Battery voltage clamp regulator

AntronX
AntronX Solar Expert Posts: 462 ✭✭
in Advanced Solar Electric Technical Forum #1
To any electronic engineers out there, will this circuit work (attached image)? I copied it from regulated power supply schematic here: http://www.electronics-tutorials.com/basics/power-supply-regulated.htm

I need to make a voltage clamp that would pass up to 10A at 14.5 V. My two 12V batteries connected in series do not stay perfectly balanced in Absorption charge. One battery reads 15.6V and another 13.4V. What transistor can I get to use in this circuit?

I also ordered two 6.8V 50W Zener diodes to connect in series with a resistor. Did not test them yet.
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Comments

  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    #2
    Re: Battery voltage clamp regulator

    I would look at the batteries as why they are different voltage.

    Are they the same type and age?
    Loose interconnect wire?

    It may be best to charge each separately to see the health of each.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #3
    Re: Battery voltage clamp regulator

    I'm with Ken,

    Check the Specific gravity of each cell in each battery,, as well as the interconnects.

    Sounds like a weak or dead cell.

    Tony
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  • lorelec
    lorelec Solar Expert Posts: 200 ✭✭
    #4
    Re: Battery voltage clamp regulator

    I think you might need to look to your batteries as the cause of your problem and find a solution there (differing age, depth of discharge, internal damage...). The circuit you describe is a standard series-pass voltage regulator. If your intention is to charge each battery with 14.5 volts with one of these circuits, then your batteries will no longer be in series...they'll be in parallel. And you'll be throwing off a huge amount of heat (145 watts with a 29.0-14.5v in/out differential at 10A). A simple zener diode shunt regulator here is not practical at all either, as the power rating of all of the components would need to be substantial -- again, 145 watts will be dissipated between zener and resistor, with the zener bearing the brunt of that dissipation as load current decreases -- power rating of the zener would be figured by {[(Vin-Vout/R)-Iout] x Vz}. Plus, the zener will not be in series with the load, but rather in parallel with it.

    Marc
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  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
    #5
    Re: Battery voltage clamp regulator

    Batteries are the ones I got in this thread:
    http://forum.solar-electric.com/showthread.php?t=4961
    They are Lifeline AGM, 12V 255Ah, 1.5 years old. Returned to the store because owner "did not like them" (translation: owner did not know what he was doing and possibly abused them)

    They are very close to each other with capacity and are the same age. One of them has slightly lower capacity and always comes up first to be charged. The difference is very small, but still is enough to get unbalanced during Absorption charge.

    I am not worried about heat generation, this would only be used at very last stage of charging. Not much should be wasted.

    I would like to know if I am on the right track with the circuit. If someone got better design to share, I would appreciate.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #6
    Re: Battery voltage clamp regulator

    If they are agms and they were abused,, it is entirely possible that they are toast.

    I would do some testing,

    Tony
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  • lorelec
    lorelec Solar Expert Posts: 200 ✭✭
    #7
    Re: Battery voltage clamp regulator

    I still vote battery problems. Two batteries in series that are even close to the same internal condition will charge at nearly the same voltage (each at half of the applied voltage). If you suspect that the batteries were abused, there's your answer.

    The circuit won't work if you intend on charging these batteries in series. It will regulate voltage only to the battery that follows it.

    Marc
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #8
    Re: Battery voltage clamp regulator

    If the batteries started out at different state of charge levels... Take the "low battery" and recharge just it to spec. (or even a light equalization).

    Once completed, do a load test on both batteries. You may find that the "high voltage" battery has a weak/open cell (battery voltage will quickly drop towards zero volts) -- or -- the "low voltage" battery has a weak or shorted cell (battery voltage drops towards ~10 volts and stays there for awhile)...

    During the discharge test (or a fast charge)--feel the batteries and see if you can find any "hot spots".

    Also read through this thread and reference documents... Adding distilled water and replacing the "sealed caps" (to replace failed catalysts) may be quite practical.

    DapDan's first post

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #9
    Re: Battery voltage clamp regulator

    this is the reason why we say to have similar batteries of similar age, but these became dissimilar to each other enough so that it makes it seem like they are different batteries altogether. a bad cell may be present in one of them so you may need another battery and will it match, who knows?
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  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
    #10
    Re: Battery voltage clamp regulator

    All 4 of the batteries I got did hold their voltage around 10.4V for 15 seconds during either 800A load or 1600A load. I am not sure which was the current because their load tester's Amp meter has two "graphs", 800A one was labeled "Battery Amps" and 1600A one was "Cranking Amps".

    The two batteries in question have very similar capacity when I tested each of them. I cannot find piece of paper I wrote down Wh of second battery, but I remember it was around 1800Wh AC, similar to 1880 Wh AC of first one.

    I kind of don't want to go back to 12V and just parallel these two, that would fix this slight misbalance issue. I am going to connect digital volt meter to each battery and watch them a little closer.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #11
    Re: Battery voltage clamp regulator

    I wouldn't call ~1.8 volts a "minor" imbalance,,

    T
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  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
    #12
    Re: Battery voltage clamp regulator

    Stupid me just fried 3 of my digital panel meters all at once :cry: I forgot to take into consideration that they are common ground type. Wanted to set up two to read each battery's voltage and third one to read mV from 50A current shunt. Right now batteries are 12.24V and 12.29V. It has been raining here during the day for a week now, and the panels are generating less than half of Wh than before.
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #13
    Re: Battery voltage clamp regulator
    AntronX wrote: »
    Stupid me just fried 3 of my digital panel meters all at once :cry: I forgot to take into consideration that they are common ground type. Wanted to set up two to read each battery's voltage and third one to read mV from 50A current shunt. Right now batteries are 12.24V and 12.29V. It has been raining here during the day for a week now, and the panels are generating less than half of Wh than before.

    Maybe it just fried the ground/V+ lead or traces. Might be easily fixable ??

    (maybe not of course but certainly worth a look)

    boB
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