New 12V system 2 Batteries

Discussion in 'Electrical Systems' started by Gertjezzz, Apr 12, 2012.

  1. Gertjezzz
    Joined: Apr 2012
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    Location: Netherlands

    Gertjezzz New Member

    Hello everyone,

    Im new here and this is my first post. I'm from the Neteherlands so my grammar and or sentences are not ideal for me. Also the language barrier gives my huge problems to make clear what the problem is, but ill try, and maybe you can help me out!

    On my boat (a De Ruiterkruiser) its a small boat 12 meters, the power supply isnt very good. Ive rewired the generator and its loading with 60Amps. the batteries are parallel switched and are loaded by a voltage regulator. due this installation I think the batteries are charging and discharging each other when the generator (dynamo) isnt delivering the power. The two batteries are 165Ah and 170Ah.

    The situation as it is:

    Here are 2 batteries for the use of lamps/waterpumps etc. One is for starting the motor. the last battery is incombination with the switch simulating the generator (dynamo).

    So I think this isnt the best wiring, I've made an other option to wire the whole system, any thoughts?

    Also i place two solarcells with a seperate voltage reagulator (these i'm planning to buy) In this situation the batteries will be loaded seperate. due the diodes the batteries will simulate one battery but cant charge and discharge each other. I know that diodes drop the voltage with 0,6 - 0,8 volts so this isnt the best option, is it?

    I hope my question is clear, and that you have an solution :)

    Thank you!
  2. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Just a few remarks:

    The red switch shouldn't be there; alternators must be permanently connected to a battery to prevent damage to the internal regulator.

    Batteries must be of the same type and age if they are to be used in a parallel circuit. There will be a minimal transport of electrons between the batteries to equalize the charge but that is quite acceptable and doesn't create any losses.

    Using diodes in the charging circuit requires an alternator with a higher output voltage to compensate the Fwd voltage drop, or an alternator with a separate sense input.
    Diodes in the load circuit are a waste of energy and a potential fire hazard unless they are mounted on a large heat sink and are used for additional cabin heating.
    If you insist on separating the batteries because of age or size differences, use relays with the proper current carrying capabilities. An anchor winch or bow thruster draws an awful lot of current!
    1 person likes this.
  3. Gertjezzz
    Joined: Apr 2012
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    Location: Netherlands

    Gertjezzz New Member

    Hello CDK,

    Thanks for the reply!

    The red switch is in real life not there. Here it is simulating the generator on/off for my to see what power will be drawn.

    By alternator you mean generator? If yes, then my alternator gives a higher output then 12V, approx 13,8-14 volts.

    So the diodes in the load circuit are a waste. I should use relais, any idea how to switch them?
  4. missinginaction
    Joined: Aug 2007
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    Location: New York

    missinginaction Senior Member

    How about an automatic charging relay?

    I'll post a link that explains how an ACR functions.

    Click on the link "where to buy" and you'll be able to find a distributor in the Netherlands.

  5. Gertjezzz
    Joined: Apr 2012
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    Location: Netherlands

    Gertjezzz New Member

    Hello Missinginaction,

    Thanks for your reply!

    But the start battery is already seperate. Its now just to charge the load batteries (called "verbruiks accu's) seperate, and discharge them combined.

    The voltage regulator I have has already 3 outputs, so I can connect my batteries. (which will load them seperate) The voltage regulator is a intellegent loader which decides what the best charge volate is for each output c.q. battery.

    Maybe i seek something like an ACR only iverted? :p Or i have to draw an relay based design myself.

    Thanks for thinking with me! :D
  6. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Exactly what I expected and why people buy ACR's.
    A standard alternator (Lichtmaschine, generator, dynamo) stops charging below 14 volts. For your diode trio you must replace the regulator with a 14.5 volt type. Most alternators like Motorola or Bosch have a regulator on the rear cover, also serving as a carbon brush holder, held by 2 screws. The older ones with discrete components could be modified, modern ones have just a small chip and are sealed.

    I fail to grasp the need for isolated house batteries. Have you checked the differential voltage at rest? If that is a significant value, one of them is bad and will soon get you into trouble.
    You could divide the users in two groups so the batteries can be discharged independently and install a left/right/both switch across them.
  7. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    Here is the arrangement I use on a 12m sailboat with three batteries total.

    The reasons for this are-

    1. I have found that I could replace three batteries every three years, four batteries every four years, or five batteries every five years. That assumes nothing breaks and that I don't do anything stupid that damages the batteries, which I am likely to do more than once every five years, so I go with the first option.

    2. The aft helm makes it desirable to have two switches so I can enable the engine without going below. I solo a lot.

    3. I rely on solar for 99 percent of my needs.

    So I use three identical cheapish batteries that stay combined almost all the time. I Isolate to start the main engine so that my electronics don't go stupid when she cranks. I also isolate during night passages so I have one good battery for starting. The system is redundant to the point I can lose a switch and can still operate normally. The loads are both connected to the common terminal of the switches and the power feeds the A and B terminals. Either switch in the A+B position will parallel the banks of batteries.

    Attached Files:

  8. hoytedow
    Joined: Sep 2009
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    hoytedow Carbon Based Life Form

    I added this to help me comprehend diagram:

    charge controller = laadstroom regelaar
    expendible batteries = verbruiks accu’s
    consumers(users) = verbruikers
    generator or alternator = dynamo
    solar panels = zonnepanelen
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