Author Topic: Converting magneto/local battery to common battery  (Read 1203 times)

Offline scottfannin

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Re: Converting magneto/local battery to common battery
« Reply #15 on: June 10, 2020, 03:40:00 AM »
Finger joints.  Wow.  So when I said it looked like little fingers I was almost right!  That would explain why searching "dovetailing" never shows anything like those. 

With the switches to avoid having, say, a P1D ringer for the "amusement", there is a new question to resolve.  Most of the phones I see do not have a PTT switch or a PDC switch or perhaps some other feature switch.  So what sort of switch could a person get/build that would look convincing?  I see a lot of generic black button/silver plastic momentary switches but they look as cheap as they are and even the few I've used (in toy cars so my son couldn't leave the lights on, they only operate when your little hand is holding the car) have tended to break.  So how to fabricate something convincing?  Acorn nuts come to mind as a possible contact surface.  It's easy to adjust the length of a screw where needed.  What about the internals?  One of those strong contact switches from a washing machine lid seems possible, but it doesn't have enough spring to force a bolt back, so it would need an assist of some kind.  Perhaps a hollowed wooden box, those things inside it, as a crude start.  Thoughts of how to improve on that?

Offline RB

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Re: Converting magneto/local battery to common battery
« Reply #16 on: June 10, 2020, 08:20:54 AM »
Not sure I'm followin the stream here, but if you are talkin bout general blade switches,
You could use a switch from an arcade game.
The blades are available in varying thickness, "which means some push back harder than others".
And the contacts vary in size also. "means more or less current carrying capability".
The switch stacks are very similar to phone switch stacks, and are hard  to break.

Offline scottfannin

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Re: Converting magneto/local battery to common battery
« Reply #17 on: June 10, 2020, 08:23:59 PM »
It's actually possible once we know what to call it.  While I might find the right deal etc., I quickly located this.  The one I used had 6 leaves, but thinking about it we only really need 3 to break and make the circuits.  One missing from the magneto means it can't connect and fry anything down the hall.

Offline dsk

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Re: Converting magneto/local battery to common battery
« Reply #18 on: June 11, 2020, 02:20:25 AM »
You  may even use a simpler one, depending on what you want. My oldest wall phone works  :) dsk

Offline Babybearjs

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Re: Converting magneto/local battery to common battery
« Reply #19 on: June 11, 2020, 05:20:15 PM »
the easiest way to convert one of these old phones is the put in a ITT network and wire it accordingly. leave all the original parts, but just have them disconnected... (except for the bell, switch hook, transmitter and reciever.) leave the original network and capacitors in place for looks. I have a old AE 901 that I wanted to try to add a dial to, but couldn't. some phones just don't like to be upgraded!
John

Offline HarrySmith

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Re: Converting magneto/local battery to common battery
« Reply #20 on: June 11, 2020, 05:24:19 PM »
the easiest way to convert one of these old phones is the put in a ITT network and wire it accordingly. leave all the original parts, but just have them disconnected... (except for the bell, switch hook, transmitter and reciever.) leave the original network and capacitors in place for looks. I have a old AE 901 that I wanted to try to add a dial to, but couldn't. some phones just don't like to be upgraded!

Did you see Stan's article on adding a TT dial to any old phone? I have used it a few times.

https://atcaonline.com/ttpad.html
Harry Smith
ATCA 4434
TCI

"There is no try,
there is only
do or do not"

Offline scottfannin

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Re: Converting magneto/local battery to common battery
« Reply #21 on: June 15, 2020, 11:36:50 PM »
DSK I don't fully understand your diagram but I saved a copy to study!  I'm not understanding how the button can perform two functions when it's a single button.  That seems like a useful technique for anything though once I understand it.

About adding a touch tone pad, I solved that with a fairly modern polarity-protected keypad.  Connect black and red wires, cut the rest off (or if that's too scary tape them).  Put a 330 Ohm resistor between the two output terminals, doesn't even take solder since you can just jam the leads in.  Put wires on the output terminals and use them to interrupt just one side of line, red or green didn't seem to matter.  Magically when you pick up you can just add the touch tone sounds and it works with anything I tried.  I have to go on hiatus and fix up my garage, taking advantage of the warm weather to work on the walls and paint.  But after that, I'm going to get some woodworking tools to put out there like a router and try to make little wooden boxes to hide the keypad, OR, make shelves with hinges and the pad is under it and the shelf is actually a lid that pops up.

For what to change or not, I'm finding that what I like to do is gut them and then re-assemble them with mostly original parts but to be common battery.  It's no fun to add modern parts.  I allow an exception for capacitors because even if the old one works, it's not 0.47 uF and there will usually be just a one-sided capacitor that says you can use it for common battery ringing or for voice, not two of them.  My replacement wooden condensers have two capacitors inside and at least look "real".  I've attached pictures of my very first complete wooden phone, finished today! 

Offline Stan S

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Re: Converting magneto/local battery to common battery
« Reply #22 on: June 16, 2020, 06:39:28 AM »

Offline scottfannin

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Re: Converting magneto/local battery to common battery
« Reply #23 on: June 28, 2020, 09:00:30 PM »
So I built the circuit above on a breadboard, or tried to.  Took me a few days to understand it, but once I do I'm good.  The magneto is a Western Electric Type 48A.  It puts out about 60 VAC if I just connect it to a meter, and bells ring weakly if I connect it to them with no capacitor (as the circuit has, where the capacitor is not part of the circuit if the magneto is in use).  The bridge rectifier puts out 48 VDC.  Calling the phone number makes the bells ring.  So, in the normal closed position, it works.  The rectifier appears to be supplying 48 VDC, which is way beyond what the relay I tried (I have a few little ones around) says it wants in the data sheet I found with Google.  It seems to want 5 VDC?  I may have fried it because now the magneto handle turns suspiciously easily.  I'm not sure what's normal though.  My understanding is that the start of cranking the magneto will cause the rectifier to trip the DPDT relay with DC and move it to the Normal Open lines, which are the magneto ones, cutting off the wall current and then letting the AC pass to the bells.  It seems to be failing at that point though.  Do I need a different relay?  Or maybe I picked a bad one?  (I selected one out of a pile of junk I had for years, no reason to expect it to work or not work, just that I don't want to fry another when I've only found a handful in the junk bag. 

Offline RB

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Re: Converting magneto/local battery to common battery
« Reply #24 on: June 29, 2020, 08:03:39 AM »
5vdc max input,
48v supplied,
= poof! :-[
you need to use a relay rated at about 60 to 100v ;)

Offline scottfannin

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Re: Converting magneto/local battery to common battery
« Reply #25 on: June 29, 2020, 10:51:01 PM »
That explains why the magneto handle turns really easily now.  I got off the phone an hour ago after talking to a friend who installs security doors to pick his brain.  He uses a lot of relays.  He said that if you put 48 VDC into a 5 VDC rated relay, you wouldn't even smell smoke it would disappear so fast.  He said I might as well have put a fuse in with a barely visible filament.  But he did say that if you put a resistor in series with the relay, you might get away with it.  Apparently the power is dissipated across all of the resistance in the circuit path.  So it seems for example if we wanted 45 of 50 volts to disappear, the resistor just has to eat the equivalent of 45/50 of whatever is going through the wire.  That would work, but there are two problems that come to mind.  1) You have to get it right, first time, every time, which would be tough if the relay is expecting to get at most 10% of what is available and 2) Typical resistors vary quite a bit, so unless you bought some of those expensive resistors used for timing applications, you would fry one now and then unless you measured every one in a pack to choose just the best ones.  So, for people who have tried this with a phone circuit, what did you use?

Offline Stan S

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Re: Converting magneto/local battery to common battery
« Reply #26 on: June 30, 2020, 12:45:05 AM »
It's amazing how the electronics industry has changed in my lifetime. When I designed that circuit in the late 1960s those relays were literally a dime a dozen. There was a load of electronic surplus stores in New York called 'Radio Row'. Relays like the one in that circuit could be bought by the handfull for $.25 each.

Well, obviously it's no longer the 1960s. I did a quick search and found a current replacement. Haven't tried one so I can't guarantee that it will be more or less universal for all magnetos. Might be worth a try:

https://www.jameco.com/z/LB2-110A-S-R-Electromechanical-Relay-Double-Pole-Double-Throw-12A-100-110VAC-3-9Kohm-Plug-In_175573.html
It appears that they are out of stock right now but should be available in a few days.

There's more to the relay than the operating voltage. The size of the contacts is also a major consideration. The two coils of a ringer present a very large inductive load. The 'inductive current' is switched by the relay contacts. The contacts have to be pretty 'beefy' or they were burn up or seize closed. That's why you have to use a fairly large relay. Tiny little PC relays regardless of the coil voltage won't do the job for very long.

What's great about the Internet is that 'stuff' never seems to go away. What's bad about the Internet is that 'stuff' never seems to go away. When I posted that article there was  Radio Shack and a source for the original parts. Wasn't life great?
Have fun!
Stan S.

Offline scottfannin

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Re: Converting magneto/local battery to common battery
« Reply #27 on: June 30, 2020, 01:07:22 PM »
Thanks for the clarification.  I'll use the little relays on order for something or other.  I ordered 4 of these "ice cube" style relays to try out.  I had been wondering why they had both when the obvious spec, the coil voltage, seemed to be the same.  Besides, perhaps with some intentional yellowing these could be left sticking out of the wooden block I usually put modern components in and it would look cool.  Sadly the Radio Shack down the street from here first closed, and then they knocked the whole building down.  I still have some soldering tools from there and a breadboard.  It was awfully useful to be able to just pay 20% extra and get a component right away on a Saturday afternoon. BTW, I just realized that it's YOUR circuit.  I feel like I have touched internet phone expert greatness!

Offline Stan S

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Re: Converting magneto/local battery to common battery
« Reply #28 on: July 02, 2020, 07:55:54 PM »
Unfortunately the article in the link I sent previously no longer exists in Google. It is lost forever.
NOT MY DOING!
Fortunately I was able to find a copy of the diagram of the ringer controller.
So all is not lost.
See below.
Stan S.

Offline countryman

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Re: Converting magneto/local battery to common battery
« Reply #29 on: July 03, 2020, 02:47:20 AM »
In fact Google still finds it when you search the title of the article, but it has been removed from the ATCA website not long ago.
Google still has a copy in it's cache. It seems to be the complete text but no pics. Some of the pics also appear in Google as separate search results, though.
The Internet Archive also has copies from several years, and a picture of your circuit. Other pictures are missing here, too.
http://web.archive.org/web/20160701000000*/https://atcaonline.com/ringercontrol.html