120vDC to 120v AC invertor

Discussion in 'Electrical Engineering' started by Chris, Aug 23, 2005.

  1. Chris

    Chris Guest

    Hi all,
    I have tried searching for a solution to no avail. I have an older Lincoln
    welder that is generating 120vdc to a standard outlet. At the start I
    thought it was AC as power saw would run fine. Not until I tried to hook up
    a cap start compressor did the smoke tell me something was wrong. After
    checking everything I could check, I in fact learned that it was a true
    generator as it was creating 120vdc. How the saws are running I have no
    idea. Unless they are universal motors??????

    Now I come to my question, getting the DC to AC. Actually the term inverter
    might be wrong as I do not need to change voltage. Should I be asking for
    an oscillator? Either way I need to get the DC into a sine wave. Not too
    picky how true it is, I just need it to run motors, more or less, at a home
    construction sight (read no solid state running off of it).

    So is there a simple circuit I can devise, or any off the shelf solutions I
    can use? Keep in mind that the unit is rated at 15amps = 1800 watts (BTW no
    breaker or fuse on it at all, which I will correct). 1800 watt new
    generators are about $400 or less, so keeping it under that cost would be
    nice.


    Any pointers, help, flames, appreciated.

    Thanks,
    Chris
    Chris, Aug 23, 2005
    #1
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  2. Chris

    Chris Guest

    Sue,
    Yes I was thinking about a UPS. I have an older one lying around. Almost
    tempted to just plug it in and see how it likes seeing only DC coming in.
    Umfortunly it has two 24dc batteries, giving 48vdc to the controller. Step
    down transformer comes to mind. I have a few, but the closest I have is
    120v down to 80v. :(

    What to do,
    Chris



    "Palindr?me" <> wrote in message
    news:...
    > Chris wrote:
    > > Hi all,
    > > I have tried searching for a solution to no avail. I have an older

    Lincoln
    > > welder that is generating 120vdc to a standard outlet. At the start I
    > > thought it was AC as power saw would run fine. Not until I tried to

    hook up
    > > a cap start compressor did the smoke tell me something was wrong. After
    > > checking everything I could check, I in fact learned that it was a true
    > > generator as it was creating 120vdc. How the saws are running I have no
    > > idea. Unless they are universal motors??????
    > >
    > > Now I come to my question, getting the DC to AC. Actually the term

    inverter
    > > might be wrong as I do not need to change voltage. Should I be asking

    for
    > > an oscillator? Either way I need to get the DC into a sine wave. Not

    too
    > > picky how true it is, I just need it to run motors, more or less, at a

    home
    > > construction sight (read no solid state running off of it).
    > >
    > > So is there a simple circuit I can devise, or any off the shelf

    solutions I
    > > can use? Keep in mind that the unit is rated at 15amps = 1800 watts

    (BTW no
    > > breaker or fuse on it at all, which I will correct). 1800 watt new
    > > generators are about $400 or less, so keeping it under that cost would

    be
    > > nice.
    > >
    > >
    > > Any pointers, help, flames, appreciated.

    >
    > What may be worth looking at is a computer UPS. I have one which has 10
    > x 12 volt sealed lead acid battieries inside and terminals* to connect
    > an external 120vdc battery bank. It generates 3kVA.
    >
    > Only a few UPS use 120v dc internally - some use 48v, some 72v and some
    > 12 v or 24 v. I suspect that, the higher the rating of the UPS, the
    > higher the internal dc voltage used, within reason! But you would need
    > to find a 120v one, ideally with external battery bank connectors to
    > connect to.
    >
    > * You cannot use ac-rated kit such as contactors and switches with dc
    > unless the manufacturer says so - and then it will be massively
    > de-rated. I got hold of some high current dc stuff from a Government
    > surplus place - I think they may have come from a submarine..I also have
    > some lovely ebony-handled, spring loaded open frame knife switches -
    > which are rated for 120 v dc. I only use them on 24v...to comply with
    > IEE regs.
    >
    > --
    >
    > Sue
    >
    >
    >
    >
    >
    >
    >
    >
    > But it may be worth looking around.
    Chris, Aug 23, 2005
    #2
    1. Advertising

  3. Chris

    Chris Guest

    Sue,

    You caught me on the transformer. I am still thinking that it is AC coming
    out of the welder. Still cannot beleive that they would bump that much DC
    at 15 amps out to a regular AC plug (yes it was designed that way, way back
    then). Worse yet, no breaker or fuse.

    Chris


    "Palindr?me" <> wrote in message
    news:...
    > Chris wrote:
    > > Sue,
    > > Yes I was thinking about a UPS. I have an older one lying around.

    Almost
    > > tempted to just plug it in and see how it likes seeing only DC coming

    in.
    > > Umfortunly it has two 24dc batteries, giving 48vdc to the controller.

    Step
    > > down transformer comes to mind. I have a few, but the closest I have is
    > > 120v down to 80v. :(

    >
    > You cannot use a transformer on dc. Sorry about that. And no, you
    > wouldn't connect your dc supply to the ac input of the UPS - it wouldn't
    > like that at all. You would connect your dc supply in place of the 120 v
    > battery bank. Now, if you had a 48 v dc supply, you would be all set
    > with your existing ups. Try shopping around for a different UPS - I paid
    > 100 GBP for mine, without batteries. They are often on ebay.
    >
    > You are probably aware that dc is scary stuff. It can really set your
    > house on fire. IIUC dc shocks are particularly nasty as they tend to
    > leave you gripping the wires, rather than throwing you away. I have been
    > very, very careful to avoid getting one.
    >
    > --
    > Sue
    >
    >
    >
    >
    >
    >
    >
    >
    Chris, Aug 23, 2005
    #3
  4. Chris

    repatch Guest

    Frankly, with what you've said in this post I think the best course of
    action would either be to drop the idea completely, or at least hire a
    professional to do the work.

    Transformers don't work at DC, they tend to blow up and start fires...

    On Tue, 23 Aug 2005 13:38:50 -0400, Chris wrote:

    > Sue,
    > Yes I was thinking about a UPS. I have an older one lying around. Almost
    > tempted to just plug it in and see how it likes seeing only DC coming in.
    > Umfortunly it has two 24dc batteries, giving 48vdc to the controller.
    > Step down transformer comes to mind. I have a few, but the closest I have
    > is 120v down to 80v. :(
    >
    > What to do,
    > Chris
    >
    >
    >
    > "Palindr?me" <> wrote in message
    > news:...
    >> Chris wrote:
    >> > Hi all,
    >> > I have tried searching for a solution to no avail. I have an older

    > Lincoln
    >> > welder that is generating 120vdc to a standard outlet. At the start I
    >> > thought it was AC as power saw would run fine. Not until I tried to

    > hook up
    >> > a cap start compressor did the smoke tell me something was wrong.
    >> > After checking everything I could check, I in fact learned that it was
    >> > a true generator as it was creating 120vdc. How the saws are running
    >> > I have no idea. Unless they are universal motors??????
    >> >
    >> > Now I come to my question, getting the DC to AC. Actually the term

    > inverter
    >> > might be wrong as I do not need to change voltage. Should I be asking

    > for
    >> > an oscillator? Either way I need to get the DC into a sine wave. Not

    > too
    >> > picky how true it is, I just need it to run motors, more or less, at a

    > home
    >> > construction sight (read no solid state running off of it).
    >> >
    >> > So is there a simple circuit I can devise, or any off the shelf

    > solutions I
    >> > can use? Keep in mind that the unit is rated at 15amps = 1800 watts

    > (BTW no
    >> > breaker or fuse on it at all, which I will correct). 1800 watt new
    >> > generators are about $400 or less, so keeping it under that cost would

    > be
    >> > nice.
    >> >
    >> >
    >> > Any pointers, help, flames, appreciated.

    >>
    >> What may be worth looking at is a computer UPS. I have one which has 10
    >> x 12 volt sealed lead acid battieries inside and terminals* to connect
    >> an external 120vdc battery bank. It generates 3kVA.
    >>
    >> Only a few UPS use 120v dc internally - some use 48v, some 72v and some
    >> 12 v or 24 v. I suspect that, the higher the rating of the UPS, the
    >> higher the internal dc voltage used, within reason! But you would need
    >> to find a 120v one, ideally with external battery bank connectors to
    >> connect to.
    >>
    >> * You cannot use ac-rated kit such as contactors and switches with dc
    >> unless the manufacturer says so - and then it will be massively
    >> de-rated. I got hold of some high current dc stuff from a Government
    >> surplus place - I think they may have come from a submarine..I also have
    >> some lovely ebony-handled, spring loaded open frame knife switches -
    >> which are rated for 120 v dc. I only use them on 24v...to comply with
    >> IEE regs.
    >>
    >> --
    >>
    >> Sue
    >>
    >>
    >>
    >>
    >>
    >>
    >>
    >>
    >> But it may be worth looking around.
    repatch, Aug 23, 2005
    #4
  5. Chris

    ehsjr Guest

    Chris wrote:
    > Hi all,
    > I have tried searching for a solution to no avail. I have an older Lincoln
    > welder that is generating 120vdc to a standard outlet. At the start I
    > thought it was AC as power saw would run fine. Not until I tried to hook up
    > a cap start compressor did the smoke tell me something was wrong. After
    > checking everything I could check, I in fact learned that it was a true
    > generator as it was creating 120vdc. How the saws are running I have no
    > idea. Unless they are universal motors??????
    >
    > Now I come to my question, getting the DC to AC. Actually the term inverter
    > might be wrong as I do not need to change voltage. Should I be asking for
    > an oscillator? Either way I need to get the DC into a sine wave. Not too
    > picky how true it is, I just need it to run motors, more or less, at a home
    > construction sight (read no solid state running off of it).
    >
    > So is there a simple circuit I can devise, or any off the shelf solutions I
    > can use? Keep in mind that the unit is rated at 15amps = 1800 watts (BTW no
    > breaker or fuse on it at all, which I will correct). 1800 watt new
    > generators are about $400 or less, so keeping it under that cost would be
    > nice.
    >
    >
    > Any pointers, help, flames, appreciated.
    >
    > Thanks,
    > Chris
    >
    >


    I would say be prepared to give up the idea. A PC UPS will not work
    for you, unless you intend to use low power motors. Your compressor
    probably needs FAR more power than a typical PC ups can provide.

    You might be better served by buying a generator sized to your needs.

    Ed
    ehsjr, Aug 23, 2005
    #5
  6. Chris

    Chris Guest

    "ehsjr" <> wrote in message
    news:jXKOe.2476$IG2.1014@trndny01...
    > Chris wrote:
    > > Hi all,
    > > I have tried searching for a solution to no avail. I have an older

    Lincoln
    > > welder that is generating 120vdc to a standard outlet. At the start I
    > > thought it was AC as power saw would run fine. Not until I tried to

    hook up
    > > a cap start compressor did the smoke tell me something was wrong. After
    > > checking everything I could check, I in fact learned that it was a true
    > > generator as it was creating 120vdc. How the saws are running I have no
    > > idea. Unless they are universal motors??????
    > >
    > > Now I come to my question, getting the DC to AC. Actually the term

    inverter
    > > might be wrong as I do not need to change voltage. Should I be asking

    for
    > > an oscillator? Either way I need to get the DC into a sine wave. Not

    too
    > > picky how true it is, I just need it to run motors, more or less, at a

    home
    > > construction sight (read no solid state running off of it).
    > >
    > > So is there a simple circuit I can devise, or any off the shelf

    solutions I
    > > can use? Keep in mind that the unit is rated at 15amps = 1800 watts

    (BTW no
    > > breaker or fuse on it at all, which I will correct). 1800 watt new
    > > generators are about $400 or less, so keeping it under that cost would

    be
    > > nice.
    > >
    > >
    > > Any pointers, help, flames, appreciated.
    > >
    > > Thanks,
    > > Chris
    > >
    > >

    >
    > I would say be prepared to give up the idea. A PC UPS will not work
    > for you, unless you intend to use low power motors. Your compressor
    > probably needs FAR more power than a typical PC ups can provide.
    >
    > You might be better served by buying a generator sized to your needs.
    >
    > Ed



    Already canned the idea for the sake of safety.and cost plus I still have
    the welder. :)
    Actually the UPS that I have is good to 2250watts, more than enough to drive
    a 3/4 hp compressor.

    Thanks again all,
    C
    Chris, Aug 23, 2005
    #6
  7. Chris

    Don Kelly Guest

    "Chris" <> wrote in message
    news:bGLOe.4360$...
    >
    > "ehsjr" <> wrote in message
    > news:jXKOe.2476$IG2.1014@trndny01...
    >> Chris wrote:
    >> > Hi all,
    >> > I have tried searching for a solution to no avail. I have an older

    > Lincoln
    >> > welder that is generating 120vdc to a standard outlet. At the start I
    >> > thought it was AC as power saw would run fine. Not until I tried to

    > hook up
    >> > a cap start compressor did the smoke tell me something was wrong.
    >> > After
    >> > checking everything I could check, I in fact learned that it was a true
    >> > generator as it was creating 120vdc. How the saws are running I have
    >> > no
    >> > idea. Unless they are universal motors??????
    >> >
    >> > Now I come to my question, getting the DC to AC. Actually the term

    > inverter
    >> > might be wrong as I do not need to change voltage. Should I be asking

    > for
    >> > an oscillator? Either way I need to get the DC into a sine wave. Not

    > too
    >> > picky how true it is, I just need it to run motors, more or less, at a

    > home
    >> > construction sight (read no solid state running off of it).
    >> >
    >> > So is there a simple circuit I can devise, or any off the shelf

    > solutions I
    >> > can use? Keep in mind that the unit is rated at 15amps = 1800 watts

    > (BTW no
    >> > breaker or fuse on it at all, which I will correct). 1800 watt new
    >> > generators are about $400 or less, so keeping it under that cost would

    > be
    >> > nice.
    >> >
    >> >
    >> > Any pointers, help, flames, appreciated.
    >> >
    >> > Thanks,
    >> > Chris
    >> >
    >> >

    >>
    >> I would say be prepared to give up the idea. A PC UPS will not work
    >> for you, unless you intend to use low power motors. Your compressor
    >> probably needs FAR more power than a typical PC ups can provide.
    >>
    >> You might be better served by buying a generator sized to your needs.
    >>
    >> Ed

    >
    >
    > Already canned the idea for the sake of safety.and cost plus I still have
    > the welder. :)
    > Actually the UPS that I have is good to 2250watts, more than enough to
    > drive
    > a 3/4 hp compressor.
    >
    > Thanks again all,
    > C
    >
    >--------------------

    Can it handle the starting inrush current?

    --

    Don Kelly @shawcross.ca
    remove the X to answer
    ----------------------------
    Don Kelly, Aug 24, 2005
    #7
  8. Chris

    ehsjr Guest

    Chris wrote:
    > "ehsjr" <> wrote in message
    > news:jXKOe.2476$IG2.1014@trndny01...
    >
    >>Chris wrote:
    >>
    >>>Hi all,
    >>>I have tried searching for a solution to no avail. I have an older

    >
    > Lincoln
    >
    >>>welder that is generating 120vdc to a standard outlet. At the start I
    >>>thought it was AC as power saw would run fine. Not until I tried to

    >
    > hook up
    >
    >>>a cap start compressor did the smoke tell me something was wrong. After
    >>>checking everything I could check, I in fact learned that it was a true
    >>>generator as it was creating 120vdc. How the saws are running I have no
    >>>idea. Unless they are universal motors??????
    >>>
    >>>Now I come to my question, getting the DC to AC. Actually the term

    >
    > inverter
    >
    >>>might be wrong as I do not need to change voltage. Should I be asking

    >
    > for
    >
    >>>an oscillator? Either way I need to get the DC into a sine wave. Not

    >
    > too
    >
    >>>picky how true it is, I just need it to run motors, more or less, at a

    >
    > home
    >
    >>>construction sight (read no solid state running off of it).
    >>>
    >>>So is there a simple circuit I can devise, or any off the shelf

    >
    > solutions I
    >
    >>>can use? Keep in mind that the unit is rated at 15amps = 1800 watts

    >
    > (BTW no
    >
    >>>breaker or fuse on it at all, which I will correct). 1800 watt new
    >>>generators are about $400 or less, so keeping it under that cost would

    >
    > be
    >
    >>>nice.
    >>>
    >>>
    >>>Any pointers, help, flames, appreciated.
    >>>
    >>>Thanks,
    >>>Chris
    >>>
    >>>

    >>
    >>I would say be prepared to give up the idea. A PC UPS will not work
    >>for you, unless you intend to use low power motors. Your compressor
    >>probably needs FAR more power than a typical PC ups can provide.
    >>
    >>You might be better served by buying a generator sized to your needs.
    >>
    >>Ed

    >
    >
    >
    > Already canned the idea for the sake of safety.and cost plus I still have
    > the welder. :)
    > Actually the UPS that I have is good to 2250watts, more than enough to drive
    > a 3/4 hp compressor.
    >
    > Thanks again all,
    > C
    >
    >


    Doubtful. Do you know what the compressor will draw
    when starting?

    Ed
    ehsjr, Aug 25, 2005
    #8
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