Date: Fri, 1 Oct 2010 15:59:29 -0500
Reply-To: mcneely4@COX.NET
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dave Mcneely <mcneely4@COX.NET>
Subject: Re: Battery placement alternatives
In-Reply-To: <9CB7F637-62FA-4ABA-A51B-970D6D3F3952@shaw.ca>
Content-Type: text/plain; charset=utf-8
Alistair, I don't think we are arguing. I asked you, as a short cut rather than looking up the chemistry I once knew. So, you think little or no hydrogen would be present, and any that was would be effectively vented if the original vent setup was in place. None produced during the jump start process.
And I did think the lid gasket was a part of the vent system to prevent gas from venting into the interior of the van. Fact is, another list member once told me that, one whom I trust to be knowledgeable about most things to do with the vehicle. But you think the gasket is mainly for noise control or something of that nature? Not to confine whatever is in the box so it doesn't enter the van?
I have a non-spec battery, and I see no nipple anywhere on it. Should I get rid of it and put in a spec battery, and a vent hose (none evident in the battery compartment).
thanks
---- Alistair Bell <albell@shaw.ca> wrote:
> the reaction during regular charge of a wet cell lead acid battery
> does not produce oxygen nor hydrogen.
> Anode (oxidation):
>
> PbSO4(s) +5H2O(l) <-----> PbO2(s) + 3H3O+(aq) + HSO4- (aq) + 2e-
> (1.685V)
>
>
> Cathode (reduction):
>
> PbSO4(s) + H3O+(aq) + 2e- <-------> Pb(s) + HSO4-(aq) + H2O(l)
> (-0.356 V)
>
>
>
> you see that no gas produced.
>
>
> Overcharging will produce, through electrolysis of the water in the
> electrolyte, hydrogen and oxygen. You can see this when you charge
> with caps off and the charging voltage is high (14-15 volts), little
> bubbles fizzing off the plates. During a boost assisted start, I see
> a spark risk, but I don't see electrolysis unless the donor
> electrical source is high, and or the battery being boosted cannot
> accept the electricity fast enough to drive the lead above reaction,
> and therefore the electrolyte undergoes electrolysis.
>
> (one thing too watch out for though, is the accidental bridging of
> the battery posts. The massive and rapid discharge is dangerous :))
>
> The practice of making your last connection during boosting, to a
> ground other than the battery neg terminal, is a prudent step in that
> one does not know how the accepting battery will take the charge, or
> if the accepting battery headspace is full of hydrogen and oxygen due
> to some previous charging malfunction. Or if the accepting battery
> has a serious screw up inside and there are internal shorts etc.
>
>
> What i was trying to convey in my original post, is that the battery
> compartment, and the lid seal is not adequate to contain any hydrogen
> gas produced. A vent tube, solidly attached to the vent nipple on
> battery, then leading out of the van, woudl be more effective (as
> Loren pointed out).
>
> I seem to always be arguing chemistry on Fridays.
>
> alistair
>
>
>
>
>
> On 1-Oct-10, at 12:36 PM, Dave Mcneely wrote:
>
> Alistair, you probably know enough to correct any error that I commit
> here. My understanding is that all lead acid batteries produce
> hydrogen gas during charging due to electrolysis of water. The
> amount of hydrogen depends on the charging rate, but even routine
> charging during driving would produce some hydrogen gas. Battery
> explosions are most commonly explosions from within the battery, due
> to gas accumulating inside, but gas can be present any time charging
> is going on. The most common ignition source for a battery explosion
> is a spark, which is why jump starting instructions specifically
> provide for making the last connection at a point distant from the
> battery.
>
> I don't think any of us think that a battery explosion is a likely
> event in our vans. Safety precautions are taken to make even
> unlikely events less likely.
>
> When one jump starts a vehicle, the donor vehicle is supposed to be
> run at faster than normal idle, to make sure the donor battery is not
> depleted during the donation. So, it is charging as if the vehicle
> is being driven. It is also delivering charge into the recipient
> battery during the brief time of the donation.
>
> Could a battery explosion take place then, and is it more likely with
> a vanagon with its battery in an enclosed box inside the vehicle than
> with a vehicle with its battery in an open engine compartment? Of
> course the battery box is open and the van is open during the
> operation, but the gas has less opportunity to dissipate than it does
> with an open engine compartment. And the precautions that are
> recommended in jump starting instructions are given for vehicles with
> engine compartment battery placement.
>
> BTW, just due to no need, I have neither given nor gotten a jump with
> my vanagon. But this discussion has prompted me to consider the
> proper location for grounding. I suppose the best place would be on
> a frame member under the vehicle, since the usual grounding locations
> in the engine compartment are all too far away. Where would you
> ground the jumper cable on a vanagon?
>
> Do you know how many vehicle battery explosions happen during a
> year? I have no idea.
>
> David
>
>
> ---- Alistair Bell <albell@SHAW.CA> wrote:
> > I would bet that any venting to the outside is not for hydrogen gas,
> > but rather to remove any sulfuric acid fumes from immediate area, to
> > reduce corrosion of nearby parts.
> >
> > you are not going to get an explosion under the seat from the small
> > amount of hydrogen gas produced by the battery. A battery can explode
> > from within if hydrogen and oxygen are not allowed to escape, but
> > that is different than the fear of vented hydrogen combining rapidly
> > with the co-produced or atmospheric oxygen, in the space under the
> > seat of a vanagon. Hydrogen and oxygen are the products of
> > *overcharging* lead acid batteries.
> >
> > its a different order of magnitude if you have a vast bank of
> > charging batteries, ie a diesel electric submarine.
> >
> > alistair
> >
> >
> >
> >
> > On 1-Oct-10, at 10:43 AM, Loren Busch wrote:
> >
> > RE: Stock battery venting
> > I'll try to get a picture and post a link to it.
>
> --
> David McNeely
>
--
David McNeely
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