Greek island

KefalaKefala Registered Users Posts: 5

I'm an English electronics engineer age 61 and run my own mail order business in England.

I live on the largest Greek island in the Mediterranean where the climate is similar to Phoenix. However, as it's an island, the weather isn't quite the same. We get a long, hot, dry summer with some humidity in July and a chilly (down to zero Centigrade - or 32 degrees Fahrenheit), mostly sunny, winter with lots of rain, snow on the mountains and occasional lightning storms. The house is 1000 feet above sea level so a tsunami is one event we don't fear!

We're on the grid (220v AC) but the cost of a unit of electricity increases according to how many we use. So reducing usage by enough to drop a "tariff" level can make a significant difference to how much we pay.

In addition, the electricity supply is somewhat unreliable in winter and we can be without it for any time between 1 minute and 8 hours. (It took 3 days to replace a transformer hit by lightning but that's an exception.)


I'm not sure if I'm allowed to post a link but here goes:

The photos show my "Power Bright APS300-12 Pure Sine Power Inverter 300 Watt 12 Volt DC To 110 Volt AC ".
I needed it to run my office computer system during periods of power outage. I mounted it in a plastic box in a shady area outside the office, with two 6V 200AH batteries (in series) and two battery chargers.

My computer is permanently connected to the 110v inverter output so, when the power goes off without warning, the system works like a large UPS.

What I'd like to do is have a couple of 170 Watt photovoltaic panels charging the batteries during the hours of sunshine, which are considerable here.

I have two problems:

1. Lack of money at present.

2. No idea how to arrange the wiring so that the battery chargers take over when the sun fails, or vice-versa.

I'm quite capable of building electronic circuits but I can't figure out how to arrange it.

I realise that I could spend lots of money on a combined charger/inverter but I'm on a shoestring budget and want to use what I've already got.

So I'm looking for suggestions?

Thanks in advance.



  • BB.BB. Super Moderators, Administrators Posts: 28,176 admin
    Re: Greek island

    Welcome to the Forum Martin.

    Links are fine that point to further information related to the discussion (i.e., as long as it does not look like spam).

    What size battery bank are your/will you be using?

    I am not sure, but it looks like you are using two completely different batteries in parallel? If so, that is usually not a good idea.

    Also, eventually you should replace the alligator clips with hard wired battery connections (nuts and bolts, battery lugs/rings etc.). Alligator clamps are just not reliable high current connections.

    Fuses and/or circuit breakers should be used on any wire leaving the + battery bus. A short or failed device can draw hundreds of amps from a smaller battery bank into a dead short and possibly start a fire with your wiring (a input fuse on your UPS probably will not have helped "saved" your inverter's input capacitor failure).

    Double check your voltage drop withe wiring you currently have. Typically short/heavy gauge wiring is required for inverter and charge controller connections. With 12 volt systems, you really only have about 0.5 to 1.0 volts of "head room" for voltage drop or the inverter will shut down (11.5 volt minimum battery voltage under load, 10.5 volt inverter cutoff voltage). Long/small diameter wiring and alligator clip wiring may have caused excessive ripple on the DC input to your inverter and helped to cook the capacitors.

    Check your AC battery charger's output voltages too with a good meter... Those look like "car battery chargers" which usually are not well designed for keeping a deep cycle battery bank charged. They may not go "high enough" voltage (around 14.2 volts for sealed batteries) for fast/complete charging. Or they may continue charging above 14.2 volts and damage the battery bank. And many car type charger cables are way to small diameter of wire--lots of voltage drop which also, in the end, slows down the charging of the battery. You might look at a good quality RV Battery AC to DC Converters/Chargers. Probably not a lot of used/junked RVs on your island--but if you hit the mainland once in a while, you might find something used.

    For a really rugged/reliable/efficient AC inverter at a good price (at least in the US)--The MorningStar 12 VDC 300 watt TSW (true sine wave) unit is really hard to beat. It is available in both 120 VAC at 60 Hz and 230 VAC at 50 Hz.

    Of course another option is to go with a laptop type computer--Already has its own battery for UPS type function and designed for low power operation (typically 20-30 watts vs 100-200 watts for a desktop computer).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Greek island

    So right now you've got an inverter and a 200 Amp hour 12 Volt battery bank. This works for you so no need to change it.
    Adding panels: assume a 10% peak charge rate, which usually works well for most situations. That's 20 Amps @ 12 Volts you need to come up with or about 240 Watts. Except that you really need the current which is going to be supplied at a higher Voltage to make the Watts so you're really looking at around 350 Watts of panel.
    They need to be "12 Volt" panels so that you don't have to buy a more expensive MPPT type charge controller (we're working on budget here!) These should have a Vmp of 17 to 18. This eliminates most of the higher Wattage panels as they tend to be "24 Volt" (Vmp well above 18 ). Do you have the full specs on the 170 Watt panels you mention? They are more likely to be 24's than 12's.

    Let's say you get some KD140's which have an Imp of 7.9. For 20 Amps charging target you'd want 3 in parallel on a PWM type charge controller capable of handling at least 20 Amps. a SunSaver 20 would be the smallest that would work. For a minimal system you could probably use two such panels, get just shy of 15 Amps maximum current and use a ProStar 15. That would be about $90 for the controller and $620 for the two panels in the U.S. What is available to you and for what price is bound to be different; just wanted to give you an idea of the kind of equipment you should be looking for.

    NAWS' page of Morningstar PWM charge controllers:

    You can leave this connected all the time, even with a battery charger also connected to the battery. You could activate the charger manually, or use a Voltage controlled switch to turn it on when battery Voltage fell below a certain level.

    How we doing so far? :D
  • KefalaKefala Registered Users Posts: 5
    Re: Greek island

    Thanks for your interesting replies. Yes, the current (excuse pun) setup is very "temporary". You are right about the battery chargers in that they seldom get the voltage above 13.5v - not good, I know. I try to give the batteries an "equalising" boost occasionally, with all loads switched off, but even then I can't get past 14.0v so it's not enough. Right now they are sitting at 12.5v because my computer and monitor are on (they are always on), so the charge rate is below the optimum.

    I've been looking at the possibility of modifying a PC power supply to give 14v. It would be more efficient than transformers.

    The solar panels that were recommended to me (by the importer on this island) were described as:
    2x aleo S_14-175 modules (550 Euros each).
    I can't find these listed and a search finds only my own post in the Apple Mac forums.

    The company is
    (Don't bother to look. It's all in Greek!)

    I can email my Swedish contact there and get more information but he knew it was for a 12 volt system so I guess they will be correct and the 175 number probably refers to 175 Watts.

    The batteries are 2 x Hoppecke SolarBlox 6V 200Ah. They give about 10 hours operation till the voltage falls to 11.0 and the inverter switches off.
  • BB.BB. Super Moderators, Administrators Posts: 28,176 admin
    Re: Greek island

    You really need the Vmp/Imp ratings of those panels... If Vmp>~17.5 to 18.6 volts or so--You will probably need a MPPT type charge controller (which starts around $300 USD) vs a less expensive PWM controller (smaller ones are under $100 USD).

    You should try to get the batteries to ~13.6 volts or so for "float" (AC power on, not needing much charging). Operating below ~12.7-12.8 volts is discharging the batteries.

    Running the batteries below ~11.5 volts can dramatically reduce their overall lifetime. Ideally, you want to only discharge the batteries to 75% or as low as 50% state of charge for daily use... The deeper the discharge, the less cycle life you will have (although, buying 2x as many batteries to last 2.x times longer is almost a financial wash in many cases).

    Taking Lead Acid batteries dead (or storing/operating them continuously below ~75% state of charge) speeds "sulfation" (soft/fluffy lead sulfate turns into hard lead crystals that no longer participate in the charge/discharging cycle).

    Taking rechargeable batteries "past dead" (where more or more cells are reversed biased and actually begin to "reverse charge") immediately kills most battery chemistries.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Greek island

    Regarding the charger, do yourself a big favour and buy one that's actually meant to recharge deep cycle batteries like this Iota unit:

    The wonderful warmth of Greece isn't doing your batteries any favours either, nor will it be good on panels (temp goes up, Voltage goes down). A remote temperature sensor on the charge controller would help with this somewhat but not all controllers have them. It's one of those cost/value trade-offs.

    I suspect the batteries have had it, given the information you disclose about their Voltage levels.
  • KefalaKefala Registered Users Posts: 5
    Re: Greek island

    Thanks again. The Iota unit is interesting. I need it to supply at least 10 Amps to the inverter plus whatever the batteries need for charging.
    The shipping cost on that particular unit is higher than its price! So I'll look for a supplier in Europe or UK.

    The batteries still run the system for as long as they did when new so I think they'll be OK for a while. But, as soon as money is available, I'll get a decent charger. The two car battery chargers were another "temporary" measure, intended to be used for a couple of months until my business picked up again. But the UK recession is worse than most people expected.

    The caravan battery in parallel is only there to keep it topped up but I think it's knackered because it boils off water in no time. Guess I'd better recycle it. :(
  • KefalaKefala Registered Users Posts: 5
    Re: Greek island

    Sheesh! I've been searching for ages but I finally found a supplier in Italy:

    I need to go to bed now but I'd be grateful if you'd take a look and tell me if you see a deep-cycle battery charger that might suit my needs.

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Greek island

    I would not be quick to recommend any of them. One of them has some odd specifications listed, including higher charging Voltages for gel batteries. The technical data sheet is in Italian which is one of many languages I do not speak.

    Some of the items listed they seem to want you to buy in large quantities.

    This might be the best choice of those listed:
    It shows more battery types in the specs which is usually a good sign.

    None of them seem inexpensive. :cry:
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Greek island sell a whole range of chargers and they're available all over europe. The price you quoted of 550 Euro for a single 175W panel is very expensive. Have a look at (run by a member of this forum and based in Spain) for more reasonable prices.
    The user "rogeriko" on another forum (;u=5115) runs a renewable energy business out of Mykonos if you'd like to get in touch.
  • KefalaKefala Registered Users Posts: 5
    Re: Greek island

    Thanks again. More lines to investigate. I'll contact those guys. :)

    This morning the battery voltage had risen to 13.1v over night. It fell to 12.6 when I put my monitor on and it's still hovering there. I think I'll switch off a Hard drive or two to try to get some positive charging. I disconnected the caravan battery.
  • servant74servant74 Registered Users Posts: 1
    Re: Greek island


    I was thinking that it might be more efficient to run you PC directly off of DC. There are DC computer power supply's available, and this way it could be wired to the batteries directly without having the inverter losses. Possibly adding some 12VDC LED lights might reduce power usage further, especially if you use the computers when sunlight is not available for desk lighting. But this might not be the case if you are running an inverter one place and using the power a significant distance away (AC power can go over smaller wire more efficiently over longer distances -- where the tradeoff is is another thing to study)

    Just a thought. ... Jack
  • BB.BB. Super Moderators, Administrators Posts: 28,176 admin
    Re: Greek island

    Welcome to the forum Jack.

    I am sort of biased to a good quality AC inverter for supplying most loads. They can be pretty efficient (85-90%+), and as you say, sending power any distance is just so much easier at 120/230 VAC vs 12 VDC.

    Other issues--Battery bank run from 10.5 to 15.5 volts volts (near dead to equalization--even higher in sub freezing weather). The standard 12 volt converters designed for cars are usually operated at around 14.2 volts maximum--and a fair number have failed at 15+ volts. DC Converters, many times, are not much different in efficiency vs a good quality inverter.

    Also, DC current can sustain arcs very easily (DC arc welders used to be the best you could get short of the newer high frequency units and other things these days). Plus even a simple car battery can supply 100's of amps into a dead short and very easily start a fire.

    All of this is why I tend to suggest AC inverter vs DC Direct connections for most folks unless they have a native DC device that works well on deep cycle batteries.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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