Solar-recharging garden lights - rewire to mains?

[JakeD]

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

 

[Nobody]

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.

That seems likely.

Do I still need to supply 4.5 volts, or will I need 4 x 4.5 volts?

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).

I have a box full of wall warts; I'm hoping one of
them will provide a suitable voltage and ampage.

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.

 

[JakeD]

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.

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

 

[ehsjr]

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

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

 

[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

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

 

[Jerry G.]

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.
======

 

[petrus bitbyter]

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

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

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

 

[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.

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

 

[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