I have a set of PTP820S to deploy. Both ends of the link have +48vdc power plants. Is there a way i can power these radios via positive DC? I know the DC input requires -48 so could i use something like the DC to RJ45 adaptor (C000000L184A) in the POE port to make this work? I’m planning to run fiber for the data due to high RFI from an FM station.
I am guessing you already received an answer somewhere else on this. Do you still need an answer? I think one of the documentation sources has information about powering the 820 S/C units using redundant capable POE injectors that can handle one or even two -48v sources but DO NOT mix and match -48 with say +24 with one injector. It also appears the 850 C documentation has information about a newer but much more expensive at least with some sources that are marketed towards the 850 S/C without the redundant option. If you check with suppliers and they don’t readily have the Cambium-branded units Ceragon-branded ones can also be used.
If you want or need to run something like a 10 gauge cable to power the unit I don’t know that using that part wouldn’t work but why not go directly to the DC inputs instead?
Also, consider things like how heavy the gauge of cable is and make sure you are working to handle grounding issues especially if you are powering these one way or another with heavier gauge cable that isn’t twisted than Cat5/6/7’ish cables would have as the risks of higher amperage change with higher gauge cables.
Those would be some of my thoughts but again I’d suggest reading documentation and checking with your supplier(s) to get their input.
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Thanks hammer185, The question was more about the actual voltage and if there was a way to power the radios with +48 instead of -48 vdc. The injectors that they offer are stupid expensive and if they only take -48 vdc then that does me no good. If they will take +24 then i can at least work with that using a buck converter. What I’d really like to do though is send dc voltage directly to the dc input on the radio and pull the power directly from my exiting +48vdc power plant. So far I haven’t been able to get a straight answer about it.
Yeah, I see in my answer I accidentally wrote -48 when I intended to write +48 concerning your question. My understanding from documentation is that there is a range of voltages that these particular radios can be powered by and that would include +48. I have used both +24 and +48, sometimes directly off larger battery arrays that have a range of voltages depending on charging algorithms and things like temperature with fusing or breakers, and sometimes with products such as Tycon and others offer that can take a voltage range and output a stable voltage output.
I cannot spend a lot of time on it today, but I’ll try to point out the parts of the documentation that point out the voltage ranges from memory. I think the documentation used something like +/- X to +/- Y where my memory is the explanation I got perhaps from Last Mile Gear and others way back and perhaps also confirmed and clarified more by Connectronics and probably Cambium too was that that means either + X volts to + Y volts as a range or - X volts to - Y volts where X and Y represent the respective low and high numbers. This is likely wrong as I don’t remember right now, but say for example X was 22 and Y was 60 concerning + in this scenario that would imply +22 to +60 where +48 is in that range.
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Thanks for clarifying. I tried a meanwell +48vdc power supply on the bench yesterday and it powered the radio right up. Then, I took it out to our testing tower, mounted it to a dish, installed it on the tower (at 6’), hooked it up to the +48vdc power plant, and got nothing… the negative side of the tower power plant is connected to earth ground and the tower is grounded. Perhaps the grounding of the power and/or the radio chassis is whats causing the radio not to power up when on the tower, but its fine on the other supply.
EDITED:
It looks like there may be what is often referred to as a positive ground system common in many telecommunications systems, oddly, often abbreviated - 48 v when 48 volts, but not to be confused with the negative post on a battery. I came across this article on a Newmar page yesterday - “Negative” 48 Volt Power: What, Why and How | Newmar Powering the Network.
That may help. Abbreviations can get confusing when + 48, as another example, could mean something like the positive post on a battery array, an overall designation generally for a nominal voltage 48 volt system that is a common negative ground as opposed to the often - 48 v telecom positive ground, or the positive terminal in something like the meanwell power supply.
Also, the Newmar article mentions these concerns and others. There are times when an expected “red” cable would normally be hooking into a terminal with a “+” indicator but isn’t. On top of that, if at a site one company is trying to use a positive ground system and another a negative ground system, and their steel racks are interconnected and not isolated, that can cause problems.
We can be thankful for things such as many radio systems and other hardware not failing if the + and - are switched. If I remember right, many of the early POE systems would fail if someone accidentally miswired the pairs.
If you are at a location with a site manager or other users, making sure you agree about how to ground and how different grounding methods create voltage potentials between devices is a good thing to consider. One user at a site using a 24v DC negative ground system, another using a 48v DC positive ground system, and another using AC power, and how they handle grounding can become problematic. Especially if a company is being set up as a future scapegoat that must have something like a $5 million insurance policy and no guidance at all about how they should handle grounding is provided.
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