There are two reason for the older machines.

 

The main reason is what is known as the DV/DT.  In simple terms the inductance of the magnets slows down the current going through the coils.  This means the magnetic field takes a while to build up.   The higher the voltage, the faster the field builds up.  This happens several times for each letter. .  Some of the newer printers have a magnet of fewer inductance and a local loop to operate that.  They can work with a external loop of much lower voltage.

 

The other reason is on machines like the 15 printer it keeps the oil burnt off the contacts of the keyboard.

 

Ralph ku4pt

 

 

 

From: [email protected] [mailto:[email protected]] On Behalf Of David V. Corbin
Sent: Thursday, July 27, 2023 2:33 PM
To: William Wuttke; Windows XD
Cc: [email protected]
Subject: Re: [GreenKeys] Power supply recommendation

 

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?????

From: [email protected] <[email protected]> on behalf of William Wuttke <[email protected]>
Sent: Thursday, July 27, 2023 2:29:26 PM
To: Windows XD <[email protected]>
Cc: [email protected] <[email protected]>
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