Completely Confused Newbie to Solar

WH6FQEWH6FQE Registered Users Posts: 27 ✭✭

I was in the process of setting up a 12-volt battery bank to operate my radios and emergency lighting during power outages, but everyone is talking me into changing it over to a 24-volt system instead. The problem is that I already purchased a lot of what I needed for the 12-volt system and was just about to start assembling it, so I am trying to not waste anything. 

Mind you, the guys that are trying to get me to change over to a 24-volt system instead of a 12-volt system are the same guys that are wanting me to set up a 14-volt system using combinations of 6-volt and 8-volt batteries and use the solar panels without any charge controller on it, so I am not putting much stock in anything they are telling me.

I currently have 12 6-volt Trojan T-105 225Ah batteries, all of the connecting cables to connect either a 12-volt or 24-volt battery bank, 4 100 watt 12-volt solar panels, 100-feet of 10 AWG solar cable and MC4 connectors and crimper, a Renogy Advanced Rover Li 40 Amp 12V/24V DC Input MPPT Solar Charge Controller, a Spartan Power DC Meter Battery Monitor & Multimeter (0-100A 6.5V-100V DC) with 100A Current Shunt.

My question is, would there be any way of me being able to utilize the 12-volt 100 watt panels if I set the batteries up as a 24-volt system or do I have to start over again trying to get 24-volt panels?



  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭

    Welcome to the forum

    There are advantages to using higher nominal voltages, usually related to minimizing parallel battery strings, conductor sizing and antisapated loads. When building a system it is best to calculate the loads and the required run time, from this the battery bank capacity is determined, then the charging source.

    Obviously there is grid available so the calculation would include the ability to change with grid power, using solar to supplement charging, and or, power loads during outages.

    With 12×6V batteries the string count would be 3 in a 24V nominal system, about the maximum desirable, so if possible use 24V, the 100W panels could possibly be wired in series as long as the combined voltage VOC is within the MPPT controller's maximum allowable input voltage at the coldest recorded temperature.

    What is the distance between the array and controller?

    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • SurfpathSurfpath Solar Expert Posts: 439 ✭✭✭

    12 6-volt Trojan T-105 225Ah batteries, all of the connecting cables to connect either a 12-volt or 24-volt battery bank...

    You seem to have pulled the trigger on a lot of equipment, including a lot of batteries. Before you choose the nominal size for your battery bank or buy anything else:

    Do you really only want to power some radios and emergency lighting? If this is so, estimate your loads. Then match your loads to a balanced battery bank / panel set up, allowing for 2 days of poor sun.

    12 Golf cart batteries entails a lot of energy storage. You will likely need way more panels than 400watts to keep these batteries happy. But, not knowing your loads, do you even need so many batteries in the first place?

    A good loads estimate is the cornerstone to a balanced happy system.

    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.
  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin

    What 12 VDC voltage do you want to feed your radios... Most that I have seen require at least 13.8 VDC to output rated transmit power.

    An off grid Flooded Cell Lead Acid battery system will generally see a battery bus voltage between 10.5 and 15.5 volts (from "dead" to equalize charging/charging a battery bank at near freezing temperatures).

    There are lots of 13.8 Volt HAM power supplies (AC to DC, and DC to DC buck+boost switchers, etc.).

    Gets into the whole losses/practical wiring questions of using a DC to DC switcher vs an AC inverter or Inverter to DC power supply.

    Another method that has been done is to setup solar for your main 24 volt (or higher) battery bank, and use an MPPT solar charge controller (or other DC to DC buck switcher) to down convert from (a variable) 24 volts to 12 volts and hold the 12 volt battery at 13.8 volts for float charging. And you still have the 12 volt bank for backup power if something failed on the 24 volt side.

    As always, actual power usage matters when designing the system... A 100 Watt transmitter will draw ~200 Watts or ~14.5 amps @ 13.8 volts. And most of the time, you are probably listening 95% of the time and only transmitting 5% of the time.

    This MorningStar MPPT 15 amp Solar Charge controller has been used in the "24/12" volt battery setup:

    You have competing requirements here (what the batteries need vs what your transceivers need)--But you are correct that you need a solar charge controller of some sort to keep the battery bank(s) "happy". Generally, you can only run "regulator free" at 1% of rated charging current for flooded cell lead acid batteries ("float charging"). Anything more than ~2%, you run the risk of damaging the batteries and possibly even boiling them dry and starting a fire.

    Generally, recommend a 5% minimum rate of charge for sunny weather/weekend/seasonal usage systems. And 10%-13% rate of charge for full time off grid usage (i.e, 200 AH battery, 5%=10 amps minimum, 10%=20 amps nominal).

    The solar array suggested for your 12x 6 volt 225 AH battery bank:

    • 12 * 7.8 volts charging * 225 AH capacity * 1/0.77 panel+controller deratings * 0.02 rate of charge = 547 Watt array "float" (not cycling)
    • 12 * 7.8 volts charging * 225 AH capacity * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,368 Watt array minimum
    • 12 * 7.8 volts charging * 225 AH capacity * 1/0.77 panel+controller deratings * 0.10 rate of charge = 2,735 Watt array nominal
    • 12 * 7.8 volts charging * 225 AH capacity * 1/0.77 panel+controller deratings * 0.13 rate of charge = 3,556 Watt array "cost effective" maximum

    A 5% rate of charge array for a fixed array in Pearl City Hawaii (69 degrees from vertical) is 4.84 Hours of sun minimum (December):

    • 1,368 Watt array * 0.52 off grid system eff * 4.84 hours of sun (Dec) = 3,443 WH per average December day
    • 3,443 WH per day / 13.8 VDC battery bus = 249.5 AH @ 13.8 VDC per December day

    Anyway--Some guesses and suggestions from my side.


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • WH6FQEWH6FQE Registered Users Posts: 27 ✭✭


    The solar panels will be set up within 10 feet of the controller and as far as the controllers maximum allowable input at the coldest recorded temperature, the coldest ever recorded temperature was a bitter 58 degrees, so I don't think cold is going to be a concern.

    So the largest the system should be is 3 sets of 24v batteries? I was planning on doubling the system capacity within the next month or so.

    I handle all ham radio intercontinental message traffic for the National Traffic System and Radio Relay International throughout the Pacific and Asia, so I have to have my multiple radios and computers available 24/7/365 even though we have frequent power outages. I want to be able to run indefinitely off-grid with it for disasters.

    I will also be installing a 400 watt wind turbine to assist the solar panels with recharging the batteries as soon as I can source the required mast for it which I have not been able to locate yet. No one want s to ship it to me.



  • WH6FQEWH6FQE Registered Users Posts: 27 ✭✭
    edited March 2019 #6


    If I keep the system as a 12-volt system, then I would only operate the 8 radios and emergency LED lighting on it, but if I can take it to a 24-volt system I would consider including an inverter so that I can also operate my two tower computers and 7 LED widescreen monitors as well instead of trying to "make due" with 2 laptops to do everything that I have to do.

    Also, as I was telling mcgovern above, as soon as I can get my hands on a suitable mast I have a 400 watt wind turbine sitting here as well that would be feeding into the system. I will be adding on additional solar panels as well.



  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin
    edited March 2019 #7


    You really need to measure your average (and peak) energy usage. Laptops are 30 watts or less... Desktop computers can draw upwards of 300 Watts each (tower running flat out, monitor, etc). Running 24x7:

    • 2x 600 Watts * 24 hours per day = 28,800 WH per day = 28.8 kWH per day
    • 28.8 kWH per day * 30 days per month = 864 kWH per month

    That is what a normal house uses in a month in North America (~500 to 1,000 kWH per month is "average").

    The solar array to run that would be (off grid):

    • 28,800 WH per day * 1/0.52 off grid system eff * 1/4.84 hours of sun per day (Dec) = 11,443 Watt Array "break even"

    Just guessing--But this is not going to be a small system.


    PS: I would suggest not even thinking about the wind turbine yet--Get the rest of the system designed first and only add the turbine as a "Freebee"--Wind is usually a "difficult" item to justify.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • WH6FQEWH6FQE Registered Users Posts: 27 ✭✭


    Ok, I am going to have to sit down and digest all of that information as the majority of it went way over my head, lol.

    Yes, the majority of the radios are mainly receive only with a very limited duty cycle. One of the VHF radios at 35 watts and a 100 watt HF radio are the main workhorses of the station and have a higher duty cycle. The HF especially in disasters where it is used to pass traffic back and forth to the Continental US, Australia, and Asia. In non-disaster times its normal duty cycle is about 90% receive and 10% transmit. Last year there were several times when it saw duty cycles of almost 50/50 for several days at a time with the volcanic eruption, severe flooding and multiple hurricanes that we experienced. As traffic is forwarded into my station via the VHF radio it is then re-transmitted back out over the HF links.

    I do have a 40amp 24-volt to 12-volt DC step down converter that I was planning on using for the 12-volt equipment if I was able to take the system up to a 24-volt system.

    It looks like I need to keep the battery capacity where it is and increase the solar panel and wind turbine capacity at this point.

    As for the solar panels, they would not be stationary, I am able to reposition them as needed throughout the year as the sun changes to get the maximum that I can from the sun.



  • WH6FQEWH6FQE Registered Users Posts: 27 ✭✭


    Unfortunately each of my MacBook Pro laptop chargers are 85 watts. They are power hogs.

    The Mac Pro tower is allowed to go into sleep mode when it is not being actively used at night, the HP Z400 Workstation tower is not. According to the spec sheet it is a 400watt. It has the digital node links to various stations around the world and has to remain on to maintain those connections around the clock.

    Once this station was installed my monthly electric bill skyrocketed, so no, it will not be a typical small system.

    I forgot to mention that I do also have a pulse desulfanating charger/maintainer/conditioner for the 12-volt batteries, but if it changes to a 24-volt system I would need to replace that with a 24-volt version, which they also have available, it just isn't in stock until next month.

    As for the wind turbine, I already have that sitting here ready to go, just waiting on locating a mast for it. Here in Hawaii we get a lot better results from wind turbines than most do on the mainland because we have the constant Trade Winds. Most Ham's here use wind turbines instead of solar panels because of that. When we set up mobile stations for parades, marathons, and other public service events, we generally use home-made wind turbines to power our stations with. The one I will be putting on this system is a commercially made turbine though as I did not want to trust my DIY turbines for this expensive of a system.

    When I was on the mainland, wind turbines were basically useless, but they do a really good job here.



  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin

    Generating power is generally a game of numbers (sorry for the math--But it does work pretty well at sizing a system for a "known" set of loads).

    Regarding wind turbines, in general, you are doing really well if you can harvest 10-15% or so of nameplate rating. There are a few major offshore (Europe 20-25%+??? as I recall) that can do. If we assume that your turbine will do 15%, then:

    • 400 Watts * 0.15 of name plate * 24 hours = 1,440 WH per day (1 year average)

    Just to "break even" with one 300 Watt tower system and 400 Watt wind turbine (assuming 15% of nameplate);

    • 300 Watts * 1/0.15 nameplate = 2,000 Watts of nameplate wind turbine to "break even" with tower computer (no inverter+battery losses included).

    And in the case of small wind turbines (not utility scale), a well made DIY wind turbine is probably better than most any you can buy (unless that has changed recently with higher grade systems).

    Looking a wind speed average--Seems like 10-12 MPH in decent months average wind... But really need know the V^3 average... Energy harvest from a wind turbine goes with the cube of the wind speed. Most horizontal axis wind turbines seem to start outputting around 10-12 MPH (on a good size 30'+ tower in "clean" / non-turbulent airflow).

    I would highly suggest that you get some numbers from somebody that has a Watt*Hour or Amp*Hour meter installed on their system and take, at least, monthly system readings and see what they actually produce.

    Today, there are a "ton" of WH meters with very pretty displays:

    You can get some pretty nice meters in the $20-$50 range--Put one on the source (wind turbine), and another on your loads--And see what is really happening.

    For AC, just a simple Kill-a-Watt or similar meter will do fine on your 120 VAC loads:

    Just measure 24-72 hours (1-3 days of typical usage) and see how many WH you actually need for each major piece of gear.

    Regarding Pulse Desulfators... Some people swear by them. Others find that they do not really do anything. We have seen a few installations here where the desulfator created enough electrical interference on the battery bus that it confused a couple MPPT type charge controllers (they generated more energy over the day if the desulfator was off). In times past, the desulfator threads were the only ones that I have had to lock because people were so "excited".

    The rating of a laptop computer power brick is not really too useful for calculating WH/kWH used per day. The compute may use 30 Watts, but take 85 Watts when running and charging the laptop battery at the same time.

    Of course, I do not know what you are using the tower computers for--But if just data logging and such, you might want to try and borrow a laptop (windows/Mac/Linux/etc.) and run it at low power (low clock speed, use one of the, smaller, computers) and see if it can keep up with the load. If the screen is too small, getting an LED HDTV might be a cheap/low power way to get big screen performance with 8-10 Watt draw.

    Anyway, the long way around is that energy conservation is going to be key to avoiding spending a huge amount of money on Wind+Solar+Genset backup power.

    At a starting point, a 3.3 kWH (3,300 WH or ~ 239 AH @ 13.8 volt) system is what I would aim for as a first time DIY type system (roughly a 2-3 kWatt maximum AC inverter/DC loading). That would be with a battery bank (flooded cell lead acid) that would be 2x your daily (no-sun) load and 50% maximum discharge (for longer battery life).

    And, at least at first, look at backup genset that can run for a week (or whatever is your need) when your HF transceiver/emergency traffic loads are.

    To size a battery bank large enough to run your "emergency loads" during a hurricane at full needed power (2x tower computers, HF transceiver running 50% transmit, etc.), this is a lot to expect from solar (and many wind turbines are designed for furl/brake at much more than 30 MPH)--Expensive, lots of maintenance, and "wasted capacity" for 95% of the year (solar is great for base loads--8 hour to 24hx7--Not very cost efficient sizing for 5% emergency outages--Unless it is what you need).


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin
    edited March 2019 #11

    I should also add... 12/24/48 volt battery buses are really based on the size of your loads and storage capacity of your battery bus.

    12 volts is popular for many portable devices. 24 volts can be found for many too.

    More or less, when you draw much more than 100 Amps from a battery bus, you really should look at going to the next higher voltage. For example

    • 100 Amp * 12 volts = 1,200 Watts (suggest 1,200 to 1,800 Watts for "12 volt bus")
    • 100 Amp * 24 volts = 2,400 Watts (suggest 2,400 to 3,600 Watts for "24 volt bus")
    • 100 amps * 48 volts = 4,800 Watts

    And there is looking at solar charge controllers... Roughly the major brands are limited to around 80 Amps +/- at 12/24/48 volts.

    A 10% rate of charge at 80 amps suggests an 800 AH maximum battery bank. If you want, for example, more than 80 amps, then you really need a second 80 amp MPPT charge controller in parallel output with the first one, to manage more charging energy. Paralleling charge controllers is not an issue... It is the $600 for a higher end controller that hurts.

    So, roughly the maximum suggested array for an 80 amp charge controller would be:

    • 80 amps * 14.5 volts charging * 1/0.77 panel+controller deratings = 1,506 Watt array (80 amps @ 12 volt battery bus)
    • 80 amps * 29.0 volts charging * 1/0.77 panel+controller deratings = 3,013 Watt array (80 amps @ 24 volt)
    • 80 amps * 58.0 volts charging * 1/0.77 panel+controller deratings = 6,026 Watt array (80 amps @ 48 volt)

    Going higher voltage on the battery bus (for larger systems) keeps wire gauges to a manageable size and allows sending power longer distance (greater acceptable voltage drop).

    However, if you are stuck with running 12 and/or 24 volt devices, then sometimes these things cannot be avoided.


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • WH6FQEWH6FQE Registered Users Posts: 27 ✭✭

    OK, FINALLY, I was able to talk Renogy into shipping 4 of their 300-watt 24-volt solar panels to me. They won't be here for about a month since they are coming by container ship. The "International Shipping Charges" were almost half the cost of the panels, but at least I finally found someone willing to ship them to me here in Hawaii.

    Question, once the new 300-watt 24-volt panels come in, is there any way that I will still be able to use these 100-watt 12-volt panels to give me what little they can into the system on a separate charge controller until I can get more 300-watt panels to replace them with?



  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin


    Let's start with your battery bank and size the system using rules of thumb. And predict what the system can do.

    12 x 6 volt @ 225 Batteries. That would either be 2x 6 volt batteries in series (for 12 volts) and 6x parallel strings. Or 4x 6 volt batteries in series and 3x parallel strings for a 24 volt @ 675 AH battery bank.

    My preference is for the 24 volt battery bank. It will keep the copper battery bank+AC inverter input wiring much smaller and easier to terminate. 10% x 675 AH = 67.5 amp rate of charge.

    If you did this with the same batteries in 12 volt configuration, that would be a 1,350 AH battery bank and 135 Amps for a 10% rate of charge. Also, I suggest that you try to limit your battery bank parallel connections to a maximum of 3 parallel strings. You can do 6 parallel strings, but things can "go wrong" and require more maintenance and heavier main bus bar to manage this many strings.

    A good starting point is to size the battery bank (or your loads) to 2 days of storage (no sun) and 50% maximum discharge (avoid going lower state of charge very often--20% minimum state of charge very seldom):

    • 24 volts * 675 AH * 0.85 AC inverter eff * 1/2 days storage * 0.50 max discharge = 3,442.5 WH per day suggested average load
    • 3,442.5 WH per day / 24 hours per day = 143 Watt average load (24x7)

    As you can see, 24x7 loads can really "kill" an off grid power system (or run your utility bill way up). This is not really enough power to run a single tower PC 24 hours per day from a battery bank.

    Next, sizing the solar array to provide 5% to 13% rate of charge--With 10%-13%+ rate of charge suggested for full time off grid power:

    • 675 AH * 29.0 volt charging * 1/0.77 solar panel+controller deratings * 0.05 rate of charge = 1,271 Watt array minimum
    • 675 AH * 29.0 volt charging * 1/0.77 solar panel+controller deratings * 0.10 rate of charge = 2,542 Watt array nominal
    • 675 AH * 29.0 volt charging * 1/0.77 solar panel+controller deratings * 0.13 rate of charge = 3,305 Watt array "typical cost effective" maximum

    And then there is sizing the array for your loads... For a "base load" system, I would suggest only using a maximum of 65% to 50% of "predicted power" for base (24x7) loads. Use minimum of 4.84 Hours of sun for Pearl City Hawaii (earlier post):

    • 3,442.5 Watt*Hours per day * 1/0.52 off grid system eff * 1/4.84 Hours of sun (December) = 1,368 Watt array to support "break even" loads
    • 1,368 Watt array * 1/0.65 base load fudge factor = 2,104 Watt array (65% base load fudge factor)
    • 1,368 Watt array * 1/0.65 base load fudge factor = 2,736 Watt array (50% base load fudge factor)

    Looking at something around 2,542 Watt array (minimum rate of charge 10%) to 2,736 to 3,305 Watt array to support your system with significant margin of "safety" in December.

    This is a pretty conservative design that should reliably supply >3,442.5 WH per day with an approximate factor of 2x fudge factor for your solar array (provide more power during bad weather--less genset runtime; and provide more power during better weather).

    I am not saying that this is "the system" you need--Or even that it would meet your needs. Just showing the math behind the recommendations and were the "fudge factors" have been used. Of course, your design decisions may be different (use genset more, or even use utility power for much of your system power, and only use the battery+solar for times when you have lost utility power).

    As you can see, a conservative off grid system design, even this many batteries and solar panels yield an anemic 143 Watt 24x7 average output capacity.

    You could, for example, say that the battery bank only needs to supply 1 day of stored energy--And that will double your average output to 286 Watts (24 hours to 50% discharge level). And you could get another 1/2 day (down to ~20% state of charge) if needed (getting parts/fuel for genset). But there are drawbacks--It will take several days of full sun/no clouds to fully recharge an FLA battery bank that low.

    And regarding your question of mixing the 300 Watt and 100 Watt panels... You can put 2x 12 volt panels in series, with 2x strings in parallel with a PWM type charge controller. And for the 300 Watt panels, you would connect them in 2x series by 2x parallel (4x 300 Watt panels) and use an MPPT type charge controller (MPPT is a more expensive/capable solar charge controller). You can put 2 or more solar charge controllers in parallel to charge a single battery bank just fine.


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • WH6FQEWH6FQE Registered Users Posts: 27 ✭✭
    edited March 2019 #14

    Bill, For the second solar charge controller for the 100 watt panels I would need to use a PWM controller and not another MPPT controller?



  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin

    Yes, no "problem" with using an MPPT controller--MPPT controllers are more expensive.

    For example, with a MPPT controller (with the appropriate Vpanel input voltage rating), you can put the 4x Vmp~17.5 volt panels in series and have a Vmp-array~70 volts.

    And a 400 Watt array on a 24 volt battery bank would need a minimum of:

    • 400 watts * 0.77 panel+controller deratings * 1/29 volts charging = 10.6 Amp minimum output rated MPPT controller

    I would guess that this is about the smallest quality MPPT controller with Vpanel-max=100 volts that would work for the above array:

    I am not in the solar business (and have never used/reviewed solar products), so if anybody has feedback on this (or other) smaller MPPT controllers, please feel free to comment.


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • littleharbor2littleharbor2 Solar Expert Posts: 1,626 ✭✭✭✭

    Morningstar makes high quality small MPPT controllers

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 540 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • WH6FQEWH6FQE Registered Users Posts: 27 ✭✭

    Well, I accidentally purchased a 40amp MPPT controller when I was wanting to order a 100amp version, so I will have the 40amp as a spare, I was hoping to use it for the 100 watt panels. It is able to do either 12-volt or 24-volt.

    However someone just let me know about another problem that I am going to have with the MPPT controllers, apparently they create RF noise right in the frequencies that I need to have available for my radios, so that is going to be a huge problem that I did not consider.



  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin

    A 40 Amp MPPT controller will work fine... You have to watch the Vpanel max input voltage (Voc-cold--In Hawaii, "cold" is not usually a solar panel issue unless you are in the high mountain(s)).

    For example, a 24 volt battery bank should have Vmp-array, at least, 1.3x the battery charging voltage:

    • 30 Volts (charging) * 1.3 = 39 volts Vmp-array minimum

    Two of your panels in series is (probably) 2x 17.5 volts = 35 volts. Generally, this means your MPPT controller is really behaving more like a PWM type controller. So, for "12 volt" panels, on a 24 volt battery bank, you really need 3x in parallel (Vmp-array~52.5 volts).

    And, many (lower capacity, imports) MPPT controllers have a maximum input voltage of ~70-72 volts. Your panels are probably around 21 volts Voc--3x 21 volts Voc = 63 volts (and in sub freezing climates, Voc and Vmp can climb as much 1.25x Standard Temperature rating). Higher end "typical" MPPT controllers run around 140-150 Vpanel maximum input rating).

    So, if your controller is not >~70 Volts Vpanel-input rated, then you can only put 3x of your 12 volt panels in series, leaving 1x unused panel. With PWM controllers, you would have 2x in series by 2x parallel strings and use all 4x of your panels.

    HAM and off grid solar power--Another $64,000 question. Yes, MPPT controllers and AC inverters can have tweeters at HF frequencies (in FM bands, RF noise is not as big of problem).

    The typical suggestions. No long loops of cables (unless you wrap them in a figure "8). Twisting cables to reduce differential noise.

    And a "trick" we used to pass FCC Class A and B, is to use at least 10' of shielded cables from noise sources. The capacitance tends to shunt RF energy back to the chassis of the source (shield/conduit needs to be connected/grounded to source chassis). Over 10' of shielding, does not do much more to reduce RF emissions.

    Using small 0.001 and 0.1 Ceramic or similar high frequency capacitors across DC outputs and inputs (to reduce differential noise). Lossy Ferrite Beads and Cores around cables to kill common mode noise--All can help.

    Watch for "slot antenna". Roughly a 1/4" slot can transmit a 1 GHz signal. Short with copper foil tape or similar. If I recall correctly, most signals under ~180 MHz come from I/O and power cables. Over that, slot antenna tend to be the radiation source.

    In the Old'en days, there were people (Mfg'rs) who believed that Off Grid solar products did not need to meet FCC Class A/B requirements. And there were only a couple of US mfg. who did go for Class A/B ratings for their products. So--Checking for FCC markings on the products was another method of finding "quieter" controllers and AC inverters.

    Here is a 10 year old discussion about HAM and charge controllers--Back then, there was only only manufacturer in the US that had FCC A/B... The Xantrex now Schneider MPPT XW MPPT 60 (60 amp) controller.

    Today, there are others (Schneider Morningstar units are FCC class B):

    I have talked with friends (HAM) that said they could hear a Prius coming a mile away on their HF sets. And the new hybrid cars seem to be dumping the AM radio because of self generated noise (and Europe is getting rid of AM band, and less than 20% of US drivers listen to AM... So it is claimed):


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • WH6FQEWH6FQE Registered Users Posts: 27 ✭✭
    edited March 2019 #19

    I checked the specs for my 40amp MPPT charge controller on the manufacturers website and it shows:

    Max Solar Input Voltage: 100VDC

    So, I think that is what you were talking about, deciding if I could use 3 or all 4 of the 12-volt panels.

    By the way, here is the page for the controller that I have:



  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin

    Yep, you got it.


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • WH6FQEWH6FQE Registered Users Posts: 27 ✭✭

    Ok, I think I may have finally figured out how to lose my HP tower computer and switch everything over to a laptop instead. I tried using a Dell Lattitude computer, but it was dismally small and way too slow to work for my needs. Its comical 2GB RAM and 80GB hard drive were definitely not going to be a replacement for my Z400 Workstation, so I switched over to a Dell Inspiron with 16GB of RAM and a 1TB hard drive which I am already running on a 12-volt cigarette lighter plugin. I will swap out the plugin for Anderson Power Pole adapters just like all of my radios and emergency lighting is as I get everything ready to add it to the system permanently.

    I ordered 3 refurbished 19" Jensen 12 volt TV's so that I am not wasting power or creating heat converting to the correct power for the LED monitors that I used on the tower computer. I also picked up 3 Diamond USB Display Adapters that will allow me to run the three monitors from the laptop USB ports. I can even go up to a maximum of 6 monitors if I need to in the future, but I highly see that being necessary.

    Since I will be able to have 3 monitors on the laptop now, I can get by with using just the laptop during power outages and not have to have the MacPro and its 3 monitors on the battery bank. That alone will save me a fortune in solar parts, lol.

    I also ordered the Kill A Watt and a AC/DC Digital Clamp Meter to start adding everything up with. One of the 24v to 12v DC/DC converters that I ordered arrived yesterday, the other one was back ordered and supposed to be here around April 2nd.

    Even though they are not due for delivery until Thursday, both of the dual-fuel 2200-watt generators that I ordered arrived on the island yesterday. Hopefully, UPS will go ahead and deliver them on Monday. FedEx is normally the only one that will make me wait until the scheduled delivery date before they deliver items here. I still don't like the idea of having fuel stored in my garage for the generators, but at this point I am not seeing a feasible alternative.

    I feel like a plan is slowly starting to come together.

  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin

    You may want to look for an SSD (silicon storage device) or similar.

    Hard drives are very slow (relative to memory chips). If your operating system and or database in the electronic storage, it may speed up your tower tremendously (if your programs are file intensive).

    As always, backup what you cannot afford to lose (hard drives tend to throw errors and lose a little bit of data. SSD and similar, tend to work great, then dead).


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • WH6FQEWH6FQE Registered Users Posts: 27 ✭✭

    The drive in the laptop I am using now is a 1TB solid state drive. I lost everything a couple years ago when a regular hard drive crashed that was unrecoverable. I then switched to using solid state drives and I also started using an online service to automatically backup my files everyday for all of my computers and laptops. A few months ago it happened again to another computer. I was able to have them overnight a new drive that already contained all of my files on it that I just swapped out. It was a life saver. I also keep my important files backed up locally on a removable solid state drive.

  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin

    Sounds like you have a good handle on what you are doing with your computers.

    One other caution... An off grid Deep Cycle Lead Acid storage battery bus can range from 10.5 to 15-16.5 volts (Dead to Charging-Equalization).

    Many "12 volt" car adapters are designed (it seems) to run from ~11.5 to 14.5 volts. We have had a few reports here of "12 volt car" to laptop computers have failed when the battery voltage approached 15.0 volts or more.

    Having spare "DC power bricks", using DC to DC converters (to 13.8 volt stable power), or using a small/efficient DC to AC inverter--And run the standard 120 VAC computer power bricks--And let the AC inverter (which usually is designed to run to 15.0 and others to 16.5 volts) "buffer" the your electronics from the deep cycle battery bus.

    If you are already using a 24 to 12 volt down converter for your 12 volt stuff--Then there should be no issue.


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • WH6FQEWH6FQE Registered Users Posts: 27 ✭✭

    Yeah, I ordered 2 of the 24v to 12v DC/DC converters but only received one so far. I just got an email today that the other one will be shipped out earlier than they originally told me, so hopefully I will have it before the end of the week.

    I have 2 identical 50amp adjustable power supplies. On one of them I am planning on putting my VHF/UHF, GMRS, and CB radios, scanner and LED lighting. My HF radio, laptop, and monitors will be connected to the other one.

    Each power supply is then connected to one of the battery isolators to allow for auto switching between AC and DC as needed, and then the 24v to 12v DC/DC converter and finally the battery bank.

    At least in my head that setup should work.

  • WH6FQEWH6FQE Registered Users Posts: 27 ✭✭

    Ok, the second 24v to 12v DC/DC converter came in today along with the 12v monitors for the laptop so I can get started on the computer changeover.

    I also now have a pair of 4,000 watt duel fuel generators on the way and should be here in a couple weeks. With 4 generators now I am trying to decide which generator I will use where, but I have a backup for both the 4,000 and the 2200 watt versions now. The only thing that I don't like about the 4,000 watt generator is that it is a standard generator and not an inverter generator like the 2200's are. I will have to "condition" the power with something before I can use it on my computers and sensitive electronics.

    I also ordered a GenTent so that I will be able to run the 4,000 watt generator outdoors in a storm if necessary. It covers the top and sides of the generator and protects the electrical connections from rain while it is running, supposedly it is designed for winds up to 70MPH, so about when it starts to get fun here, lol.

    I'm going to put one of the 4,000's on my lanai padlocked with a heavy chain to the railing right at the front of my house next to my radio room. If the HOA doesn't like it, we will just have to fight it out. I may mount the other one in my cargo trailer that sits in my driveway directly under my radio room. They are 90 pounds each, so if I need to switch from one to the backup, I won't be able to just pop downstairs and carry it up here real quick. With it being down there I can just unplug the extension cords from one generator and toss them over the lanai railing to the other generator and plug them in.

    I am still hoping to work out the solar system so that I won't need to use the generators, but they are there just in case so I sleep better at night now, at least until the wife figures out that I have bought 4 generators in the past two weeks. Not sure how my sleep will be after that, lol.

  • WH6FQEWH6FQE Registered Users Posts: 27 ✭✭

    I decided to fight my HOA and install a fuel storage shed outside as far away from the house as I can. It's not quite far enough away, but it's better than nothing. I will store the gasoline cans and propane tanks in it instead of the garage. It has only been there one day and they have already noticed it. I saw their inspector standing out on the sidewalk this morning taking photos of that area of my yard. I will get another one of their nice "love letters" in the mail in a few days, then the battle begins.

    I had to fight them tooth and nail for my greenhouse for several years before they finally gave in. The only reason they caved was that my greenhouse is used to grow my medical marijuana plants which the state allows me to grow for my severe migraines. I let them know that the plants will be grown on my property, they can either let me keep them out of view inside a greenhouse or have them out in the open for everyone to see. I guess they didn't want everyone seeing them, lol.

    I'm going to fight for the fuel storage shed for the safety concerns of my family. I have a Fire Chief willing to write a letter to the HOA Board if necessary explaining the safety reasons for using the shed instead of an attached garage for fuel storage.

    Will have to see how it goes.

  • VicVic Solar Expert Posts: 3,112 ✭✭✭✭

    Hi Robert,

    The following DIscussion touches on a number of issues with RFI from MPPT Charge Controllers,   etc

    You might find that DC - DC converters make as much,  or more noise than do MPPT CCs.

    Common-Mode RF chokes can be quite effective for quelling RFI from these devices.

    73,   Good Luck,     Vic

    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • WH6FQEWH6FQE Registered Users Posts: 27 ✭✭


    Great, so in other words, I have set up my system now to create noise and keep me from using my radios, which was the purpose of setting the system up in the first place?

    i had no idea the 24v to 12v converters were going to make even more noise. Since I switched everything from my 12v system over to a 24v system now I have no choice but to use them because EVERYTHING I have runs on 12 volt.



  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin

    They may make more noise... It all depends on their design (and many are open frame switching supplies--You may find you need to make a metal enclosure for them if the noise is a problem.

    And for DC, common mode chokes are what normally are spec'ed (both wires go through choke, wired in the same direction).

    Single wire chokes don't usually work well for DC power circuits--Most magnetics (lossy ferrites) that are generally available staturate over a few Amps of DC current.

    Wrapping both +/- wires the same way through the choke--The opposite current flow creates zero magnetic field (self canceling) and work well at reducing the RF noise.


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • VicVic Solar Expert Posts: 3,112 ✭✭✭✭

    Hi Robert,

    We have set up tow off-grid sites for HF Communication.   We took a number of precautions in designing the systems.  Teses systems  have minimal  RFI on the HF bands.

    If there ever is some interference (a birdie),   The Charge Controllers can be shut off for some period of time,  if necessary.

    As noted in that previous Link,   separating antennas from the PV modules,   run AC cables underground,   and use either common mode chokes or LC filters on these cables. all have a great benefit.   This is all touched-on in that long Linked Discussion.

    DC-DC converters can be noisy,   but should respond well to common mode chokes.

    For VHF/UHF radios,   FCC Class B CCs and Inverters can well have loser Emissions,    in these frequency ran,   as  Class B Radiated  Emission testing begins at 30  MHz,   for devices which do not connect to the AC power lines  --  like CCs.

    FWIW,   fear not,   almost all of the RFI Reduction techniques a straight forward.   73  GL   Vic

    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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