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Neon Indicator - Parallel or Series?

Discussion in 'General Electronics Discussion' started by Graham, Nov 10, 2009.

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  1. Graham

    Graham

    30
    1
    Nov 10, 2009
    Hi all - I'm new to this forum and am not sure if you deal with 'electrical' as well as 'electronics' related stuff - so forgive me if I'm posting in the wrong area, or shouldn't even be at this site...

    My query is this... I have a water heating booster element in my solar water tank on the roof (one of the advantages of moving from UK to Oz), which I want to control using a 24 hour timeswitch (20A timeswitch for the purpose obtained already). Since the timeswitch will be hidden away in a cupboard, I'd like to wire a neon indicator into the circuit, so it is more evident when it is switched on or off (not bothered about whether the thermostat has actually kicked in the element or not, JUST whether the circuit is being supplied with electricity, so we don't inadvertently leave it overridden during 'peak' time). I am 99.9% certain that the neon (with appropriate resistor) should be wired in parallel with the load, across the 2 output terminals of the timeswitch otherwise it would be acting like a fuse - and I don't think it would last long having 20A drawn through it... am I right?

    Cheers,
    Graham
     
  2. cj_elec_tech

    cj_elec_tech

    62
    0
    Oct 7, 2009
    Hi Graham, welcome to the forum.

    <CJ climbs onto his soap-box>
    RULE 1:
    If you are going to be installing or modifying ANY mains wiring, BE SAFE.
    For your own sake, if not for anyone else's, please follow Australian Standard AS3000 to the letter and if you have little experience with mains wiring PLEASE get a registered Electrician to do it, or at least get someone with knowledge and experience to check your work.
    That being said ;) I don't give a rat's ass if you or any person is 'not qualified' for this type of work - my comment is all about keeping it safe for everyone. :)

    RULE 2: - refer to RULE 1

    <CJ climbs off his soap-box>

    OK lecture over ;)

    What you're suggesting sounds about right.
    If you want the Neon to light when the timer is on, wire it (with appropriate series resistor: anything around 220kOhms or a little greater will be fine), in parallel with the heater circuit: i.e. from the switched Active output of the timer to Neutral.

    If you were to wire the Neon in series (with it's resistor), it would only glow when the timer was on: the heater would not heat at all.
    It wouldn't try to conduct 20A, the heater would (in effect) appear as a short circuit to the neon, only increasing the value of the series resistance a tad above 220k, so the heater current would automatically be limited to the current through the neon - typically 1/2 to 1 mA.

    Does this answer your question?
    Please let us know how you go.

    CJ
     
    Last edited: Nov 14, 2009
  3. Graham

    Graham

    30
    1
    Nov 10, 2009
    Hi CJ - and don't worry about giving me the the soap-box lecture ;-)
    I completely agree about safety, and not attempting to anything you don't understand. I have come here to Australia from the UK, where the homeowner can legally undertake any work on the consumer side of the main fuse. I'm fairly handy at DIY, and also a stickler for 'doing things properly', so over the years, I've accumulated a fair amount of knowledge and wiring plans for various domestic situations, and a goodly amount of first hand experience while substantially rewiring a 90 year-old house, running power to a detached garage, and installing a subsidiary distribution board with CBs for the lights and power, and a timed circuit for security lights (doubled for Christmas lights during December ;)), but I've never had to put in a separate neon indicator before:rolleyes:

    If I weren't the wrong side of 45, with a mortgage to pay, I would quit my depressing IT job and retrain to obtain the Australian sparky's qualification myself... I enjoy the combination of logical thinking and manual application.

    Anyway, thanks for the confirmation on wiring the neon in parallel, and for the sizing of the resistor (that was going to be my next item of research :D).

    Your explanation of the 'series' wiring makes sense to me now too (it just seems soooo wrong that a teeny little neon will stop a whopping great water heater from working - a bit of a David and Goliath situation, eh?)

    I guess my next problem is actually finding one... Back in the UK, I had one I uninstalled during a kitchen refit, which was already mounted in a faceplate and even had the wording 'Hot Water' etched above it... sadly, it looks as though I didn't bring it over with the rest of the junk I shipped. Now of course, I find that apart from the plugs, sockets and light switches I can get through Bunnings, anything else electrical is availble to tradies only and very difficult to source. Ho hum...

    Cheers,
    Graham
     
    Last edited: Nov 10, 2009
  4. cj_elec_tech

    cj_elec_tech

    62
    0
    Oct 7, 2009
    No Worries Graham, glad I didn't offend you; From what you wrote in your post, I had a feeling that you had some experience :)
    Yeah, the 'rules' in Aust suck with regard to working on mains wiring :(
    I thought I'd do the WARNING though, as many people read these posts and (unfortunately) there are some people who can, shall we say, bite off a little more than they can chew! ;) and I'm a strong supporter of Occupational Heath & Safety!
    (I know a 'DIY Guy' who's electrocuted himself more than once, and has actually caught his clothes alight 3 TIMES on his own mains jobs!: :eek: - yes he's still alive....)

    Anyway, as to the Neon - hey that's easy!
    In Syd. there are a number of Electronic hobbyist stores that sell them - you can get them in a nice bezel, with the appropriate resistor already installed inside, ready to connect to the Mains - you don't need to 'muck about' with the 'bare' neon at all! They only cost $2 - $3 I expect!
    Have a look for the nearest Dick Smith, Altronics, Force Electronics, Jacar (just to name some off the top of my head) and they will have them in stock.

    Hope this helps, please let us know how you go.

    Best regards

    CJ
     
    Last edited: Nov 14, 2009
  5. Graham

    Graham

    30
    1
    Nov 10, 2009
    Hi CJ,
    There's a Jaycar not too far from where I work - I pop in there quite often for bits and bobs when I'm making up audio leads and so on, but I never paid much attention to mains stuff - I'll try there one day this week. In the meantime, I have wired in the timeclock without the indicator, and it all seems fine EXCEPT... the wires run just very slightly warm when the heater is on. Not hot by any means, but there is sufficient change to make it evident when the circuit is running and when it isn't (perhaps I don't need the neon after all, just leave a loop of wire to feel :rolleyes:) Is this 'normal' for a high draw circuit such as a 20 amp water heater, or should I be worried?

    I've used the same gauge cable as the existing setup, and having contacted Rheem, they've assured me the heating element is either 3.6kW or 4.8kW. The hot water circuit in my fuse box has a 20A rated switch and one of those horrible old porcelain fuse holders (it says it's a 16A but I have no idea if it actually has 16A fuse wire in it - all I know is that it ISN'T a paper clip - as I have heard of some people using when they didn't have any fuse wire handy :-o ) Assuming the 16A fuse actually has 16A wire in it, then I presume I must be on a 3.6kW element drawing 15A rather than the 20A I'd assumed previously. I've just been outside and checked on the back of the fuse board, and found that the wire that comes off the back of the fuse and into the house is also running slightly warm (it goes from main fuse to one side of switch, then other side of switch to fuse, and then fuse to internal wiring) - so perhaps it is normal - that or my entire house is a ticking time bomb of dodgy wiring thanks to the previous owner - who seems to have been a bit of a 'Bodgitt and Leggitt' type.

    Cheers,
    Graham
     
    Last edited: Nov 15, 2009
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