Solar-recharging garden lights - rewire to mains?

Season's greetings,

I bought three sets of Christmas lights for my garden. Each set consits of 4 tiny bulbs (maybe LED's) that change colour. Each set has a battery box faced with a small solar panel intended to recharge the batteries during daytime. Each battery box contains three Ni-Mh AA cells.

Unfortunately, the small solar panels only recharge the batteries enough to prvide about 30 minutes of lighting. (I live at rather a far-northerly latitude, which may be the problem.)

So, what I would like to do is disconnect the solar-powered battery boxes and connect all 12 lights together, and run the whole lot off my mains supply. Can anyone advise what is the correct voltage and ampage I need to supply to the 12 lights with? I presume the lights are connected in parallel. Do I still need to supply 4.5 volts, or will I need 4 x 4.5 volts? I have a box full of wall warts; I'm hoping one of them will provide a suitable voltage and ampage.

Thank you kindly for any help.

JD

Reply to
JakeD
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That seems likely.

A Ni-MH cell is nominally 1.2V, varying from 1.4V (fully charged, no load) down to 1.0V (discharged), so 4.5V would be a little on the high side.

OTOH, it may be that the LEDs were designed for use with 3x1.5V alkaline batteries, which might explain why you only get 30 minutes out of them (if you uses 1.2V rechargable batteries in something designed for 1.5V batteries, it often stops working when the batteries are still 75% charged; my mother's digital camera behaves this way).

Assuming that you keep them wired in parallel, you would want to mimic the batter voltage (3.6V-4.5V). If you want to run all 3 sets from the same source, it would be safest to wire the sets in parallel also; series connection could be problematic (there's no guarantee that the voltage would be divided equally between the three strings, as the current may vary depending upon which colour LED is lit).

Unless you can find a specification for the current draw or power consumption, you either need to measure it or choose a supply which is bound to be adequate. But some wall-warts are unregulated linear supplies, whose voltage varies with load, resulting in a higher-than-specified voltage when under minimal load.

Reply to
Nobody

Thank you for your help! Since you think the voltage supplied should be the same (3.6V-4.5V), whether it is 4 of the bulbs in parallel or

12 of the bulbs in parallel, the wall-wart idea seems non-viable. Another plan would be to remove two of the battery boxes, and connect all 12 lights in parallel to one of the battery boxes. I would locate that box inside the house with the back unscrewed, so that I can put three freshly-charged Nm-H batteries in it every evening. I can charge these using a mains-fed battery charger. Does this sound OK?

Thanks again,

JD

Reply to
JakeD

3 NiCds produce 3.6V nominal, and 4.29 volts at full charge. The circuit below will produce ~4.1 volts, and can be wired to the battery box in each light sets. You can leave the batteries in or remove them, your choice.

------- 10W ----- | Wall +|---[5R]---in|LM317|out---+------+-------+-------+ | Wart | ----- | | | | | | Adj [220R] [D2] [D3] [D4] | 9V | | | | | | | -|---+ +---------+ [Set1] [Set2] [Set3] ------- | | | | | | [510R] | | | | | | | | | [D1] | | | | | | | | +-----------+----------------+-------+-------+

Each light set takes care of the current and voltage requirements of the lights with its own circuit. The circuit above merely replaces the batteries, or if you keep them, maintains the charge on them. Diodes D2, D3 & D4 solate the batteries so they don't discharge into one another or into the LM317, and D1 increases the output of the LM317 to make up for the voltage drop in the isolating diodes. The 5 ohm, 10 watt resistor is there to limit current if the batteries draw high current during initial charging.

Mount the LM317 on a heat sink. If you do not have a

9V wall wart, you can use one rated at 12 volts by adding 4 diodes in series between the wall wart and the 5 ohm resistor.

Ed

Reply to
ehsjr

Wonderful! Thank you. Yes, I have a bucket full of 9v wall warts, so it looks like it's time to dig the soldering iron out...

JD

Reply to
JakeD

Without going through all the math, if your lamps are the 4.5 Volt type. I have done this one.

Remove the batteries. Solder on to the battery connections, and string out wires to use a common supply. Use wire that shows polarization, so you can know which is the plus and minus side. If you get the polarity wrong, you will probably instantly scrap your lamp unit. They are not protected against this.

The supply will need 120 to 150 ma (milliamps) per unit with proper leaway. You can buy universal supplies that can put out 4.5 Volts at

500 ma. These are not very expensive. a 500 ma supply should be able to safely run 3 of these lamp units. for 9 units, you will need 3 supplies. If you can find a 4.5 Volt / 1.5 Amp, this can easily run 9 units.

Make sure that your supply does not exceed the voltage rating of the lamp units and that the polarity is not reversed, or the LED's will be damaged.

Jerry G. ======

Reply to
Jerry G.

"JakeD" schreef in bericht news: snipped-for-privacy@4ax.com...

There's one drawback: Long thin wires are resistors that can cause considerable voltage loss at the lights. This depends heavily on the length of that wires of course. So when you have a wallwart that can provide enough current at 9V or even 12V, feed that voltage to the lines and place a regulator in every light.

petrus bitbyter

Reply to
petrus bitbyter

Thank you! This looks a lot easier than building a special circuit. I do have a power supply that has variable voltage. I will try and find it tomorrow. I expect one of the voltage settings will suit.

Thanks for the warning about polarity.

JD

Reply to
JakeD

Just for the record - in case it is of any interest, I connected all

12 lights in parallel, and used just one of the solar-panelled battery boxes, which I fitted with three fully charged NiMh AA rechargeable batteries (each 2500 mah). That was three days ago. The lights have been on ever since. I haven't even switched them off at night, and they are showing no signs of dimming yet! And the solar panels aren't even exposed to any light, so the batteries are just runnung on their initial charge. Remarkable...

Happy Christmas, JD

Reply to
JakeD

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