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Old 30th May 2019, 3:45 pm   #21
dagskarlsen
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Default Re: Incorrect bell?

I did measure at 25Hz 70V, The transformer mentioned over, load 47 ohms resistor, and I used a 2.2 uF capacitor in series with the transformer.
The current was about 0.022A and the load is approx 3650 ohms or a REN load close to 2 after the old standard.

I guess a 240 to 24 small transformer from an adapter will do the job.

I did also try to change the 47 ohms resistor with a DC ringer of 37 ohms, and it rang loud enough.
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Old 30th May 2019, 10:38 pm   #22
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Default Re: Incorrect bell?

Nicely, nicely, Sporty Spicely! I like it when practice agrees with theory; it means the theory must have been right!

In the UK, 4kΩ was REN=1 and a line is guaranteed to support up to REN=4, so your 3650Ω was not far off at all. The voltage ratio of your transformer was about 6:1, so we'd be looking at a 20-0-20 mains transformer. That's an unusual value; 18-0-18 or 24-0-24 would be the nearest likely available (lower voltage ⇒ lower power ⇒ lower REN).
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Old 31st May 2019, 7:05 am   #23
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Default Re: Incorrect bell?

In theory, there is no difference between theory and practice.

If the practice comes close, the theory will probably be right

PS The REN calculation is including the Capacitor like they e.g.do in USA. The measurement is done according to the setup described in Old-time Telephones! Design, History, and Restoration by Ralph Meyer (https://bre.is/Qt3O_IRJS) DS

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Old 31st May 2019, 8:08 am   #24
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Default Re: Incorrect bell?

REN measurement may be done like on the picture:

I have used this spreadsheet and collected some data: https://goo.gl/yxfWg5

I guess the accuracy are far better than +/- 10 %
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Old 31st May 2019, 12:15 pm   #25
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Default Re: Incorrect bell?

Quote:
Originally Posted by julie_m View Post
I like it when practice agrees with theory; it means the theory must have been right!

In the UK, 4kΩ was REN=1 and a line is guaranteed to support up to REN=4, so your 3650Ω was not far off at all.
Not true. REN is not a simple resistive calculation. Inductance comes into it as well.
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Old 2nd Jun 2019, 1:38 pm   #26
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Default Re: Incorrect bell?

Delighted to report back with a semi success story!

I used a very small SMPSU rated primary 100V~ @ 50-60hz and secondary DC 9V as per attached photo. The bell rings, although it struggles a bit! It's not got a great rhythm (which suggests that the circuit doesn't have time to get up to speed each time the ringing current is applied on the primary side as per Julie's earlier advice). But it's a nice volume; I wouldn't want it a lot louder, but I would like it to be more regular...

Measuring the voltage on the secondary side my multi-meter (with the reading struggling to keep up with the ring cycle - quite a slow 'sample rate' on this one I guess) reads no more than ~4V which makes sense... this is in proportion with the 50% drop in frequency, and a further loss in proportion with the expected 70V on the line. So ideally I would find an alternative PSU which is going to A) deliver within the range of 6-12V (which is what the bell I'm using is rated at) and B) 'charge' up quickly so the rhythm is better.

The bell has a resistance of 50 Ohms. So if I'm going to look for a PSU capable of 9V at 0.2A. I might need to put a resistor in line if it's too loud I guess.

But I'm not sure how to ascertain whether the PSU I find will 'charge' quickly enough... I have shortlisted the following components as suitable:

https://uk.rs-online.com/web/p/embed...-smps/1812110/

https://uk.rs-online.com/web/p/embed...-smps/1358918/

They are both rated min 85V AV on the primary side - I don't think that's too much of a problem though is it?

And I can't see any published info on the minimum 'charge' length for the secondary circuit to become active but would expect these devices to be pretty quick... a reasonable assumption, do you think?
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Old 2nd Jun 2019, 1:48 pm   #27
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Default Re: Incorrect bell?

Quote:
Originally Posted by ThePillenwerfer View Post
Joe - is your website down for maintenance?
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Old 2nd Jun 2019, 2:17 pm   #28
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Default Re: Incorrect bell?

I guess this one rectifies the AC in, and then you will see a capacitor so the circuit is fed by DC, double or more that capacitor, and it will probably give a more stable output, but give a higher ring load.
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Old 2nd Jun 2019, 2:39 pm   #29
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Default Re: Incorrect bell?

Quote:
Originally Posted by PickleRick63 View Post
Joe - is your website down for maintenance?
No, and that link just worked for me. It could have been off briefly without my knowing.
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Old 2nd Jun 2019, 2:43 pm   #30
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Default Re: Incorrect bell?

Or try no capacitor, it may well ring more like a telephone bell.
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Old 2nd Jun 2019, 3:46 pm   #31
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Default Re: Incorrect bell?

Quote:
Originally Posted by ThePillenwerfer View Post
No, and that link just worked for me. It could have been off briefly without my knowing.
The link works for me too, but using a solid state relay may even simplify that circuit. https://bre.is/zyyF_VznG
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Old 2nd Jun 2019, 4:19 pm   #32
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Default Re: Incorrect bell?

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Or try no capacitor, it may well ring more like a telephone bell.
Which capacitor are you suggesting I try removing Merlin? The one in the master socket?
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Old 2nd Jun 2019, 7:19 pm   #33
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Default Re: Incorrect bell?

The one on the primary side of the SMPS.
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Old 8th Jul 2019, 11:08 am   #34
PickleRick63
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Default Re: Incorrect bell?

Hi everyone again - hope you are all well.

I was coming back to this little project and wanted to ask particularly merlinmaxwell (and dagskarlsen). You suggest removing the capacitor on the primary side of the PS... do you mean the primary side when in normal operation (ie AC to DC)? I can see what look like 3 capacitors - I've marked them red green and blue on the attached. To which are you referring?

Thank you
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Old 8th Jul 2019, 2:56 pm   #35
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Default Re: Incorrect bell?

The parts you have marked are on the secondary side. The red and green are capacitors, but the blue looks more like an inductor (coil) which would give a multi-stage filtering effect.

The other two electrolytics (one of which is dfesignated C1; I can't read the number on the other) are on the primary side. The green-blue component L1 mounted "standing up" between them is another inductor.

You will need some capacitance on the primary side to persuade the power supply to start up. You could try removing one or the other capacitor; probably try the larger one.
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Old 8th Jul 2019, 5:59 pm   #36
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Default Re: Incorrect bell?

To remove a capacitor in that circuit is something I never would have considered. That does not mean that it is a bad idea, just outside my comfort zone.

dsk
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Old 9th Jul 2019, 11:39 am   #37
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Default Re: Incorrect bell?

Thanks Julie & DSK

I thought that the primary side is the input side (where the device is connected (normally) to 230v AC circuit) and the secondary side is the output side (where normally the device is connected another circuit that's looking for 8v). Is that incorrect? Just want to make sure I've got this the right way around...
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