DIY Solar panel setup on a budget

Discussion in 'Hobby Engineering' started by Mathuisella, Oct 15, 2013.

  1. shane41

    shane41 Member

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    Thinking that myself, smaller lighter & last longer. LoL group buy for OCAU. Shipping component though :Paranoid:
    ______
    Sunder what is the search your typing in for alibaba aliexpress? Useful link perhaps?
     
  2. Sunder

    Sunder Member

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    The screencap I showed you was from a distribution list for past buyers. Here is the "public" link:

    https://www.alibaba.com/product-det...ml?spm=a2700.7724838.2017115.1.60887839NzjIwg

    Knowing that $38USD is being offered to me, you probably could get it down to the lower end of their range with reasonable quantities without too much pressure. If you want I can forward you the whole PDF price list, and you can refer to that as the "list price". PM me your email if you're serious.

    Edit: If you don't want to negotiate, here's one that is fixed price $40USD per unit -

    https://wholesaler.alibaba.com/prod...449.html?spm=a2700.7782932.0.0.d8e91e7aw6UoAB

    They are claiming 58Ah, but I'm pretty sure it's the same product, with built in China exaggeration. One of the reasons I trusted OSN was that every single cell I received was 3-10% OVER the rated capacity. Very rare for Chinese sellers to be accurate, let alone conservative.
     
    Last edited: Mar 13, 2018
  3. shane41

    shane41 Member

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    I won't be serious for a good while yet. Too many project on the go here all @ the moment killing my funds.
    But thankyou :thumbup: Now I have reference & other member too on good batteries.

    In the future if you were gone from the forum ... how could we know about this? Community thing, we all do better
     
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  4. vk2fro

    vk2fro Member

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    have you tried using google translate or a similar app on your phone to cover the chinese to english translation of the board markings?

    edit: JabTronic beat me to it by a mile - my post stalled for some reason. Stupid internet
     
    Last edited: Mar 14, 2018
  5. OP
    OP
    Mathuisella

    Mathuisella Member

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    Yep, if i had panels i'd be getting 500AH @12V worth of these

    that would do me overnight :)

    A single person could be electrically independant for $1500 :O
     
  6. OP
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    Mathuisella

    Mathuisella Member

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    so say, 50AH @ 12V for each lot of $40

    500AH @ 12V for $400 or 25AH @ 240V

    so if someone was to run just a laptop/tv/radio ect in the evening until bedtime, say 8 hours post sunset you could be off grid :p

    but a better approach would be to get 1000 AH @ 12V to give 50AH @ 240V.

    but if one was to have a family with a tv, PC or two ect: spend $4000 and get 5000AH @ 12V, 250AH @ 240V which should last few rainy days and evenings if you don't go crazy.
     
  7. Sunder

    Sunder Member

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    Definitely. Well, at least in summer. there's only 8 hours of sunlight and 16 hours of dark in Winter, and my gas heater needs electricity for fans anyway (probably only 20-30w, but still needs to be considered.) edit: just noticed I misread your post. you said 8 hours post sunset, which for me means assuming sun sets at 4pm. That's a fairly good worse case assumption.

    You'd probably want higher than 12v if you can as well. As the last page noted, even short runs at high currents can get you big voltage drops, so running a house off 12v will either need you big cables, or you need to have very short runs to avoid loss. a 48v system would still be safe, but drop your current by a factor of 4.
     
    Last edited: Mar 15, 2018
  8. vk2fro

    vk2fro Member

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    Even 24V is a factor of 2 - running stuff off 12v is really only good for vehicles, camping, or the odd farm shed running lights and say an electric fence. 24V stuff is common, and your battery draw will be half that of 12V. Plus panels to keep a 24V battery happy are also common, and can be controlled with an MPPT charge controller for best effeciency.
     
    Last edited: Mar 15, 2018
  9. rainwulf

    rainwulf Member

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    24 is a nice even factor for medium sized installations. 24volt gear is cheap thanks to trucks/busses, and you get to use thinner cables and have less issues with voltage drops causing inverter cut outs.

    Most if not all MPPT controllers are current limited in their capabilities. You will find that most of them will also do 12/24 volt setups. So simply doubling the voltage, at the same current, instantly doubles the power output of a controller.

    For example the 2 MCP60x i have are rated at 3.2kw each. That's a max of 60amps output at 48 volts. If run a bank of 12 or 24, its still 60 amps max, but you reduce your power output accordingly.

    60 amps at 12 volts is 1/4 of the actual power of 60 amps at 48 volts.

    The problem with 48 volts is that there is a lack of hardware out there, and price goes up very fast at the 48 volt level. Even your standard step down converters from ebay often top out at 32 volts absolute max input voltage, so you need to get specific equipment. Plus, 48 volts is getting into the area of extremely dangerous self sustaining arcs if something goes wrong, so you need special breakers as well, its also an electrocution risk as you can easily feel 48 volts, and if you get hit by it, your muscles dont let go.


    My system bus is 24 volts, and i will be running a 24 volt ring bus around under my house and tapping that off as needed to 24 to 12, or 24 to 5 volt as required. I wont be needing a low voltage disconnect as there wont ever be a situation where my main bank will get below 12.4 (24.8) volts. Even on a rainy overcast day with the 240 volt loads in bypass i get plenty of charging power. That is my main aim, a fully self sufficient automatically switching/bypass off grid system that looks after itself without dangerous discharge levels.
     
  10. Sunder

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    I had noticed you had to go to pricier gear to get 48v, but depending on what you're running, I feel even 24v needs a bit of care. There are many, many things that are designed to be 2400w. (Usually heating of some sort) At 24v, that's 100A. Add in 15% for the step up, and you're talking at least 115A at the battery cable. Now, if your fridge, PC and a couple lights are on, you're probably looking at 150A.

    50V is the "official" ELV cutoff, but 48V batteries can be up to 60V fully charged, so you have a point, but I think we're talking very, very low risk there.

    Hell, if I had my way, I'd have straight 240VDC to 240VAC, and I had considered buying a dead UPS to do that.
     
  11. rainwulf

    rainwulf Member

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    You cant go from 240vdc to 240 AC due to RMS.

    You need at LEAST 370vdc to make an ac waveform.

    But to make that waveform is a piece of cake.

    https://www.ebay.com/itm/2000W-Pure...705605?hash=item1ea84e0a45:g:tH0AAOSwbtVZQlZA

    Boom. Feed it 400 vdc, out comes AC.


    400vdc, hell 240vdc would be scary to work with.


    The other thing to consider and this is important is that there are very few things in your house that NEED 240 AC. Only things that have transformers, induction motors, and triac based dimmers actually need 240 AC. Everything else could safely run of DC.
     
  12. Sunder

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    Interesting. I was talking to a guy only a couple months ago about the opposite - How to turn 240vac into DC in a cheap and dirty way. He said that if you use a rectifying diode, you can do it, but the voltage goes up. I understood that because the 240v is the RMS of the sine wave, where as once "flattened", would be higher. Never thought it would apply in reverse, but obvious now you say it.

    I've shorted a 150vdc battery. Don't even think it was the full 150v. Soldering iron was working on the positive terminal, when the iron melted through the insulation of a balancing wire. Balls of molten metal everywhere. Had it touched the negative terminal, the result would have been much worse.

    19275302_10156521686678438_5374241426069077110_n.jpg

    If I ever work on such high DC voltages again, my intent is to build everything into 50vdc packs or less, have switches between each pack, and one switch with an inrush current limiter. Everything would have to be double insulated.


    Edit: This may be now pulling it off topic, but the item you linked seemed to be pitched as a Modified Sine Wave to Pure Sine Wave converter. So, I would guess that you would use rectifying diodes to turn your 240VAC modified sine to 380VDC. You then feed that into the device something, something, dark side, and you get pure sine 220VAC out the other side.

    It's that something, something, 16VAC that I'm confused about. What's that all about?
     
    Last edited: Mar 15, 2018
  13. rainwulf

    rainwulf Member

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    Its a board that allows you to convert a MSW inverter to pure sine wave. The front end is the same, 12-24 to 400 volts, recitified and filtered. A msw then just chops it up and hands it out, that device i linked can replace, or in addition to the MSW output stage, takes that 400 volts and spits out pure 240 volts ac. You could also recitify the output of a MSW but that starts to get a bit messy. 16VAC is the power source for the unit, it doesnt have any way of powering itself from that 400 volt rail, so you need to feed it an external rail to run itself. Most MSW inverters have an internal low voltage isolated rail thats used to power the output stages. Its usually just a small tap on one of the step up transformers, or just a small transformer that is run from the 400 volt ac output of the up-converter stage.

    This keeps the output high voltage stage galvanically isolated from the input stage.

    Those pure sinewave output boards also make fantastic AVR filters. All you have to add is a 400vdc supply, which you can make with a bridge rectifier and a capacitor, with some inrush protection.

    The output of often way cleaner then the mains, and automatically voltage regulated.
     
    Last edited: Mar 15, 2018
  14. Sunder

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    Ah, nice. My dad has a 5kw MSW generator which is mostly useless, because everything at the farm complains. Fridge motor makes bad noises and I suspect is getting hot. Laptop chargers light up but won't charge, even the battery charger won't charge on that generator.

    I was hoping to build a post output MSW to PSW box, but I doubt there'd be anywhere I could pull 16vac from a generator. It'd be straight from 400vdc to 240vac.
     
  15. rainwulf

    rainwulf Member

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    Just use a 12vac transformer. It will handle the MSW and give out 16vac peak to drive the converter board.
     
  16. Sunder

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    Thanks for that. for <$100, I do want to try that, but right now, with a bathroom renovation on (my house, not the holiday home), it's right down the bottom of the list, just below "remember to take a shit" or something unimportant like that. It is really good to be learning these things though.
     
  17. MUTMAN

    MUTMAN Member

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    'hazardous potential' any differential voltage that exceeds the levels defined as 'extra low voltage' in AS/NZS 3000 - (clause 1.5.7(a)) - exceeding 50VAC or 120 V ripple-free DC

    The funnier definition of Low Voltage
    Over ELV but under 1000VAC or 1500VDC ....
    errr thats not my definition of 'low' :o

    what that also means is if you were to build a string of panels, it's open circuit voltage can not be over that 120VDC limit.
    Big fines do apply. So be very careful when talking to neighbours
     
  18. rainwulf

    rainwulf Member

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    Mutman i had a look at that charger, its a weird ass design. About 20 taps on the transformer, no large capacitors at all, weird ass scr/inductor combo for charging. Uses some form of step down inductive system. No high current windings on the transformer though. Still its got some nice tasty tidbits, and the transformer is going into my multi voltage power supply/battery charger.

    I put together the ebay driver board and another UPS transformer together and ran it last night. Very impressed. Super quiet, barely any heat at all from the driver board. Transformer got a bit warm though, so im still hunting for a gigantic transformer to use for this thing. Overall though im pretty impressed with the board.

    I would like a large toroid, but man they are expensive!

    Anything over 300va becomes enormously expensive. I am going to have to do make up at least 1kw out of a matched set of transformers.. dammit.
     
    Last edited: Mar 17, 2018
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  19. MUTMAN

    MUTMAN Member

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    Someone on the forums had matched TX ages back ... sorry cant remember who it was :(
    They were from old welders. Might be a good search ???
     
  20. rainwulf

    rainwulf Member

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    Well i managed to get it working with two matched transformers from old 1100 va UPSes that had actual copper windings. Nearly every UPS transformer i have has aluminium windings!

    The matched set where center tapped, so i had to rewire them into single mode, which meant parallelling the windings. I am ok with this.

    Here it is before i changed the output filter to something with a bit more capacitance, and changed the output winding tap. The original tap was the higher voltage tap, which meant that the inverter board was switching at lower voltage but higher current, causing higher I2R losses.

    The transformers have two output taps, black to yellow 240, and black to blue 200 volts.

    This is so in a ups, when they are charging the battery, they use the 200 volt tap, which causes the output voltage at the high current windings to be greated then the batteries allowing charging to take place. There is a 240 to 24 conversion going on at a sine wave, so its an RMS conversion.

    When there is AC loss, the 240 tap is then used, which allows the batteries to create 240 volts from their output as a modified square wave, where there is no .707 RMS factor involved. Cheap and simple and works quite well.

    In my case however, the inverter board has output voltage correction, so you can use any tap you want as long as the final voltage will get you your 240 volt output voltage. The larger the ratio though, the higher current/lower voltage is used to drive the high current windings causing losses. So the aim is to use the smallest ratio you can get away with which reduces the current and increases the voltage that the driver board has to create, but UNDER the bank voltage.

    Think of it like this, your load is 1000 watts at 240 volts. Thats 4.166 amps.
    If the transformer had a 1:20 ratio, the input sine wave would have to be 12 volts, at 83 amps.
    At a 1:10 ratio, it would be 24 volts, at 41 amps for exactly the same output. Thats one quarter of the losses simply by using a different ratio.

    The issue however is that with say a battery bank voltage of 28 volts, your max peak voltage will just be 28 volts, which is actually 19.796 volts RMS. You cant create a sine wave with a higher peak voltage then your DC supply.

    So you pick the tap that can create your 240 volts at say.. 20 volt peak. Which is 14.14 volts RMS. So you pick the tap that will give you 240 volt rms, with an input of around 15 volts rms.

    In my case with these transformers, i get 240 volts RMS with an input of 17 volt RMS. Thats 24 volts peak. Just under the minimum bank voltage, yet the highest voltage available which reduces the switching current.

    This inverter passes the hairdryer test, will run at 1200 watt mode indefinitely, and runs 1800 watts for around 10 seconds before shutting down due to low output voltage. Thats way beyond what i expected, as i only need 600-800 watts continuous, with a massive peak as needed by the bar fridge. Which is spins up with zero issues.

    All thats left now is the fan cooling, an LCD monitoring panel and a decent enclosure.

    I have an ACS current sensor for measuring the input current, and voltage.

    [​IMG]
     
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