Story:
I have a solar powered address sign that is more in the shade than it is in the light. It uses two rechargeable AA batteries. I would like to run power directly to it through the brick and up into my attic. It uses six white LEDs. Of course I would cut the leads to the solar panel and remove the batteries.
I have a spare 8v 10A powered transformer that was used for a second door bell. (Don't ask me why the previous owners had separate door bells and two transformers - I replaced that system with one 16v transformer, etc)
I was going to put a 3volt 300mA voltage regulator and components inside a box and use some 18ga thermostat wire to hook it up. I was going to research this further but...
I have another option.
I have unused outlets in the attic right above that area. I found an old cell phone charger (wall wart) with an output of 4VDC / 200mA.
I believe the second option is easier, quicker, and more cost effective but I do not have the knowledge to pull this off -- yet.
I have no specs on the LEDs. There are six LEDs but only three wires coming from that section (glued - no access) There's a circuit board near the batteries where the three LED wires go to. All three wires appear to be voltage/current regulated. So I think the 200mA output should be fine as I hope the board will regulate it. Even so most white LEDs appear to use 25mA or greater it seems. So 25mA x 6 = 150mA on the low end.
Anyway....
MAIN QUESTION:
How do I easily limit the current to 3 volts from the 4 volt sealed transformer? The wire will be cut and soldered/spliced to 18ga wire about 15-25 feet long.
I found this calculator on line [credit given]:
I have 10 Ohm 1/2 watt resistors. Is this enough? According to another calculator 200mA @ 4v gives me 20 Ohms resistance with 0.8 watts. I take it that if resistors will work for my situation then I will need at least one watt sized resistors.
The only other thing that I need to wrap my head around is the +/_ in that picture.
Is the top line (Vin) the positive side from the transformer and the bottom (Vin) line the return/negative line with a resistor going in between the two?? I like to occasionally release the white smoke but I usually do not 'cross the streams' ha-ha. But this is DC and low voltage so I am not sure.
This is what I picture -
_+__10ohm/1watt__|______________+ to LED PCB
/ |
Transformer< |30ohm/1watt
4V/.2A \_ -_______________|______________- to LED PCB
Thank you for any help. The more that I learn the more that I second guess the simple stuff. If I am totally off base with this then please steer me in the right direction. I do try to research before posting. Sorry for the length but it should be complete.
My 'art' did not come out right. See below please.
I have a solar powered address sign that is more in the shade than it is in the light. It uses two rechargeable AA batteries. I would like to run power directly to it through the brick and up into my attic. It uses six white LEDs. Of course I would cut the leads to the solar panel and remove the batteries.
I have a spare 8v 10A powered transformer that was used for a second door bell. (Don't ask me why the previous owners had separate door bells and two transformers - I replaced that system with one 16v transformer, etc)
I was going to put a 3volt 300mA voltage regulator and components inside a box and use some 18ga thermostat wire to hook it up. I was going to research this further but...
I have another option.
I have unused outlets in the attic right above that area. I found an old cell phone charger (wall wart) with an output of 4VDC / 200mA.
I believe the second option is easier, quicker, and more cost effective but I do not have the knowledge to pull this off -- yet.
I have no specs on the LEDs. There are six LEDs but only three wires coming from that section (glued - no access) There's a circuit board near the batteries where the three LED wires go to. All three wires appear to be voltage/current regulated. So I think the 200mA output should be fine as I hope the board will regulate it. Even so most white LEDs appear to use 25mA or greater it seems. So 25mA x 6 = 150mA on the low end.
Anyway....
MAIN QUESTION:
How do I easily limit the current to 3 volts from the 4 volt sealed transformer? The wire will be cut and soldered/spliced to 18ga wire about 15-25 feet long.
I found this calculator on line [credit given]:
I have 10 Ohm 1/2 watt resistors. Is this enough? According to another calculator 200mA @ 4v gives me 20 Ohms resistance with 0.8 watts. I take it that if resistors will work for my situation then I will need at least one watt sized resistors.
The only other thing that I need to wrap my head around is the +/_ in that picture.
Is the top line (Vin) the positive side from the transformer and the bottom (Vin) line the return/negative line with a resistor going in between the two?? I like to occasionally release the white smoke but I usually do not 'cross the streams' ha-ha. But this is DC and low voltage so I am not sure.
This is what I picture -
_+__10ohm/1watt__|______________+ to LED PCB
/ |
Transformer< |30ohm/1watt
4V/.2A \_ -_______________|______________- to LED PCB
Thank you for any help. The more that I learn the more that I second guess the simple stuff. If I am totally off base with this then please steer me in the right direction. I do try to research before posting. Sorry for the length but it should be complete.
My 'art' did not come out right. See below please.
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