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How to build a WE500-based bellset?

Started by twocvbloke, February 02, 2012, 02:10:49 PM

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dsk

#15
The master socket will have 1.8-2µF cap, an this may be to much. It will work well, but the load may be to high together with all the other telephones.

This page tells a little about capacitors, and markings; http://tinyurl.com/8672d35
Not easy at all, but it seems like the caps you have are to small.

dsk

twocvbloke

I think I'll just buy a 0.47µF capacitor... :D

twocvbloke

Well the bells have arrived, managed to get them ringing with the use of an ADSL filter and my scrappy 746's scrappy cable, I've got pics of my "testbed" whch I'm sure will amuse...  :D

(can't upload them at the moment cos I'm using my mobile phone to type this out!!)

twocvbloke

Here's the pics, using two croc. clips and a spanner to hold wires together to make temporary connections...  ;D

And yes, the short-circuit protection feature in the linesman phone was tested... :D

And the ADSL filter, which is what I use with that linesman phone, I do have a spare which I could probably pop the capacitor out of, which is marked as "F105K h 250MEF1", with to me means nothing... ???

wds

I have looked and looked for a .47 uf, 200-250 volt cap., non polarized and non electrolytic, but can't find one.  Radio Shack tells me they don't have them either.  Does anyone have a part number for the correct Cap. needed for these ringers?
Dave

twocvbloke

You know, I've been looking for them too this evening, on ebay though, cos I get bored of online electronics stores and their endless lists which take ages to trawl through...  :D

I've found a few myself, that are located in the UK rather than china, but can't get any until I know how much I have to spend on shipping stuff from the US (including my Cortelco 2554), so it'll have to wait... :(

wds

#21
I located a 1.0uf cap from Radio Shack, and some .47 uf caps from another source.  I noticed right away that the 1.0 uf allowed the bell to ring much louder than the .47 uf.  Can someone explain why?  Is .47 the wrong size to use for ringesr?
Dave

wds

#22
After reading some in the Old Time Telephone book by Ralph Meyer, (table 6-1) it seems that the correct cap for an older ringer is a 1 uf, as it gives better matching of resistance to the ringer, especially anything older than the 302 ringer.  The 302 ringer (and newer) has a much higher resistance, and was designed to use a smaller cap, ie, .47uf, to help reduce the size of the cap.  The older 1uf caps were quite large, and by changing the impedance on the ringer,, they could use a much smaller cap.  But even testing the 302 ringer I still noticed that the ringer was louder using a 1 uf cap as compared to the .47 cap.  As the size of the modern caps are so small, it seems that the correct cap to use in almost all cases is the 1 uf, and not the .47 uf.   Radio shack part # 272-1055 seems to be the best cap to use with these older ringers.  Does anyone else have any comments about their use of different size caps?

I have a bag of .47 uf caps that I'll make someone a good deal on............
Dave

mst269

Quote from: wds on February 17, 2012, 02:03:44 PM
After reading some in the Old Time Telephone book by Ralph Meyer, (table 6-1) it seems that the correct cap for an older ringer is a 1 uf, as it gives better matching of resistance to the ringer, especially anything older than the 302 ringer.  The 302 ringer (and newer) has a much higher resistance, and was designed to use a smaller cap, ie, .47uf, to help reduce the size of the cap.  The older 1uf caps were quite large, and by changing the impedance on the ringer,, they could use a much smaller cap.  But even testing the 302 ringer I still noticed that the ringer was louder using a 1 uf cap as compared to the .47 cap.  As the size of the modern caps are so small, it seems that the correct cap to use in almost all cases is the 1 uf, and not the .47 uf.   Radio shack part # 272-1055 seems to be the best cap to use with these older ringers.  Does anyone else have any comments about their use of different size caps?

I have a bag of .47 uf caps that I'll make someone a good deal on............

I'm fairly new here but I'll put in my two cents.  I apologize if I'm long-winded but I think knowing the whole story helps understand it, and go on to learn more-

The amount of electro-magnetism a coil is generating is measured in Amp-turns, that is, the current in amps flowing through it multiplied by the number of turns in the coil.  So to get more magnetic strength, you can increase the current, or increase the number of turns- either one works pretty much equally well.

If your ringing frequency stays the same, and the ringing voltage generated by the CO stays the same, increasing the amount of capacitance will increase the amount of ringing current that can flow through the capacitor.

A coil with more turns of wire on it, assuming the same size of wire, will have a higher resistance and impedance than one with less turns, because the length of wire is longer.  But- maybe to wind lots and lots of turns, you could use a really fine wire, so the coil doesn't get huge.  It just makes the resistance and impedance higher yet.

The CO, or PBX, or whatever, can only source a certain amount of ringing current before the voltage starts to really sag.  This is where the concept of REN comes in.

So, we've established all that.  Why should you keep your bag of .47 uF caps?  Older ringers were lower in impedance.  This is because they didn't have as many coil turns.  Therefore, the idea was that you pushed more current through them to get the ringer to move hard enough to give you the volume you want.  To get the current, you need more capacitance.  0.47 uF gives you a feeble ring, because you can't get many amp-turns.  The turns aren't working for you!  So you use 1 uF, or sometimes even more capacitance, to get that current to flow.  You can't have many ringers in your house if they're going to be this thirsty, though.

Newer phones were built with higher-impedance ringers, and a capacitance of around half a microfarad was agreed on to limit ringer current.  Now those turns are working in your favor- let's say you can get four times as many turns onto the ringer, now each amp of current does 4 times the work moving the clapper.  Good deal!

Even with a newer ringer, a larger capacitor will get you more amps, more amp-turns, and thus louder ringing, although the Law of Diminishing Returns kicks in pretty soon and hard here.  Why?  You can only cram so many "magnetic lines of force" into a piece of steel.  Different grades of steel permit different amounts of lines of force.  More amp-turns produce more lines of force, until the steel coil core and magnetic circuit of the ringer has been "magnetically saturated".  Above that point, the extra current is just wasted in making all of your phones ring poorly, because of that voltage sag.  That .5 uF figure will permit at least 5 phones on a normal line.

0.47 uF caps are really useful for telephone people.  One apiece in modern phones (if there isn't one already in a network), two (or perhaps three) in parallel in old phones.  Makes up the right size capacitor for the job.

Richard


twocvbloke

Now here's a question, as we brits have the BT Master socket system, with a 1.8uF cap in the master, does that mean that 2-wire devices, such as american telephones which have their own cap, have in theory little or even no REN at all?  ???

I remember that from another forum, when I asked about making a BT Viscount into a 2-wire phone, and someone said that the REN would drop from 1 to some fraction of a REN figure..... ???

dsk

This Ren calculations is definitely no accurate thing when it comes out of the laboratory.
The UK master capacitor limits the load tho what is possible to send through the  capacitor. This will make it possible for the customer to actually put in and test whats possible to run on the line, and when one or more ringers stop ringing , the load is to high. The old ringers with 1000 ohms ringer and 1 microfarad cap will give a Ren of 2-2.5.  Putting in a smaller cap, or a resistor in series, the ren, and sound-level decreases.
It seems like the  interest of making less than 1 ren  ringers with gongs are low, so you could usually deem a mechanical ringer to be at least 1 ren.  (exception observed so far is some small external ringers from Ericsson)

Another issue is that 1 ren + 1 ren not always turns out to be exactly 2 rens. (But not far from 2)

I guess this may be as well as confusing as before. 

The advice will be, just add on ringers, but test to be sure it works.  If you want to have some safety remove one more ringer.

dsk

twocvbloke

I dunno, I never did understand the REN rating, all I know is that most phonelines here in blighty can operate on average 4 phones, though you can call up the supplier and ask them if they can up the power on the line for more phones, or if the lines are old or losing too much power between the exchange and the customer... :-\

It'd be easier if they used amp ratings, like on other electrical devices (seeing how phones are electrical), but I guess the ringer equivalence is just too ingrained now to change it... :D

dsk

By my experience, one REN equals 10-11 milliampere (AC) at my line.   The equipment in the other end are probably different, but from this you should be able to draw at least 45 mA. Maybe less on extremely long lines, and definitely less from an ATA.

A wireless jack as digijack will supply a few REN and draw about zero REN from the line. You will also be electrically divided from the real line, and they may not measure what you have hooked up. The big drawback is the lack of pulse dial support.

dsk

twocvbloke

Us brits haven't really gotten to the stage of wireless jacks and digital VOIP lines (well, BT has their HomeHub things which I think have VOIP phones attached), I guess we're just too old fashioned, or BT (and the cable co's) just doesn't like anything other than phones & modems connected to their lines... :D

I think if I'd get ATAs, they'd be hooked up to a PBX, rather than directly to phones, with one line connected to the actual phoneline, and wire up the existing extensions as PBX extensions... :D

dsk

Usually every short and easy answer tends to be made in lack of competence ;D
Since you not use your master socket capacitor, but rather one in each telephone, I will be very surprised if you get problems whatever you hook up as far as the total value of the capacitors not exceed 3.6 uF.  In this case no extra resistors in series should be needed.   3.3k resistors in series with the low ohm ringers may make it possible to rise the number of ringers, but each ringer will generate less volume. By my opinion a smaller capacitor is better than a series resistor.  (A series capacitor reduses the capacitor value. 1+1 uF in series = 0.5 uF)

dsk