TVs used to have a hot chassis. They were in a wooden box though...
-----Original Message-----
From: ch...@wbmfg.com
Sent: Friday, August 19, 2016 5:38 PM
To: af@afmug.com
Subject: Re: [AFMUG] 48v and -48v
I understand why an an engineer using a RF device would do that, they want
zero impedance from the RF ground to the rest of the world. You can still DC
isolate it but it takes a little bit of doing at microwave frequencies.
If you choose 48 volts as a design engineer, you are choosing a voltage that
historically has been -48 in the telcom industry.
I don't understand why a router designer would need to bond their logic
grounds to the chassis.
If it is phy isolated ethernet in and out, there is no problem in having a
hot ground plane with respect to the case of the device.
So, I guess you could make an isolated mount for MT routers...
-----Original Message-----
From: George Skorup
Sent: Friday, August 19, 2016 5:32 PM
To: af@afmug.com
Subject: Re: [AFMUG] 48v and -48v
Every MikroTik, UBNT and Canopy radio I've ever used bonds board/chassis
to ground. And those are definitely negative ground.
On 8/19/2016 6:27 PM, ch...@wbmfg.com wrote:
Are they truly +48 or just 48?
-----Original Message----- From: Gilbert T. Gutierrez, Jr. Sent: Friday,
August 19, 2016 4:42 PM To: af@afmug.com Subject: Re: [AFMUG] 48v and -48v
I looked it up, you are correct that everything you listed is +48v. The
CCR uses a bullet connector so there is no ground from the power source
but since it can also be powered via PoE, I expect it to be +48.
The site has a Dragon Wave and that old Cambium radio that are both -48v.
Oh the joys of moving away from AC power bricks to straight DC.
Gilbert
On 8/19/2016 1:16 PM, George Skorup wrote:
AF5 and 24's. Virtually any 802.3af or at device. Multiple MikroTik
products. Other UBNT stuff. I'm sure there's more.
On 8/19/2016 11:11 AM, Gilbert T. Gutierrez, Jr. wrote:
I believe both my Netonix Switch and Mikrotik CCR both are +48v.
Gilbert
On 8/19/2016 7:06 AM, Chuck McCown wrote:
Curious, what types of things use +48?
-----Original Message----- From: Gilbert T. Gutierrez, Jr.
Sent: Thursday, August 18, 2016 7:19 PM
To: af@afmug.com
Subject: [AFMUG] 48v and -48v
I have a site that I am converting to DC from AC. All of the gear
powers
at traditional 48v with a negative ground. I have a PTP800 though that
I
am told is -48v (ground tied to positive). How do I get -48v for the
PTP800?
The site has a NewMar DIN-UPS 48-10. It states that the outputs are
isolated (it has 2) but I do not think they are isolated from each
other, just from ground. To tell you the truth I am lost. I was
thinking
maybe a DC to DC converter of some sort.
Thank you,
Gilbert
