3.2 lipo battery cell, transformer 3 to 12 volts

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

  1. upchurchmr
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    upchurchmr Senior Member

    Thanks.
     
  2. gonzo
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    gonzo Senior Member

    Do you know the chemistry type of the cell?
     
  3. markstrimaran
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    markstrimaran Senior Member

    lithium iron phosphate.
    Lifepo4
     
  4. BertKu
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    BertKu Senior Member

    Mark, you have me now totally confused. Now suddenly you are talking about 4 cells and not just only using 1 cell to save money outlay. If you stick to only one cell, I strongly would advise you to inquiry about the 12 to 24 Volt DC to DC converter primary 20 Ampere /secondary 10 Ampere. To ask them what the lowest input voltage is allowed to have a double voltage output. I thought that you had a brilliant idea by saving some money using 2 x 3.2 Volt cells and slowly starting in building your battery pack with more cells, when money is available. Or the same apply for 12 Volt to 48 Volt and only using 1 cell. But a 2 Ampere system does not get you far enough. The 20 Ampere would be a better option. Bert
     
  5. BertKu
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    BertKu Senior Member

    Mark, I am using already for 7 years now 10 x LiFeP04 parallel and 4 sets in serial. I use a normal battery charger , with a difference that it current is higher at voltages of 10 to 11 Volt and it has only a leakage current of 2 micro-Ampere at 14.4 Volt. Most LiFeP04 has a maximum charging voltage of 3.65 Volt per cell. It is a good choice LiFePo4 , but more expensive then other lithium batteries. However very stable. Bert
     
  6. markstrimaran
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    markstrimaran Senior Member

    I am going to start with one 3.2 volt unit. Then try the 2 amp dc to dc converters.

    3.2 volts x 2 amps = 6.4 watts max per converter.

    12.7 volts at 500millamp= 6.35 watts.


    5 converters running parrel is 2.65 amps at 12 volts. About 30 watts.
    Their is a 4 amp converter, also so 2x at 5.12 amps at 12 volts.
    My fish finder pulls .258 millamp. @ 12 volts,
    My GPS pulls 1 amp @ 12 volts.
    My nav lights draw .35 watts each.
    My bilge pump pulls 150 watts, so I will have to wait, for a 6 volt pack, and then run it at reduced voltage. But 3.2 volts, might work? It usually never runs.
    To charge I will use 10 watt solar into a 12 volt 10amp/hr lead battery. Then use a 3.6 volt step down converter.
     
  7. BertKu
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    BertKu Senior Member

    The big question is, how are you going to charge the 3,2 Volt cell ? For a person like me, no problem. I use a converted computer 5 Volt power supply with constant voltage of 2 uA at 3.6 Volt and high currents of 10 Ampere at battery voltages of 2 Volt and higher, tapering of at 3.4 Volt. How are you going to charge the first 3.2 Volt cell without a chance you exceed the constant voltage requirement for a LiFePo4 battery at 3.6 Volt (low current)?
    The bilge pump may work very badly at 1/4 Voltage and a 1/4 current = 1/16 power thus not on 150 watt, but at 9 watt. I cannot see that that will work. If you have 6 Volt it would be at 1/4 power i.e. 38 watt. It may pump a little but not much. If you use a DC 12 Volt to 24 Volt 20 Ampere converter at 6 Volt, you can pull 120 watt maximum and you overload the converter and the voltage drops. It may work, it may not work. You could then put a small heavy duty resistor in serial to bring the overall load to a maximum off 120 watt total. But you have to take a chance and use a 12 DC to 24 Volt converter. I personally think it will work after my experiences with all other DC to DC converters. Bert
     
  8. markstrimaran
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    markstrimaran Senior Member

    Something like this, should charge the battery. I really have not got that far. I have some other constant current ac to dc, laying around from some LED, projects.
    I still have a bit to learn, about how not to blow up one self with lithium batteries, hence the fondness of liFePo4 chemistry.
     

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  9. markstrimaran
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    markstrimaran Senior Member

    20171012_170519.jpg
    13.45 volts, and fish finder is working from a single 3.2 lifepo4 cell. Now to charge it 1507849245488441317791.jpg Ok, it would be nice to read Chinese, 3.3 volts at 20 amps, should, get me by in a pinch.
     
  10. Jim Caldwell
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    Jim Caldwell Senior Member

    That is NOT a Cell, a Cell is 3.2 volts. It is a 4 cell pack also call a battery. You need to do more research before hurt your self or burn the house down.
    People have died and or lose hands, fingers!
     
  11. markstrimaran
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    markstrimaran Senior Member

    It is a 3.2 volt 100 amp/hr. LiFePo4 single cell, or perhaps a container of 3.2 volt cells in parrel.
    The 12 volts is off a converter. The lithium cobalt are the dangerous ones.
     
  12. BertKu
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    BertKu Senior Member

    The problem is, although a lithium LiFeP04 cell charges already by 2 Volt, your 3,3 Volt computer? power supply providing 3,3 Volt and 20 Ampere maximum may not charge your cell fully. I have never tried and actual are not able to verify this. I charge my cell 3.35 Volt and 50 Amph with 3.6 Volt although the manufacturer states not to exceed 3.65 Volt. This, I assume that 3,6 volt is basically 99% full. Your 3,3 Volt may charge the battery to 90% , SOWHAT? probably goo enough. Good choice to charge your cell in 5 hours when empty. You must just monitor the temperature. But 20 Amp of 100 Amp cell, means 0,2 C and I do not think your battery gets warm, nor hot during charging. I will try to get a 3.3 Volt computer power supply and see how it compare with my charging from 5 Volt down graded to 3.6 Volt. Bert
     
  13. markstrimaran
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    markstrimaran Senior Member

    I have always used 12volt lead batteries. So I am learning here.
    What I have gathered is that in a 4 cell battery, the first cell to become full. Will not absorb any electricity, so the 4 extra volts goes into and overloads the other cells.
    Lead acid, will just boil away electrolyte at this point.

    So charging a single cell of 3.2 volts, avoids this pit fall. And negates the need for special charge controllers, battery management systems, aka Bms circuit boards.

    With 12 volt lead chemistry, too much charge too fast makes alot of heat. We're the lifepo4 are built for speed charging, it's a good selling point. I would not think it is required,.
    The 3.65 charge voltage, of a 2hr fast charge equilizes at 3.2 .
    Just as a 16 volt charge into a 50% charged lead acid will show 15 volts on a volt meter, shortly after removed from charging. Then drop to 12.4 being only half charged.
    Same thing trips smart chargers on highly sulphinated lead cells.

    Electricity flows according to laws of physics. So 3.3 volts should bring a lifepo4 cell 99.99 full. The only thing I can think of that might cause problems. Is when the cell is 90% full. It might not be able to equilizes as fast as the 20 amps is flowing in, causing gas, heat. So the last 10% would be done with out the amp load.
    I would like to find a 3.2 volt 500millamp charger, just to see the effect. On its charge state, small solar charger. Maintainer charge.


    To think that after 10 years 1000 cycles of full discharge, they have only lost 20% capacity. My old deep cycle has lost 90 % in 300 cycles.
    Screenshot_20171012-205405.png
     
  14. BertKu
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    BertKu Senior Member

    Mark, I agree with you for most of it, but I am not too sure that if you keep the 3.3 Volt charger for extended period of time on the 3.2 Volt battery (actual mine are is 3.35 Volt when 100% full) whether there is really any damage to the battery. I assume the law of physics is, if the battery is full at 3,3o Volt (or 99.99 % in my case) and the charger is 3.3 Volt, there is no 20 ampere flowing into the battery. Maybe 1 milli Ampere or less. I think it just takes a little longer to charge the battery, as at 3,1 Volt the current starts tapering off. Maybe already at 3 Volt. I made a charger from an old 5 Volt computer power supply and if 3.6 Volt is reached, it switches over to constant voltage for 1 minute at 3.6 Volt. My official manufacturer specification does not state that I cannot charge it at 3.3 Volt. In my view, you can leave (like I do with my lead acid batteries ) leave for 1 month my battery at 13.6 Volt (just below the gassing voltage) and I have this done for 8 years and the batteries are still fine. The only problem is, that I sometime get some corrosion on my connection after 1 month and have to clean it. Thus I assume that if you keep the LiFeP04 battery at 3.3 Volt, I do not think you have a problem, but not for a month, but just some hours or maybe a few days. Are your LiFeP04 batteries really 3.2 Volt or also 3.35 Volt per cell. Bert
     

  15. BertKu
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    BertKu Senior Member

    Mark, I forgot to mention. For my 12 Volt ( actual 13.4 Volt LiFeP04) battery, I use my normal lead acid charger which charges till 13.6 Volt, I have not noticed that my 50Ah cells has had any negative behaviour over the 7 years. However at 13.4 Volt the current is only a few milli ampere and at 13.6 Volt micro ampere, It is a constant voltage charger at 13.6 Volt. Thus you should be able to charge your 100Ah cell at 3.3 Volt switch mode power supply module, without too many risk. Maybe you may have to place a small resistor in serial to avoid that the batteries still get an too high current. Bert
     
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