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18vdc to 6vdc

Discussion in 'General Electronics Discussion' started by daveelochow, Sep 12, 2009.

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  1. daveelochow

    daveelochow

    2
    0
    Sep 12, 2009
    Hello
    I have a PAPR (powered air personal respirator) that the company has gone belly up. The small fan that pumps the air is 6vdc and i would like to power it with Ryobi 18vdc batteries that we currently use (pun intended). What is the best way (not to waste power) to convert this?
    Second question: Why do all these types of batteries have 3 contacts with 6vdc on 2 of them from the 3rd?
    Thanks,
    Dave
    PROJECT: 1-4-u-2rESpiRE :)
     
  2. neon

    neon

    1,325
    0
    Oct 21, 2006
    safety first you can waste power and add a resistor in series or use a lm117 regulator
     
  3. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    You'll have to define your skill level and the power needed by the pump in order to enable a proper reply.
    In order to conserve power you'll need to use a switch-mode buck converter.
    Maybe you can find a universal car lighter psu adaptor using switchmode technology capable of supplying the neccessary current. It's likely to handle 18V as well as the 14.7V that a car can supply, and maybe the pump can manage with 5V so you can use an USB lighter plug PSU.
    The third contact on the batteries are usually connected to a thermistor inside the battery pack, and is used for terminating the charge when the pack starts to warm up.
     
  4. daveelochow

    daveelochow

    2
    0
    Sep 12, 2009
    To resqueline:
    My skill level is not so proficient in electronics, but great at mechanical and design. this is the motor unit from 3M (no specs)- (3M™ Powerflow™ Replacement Motor Blower Assembly 024-00-02R01 1/Case)
    I found this unit- (Jacar cat. no. aa0218) (can't post links)
    Will this work with efficiency?
    Thanks
    Dave
     
  5. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Ok, so it best for you to use a ready-made dc-dc converter then, and you can make up holders and contacts..
    Manual says the Powerflow originally uses a NiCd battery of 726g which lasts for 8 hours.
    This corresponds with a capacity of 5Ah and 30Wh/kg which seems plausible for NiCd.
    The current draw would be approx. 625mA then. How big is the original pack btw.?
    Jaycar Cat. no. AA0218 or MP3038 would both work, but it's hard to tell if they're switchmode.
    But this one here says it is: http://www.quasarelectronics.com/cva531-12-24v-universal-car-voltage-adaptor.htm
     
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