[GreenKeys] Model 14/15 Selector magnet inductance

[Ralph Mowery]

I can not help with the 14, but the inductance for the 15 depends on which
set of coils are used.  There are the pulling magnets which use the larger
coils in series and have 4 henries of inductance and the holding magnets
which are 2 henries when in parallel for the 60 ma current loop.

Part of the problem could be the coil is not pulling the selector part in
all the way during the time the capacitor has lots of voltage on it.  Then
the holding voltage (current) would not be enough  to hold the selector part
in place for the other 20 or so milliseconds of the character.


> -----Original Message-----
> From: GreenKeys [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of
> John Nagle
> Sent: Wednesday, April 26, 2017 11:44 PM
> To: greenkeys at mailman.qth.net
> Subject: [GreenKeys] Model 14/15 Selector magnet inductance
> 
>     What's the actual inductance of the selector magnet on a Model 15
> and a Model 14? Are they the same?
> 
>     I've been working on a new driver board for 60mA Teletype machines,
> and while it works on one Model 15 I have, it doesn't work on two
> different Model 14 machines.
> The board works by charging up a 1uf capacitor to 120V during SPACE,
> using a custom switching power supply powered from a USB port. On
> transition to MARK, the capacitor is dumped into the selector magnet,
> and then a 12V supply provides sustain current.
> 
> Technical details of the new board at
> 
> https://github.com/John-Nagle/ttyloopdriver/
> 
> Scope trace of current and voltage into selector magnet:
> 
> https://github.com/John-Nagle/ttyloopdriver/issues/4
> 
> 
> 			John Nagle
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