# Is it possible to break down 12VDC to a 1.5Vdc?



## Chosen

just like the name says i need to break the 12VDC coming from the ps to a 1.5V which is what the temp montior i bought from wal-mart is. It takes AAA batteries but i want to strip it down and mount it in one of my 5.25 bays anyone know what resistors to use or anything else? Thanks


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## Chosen

eh any voltage guru's know if this indeed possible it would be a sick mod, and most likely help others.


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## Jacks Smirking Revenge

You COULD fasion a potential divider to knock the voltage down from 12 to 1.5 volts.

essentially by placing 8 equal resistors in sires, then "tapping off" the voltage after 7 of them, you get 1/8 the voltage.
(see link) => http://www.electronics2000.co.uk/dat...smr/potdiv.htm
So R1 in the diagram would have to be 7times the resistance of R2.

Also, you'd need to reduce the current to the desired level be placing another large resistor in parralel with your potential divider.

I *think* I've got the right idea but I wouldn't reccomend it myself.


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## Chosen

well ill try that on a work station psu and this temp monitors 7$ but hey all in the name of science eh? thx for link and actually responding to my thread. But that page is pretty difficult to understand for a novice like me? Can anyone summarise for a noob?


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## Renegade5399

Radio Shack also sells a step down Transformer. Tiny lil guy, can only handle up to 1 amp (on the 1.5V output side), but it takes 12VDC and steps it down to 1.5VDC and it's tiny. I can't get to their site from here at work as they block it.








But there's another option for ya!


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## Chosen

Wow never even thought of that alternative lol and to think i was going to fabricate an elabrate mess of resitors and such thanks! ill look for one on monday!


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## Lucid

so..... how did it go ?


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## Chosen

My local radio shack dosent have any im going to have to travel atleast 50Miles out of town to go to another radio shack


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## RocKerClocKer

Quote:


Originally Posted by *Renegade5399*
Radio Shack also sells a step down Transformer. Tiny lil guy, can only handle up to 1 amp (on the 1.5V output side), but it takes 12VDC and steps it down to 1.5VDC and it's tiny. I can't get to their site from here at work as they block it.








But there's another option for ya!









A transformer will not work!

you can go to any radio shack in the world and not find it, because there is no such thing as a D.C. transformer.

A transformer can only work in an AC circuit, not DC.

There is such a thing as a DC Current Transformer, but that is a horse of a different color.

I know you are thinking 'well I have a wall transformer that supplies DC voltage, isn't that a transformer?'

actually, yes and no

It is a power supply, that is to say a regulated DC source.

In order to 'supply' 1.5 volts to a load, (in this case the temp monitor) you will need a voltage regulator.

simply constructing a voltage divider circuit may work given that the device has been designed to operate over a range of voltages, because the battery voltage decreases as it discharges.

when you add a load to any circuit it changes the circuit dynamics thus changing the output.

I would suggest going to www.newark.com and get a Linear Technology LT3021ES8-1.2/1.5/1.8 which has a Vin (input voltage of 10 to 1.4v) and use the 5VDC power supply rail instead. The output is selectable 1.2 1.5 or 1.8 VDC

You can construct a small board with the appropriate circuitry and viola.

Hope this helps


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## Renegade5399

Go to:

http://www.alltronics.com/power_sources.htm

Scroll down and look for:

OTOMEK Model AT-100
Regulated DC-DC Automotive Adapter

This is what I use for testing 1.5V items. I have the cig lighter in my PC, so I got this as it fit my needs.

Also, if you have an understanding of basic electrnics, you can do this:

An LM317 regulator should do you just fine.
Place a 240 ohm resistor from the Vout terminal to the Adj. terminal and a 51
ohm resistor to from the Adj. terminal to the Battery neg. (12V- or Gnd). This
will give you 1.5 Volts between Vout and 12V- for any input voltage (Vin to
12V-) from about 4 to 40 Volts. -From Credit

It's easy to put together and there's plenty of 12 volts in a PC to tap off from!


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## tgtruman

The stepdown is easy, that's not the problem... in order to charge AA batteries you need to drop your Amp. to around 150mA


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