Wet/Lead Acid "Maintenance Free" car battery Charging

Wanderman
Wanderman Solar Expert Posts: 180 ✭✭✭
OK...if I was to leave a circuit open to the chassis battery (a plain old group 27 lead acid) and my MPPT Morningstar is set to battery type #6 :

Flooded 14.70 Absorb 13.50Float 15.40 Equalize

what will happen to my chassis battery if left in the circuit indefinitely?

If this will boil out the battery and kill it, is there a type of battery that will take the charging numbers while giving me decent CCA?

Just curious, I can wire a workaround, but I'd rather not.

Another tack, what about a hybrid deep cycle/starting battery? I could attach a low voltage disconnect (i.i "Battery Saver") and perhaps be able to utilize a few more amp/hrs?

Opinions? Suggestions? Comments?

Rick

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Wet/Lead Acid "Maintenance Free" car battery Charging
    Wanderman wrote: »
    OK...if I was to leave a circuit open to the chassis battery (a plain old group 27 lead acid) and my MPPT Morningstar is set to battery type #6 :

    Flooded 14.70 Absorb 13.50Float 15.40 Equalize

    what will happen to my chassis battery if left in the circuit indefinitely?

    If this will boil out the battery and kill it, is there a type of battery that will take the charging numbers while giving me decent CCA?

    Just curious, I can wire a workaround, but I'd rather not.
    My two cents worth... Unless you isolate the chassis (vehicle battery) from the RV House Battery Bank--you will:
    Starting (sometimes called SLI, for starting, lighting, ignition) batteries are commonly used to start and run engines. Engine starters need a very large starting current for a very short time. Starting batteries have a large number of thin plates for maximum surface area. The plates are composed of a Lead "sponge", similar in appearance to a very fine foam sponge. This gives a very large surface area, but if deep cycled, this sponge will quickly be consumed and fall to the bottom of the cells. Automotive batteries will generally fail after 30-150 deep cycles if deep cycled, while they may last for thousands of cycles in normal starting use (2-5% discharge).

    Second, the "high voltage" charging of the House Battery bank will probably consume water with the vehicle battery. It may also cause the battery to fail a bit sooner than "normal". Vehicle batteries seem to like running around 13.8 to 14.2 volts... running 14.5-15+ volts is probably a bit hot for them.
    Another tack, what about a hybrid deep cycle/starting battery? I could attach a low voltage disconnect (i.i "Battery Saver") and perhaps be able to utilize a few more amp/hrs?

    Sort of the catch 22... Run all deep cycle batteries in one bank--and if you accediently run the bank dead, your vehicle won't start either.

    What are your needs? To have as much power (in battery form) as possible in an RV format (limited space/weight)?

    Do you need "backup power" to start the vehicle?

    Sharing a vehicle electrical system with a 12 volt Solar RE system can be a bit problematic--I am not sure I would trust vehicle 12 VDC electronic on a solar RE battery bank much above 14.5 volts... Running 15-15.5+ volts (equalization) may be damaging.

    Are you trying to share the vehicle alternator for charging when on the road/in place of a backup AC (or DC) genset?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Wanderman
    Wanderman Solar Expert Posts: 180 ✭✭✭
    Re: Wet/Lead Acid "Maintenance Free" car battery Charging

    BB,
    that was/is a very concise thoughtful reply. I will do my best to shed some light on the purpose and concepts.

    Right now the chassis battery is isolated like most RV systems. When running the alternator will charge the chassis battery first then release current to continue charging the house batteries.

    Since I leave the motorhome plugged in when not in use, to be ready to go when I have a few days to string together, the batteries were being charged and maintained by a 4 stage charger unit built into the converter/charger assembly I replace. (Progressive Dynamics PD4645) it would max out at 45 amps to the batteries. It was designed to max out for charging at:

    BOOST Mode 14.4 Volts - Rapidly brings RV battery up to 90% of full charge.

    NORMAL Mode 13.6 Volts - Safely completes the charge.

    STORAGE Mode 13.2 Volts - Maintains charge with minimal gassing or water loss.

    DESULFATION Mode 14.4 Volts every 21 hours for a period of 15 minutes to prevent battery stratification.

    this is fine for "regular" batteries.

    As we know Trojan Deep Cycles prefer a bit different profile based upon 14.8 V.

    Now, when I leave the RV plugged in, the main charger charges up to its limitations and the Solar charging system "finishes" off the charge to the upper limit.

    I COULD isolate the solar charging system and in fact there is a battery selector switch (On/Off/Bat 1/Bat 2/ALL) AND a knife style switch at the chassis battery terminal.

    Originally, I was simply looking to NOT change the process and leave everything in the charging circuit.

    Then I figured if the system to charge is in place, perhaps I could add a wee bit of capacity to the system overall. Perhaps by leaving the circuit open to all batteries and then when on Solar/Battery only switching the chassis battery out of the circuit until it was needed/wanted for additional amp hours. I would place a battery saver type device on the chassis battery so it could not go below the point of being able to start the main engine.

    This is the simplest solution, though may not be the best. I may have to replace the standard starting battery with something else (Marine Deep Cycle/Start Hybrid?) to survive the higher Trojan style charging profile.

    The other way to do this and NOT have the benefit of extra "emergency" storage would be to run a small 12V maintenance charger from a handy 12V line to keep the existing chassis battery topped off.

    I suppose what i am looking for here is fact based opinions.....

    Thanks again,

    Rick
  • Wanderman
    Wanderman Solar Expert Posts: 180 ✭✭✭
    Re: Wet/Lead Acid "Maintenance Free" car battery Charging

    There is another option.

    I have read that I can use a deep cycle as a start battery without harm. As long as it is oversized 120% or so. Ie Group 27 to group 31. I have it setup to be a 2nd battery bank...hmmmm

    Rick
  • Wanderman
    Wanderman Solar Expert Posts: 180 ✭✭✭
    Re: Wet/Lead Acid "Maintenance Free" car battery Charging

    So any opinion on using a deep cycle as the start battery with a low voltage or smart battery saver device to prevent a no start condition?

    Rick
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Wet/Lead Acid "Maintenance Free" car battery Charging
    Wanderman wrote: »
    So any opinion on using a deep cycle as the start battery with a low voltage or smart battery saver device to prevent a no start condition?

    Rick

    Yes; don't do it.
    Your vehicle charging system isn't designed to provide the kind of charging profile a deep cycle needs. Eventually the battery will sulphate, long before its life should be up, and you will have spent a lot of money on a starting battery for no particular gain.

    In my opinion, and anyone can disagree - it's not my money being spent, you're better off keeping the two systems separate and only connecting them if needed. As in emergency jump start from the house battery or emergency charge of the house from the vehicle.
  • Wanderman
    Wanderman Solar Expert Posts: 180 ✭✭✭
    Re: Wet/Lead Acid "Maintenance Free" car battery Charging

    CB,
    The way the systems can be bridged will allow the vehicle charging system to "fill" the secondary deep cycle to 14.4-ish V. I would be relying on the Morningstar to keep it's profile to spec (14.8V and equalize)

    I'd entertain other suggestions, but if you read my post I do have a few options.

    Rick