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Naio's avatar
Naio
Explorer II
Jun 29, 2015

Series/parallel charging question for les tinkerers grandes

I have 2, 12v AGM batteries that I use in series to run a 24v motor. The system has a solenoid controlled by an on/off switch that interrupts the power from batteries to motor.

When not in use, the switch is off. Am I correct in thinking that the batteries are not considered to be connected in series at that time?

Except: There is a 24v charging port on the system, which connects to the batteries via tiny (18ga?) wires. THAT is the only thing completing the circuit.

I usually use a 24v charger, but sometimes use a 12v (connect to one battery, then to the other, till full or for a set period of time).

I was thinking that I could use a solar or alternator-charging setup the same way I use the 12v charger. But then pianotuna said some stuff I do not fully understand:

The charging of one 12 volt battery followed by the other one may cause them to become out of balance which would require more frequent equalization...Balance is a whole bunch more important that most folks realize for longevity of a battery bank.


I understand that one battery might be at, say, 12.9 and the other at 12.97. Is that what is meant by balance? Frankly, this happens all the time with the 24v charger - maybe because my batteries are old? They still perform very well.

And what does this have to do with equalization?

Then smkettner said I should get a switch to switch them from series to parallel.

But I had not mentioned the solenoid to these/you guys. I only thought about it later. Does the solenoid make the whole issue moot, or do I still need to think about a switch and balancing?

58 Replies

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  • MrWizard's avatar
    MrWizard
    Moderator
    Jun 29, 2015
    The discharging use...is exactly the same for two batteries in series
    And recharging in series sends the amps back thru both batteries at the same rate ( or it should )

    Can you guarantee that when you recharge them separately, they will be charged at exactly the same rate and voltage for exactly the same amount of time, without any difference in amps, volts, time and battery temp
    Use the slow 24v charger , 24 solar system, or a new 24v charger
    There is only ONE WAY to do this correctly and insure battery life, series charge with the correct voltage

    I understand you want to speed up the recharge process
    Do you want to kill the batteries before their time and buy new and start over doing the same thing ?
  • 2oldman's avatar
    2oldman
    Explorer II
    Jun 29, 2015
    Naio wrote:
    ...what exactly is the bad thing that happens if I charge them seperatly?
    I don't know. I'd go with Mex's answer. I know from experience that drawing from one of them is not a good idea.
  • Naio's avatar
    Naio
    Explorer II
    Jun 29, 2015
    2oldman wrote:
    Naio wrote:
    I hesitate to try to do a schematic in ASCII.
    Does this count as series?
    Ascii? Use a graphics program like Paint.

    As long as there's a cable from A- to B+, yes.


    Ok, thanks.

    I really don't know what the point of your question is.


    ...what exactly is the bad thing that happens if I charge them seperatly?

    Or simultaneously, on two 12v charger outputs?
  • 2oldman's avatar
    2oldman
    Explorer II
    Jun 29, 2015
    Naio wrote:
    I hesitate to try to do a schematic in ASCII.
    Does this count as series?
    Ascii? Use a graphics program like Paint.

    As long as there's a cable from A- to B+, yes. I really don't know what the point of your question is.
  • Naio's avatar
    Naio
    Explorer II
    Jun 29, 2015
    2oldman wrote:
    Naio wrote:
    When not in use, the switch is off. Am I correct in thinking that the batteries are not considered to be connected in series at that time?
    A little difficult to answer without a schematic, but, unless your switch is on the battery interconnect cable, no, they are still connected in series. Whether they're powering anything is irrelevant. Does that answer?


    I hesitate to try to do a schematic in ASCII.

    There is a cable connecting A- to B+.
    And B- goes to the motor.
    But the cable from A+ has a solenoid in it, so it goes nowhere when the solenoid is off.

    Does this count as series?

    And what exactly is the bad thing that happens if I charge them seperatly?

    Or simultaneously, on two 12v charger outputs?
  • MrWizard's avatar
    MrWizard
    Moderator
    Jun 29, 2015
    the are 24v series used
    they should be 24v series charged..for best results

    they are still in series
    your power solenoid is between the batteries and the motor
    not in between the batteries

    can you charge them individually yes.. is it the best way NO!
  • 2oldman's avatar
    2oldman
    Explorer II
    Jun 29, 2015
    Naio wrote:
    When not in use, the switch is off. Am I correct in thinking that the batteries are not considered to be connected in series at that time?
    A little difficult to answer without a schematic, but, unless your switch is on the battery interconnect cable, no, they are still connected in series. Whether they're powering anything is irrelevant. Does that answer?
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Jun 29, 2015
    If the batteries are dedicated to the job there is nothing at all wrong with charging them individually. CAVEAT Make sure the batteries BOTH get charged 100% and do not run the pump while you are charging one or both.

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