I was once told that the telco industry standardized on -48 but the cellular industry (and maybe cable companies) standardized on +24. I’ve been told a lot of wrong stuff though, and sometimes I mis-hear or mis-remember things.
I also remember when I was in the product design side of things there being some max voltage like 24 VAC or 30 VDC that let you use a Class 2 power brick and then your product didn’t have to meet the more stringent safety specs. It seems that an 802.3af POE would not be a Class 2 power supply. From: AF <[email protected]> On Behalf Of Chuck McCown Sent: Saturday, November 24, 2018 11:05 AM To: AFMUG <[email protected]> Subject: Re: [AFMUG] 48v Power Supply Switches Radios all have power RF amps and all semiconductor power amps I have ever seen use the chassis ground as RF ground and use a positive Vcc type of semiconductor. To DC isolate the RF grounds would be a huge PITA for RF designers. But the old big iron microwave stuff like Alcatel and Harris was all –48. Probably had DC-DC converters in its power supply. Our whole semiconductor world has been build around positive rails. I presume it dates back to NPN having some advantages over PNP or some such thing. Seems a bit odd as JFETs work well as vacuum tube replacements and they were almost all positive plate voltages. Even back in the vacuum tube days, vendors would ground the plates so they could power the tubes with –48 volts. From: Mathew Howard Sent: Saturday, November 24, 2018 9:58 AM To: AFMUG Subject: Re: [AFMUG] 48v Power Supply Switches I think it would be more accurate to say a lot of the equipment WISPs use, rather than ISPs... I don't see too many radios that require -48 (a lot, or even most appear to be able to handle -48v though), but it seems like rack mount stuff does tend to need (or at least tolerate) -48. On Sat, Nov 24, 2018 at 9:41 AM Chuck McCown <[email protected] <mailto:[email protected]> > wrote: I guess my experience is the reverse. Having spent 40 years in telecom, seems that almost everything rack mounted is –48 if you want DC power. I don’t recall ever finding +48 rack mounted telecom equipment. From: Ken Hohhof Sent: Saturday, November 24, 2018 7:43 AM To: 'AnimalFarm Microwave Users Group' Subject: Re: [AFMUG] 48v Power Supply Switches I have one site with an Eltek/Valere system and it does its job quite nicely, my question for you: how do you deal with the Eltek Systems mostly being designed for -48 yet a lot of the equipment ISPs use wants +48? My one Eltek site has an old Purewave WiMax basestation that I am about to decommission but I will need +48 and I don’t want to put in a DC-DC converter if nothing will be running off the -48. From: AF <[email protected] <mailto:[email protected]> > On Behalf Of Chuck McCown Sent: Saturday, November 24, 2018 8:13 AM To: AnimalFarm Microwave Users Group <[email protected] <mailto:[email protected]> > Subject: Re: [AFMUG] 48v Power Supply Switches +1 Sent from my iPhone On Nov 24, 2018, at 3:13 AM, Gino A. Villarini <[email protected] <mailto:[email protected]> > wrote: We go direct to Eltek/valere -48 system. It has redundant rectifiers, web/snmp and LVD Gino Villarini Founder/President @gvillarini t: 787.273.4143 m: <http://www.aeronetpr.com/> <https://www.inc.com/profile/aeronet> <https://www.facebook.com/aeronetpr/> <https://www.instagram.com/aeronetpr/?hl=en> <https://www.linkedin.com/company/aeronet-broadband-corp> <https://twitter.com/AeroNetPR?ref_src=twsrc%5Egoogle%7Ctwcamp%5Eserp%7Ctwgr%5Eauthor> <https://www.youtube.com/channel/UCr2Q9WBrAYVm3Fn970Jd6VA> <http://www.aeronetpr.com> www.aeronetpr.com | Metro Office Park #18 Suite 304 Guaynabo, PR 00968 From: AF <[email protected] <mailto:[email protected]> > on behalf of Alex Davidson <[email protected] <mailto:[email protected]> > Reply-To: AnimalFarm Microwave Users Group <[email protected] <mailto:[email protected]> > Date: Friday, November 23, 2018 at 11:13 AM To: "[email protected] <mailto:[email protected]> " <[email protected] <mailto:[email protected]> > Subject: [AFMUG] 48v Power Supply Switches Hey guys, we are stepping up to some 48v equipment on a tower and in looking into power supply switches. This seemed to be something that would work for us (Mean Well SE-1000-48). Any thoughts or pros and cons that yall have found with this unit. Any units of similarity that might work well in place of this one. Thanks -- AF mailing list [email protected] <mailto:[email protected]> http://af.afmug.com/mailman/listinfo/af_af.afmug.com _____ -- AF mailing list [email protected] <mailto:[email protected]> http://af.afmug.com/mailman/listinfo/af_af.afmug.com -- AF mailing list [email protected] <mailto:[email protected]> http://af.afmug.com/mailman/listinfo/af_af.afmug.com _____ -- AF mailing list [email protected] <mailto:[email protected]> http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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