# Step-Up Voltage??

Discussion in 'The Projects Forum' started by goldeneye123454321, Oct 1, 2008.

1. ### goldeneye123454321 Thread Starter Member

Oct 1, 2008
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Hey, iv been messing around with circuits for a while, but im still a noob to the things one should know. But anyways, i need a circuit, relatively small one, to boots a 5.1 ~ 5.2 VDC up to 12 ~ 13 VDC. I need it because i am building a circuit that powers 2, 12VDC fans. I would like to make it so that it has a pot to contol the fans power, a bar graph LED read out to show how much power is being produced, and swich to choose fan 1, or fan 2, or both. Also there will be 3 LED light that correspond to one fan. The input Voltage will be from a cell phone charger @ 5 VDC. Any help or advice would be GREATLY appreciated!!!

2. ### scubasteve_911 Senior Member

Dec 27, 2007
1,202
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You need what is called a boost converter to bring the 5V up to 12V. You need to ensure that the 5V source has sufficient power to drive your fans. So, the product of the 5V with current must exceed the product of the 12V X current rating of fan. You should also consider the inefficiency of the boost regulator.

Then, you can rig up a cheap LM3914 circuit to do the bargraph display. This is if you can find one, I am not sure of a suitable replacement.

I'm not really sure how to power the fans without knowing more. Are these computer fans?

Steve

3. ### iONic AAC Fanatic!

Nov 16, 2007
1,422
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Based on the Cell phone chargers I have, Their output max is about 1A at 5V.
So after boosting to 12V you will probably have less, far less. If the two fans are computer cooling fans you may need a minimum of 350mA each, most likely more, depends on fan and size of fan. Best bet might be to start by powering the fans with 12V and measure the current they take to run, double it, and whatever that totals you will need current from your boots IC of at least that.

It would be helpful to know the current draw from these fans if you can manage to obtain this. Sometimes they will print this info on the fan label, but often they do not.

4. ### SgtWookie Expert

Jul 17, 2007
22,183
1,728
The best you can hope for in a boost circuit is around 90% efficiency.

If you're going from 5v to 12v, that's a sizeable jump.

Rough calculation:
350mA @ 12v from a 5v supply bumped to 12v will require about 0.94A, or nearly 1A. This is assuming a 90% efficient DC-DC converter, which is assuming a lot. Your mileage will vary considerably. If you are trying to power this thing from a USB port, stop now.

5. ### iONic AAC Fanatic!

Nov 16, 2007
1,422
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I think unless the 5V cell phone charger is at lease 2A, and I doubt it is, then I think the best bet is to get a 12V adapter rated about 1A.

6. ### iONic AAC Fanatic!

Nov 16, 2007
1,422
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I think unless the 5V cell phone charger is at lease 2A, and I doubt it is, then I think the best bet is to get a 12V adapter rated about 1A.

As far as the LED circuit, if you can't find an LM3914 IC you can accomplish a similar effect using a variation of the circuit located here:
http://www.circuitdb.com/circuits/id/155

7. ### goldeneye123454321 Thread Starter Member

Oct 1, 2008
19
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hey, sorry i did not give you more info. the fans are micro fans from radio shack. if its not posible or sencible to run two, i will run one, the newer, more efficient and powerfull one. i beleave the charger gives one amp, @ 5.2 volts. the reason im not using the 12v converter i already have is because i want to go smaller, relitivly small. i would like to have some diagram on how to do this. ill upload a photo of the metal plate im using. it used to be a battery charger for a rc battery pack, but it broke. so im using the face plate. all the leds and switches but one are already built in. i dont know how to find the amp rating or calculate it, as well as finding the watage. well i hope i helped a little. thanks

8. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
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So you actually do want a power meter.

You'll need to measure the current by measuring the voltage across a current sensing resistor. This is a small value precision resistor which allows you to use Ohm's Law to determine current.

Then, you can either feed voltage and current signals into an old fasioned \$14 to \$25 analog voltage multiplier chip, or you can sample the two signals with the ADC inputs of a microprocessor and drive the LED bar based on software calculation.

9. ### iONic AAC Fanatic!

Nov 16, 2007
1,422
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Last edited: Oct 2, 2008
10. ### goldeneye123454321 Thread Starter Member

Oct 1, 2008
19
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its 1.5 inches by 1.5 inches i believe. how do i find the amps, when it only gives me wats and voltage?

Dec 27, 2007
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12. ### goldeneye123454321 Thread Starter Member

Oct 1, 2008
19
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well, the reason im doing this is because i look every where for a small 12v converter. i already have one, but its big. the reason i would like to run it of the cell phone charger is because its small. again, how do i find amps, watage, potential and current?

Dec 27, 2007
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14. ### goldeneye123454321 Thread Starter Member

Oct 1, 2008
19
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my current 3-12v adapter is around 3x5x2inches. and is gets hot. i dont know if this is normal. could it be that im overloading the adapter?

15. ### goldeneye123454321 Thread Starter Member

Oct 1, 2008
19
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thats what the face plate looks like. every things is already there. the leds, switches. and thats what the adapter needs to fit in.

16. ### scubasteve_911 Senior Member

Dec 27, 2007
1,202
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That's actually a full out battery charger. It isn't just a power supply, there is quite a bit of circuitry in there already that checks the conditions of the batteries, etc. If you start taking it apart and messing around, you may ruin it or hurt yourself from the AC.

Steve

17. ### iONic AAC Fanatic!

Nov 16, 2007
1,422
68
I have a Switching 12v power supply for a portable hard drive rated at 2A that if removed from it's housing would measure about 3x2x1 inches. You can't get much smaller than that!
The adapter is made by CD (Coming Data) Model CP1220. Don't know where you could find one but it might just fit inside you existing 3-12V power supply.

18. ### goldeneye123454321 Thread Starter Member

Oct 1, 2008
19
0
ok, this is all point less. lets start some where more sencible.

Im going to make a whole new case. that will have one input @ 12-24VDC and 2-4 outputs. the output will be controld by 1 pot for 2 outputs. so up to 2 pots. i would also like a red led to come on when the thing is pluged in and is receving power from the adapter, and a green led for each output. the green led will be on when some things is making a load on that plug, and the plug is geting power from the pot. after we get that figured out, i would like to make a yellow led go off if one of the plugs is overloaded. and after that, a built in safty shut of if there is a unsafe suge in power to the input, that way, the components are not damaged. the output will go to fans that can plug in and out. that way there is no pernament conection, and i can add, or take away fans if nessesary. i hope this helps some.