Solar Power Supply V3.0




Introduction: Solar Power Supply V3.0

After two previous generations of my Solar Power Supply receiving positive feedback on here and YouTube, I thought it would be time to share with you my third generation design.

Much like the previous version, this design improves from the second with a higher capacity battery bank, a more efficient charge controller, better electrical safety in terms of fuse implementation, more outputs and digital displays that show you just how much power is being generated and consumed.

So whether your after a solar power station yourself or are just interested in what's new this time around please read on...

Step 1: What Do You Need Your System to Do?

The first thing to plan is to work out what you will be wanting to power from your system, as mentioned in my previous Instructable, the whole of your house would be nice but seriously expensive and definately not portable. My system will only power small items such as an LCD TV, a couple of 12V energy efficient lightbulbs, a free-to-air receiver, a CD player and radio and to charge mobile phones and other miscellaneous items.

With your power intentions in mind it's important to now figure out the prices for each of the components, I wanted the best of the best so I settled for a top of the range PS-30M 30 Amp Morningstar Charge contoller from at £198.00 or $315.
This charge controller uses Pulse Width Modulation (PWM) to float charge the batteries once fully charged to maintain them whilst incorporating an LCD display to show the battery voltage and solar input current.
For the batteries I went for two Trojan T-105's, being six volts a piece to total 12 volts at 225Ah, this meant that the storage capacity of this bank would be huge, enough to power high drain devices for many hours.

With my two previous generations I used Maplin Electronics and Ebay to source all of my components but this time money wasn't as much as an object so I ended up splashing the cash on a multitude of sites.

The main items to power from the system are then used to calculate just how much power is needed and generated. The LCD TV and receiver draw 2.2 Amps DC on 12 volt, energy efficient lighting draws just under 1 Amp for a 12 watt bulb whilst the phone/GPS chargers draw very little power. Using the TV for say, 3 hours a day max would equal 6.6Ah consumed, lighting used for 4-5 hours a night would consume roughly 4Ah while all the charging of portable devices would be around 2Ah while pumps for air-beds wouldnt run for long so maybe only consuming around 1Ah, totalling 13.6Ah. Deep Cycle batteries shouldn't be discharged below 50% of their rated capacity, the smaller the discharge cycle, the longer the battery will last, therefore a battery of 30Ah would suffice. The UK receives on average 6 hours of sunlight per day during summer, which is the time of year we go camping, the main reason for building this system, therefore replacing 13.6Ah into a battery would take a 50W solar panel roughly 5 hours to recharge.

(Watts = Voltage x Amps)
(Average solar panel voltage at max power = 17 Volts)
(50 watts/17 volts = 2.94 Amps)

It's easier to draw power from a battery than to replace, requiring usually 10% more power to recharge than what was consumed, therefore:
(14Ah / 2.94 Amps = 4.76 hours of direct sunlight)
In a real world situation this will never happen due to too many different factors such as;
Solar panel shading,
Overcast conditions,
Battery temperature,
Size of wiring,
Other losses.

Therefore it's safer to use a larger battery bank, where power can be used up repeatedly if weather conditions the day after aren't suitable for efficient solar charging to completely recharge the battery. My 225 amp hours is way overkill but it's better to have more power than required.

I already had my solar panels from my previous solar power supplies consisting of two AKT 80 Watt solar panels, one BP 80 Watt solar panel and four BP 12 Watt panels totalling a theoretical 290 watts. All of my panels were sourced from eBay over the years.

Step 2: Plan What You Want...

The second step is to plan out what you want your final product to look like. I went through a number of different designs of which I drew up in Microsoft Word of all programs, this really helps you to see just what components will go where and helps to understand any design aspects that won't work.

In the previous versions I used blue LED volt and ammeters whereas this time I wanted a more useful way to show me how much power is being produced and consumed, therefore I ended up purchasing two Turnigy Watt meters, most commonly used for model airplane enthusiasts. These intelligent meters display voltage, amperage, watt-hours, amp-hours, minimum voltage and max amperage consumed and are perfect for use in an off-grid solar power system. I bought two from eBay at £30 a piece and will look great in my system. Using these I can monitor how many volts the solar array is producing aswell as how many watts and amp-hours per day, whilst the other meter shows me how many watts I'm using and have used since the meter was reset.

After many possible versions with components mounted in separate locations, external and internal battery banks and wider and slimmer designs for example, I finally chose the version with a sloped front, a vertically mounted charge controller and separate battery bank for ease of transportation.

I will be reusing the solar panels, Sony car radio, UK mains double gang faceplate, thermostat for the cooling fan and 600 watt mains inverter. With the addition of another cigarette lighter 12 volt output this version of solar supply will have three accessory sockets.

Step 3: Start Building...

The first step was to build the external battery box. 12mm thick MDF (Medium Density Fibreboard) was used for all of the construction and with the Trojan batteries totalling 56 Kilograms, plenty of bracing, heavy duty castors and handles were required in order to move the bank around.

The dimensions were measured up and drawn on a large sheet of MDF, were then cut out and constructed as shown in the images, the more bracing with pine wood the better.

So far so easy...

Step 4: The Main Unit...

Once the battery bank was constructed it was time to build the main unit. As before, a large sheet of MDF was laid out on the floor and the dimensions planned in Microsoft Word were sketched out on the sheet before being cut out in the garage with a wood hacksaw.

It's easiest to cut the longest straight lines first on the workbench, allowing the large piece of wood to be broken down into smaller more easily manageable pieces. Using a hacksaw was the easiest way of doing this although it meant tidying up the edges of the wood after cutting with some sandpaper. It could also have been done using a jigsaw, a lot easier and possible quicker but your lines won't be as straight.

Once all of the panels are cut-out its a case of matching the locations on your diagram and making sure that they're in the right place and are the right size. Once sure, use thicker pieces of wood, some 20mm by 20mm square of pinewood to use as the skeleton for the unit, holding it all together, using 30mm wood screws and a drill to make pilot holes this took no time.

Once the main wooden construction was complete it was time to mount all of the electronics. I initially started with the sockets on the front panel as they're the easiest to mount and wire up, including a two socket UK mains wall socket and three car accessory cigarette lighter sockets, the most efficient way to power devices, directly on 12 volt.

The next things I mounted were the switches, radio, charge controller and meters. The meters as supplied by Turnigy are enclosed in a plastic housing that is easily removed by taking out four little screws. The bare-bone meter is quite compact and is easier to mount in your own enclosure as all you need is a clear rectangular plastic window. The meter LCD's are soldered directly to the board meaning it is very good for incorporating into your own projects as there's no messing around with zebra strips contacting the pcb to the lcd with the products housing.

I used three millimetre plexiglass sourced from eBay for the meter windows. this was cut using a knife to scortch the plastic a number of times before snapping the piece off. This was mounted to the front panel with plenty of hotmelt glue and will not be budging from the case anytime soon.

The switches used this time are of a chrome metallic type. They are all double pole switches which allows them to be very handy for almost any project whilst the colourful LED ring is illuminated with 12 volts DC. I will go into the wiring diagram later on in this Instructable.

The charge controller is simply bolted onto the back panel of the unit with four 1/2 inch bolts, plenty of support is needed here as excluding the batteries, this component is the most expensive on this particular project.

The back of the unit is home to plenty of ports, eight in/outputs for the radio including 4x speaker outs, 2 pre-outs, 1 microphone in for the handsfree feature and 1 sub out for a subwoofer.

Step 5: Wire It All Up!

Once all of the external components are mounted exactly as you want them it's time to wire all of them up, and this is the long difficult bit, lets start initially with the batteries.

Power leaves the batteries in my case through a 50 amp car audio fuse which is the safety between the bank and the main unit itself. It would be pointless simply fusing the system in the main unit itself as if a short developed in the cable to the external battery bank, there could easily be a fire. The cable from the batteries is high grade multi-strand wire rated at 4 AWG (American Wire Guage), allowing the system to have a high capacity for discharge with cables allowing 50 amps to flow with ease, meaning a theoretical 600 watts may be drawn from the batteries safely.

Having the batteries constantly connected to the main unit would be a bit silly so therefore I used a heavy duty Anderson Powerpole connector that is rated also at 50 Amp which allows a quick disconnect to be able to transport the system to wherever it's needed, much easier than all the components and batteries at once which would be near enough impossible to lift using one person.

These cables enter the main unit at the back and go straight to an eight way fuse block which adds more safety to the system again, with the initial fuse in here being rated at 40 Amp, this is still alot of current capacity that can be used. Power then goes through a heavy duty car-style relay rated at 40 Amp which is used to totally disconnect all components through a single power switch, except from the charge controller that needs to be connected to the battery all of the time through a 30 Amp fuse and the car headunits constant power cable which is needed for the radio to retain all of its settings and memory, this time through a 15 Amp blade fuse.

Power is then fed to all parts that need it, the meters, the switches, the relays, radio, sockets, LED's and cooling fans. The eight fuses are as follows: one 40A as the main, three 10A fuses (one for each cigarette output), one 30A for the charge controller, one 15A for the solar input, one 15A for the radio and one 5A for the meters, fan, LED's and relays as they don't draw much power combined. The power inverter has its own fuses so doesn't have it's own fuse, it's still key that it shares the main power fuse for safety though.

There is plenty of wires in this solar supply and with the radio and inverter being powerful items, air circulation is a necessity and is provided by a 12cm green illuminated fan at the back of the unit. This fan is activated when the internal air temperature gets around 28 degrees Celsius and is activated by the battery powered central heating thermostat that was used in my last solar power box. It doesn't require powereing from the main system and with it drawing very little power, the batteries last a LONG time.

The Solar panel input is through the use of a Tamiya style remote controlled car battery pack connector which allows me to quickly and easily disconnect the solar array. This input is fused with a 15 Amp fuse before entering the charge controller, it's better to be safe than sorry.

One thing to note is that the Turnigy meters can be powered from the source they are measuring but also an external power supply so that they can measure down to 0.1 volts. The solar input meter must use a relay to disconnect the voltage measurement lead from the solar input when the meters are turned off, otherwise when the sun rises the voltage slowly climbs which illuminates the meter but is not instantly enough for the meter to boot up. The external power input is used via the use of a 12 volt DC to 12 volt DC converter which allows the meter to be used even when the sun goes down to provide statistics for energy produced during the day but also provide safety to not bridge the gap over the charge controller.

Please refer to the brief wiring diagram in the next step to see how all of the components were connected...

Step 6: Circuit Diagram...

This step includes a brief diagram to the wiring arrangement of my system, note the different thickness of power lines, the thicker cable carries more current than the thinner.

Step 7: Finishing Touches...

Once the majority of the project is complete it is time to make it look nice using labels. In my previous Instructable I showed you how I design my labels in Microsoft Word, print them out, cover them in sellotape then apply double sided sticky tape, this time I went the easier route of using my Brother label printer. While you can't include pictures and colour into your labels this way, it's much quicker and easier and I think looks better. Simply type your own label, with or without borders, styles or symbols, hit print, then cut the printed label to the correct size and stick on.

I purchased mine from, yes you guessed it, Maplin Electronics for £14.99 and is still available at that price with two tape cartridges at: (

Step 8: Improvements/Alterations

Under heavy discharge the battery voltage displayed on the meters and charge controllers LCD screen sagged a little by upto 0.3 volts, which is alot in terms of lead acid battery voltage monitoring so something had to be done about it. The easiest way to fix this issue was using a separate cable from the battery terminals and use them as the voltage sense source. Current isn't drawn by the system through these wires so their voltage doesn't sag under load.

I used two core mains cable, both wires fused in the battery box with a three amp fuse each before the cable terminates at the main unit through a locking-multipole connector available from Maplin Electronics at ( This allows me to easily disconnect the unit from the batteries easily, but also allows me to have a good reference voltage source to judge how charged my batteries are.

Another improvement I implemented was the addition of two bright white LED's, one for each meter as the standard blue ones make the displays quite difficult to read. Soldering the leads to the LED's before heatshrinking the whole LED except the lens output end allowed me to get the placement spot on behind the factory blue LED, a spot of Blu-Tac allowed me to position it before covering it in hot-melt glue. Two 1K Ohm resistors supply enough current limiting to the LED's to brightly light the displays to see easily with the eye from quite some distance away.

As in the previous solar box design I added the portable USB hard drive that stores over 20GB of music that I can search through on the Sony MEX-BT3800U headunit and allows the unit to act as a media center. Hard drive activity is indicated by the flashing HDD LED on the front panel just to the left of the meters which is transferred by a light dependant resistor circuit which you can find in my previous Instructable.

Step 9: Useability and Final Thoughts.

My system can provide alot of power once the sun has gone down. With the two Trojan deep cycle batteries I can easily power a 30 watt mains halogen bulb, the radio, a lava lamp and a subwoofer for the radio all night with ease. If these items are left on for around six hours the number of amp hours consumed is around 25Ah, whereas a possible 110Ah is available to consume (half of the batteries capacity). This system is the best one that I have built yet and wish to keep it in operation for years to come and not to upgrade to a better one after a year. The best thing is when I have my items running off of my solar power supply at night and then suddenly residential mains power goes down so everyone else in the neighbourhood is in the dark whereas I'm perfectly fine and quite often don't even notice that utility power has gone offline.

The only possible way I can think to improve on this design is to allow my battery bank and solar array capacity to grow as all of the components in the middle are fine as they are. O.k, maybe a pure sine wave inverter for any picky mains electrical items would be nice, although I've failed to find an appliance or device that won't accept a modified sine wave input.

However your off-grid solar power supply goes I wish you the best of luck with the design and manufacture, but remember, Have Fun!

Step 10: PICTURES!!

Here's a few pictures of my off-grid solar power system, I will hopefully put together a video sometime in the near future when I have time.  Well that's all for now, If you have any questions please don't hesitate to ask in the comments below and thank you for reading.

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    41 Discussions

    You said that "I wanted the best of the best so I settled for a top of the range PS-30M 30". Why didn't you go with an MPPT controller ( They'll harvest up to 33% more energy from your panels over a PWM controller.  Looks like a fun project though and I know what you mean about "admire my baby" as I have several projects of this nature although you've taken yours to a nice finished case and all.  Mine never seem to make it past the its working great stage but don't get the fit and finish job you've so nicely done with this unit.  Also with that box venting issue, you might consider a small say 20 to 40mm 12v fan and about 5 diodes in series to drop the voltage to the fan.  It will run very slowly except during peak charge voltage time when the batteries start to gas at the end of the absorb cycle and use almost no energy (about 250mw w/80mm fan).  You can always put a manual over-ride switch (SPDT) on the fan to remove the diodes and run full speed when you want extra venting and turn off the fan altogether for storage or when you just don't have a need for venting.  The fan will turn so slow most of the time that you won't hear it operating.  I use a similar setup for one of my whole house battery banks that is kept inside my garage (1300amp/hrs@12v).  It is vented to the outside using a clothes dryer venting kit modified with an 80mm 12v fan (computer case fan).  This way there is about zero risk of gasses building up and exploding.

    Cool Toy ......... enjoy

    1 reply

    Hello there,

    I just wanted a reasonable PWM controller as the energy increase using an MPPT controller isn't always as good as advertised. Sure if I had the funds to allow for a MPPT charge controller then fair enough, but my current PWM is fine for my needs, it beats my previous shunt style on-off regulators used in my previous supplies.

    Thanks for the comment,

    Nicely done.
    How much are you using the AC inverter? The crazy thing about AC is, of course, 99% of the time it gets converted to DC for use in the device. It would be easy enough to add a few DC-DC converters to replace wall-worts and other external AC adapters. Items that plug directly into an AC outlet would need to have their warranties voided by removing/bypassing their internal power supplies... but I'd think that would be more efficient overall? Maybe not. Plus, sometimes it's just nice to plug stuff into an AC outlet and not worry about it.

    1 reply

    Thanks :)

    I don't use the inverter that much as I know how inefficient converting DC-AC to DC again. That's why I have the three dc output plugs as I prefer to use DC over the inverter whether it's for charging phones, headsets, cameras, powering tv's, lighting, clocks or fans to name a few.

    Thanks for the comment,

    Oh, I love the wooden case you built for this! I have a small system I built when I lived in NM, and it's in an ammo box and an old steamer trunk I lined and vented. It works, but yours sure is prettier!

    1 reply

    Perhaps you have made a little "slip- up" in your instruction regarding lead acid battery maintenance. To check charge status, a HYDROMETER is used to test SPECIFIC GRAVITY, NOT A hygrometer.

    1 reply

    Aha, so I did, maybe I wanted to measure the humidity of the batteries though ;),
    Thanks for alerting me,

    Acid based batteries with vent caps can release hydrogen gas while charging. These are not like the sealed batteries used in UPSes and flashlights.

    Storing your batteries inside while charging can create a real explosion hazard.

    1 reply

    Yeah I know that they do, but only two batteries releasing a little hydrogen gas that floats as it's lighter than air in a well ventilated room in reality wont pose much danger, trust me I know enough about the hazards and risk assessment as I've just finished a three year course on risk management and assessment at university.

    Very nice system.

    Clearly this is something that has evolved over time.

    What would you say your total investment is ?

    Doesn't seem necessary to keep the battery right there in your living room. Seems like that could be kept out of the way like in closet, garage or basement & then only have the control unit in your living room. Looking at the setup i'm thinking thats more for vanity than practicality. I'm thinking you like having it all front and center so you can admire your "baby" and show off the system to your friends. Absolutly nothing wrong with that. ;)

    Nice job.

    3 replies

    Thanks :)

    This is the third version of my solar power supply, and if I do say so myself, the best one yet.

    If I built this version from scratch without using parts from my older ones I would say that it would cost me around £1000 ($1600). But seeing as I used my existing radio, solar panels and inverter I'd say that it cost me around £550 ($880)?

    It's for pure practicality that the battery sits next to the unit as running heavy grade DC cables from one room to another would not only be expensive but the voltage sag at the end of such a cable run wouldn't be worth considering. As you say, I like to admire my 'baby' whilst using it as a handy but heavy, bedside table ;),

    Thanks for the comment,

    How many AH are those batteries? They look huge.

    You should be able to run quite a bit more off your system. I used to have a 27" CRT running off my 45 watt system.

    Hey there,

    The batteries are rated at 225Ah, tonnes of power available for whenever I need it.

    Thanks for the comment,

    Very impressive.

    Shouldn't the the battery container be vented ?... (maybe I'm making a fool of myself by asking such a question … but then again … :D

    2 replies

    Ah whoops, forgot to mention about that :). Yeah the battery container has to be vented and I achieved it simply by drilling some 20mm holes in the back of the container in a line, one of which the main power wires come out of.

    If I discharge the system quite a bit during the night, upon reaching full charge the next day it is normal to hear the batteries bubbling and gassing when they approach full charge.

    Compared to the sealed maintenance free batteries used in my previous designs these batteries require occasional topping-up of distilled water whilst more than occasional battery monitoring with a hygrometer is critical not not allow the specific gravity to fall too low. Just remember to wear eye protection when dealing with sulphuric battery acid :).

    respohrasing question: if i have a computer that never turns off, using (in theory) between 415W and 850W+60W for inneficency at all times, not sure how wattage works on those, just thats the component "power draw" from a monitoring software, then how do i go about figuring out what parts i need to make a solar bank/supply system to power this gaming/workstation/server in a reliable manner? because im pretty sure if i can take this off my electric bill it would save a ton in the long run, but i know nothing about electricity. i guess for worst case assume the max load of 850 + 60W "loss" so 940W @ 24Hrs/ 365 day

    Hi Lewis. I am currently doing a portable solar power supply.

    Here is my question. Do I need to connect a circuit breaker between the battery and solar charge controller. For me to switch off if it is not in used? Or the solar charge controller will auto switch off when it is not in used or it will run for 24 hours??

    Thank you.

    1 reply

    The solar charge control unit will balance and discharge the power so battery's will not get over charged, you do not need a switch between solar panels and a charge control unit. That is its function, to divert and control the power going into the battery's