Charging batteries from solar panels

[Barmybaz]

I wish to charge 4 AA (6 volt) rechargeable batteries from solar panels, but was thinking there has to be some sort of formula or guidelines as to voltages and current for optimum performance,
could just put a diode inline to stop batteries discharging through panels at night?
is there a simple answere, I'm not very good at maths or electronics,


Baz

 

[Nigel Goodwin]

It depends on the spec. of your batteries and your panels (and your intended use) - assuming they are specced so as not to be capable of overcharging, then all you need is a diode to stop then discharging the batteries.

 

[MikeMl]

Are your batteries NiMh or NiCd?

Will they start out every morning almost totally discharged?

 

[Barmybaz]

O/K
lets start from the beginning, ( I have been told about that before) (perhaps I should start a new thread)
I want to deter snails from my beans,
Last year I tried copper strips around box, limited success.
So I thought this year I could try putting a small charge through the strips, just enough to make the pesky blighters go away,
I have various Ni-MH batteries, from 2600 mAh through 1300 mAh to 600mAh,
I also have various solar panels, unknown spec, Perhaps I need new.
I guess there would be NO or VERY LITTLE discharge overnight, so it may be just a case of keeping the batteries topped up,
Would I need a dummy load say a LED, what if a short circuit accurred?
Could I just put a diode in circuit to avoid discharge in the day?


Baz

 

[ericgibbs]

hi Barmy,
Look here
https://www.electro-tech-online.com/posts/1220666/

 

[MikeMl]

What is the leakage current that flows into the copper strips? Sketch a diagram of how the strips are configured. What happens if it rains?

Some solar panels have the reverse-leakage diode built-in; others don't. Do you know how to determine if a panel has one?

 

[Barmybaz]

There is no readable leakage, (According to my meter,) the strips are attached on the side of the box under a lip was hoping this would be enough protection from rain.
perhaps I should be asking what solar panels do I need?


Baz

 

[Barmybaz]

Sorry
started asking one question, and ended up wanting answere from another.
I'm sure you can help me



Baz

 

[MikeMl]

I have a vision of putting my tongue on a battery... (poor slug)

Since there is hardly any leakage during the 24hr period you want to set up the solar charger such that it puts out a current that the NiMh will tolerate about 8 hours a day without drying it out. I think about 0.05C would do that, which is not much current.

I would look for a small panel that has an open circuit voltage output about twice the battery voltage, say 12V for a 6V battery. A simple current-limiting resistor between the panel and the battery would set the trickle charging current.

 

[Mosaic]

He may just need to create a copper & zinc barrier strip so when sluggo bridges it a battery is formed and sluggo loses his appetite.

 

[Barmybaz]

Thanks Mike,
sorry if I got it wrong (again)
didn't want to fry the creatures, (apparently they don't taste the same as escargot )
just wanted them to P--- off to a neighbours garden
Sensible bit,
So I'm looking for a 12v panel, with reverse leakage current protection,
I Think I need to buy a panel,
I guess the charge rate could be much lower than capacity rating of the batteries,
I have a mains charger so they could be fully charged when fitted,
just want to keep them topped up,


Thanks for your time patients and knowledge,


Baz

 

[Mosaic]

Barmy, just go get a solar garden light and tap it for power....job done!

 

[Barmybaz]

thanks Mosaic,
Zinc ! isn't that lead,
"Thinking" if one of the strips was Tinned (perhaps not ! !, lead is banned from solder)
that would improve the system,
so which would be anode and which would be cathod ?



Baz

 

[Mosaic]

Zinc is not lead.

Zinc is found on all galvanized metal for roofing and all iron pipes for potable water. Zinc is used in anti fungal ointments and is found in lozenges for strep throat.
The electro chemical series shows that zinc is negative relative to copper. A zinc copper battery is well known.

Have a look:
https://en.wikipedia.org/wiki/Lemon_battery

When sluggo slides over the zinc copper boundary he becomes the 'lemon' and gets a mild zap from the movement of the electrons.

Volta (who coined the term 'volt') developed man's first documented battery....a copper, zinc, brine battery.

 

[MikeMl]

Like this:

 

[Barmybaz]

just go get a solar garden light and tap it for power....job done

I have solar lights all over garden, (maybe that's what's attracting the snails, they can see what there eating)
not taking the P--- (just have a weird sense of humour)
An idea worth pursuing,


Thank's for the comments on Zinc, often wondered why my tooth adhesive claims to be "Zinc Free"
Why would anybody put zinc in tooth glue? "fungal ointment" explains it,


Baz

 

[Barmybaz]

Brilliant Mike,
Think I got it sorted now,
Maths not too complicated for me,

Thanks again for your time patients and knowledge,


Baz

 

[Flyback]

solar chargers, in bright sunlight try to draw current out of the panel at the "maximum power current " level of the panel...form its datasheet. It tends to be the case that the solar panel voltage is best regulated to 10% BELOW ITS NOMINAL VALUE WHEN ITS GIVING MOST current (woops capitals)......So you can regulate it like that...an input current regulated charger, or in dim conditions, you just have a big cap after the diode (the diode which stops backflow into the panel) and top up the big cap with the panel..when you get enough voltage on the cap you push it through to the battery with a charger.....you can of course use a pfet instead of the diode if you wish...but only in sunny conditions and when you are actually drawing current out of the panel.

 

[MikeMl]

solar chargers, in bright sunlight try to draw current out of the panel at the "maximum power current " level of the panel...form its datasheet. ...

In Baz's application, MPPt is not on the table. His load is battery overnight self-discharge only (and occasionally frying a slug), so the battery is 99% charged the next morning.

 

[audioguru]

Energizer battery manufacturer says that a Ni-Cad battery can be trickle charged continuously at up to 1/10th its capacity rating. They say that a Ni-MH battery must not be trickle charged at more than 1/40th its capacity rating.