Results 1 to 6 of 6

Thread: n:(n+1) 120 VAC transformer?

  1. #1
    Join Date
    Jan 2008
    Location
    Fountain Valley, CA (Orange County, So. Cal)
    Posts
    2,147
    Post Thanks / Like

    Default n:(n+1) 120 VAC transformer?

    Has anyone used something like a 3:4 (or 4:5 or n: (n+1)) transformer for 120 VAC? If so, where did you get it, or did you make it? All I can find are 1:2.

    Rather than cutting down a bunch of mini-light strings for half-wave use with channel doublers, I'm considering just stepping up the supply voltage. I realize that this will shorten the bulbs' lifespans, but I figure I can live with that (since LED strings will be coming down in price over the next few years, and then I can switch over).

    To maintain full brightness, I would need to run a half-wave string at ~ 170 VAC RMS, which would be a ~ 40% step up from 120 VAC RMS. According to the overvoltage derating formulas I saw (new voltage / old voltage ^ (-12 to -16)), that would reduce the bulb life to 0.5% - 1.5%, which is a little too severe. So, I think I actually want more like a 5:6 step-up transformer, which would still give about 85% brightness but only shorten the lifespan to 5% - 10%.

    I've read how some guys do their own custom rewinding. It sounds doable. I've heard that microware oven transformers are a good source, since they are typically rated for 1 KW.

    Has anyone done custom transformer rewinding, and, if so, how did it turn out?

    thanks

    don
    Click for display details >>
    web site: http://www.eShepherdsOfLight.com or http://www.facebook.com/eShepherdsOfLight
    technical articles: http://downloads.eshepherdsoflight.com

  2. #2
    Join Date
    Jan 2008
    Location
    Fountain Valley, CA (Orange County, So. Cal)
    Posts
    2,147
    Post Thanks / Like

    Default Re: n:(n+1) 120 VAC transformer?

    Quote Originally Posted by djulien View Post
    Has anyone used something like a 3:4 (or 4:5 or n: (n+1)) transformer for 120 VAC? If so, where did you get it, or did you make it? All I can find are 1:2.
    Okay, I finally found some. I didn't think to seach for the keywords "autotransformer" or "variac". Thoes turned up lots of hits.

    don
    Click for display details >>
    web site: http://www.eShepherdsOfLight.com or http://www.facebook.com/eShepherdsOfLight
    technical articles: http://downloads.eshepherdsoflight.com

  3. #3
    Join Date
    May 2007
    Location
    Apple Valley, MN
    Posts
    3,755
    Post Thanks / Like

    Default Re: n:(n+1) 120 VAC transformer?

    Be careful with these. The current is at maximum at 120 volts but goes down the same percentage away. A 10 amp VARIAC is only 5 amps at 60 or 240 volts.
    [I]A mediocre person tells. A good person explains. A superior person demonstrates. A great person inspires others to see for themselves.[/I]

    <a href="#" onclick="return(showhide(this));">Click here to show/hide my display details ...</a>
    <script language="javascript">function showhide(anc){ for(; ; ){ if(!anc.nextSibling) break; if(anc.nextSibling.nodeName == "DIV") break; anc = anc.nextSibling; }//<br />
    var Y='block', N='none', det=anc.nextSibling; //<br />
    if (!det) det=document.getElementById('details'); det.style.display=(det.style.display!=N)?N:Y; return false;}</script><div id="details" style="display:none;"><br /><img src="http://www.vixenlights.com/sig/sig_h.php/128/All.gif" border="0" alt="" /></div><a href="#" onclick="return(showhide(this));">Click here to show/hide DIYC Links ...</a>
    <script language="javascript">function showhide(anc){ for(; ; ){ if(!anc.nextSibling) break; if(anc.nextSibling.nodeName == "DIV") break; anc = anc.nextSibling; }//<br />
    var Y='block', N='none', det=anc.nextSibling; //<br />
    if (!det) det=document.getElementById('details'); det.style.display=(det.style.display!=N)?N:Y; return false;}</script><div id="details" style="display:none;"><br /><b>Chat link</b> - <a href="http://doityourselfchristmas.com/forums/addonchat.php" target="_blank">http://doityourselfchristmas.com/forums/addonchat.php</a>
    <b>Christmas Wiki link</b> - <a href="http://doityourselfchristmas.com/wiki/index.php" target="_blank">http://doityourselfchristmas.com/wiki/index.php</a>
    <b>File Library link</b> - <a href="http://doityourselfchristmas.com/forums/dynamics/index.php" target="_blank">http://doityourselfchristmas.com/forums/dynamics/index.php</a>
    <b>Who's in chat?</b> - <a href="http://doityourselfchristmas.com/forums/chat/info.php" target="_blank">http://doityourselfchristmas.com/forums/chat/info.php</a>
    </div>

  4. #4
    Join Date
    Jan 2008
    Location
    Fountain Valley, CA (Orange County, So. Cal)
    Posts
    2,147
    Post Thanks / Like

    Default Re: n:(n+1) 120 VAC transformer?

    Quote Originally Posted by ErnieHorning View Post
    Be careful with these. The current is at maximum at 120 volts but goes down the same percentage away. A 10 amp VARIAC is only 5 amps at 60 or 240 volts.
    For clarification, do you mean the actual current drawn, or the current rating of the transformer?

    don
    Click for display details >>
    web site: http://www.eShepherdsOfLight.com or http://www.facebook.com/eShepherdsOfLight
    technical articles: http://downloads.eshepherdsoflight.com

  5. #5
    Join Date
    May 2007
    Location
    Apple Valley, MN
    Posts
    3,755
    Post Thanks / Like

    Default Re: n:(n+1) 120 VAC transformer?

    A VARIAC that is rated at a maximum of 10 amps at 120 volts can only supply 5 amps at 60/240 volts. AT 12 volts you shouldn’t go over 1 amp. Any more than this and you could fry it; if you’re lucky it just gets hot. Below the input voltage it’s going to look like a potentiometer across the line. At the low end, it’s going to be dropping a lot of voltage. Ohms law still applies.

    I got a freebie because of this I think. It was in the trash at work. All that was wrong was that a wire came un-soldered from the low end of the coil. I’m only assuming that they over heated it, but not by much. Works fine now.
    [I]A mediocre person tells. A good person explains. A superior person demonstrates. A great person inspires others to see for themselves.[/I]

    <a href="#" onclick="return(showhide(this));">Click here to show/hide my display details ...</a>
    <script language="javascript">function showhide(anc){ for(; ; ){ if(!anc.nextSibling) break; if(anc.nextSibling.nodeName == "DIV") break; anc = anc.nextSibling; }//<br />
    var Y='block', N='none', det=anc.nextSibling; //<br />
    if (!det) det=document.getElementById('details'); det.style.display=(det.style.display!=N)?N:Y; return false;}</script><div id="details" style="display:none;"><br /><img src="http://www.vixenlights.com/sig/sig_h.php/128/All.gif" border="0" alt="" /></div><a href="#" onclick="return(showhide(this));">Click here to show/hide DIYC Links ...</a>
    <script language="javascript">function showhide(anc){ for(; ; ){ if(!anc.nextSibling) break; if(anc.nextSibling.nodeName == "DIV") break; anc = anc.nextSibling; }//<br />
    var Y='block', N='none', det=anc.nextSibling; //<br />
    if (!det) det=document.getElementById('details'); det.style.display=(det.style.display!=N)?N:Y; return false;}</script><div id="details" style="display:none;"><br /><b>Chat link</b> - <a href="http://doityourselfchristmas.com/forums/addonchat.php" target="_blank">http://doityourselfchristmas.com/forums/addonchat.php</a>
    <b>Christmas Wiki link</b> - <a href="http://doityourselfchristmas.com/wiki/index.php" target="_blank">http://doityourselfchristmas.com/wiki/index.php</a>
    <b>File Library link</b> - <a href="http://doityourselfchristmas.com/forums/dynamics/index.php" target="_blank">http://doityourselfchristmas.com/forums/dynamics/index.php</a>
    <b>Who's in chat?</b> - <a href="http://doityourselfchristmas.com/forums/chat/info.php" target="_blank">http://doityourselfchristmas.com/forums/chat/info.php</a>
    </div>

  6. #6
    Join Date
    Jan 2008
    Location
    Malden MA
    Posts
    988
    Post Thanks / Like

    Default Re: n:(n+1) 120 VAC transformer?

    Also, remember that it's an autotransformer - it doesn't isolate the output, so you should treat the output as if it was at full mains potential with respect to insulation and safety.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •