1. New to Christmas lighting? Get started with the AusChristmasLighting 101 Manual:
    auschristmaslighting.com/wiki/AusChristmasLighting-101

Is anybody here running on 55V/0/55V center tapped earth?

Discussion in 'Power Supplies' started by deonb, Jan 27, 2015.

  1. deonb

    deonb New Elf

    Joined:
    Jan 4, 2015
    Messages:
    12
    Likes Received:
    0
    At the risk of being crucified again on here, I know this is mostly a D.C. forum. Unfortunately I don't have good access to D.C. lights, outside of pixels. Most of my lights are 110V, but my supply is 240V.

    However, I can get access to a 240V to 55V-0-55V center tapped earth transformer, and I can put a 5 mA RCD with open-neutral protection on it.

    My thinking is that a 55V-0-55V center tapped transformer would be safer than either a 240V->110V autotransformer (0-110V) or a 240V->110V isolation transformer, provided that the RCD has open-neutral protection.

    I was wondering if someone on here is/was running in such a setup, and if you found any caveats or safety issue. E.g. does any Christmas light equipment have a problem with having a voltage above ground on the neutral wire?
     
  2. Benschristmaslights

    Benschristmaslights Dedicated Elf Global Moderator Generous Elf

    Joined:
    May 2, 2010
    Messages:
    2,125
    Likes Received:
    7
    Location:
    Elderslie
    Find Me On:
    no one that I know does this on this site sorry.

    sounds like more work then it is worth what location are you??? as I find it hard to believe you can not get access to dc lights
     
  3. Fing

    Fing Full Time Elf Generous Elf

    Joined:
    Dec 31, 2014
    Messages:
    349
    Likes Received:
    29
    Location:
    Muswellbrook
    Find Me On:
    Hi,


    I don't know what you are trying to do with the centre tapped tx. Are you proposing earthing the centre?


    normally you would use a quality 240:110 transformer that also has isolation between the primary and secondary. I would avoid using an autotransformer as it has no isolation and under the right (or wrong?) conditions it can put 240v onto the secondary side.


    110v lights should work ok if the +ve and -ve are floating. It's not usual to earth 110v from my experience, but you should be able to do it, just earth one of the outputs. The trouble is that you have to know what it is you're protecting by earthing and you should be able to test the circuit to see if the protection will work as you desire.


    Unless you have some knowledge on this or are willing to find an electrician you could create a more dangerous situation then you think.


    I agree with Ben - go DC, less chance of frying the neighbours cat.


    Cheers
    Fing
     
  4. OP
    OP
    deonb

    deonb New Elf

    Joined:
    Jan 4, 2015
    Messages:
    12
    Likes Received:
    0
    South Africa. My choices are either to use indoor-rated 240V equipment from local distributers in South Africa, or import. It is highly uncommon in South Africa to have outdoor lights, and when people do, they use indoor equipment that disintegrate within a season. Not even - 2 weeks in, and all your lights are faded.

    So there are no group buy opportunities - I have to bear all the cost of import myself. I do however have access to a regular LCL shipment from the U.S. so I can import from the U.S. for a fraction of the cost than importing from Europe. However, nobody in the U.S. uses DC lights, other than for RGB.

    Hence... no good access to D.C. lights.


    A center tapped earth transformer, commonly used in the U.K. on worksites (I think required standard), gives a 110V output by alternating between -55V and +55V instead of 0V to 110V. You use standard 110V equipment on it.

    That way if you drop your drill etc. into water, you will only get a 55V shock instead of a 110V shock for the 25m/s or so until the RCD kicks in. Generally 55-0-55 is said to be 16 times safer than 240V (P =V^2/R).

    The downside is that you have a voltage-above-ground on the neutral wire. Most things don't care, but some things do.

    I could go with regular old 110V, which I'm comfortable with, and I use myself while I'm in the U.S., but I figured 55-0-55 might be safer. I just haven't dealt with it. (Well, I've dealt with 110-0-110 Center Tapped of course, but not 55-0-55).


    Happy to.

    Will you be able to ship 100'000 DC lights, which take up around 2 cubic meters, for me to South Africa for ~ $1500, including cost of lights, shipment & customs duty? Or even within 5 times that?
     
  5. Habbosrus

    Habbosrus New house (again) 2017

    Joined:
    Dec 5, 2012
    Messages:
    750
    Likes Received:
    0
    Location:
    Swansea, NSW
    Find Me On:
    Hi, there is at least one other member that is from South Africa on ACL. His name is Charl Marais. Maybe you could send him a pm to see how he gets his lights or what kind of setup he has. He may have been through many of the things you're experiencing now. It's just a thought, but may be beneficial.
    There is at least one other ACL from South Africa that I know of, but I can't remember their name off the top of my head.
     
  6. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

    Joined:
    Apr 26, 2010
    Messages:
    6,487
    Likes Received:
    19
    Location:
    Albion Park NSW
    Find Me On:
    The majority here do not use group buys for lighting but buy direct from China. It can be an expensive exercise importing things into South Africa, but then the lights you buy in South Africa would also have paid those shipping costs and duties.

    In South Africa do they only sell 240v mains lights or do they sell 24v lights because you mention these are 110v lights and i would tend to think these shouldnt be available in your country and in Australia most lights are sold as 24 volts and what is done is to just remove the controller and run these directly from a 31v DC power supply. So are you importing these lights anyway because it seems odd that you are using 110volt lights in SA. Be careful of of buying very cheap 110v lights you pay for what you get.

    Are these LEDs or incandecent light strings you are going to use and will these have a controller or be directly connected.

    The reality is that a centre tapped transformer is not really different to a normal transformer, the difference is a centre tapped transformer is more flexible as it gives you more than one volatge output and then when you tie these outputs together you get the sum of both voltages. What you are creating is a 3 wire 2 phase 55V output. The ground is needed because an ungrounded center tapped transformer can produce unbalanced voltages in the two secondary windings due to unsymmetrical currents flowing in the common third connection because of unbalanced loads.

    Centre tapped transformer are normally used with a full wave rectifier as these 2 voltage will be out 180 degrees out of phase from eachother and so a full wave rectifier is used to bring these two voltages back into phase with eachother

    In general if just being lights then this shouldnt be an issue but if using LEDs the i suggest using the bridge rectifier as this will stop the lights from having that flickering effect.
     
  7. AAH

    AAH I love blinky lights :) Community Project Designer

    Joined:
    Dec 27, 2010
    Messages:
    2,537
    Likes Received:
    13
    Location:
    Eaglehawk
    Find Me On:
    Depending on what sort of lights you are looking at and whether you are looking at sequencing them you really should look for low voltage DC ones. If you're using 240V or 110V mains lights then to control them you either have to use a Light-O-Rama AC controller that works out to something like $AU10 per channel or a DIY one. With low voltage DC there are controllers that let you control your channels for between $AU2 and $AU4. The difference in cost per channel is often comparable to the cost of the DC lights you could put on there. If the lights are US sourced 110V ones then there is a pretty fair chance that they are incandescent which could introduce problems for your proposed transformer idea as the wattage can get quite high fairly quick.
    http://auschristmaslighting.com/wiki/Controllers has a list of AC and DC controllers.
    Ray Wu who is 1 of the most common suppliers ACL users buy from no longer supplies fairy lights and mysolarled who used to supply excellent quality fairy and icicle lights don't appear to be trading still but there are plenty of aliexpress based Chinese suppliers who can provide almost any type and quantity of led light. Finding 1 that does good quality is the problem. The couple of dozen led fairy light strings I got from Ray Wu years ago are still going strong and they cost about $7 each landed in Australia.
     
  8. OP
    OP
    deonb

    deonb New Elf

    Joined:
    Jan 4, 2015
    Messages:
    12
    Likes Received:
    0
    They only sell 240v mains lights - and only for indoor use. No 24v. The 110v lights are imported from the U.S., since I mostly live in the U.S, and have access to a periodic LCL, I can cheaply import it. Not so with China.

    I'm aware. The 110v lights I'm using is of FAR better quality than the 220v lights sold in SA. Bigger gauge, much bigger insulation. UV rated. Fused. The insulation doesn't crumble under your fingers after a couple of week in the sun, and a blue light bulb is still blue a month later.

    Controller. I'm aware of the math of using a DC controller + DC lights, vs. an AC controller with AC lights. If the AC controller is LOR, then DC lights might become economical. But not so with Renard + DirkcheapSSR.


    I know! But they sell them for so much more... You're essentially paying triple for 2 inches more of copper. :eek:

    Yes, if I were to tap the center tap, that would be true. But a worksite transformer doesn't even give you access to the center tap - it just grounds it, and you always use the outside 2 wires.

    So it's always used as an ordinary 110V supply - and always symmetrical. The only difference is the potential difference to earth on those legs.

    I agree, the LEDs need full wave rectifiers. They look terrible otherwise. Even just with a normal 220v supply.
     
  9. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

    Joined:
    Apr 26, 2010
    Messages:
    6,487
    Likes Received:
    19
    Location:
    Albion Park NSW
    Find Me On:
    I can now understand your situation

    I would only use these tranformers if they were given to me beacuse as you noted they cost a lot more.

    But for your purpose they should do the trick if you got them cheaply or for free.
     
  10. AussieDoug

    AussieDoug Full Time Elf

    Joined:
    Dec 1, 2012
    Messages:
    375
    Likes Received:
    0
    Seeing you mostly live in the US can you buy from China to US then use your cheap shipping that you have access to, to ship them home? Might be a way around getting some DC lights.
     
  11. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

    Joined:
    Apr 26, 2010
    Messages:
    6,487
    Likes Received:
    19
    Location:
    Albion Park NSW
    Find Me On:
    He doesnt even need to buy from China as there are a few US local dealers he could buy from who deal in DC lighting and then he can import from US to SA in the same way as the 110v lights.

    But from what I can gather deonb is an Amercian living in South Aftrica and wants to do what he did back at home in the US for South Africa using the knowledge he already has with 110v mains lighting which is understandable.
     
  12. OP
    OP
    deonb

    deonb New Elf

    Joined:
    Jan 4, 2015
    Messages:
    12
    Likes Received:
    0
    That's probably for 50 count lights.

    My cost for 100 count lights landed are $1.50 each. Add the cost of the 110V transformer, which works out to around another $1.50 per string. My A/C controller cost per channel (Ren32 + DirkCheapSSR) is around $2.00 each.

    So now we're talking about $5.00 per 100 lights controlled, vs. approximately $7 x 2 + $1 for the controller = $15 - and that's before adding the cost of the DC transformer, and larger DC wires.

    And all of that is only IF I can get the same shipping rate from China to South Africa as you can get from China to Australia, which I doubt, just geographically speaking.

    I'm having a hard enough time getting a good supply of RGB pixels, so the thought of paying 5 times more and now having to also deal with those kind of quality and supply issues for my tree/arch/icicle/prop lights as well isn't all that appealing to me.
     
  13. OP
    OP
    deonb

    deonb New Elf

    Joined:
    Jan 4, 2015
    Messages:
    12
    Likes Received:
    0
    That's actually exactly what I do for pixels, but the math doesn't quite work out for general DC lights. It is cheaper than shipping directly to South Africa, but nowhere near the price range of 110V lights.

    Not really. Apart from RGB strings, there aren't really mainstream DC light dealers. There's definitely no store you can go to and pick some up, and even online the pickings are slim. How I wish I can just back in my truck into a hardware store or Walmart and load up on a ton of 24v/48v lights, but alas, I can't.

    Close!

    South Africa living in America for last 18 years. But going back to South Africa ever so often. But you're right - my knowledge & experience is substantially on the 110v side of things.

    However, thanks for the support! :D
     

Share This Page