How does this not ruin a start battery?

Discussion in 'OnBoard Electronics & Controls' started by BoraBora, Sep 8, 2021.

  1. BoraBora
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    BoraBora New Member

    In this design example, a Sterling DC to DC converter is used to charge a lithium house bank with the Start battery as the "Source". So for example, if we are charging the Lithium Bank at 60Amps over 3hrs, how is this justified when a Start battery is not designed to provide high current over a long period of time?

    < mod note: uncertain about image copyright notice; if this is not your photo, could you please reference original source (url/page this appears on) instead >
     
  2. BlueBell
    Joined: May 2017
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    BlueBell "Whatever..."

    BB,

    Welcome to the Forum but what are you talking about?

    Why would anyone charge a house battery bank with the starting battery.
    You need to find another source for charging your house battery.

    Can you post some of the literature you're working from here?

    BB
     
  3. Rumars
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    Rumars Senior Member

    The given arhitecture is not intended to charge a house bank from a starting battery, since that would imply the starting battery is bigger then the house bank. The electricity for the house bank comes from the alternator, the starting battery is just a big capacitor and safety load for the alternator. It's the same scenario that happens in your car, everything electric is powered by the alternator not your battery, although everything is connected to the battery.
     
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  4. fallguy
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    fallguy Senior Member

    Rumars has it.

    The starter battery is not the source; just a big node and a place for the current to hang out for a bit until used.

    I am using two Victon 12/24 step up chargers in my boat. They send current to the house bank if needed from the alternators.. Also, your example of the current flows are regulated. If the chargers are demanding no current, the voltage regulator in the outboard 'sees' this and stops sending current.
     
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  5. sdowney717
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    sdowney717 Senior Member

    That seems very poor way to charge using a start battery to charge a house bank.
    You have not said what is charging the start battery.
    But if the start battery has a decent charger full time, the charger is going to charge the start battery and charge the lithium bank all as if it were all one battery.
    Is there some kind of voltage or isolator converter between start and house?? The charger will sense both loads as one load as they are all on the same wire.
    Bad thing about that, the charger will overcharge the start battery trying to charge up the lithium bank, as it is connected in some fashion together, I would thinkso.

    And the lithium bank will discharge into the start battery and vice versa.

    There is a reason marine chargers charge multiple banks, many can do 3 banks.
    Some can do multiple different profiles customized to each bank.

    None of your pictures show. Garbage in, garbage out...
     
  6. fallguy
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    fallguy Senior Member

    No. The lithium bank does not charge through the device back to the starter. There is a diode or device that prevents the current from flowing that way.
     
  7. sdowney717
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    sdowney717 Senior Member

    Ok, the sterling DC converter stops that per #4.
    Wonder which one he has. I have an Onan MCCK AC generator onboard and a Victron 3 bank charger, which I have found having an AC generator is better than an inverter that runs down the batteries FAST, and can't run the AC.

    But DC-DC setup cant charge the lithium bank very long unless the main engine DC alternator runs, charging the output battery (source, starter battery) Input battery (battery receiving DC-DC converter power) is the lithium bank, per item #4, that is how I read that, in and out could be reversed, so confusing me on their terminology.

    Sterling Power battery to battery charging system - DC to DC smart battery charger, marine grade DC powered charger 24v to 12v (sterling-power-usa.com)
    1) Multiple Activation Modes: Automatic for most non vehicle applications,

    Manual for remote activation.

    Regenerative braking (requiring ignition feed),

    Automatic regenerative braking, requiring no ignition feed.

    2) Input 24v & Output charging at 12V

    3) Much larger model up to 3000W coming soon.

    4) Current is NOT taken from the input battery and given to the output battery. The B2B uses alternator power to charge the output battery. Manual mode and regenerative braking mde allows you to override this.
     
  8. fallguy
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    fallguy Senior Member

    The dc-dc setup does not charge at all without the alternator. If there is no input flowing; the starter batteries are not depleted to the house. And the lithium house never charges the starts.


    I'd say the device is smart enough to not allow any charge to flow off the starter battery. If the starter battery is set to 13v and the house to 12.5 (kiss rule), the charger won't flow current off the start to level afaik..
     
  9. sdowney717
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    sdowney717 Senior Member

    (1) Fast Caravan Battery Charging : Sterling Power - YouTube
    Video showing it working. the DC-Dc charger isolates the start battery on the car. It uses the car alternator to charge the 'caravan' battery.
    He makes the point that when connecting directly from the rear bumper port, the volts and charging is low and slow compared to their charger.

    BUT THIS, why not connect the car battery direct to the Caravan battery using those large wire cables... and get the 40 to 50 amps... You already have to use those large long cables to power the DC - DC converter.
    The only negative thing, you could run down the start battery doing that if the engine is OFF.

    BUT!!, you can get a Blue Sea ACR to connect the caravan bank to the car and it will work just like it does on a boat and dont bother with the DC-DC expensive converter.
    Hint!, this DC-DC device is a technology solution that is more expensive than using an ACR. The ACR will only join the 'caravan' battery when the alternator is running.
    PLUS!!, there must be some efficiency lost in this DC-DC power conversion step, so you have lost that permanently using the DC-DC converter.

    PLUS, this device is just one more device to fail, an ACR is going to be more robust.

    Of course that is all great except if your changing voltages like 12 to 24, then you have to use a DC converter, otherwise there are better ways to do this.
     
  10. sdowney717
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    sdowney717 Senior Member

    And for an even cheaper solution than a Blue Sea ACR, use a 12v golf cart continuous duty relay of 80 amps. You can get them for 12, 24, 36, 48 volt coils
    Most people will only need 12v ones.
    Wire the relay coil to the on ignition switch.
    The relay will only join the banks when the engine alternator is running.
    Add a second on-off switch in series with the relay control wire so you can turn the golf cart relay on and off when the engine is running.

    Again it wont of course work if your bumping volts from 12 to 24, etc.. between battery banks.
     
  11. sdowney717
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    sdowney717 Senior Member

    To answer OP, it wont ruin the start battery as it is an isolated PSU that charges off the alternator.
     
  12. fallguy
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    fallguy Senior Member

    The ACR is really not used in the fashion described because of the voltage differences afaik. I ran into same running a 24v house and 12v charging. My house will not charge my starts..but they can support each other.
     
  13. sdowney717
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    sdowney717 Senior Member

    ACR only will work if keeping the voltage across banks the same.
    For myself, I doubt I will ever run into it, a 24v house and 12 v start, I am just not in the market to buy anything new.
    I would like to buy a large travel trailer to pull behind my diesel Ram dually 4x4, to go camping with wife, kids and grandkids.
    May or may not ever happen.
    Not a question of money or time, just getting round to it.
    For now, I have been researching them, most are not well made.
    And some places dont like them older than 10 years.
     
  14. Rumars
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    Rumars Senior Member

    There reason you see this dc-dc chargers is to be able to integrate lithium housebanks into existing lead acid systems. Lithiums don't react to charging like lead acid and need a different alternator control and system arhitecture in order to keep the alternator happy. The dc-dc charger allows you to limit amperage to a safe level for the alternator while simultaneously keeping the lead acid control components and correctly charging the lithiums. They are not an elegant solution but a very practical one.
     
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  15. sdowney717
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    sdowney717 Senior Member

    LiFePO4 Batteries On Boats - Marine How To
     
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