12v to 9v circuit

[snake21]

hello guys,i have 2x9v batteries 280mah,the rectangular, one which i want to charge using my 12v battery which gets charged by my wind turbine to 13.8 volts.

can someone help me to get the schematic?

thanks

[OperaHouse]

Use a 7805 regulator leave common pin not connected.
From the output connect a 5.1K  to the common pin
from common pin to supply neg connect a 4300 ohm resistor.
See application notes for further explanation.

[wooferhound]

You could get a
Basic and Simple Variable Voltage Supply Kit for a few dollars from Ghurd
It's part-way down on this page
http://www.ghurd.info/dc_buy.html

[snake21]

hello,thanks for the reply.ghurd's  Variable Voltage Supply Kit has input voltage 18 to 30 v,i nee an input of minimum 12v and an output voltage is good but i think 1.5 amps to charge a 9v battery is too much.

any idea please?

thanks

[wpowokal]

Contact Ghurd and he will solve your problem

[Nothing40]

It looks like Ghurd's kit uses a 7809 (or similar) regulator. It should work with an input from about 11V,to 30V or so. It should be fine from a ~13.8V source.

One caveat with these (linear) regulators is that they require a couple of volts 'overhead' on the input. So,for this example it's 9V out,so it will need at least 11-11.5V input to maintain regulation,no problem here.
There are some "low dropout" type regulators that only need about 0.7V 'overhead' on the input,but that's not an issue here.

[ghurd]

My kit uses a 1.5A 7809.  BTW- it states that fact.
I said it requires a higher input, 18V, because without a higher input it would not reach an output voltage high enough to calibrate a controller to where most people want them set.

The main problem with charging a tiny battery like that (0.280 ah) will be limiting the charging current.  Do not want to just send 1.5A into it.
A couple small power resistors can fix that problem.

Another problem is you do NOT have a '9V battery'.
What is the "real" voltage of the "9V" battery?  It depends.  But it is not 9.0V.
There are several versions, and several sub-versions.  Mainly and basically, 7.2V, 8.4V, and 9.6V nominal.  With a simple charging system, they would be charged to about 8.4V, 9.8V, and 11.2V.

Of those, most common is the 7.2V.  It has 6 nicd or nimh cells.
Considering it would want charged to no more than 8.4V, a simple system using a 7809 will not work because they can not be adjusted below 9.0V.
You could use the schematic for my kit, but use a 7806 instead of a 7809.

Still need to regulate the max charging current. 
I would try to limit it to 10% (28ma), and consider it a 12~16 hour charger.

Pre-coffee guestimate: My circuit, with a 7806 instead of 7809, and a 180 ohm 1/4W resistor in the power supply wire (between the 13.8V and circuit positive input).

There are many ways to skin a cat.
G-

[mab]

I would suggest the simple solution - if you're looking for a 16hr re-charge then you want max 28mA. I would just use a resistor. If you're slow charging nicd's you don't need to be very precise - you only need careful current control and timing for rapid charging.

if your source is max 13.8v and your nicd is a nominal 7.2v, then a resistor R=(13.8-7.2)/28 = 235 ohms.

I would go for a 220 Ohm series resistor (1/4 watt would suffice). The charge I would go slightly over 10% if the 12v source is at 13.8, but not significantly.

If the 12v battery was down at 12.0v (very low), you would only get 22mA so you might want to increase the charge time accordingly.

mab

[ghurd]

I would suggest the simple solution - ...

mab

I considered it.
The Pink Bunny people formerly had tech data about it online.
IIRC, they considered a NON voltage-dependant, unregulated charging current past 5% C, as very un-good.
There was more.
They must have decided somthing was wrong, and removed all that data.

My brain paraphrased the data as "keep it about 10% C max charge current, and limit the voltage to 1.4V / cell".
Some of my abused nicds are >10 years old.
It works for me.
G-

Edit- "a NON voltage-dependant"
Meaning you could send 5% to the battery 24/7 without serious harm.
IIRC, they recommended less if that was the intentional case.

[Bruce S]

Snake21;
Just curious , which one of the voltages did you end up having?
Are the NiCDs or NiMhs? most ALL new one Are NiMh and are they old or new?
the 280mAh tells me they may be fairly new since the older ones were usually is the 150mAh size.
Cheers;
Bruce S

[Simen]

Strangely; nobody have mentioned the LM317? It's much like the 78xx series, but variable in nature, and very easy to set up as an constant current regulator. Add an suitable zener to limit the charge voltage, and you're safe.

Edit:
A diagram from the lm317 spec.:

[ghurd]

Simen,
Snake is in "a fairly remote location" when related to obtaining parts.
(he is a long way East of a tiny dot on the map of the ocean, and his island is a lot smaller than a dot on that dot that shows)

Myself, I was mostly thinking about very common parts that could be salvaged.
Or parts he may already have.
Or parts he could get as a package from somewhere cheap, like Woof was thinking.

Personally, I like to taper charge nimh or nicds when RE is the power source.  Limit the voltage and the amps.
There are fancier methods which are supposed to work better.
I still have and use AA nicds that must be near 15 years old by now.  The capacity is considerably lower but they still work.
I do not fix it if it ain't broke.  And it still works for me.   
G-

[Simen]

Well, the lm317 are not that uncommon, and if not available within his salvage horde, an 200mA lm317lz have a pricetag of 50cents...
It would just be the matter to try to get a package to that dot on a dot in the ocean.

Talking about salvage; the 7805 would be even more common than the 7809, and could easily be used in your circuit instead of the 7809? Operahouse's idea would also work nicely...

For simplicity, the one resistor mentioned by Mab would be it. If aiming at 10% charge current, careful monitoring would be required. But Snake said he had 2 batteries; if he only use one at a time while the other are charging, he could aim for 3% charge current, and be safe. (Though, charging time would be days...)