3.2 lipo battery cell, transformer 3 to 12 volts

Discussion in 'OnBoard Electronics & Controls' started by markstrimaran, Oct 8, 2017.

  1. markstrimaran
    Joined: Dec 2014
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    markstrimaran Senior Member

    20171105_150435.jpg
    5 amp step down dc to dc converter.
    18 volts from 5 watt solar panel. Into 3.63 volts( adjustable) charge voltage into a 3.3 volt lipo4 single cell.
    Battery is at 3.18.
     
  2. BertKu
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    BertKu Senior Member

    Well done, just make sure that your current at 3.65 volt (preferable only 3.6 Volt) is micro Ampere otherwise you will harm your expensive battery. This has nicely solved your problem. Bert
     
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  3. markstrimaran
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    markstrimaran Senior Member

    Why less than one amp?
    The 5 watt is producing .30 amps at 18 volts.
    Converted into 3.6 volts at 1.2 amps.

    Lipo4 batteries in a 4 pack full 13.2 volts. Can absorb 10 amps, if drained? Maybe I am not thinking correctly.

    They can be fully charged in about 4 hours? A 100 amp/ hr battery would be taking in 25 amps per hour.

    My little solar should take about 80 hours to charge a dead battery.
    3.3 volt at 100 amp/hr capacity.
     
  4. gonzo
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    gonzo Senior Member

    If your battery capacity (C) is 0.3 A, then the max charge can be up to 5C (1.5 A) but the temperature must be controlled. Otherwise, you need to adjust the charge current to the temperature. That maximum will depend on the electrolyte, not the chemistry type of the battery.
     
  5. markstrimaran
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    markstrimaran Senior Member

    The cell has a capacity of 100 amp/hr.
     
  6. gonzo
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    gonzo Senior Member

    OK, so that means 5 A for 20 hours. 5C is 25 A, but that is a maximum in ideal conditions. The manufacturer should have a table or graph of curves showing charge rate vs temperature.
     
  7. markstrimaran
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    markstrimaran Senior Member

    Thanks Gonzo.

    That refreshed my memory a bit.

    The cell started at, 3.18 volts.

    It is a 3.3 volt cell, so it is not fully charged.

    It is also used, and only has about 80amp/hr capacity as tested.

    After 12 hours on the 5 watt solar, ( very cloudy) It has increased to 3.22 volts.

    It is cold out side 32'f.

    I am not sure how % it is full since the voltages are so flat, as it is discharging.
     
  8. BertKu
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    BertKu Senior Member

    The curve will still be quite flat until it has 10 to 15% and then it will sharply go down to 2 Volt what is your absolute maximum low voltage you should go to. Less than 2 Volt will start damaging you battery. I personally would not charge the battery at 3 c = 300 Ampere, or even worse 5C = 500 Ampere. Yes it will be quickly charged but how will you then control the heat produced? No, your 1 Ampere is low and it will eat into your reserve. A 20 Watt panel would have been more appropriate. But cost is probably a problem for you. Bert
     
    Last edited: Nov 7, 2017
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  9. BertKu
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    BertKu Senior Member

    I checked my factory specifications.
    Normal charging 0.5 C = 50 Ampere for your 100 Ah cell (or less)
    Fast charging 1 C = 100 Ampere for your cell, but temperature is not allowed to move over 45 degrees Celcius.
    Normal Voltage = 3.2 Volt
    Maximum charging voltage 3.65 Volt at 0.5 C = 50 Ampere, thereafter constant voltage charging at 0.01 C until cut off. (whatever that means I haven't figured that out, but I charge my batteries already for 6 years only at about 0.1 C till 3.60 Volt. ) They seem to have survived. !!!!
    discharge maximal 5 C = 500 Ampere for your cell and maximum 60 degrees.

    I assume that your LiFeP04 is similar then mine.
    Bert
     
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  10. markstrimaran
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    markstrimaran Senior Member

    Thanks Bertku

    I do have a 45 watt panel. I was concerned about the buck converter getting over powered so I started light.
     
  11. BertKu
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    BertKu Senior Member

    Sorry to learn that. A 45 watt panel would have given you approx 4 Ampere. Times 4 would have been 16 Ampere, beautiful to keep your batteries for a long time up to 10 maybe more years. I personally belief that continuous doing something at the maximum reduces lifetime. Thus at 16 Ampere, it would have been a winner. Now you have to consider to buy a MPPT relay. It gives you slightly more power. But it is not a good solution. You stated 100 Ah battery at 0.5 C would mean 50 Ampere charging and if I compare that with my manufacturing info for the LiFePo4 batteries I am using, it would be 2,5 hours charging at 0,5 C to get a 100 % charge . To charge your battery from 20% to 100% would mean 2 hours at 50 Ampere or at 16 Ampere 6,25 hours or at 2 Ampere 50 hours or 5 days sunshine. You may have to dig deep in your pocket for another panel if your 45 watt panel is not to your liking. I would suggest a 100 watt panel, approx 8 to 11 Ampere , depending on the open Voltage and type of MPPT you consider to buy. Here in Port Elisabeth is a company Microcare who makes a 10 Ampere MPPT solar unit 12/24V , but it puts you 70 USA dollars out of your pocket. P.S. I remember that I suggested that you should consider the 20 Ampere? Pity that you went for the smaller one. Bert
     
  12. BertKu
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    BertKu Senior Member

    Mark, don't feel bad. One can only learn from mistakes, never from the good things one does in life. Any chance in modifying your 12 Volt to 3.3 Volt? By rewinding and using more powerful components? It will be a difficult task. Bert
     
  13. markstrimaran
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    markstrimaran Senior Member

    Well. No big mistakes yet, lol.
    All my panels, were purchased for other projects. The 45 watt is actually 3. 15 watt smaller ones.

    This project is for my very small. trimaran. It sits out of the water, when not in use. 20170318_121334.jpg
    I plan on mounting a solar panel, on the out board side of the ama. So it will charge the boats batteries between weekends.
    I have no room for a 100 watt solar panel. 20170424_200852.jpg
    The black mast on the stern, is really the only place, maybe a small flexible solar panel, that I could wrap around it.

    The 4 amp buck converter, is adjustable, from .025 thru 4 amps current.

    It holds the output voltage constant regardless of the fluctuations of the solar panel .+/- .05 volts. From 12 volts to 18 volts
     
  14. markstrimaran
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    markstrimaran Senior Member

    Then eventually the gas outboard will be replaced with an electric trolling motor, it will be used maybe for about 20 minutes. When loading at the boat ramp.
     

  15. BertKu
    Joined: May 2009
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    BertKu Senior Member

    Are you convinced that wrapping around a pole would not create dark spots and your current would be too low. You should only do that if the flexible solar panel consist of rows of separate solar panels, whereby if there is a dark spot at least some of the left over cells would give you some energy. But 45 watt would help you to get your battery charged. Bert
     
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