Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

12V 150AH emergency power

  1. Nov 20, 2007 #1
    The conventional solution to getting 12V 150AH emergency power from a lead acid battery is to have a fully charged battery constantly being trickle charged. This is an unappealing solution for three reasons. (1) It seems like a waste of electricity when a year or more may go by before the battery is used to provide emergency power. (2) The additional cost of the charger is objectionable. (3) Some monitoring of the battery and charger would be adviseable, even if there isn't much that could go wrong. Simplifying my life is what I want; I don't want to have to a charging battery in the back of my mind.

    What is much more appealing to me would be a battery that is activated chemically. That is, having a dry casing holding the lead electrodes and a separate container of sulphuric acid on a shelf. When the emergency power is needed, all that must be done is to pour the sulfuric acid into the cells of the battery.

    If there is such a battery commercially available, I'm not aware of it. If it is available commercially, it's probably very expensive since it isn't being widely used. I can't see why such a battery isn't being widely used.

    A major obstacle to being able to chemically activate a 12V lead acid battery is that nowadays they are sealed. Has anyone else attempted what I am describing and knows of a battery that is unsealed, that is, there is access to the electrolyte in each cell of the battery?

    My idea is to remove the electrolyte from a fully charged "unsealed" 12V battery with a corrosive-resistant small pump and store it in a plastic bottle. My assumption is that the electrolyte won't degrade when stored separate from the lead electrodes. I also assume that the lead electrodes won't disintegrate when exposed to air for a long period. Has anyone else tried this and/ or does this sound like a workable technology?

    Thanks in advance for your comments or suggestions on my proposal for a chemically-acitivated 12V battery. In particular, I would like to hear from anyone who has given what I'm proposing a try.

    -Pete
     
  2. jcsd
  3. Nov 21, 2007 #2

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Trickle charging isn't really necessary - you do have to top up the charge every week or so to prevent sulphate forming on the plates.

    I haven't heard of an empty battery. I suspect that after you add th electrolyte it migth form a thin surface layer of lead sulphate which needs an intial charge to remove.
    Also once you have added the acid you can't empty it again without carefully washing out the battery - otherwise oxides/salts will form on the electrodes.

    Generally for long shelf-life, emergency use, Litium Ion batteries are used.

    There is usually access to the electrolyte in a sealed battery - if you tear the label off there are usually plugs underneath. Even 'sealed' batteries sometimes need topping up with distilled water after a few years.
     
  4. Nov 21, 2007 #3
    reply to post by mgb phys on 11-21

    Thanks for the information that it may be possible to access the cells of a sealed battery.

    Even if the type of charging required is topping off rather than trickle charging, that still necessitates some type of automatic charging mechanism or worse yet periodic manual charging.

    If the electrolyte is removed when the battery is fully charged, then putting it back into the cells at some future time is identical to restoring the battery to its state when it was fully charged. The electrodes develop an insulating layer of lead sulphate that gets progressively worse starting when current is first drawn from the battery. I don't see the logic of your statement that adding the electrolyte might (immediately?) form a thin layer of lead sulphate.

    My guess is that a 12V 150AH lithium ion battery would be very expensive. In my starting post I object to the extra cost of a charger dedicated to the emergency battery, so that should be a clue that I'm not discussing emergency power where cost is no object.

    -Pete
     
  5. Nov 21, 2007 #4

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    No, I didn't think Li-Ion would be a practical system!

    Not really an expert on battery chemistry, the batteries need an initial 'priming' charge when new - not sure why or what it does. I was guessing that there is some chemical reaction with the new plates and the acid.

    Removing the acid is in theory would be equivalent to uncoupling a charged battery - except there is now lead + air + residual sulphuric acid. I'm guessing that's going to create an oxidation / suphating problem quickly.

    Easiest way might be just a low 2A plugin charger and a mechanical timer switch that turns it on for 30mins in every 24 hours or so.
    The alternative energy / off-grid power sites might be a good place to look. Their favorite seems to be used forklift truck battery packs for best power/size/cost.
     
  6. Dec 25, 2007 #5

    RonL

    User Avatar
    Gold Member

    Do you need backup, to operate while the power is off, or just to allow time for the computer to shut down ?
     
  7. Dec 25, 2007 #6

    Q_Goest

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Hi Pete,
    Back about 30 years I used to work behind the parts counter at a motorcycle dealership. All the batteries (lead acid) for motorcycles at that time were dry. We had a large container of sulfuric acid to fill them with when someone came in to buy one. Once filled, no charging was needed. Don't know if they still make them that way or not, but you might ask around.
     
  8. Dec 25, 2007 #7

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Yes but they then need an initial charge to condition them.
    What the OP wanted to know was could he charge a battery, empty it and then refill it so that it was already charged.
     
  9. Dec 26, 2007 #8

    Q_Goest

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Hi mgb. I don't think they need a charge after filling. We never did that, just filled them and sold them at that point. No charging necessary.

    As for dumping out the sulfuric acid though, I don't know if that would work.
     
  10. Jan 1, 2008 #9

    brewnog

    User Avatar
    Science Advisor
    Gold Member

    We ship lead acid batteries 'dry' (ie without the acid) due to air freight regulations. When filled with sulphuric acid (mixed to the correct specific gravity) they're ready to go, and have sufficient charge to start an engine. I wouldn't want to leave a 'dry' battery that way for long though to prevent oxidation of the plates.

    Perhaps your invention could have a nitrogen blanket over the plates until the lights go out?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: 12V 150AH emergency power
  1. Power supply (Replies: 3)

Loading...