General battery charging question - AGM

stereoman405stereoman405 Solar Expert Posts: 56 ✭✭✭✭
No solar specific, but I figured the same principals should apply.

I have an aftermarket dual battery setup in my rig and have a charging question for you.

It basically consists of an isolator that both batts hook up to, and there is an in cab switch that essentially lets you choose between charging each batt together (in parallel) or keep them isolated. (Saves one in reserve.) I just installed two high end 68AH 12v Odyssey AGM's.

When the engine is running and both batts are linked and charging, I noticed that the isolator itself causes a rough .24V drop going from one post to the other. I then add that to another rough .50V loss from the 4' of wire going to 'Batt B' for a net .75V or almost 1V loss from alternator to Batt B.

To sum up, when the alternator is putting out 14.39V to batt A, batt B will only get 13.34V. So it is a lopsided charge.

My concern is that if its impossible for batt B to ever break 13.3V of charge, then that might mean it will never get fully charged and suffer a shorter life.

So my question is, will 13.3v be enough to keep and AGM relatively healthy? I know an automotive alternator is less than efficient to begin with but I'm wondering if it's worth the cost to run larger cabling to cut loss down, or try to figure something else out.

The nice thing is that when they are paralleled, both batts are being drawn from so 'Batt B' is still getting a little workout, not just a float charge.

Comments

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: General battery charging question - AGM

    13.3v is about a float voltage for most agms so i believe it would be maintained, but getting to a full charge in the first place without exceeding the battery's max voltage is the main goal. check the manufacturer's specs on bulk and float charge levels to see how well you are actually doing.
  • landyacht.318landyacht.318 Solar Expert Posts: 82 ✭✭✭✭
    Re: General battery charging question - AGM

    What type of isolator are you running?

    Is it a Diode type with the cooling fins?
    or
    Is it a rounded cylinder Solenoid/ Relay which is activated by a switched 12 volts?

    I would not be happy with 13.39 volts when charging an expensive battery, unless it were already fully charged.

    The Diode type isolators are known for their voltage drop. There is one brand out there that claims only a 0.05volt drop. I forget the brand.

    The Solenoids vary greatly in quality. The contacts inside can wear out and cause the whole thing to heat up over time.

    There are smart solenoids that only parallel the batteries after the starting battery is fully charged, and do not require wiring in of a switched 12 volts from the ignition.


    I personally have gone with a Boat Battery1/2/both/off Manual Switch. But it is not an idiot proof method.

    There is an excellent thread on the following link that will inform you of brands and types of battery isolation for Vehicles.
    http://expeditionportal.com/forum/showthread.php?t=35667

    If you choose to keep your current isolator/separator, you should use 4 AGW wire with minimum amount of connections between alternator and battery. The ground wire from alternator should be the same gauge as the positive. This will allow maximum alternator recharging and battery longevity.
  • stereoman405stereoman405 Solar Expert Posts: 56 ✭✭✭✭
    Re: General battery charging question - AGM
    niel wrote: »
    13.3v is about a float voltage for most agms so i believe it would be maintained, but getting to a full charge in the first place without exceeding the battery's max voltage is the main goal. check the manufacturer's specs on bulk and float charge levels to see how well you are actually doing.

    I think they both metered about 12.6 new. Are you saying that I should top them off with my Truecharge 10 first before runnig them any longer in the vehicle?

    How does a 'first time' charge affect things? I didn't realize you needed to do that.
  • stereoman405stereoman405 Solar Expert Posts: 56 ✭✭✭✭
    Re: General battery charging question - AGM
    What type of isolator are you running?

    Is it a Diode type with the cooling fins?
    or
    Is it a rounded cylinder Solenoid/ Relay which is activated by a switched 12 volts?

    I would not be happy with 13.39 volts when charging an expensive battery, unless it were already fully charged.

    The Diode type isolators are known for their voltage drop. There is one brand out there that claims only a 0.05volt drop. I forget the brand.

    The Solenoids vary greatly in quality. The contacts inside can wear out and cause the whole thing to heat up over time.

    There are smart solenoids that only parallel the batteries after the starting battery is fully charged, and do not require wiring in of a switched 12 volts from the ignition.


    I personally have gone with a Boat Battery1/2/both/off Manual Switch. But it is not an idiot proof method.

    There is an excellent thread on the following link that will inform you of brands and types of battery isolation for Vehicles.
    http://expeditionportal.com/forum/showthread.php?t=35667

    If you choose to keep your current isolator/separator, you should use 4 AGW wire with minimum amount of connections between alternator and battery. The ground wire from alternator should be the same gauge as the positive. This will allow maximum alternator recharging and battery longevity.

    It is the round solonoid style. Called a 'Painless' kit I beleive. I'm familiar with the diode style. I have a Bluesea setup on my boat that uses a diode.

    Are you saying I should run a 4awg from the alt to each batt? Right now tha alt ties into post #1 on the solonoid along with a cable to batt A. So batt A is always tied to teh alt. Batt B only ties in when the ignition is on. I beleive its the OEM 6AWG wire. I am planning on putting in a higher output alt with 2AWG after I get this squared away.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: General battery charging question - AGM
    I think they both metered about 12.6 new. Are you saying that I should top them off with my Truecharge 10 first before runnig them any longer in the vehicle?

    How does a 'first time' charge affect things? I didn't realize you needed to do that.

    what i was saying is that 13.3v will not recharge the battery, but 14.39v will give it it's bulk charge.
  • landyacht.318landyacht.318 Solar Expert Posts: 82 ✭✭✭✭
    Re: General battery charging question - AGM

    If you ran a wire from alternator to each battery, then they would not be isolated, ever.

    Just run a fatter wire from the one side of the solenoid to the second battery. And make sure the connections are clean and tight. Also make sure the second battery has a good ground.

    6 awg should be okay. If the wire from the solenoid to the second battery is already 6 awg, then you are loosing way too much voltage over the solenoid and it's connections.

    After you deplete the batteries below 80% SOC and start the engine, see how hot the solenoid gets. Hot is bad.

    If you left the stock wiring harness, the original engine battery might have 2 wires feeding that battery Current could be flowing through the stock OEM charging circuit AND the cable you added to the one side of the solenoid from the alternator. If you dashboard has an Ammeter, not a voltmeter, the current flows through this meter as well. With the additional wire you ran from the alternator to solenoid, this dash ammeter is not seeing the full output of the alternator.

    The second battery will only be seeing what makes it through the solenoid the way you have it wired now. If the engine battery has 2 charging circuits, It might explain the large voltage difference between the batteries with the engine running.

    It's always good to have a 120charger volt top up the batteries before installation, and after, but it could be argued that the battery(s) should not be hooked to the vehicles wiring while charging.

    Keep in mind a Higher amperage alternator will only output more amperage at idle speed if the case is physically larger, or the drive pulley is smaller.
Sign In or Register to comment.