€™t rely on the battery internals resistance to regulate all of your specs.

This is where the buck boost regulator comes in because what it does â€œset by your valuesâ€

MrAl · Post by **MrAl** » Thu Dec 21, 2006 10:16 am

Hi again,

Chris...
While we are on the subject of solar panels, i was thinking of setting
something like that up too with 18v, but i could probably get
away with a 9v to 12v panel(s). What do you think would be the
best price i can get on the web or elsewhere for a 12v panel
that puts out 100ma in full sunlight? Worst case 9v panel to charge
a 6v LA battery.

dacflyer · Post by **dacflyer** » Thu Dec 21, 2006 1:18 pm

MrAl >> seen many panels and individual cells (build your own)
they are decent priced on e-bay...

heres some other links for solar electric
these might help you...

http://www.cetsolar.com/solar.htm
http://www.morningstarcorp.com/
http://www.mrsolar.com/
http://www.sollatek.com/Lumina.htm

hope this helps ya.

rshayes · Post by **rshayes** » Thu Dec 21, 2006 1:49 pm

MrAl,

Harbor Freight Tools (www.harborfreight.com) sells a solar battery charger (44768-2VGA) that may be similar to what you are looking for. Normal price about $20, sometimes on sale at $10.

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