Tying two ac-dc adapters together

Discussion in 'The Projects Forum' started by anbudmor, Mar 12, 2016.

  1. anbudmor

    Thread Starter New Member

    Mar 12, 2016
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    I have a strimmer in which the lead-acid batteries have worn out. It is a 24v tool. I also have a box of ac-dc adapters from all sorts of stuff. A 6v adapter has had the connection part removed. Can I take it and an 18v adapter and put the wires together and tie them into the strimmer?

    I have already (under)powered the machine with the 6v adapter.

    As I want to get a total of 24V, I should be connecting them in series, but this just seems like an odd thing to do.

    Any suggestions?
     
  2. Colin55

    Member

    Aug 27, 2015
    191
    19
    Connect them in series one way and the motor will be weak. Connect them in series the other way and the motor will roar.
     
  3. wayneh

    Expert

    Sep 9, 2010
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    If they are old fashioned wall warts (large heavy transformers), then yes. The secondary, low voltage sides of these are isolated from the primary side, so you can stack them together as if they were batteries. But, be sure both are rated for the current required by the load. Both should be either DC or AC. Don't mix.

    What's a strimmer?

    Modern adapters might be ok to put in series also but I'd like to hear confirmation of that.
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    Take the two adapters you are planning to use and measure the voltage between all possible pairs of output leads with a DC voltmeter. You should get 0V, or nearly so, except when measuring between the pairs belonging to single adaptor. If you see voltage between any other pairs, it means that they aren't really floating.
     
  5. anbudmor

    Thread Starter New Member

    Mar 12, 2016
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  6. wayneh

    Expert

    Sep 9, 2010
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    I suspected it was short for "string trimmer", but I think you have divulged your location by using the term "strimmer". Doesn't exist on this side of the pond.
     
  7. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,030
    1,622
    The fatal flaw that is apparently being overlooked her is relevant power capacities.

    Unless your power packs are the size of automotive battery chargers the odds are they won't do much in terms of powering your strimmer motor being it's a 24 volt unit thus more than likely needs 200 - 400+ watts to run and your wall warts maybe put out 10 - 20 watts combined.
     
  8. WBahn

    Moderator

    Mar 31, 2012
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    I must have been thinking of another recent thread where someone wanted to do something similar and had included the current requirements in the first post. You are absolutely correct.

    @anbudmor : Look at the labels on your strimmer and see if you can find current or power requirements listed.
     
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