Potentiometer w/Switch wiring for lamp

Discussion in 'The Projects Forum' started by fippy, Jan 16, 2013.

  1. fippy

    Thread Starter New Member

    Jan 16, 2013
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    0
    Hi this is my first post so please go easy, any help would be greatly appreciated.

    As a home project I am trying to make table lamp with a dimmer switch. I have purchased a lampholder (http://www.spares2you.co.uk/E27-Threaded-Nickel-Plated-Lampholder) along with a range of pots with variable resistance all w/switches (see http://www.lorlin.co.uk/PDF/MDST.pdf).

    I plan keep things as simple as possible to start. I'm using a 60w incadescent light bulb (ES/E27 fitting to match lampholder) and the lamp will run off the mains which in the UK is 240v supply (so running at about 0.25amps) The mains cable I have at the moment (plugged for UK use) comes as live (brown), negative (blue) and earth (yellow/green) - I plan to use a 1amp fuse.

    I have read here that pots shouldn't be used as dimmers certainly not running directly off mains, however this pot seems to be designed specifically for this. If you read the specs it is rated for mains and is indeed marketed as one (see "MDST Main Switch + Potentiometer" on the following webpage: http://www.lorlin.co.uk/products.php)

    If it is ok to use, my initial question relates to the correct wiring of the Rotary Dimmer Switch (Potentiometer w/switch) and the lampholder. (Please see images attached.)

    From reading a little about the wiring of pots my current understanding is to wire the ground should go to point 1, 3 should go to the input of the lampholder with 2 (the middle) receiving the output of the lampholder. Is this correct? Should I continue the earth up to the lampholder's earth? more importantly the two connections on the back of the pot w switch (4&5) what are they and how should they be wired. My initial research shows these are to do with the on/off capacity so I cannot simply wire it as a pot.

    All and any help would be greatly appreciated.
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,086
    3,024
    Don't do it!

    At least not until you confirm that your pot can take the heat. It should be rated to 100W or more, and I doubt that it is. Only a large and expensive pot can tolerate such usage.

    An AC light dimmer does its job by chopping the AC waveform, so that the light sees only a fraction of it. It is NOT a simple resistive load.

    [update] Read the specs carefully. The SWITCH capacity is fine for your load, but the TRACK capacity is much smaller and won't work. My warning stands; don't proceed. Your pot will rapidly act as a fuse and emit smoke as it pops.
     
    Last edited: Jan 16, 2013
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    The switch is designed for line voltage, but the pot is intended to be part of a dimmer circuit, not directly dimming a lamp.

    Save you self a lot for grief (and maybe a fire), Google: torche lamp dimmer

    Ken
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    896
    The potentiometer in the light switch is designed to control a light dimmer circuit (its maximum power is rated at only 0.2W). Then a power Triac does the hard work.
     
  5. DickCappels

    Moderator

    Aug 21, 2008
    2,647
    631
    [​IMG]


    You might have trouble finding a Diac. If so, you can make your own:
    http://cappels.org/dproj/dimmer/Triac Lamp Dimmer With Simulated Diac.html

    Please...most likely the switch is made to be connected to the line, but please make sure the pot is designed to be used at line voltage and that there is no chance of getting a shock from the shaft.

    By the way, the Brown wire is Line, the Blue wire is Neutral.

    Before building this, study up on safety practices when working with line voltage. The basic rules are 1) If its connected to the line, don't touch it, and 2) Keep one hand in your back pocket at all times (don't allow a path between limbs that passes through the heart). But read up on safety first.

    Good luck and be careful.
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    As Audioguru already pointed out the pot track is rated for .2W
    It will be destroyed instantly when used as the OP intended..
     
  7. fippy

    Thread Starter New Member

    Jan 16, 2013
    4
    0
    Ok great so I need a triac and possibly a diac (strictly necessary???) any specs on these components?
     
  8. sheldons

    Active Member

    Oct 26, 2011
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  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,979
    3,693
    Your final project should all go into a box that will not ignite if a spark / arc is generated in the box. It must also isolate any user from shock. The cords must be secured inside the box so any tugging will not break the wires from their lugs or solder joints. Also, no sharp edges on the box that can cause damage to the cord over the next 20 years of use.

    You may notice from my tone, I am not a fan of mains power projects for everyday items. Commercially available items that function like your design are recalled on a monthly basis. There are just too many safety issues that even professional designers overlook. I can't imagine what safety issues will exist when completed by a rookie.

    Even if you are living alone today and you are sure nobody will get hurt, you have to think ahead, will you have visitors, will any kids be using the lamp (ever), will it be idiot proof by the time you are done?

    Please be safe. It is not just about electric shock, it is also about fire. It can happen immediately or 10 years from now.
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    Please post a video of the circuit catching on fire and burning down your entire neighbourhood.

    Why don't you buy a certified safe light dimmer instead??
     
  11. fippy

    Thread Starter New Member

    Jan 16, 2013
    4
    0
    Ok, I'm heeding the warnings and would be happy to purchase a pre-built dimmer to start but I need a rotary only (no push on/off) switch and something as small as possible (the smaller the better!!!)

    Following the comments above am I correct in thinking that a rotary dimmer module like (http://cpc.farnell.com/pro-elec/5sd.../dp/PL09927?in_merch=Products From This Range) would be a better way to go? Can I simply wire such an enclosed module to a mains plug, fit it, secure knob and away I go...?

    If so I have seen several which may do the trick (please advise):

    (40-250w) http://cpc.farnell.com/jsp/search/productdetail.jsp?sku=PL09926

    (60-400w) http://cpc.farnell.com/jsp/search/productdetail.jsp?sku=PL09927

    http://www.aurora.eu.com/ProductPag...count-electrical.co.uk/product.php/387718918/

    http://www.aurora.eu.com/ProductPages/PowerProductDetails.aspx?g=8664&c=576&b=103&oc=576 (though might be a push on/off switch)/http://www.discount-electrical.co.uk/product.php/394149952/

    http://www.screwfix.com/p/varilight...al/38416#product_additional_details_container
     
  12. wayneh

    Expert

    Sep 9, 2010
    12,086
    3,024
    Excellent news. You'd be amazed how many visitors here get mad and go ahead and do something crazy anyway.

    I didn't check all your links but that first one looks fine. As for your build, see the comments above. The safety level you build to MUST be in line with the intended use and the unintended consequences. Cat knocks over pitcher of water onto device, etc. etc.
     
  13. Audioguru

    New Member

    Dec 20, 2007
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    I think it will be used in England where they do not have "water". Instead they have "wotah".;)
     
  14. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Bostonians also have "wotah"...
     
  15. Audioguru

    New Member

    Dec 20, 2007
    9,411
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    Lots of people talk funny.
    In the USA millions of people are Africans and Mexicans who talk funny.

    Here in Canada there are thousands of people who talk in FRENCH. In skool I was forced to study FRENCH but I have never talked nor written to anybody in French in my life.
    Also there are many immigrants who speak in their original language (mostly Chinese and Indian).
     
  16. fippy

    Thread Starter New Member

    Jan 16, 2013
    4
    0
    You will all be pleased to know that to start with I have purchased:

    1 x ROTARY 60-400W MODULE (http://cpc.farnell.com/jsp/search/productdetail.jsp?id=PL09927&Ntt=PL09927 )

    plus

    1 x K8026 3.5A VELLEMAN DIMMER KIT (http://cpc.farnell.com/jsp/search/productdetail.jsp?id=HK00752&Ntt=HK00752)

    I figure the kit can get me started understanding the components and then I will use the module all being well in the lamp itself as it should be fully compliant.

    Thanks for the initial help and I will come back to you guys with further questions and updates if thats OK?
     
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