I remember some TVs had a warning sticker on the back about hot chassis.
I had a big home made discharge probe thingy. Couple pieces of broom stick
for handles.
Bored through the middles for a wire. Bare wire sticking out the ends.
One to chassis and slide the probe wire up under the anode rubber thingy and
POW.
Picture tubes didn't bother me so much but caps had more of a wallop.
They would blow sparks and bits of molten wires etc.
In college we had these nice lab benches with switched outlet strips built
in.
Some joker would plug in an electrolytic cap now and then and wait for some
poor unsuspecting soul to switch on the power.
Lots of noise, confetti, smoke and flying cap shards.
Always wondered how toxic the smoke was.
-----Original Message-----
From: Ken Hohhof
Sent: Friday, August 19, 2016 6:05 PM
To: af@afmug.com
Subject: Re: [AFMUG] 48v and -48v
Around 1976 I worked for a company that made OEM TV sets for Sears and
KMart. We never had one with a hot chassis, I would have remembered that.
I do remember that one of the high voltage designers electrocuted himself.
At home. On his ham radio setup.
I never got used to discharging the second anode on the CRT. 25 kV is
scary. CRT is a capacitor and holds a charge, as do triplers. As do
electrostatic voltmeters. But that 2 kW ham radio amp had lots of voltage
and current available. Stopped his heart. He was able to tell his wife to
call 911 but they were too late.
-----Original Message-----
From: ch...@wbmfg.com
Sent: Friday, August 19, 2016 6:41 PM
To: af@afmug.com
Subject: Re: [AFMUG] 48v and -48v
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
