[GreenKeys] Power supply recommendation

[Nick England]

A good question. High voltage with a current limiting resistor is used to
overcome the inductance of the selector magnets and make the selector
armature move quickly enough. Inductors resist a rapid change of current
and the time constant is proportional to L/R, so a larger R means quicker
movement.

There are transistorized selector magnet drivers using a lower magnet
voltage, but 120vdc with 2000 ohms in series is the most common setup.

On Thu, Jul 27, 2023 at 2:32 PM David V. Corbin <
david.corbin at dynconcepts.com> wrote:

> Just curious. Current loop
> Is fixed current (or open) so the need for voltage is dependent on the
> loop resistance as per Ohms law… so given that most modern installs are
> “short loop” (ie often in the same room), why the need for something that
> can supply that much voltage?????
>
> Get Outlook for iOS <https://aka.ms/o0ukef>
> ------------------------------
> *From:* greenkeys-bounces at mailman.qth.net <
> greenkeys-bounces at mailman.qth.net> on behalf of William Wuttke <
> wcwuttke at gmail.com>
> *Sent:* Thursday, July 27, 2023 2:29:26 PM
> *To:* Windows XD <antech6586856 at gmail.com>
> *Cc:* greenkeys at mailman.qth.net <greenkeys at mailman.qth.net>
> *Subject:* Re: [GreenKeys] Power supply recommendation
>
> I would recommend picking up a TU. You will probably want to print ITTY at
> the very least. Most TU's have an internal 60 ma loop supply except for the
> HAL ST-8000 and 8000A. Keep checking eBay. Some can be had very reasonably.
> 73,
> Bill
> KE3BK
>
> On Thu, Jul 27, 2023 at 11:17 AM Windows XD <antech6586856 at gmail.com>
> wrote:
>
> I’m very new to teletypes, and I want to get my model 19 running. I’ve
> done the hard part of cleaning, but now I need a 120VDC 60MA power supply.
> Is there any that you would recommend?
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-- 
Nick England K4NYW
www.navy-radio.com
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