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  • Radio repeater site

    I have a small solar job and thought I'd post my calculations here if anyone might want to help double check. It's a 12V radio repeater that uses 12W 80% of the time and 250W 20% of the time.

    For energy use I come up with (0.2 hours x 250W) + (0.8 hours x 12W) = 60 Wh per hour or 1,440 WH per day.

    Since it's used for public safety radio, I'm thinking ten days of autonomy instead of 5, so 14,400 KWh battery, or 1200 Ah at 12V.

    With an MPPT charger and 3 "sun hours" per day in the winter, the 1440 WH/day needs 720W of panels.

    There will be a 15 KW propane generator with at least two 500 gallon tanks.

    Does this look good? It's a mountain top radio site that gets snowed in for several months of the year.

    Thanks for any feedback!

    Steve

    Steve Dold
    Say NO to useless over-quoting

  • #2
    Why such a big generator?

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    • #3
      There's a 48V system that it also needs to back up.
      Steve Dold
      Say NO to useless over-quoting

      Comment


      • #4
        Steve you know who to ask, I have only done a few hundred radio sites, so what do I know huh?

        You are on the right track but throw away most guidelines you see used here for domestic applications. This is Mission Critical where you want 99.99% availability, not 80%.

        OK you are right, 10 days antinomy is crucial for mountaintop repeater. So with 1440 wh you are looking for a 14,400 wh battery capacity and at 12 volts is 14,400 / 12 volts = 1200 AH. Definitely 2 or 4-Volt battery territory. Highly suggest a Trojan IND23-4V a 4 volt 1270 AH battery with 8 full year warranty and no real PSOC operation issues.

        OK throw away all the rules of Sun Hours and all that other garbage. Will not work with 10-day antinomy. You are shooting for a C/10 charge rate. That would be 120 to 130 Amps x 13 volts my friend. Yep 1500 to 1700 watts with 2 expensive 60 to 80 amp Charge Controllers. Note if you use 5 day mentality here, your charge rate will be to low of around C/20. Not acceptable. Yes you will be over powered exactly as planned. You can go 5-days without Sun or a Generator, and just one day of Sun gives you 2 to 3 days of run time depending on time of year.

        Plan B would be my plan so to include your 48 volt battery, just use a 48/12 converter unless Positive or Negative ground gets in the way. Still requires the same size 14,400 wh battery and panel wattage but at 48 volts is 300 AH battery and only a single 30-Amp to 40-Amp Charge Controller. More than enough cost offset to pay for a good 48/12 converter. Good battery candidate is Trojan IND9-6V.

        Last peice of advice is get a good energy management system. Something with some Smarts to control the genny remotely. With 5 days of no sun battery capacity, no reason to run generator until the end of the 5th day. Size genny to 1.5 times the Kw load of a 8 hour charger.




















        ind
        Last edited by Sunking; 08-11-2017, 03:49 PM.
        MSEE, PE

        Comment


        • #5
          Hey Dereck! So it looks like I was heading for C/20, I'm glad you caught that. I always miss something and that was it.

          Thanks for the tip on the Trojans. We usually buy Deka Unigy but I couldn't find a 2V 1200 AH cell. I don't want to use a DC converter but I don't want to mix the systems because the microwave serves more than just this site and I don't want one system to depend on the other. Plus the MW system is -48V and exists and I don't want to add loads to it.

          Steve Dold
          Say NO to useless over-quoting

          Comment


          • #6
            Originally posted by sdold View Post
            Hey Dereck! So it looks like I was heading for C/20, I'm glad you caught that. I always miss something and that was it.

            Thanks for the tip on the Trojans. We usually buy Deka Unigy but I couldn't find a 2V 1200 AH cell. I don't want to use a DC converter but I don't want to mix the systems because the microwave serves more than just this site and I don't want one system to depend on the other. Plus the MW system is -48V and exists and I don't want to add loads to it.
            You are welcome. Deka Unigy are great Station Batteries made for Standby Float Application. You know, everything runs off rectifiers 99.9% of the time or genny. Rarely are Station Batteries ever used and not designed or made to be cycled. They have more in common with an SLI battery including lead calcium alloy. You do not want that, you want a Industrial Grade Deep Cycle batteries, something you know will work for 10 years. Trojan Industrial line up, Crown Fork Lift batteries, Saft Fork Lift, or GB Fork Lift batteries. I have even used Rolls 5000 Series.

            Hard to go wrong with Trojan in CA as there are quite a few factory distributors scattered around CA. Warranty claims and service level should be high. Especially considering the client is the State.

            Yeah that is why I said Plan B. I kind of figured you wanted things with dedicated plants. Just do not forget the hierarchy. If you loose a LMR channel form low power is one thing, Loose transport and none of the rest of the equipment matters as it is all down without transport aka Cloud today.
            Last edited by Sunking; 08-11-2017, 06:47 PM.
            MSEE, PE

            Comment


            • #7
              Steve a couple nuggets if experience and wisdom you do not want to learn like I and other cell techs had to learn.

              I assume you radio techs and yourself are familiar with conventional Dc Power Plants made for Float Service. You know where the equipment runs on Rectifiers and the batteries Float their whole lives at 13.5, 27.0 and 54.0 volts right? Life is simple and easy.

              All that changes with Daily Cycle applications. Not only do the battery types change, but so does Charging and Maintenance and it will bite you in the butt. Float batteries spend their whole lives at Float Voltages. They never come close to GASSING VOLTAGE except maybe once a year if Equalized. Even then EQ voltage on a 12 volt Station battery is only 2.35 vps or 14.1 volts on a 12 volt battery. GASSING VOLTAGE is 14.2 and above.

              Guess where Daily Cycle batteries spend several hours everyday of their miserable lives? Yep above Gassing Voltage of 14.2 to 14.8 volts, and EQ at 16 volts. Life is a GAS when you get cycled every day using lots of WATER.

              The radio techs must make Battery PM a religion of at least every 4 weeks. Taking temps, SG, and voltage measurements followed by adding water, a good full charge followed with a EQ charge from time to time. They will need to watch SG and make seasonal Voltage Adjustments up and down with the seasons. Charging can be done remotely, but not PM. Trust me you do not want to learn that lesson in a year with a battery replacement. I all ready did it for you.

              I hope you are listening because I will only tell you once my friend. Don;t let a Radio Tech or failed Battery tell you again.
              MSEE, PE

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              • #8
                We used to use FLA but for the last 20 years or so we've only used AGM. Usually Deka Unigy, GNB, Absolyte. I was never involved much in battery selection but since many of the sites aren't accessible in the winter except by snow cat, that might have been why, although most of the sites do have AC power. Is there anything special we need to know about AGMs and solar that guys used to float service wouldn't expect?
                Steve Dold
                Say NO to useless over-quoting

                Comment


                • #9
                  Originally posted by sdold View Post
                  Is there anything special we need to know about AGMs and solar that guys used to float service wouldn't expect?
                  The reason I ask is that I assume what you said above referred to FLA.
                  Steve Dold
                  Say NO to useless over-quoting

                  Comment


                  • #10
                    Originally posted by sdold View Post
                    We used to use FLA but for the last 20 years or so we've only used AGM. Usually Deka Unigy, GNB, Absolyte. I was never involved much in battery selection but since many of the sites aren't accessible in the winter except by snow cat, that might have been why, although most of the sites do have AC power. Is there anything special we need to know about AGMs and solar that guys used to float service wouldn't expect?
                    Steve first thing is Deka/East Penn, GNB, Absolyte and others like that make very good Commercial/Industrial battery manufacturers. Just about every cell phone tower and mountaintop repeaters use VRLA aka AGM batteries. However there is an issue as already discussed. Most are Station Batteries, not Deep Cycle. Just make sure the batteries you buy are Deep Cycle.

                    As for using AGM, well no problem, they make deep cycle AGM's as long as you can afford it. Why use AGM? Well they do have a place and one of the justifications is Cold Harsh environments like a Mountain Top repeater only accessible by Snow Cat or Helicopter in winter.

                    Take a look into Concorde PVX series of AGM batteries or SBS
                    Last edited by Sunking; 08-13-2017, 11:46 AM.
                    MSEE, PE

                    Comment


                    • #11
                      I didn't realize there was as much of a difference in the types for different service, I'll take a look at the Concordes.
                      Steve Dold
                      Say NO to useless over-quoting

                      Comment


                      • #12
                        What about using a MPPT controller to maintain 12v float from the 48V bank, if that's the one the generator backs up? or do you need totally redundant redundant systems ?
                        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                        solar: http://tinyurl.com/LMR-Solar
                        gen: http://tinyurl.com/LMR-Lister

                        Comment


                        • #13
                          Mike, not a bad idea but at this site the MW battery is sized for the system and I can't add this much load to it.

                          In general we run completely separate systems so that one won't take down the other. For example, if the base stations running on the 12V system start using a lot of power, either through a lot of use or one of them going into key down mode indefinitely, we don't want it to affect the microwave system because at most of these sites the microwave is part of a backbone that serves a lot of other sites. Having the 12V loads drawing off the 48V system makes the 48V load somewhat unpredictable, because while the microwave draws the same current 24/7 regardless of use, the 12V varies with the amount of use.
                          Steve Dold
                          Say NO to useless over-quoting

                          Comment


                          • #14
                            Originally posted by sdold View Post
                            In general we run completely separate systems so that one won't take down the other. For example, if the base stations running on the 12V system
                            Well for one, you got that right. Transport has higher priority than local area service. It is one thing to have a town area OOS, vs a Sate Wide OOS.

                            What I always disliked about LMR was the selection of 12 volts for both mobile and station equipment. I understand why so they are interchangeable with each other. Makes it much easier and less expensive on the manufacture if both mobile and base stations are the same radio. 12 volts makes things restrictive and expensive in a Base Station Application like a Repeater. Example at 12 volts, you are pretty much limited to 100 watts TX Power. I know in Business bands repeaters can run on 100 and up to 250 watts. 250 watt units required 120 VAC supply because it requires a RF Tube operating at several hundred volts DC. 24 or 48 volt base radios would be nice, and then you can run 250 to 500 watts on Solid State.

                            When you move to the Commercial side of cellular telephones, today their equipment works on both 24 and 48 volts. New generation 5G only uses 48 volt. Well heck today the radios are not in the Equipment Shelter. Cellular and Microwave Carrier is moving out of the Equipment Shelter to on top of the Radio Tower with the Antennas called RRH (Remote Radio Heads). No coax at all in the Shelter. Just a short jumper at the top of the tower. All the radio needs is DC Power and a pair of fiber optic cables. For power they take 48 volts, and convert it to 130 volts DC. Nokia RRH use 48 volts, but limits maximum height. They use 6 AWG which is expensive and heavy, but even 6 AWG is limited to 200 feet 1-way cable distance. To get above 180 feet requires a higher voltage.

                            If I were a young man again in this day and age, I would start a new business I know would be a cash cow. Moving all that equipment out of the equipment shelters and up on a tower, eliminates the cell site technician job load and jobs. They cannot climb towers, they have to hire a contractor to climb towers to repair and replace the equipment. Tower crews today cannot keep up as there is not near enough of them or have the training. Anyway so I won't do it, but I gave my Son a company to run and told him to add it on. Doing quite well.
                            Last edited by Sunking; Yesterday, 04:44 PM.
                            MSEE, PE

                            Comment


                            • #15
                              Dereck, there sure are a lot of entities like PG&E ditching their 6 GHz space diversity systems and going to tower-mounted spread spectrum unlicensed microwave. The microwave is turning into a black box (actually tan or beige) hanging on the back of a single 2ft dish. The microwave techs are going the way of the TV repairman. The part that amazes me is that it all works. For public safety we still use the big 6 GHz radios for the backbones, but they aren't as big anymore. Now they are just 2' or rack space, and that includes the MUX. I think you are right, the old guys are running out of work and the young guys that don't mind climbing are just changing parts. It sounds like your son is in a good field at just the right time.
                              Steve Dold
                              Say NO to useless over-quoting

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