Re: [smartBridges] 18v power?

[Brian Winter]

Noted and thanks. So fwiw:

 

Volts    Ohms   Metres     Feet
13       2.86    12.70    41.66
14       5.71    25.40    83.32
15       8.57    38.10   124.98
16      11.43    50.79   166.65
17      14.29    63.49   208.31
18      17.14    76.19   249.97
19      20.00    88.89   291.63
20      22.86   101.59   333.29

 

The 48v PoE must work by current sensing and adjusting the voltage applied to suit the DC resistance.  This is smart (sic) as it will take all the other factors into consideration, incl temp variations of cables and radio, different cable types and their DC resistance, whether using one leg or two (one or both ways), RJ45 connectors (and how corroded they are !)

 

I guess then in answer to a previous posting, sB do have a certified PSU for all cable lengths etc.  Moving on .....

 

 

 

Just for a laugh.  See how an 18v psu runs out of steam at <80metres/~260ft (ie <12v available at the radio).  This'll never get to 300ft max mentioned earlier.

 

Note: Don't take this too seriously (although this is the BEST it can get).  I've assumed the radio behaves the same throughout the range, and as already noted, thats not very likely - It'll probably "fry and die" if its asked to disipate an extra 2.41W of heat on the end of a short cable - Nice and cosy during the winter though.  Also taken no account of connectors etc

 

Volts  Metres   Ohms     Amps  [EMAIL PROTECTED]  Heat(W)
18         10   2.25    0.49    16.89    2.41
18         20   4.50    0.46    15.91    1.82
18         30   6.75    0.44    15.04    1.33
18         40   9.00    0.42    14.26    0.94
18         50  11.25    0.40    13.55    0.61
18         60  13.50    0.38    12.91    0.34
18         70  15.75    0.36    12.33    0.12
18         80  18.00    0.34    11.80 
18         90  20.25    0.33    11.32 
18        100  22.50    0.32    10.87 

 

----- Original Message -----

From: "John Banes" <[EMAIL PROTECTED]>

To: <[EMAIL PROTECTED]>

Sent: Friday, November 07, 2003 10:13 PM

Subject: Re: [smartBridges] 18v power?

> And it gets more complicated with Smartbridges. The older models used 2
> wires up and 2 wires down for power. The newer models use 1 wire for power
> and one wire for reset and 2 wires for return. They also have the new 48
> volt POE injector that is supposed to be able to sense cable length and
> supply the correct voltage to the radio irregardless of cable length.
>
> John
>
> ----- Original Message -----
> From: "Brian Winter" <[EMAIL PROTECTED]>
> To: <[EMAIL PROTECTED]>
> Sent: Friday, November 07, 2003 02:04 PM
> Subject: Re: [smartBridges] 18v power?
>
>
> > They can't "certify" this.  It depends on the cable you use and how good
> the
> > regulated supply is. Assuming a psu man enough for the task, Cat5 cables
> > will be similar so as a guide:
> >
> > Woodhead outdoors cat5 FTP and UTP 24 awg solid has DC resistance of 150
> > ohms/Km (at temperature +20C)
> > PoE uses 2 wires up, so half the resistance,  and 2 wires back, so double
> > that to get you back where you started.
> > APPO requires 350mA at 12v
> >
> > So working backwards, if you want to lose 1v (ie a 13v psu) at 350ma, you
> > need 2.86 ohms: thats 19.05 metres (62.49 feet)
> >
> > Heres the rest:
> > Volts   Ohms    Metres  Feet
> > 13      2.86     19.05   62.49
> > 14      5.71     38.10   124.98
> > 15      8.57     57.14   187.48
> > 16      11.43    76.19   249.97
> > 17      14.29    95.24   312.46
> > 18      17.14   114.29   374.95
> > 19      20.00   133.33   437.45
> > 20      22.86   152.38   499.94
> >
> > You can see why they don't bother quoting above 18v. 100+M of CAT5 is
> > getting a bit long !!
> >
> > In reality the APPO etc will have an on board regulator (they would be
> > unlikely to get it certified without), so there'll be some considerable
> > tolerance to this.  DC resistance of cable and power requirement of radio
> > will change with temp too.
> >
> > bw
> >
> > ----- Original Message -----
> > From: "Breiland, Derek" <[EMAIL PROTECTED]>
> > To: <[EMAIL PROTECTED]>
> > Sent: Friday, November 07, 2003 5:07 PM
> > Subject: RE: [smartBridges] 18v power?
> >
> >
> > > Exactly, hence the need for certification.  :)
> > >
> > > -----Original Message-----
> > > From: Hugh Carmichael [mailto:[EMAIL PROTECTED]
> > > Sent: Friday, November 07, 2003 11:01 AM
> > > To: [EMAIL PROTECTED]
> > > Subject: RE: [smartBridges] 18v power?
> > >
> > > My cable run is about 250 feet.  I ended up using an 18V adapter from my
> > > notebook PC.  The SB site says 15-18V for runs longer than 180 feet.
> > >
> > > My question is do you use 15V at 200 feet, 16V at 225 feet, 17V at 250
> > > feet etc.  It seems like a pretty big gap between 12V to 18V to allow
> > > for an additional 120 feet (to the max of 300)
> > >
> > >
> > >
> > > -----Original Message-----
> > > From: [EMAIL PROTECTED]
> > > [mailto:[EMAIL PROTECTED] On Behalf Of Breiland, Derek
> > > Sent: Friday, November 07, 2003 11:50 AM
> > > To: '[EMAIL PROTECTED]'
> > > Subject: RE: [smartBridges] 18v power?
> > >
> > > It would be really nice if Smartbridges were to actually certify at
> > > least
> > > one if not several power supply options.
> > >
> > > When we start talking about "be careful of the smoke" we are just
> > > guessing
> > > and in this business there is no room for guess work.  If we had a
> > > certified
> > > product recommended from Smartbridges I think we would all feel better
> > > about
> > > using it and in the event we needed support on a problem from
> > > SmartBridges
> > > we would know we are using certified equipment to rule that out.
> > >
> > > I am awaiting the release of the POE outdoor.  Even though I have no
> > > intentions on using it outdoors it does provide for a higher voltage
> > > level
> > > for long cable runs as well as some surge protection the way I
> > > understand
> > > it.  Not the cheapest solution but just like anything else you get what
> > > you
> > > pay for.
> > >
> > > Something bothers me about going out to the local Radio Shack for a
> > > power
> > > supply to run my AP's etc..  Not to knock Radio Shack but this is a
> > > situation that needs a commercial grade type solution, not an 18VDC
> > > power
> > > supply intended for the general public.
> > >
> > > -----Original Message-----
> > > From: John Hokenson [mailto:[EMAIL PROTECTED]
> > > Sent: Friday, November 07, 2003 1:29 AM
> > > To: [EMAIL PROTECTED]
> > > Subject: Re: [smartBridges] 18v power?
> > >
> > > Mouser Electronics....
> > >
> > > JH
> > > ----- Original Message -----
> > > From: "Jeremy Oswalt" <[EMAIL PROTECTED]>
> > > To: <[EMAIL PROTECTED]>
> > > Sent: Thursday, November 06, 2003 6:41 PM
> > > Subject: [smartBridges] 18v power?
> > >
> > >
> > > > Okay, I can't seem to find the articles in the archive concerning
> > > where to
> > > > get an 18v DC power supply that works with the Smartbridges.  I know
> > > > Smartbridges is coming out with one, but I can't wait another week.  I
> > > need
> > > > two for a 170' run.  Any recommendations?
> > > >
> > > >   _____
> > > >
> > > > Jeremy
> > > >
> > > >   _____