There is a reason. If you have a fault in a buried copper telephone cable,
if a conductor is -48 to ground, electrons will flow out of the fault and
ions will flow in. The wire will actually get larger due to electrolysis.
If you have +48, the copper wire would copper plate the surrounding earth.
And of course the wire would go away.
-----Original Message-----
From: Dennis Burgess
Sent: Monday, May 2, 2022 4:02 PM
To: AnimalFarm Microwave Users Group
Cc: Chuck McCown
Subject: RE: [AFMUG] -48vdc site
So, this is interesting thread, my question is why?
What is better -48 or +48? Or any of those options. Why does telcom
standardize on -48? There has to be a reason?
Dennis Burgess, Mikrotik Certified Trainer
MTCNA, MTCRE, MTCWE, MTCTCE, MTCINE, MTCSE, HE IPv6 Sage, Cambium ePMP
Certified
Author of "Learn RouterOS- Second Edition”
Link Technologies, Inc -- Mikrotik & WISP Support Services
Office: 314-735-0270 Website: http://www.linktechs.net
Create Wireless Coverage’s with www.towercoverage.com
-----Original Message-----
From: AF <af-boun...@af.afmug.com> On Behalf Of Chuck McCown via AF
Sent: Monday, May 2, 2022 2:25 PM
To: AnimalFarm Microwave Users Group <af@af.afmug.com>
Cc: Chuck McCown <ch...@go-mtc.com>
Subject: Re: [AFMUG] -48vdc site
+ goes to +
- goes to -
Always.
Giving something -48 means you have grounded the + side of the power supply.
Giving something + 48 means you have grounded the - side of the power
supply.
Giving something 48 might mean neither side is grounded and it is a floating
power supply.
Some devices use chassis ground in common with the power input. If a device
grounds the negative side of the power input internally, then it will need a
positive or floating supply.
If a device grounds the + side of the power circuit internally then it needs
a negative or floating supply. Lots of telecom gear is in this category.
If you take a device and measure each side of the power input to ground, and
find continuity from + or - to the chassis, you need to match that to the
polarity.
If you measure it and find no connection to the chassis, there is a chance
it does not care. However powered off continuity measurements could change
with power on. If you have it powered on on the bench and measure from the
chassis to either side of the power input, and get a strong reading matching
the input voltage on one of the leads, the the input of the device is
definitely using the chassis as a ground. The ground can be positive or
negative, whatever the designer decided it was.
But you can still run -48 devices off of floating 48. And you can run them
off of +48 under certain circumstances.
1) You have to insulate the chassis from ground. Best to put a warning
sign on it that the chassis is hot.
2) It cannot have any external connections that contain a chassis
connection like a coax with the shield connected to the chassis. A CAT5
cable drain wire would also short it out. As would most POE configurations.
If it is a router, in a plastic box, without POE connections, you might get
away with it.
-----Original Message-----
From: Christopher Tyler
Sent: Monday, May 2, 2022 1:08 PM
To: AnimalFarm Microwave Users Group
Subject: Re: [AFMUG] -48vdc site
So when I hook that up to -48vdc, do I just give it -48 or do the leads need
to be reversed?
--
Christopher Tyler
Senior Network Engineer
MTCRE/MTCNA/MTCTCE/MTCWE
Total Highspeed Internet Solutions
1091 W. Kathryn Street
Nixa, MO 65714
(417) 851-1107 x. 9002
https://imsva91-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=www.totalhighspeed.com&umid=DA1B4682-DE0E-8C05-B4D1-EEC052AE5800&auth=079c058f437b7c6303d36c6513e5e8848d0c5ac4-1b5009a16c4202d4b572fc090c86aa255586d48f
This institution is an equal opportunity provider and employer.
Esta institución es un proveedor de servicios con igualdad de oportunidades.
----- Original Message -----
From: "castarritt" <castarr...@gmail.com>
To: "AnimalFarm Microwave Users Group" <af@af.afmug.com>
Sent: Monday, May 2, 2022 1:58:47 PM
Subject: Re: [AFMUG] -48vdc site
I asked this list the same thing a while back and the answer was
Meanwell RSD-500C-48. You can probably get away with a lower power
rating than the
500
watt I chose if you are only powering a 'tik and not a pile of Cambium
radios like I was.
On Mon, May 2, 2022 at 1:48 PM Christopher Tyler < [
mailto:ch...@totalhighspeed.net | ch...@totalhighspeed.net ] > wrote:
Need some help from the smarter than me electrical engineers here on
the list...
What is the best way to power a Mikrotik router that takes +18-56vdc
from -48vdc source? Providing part numbers or model numbers would be
greatly appreciated.
We tried the redneck engineering approach of just reversing the
polarity and it popped the fuse, nice little light show, but
ultimately unproductive.
--
Christopher Tyler
Senior Network Engineer
MTCRE/MTCNA/MTCTCE/MTCWE
Total Highspeed Internet Solutions
1091 W. Kathryn Street
Nixa, MO 65714
(417) 851-1107 x. 9002
[
https://imsva91-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=http%3a%2f%2fwww.totalhighspeed.com&umid=DA1B4682-DE0E-8C05-B4D1-EEC052AE5800&auth=079c058f437b7c6303d36c6513e5e8848d0c5ac4-8afeff0d3de40be7cc2ad8e7616a489241467f52
|
https://imsva91-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=www.totalhighspeed.com&umid=DA1B4682-DE0E-8C05-B4D1-EEC052AE5800&auth=079c058f437b7c6303d36c6513e5e8848d0c5ac4-1b5009a16c4202d4b572fc090c86aa255586d48f
]
This institution is an equal opportunity provider and employer.
Esta institución es un proveedor de servicios con igualdad de
oportunidades.
--
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