Charging 24v. system

[Chaz]

Just a quick question....
Do I HAVE to seperate the 8D's to charge them with a 12volt charger (albeit a good charger) or can i leave the connections together and charge both at the same time but slower?
  Thanx
     Chaz

[Blacksheep]

Don't you already have a 12v system?

[H3Jim]

You don't have to, but they may not charge evenly if you leave them together.  For practical purposes, if they are both in the same condition and one is not a lot worse than the other, if might be ok.  You may not get quite as long a battery life doing it that way.

You might try it.  Then separate them and check charge levels.

[Blacksheep]

My mistake! I thought GM's were 12v, not 24v. If it were mine, I would either seperate them or get a 24v charger!

[Chaz]

Got it. Thanx guys. I just didn't want to always have to seperate them if I didn't have to. (hopefully it won't be that often! )
My bus didn't want to start yesterday and i ran it down a little. She was still turning over ok, but starting to get a little slower. So I thought I'd give'em a little juice before I try it again.
Next I have to figure out why she turns over ok but won't "hit". It trys a little bit, but no avail.

Always sumtin,
   Chaz

[Sojourner]

About using 12v charger on 24v series set........no need to seperate the terminals. You can charge one at time with 12v charger or two 12v charger. One for each battery.
http://batterytender.com/connecting.php/#5

FWIW

Sojourn for Christ, Jerry

[Tenor]

A variant of the same question,
If you have a vanner equalizer and you are charging one battery at a time, will it be sending a balanced load to both batteries?

Glenn

[Chaz]

Thanx Jerry, but it didn't show my situation. (At least I don't think I missed it ) I have 2 batteries in series -24v- and one 12v charger.
So I guess the best way is still one at a time............Dang.

By the way, the bus started. I plugged in the heater for awhile, believe it or not, and she fired. I will do my radiator check and when I get back I'll let her sit over night and see if there was some kind of "fluke" or something. I CERTAINLY HOPE I don't need the heater in 8o* weather now. I'm not all that versed in DD's but I know THAT wouldn't be good. Hopefully just some sort of flukey thing. (Please, please, please..............) 

Thanx
  Chaz

[edroelle]

The Vanner will equalize the voltage between batteries IF the upper battery (24 volt post) is at a higher voltage.  Unless they changed their design, you cannot charge the lower battery (12 volt and ground posts) and expect it to equalize to the upper.

Ed Roelle
Flint, MI

[Tim Strommen]

Hi Chaz,

If you are running a two 8D battery 24volt setup, there are two potential problems you may need to contend with:

• 12-volt loads tapped off the lower battery causing it to be discharged more than the upper battery
• uneven charging for the two batteries from a 24 volt charging source (like an alternator or shop charger)

The 12-volt loads can cause the lower battery to be more "dead" than the upper battery which can aggravate the second point - uneven charging.  A discharged battery will like to get its bulk current during recharge for a while.  Depending on how discharged the battery is, is will need more current to be replaced.  If you have one battery that is not charged, in series with one that is charged, the charged battery will act like a current limiter for the discharged battery.  When the charger stops providing current at the voltage set-point, the lower battery will still be discharged (and plate erosion will begin to take place - due to the constant discharge state).  The upper battery will have to try to pass the current that the lower battery is demanding from the charger, which can overheat the upper battery and boil off the water and warp the plates.

This cycle (left unchecked) will eventually kill the lower battery (and will probably take the upper battery with it, since the upper battery will being more charged will be outputting more current from 24volt draws, and may have warped plates or low water causing plate erosion).

A Vanner is really only designed to ensure that the lower battery gets current/voltage priority during the charge state, and that the upper battery is as discharged as the lower battery durig the load draws.  It does this by using an isolated switched supply, which takes power from the upper battery and by creating an AC waveform - puts it through an isolation transformer, then rectifies it back to DC.  This way you CAN hook parallel the batteries while they are still hooked up in series.  Since the Vanner's circuit is only designed to go one way, if you have a problem with the upper battery - it will do nothing (and will still probably take out your lower battery.


The best way to ensure each battery is getting its best charge - is to hook them up individually to a charger.  The solar 12v chargers are usually encased in plastic so they are isolated, which mean you could put two moderately sized pannels (like 15Watts) for each battery on the roof to keep your batts topped off.

If you are starting, then running your engine only for a few mintues, you're probably not replacing the start current draw.  A starter can draw anywhere from 600-1200 amps for a few seconds, and the your alternator can probably only output 200amps (at that is if it is spun at 6K RPM for an hour...).  If you are having to press the start switch for about 15 seconds (the longest that it's recommended to do that), at 600 amps draw you are pulling roughly 60AHr out of your batteries.  You need to let your batteries recover a bit before trying again (they are not built to continuously provide "surge" output).  Remember also, whatever you take out of a lead acid battery, you usually need to replace with 110% of that draw (so about 70AHr).

You should also check the voltage of the batteries before starting.  A fully charged battery should show 12.65 or higher volts or a specific gravity of between 1.265 to 1.285 at 25C ambient.

-Tim

[Chaz]

Just curious...........
would flipping the batteries from top to bottom every so often be of any advantage??

[Tim Strommen]

...would flipping the batteries from top to bottom every so often be of any advantage??...

Just like rotating your tires, there is a slight wear-leveling advantage to this.  However, you will notice more improvement if you are always ensuring that your batteries are topped off (both water and charge) before storage.

If you plan on leaving the rig parked for more than a week, I personally recommend taking the start batteries out of the rig, bringing them home - and attaching them to an AC battery charger to keep them up (and not letting them get too cold).  For the house batteries this can be a bit of a challenge (you may have over 1,000lbs of batteries to move...) - so solar battery chargers are a better bet for charge maintaining.

-Tim

[Chaz]

Thanx Tim.
My bus sits right outside my studio so i keep it plugged in. I also have a 4024 inverter which I understand is a good thing.  But I have yet to tie the house batts to the start batts. I would imagine that would be a plus.    (just not enough hours in a day!        )

  Thanx for the info!
     Chaz