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Using 2 AA batteries, recommendations for a DC to DC voltage booster? — Parallax Forums

Using 2 AA batteries, recommendations for a DC to DC voltage booster?

vanmunchvanmunch Posts: 568
edited 2014-04-01 14:15 in General Discussion
A quick question. Does anyone have any recommendations for a SM or small TH DC to DC voltage booster? I want to increase 3V to above 3.3V but less than or equal to 5V.

I’d like to use just two alkaline AA batteries for a wearable project using a propeller and an XBee. I know that they will both work with just 3V, but I’m worried that it will stop working after the batteries are used for a little bit and their voltage drops. The XBee's data sheet (link to product below) mentions that the range decrease once the voltage is under 3.0.

I haven’t used a booster before so I figured I would ask the collective wisdom of the forums :)

Thanks for your time!

Dave

Xbee data sheet:
http://www.parallax.com/product/32407

Comments

  • User NameUser Name Posts: 1,451
    edited 2014-03-14 08:41
    As an alternative to a boost converter, you could use two NiZn cells. By the time they discharge to 1.6V/cell, it's time to recharge them, anyway.
  • ercoerco Posts: 20,256
    edited 2014-03-14 11:09
    David (my other favorite DD, along with Duane Degn): I've been using these USB 5V boosters on all my little bots recently: http://www.ebay.com/itm/1PC-0-9-5V-To-5V-600mA-USB-Charger-DC-DC-Converter-Step-Up-Module-New-/350799697191?pt=LH_DefaultDomain_0&hash=item51ad4a9527 or
    http://www.ebay.com/itm/2pcs-DC-DC-Converter-Step-Up-Module-1-5V-to-5V-500mA-Power-Module-New-/351000268368

    Cheap & work great. Hunt around and find them for a buck, some have a USB port, some don't. Ratings vary from 500-800 mA. My bots are powered by a single 3.7V Li-Ion, which drives motors & servos directly, but all the electronics & sensors get 5V through the boost converter.
  • vanmunchvanmunch Posts: 568
    edited 2014-03-14 12:51
    Thanks Guys!

    I went ahead and bought 10 of those step ups without the USB.

    erco, I was organizing my robot pictures and found the folder form the 2012 UPE with this picture... :)

    DSCN1970.jpg
    DSCN1970.jpg
    1024 x 768 - 101K
  • ercoerco Posts: 20,256
    edited 2014-03-14 14:55
    As I remember, it was a cold day and this cowpoke was just trying to stay warm by rubbing two robots together... :)

    Since you bought ten DC boosters, maybe you can be the first to answer the question, what happens when you hook up more than 5V to the input? Magic smoke?

    Also, could you use a single rechargeable Li-Ion (18650 or an AA-sized 14500) to power your project? Just over 4V fully charged, nominally 3.7V.
  • LawsonLawson Posts: 870
    edited 2014-03-15 07:45
    erco wrote: »
    maybe you can be the first to answer the question, what happens when you hook up more than 5V to the input? Magic smoke?

    I've now made a few DC-DC boost supplies on my boards, and all the chips that need an external diode (most of the chips) will just shut down if you externally power the output at a higher voltage. (only chips like the MCP1640 with synchronous rectification are likely to give trouble) That said, you still need to keep under the absolute maximum voltage of the chip which can be as low as 6 volts. If you can find the datasheet for the controller chip on that DC booster board, I can give you a more definitive answer.

    Back on topic. If you want to roll your own voltage booster I just built one using the MCP1640. Followed the data-sheet circuit and it worked as expected with no fiddling.

    Marty
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2014-03-15 08:19
    Voltage boosters, voltage regulators, switcing or linear -- all eat up a substantial percentage of the battery's power (at least 20%).

    So if you can just find a battery that fits, everything is best.

    There are the NiZn cells that will indeed offer a higher voltage. I had high hopes for these and ordered 4 with a charger out of Hong Kong about a month ago. Nothing has arrived. I guess I have to see if a charge needs to be removed from my credit card.

    Of course, there are a bunch of nice Lithium cells that are 3.3v. But the easy to buy ones are actualy 3.7v with a minimum near the 3.3 level. Some are even in a package that is a wee bit longer than an AA. I believe it is a 14500.

    If you can find a way to make these work in an unregulated setting, you will be way ahead of the game in terms of total available power.
  • CuriousOneCuriousOne Posts: 931
    edited 2014-03-16 02:52
    If you apply Vin higher than Vout of typical step-up circuit, at output you will have Vin-Vdrop on diode. There will be no smoke at all, if your input voltage does not exceeds maximum allowed for the particular chip.

    These chinese cheapo step-ups are surely cheap, but real life eficiency is quite low, around 60%. Boosting such low voltages is quite tricky, so if you need super-duper efficiency, synchronous rectifiers are your only way to go (TI's TPSxxxx series of chips). I personally use Linear's LT1370 for high powered ones and LT1308 for lower power devices.
  • vanmunchvanmunch Posts: 568
    edited 2014-03-31 19:10
    Lawson wrote: »
    I've now made a few DC-DC boost supplies on my boards, and all the chips that need an external diode (most of the chips) will just shut down if you externally power the output at a higher voltage. (only chips like the MCP1640 with synchronous rectification are likely to give trouble) That said, you still need to keep under the absolute maximum voltage of the chip which can be as low as 6 volts. If you can find the datasheet for the controller chip on that DC booster board, I can give you a more definitive answer.

    Back on topic. If you want to roll your own voltage booster I just built one using the MCP1640. Followed the data-sheet circuit and it worked as expected with no fiddling.

    Marty

    What inductor did you use? I know that it needs to be 4.7μH, but I didn't know how much current I should choose... 1A just to be safe?
  • LawsonLawson Posts: 870
    edited 2014-03-31 21:01
    The datasheet for the MCP1640 has detailed specifications and a few suggestions in a table and in the notes on each example circuit. That said, I used a 587-1671-1-ND off Digikey. It's overkill but the lower series resistance helps boost efficiency a bit. While I was relocating that part number, I found the CVH252009-4R7MCT-ND which is much smaller but should still have enough peak current capability to use with the MCP1640.

    Marty
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2014-03-31 21:22
    'Late to this thread, but ...
    Loopy Byteloose wrote:
    Voltage boosters, voltage regulators, switcing or linear -- all eat up a substantial percentage of the battery's power (at least 20%). So if you can just find a battery that fits, everything is best.

    I'm not so sure about that. If a boost converter lets you suck the last vaporous gasp of energy from a dying battery, all the way down to 0.9V, it seems to me you're better off with that than with a battery that fits but no longer powers the system at 85% of its full-charge voltage.

    -Phil
  • ercoerco Posts: 20,256
    edited 2014-03-31 23:45
    Phil Pilgrim (PhiPi) wrote: »
    'Late to this thread, but ...



    I'm not so sure about that. If a boost converter lets you suck the last vaporous gasp of energy from a dying battery, all the way down to 0.9V, it seems to me you're better off with that than with a battery that fits but no longer powers the system at 85% of its full-charge voltage.

    -Phil

    +1 PhiPi... we've all had digital cameras that don't work with batteries below ~1.3V or thereabouts. The battery manufacturers rate alkaline capacity down to 0.8V (a joke these days). So rather than toss those batteries in the landfill (OK, battery recycling bin), why not strive to get all the power possible out of a cell?
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2014-04-01 00:35
    Well, if you are using rechargible NiMH or ZnNi or Lithium cells, they suffer irreversible damage if you go below their limits.

    The trade off is recharge or no recharge.

    My ZnNi cells arrived and my battery driven electric razor performs much better than it ever did with NiCd or NiMH.

    I suppose you can abuse NiCd like Alkaline cells, but that is about it.
  • Alex.StanfieldAlex.Stanfield Posts: 198
    edited 2014-04-01 14:15
    If you are willing to add another battery or even use a 9V batt then you could use the HT7533. It's cheap, very low quiescent current, outputs a fixed 3.3v and no messing around with step-ups or inductors.

    I'm actually using this with an Xbee based fob (garage opener) which uses 2 CR2032. Does pretty well.

    Alex
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