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Is it possible to combine two AC power circuits to double current? (limited household current proble

Discussion in 'Electronic Basics' started by [email protected], Feb 17, 2005.

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  1. Guest

    I'm in a situation where I need around 20-24 amps continous of 110V
    (for a milling electric motor), but my strongest circuit in my breaker
    box is 20 amps. I have 3 15 amps and 2 20 amps. Is it possible to
    have the AC circuits in parallel somehow to be able to safely
    (relativly) use the combined currents? What hardware would I need? Am
    I concerned with the ac cycles being off in some way?

    Any other ideas?
  2. I am addressing only the technical aspects of your question.
    Nothing I say should be taken as a recommendation that
    you do this rather than getting your electrical service changed
    to suit your needs in a conventional, code-conformant manner.

    It would be possible to design something that would do what
    you wish safely. It would have to have relays (or equivalent)
    to be sure that unplugged male plugs did not have exposed
    line voltage on them, either before starting paralelled operation
    or in the event a plug was pulled out during operation. Such a
    system would not be simple to build and would likely cost more
    than having a electrician come in and do it conventionally. The
    relay controller would likely require some electronics. And
    the available power would not necessarily be a simple sum of
    what is available from each socket unless even more cost and
    complexity was added to the custom gizmo. It is likely that the
    currents taken would not be well related to the breaker trip
    points due to differing wire run lengths, socket resistance, and
    breaker resistance.
    I have not seen such a device for sale. I suspect this is because
    of the cost issue I mention above.
    You'd better be. With no offense intended, I must say that
    question leads me to believe you should not be devising such
    a device and calling an electrician is your best bet.
    A generator? It would have other uses and probably be
    cheaper if your time is worth much.
  3. Guest

    You'd better be. With no offense intended, I must say that
    question leads me to believe you should not be devising such
    a device and calling an electrician is your best bet. <

    True, I have no practical knowledge of power AC systems, that is why I
    am asking the question. I am sorry if that leads you to believe I have
    no business this matter.

    Upgrading the circuits is not what I am asking about, I know about this
    option. Circumstances make this approach better for me. Also this is
    indoors, so a generator would not work either.

    Despite all you posted, I still don't have an answer... from what I
    know from books and school, I don't know what kind of circuits and
    devices you would need to (assuming you could) combine two ac sources
    to form one source with (minus losses) twice the power. So any help
    on this would be great.
  4. First, have you tried running it on a 20? Its not a good idea to put two
    20s in parallel but it'll work, its all the same phase, frequency, and
    voltage.. If your wiring will handle the current put in a 25 or 30 amp
    breaker and feed your mill by itself off that circuit.
  5. Perhaps you would take less offense if I expand on that.
    Given your unfamiliarity with the electrical issues, you are
    extremely unlikely to be able to design a safe device for
    doing what you want. If you go ahead anyway, you or
    somebody you care about could be electrocuted. If you
    have to hire that expertise, the whole design and build job
    will cost more than that electrician.
    If safety is not an issue, just wire some plugs together,
    taking care to wire hot to hot, neutral to neutral, and
    be sure not to plug them into any oppositely phased
    outlets. This is a very dangerous solution, which I
    would not use myself if I had your problem.
    The generator would not have to be indoors.
    You need relays that are well enough protected from
    over-current to not get welded closed and a control circuit
    to operate the relays according to the criteria that I stated
    in my earlier post. If that is not an answer, then you appear
    to be looking for a complete design. Most likely, to get one
    you will have to pay money, and more than you would pay
    to take the solution you already know of.

    Good luck getting a more satisfactory answer.
  6. In many breaker panels, alternate breakers are fed from power from
    opposite sides of the 220 volt input. Paralleling two breakers that
    are not fed from the same side of the line will result in possible
    destruction of one of both breakers. You also do not get proportional
    current sharing when two breakers are paralleled, so you do not get
    the combined ratings as the effective trip point. Besides, any wiring
    that is presently protected by either breaker is no longer protected
    for the same trip current by the parallel combination.

    I think you need to try to find a 30 amp breaker to replace one of the
    ones now in the panel (preferable a spare) and wire your load to that,
    following the electrical code for wiring size and practice. If your
    place burns down after this, you had better hope that your insurance
    company does not find out you have been doing such wiring, or they
    will probably disallow your claim, regardless of whether your work was
    involved in the fire. All that assumes you have not electrocuted
    yourself before that.
  7. Get a big DC to AC converter. ($189 here:

    Power it off of a 12V auto battery, which you keep charged with a
    trickle charger off of the AC you have. If you need more time, add

    It's not going to power the milling motor all day, but it'll work for a
    while, and recharge overnight.

    Robert Monsen

    "Your Highness, I have no need of this hypothesis."
    - Pierre Laplace (1749-1827), to Napoleon,
    on why his works on celestial mechanics make no mention of God.
  8. Chris

    Chris Guest

    Hi. Many electrical motors are made to be wired for either 120VAC or
    240VAC service. If you're not interested in hiring someone to upgrade
    your service, it may be easier to look at the motor and see if you can
    rewire it. If the motor requires 20-24A @ 120VAC, it will only require
    10-12A @ 240VAC if it is a motor of that type. Then, if you have
    240VAC @ 15A or 20A service available in your work area, you can just
    plug it in.

    I had to do this once for a motor I needed to run in a basement. They
    happened to have a 240VAC outlet available at their electric dryer, so
    there was no problem.

    DO NOT put AC circuits in parallel. It's not a good idea, even if you
    don't accidentally short phases.

    As has been mentioned in several other responses, if you don't know
    what you're doing with line voltage, let someone else who does give you
    a hand.

    Good luck
  9. Guest

    After all the responses I will give in to sanity and NOT try to
    parallel the AC circuit (not that I would have tried it before knowing
    it was safe)

    As for the the battery idea, that seems like something I may try. The
    url your pointing to I think is wrong though, (I will need an inverter,
    not a ac-dv converter)

    The only thing that concerns me is the safety of using car batteries
    inside (they need a well ventilated area I think, and there is always
    some danger of rupture) since I live in an apartment. And also finding
    batteries that can stand that much abuse.

    So far I what I find is this that may do the trick:
    Qustions is now, what the heck is modified sine wave? (Just how
    modified is it?) A true sine out is probably too much to ask for at
    this power I guess.
  10. All in all, taking into account the warnings from others (and me !!), it
    would very likely be the most economical to have another breaker installed,
    most certainly the safest. The other option of the dual volt motor could be
    your saving if you have it.
  11. Rich Grise

    Rich Grise Guest

    Adding a battery and inverter is a really stupid idea.

    Check the wire from the box to where the motor is. If it's #12 or #14,
    replace it with a #10, and probalby replace the white neutral with a #10,
    and replace the breaker with a 30A unit, and you're done. You can rent
    a fish tape for a few bucks and pulling new wires isn't hard at all,
    although could be tedious if it's a long run or has splices in the middle
    somewhere. Do a good job, because if you want to sell the house, it will
    have to pass inspection.

    And, just for the sake of reduncancy, adding a battery and inverter is
    a really stupid idea. And even if you did want to use a battery and
    inverter for something else, don't use a car battery. Use a deep-cycle
    marine or RV battery.

    Have Fun!
  12. Are the apostrophes in the wrong place?
    Lets tear up some walls and pull wire, without any knowledge of proper
    codes. It's like your recent suggestion to replace the fuse box to add
    grounding. "Just yank it out! remember where the wires go!" Who needs
    electricians? (Bzzzap!) Perhaps you are a member of the Burridge school
    of electrocution theory: "Nobody ever dies of electrocution, they just
    move into another reality where they didn't actually die, they only came
    Why exactly is it a stupid idea? Is it dangerous? Expensive? What's the
    problem? Educate me. 30A inverters are relatively cheap, as are auto
    batteries. Seems far safer than trying to merge two circuits. Hell, you
    don't even know how often or for how long he is using the thing. If he
    uses it once a month, seems like a waste of money to have his circuits
    upgraded and his wiring replaced.

    Robert Monsen

    "Your Highness, I have no need of this hypothesis."
    - Pierre Laplace (1749-1827), to Napoleon,
    on why his works on celestial mechanics make no mention of God.
  13. Rich Grise

    Rich Grise Guest

    It's an unnecessary expenditure, and comes with all the pains in the
    ass concomitant with battery power.
    Merging two circuits is also stupid. And saying "use a car battery", I'm
    sorry to report, is also not a good idea, even if he _was_ foolish enough
    to want to use a battery and inverter for a mill motor.
    You didn't read the whole post. I said, if it's #12 or thinner, replace
    it with #10. #12 would probably hold up, but you want a safety margin.
    The reason for codes is that house fires are very expensive all the way

    Heck, he could just run it the way it is, or get a breaker that's designed
    for a motor load and it'd work fine!

    I _don't_ want him to burn his house down or electrocute himself, contrary
    to what you seem to have surmised here.

    And I _have_ replaced a circuit breaker panel - the whole panel, in an
    industrial setting, i.e., 240V 3-phase. And, if, as he mentioned, he has
    some experience with not getting electrocuted, it's almost trivial as
    far as technical competence is concerned.

    On top of that, he says he wants to install a spa. He'll not only need
    a new panel, but probably have to call the electric company to see if he
    needs to get his service upgraded.

  14. Kitchen Man

    Kitchen Man Guest

    There have been a lot of interesting replies to this question, and I am
    glad to see that you are accepting those that steer you in the direction
    of caution. I've got some questions that, if the answers are right,
    might get you going safely and easily.

    You say you have three 15A and two 20A circuit breakers. That's not a
    lot, what environment are you in? It doesn't sound like a typical
    residence. Are you in a separately wired shop or garage? If so, and if
    you have to rewire, the job could be a lot easier than in a typical

    You've already decided to not try to parallel two circuits. Good. Now,
    if you are confident enough in your ability to not poke around with your
    fingers in places where they might get burned, take the cover off your
    CB panel and look at the wires. In my house, I have a 20-amp breaker
    that is dedicated to the kitchen range. Since I have a gas range, that
    connection doesn't require much power, and is probably why the breaker
    is only a 20, instead of a 40 or 50.

    The wiring, however, is big (three conductor, 8 awg), so if I ever
    installed an electric range, I could put in a bigger breaker, and Bob's
    your uncle. If you have a similarly wired circuit, you could do that -
    replace the breaker *and* the outlet (there are particular plug
    configurations for different voltage and amperage capabilities).

    Failing that, you'll have to rewire one of your circuits. If you are
    talking about a shed or a garage, it might be a really easy job. If
    it's a long run through a house, I'd consider the professional help.
    Finally, if you have 220V capability, find out if you can run your motor
    on 220 and put in a 220V circuit breaker. You could have a pro do that
    last job, too; it shouldn't cost that much.
  15. Beeper

    Beeper Guest

    You can use a 220 volt circuit if your motor is set up for it. By going with
    220 you cut your amps in 1/2. So instead of using 20-24 amps, you'll draw
    10-12 amps.
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