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Thread: Electronic doorbell vs electromagnetic chime

  1. #1
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    Electronic doorbell vs electromagnetic chime

    Hey, all. A customer requests troubleshooting for an extension door chime for her rear patio, paralleled to the main inside chime and operated by a single door button. There was an old electronic chime that supposedly "worked for a few days" and then both rang when it shouldn't and failed to ring when it should.

    I replaced the old unit with a standard solenoid-type chime, which immediately pulled in due to the diode across the button. I know that the diode is required by the inside electronic chime to allow it to complete the programmed chime pattern. The diode also prevents the new chime from releasing, so it hums.

    I tried coming up with a way to wire them to operate together, but I can't come up with one. It just so happens that the cables from front door and to inside chime have three wires, but I still can't come up with a way to have the diode supply the inside chime without also energizing the new chime for the outside.

    So, my question is whether two electronic chimes will operate in tandem on a single button, as long as they're both the type that require a diode across the button. Have any of you had success with such a setup? We need consistent proper operation without improper "phantom" chiming at the wrong time. Help!
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  2. #2
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    Larry Fine:

    So, my question is whether two electronic chimes will operate in tandem on a single button, as long as they're both the type that require a diode across the button.
    My guess is yes. This assumes the pushbutton diode can handle the load.

    I believe that functionally you can parallel two or more chimes. I have never seen or played with these. All I know about these is from a prior discussion.

    The assumption is that the chime must also have an internal diode used to charge a capacitor in the chime to supply enough energy to power the chime during its chiming period. At least to provide filtering to get fairly clean DC. Assume for convenience this occurs on a positive half cycle. If two parallel chimes exist and are wired correctly, then both chimes get energy stored during this positive half cycle.

    The pushbutton diode prevents current flow on the negative half cycle. Actually once the chime capacitors are charged only a small amount of current flows toward the chime and this is near the voltage peak. While the chime is chiming there will be more current flowing on these positive peaks. So energy for chiming is not totally dependent on capacitor precharging.

    It was conjectured in a previous discussion that when the button is pressed bypassing the diode that then the negative pulse is used to trigger the chime.

    If things work this way, then any number of chimes could be paralleled.

    Experiment, phasing is important, and see if it works. Diode current capability and load current need to be studied.

    .

  3. #3
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    Some mechanical (solenoid) chimes can work on half wave DC, although possibly drawing higher current.
    If you have to parallel such a chime with an electronic chime requiring a diode across the button, you can place an oppositely oriented diode in series with just the mechanical chime. It will then see zero current while the button is open and half wave DC when the button is pressed.

    Sent from my XT1585 using Tapatalk

  4. #4
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    How about making the pushbutton power a relay - you can then use relay to trigger both the mechanical chime and the electronic chime.

    Though chime systems are typically 16VAC, a 12VDC relay might work - if not put a diode in series with it and try it. It only needs to be able to close it's output momentarily.
    I live for today, I'm just a day behind.

  5. #5
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    I'm not sure I follow your question. You start out with an old electronic chime, then replacing it with a mechanical one then you want to use two electronic chimes- is that correct?

    I don't suspect that you will have a problem if you replace BOTH with new electronic chimes, both the same model. Diode stays.

    Likewise, you could replace both with mechanical chimes, remove the diode and maybe up the transformer VA.

    -Hal

  6. #6
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    Quote Originally Posted by hbiss View Post
    I'm not sure I follow your question. You start out with an old electronic chime, then replacing it with a mechanical one then you want to use two electronic chimes- is that correct?

    I don't suspect that you will have a problem if you replace BOTH with new electronic chimes, both the same model. Diode stays.

    Likewise, you could replace both with mechanical chimes, remove the diode and maybe up the transformer VA.

    -Hal
    he started out saying he was troubleshooting an electronic chime that was added in parallel to an existing mechanical chime. probably never worked right from the day it was installed.
    I live for today, I'm just a day behind.

  7. #7
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    The first post was confusing until the last paragraph.

    GoldDigger's post made sense and probably would work. And would work with with a Mallory Sonalert. Huge number of models http://www.mallory-sonalert.com/Sear...aspx?Code=30ST

    Some of the other responses had confusion and errors. DC relays just don't work with AC excitation, try a straight DC relay on AC, even at 4 times the voltage, and you will observe why. Most AC relays will work on DC, but at a much lower voltage, like 1/4, or the coil will burn out. There is a very logical reason.

    Why are some door chimes made with a diode pushbutton requirement? My conjecture:
    1. No change in existing wiring.
    2. Power needs to be supplied to the chime longer than the door button may be pressed.
    3. The diode in the button means power can be supplied to the chime constantly without having to rewire and provide a power wire to the chime.

    Could a chime have been designed with a large enough capacitor that it could be easily charged on pressing the door button and have enough stored energy for whatever duration of chiming was thought to be needed? I don't know.

    .

  8. #8
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    Quote Originally Posted by gar View Post
    180605-0950 EDT

    ...
    ...
    Could a chime have been designed with a large enough capacitor that it could be easily charged on pressing the door button and have enough stored energy for whatever duration of chiming was thought to be needed? I don't know.

    .
    Possibly. But it would put a much heavier than normal short term load on the transformer, which probably has relatively high internal resistance for self protection. And the surge to charge the capacitor could well damage the contacts of the doorbell pushbutton.


    Note also that all of the scenarios mentioned will be complicated, possibly to the point if unfeasiblity, if you try to use a lighted pushbutton!

  9. #9
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    Sorry, guys, I didn't realize I was unclear. The original situation I encountered was an electronic chime, a lighted button with a diode across it, and a multi-tap transformer with 8/16/24v terminals connected as 24v. Plus, there was a second electronic chime in the crawlspace which had space for three C-cell batteries, apparently meant to be used either with or without a transformer, which was wired in parallel with the main chime.

    The original doorbell system worked perfectly, despite the over-voltage, and the push-button light still works. Both chimes were wired using the front-door and common (transformer) terminals, as desired. The issue was that the second chime stopped responding to the button and began chiming randomly, and the 24v transformer was apparently part of repeated attempts to make it work correctly, which never happened.

    We installed the original transformer and the electro-mechanical chime, which is when we discovered the constant pull-in, and then the diode, then the electronic original. We tried both without the diode, and of course the electronic chime stopped the moment the button was released, and the new electro-mechanical chime worked correctly. The customer preferred two electronic chimes to two electro-mechanical ones.

    Today, we rewired the entire system, noting and using wire colors carefully, with a new, inexpensive electronic chime in the crawlspace, and we installed the diode, but with one twist: we installed the diode in the indoor chime. We connected one diode wire to the transformer "hot" (to the button) via the third wire to the chime, and the other end of the diode connected to the 'front' terminal in the chime (from the button).

    In other words, you could say we have an "always-hot" wire at the chime in addition to a "switch leg" and a "neutral". The first two are the two wires the diode would be connected to had we put the new diode where the original was, on the button, which was a PITA. The new diode also has heavier wires than the original had, one of which broke due to repeated handling. Everything works perfectly now, and we got paid.

    ​Added:
    I don't believe charging a storage cap is part of this type of chime circuitry. The diode provides constant DC (half-wave) power to the chime (which is why the diode polarity matters), while the AC (full-wave) is used to trigger the chime. Once triggered, the entire tune (Westminster in this case) continues, and will restart if the button is held. The rear chime also receives the DC as it is in parallel with the front (just ding-dong).
    Last edited by LarryFine; 06-05-18 at 06:53 PM.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  10. #10
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    Larry Fine:
    I don't believe charging a storage cap is part of this type of chime circuitry. The diode provides constant DC (half-wave) power to the chime (which is why the diode polarity matters), while the AC (full-wave) is used to trigger the chime. Once triggered, the entire tune (Westminster in this case) continues, and will restart if the button is held. The rear chime also receives the DC as it is in parallel with the front (just ding-dong).
    A diode between a sine wave voltage source and a resistive load does not provide a constant DC voltage to the load. What you see across the load is a positive (or negative as you choose) sine wave for 1/2 of the AC source cycle and zero for the other half. Change to a full wave rectifier and you see two positive half waves side by side.

    If the peak sine wave source voltage is 100 volts, then the output peak is 100 - diode drop. But for simplicity assume the diode drop is zero. Then the average half rectified DC voltage is 0.318 * 100, and the full wave average is 0.636 * 100. The half wave has an added large 60 Hz AC component, and harmonics. The full wave has 120 Hz and harmonics.

    Thus, to avoid output hum I believe the chime has a large internal filter capacitor. Roughly the filter capacitor charges to the peak AC voltage even though the average DC voltage is much less.

    When the load on the diode is a large filter capacitor with some shunt resistance, then only short current pulses flow thru the diode from the AC sine wave source at the peak of the AC voltage source. This is why the capacitor takes on a voltage near the AC peak.

    .

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