Electrical Question - Fiberglass RV


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Old 08-08-2007, 03:59 PM   #1
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How could I take a 12volt line from my battery and step it down to 4volts?
I have some old 4 LED solar yard lights I want to power.
Thanks
Dave
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Old 08-08-2007, 04:22 PM   #2
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Crap-Shack sells a device that plugs into a cigarette lighter receptacle and it has a sliding switch for the output voltage. They also sell a transformer that U plug into a 110VAC outlet and it has a sliding switch that you adjust to the DC voltage that you require.
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Old 08-08-2007, 04:30 PM   #3
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Quote:
How could I take a 12volt line from my battery and step it down to 4volts?
I have some old 4 LED solar yard lights I want to power.
Thanks
Dave
First off I question the 4 volts number. It's probably 3 volts, 2 nicad rechargable batteries = approximately 3 volts.

The simplest way is to connect all 4 in series. You would have to turn all 4 on or all 4 off by doing that. Other methods are more complicated. If you're going to rely on the light sensors to turn them on and off, all will turn on when the last one is ready to turn on.

If you're going to use them outside as decorative lights around your trailer, I'd just use the internal nicad batteries. You can purchase replacements and a charger if needed.
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Old 08-08-2007, 05:51 PM   #4
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Quote:
First off I question the 4 volts number. It's probably 3 volts, 2 nicad rechargable batteries = approximately 3 volts.

The simplest way is to connect all 4 in series. You would have to turn all 4 on or all 4 off by doing that. Other methods are more complicated. If you're going to rely on the light sensors to turn them on and off, all will turn on when the last one is ready to turn on.

If you're going to use them outside as decorative lights around your trailer, I'd just use the internal nicad batteries. You can purchase replacements and a charger if needed.
Ok.. HEres what I gots...
The lights are like spot lights for trees.
There are no batteries in the lights themselves.
The batteries are mounted on the back of the solar panel.
There are 3 batteries there.
Where the 4 lights plug into the solar panel it says "4volt DC" and shows the plus/minus setup of the plug.
These lights have pretty long cords on them so I could feasibly use them for outside lighting on the trailer. So if I had a way to step the 12volts down to 4 volts I could use the 4 jacks off the solar panel and hook the 4 volts to it and then plug the lights into that. Not using the photo cell at this point although I probably could.
So I am just wondering what device I can hook to the battery and end up with 4 volts. Sounds like the "crap shack" plugit into the lighter thing might work. I could cut off the lighter thing and wire it direct with a switch somewhere.
Dave
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Old 08-08-2007, 08:24 PM   #5
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What is the 1000mA telling me about this adapter? I have 4 of these lights I would like to power off the one DC adapter. Each light has 4 LEDs in it. is 1000mA output good or no?

4.5-Volt Vehicle DC-to-DC Adapter
Model: 273-1857 | Catalog #: 273-1857

This adapter has a 1000mA output. Fuseless, self-resetting technology. Links 12/24VDC car accessory ...

http://www.radioshack.com/product/index.js...p;tab=techSpecs
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Old 08-08-2007, 09:14 PM   #6
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Yup, 3 batteries = 4 to 4.5 Volts.

The Rat Shack inverter should work just fine. The 1000mA means 1000 miliamps or 1 Amp. That's the available current out that inverter. That's more than enough to run 4 LED lights that typically run on rechargable batteries.
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Old 08-09-2007, 12:18 PM   #7
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I wonder if the adapter is not just more than enough, but too much?

I have some really cheap LED flashlights which I have examined. They use three AAA cells (batteries), which is annoying since AA are cheaper and have much higher capacity. In each case, the LEDs are all just wired in parallel with no controlling device - not even a resistor. My guess is that the internal resistance of the AAA battery is so high that it regulates the current flow (if the LEDs allow more current, the internal resistance drops more voltage - the battery output voltage goes down - reducing the LED current).

An adapter which supplies 4.5 volts, and can keep that up at much higher current than required, could allow too much current to a completely uncontrolled LED load... is 1 amp too much for the LEDs? If it is not too much for the set of connected LEDs, then there's no problem; if it is too much, adding a resistor of the right resistance (that would be for someone else to calculate....) might be appropriate.
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Old 08-09-2007, 12:57 PM   #8
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Most LEDs have a wide range of voltage. The 4V LED may go all the way up to 8 or 10 volt.
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Old 08-09-2007, 01:10 PM   #9
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I wonder if the adapter is not just more than enough, but too much?

I have some really cheap LED flashlights which I have examined. They use three AAA cells (batteries), which is annoying since AA are cheaper and have much higher capacity. In each case, the LEDs are all just wired in parallel with no controlling device - not even a resistor. My guess is that the internal resistance of the AAA battery is so high that it regulates the current flow (if the LEDs allow more current, the internal resistance drops more voltage - the battery output voltage goes down - reducing the LED current).

An adapter which supplies 4.5 volts, and can keep that up at much higher current than required, could allow too much current to a completely uncontrolled LED load... is 1 amp too much for the LEDs? If it is not too much for the set of connected LEDs, then there's no problem; if it is too much, adding a resistor of the right resistance (that would be for someone else to calculate....) might be appropriate.
Sorry Brian, but it don't work that way. No need for a resistor. The inverter will supply only the amount of current demanded by what ever is attached to it. Since his LED lights are already designed for a 4 to 4.5 volt supply therefore any 4 to 4.5 volt supply will work as long as it can supply enough current. The same holds true even for your LED flashlight, 3 batteries (AA or AAA or C or, etc.) will produce 4 to 4.5 volts, depending on the type of batteries and any 4 to 4.5 volt source will work if it can supply enough current.
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Old 08-09-2007, 03:03 PM   #10
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Quote:
How could I take a 12volt line from my battery and step it down to 4volts?
I have some old 4 LED solar yard lights I want to power.
Thanks
Dave
Here is a couple of bad pictures for the heck of it.
4 LEDs on each of 4 lights
The circuit board has nothing on it but the LEDs
Dave
Attached Thumbnails
solar_light_001.jpg   solar_light_002.jpg  

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Old 08-09-2007, 04:13 PM   #11
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Most LEDs have a wide range of voltage. The 4V LED may go all the way up to 8 or 10 volt.
In this case it's NOT a 4 Volt LED. It's 4 LEDs, big difference. If you tried to run them at 8 or 10 volts they'd probably die.
Packaged LEDs can be any voltage because they have a dropping resistor in the package. (Packaged means other components inside the LED) The size of the dropping resistor determines the voltage rating of the package.
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Old 08-09-2007, 04:16 PM   #12
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Here is a couple of bad pictures for the heck of it.
4 LEDs on each of 4 lights
The circuit board has nothing on it but the LEDs
Dave
Since this was designed for 4 to 4.5 Volts it will work with 4 to 4.5 Volts, batteries, power supply, inverter, etc. It dosn't matter what the source is.
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Old 08-09-2007, 04:27 PM   #13
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I have some really cheap LED flashlights which I have examined. They use three AAA cells (batteries), which is annoying since AA are cheaper and have much higher capacity.
Slightly off-topic, but I have several LED flashlights that use AA (I try to pick all my battery stuf to use AAs, not only so I can swap batteries around if needed, but because the batteries from GPS, camera, etc., will still run a long time in the flashlights). One kind takes 4 AA cells and the other only uses 1 AA.

BTW, there are now replacement bulbs for the AA MagLites that are LED.

According to Wikipedia, LEDs can come with built-in resistors, which certainly would have to match the voltage of their intended use.

Here's an LED with a 'typical voltage of 2 and a max of 12.0', which means to me that it takes 2V to light it and 12+V would burn it out (would need to be protected in an RV/Automotive use because voltages exceed that.
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Old 08-09-2007, 06:17 PM   #14
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Pete, voltage of 2 and a max of 12.0' tells me that it will work OK at 12 Volts.

I think he should connect one of his LEDs to 12 Volt to see what happens. If it works he's home free and if it burns out he has something to recycle.

Note: Because it is a diode, it is polarity sensitive meaning it will work when connected to the correct + and - terminal and will not work if connected backwards.
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