Door Bell

Discussion in 'Electricians' Talk' started by carl42, Dec 15, 2003.

  1. carl42

    carl42 New Member

    I live in a new build home - so assume the sparks have been completed by competent people but I have a problem with my door bell! I have 2 bell boxes connected to the front door button, but only the one by the front door rings. On the sound one, the hammer only move about an 1/8 on an inch and doesn't strike the chimes. Reading other thread in this forum about voltage drop etc, I think this may be my problem but how do I fix it? The transformer in on the consumer unit and is 16KVA (2 x 8v, 2a) do I need to upgrade the transformer?

    Thanks
     
  2. Wheel-nut

    Wheel-nut Member

    I think you mean 16VA. But, something doesn't add up. If there are two secondary windings, each giving 8V @ 2A, the transformer would be rated 32VA. I suspect that each winding is rated 8V @ 1A.

    If this is true, and the secondary terminations are all accessable, you can use them in parallel BUT YOU MUST GET THE POLARITY CORRECT. The terminals pairs would be marked 0 and 8V. Make sure that you connect the two 0's together and the two 8V's together and you will then have 8V @ 2A available.

    I have made some assumptions here:
    1) That the bells require 8V
    2) That the transformer is wound "bi-filar"
    3) That the transformer has not already been damaged. If it has any shorted turns, it will be burning up already!

    You do this at your own risk. If in any doubt, come back and ask ... or get an accredited electrician to look at it.
     
  3. carl42

    carl42 New Member

    I have had another look at the transformer, although there are 4 terminals on the low voltage side only 2 (terminals 1 & 3) are active. So that is 1 feed of 8v 2amps
     
  4. ban-all-sheds

    ban-all-sheds New Member

  5. Wheel-nut

    Wheel-nut Member

    Nice one B-A-S :) .

    Carl, I don't understand what you mean by "active". Do you mean that both bells are connected to terminals 1 & 3 or do you mean that only terminals 1 & 3 have windings terminated to them?

    If there are two pairs of terminals, each pair will probably only give you 1A which will not be enough to drive two chimes. You need to connect the two windings in parallel as I suggested earlier.

    Previous caveats apply.
     
  6. carl42

    carl42 New Member

    B A S - I would have thought that transformer would have been enough to power my door bell.

    Wheel-nut - only terminals 1 & 3 have windings terminated to them.
     
  7. Wheel-nut

    Wheel-nut Member

    Carl,

    Try disconnecting the chime which works and then see if the other one come to life. If it does, replace the Transformer with a meatier one. If it doesn't, condider replacing the chime.

    Does the one which works sound good and loud?
     
  8. carl42

    carl42 New Member

    Disconnected the one by the front door and the other one now works properly, when I reconnected the one by the front door it is nice and loud, but the other one stooped working. Looks like I need a bigger transformer, any suggestions on what I should get?

    Cheers
    Carl
     
  9. Wheel-nut

    Wheel-nut Member

    Carl, Check the Chimes to see if they require 12V rather than 8V. Friedland make both 12V and 8V transformers but the highest current I can find is 1A. The problem appears to be poor regulation of the transformer and possibly excessive Volt drop on the cabling to the switch which is carrying the total current for the two chimes.

    If the chimes will take 12V, you could change the Tx for a 12V unit. B&Q sell them and they are also listed at TLC http://www.tlc-direct.co.uk/Main_Index/Door_Bells_and_Chimes_Index/Door_Bells_and_Pushes1/index.html

    The TC TR7 Transformer 1 Amp for Bells and Chimes @ £5.50 has tappings for 4V, 8V and 12V
     
  10. carl42

    carl42 New Member

    Wheel-nut,

    The chimes are Friedland 'type 4' 8 - 16v ac, 6v DC Max 15w. The transformer is mounted in the CU and is a Grothe GT 1965 16va 8v/2amp http://www.grothe.co.uk/
     
  11. Wheel-nut

    Wheel-nut Member

    I can't see a GT 1965 on the website ... but I have noticed that the transformers ate protected by a PTC.

    Does you Bell push switch have a lamp in it? If so, it could be drawing enough current to cause the PTC to go high impedance. Try removing the lamps from the front and back door bell push switches; then switch off the transformer wait a couple of minutes and switch it on again.

    If that fixes it, throw the lamps away!
     
  12. carl42

    carl42 New Member

    The bell push does have a lamp in it, but it seems to be integral with the switch mechanism - can't remove the lamp. I will get another bell push with no lamp and let you know how I get on.

    Wheel-nut - Thanks for your help.

    Regards
    Carl
     
  13. Wheel-nut

    Wheel-nut Member

    Carl, It's easier than that.... disconnect one wire from each Bell Push, then after 10 mins, reset the Transformer and then try the bell by shorting the bell push wires.

    No point in buying new switches unless it works!
     
  14. carl42

    carl42 New Member

  15. Dr Who

    Dr Who New Member

    Basically, from the specification you gave earlier your transformer is not able to supply enough juice to run two of these chimes.

    Now its time for the science part.........

    Taking worst case scenario -

    Power = Current x Voltage
    P = I x V

    I = P/V

    I = 15/8

    = 1.875A

    (15W taken from the DC part of the spec, which may also apply to the AC but without the spec I cannot tell; even so it gives rough idea of the max power consumption is. 8 Volts is what is supplied from the ******)

    Worst Case for 2 chimes would be 3.75A @ 8V which far exceeds the 2A from the ******; and this is not including any additional lights in the switches.

    Oooopps! I am not 'in the trade' so better be quiet noW!!

    Dr Who
     
  16. Dr Who

    Dr Who New Member

    I think I might modify my previous assumption slightly, as the 15W max is more likely to relate to the AC at its max 16v rms...

    I = 15/16

    = 0.9375A

    Therefore, at lower voltages the current will be less than this figure and therefore your ****** should be capable of driving both chimes!

    As it happens do you have a multimeter to measure the Amps and voltage when the load is applied??

    Must not rush into post to quickly next time!

    Dr Who
     
  17. supersparky

    supersparky New Member

    better not talk as your not in the trade? SHUT THE **** UP THEN
    that formular aint gunna help him solve his problem
    like has been said before, connect them in paralel
    taht way your current is shared evenly, also what is lengh(s) of cable run(s) and what size is the cable? maybe worth changing it for 4mmflex to compensate volt drop, you could try disconnecting both bells from the wall and cable, then using a short test wire rig em up directly to the ******, if they work here, its V drop if not is ******

    BR
     
  18. Wheel-nut

    Wheel-nut Member

    Doc, I think that the word "max" is the clue to the discrepancy in the specs of the chimes and the Tx. Most of the Friedland Transformers are spec'd at 8V 1A so I suspect that the 15W max is the dc power dissipated. Since the load is inductive, I suspect that the ac power may be considerably less. Also, the lamp load for the activated switch comes off when the chime is activated so only one lamp (the other door) needs to be counted.

    I still think that the PTC thermistor is the culprit. But, it is after all included to prevent the Tx bursting into flames inside the CU.

    Also, the chimes require 8 - 16 volts and a 12V Tx would have been more appropriate.
     
  19. Dr Who

    Dr Who New Member

    I am assuming that the chimes are already in parallel and not in series; I suppose that a single chime could operate at whilst another wouldn't when in series.

    In the fault finding process 'that formula' IS going to HELP him solve his problem such that it ensures the ****** is matched to the load requirements - if it is, then great he has ruled that out of the list of possible problems with this thing not working - he can then look at the next 'possible' problem!

    'sharing current' - Kirchoffs law by any chance? - you don't need to be 'in-the-trade' to know stuff you know! <not a specific dig at you SS just making a general point about the range of skills, knowledge and experience we can all bring to a forum like this, whether you are trade or DIYer>

    Dr Who
     
  20. supersparky

    supersparky New Member

    as i knew he had already disconnected one of the bells and the non working one worked, so he could work out the wattage by looking at the raitings of the bells, adding together,and taking away from ****** rating, btw, the freidland trannys are the dogs and if the two bells are freidland aswell they will take it

    'Oooopps! I am not 'in the trade' so better be quiet noW!!'
    thats what i dident like about your post, it was a cheep attempt at humour, not funny. if you hadent said it i would not have said anything, you dont need to be trade,no, but we do this day in day out, so your remark is just plain insulting and cheeky, you will be screwed with the intro of part p, i wont be here and i def wont be giving advice to ungreatful diyers!
    You have no idea how many times i would have meggered you by now if you were on site with me!

    BR
     

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