Voltage Doubling on the cheap...

Discussion in 'The Projects Forum' started by DreadNought, Feb 8, 2013.

  1. DreadNought

    Thread Starter New Member

    Jan 31, 2013
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    Here is the situation, I have a 4v 1500mah lithium ion battery that needs a kick in the butt. I intend to power a variable voltage regulator with this battery but I first need to make a tiny & efficient voltage doubler or something along those lines to satisfy the voltage regulators needs, the variable voltage regulator is already made and has an adjustment range from 2v to 8v and with the battery alone won't perform above 4.5v. The problem is that after hours of web searching I can't find anything that will convert my 4 volts input into a min 7 volts, max 9 volts output. Basically I need to double the power output of my battery while keeping it tiny and inexpensive. A little more info, this unit will not be constantly in the on position it will only be on for 3 to 10 seconds at a time and requires a fast (instant) power up, it will be under loads of 1.5ohm to 5ohm depending on my selected voltage output setting on the regulator, & the case and battery are pretty well set in stone as the project is nearly complete aside from the input voltage situation. If anybody can help me with this situation in the form of general know how, schematics &/or a parts list it would be greatly appreciated...
     
  2. tindel

    Active Member

    Sep 16, 2012
    568
    193
    For a 8V supply driving a 1.5ohm load (5.3A) you'll need 42.67W of power. Assuming you produce a 70% efficient converter you'll need 60.95W of power out of your battery or approximately 15.2A out of 4V battery. This will give you approximately 6 minutes of battery life.

    Most IC manufactures produce step-up converters. Linear tech is a good start, but may not be able to produce the powers you're after. This might not be cheap or easy.

    I'd keep a fire extinguisher near by and do initial testing under a vent hood... Li-Ion is nasty stuff. A C/.1 discharge rate is pretty high! I'd be sure to understand the batteries spec sheet very well before attempting this. My guess is even if this works, a discharge rate like that will at least reduce the battery life.

    I'd suggest a different power source, really - have you considered using 2 batteries? It will put you right at your 7 to 9 volts and double your battery life. This will be your fastest and cheapest option, though it may increase your volume and mass.
     
  3. tindel

    Active Member

    Sep 16, 2012
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  4. MrNixie

    New Member

    Feb 8, 2013
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    I have to agree with Tindel's comments. Yes, Voltage doublers exist and do work, but at the voltages you are starting from and the currents you are looking for, you are going to see to significant conversion losses and be placing some pretty heavy demands on your source power.

    I would consider increasing the source voltage (two cells in series?) and so saving on voltage conversion. Look up "18650" Li-ion batteries on eBay for some ideas. Hint! "state of the art" for these batteries is a capacity of about 3000mAhr, so walk away from people advertising 4200mAhr and above - they LIE.

    You could just shell out the 13 bucks for the eBay converter that Tindel has found you, and learn from that! (no bad thing). But I don't think it is up to the job as you've defined it thus far, however.
     
  5. tindel

    Active Member

    Sep 16, 2012
    568
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    Actually - I miscalculated - a second battery will get your storage capacity up to 3Ahr, give you 7-9V, and since your current will still be 5.3A it gets you to a more manageable dissipation of 1.8C. And it will increase your battery life to about 33 minutes - way more than double - more like a factor of 5.

    That's a huge price to pay for a boost converter.
     
  6. GRNDPNDR

    Member

    Mar 1, 2012
    435
    7
    Try a MAX1044

    I found this, but googling turns up a bunch of results for this chip.

    [​IMG]
     
  7. crutschow

    Expert

    Mar 14, 2008
    13,039
    3,243
    If you had googled the chip itself you would have found that it's output is only good for about 10mA. :rolleyes:
     
  8. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    Then you must add a second battery. No circuit on earth can double the power of anything. You can double the voltage but the available power is constant.
     
  9. GRNDPNDR

    Member

    Mar 1, 2012
    435
    7
    *facepalm*

    I just remembered the chip and got excited....didn't bother double checking the specs lol.
     
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