Batteries

Discussion in 'Boat Design' started by FAST FRED, Jan 22, 2016.

  1. FAST FRED
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    FAST FRED Senior Member

    Read this on another site and wonder if it could be true?


    "Corrosion on the terminals is due to hydrogen gas being released from the acid in the battery.

    It mixes with other things in the atmosphere under the hood and produces the corrosion you see on the terminals.

    Generally, if the corrosion is occurring on the negative terminal, your system is probably undercharging. If on the positive side, it is probably overcharging.

    Most often it will be seen on the negative side because the battery is usually in an undercharged situation. This is just the nature of the beast, I'm afraid."
     
  2. hoytedow
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    hoytedow Wood Butcher

    That is interesting. If so, the better the battery area is ventilated, the less concentrated the hydrogen gas will be, thereby reducing the opportunity for the gas to promote corrosion.
     
  3. gonzo
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    gonzo Senior Member

    That's not correct. The greenish blue fuzzy material you see as "corrosion" is copper sulfate. It is formed by sulfuric acid combining with copper and not hydrogen. If they refer to electrolytic corrosion, for the negative side to be damaged the battery's polarity would have to be reversed; not simply discharged. It is the same process as in plating. The atoms go from the negative charged pole (marked as positive in the battery) to the positively charged pole(marked as negative in the battery)
     
  4. philSweet
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    philSweet Senior Member

    @Fred, sounds like nonsense to me. Corrosion occurs in SLABs because of gas leakage/permeation past the seals around the terminals. Overcharging causes more of this, but I can't think how it would know which to leak past.
     
  5. daiquiri
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    daiquiri Engineering and Design

    As Gonzo said.

    If the hyderogen was allowed to accumulate under the hood for the time necessary to create the corrosion of the terminals, then the corrosion would be the least of your problems. :D
    Hydrogen is the most volatile of gasses, and its molecules are the smallest of the whole periodical table of elements. So, it will escape through even the tiniest fissure or crack and will fly away very quickly.
    But it is also a very inflammable gas, one of the most inflammable ones, so if it was allowed to build up under the hood, a tiniest spark would be sufficient to cause an explosion.
    All these problematic characteristics of hydrogen are the main reason why hydrogen is still not in use as energy storage for cars, contrary to many forecasts we've heard over the last 10-15 yrs. It is a very dangerous gas.
     
  6. fredrosse
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    fredrosse USACE Steam

    "All these problematic characteristics of hydrogen are the main reason why hydrogen is still not in use as energy storage for cars"

    I think the actual reason why Hydrogen is not making progress in automotive futures is the difficulty of storing enough of it for reasonable range, not safety concerns based on it's flamability. Many vehicles use natural gas (for example, busses in China), or LPG (propane), both gaseous fuels with leakage, ignition and explosion issues similar to Hydrogen, although Hydrogen is the worst of them.

    20 gallons of Diesel fuel has 2.8 million BTU energy storage. A 20 gallon Hydrogen storage tank, pressurized to 3000 PSI, has only 0. 17 million BTU energy storage, about 6% of the Diesel Fuel. Available energy density is very poor here. Never mind the safety implications of a 3000 PSI fuel tank!

    There are concentrated efforts to develop minerals and chemicals that will absorb Hydrogen fuel (similar to the way Acetelene is stored in Acetone), so Hydrogen fuel tanks would not have to run at such high pressure, but what is actually available will not do the job in a cost effective manner.

    Making hydrogen fuel, by directly dissociating water into Hydrogen and Oxygen, is a very desirable future energy sourse, but the Hydrogen storage just takes up far too much volume for vehicles.
     
  7. fredrosse
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    fredrosse USACE Steam

    Nonsense

    "Corrosion on the terminals is due to hydrogen gas being released from the acid in the battery."

    Who dreams up such nonsense?
     
  8. philSweet
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    philSweet Senior Member

    Um, I'll bite. The quote isn't real helpful as far as illuminating the whole process, but if you eliminate the H2, you basically stop the terminal corrosion. Back in the bad old days of wet lead, the sulfur could get out. When was the last time you saw a wet lead battery under the hood? Impregnated felt washers are still about the most convenient terminal corrosion prevention method. They help keep the H2 from stripping metal oxides off the terminals. They clearly do nothing to keep underhood vapors off the terminals.
     
  9. gonzo
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    gonzo Senior Member

    Last time was yesterday when I refilled my windshield washer fluid. Lead/acid batteries are what the large majority of cars have under the hood. There are two basic types: flooded and AGM. Both have sulfuric acid. If hydrogen stripped the metal oxide, the terminals would be always shiny and clean. The opposite is true, because the sulfur reacts with the lead terminal to create a salt, not an oxide.
     
  10. philSweet
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    philSweet Senior Member

    What sulfur? No sulfur compounds are escaping from your car battery. Zero. Zip. That is why sealed batteries were invented - to keep the sulfur in (thereby reducing the shipping restrictions on the things). We aren't talking about batteries with caps here, we're talking about the standard auto start battery, which is a SLAB, or more correctly, a VRLA.

    (I could have used a better term than "wet lead" in my earlier post. Sorry about that. VRLAs can be wet lead, but I meant batteries with caps)
     
  11. messabout
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    messabout Senior Member

    I believe that Gonzo is correct. Batteries have the electrolyte H2So4 ...Sulfuric acid. The radical So4 reacts with the lead terminals (Pb) to form PbSo4 or lead sulfate. It is an acidic salt. You can neutralize it with a basic solution such as Bicarbonate of soda. The little felt washers that keep the terminals reasonably clean are saturated with a basic solution that defeats the chemical action of the lead acid reaction.

    Corrosion problems of another kind haunt our boats' electrical gear. Terminals where a copper wire is involved can and do develop green corrosion that is copper oxide. Not the same as a salt but just as troublesome. Isolating the copper element from atmospheric oxygen will avoid the problem. Copper oxide does not conduct electricity well. That's why lights and other items conk out just when you need them most.
     
  12. gonzo
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    gonzo Senior Member

    I do battery research and work on them all the time. We hand build and test them. The green "corrosion" is from acid leaking around the seal in the post. I'll take some photos of the inside of a battery tomorrow and post them.
     
  13. philSweet
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    philSweet Senior Member

    I think we are agreeing on more than we are disagreeing about. I don't deny that sulfuric acid can do that. Only that it only occurs these days in damaged car batteries. Most people will never see green fur on their car's battery terminals. But they still will have plenty of other battery problems. The OP wanted to know if corrosion would end up on one terminal or the other due to the charging regimen. I still can't think of any reason that would happen.
     
  14. gonzo
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    gonzo Senior Member

    I would like to know what the "other things under the hood" the hydrogen is supposed to mix with are.
     

  15. WestVanHan
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    WestVanHan Not a Senior Member

    Hydrogen isn't going to stick around long enough to do anything.

    I forget the speed it travels in the atmosphere but it's a few meters per second.
     
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