[GreenKeys] Loop power supplies

[drlegendre .]

I made my own 120V / 60mA supply from a cheap, extremely common 28V / 1A
control transformer. The key here is to wire the transformer with caps &
diodes as a voltage +tripler+ (google it). For me, this yields just a bit
over 120V DC which I limit to 60mA with a 2K / 25W resistor.

Technically, a 10W resistor is OK, but they get awfully hot. I use a 25W
Dale in a finned aluminum case which is mounted to the chassis of the
supply and even that makes a fair amount of heat. You can also use a 24V
transformer. The voltage will be around 105V DC, which is still way, WAY
more than enough for the kind of work we do.

On Sat, Mar 3, 2018 at 3:12 AM, Paul Birkel <pbirkel at gmail.com> wrote:

> A previous thread on the topic suggested a pair of 48VDC supplies in
> series as being more-than-adequate for use-cases involving local-loops.
>
>
>
> Some inexpensive examples (Hengfu):
>
>
>
> http://www.mpja.com/48V-057A-25W-Power-Supply-Hengfu/
> productinfo/17325%20PS  ($15)
>
> http://www.mpja.com/48-Volt-Power-Supply-08A-40W-
> Switching/productinfo/16004%20PS  ($16)
>
> http://www.mpja.com/48-Volt-Power-Supply-13A-60W-
> Switching-Hengfu/productinfo/16009%20PS  ($20)
>
> http://www.mpja.com/48-Volt-Power-Supply-22A-100W-
> Switching-Hengfu/productinfo/16016%20PS  ($26.50)
>
>
>
> I have no personal experience to offer.
>
>
>
> *From:* greenkeys-bounces at mailman.qth.net [mailto:greenkeys-bounces@
> mailman.qth.net] *On Behalf Of *Jordan Spencer Cunningham
> *Sent:* Saturday, March 03, 2018 3:52 AM
> *To:* Green Keys
> *Subject:* [GreenKeys] Loop power supplies
>
>
>
> For those of you who have aftermarket ~120-150v DC power supplies for your
> loops, can you share where you got them? If something is commercially
> available at a reasonable price, I will elect that route, but I'm still
> interested in custom designs. I've read of a very simple one I may try if
> nothing else.
>
>
>
> I have an original 20ma loop power supply built into my Model 19 table,
> but I'd like to get more compact versions for mobility's sake. Plus I'd
> like to be able to operate more than one loop at a time.
>
> I've been doing research on regulated supplies from parts stores like
> DigiKey, Jameco, and Mouser, but there's unfortunately not much that meets
> the necessary criteria that I've been able to find. Acopian makes more
> obscurely voltaged supplies like this, but not for less than $200.
>
>
>
> Thanks much.
>
>
>
> --Jordan
>
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