Author Topic: Intercoms--Suggestions Appreciated!  (Read 8587 times)

Offline stopthemachine

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Re: Intercoms--Suggestions Appreciated!
« Reply #30 on: March 01, 2011, 02:22:26 AM »
Maybe DavePEI will see this and comment. Didn't someone determine that old cell phone chargers have very well filtered DC battery? I think Dave used some to power his magneto phones. Old cell phone chargers are usually easy to locate.

Terry
That sounds interesting, Terry.  It seems like everyone has at least 4 of these that aren't needed anymore too.  That'd be perfect.  :)

Offline DavePEI

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Re: Intercoms--Suggestions Appreciated!
« Reply #31 on: March 01, 2011, 06:02:07 AM »
Maybe DavePEI will see this and comment. Didn't someone determine that old cell phone chargers have very well filtered DC battery? I think Dave used some to power his magneto phones. Old cell phone chargers are usually easy to locate.

Terry
That sounds interesting, Terry.  It seems like everyone has at least 4 of these that aren't needed anymore too.  That'd be perfect.  :)

What it is is that modern flat cell phone supplies are switching supplies. They don't contain more filtering, but the switching design of the supplies, puts the hum at a much higher frequency than the 60 cycle hum you get out of an older cell supply.

The two types I use are Motorola SPN5185A (5 v), and the SPN4278D (4.4 v) - I got a real deal on a bunch of these. However, I am sure practically any of the flat style switching supplies will work.

Any noise they make is well above the frequencies you can hear in the receiver. I have eight or nine of them providing power for the magneto sets in the museum, and one for the switchboard. Each set will require its own supply.

Dave
« Last Edit: March 01, 2011, 06:16:46 AM by DavePEI »
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Offline stopthemachine

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Re: Intercoms--Suggestions Appreciated!
« Reply #32 on: March 01, 2011, 08:57:18 AM »
Maybe DavePEI will see this and comment. Didn't someone determine that old cell phone chargers have very well filtered DC battery? I think Dave used some to power his magneto phones. Old cell phone chargers are usually easy to locate.

Terry
That sounds interesting, Terry.  It seems like everyone has at least 4 of these that aren't needed anymore too.  That'd be perfect.  :)

What it is is that modern flat cell phone supplies are switching supplies. They don't contain more filtering, but the switching design of the supplies, puts the hum at a much higher frequency than the 60 cycle hum you get out of an older cell supply.

The two types I use are Motorola SPN5185A (5 v), and the SPN4278D (4.4 v) - I got a real deal on a bunch of these. However, I am sure practically any of the flat style switching supplies will work.

Any noise they make is well above the frequencies you can hear in the receiver. I have eight or nine of them providing power for the magneto sets in the museum, and one for the switchboard. Each set will require its own supply.

Dave
Interesting--how do you connect them to the phones and intercoms? 

Offline DavePEI

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Re: Intercoms--Suggestions Appreciated!
« Reply #33 on: March 01, 2011, 09:52:03 AM »
Interesting--how do you connect them to the phones and intercoms? 

Just take off the ends, and connect the power leads from the charger to where one would normally attach the battery...

You may have to use a multimeter to identify the output leads of the charger...
The Telephone Museum of Prince Edward Island:
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Offline stopthemachine

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Re: Intercoms--Suggestions Appreciated!
« Reply #34 on: March 01, 2011, 10:08:41 AM »
It's times like these that I wish I were more mechanically inclined. Haha.  Hmmm... anyone care to simplify this for the electronically ignorant such as myself?

Offline stopthemachine

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Re: Intercoms--Suggestions Appreciated!
« Reply #35 on: March 02, 2011, 08:57:41 PM »
Interesting--how do you connect them to the phones and intercoms? 

Just take off the ends, and connect the power leads from the charger to where one would normally attach the battery...

You may have to use a multimeter to identify the output leads of the charger...
Dave, is there any chance you have a picture as to what this set up looks like?  (A cell phone charger connected to an old magneto...or better yet, intercom phone.)  I'd really like to try this soon, but I'm scared I'll mess something up or cut the cell phone charger wrong. 

Offline DavePEI

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Re: Intercoms--Suggestions Appreciated!
« Reply #36 on: March 02, 2011, 11:52:12 PM »
Interesting--how do you connect them to the phones and intercoms?  

Just take off the ends, and connect the power leads from the charger to where one would normally attach the battery...

You may have to use a multimeter to identify the output leads of the charger...
Dave, is there any chance you have a picture as to what this set up looks like?  (A cell phone charger connected to an old magneto...or better yet, intercom phone.)  I'd really like to try this soon, but I'm scared I'll mess something up or cut the cell phone charger wrong.  

Well it is so simple, a photo wouldn't help. Find out first where you need to attach battery to the phone. That will have to come from its own schematic. Cut the connector off the cord, find the two power leads with a voltmeter (most have a sensing lead) then connect the negative to the negative on the phone, and the positive to the positive. You need a charger for each phone. As far as cutting the charger wrong, just clean cut off the plug, then strip the wire back a couple of inches...

Dave
The Telephone Museum of Prince Edward Island:
http://www.islandregister.com/phones/museum.html
Free Admission - Call (902) 651-2762 to arrange a visit!
C*NET 1-651-0001