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Thread: Powering car from a 13.8V power supply ok?

  1. #11
    FLAC
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    Quote Originally Posted by TruckinMP3
    BS... that is why float and trickle chargers are made.



    BS... Car charging systems use a voltage regulator to prevent damage to the battery.




    Again, BS... See above for car system.
    Truckin, You're flinging a lot of BS everwhere and it's piling up.

    The other guys right, the Voltage Regulator in a car maintains a Constant Voltage of around 13.8 volts.

    The only reason they have trickel chargers is to extend battery life as charging with large currents, while charging batteries fast, limits their life.

    There are a lot of cars out there that don't try to limit the current on their charging systems, and since most car batteries are classed as starting batteries, they are not designed to get very depleted. This is not a problem for day to day life. Now if your using a deep cycle battery, that's another story. Most of the time when you bring out a car charger, you killed your battery and you want to charge it in a way that will preserve it's useful life. THATS why they have float and trickel chargers.

    Jeff
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  2. #12
    FLAC Jahntassa's Avatar
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    Moral of the story is you can probably power your CarPC off it, but put some sort of Diode or Relay between it and the car so you aren't trying to power the whole car or charge the battery while the power supply is on.

  3. #13
    Self proclaimed spoon feeder TruckinMP3's Avatar
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    http://www.carcare.org/Electrical/vo...egulator.shtml

    "Description: The voltage regulator is an electronic device that regulates alternator output according to the battery’s state of charge and accessory loads. "

    Not constant but Load dependant, part of the load is the battery's state of charge.


    It is not that "the battery only accepts the charge untill full" The charging system, in the car or an external charger, needs to protect the battery from overcharging that can damage the battery. Cheap charging systems need to be monitored, more complex chargers use circuts to protect from this over charge possibility. The Auto's voltage regulator performs this function as well as maintaining the correct voltage to run the accessories up to the limit of the alternator's output.
    TruckinMP3
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  4. #14
    FLAC
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    Quote Originally Posted by TruckinMP3
    http://www.carcare.org/Electrical/vo...egulator.shtml

    "Description: The voltage regulator is an electronic device that regulates alternator output according to the battery’s state of charge and accessory loads. "

    Not constant but Load dependant, part of the load is the battery's state of charge.


    It is not that "the battery only accepts the charge untill full" The charging system, in the car or an external charger, needs to protect the battery from overcharging that can damage the battery. Cheap charging systems need to be monitored, more complex chargers use circuts to protect from this over charge possibility. The Auto's voltage regulator performs this function as well as maintaining the correct voltage to run the accessories up to the limit of the alternator's output.

    I still think your wrong here. The wikipedia says this about an alternator:

    "Modern automotive alternators have a voltage regulator built into them. Typical car alternators generate the field using a DC current through slip rings. The field current is much smaller than the output current taken from the fixed stator windings, and so heavy duty slip rings are not required. For example, in an alternator rated to produce 70 amperes of DC, the field current will be less than 2 amperes. The voltage regulator operates by modulating the small field current in order to produce a constant voltage at the stator output."

    It provides a constant voltage to the battery. The battery charges till it reaches that voltage and then current stops flowing. This is for Lead Acid Batteries. Not for Ni-cad or nickel metal hydride. Look at any gel cell 12 volt battery, it has a range for constant voltage charging. This is the same for wetcell batteries too.

    The regulator reacts to changes in loads by providing more current, but the result is a constant voltage.

    -Jeff
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  5. #15
    Self proclaimed spoon feeder TruckinMP3's Avatar
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    And is controled by the volatage regulator... the battery has no control over the flow of energy in volts or amps.

    The post I called BS on indicated the battery just stoped being charged.... the voltage regulator (whether internal or external to the alternator) is in control not the battery.

    We may be saying the same thing... the battery does not decide to 'accept' or 'decline' the energy if it is provided.
    TruckinMP3
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  6. #16
    FLAC
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    Quote Originally Posted by TruckinMP3
    And is controled by the volatage regulator... the battery has no control over the flow of energy in volts or amps.

    The post I called BS on indicated the battery just stoped being charged.... the voltage regulator (whether internal or external to the alternator) is in control not the battery.

    We may be saying the same thing... the battery does not decide to 'accept' or 'decline' the energy if it is provided.
    But that's wrong. The Battery is in control of the flow of current.

    Think of it like this:

    A ni-cad battery is like a water balloon. The pressure is the voltage and the current is the ammount of water flowing and the capacity is the total volume of water. If you put the ballon on the hose with 80 psi (voltage) , the ni-cad battery will fill up and if you don't limit the current, eventually the ballon will explode.

    The car lead-acid battery is like a bottle. It will only take as much from the hose as it has capacity for, if you keep it on, it will just fill up and stop taking water because the container is designed to take constant pressure (voltage).

    The alternator puts out a constant voltage (13.8 volts) and the battery decided when it is full and stops drawing current. The alternator only provides more current if it is asked, aka depeleted battery, headlights turned on, car computer, etc. But it is the battery asking for more current, not the atternator telling the battery when it is done charging it.


    Deep cycle battery chargers are smarter and limit the current which inturn limits the voltage, but this is Not what they have in cars.

    -Jeff
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  7. #17
    Self proclaimed spoon feeder TruckinMP3's Avatar
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    I understand your example but I do not agree.

    Can you show a link that backs the bottle vs balloon concept?
    TruckinMP3
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  8. #18
    Self proclaimed spoon feeder TruckinMP3's Avatar
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    I went looking and found this:
    http://www.uuhome.de/william.darden/carfaq9.htm

    "Three stages--bulk, absorption and float are normally used for wet car and motive deep cycle batteries with an optional equalizing stage. Three stages--bulk, absorption and float are normally used for AGM (Ca/Ca) and Gel Cell (Ca/Ca) VRLA car and motive deep cycle batteries. Three stages--bulk, float and equalization are normally used for wet stationary deep cycle batteries and two stage--bulk and float are normally used for VRLA stationary deep cycle batteries with an optional equalization stage is some cases.
    9.1.1. The BULK stage is where the charger current is constant and the battery voltage increases, which is normally during the first 80% of the recharge. Give the battery whatever current it will accept as long as it does not exceed 25% of the 20 hour (expressed "C/20") ampere hour (AH) capacity rating, 10% of the Reserve Capacity (RC) rating, wet batteries do exceed 125° F (51.5° C), and VRLA batteries do not exceed 100° F (37.8° C).
    9.1.2. The ABSORPTION stage is where the charger voltage, depending on the battery type, is constant between 14.1 VDC and 14.8 VDC at 80° F (26.7° C) and the current decreases until the battery is fully charged, which is typically the last 20% of the recharge. For wet batteries, gassing (making a bubbling sound) usually starts at 80% to 90% of a full charge and is normal. A full charge typically occurs when the charging current drops off to 2% (C/50) or less of the AH capacity of the battery and each cell of a wet battery is moderately gassing equally. For example, end current for a 50 AH (C/20) battery is approximately 1.0 amp (1000 milliamps) or less. If the battery will not "hold" a charge, the current does not drop after the estimated recharge time, and a wet battery is hot (above 125° F (51.5° C)), then the battery may have some permanent sulfation. (Please refer to Section 16 for more information about sulfation and how to remove it.) Manual two stage chargers that have a bulk and absorption stage must be turn off when the battery is fully charged to prevent overcharging.
    9.1.3. The optional FLOAT stage is where the charge voltage, depending on the battery type, is reduced to between 13.0 VDC and 13.8 VDC at 80° F (26.7° C), held constant. It can be used indefinitely to maintain a fully charged battery to overcome the natural self-discharge of the battery. The current is reduced to approximately 1% (C/100) or less. Three stage "smart" chargers usually have the bulk, absorption and float stages. (Please refer to Section 13 for more information about storing batteries and continuous float charging.) Three stage chargers usually have the bulk, absorption and float stages."



    I think this says the Volts and the Amps supplied change depending on the complexity of the voltage regulator circut.
    TruckinMP3
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  9. #19
    FLAC
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    Quote Originally Posted by TruckinMP3
    I went looking and found this:
    http://www.uuhome.de/william.darden/carfaq9.htm

    "Three stages--bulk, absorption and float are normally used for wet car and motive deep cycle batteries with an optional equalizing stage. Three stages--bulk, absorption and float are normally used for AGM (Ca/Ca) and Gel Cell (Ca/Ca) VRLA car and motive deep cycle batteries. Three stages--bulk, float and equalization are normally used for wet stationary deep cycle batteries and two stage--bulk and float are normally used for VRLA stationary deep cycle batteries with an optional equalization stage is some cases.
    9.1.1. The BULK stage is where the charger current is constant and the battery voltage increases, which is normally during the first 80% of the recharge. Give the battery whatever current it will accept as long as it does not exceed 25% of the 20 hour (expressed "C/20") ampere hour (AH) capacity rating, 10% of the Reserve Capacity (RC) rating, wet batteries do exceed 125° F (51.5° C), and VRLA batteries do not exceed 100° F (37.8° C).
    9.1.2. The ABSORPTION stage is where the charger voltage, depending on the battery type, is constant between 14.1 VDC and 14.8 VDC at 80° F (26.7° C) and the current decreases until the battery is fully charged, which is typically the last 20% of the recharge. For wet batteries, gassing (making a bubbling sound) usually starts at 80% to 90% of a full charge and is normal. A full charge typically occurs when the charging current drops off to 2% (C/50) or less of the AH capacity of the battery and each cell of a wet battery is moderately gassing equally. For example, end current for a 50 AH (C/20) battery is approximately 1.0 amp (1000 milliamps) or less. If the battery will not "hold" a charge, the current does not drop after the estimated recharge time, and a wet battery is hot (above 125° F (51.5° C)), then the battery may have some permanent sulfation. (Please refer to Section 16 for more information about sulfation and how to remove it.) Manual two stage chargers that have a bulk and absorption stage must be turn off when the battery is fully charged to prevent overcharging.
    9.1.3. The optional FLOAT stage is where the charge voltage, depending on the battery type, is reduced to between 13.0 VDC and 13.8 VDC at 80° F (26.7° C), held constant. It can be used indefinitely to maintain a fully charged battery to overcome the natural self-discharge of the battery. The current is reduced to approximately 1% (C/100) or less. Three stage "smart" chargers usually have the bulk, absorption and float stages. (Please refer to Section 13 for more information about storing batteries and continuous float charging.) Three stage chargers usually have the bulk, absorption and float stages."



    I think this says the Volts and the Amps supplied change depending on the complexity of the voltage regulator circut.

    This document is targeted at charging deep cycle batteries which is a battery that goes down to like 10% charge or so. Cars do not implement the bulk stage, and they don't need to because by design the battery never is suppose to get below 80%. That's what I said in the previous post. Deep Cycle batteries are different than the ones you get at the auto parts store, which are Starter batteries. Ever wonder why they are spec'd in cold cranking amps rather than amp hours? It's because they are only suppose to be used for starting the car and never going below 80%, thus again, by design, the Bulk phase is not implemented.

    It also mentions the optional last stage. It is too much work for auto manufacuters to bother with this optional stage and there is a constant fluctuation of loads on the battery under normal driving conditions. Keeping the battery from discharging is just not practicle because there is always some kind of load. This is only useful if you want to keep the battery topped off for 6 months over the winter.


    So if you get rid of the Bulk stage and the Float stage, you have exactly what I said you have in a car, a constant voltage charger circuit from a constant voltage alternator regulator output.

    -Jeff
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  10. #20
    FLAC
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    Here, I'll back up my claims from that same article you posted.

    http://www.uuhome.de/william.darden/carfaq9.htm#vehicle

    "Vehicle Charging System

    A vehicle charging system is made up of three components, an alternator (or DC generator), voltage regulator and a battery. Usually when a vehicle is jump started, it is NOT driven long enough to fully recharge the battery. The length of time to fully recharge the battery depends on the amount of discharge, the amount of surplus current that is diverted to the battery, how long the engine is run, engine speed, and ambient temperature. An alternator is sized by the vehicle manufacturer to carry the maximum accessory load and to maintain a battery and NOT to recharge a dead battery. For example, if 300 amps were consumed for two seconds to start a car from a fully charged battery, it will take an 80 amp charging system approximately 7.5 seconds to replace the .167 amp hours of power used. If 25 amps are available to recharge the battery, it will take 24 seconds and 10 minutes at one amp. With a dead 120 minute RC (60 amp hour) battery, it would take approximately 90 minutes at 80 amps, 4.8 hours at 25 amps, or 120 hours at one amp to fully charge (100% State-of-Charge) it."
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