24V SOLAR CHARGER

[bigred]

Will a 12v solar charger keep the 24v battery bank on my bus charged? If so ,how do I hook it ?? Just as I would a 24V battery charger?  I know that the solar charger puts out about 14v.

[gumpy]

What do you mean by solar charger? Do you mean one of those little 3x6 solar cells you plug into the cigarette lighter that won't even keep up a car battery?

The best way to get a 12v charger to work on a 24v battery set is to rewire the battery to 12v.

In theory, if you have an equalizer hooked up and you hooked up the 12v charger to one battery, the equalizer to keep the other battery equalized with it. Are you willing to risk $250-$400 worth of batteries on that?

[ol713]

      Short answer is  - - - -  no!  If you are thinking about one
      of the chargers you plug into a cigarette lighter, it is way
      under rated. 
                            Merle
                                     

[Iceni John]

To effectively charge a 24V battery requires up to 29.4V during the Absorb stage, so at the minimum you'll need big grid-tie panels that typically produce just over 30V each.   However, this still may not be enough due to cable losses and charge controller inefficiences, unless you have pairs of GT panels to provide about 60V to the CC.   MPPT charge controllers work best when the panel voltage is no more than twice the battery voltage, but cheaper CC's will just chop off the unneeded voltage.   Flooded lead-acid batteries should be charged at between 5 and 13% of their 20-hour rate  -  this will determine how many and what size panels, and how many amps output of the CC.

John   

[bevans6]

Warning Warning - Contrarian answer coming!  Ah-ooogha Aooogha   

I was thinking about this the other day, and came up with this answer for a buddy.  It assumes all you want to do is trickle charge the batteries at a maintenance level - keep ahead of their natural tendency to discharge for a period of time.  Your batteries are connected in series for 24 volts, chassis ground up to plus 24 volt terminal.  If you get two of those panels, you can connect them in series as well, and charge both batteries at the same time.  Connect the negative of one panel output to negative of the battery pair, positive to the center connection between the two batteries, negative of the second panel to the same place, the center connection between the two batteries and the positive of the second panel to the plus 24 volt terminal.  Best to throw the disconnect switch to disconnect the batteries from the bus to eliminate phantom loads.  If your panels can supply rated up to 20 - 40 watts, they will be able to keep the batteries topped off if the batteries are good and charged to start with.

[Oonrahnjay]

Warning Warning - Contrarian answer coming!  Ah-ooogha Aooogha   

I was thinking about this the other day, and came up with this answer for a buddy.  It assumes all you want to do is trickle charge the batteries at a maintenance level - keep ahead of their natural tendency to discharge for a period of time.  Your batteries are connected in series for 24 volts, chassis ground up to plus 24 volt terminal.  If you get two of those panels, you can connect them in series as well, and charge both batteries at the same time.  Connect the negative of one panel output to negative of the battery pair, positive to the center connection between the two batteries, negative of the second panel to the same place, the center connection between the two batteries and the positive of the second panel to the plus 24 volt terminal.  Best to throw the disconnect switch to disconnect the batteries from the bus to eliminate phantom loads.  If your panels can supply rated up to 20 - 40 watts, they will be able to keep the batteries topped off if the batteries are good and charged to start with. 

      My thought was simpler (not saying it's any good).  Assuming that it's for trickle storage, as Brian outlines, turn off your isolator switch so that the batteries are not connecting to anything and under no load.  Get two 40 watt solar panel charger and attach one to the pos pole of one battery and its other connection to the neg pole of the same battery; do the same thing with the other one so that you're supplying a separate charge to each battery (I am pretty sure that it doesn't matter if you leave the jumper between the two connected for this). 
      That should work, but I have one question -- how good is the voltage regulation on these solar battery chargers?  If you start with something like a Group 31, fully charged and in good condition, and put a charger (any charger) on it that gives an excessive voltage -- even at fairy low wattages -- that battery will begin to get overcharged and overheated after a couple of days.  After that, you're just running a slow but definite damage to the battery and over time you'll find that you've cooked it.  And you SURE that these solar things are good quality and provide the proper voltage regulation?

[bevans6]

Bruce, your idea is exactly the same as mine!  I actually have such a charger, glued to the roof of my truck camper.  It has a little regulator box that controls the charge.  I'm sure the new ones would have a similar option.

[luvrbus]

The refer trucks with the Thermo King units have been using solar charging for years,all I know about one is they work 

[Iceni John]

Whatever you get, just make sure it's a proper 3-stage charger  -  Bulk, Absorb and Float.   Then it won't boil the batteries (or worse).   Also, it's probably best to not get one of those "smart" or "intelligent" chargers, because they won't charge correctly if there's any load also on the battery at the same time.   Morningstar makes some good inexpensive solar charge controllers.

John

[bigred]

On my Prevost conversion ,CC does not provide chassis battery charging from the generator thus the only way I can charge the bus batteries is to hook a  24v battery charger to an AC outlet then running the genset to power the AC outlet'. Just trying to figure out a better way !!!

[chessie4905]

Is there room on the generator to install a 24 volt alternator instead or in addition to the 12 volt alternator?

[bigred]

I am thinking yes,but will have to check.To be honest ,I haven't noticed an alternator on the gen-set but I haven't really looked .

[Tikvah]

Could he simply hook the 12v charge to the equalizer and send 24 out... In other words, run the equalizer backwards?