Simple solar charge design question

Discussion in 'OnBoard Electronics & Controls' started by L'eau.Life, Aug 13, 2016.

  1. BertKu
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    BertKu Senior Member

    By the way, I have a few regulators here for repair. I agree regulators never break down. One never knows. Bert
     

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  2. BertKu
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    BertKu Senior Member

    Your maximum current from a 20 watt panel is about 2 Ampere. Don't worry about the thickness of the copper. Anything above 0.75 mm2 will do the job, even if you have some losses along the line. What is more important, you must use UV resistant cable from your panel to the regulator. Your leakage current is low, about 1/100 of your panel current. It is the short circuit procedure of your regulator what takes the 2 Ampere off your panel.
    Leau.Life, at least you have now all the answers. You do not need to worry anymore while away. Bert
     
  3. BertKu
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    BertKu Senior Member

    Personally I like the MicroCare, you connect a load and do not short circuit the solar panel. Much more intelligent, it is a South African product from PE.
     
  4. L'eau.Life
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    L'eau.Life Junior Member

    Many thanks Bert!
     
  5. CDK
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    CDK retired engineer

    I have no idea Bert, that is quantum physics, but I guess the electrons have no option other than to weep and wait until the sun sets. They can't do anything useful because there is nowhere to go.
    There is of course a thermal effect, equally distributed over the surface. Approx. 100 W. per square meter, so no big deal.

    My oldest 4 panels are Siemens M50. After 25 years of exposure they lost 15-20% of their nominal output, mainly because the resin between the cell surface and the glass has turned brown. The Solarex panels have no resin there but show corrosion of the cell grid and also deteriorated around 20%.
     
  6. BertKu
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    BertKu Senior Member

    Yes, we all are in the dark. What I know is the photons hammers the negative electrons out of the outer ring of the molecule and then the core becomes positive. The negative electrons opens up an umbrella and collect themselves in the negative bus bar. All jokes aside, at least we know now that an open circuit panel is less degrading.
    I had a gut feeling that it was less degrading in open circuit then in a closed circuit. However 0,2% per year is not a big deal. I was hoping for a higher percentage.

    I quite like the 2 reports on solar panels.

    I see, you still have the French Philips Solarex panels. When they came out for the first time, we were demonstrating them by jumping on them with shoes and the audience was gasping how we could do that. Siemens had a trade agreement, before they started to manufacturer their own panels. I had one with a crack, which I mounted for my electronic gate I build, After 11 years, I still did not notice much of a degrading. They are/were good panels. Bert
     
  7. philSweet
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    philSweet Senior Member

    BurtKu said
    Yep, they sure will. And yes, a smaller PV panel is much safer in this regard. I leave a small load on to limit the risk, but the batts can be boiled dry in sort order if the controller fails. I use cheapo batteries for this reason. I also have learned to use overrated controllers. I currently have a 60A controller on 2 X 130W panels.
     
  8. BertKu
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    BertKu Senior Member

    Yes, that is life. I wish that Leau.Life could get hold of a
    hobbyist, who could make a voltage regulated unit with a 2N3055 for him. The cost is minute. for 2 batteries 2 x 2N3055 = 2,5 dollar. 4x zener diodes 15 dollar cents each, 2 resistors at 0.01 cents each. A piece of aluminum as heatsink. A piece of printed circuit board from off cuts and a box to put it in. The working is simple. As soon de sun comes up, the voltage increases. The 2N3055 start opening up via the base resistor. As soon the batteries reaches the 13.0 - 13.1 Volt the 2 zener diodes of 2 x 6.8 Volt/400 mw limits the voltage of the transistor to 13.6 Volt. The loss of the base to emitter is approx. 0.5 Volt. which leaves you approx. 13.6 - 0.5 = approx. 13 volt to keep the battery topped up. If the battery is full, the emitter voltage goes up and the zener diodes + base blocks the voltages to rise higher that the 13.0 Volt. As soon the sun goes down, the transistor blocks the battery from discharging over the solar panel The Forward voltage is 60 Volt VCE and if he is concerned, he can place a 5 ampere diode of a few hundred volts to make sure nothing will happen. He must just lift the 2 zener diodes by 0,5 Volt. i.e. 3 zener diodes totaling 14.1 volt. i.e. 2 x 5.1Volt + 3.6 Volt or 3 x 4.7 Volt.
    0.1 volt - 0.3 Volt is not a problem as the overall voltage stays below the 13.8 Volt gassing voltage. Bert
    p.s. the OP must logical charge the batteries fully, before going on a 3 month holiday. The system can stay in place if he starts the generator, or charge the batteries in the future with a 100 watt panel.
     
    Last edited: Aug 20, 2016
  9. BertKu
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    BertKu Senior Member

    I had an hour’s time and the sun was nicely shining on this winter’s day. I quickly cut a double sided printed circuit board and cut some groves to separate the various components from short circuiting.

    Please note: One must not short circuit the 2 layers as the one side is the plus of the solar panel and the other side is the minus of the battery.

    I made one change. I decided to place a diode between the battery and the Voltage regulator system. The reason is to avoid unnecessary high leakage current when the transistor is blocking the battery from discharging over the dark solar panel. In the above case, I could have used a 1 Amp diode as my panel has only a 0.73 Ampere short circuit current. If a 20 watt panel is used, it is better to have a 5 Ampere diode. The reason is, if the battery was forgotten to be charged, before going on holiday. The solar panel will charge the battery by up to 1 Ampere shared if only 1 battery is charged instead of 2, or if the second battery was full and the other one get charged with 2 Ampere.

    I did not have the correct zener diodes as per diagram and used a combination to get the end result of 13.11Volt
    The standard range is 4,7V - 5,1V – 5,6V – 6,2V¬ - 6,8V – 8,2V – 9,1 V – 10V - 11V – 12V - 13V – 15 Volt

    I used more than 2 zener diodes to spread the power dissipation over 3 devices, but 2 devices will do the job. 270 Ohm and bright sunlight has a current flow of 40 mA through the resistor and the minimum power required at the 14.3 Volt result in a total power used of 560 mW i.e 2 x 400 mW gives enough safety factor. One could use a 1 watt zener diode, but the range does not have a 14,3 Volt type.

    Photo1 Shows the 10 watt panel and the 12 Volt Lead acid battery setup with the voltage regulator.

    Photo2 Shows the open charging voltage of 13.11 Volt. (do not make it more than 13.6 Volt)

    Photo3 Shows the 2N3055 mounted on a double side pc board.

    Photo4 Shows the zener diode current of 40 Milli Ampere with the pcb and the few components. (without the 5Ampere diode)

    Photo5 Shows the 10 Volt of the one cell faulty 12 Volt battery. But it even demonstrate the exercise even better.

    Photo6 Shows after charging of 1 hour. During the 1hour the full 0.72 Ampere was pumped into the battery

    Photo7 The leakage current at 12,6 Volt voltage regulation, being 20 mA

    Photo7 Also shows you the battery voltage after charging. Shows you the transistor temperature during charging/leakage current compensation. Way below the maximum temperature of 85degrees Celcius. Ambient temperature during test was 25 degrees
    Solar panel 20.6 Volt open Voltage , 0.73 short circuit current.
    2N3055 maximum 15Ampere and 115 watt power dissipation. At a 10 Watt panel it will only be absolute maximum of 7,5 watt and also if 2 batteries are charged from a 20 watt panel.

    270 Ohm should be a minimum of 1 watt, but preferable 2 watt.

    Good performance during very hot summer (up to 40 degrees Celsius Ambient) and cold winter weather (up to minus 10 degrees Celsius) can be expected.

    Components required
    1 x transistor 2N3055
    1 x 5 Ampere diode
    2 x 6.8 Volt 400 mW zener diode
    2 x 7,5 Volt 400 mW zener diode
    1 x 2 or 1 watt resistor 5% 270 Ohm
    single side pc board with an aluminum heat sink or
    double side pc board.

    Hope I do somebody a favor with the above circuit and demo.
    Bert
     

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  10. BertKu
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    BertKu Senior Member

    There is reason why I prefer a voltage regulation unit, over others. some 15 - 20 years ago I made electronic timers for the horse riding and dog jumping showjumping clubs. Each unit had 8 small 6 Volt or 12 volt Sealed lead acid batteries. It was wireless and therefore each pole had 1 battery. My problem was (my apology to woman readers) woman could not keep batteries charged, they either forgot or they overcharged the batteries. Special in Mauritius and Europe. Thus I had to come up with a solution to have it in a simple way charged and keep the batteries for weeks and months on the charger without damage. Therefore I made battery chargers each capable of charging 8 batteries. The same problem is also applicable to sailing. Lots of people like to be away for weeks and months and don't like to lift the heavy battery of their boat and place them back. With this simple 5 component robust system, their problem could be solved in the same way. A lead acid battery has no long term effect, if charged below gassing Voltage i.e. 13.8 Volt, continuously i.e. 13,1 - 13,5 Volt. A 100 Ampere battery will be most likely be flat after 9 - 12 months. i.e. 100 ampere divided by +/- 200 days = 280 milli Ampere per day. or 53 milli Ampere per hour. A small solar panel will be able to keep, even with some cloudy days, the battery topped up. The overseas units are still working after all those years. Some have bought new batteries, some I don't know whether they replaced them or not. I have here some small 12 Volt sealed lead batteries charged with the same principle as per previous drawing and explanation for more than 7 years.
     

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  11. L'eau.Life
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    L'eau.Life Junior Member

    The final decision . . . . ?

    As always; thanks for all the input - even though I understand almost nothing of it! :)

    What I've ended up going for is a dedicated 120mA "off the shelf" solar trickle charger on each engine battery that clip on to existing external roof hand rails with some pipe clips I epoxied on their backs. Hopefully that should "maintain" the start system without any fuss.

    For the House systems I've ordered a 50W flexible panel to go with the 10A duo battery controller mentioned earlier. From my understanding this panel will give me >4A charging in bright sunlight that from [say] 50% charge on the 2x120A batteries when I moor up on Sunday evening and an assumed minimum 6hrs daily summer sun, should have everything topped up nicely come Friday when we want to head out again!

    As to the fridge; it is an Electrolux dometic and from what I can tell it draws 1.5A @ 220V (330W ?) so am I right in thinking that if there were no cable or inverter losses, that would equate to 27.5A draw at 12V?
     
  12. CDK
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    CDK retired engineer

    The fridge will draw much less unless you leave the door open all day long.
    Dometic..... isn't that an absorber fridge? If yes, it can also run on 12V or LPG but is very inefficient, not a good candidate for solar power.
     
  13. L'eau.Life
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    L'eau.Life Junior Member

    Hi CDK
    Yes, dometic and I usually run it on gas but had thought to use 220v while the boat is moored so we had a cold fridge ready when we arrive to use the boat but clearly, that is not a viable option.
    Thanks!
     
  14. BertKu
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    BertKu Senior Member

    That is an excellent decision. Bert
     

  15. BertKu
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    BertKu Senior Member

    Hi L'eau.Life
    In the meantime you should have some experience with your little 120 mA charger. How did it go? Did the charger had a diode build in? To prevent the battery discharging when the solar panel is in the dark? Unfortunately I just discover that not all solar panels have a diode build in, to prevent the battery from discharging via the solar panel when dark. For that reason I have enclosed an update of the circuit diagram I suggested and has proven to be inexpensive and it keeps your battery charged whatever. My apology, all my solar panels have a diode build in and did not realise that very old panels and some new panels do not have anti discharge diode build in.

    Bert
     
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