More Exploding Batteries [RE-wrenches]

[Hugh]

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At 9:44 AM -0800 7/12/04, Matt Tritt wrote:
>
>
>This is something I got from the AWEA layman's list on small wind. 
>Even though it shows an incredible level of naiivitee' on the part 
>of the author, the explanation of how batteries can explode without 
>warning is pretty interesting!

Dave is much more intelligent than he makes himself out to be.  Don't 
be fooled, and I don't think it is appropriate to scoff either.

>
>"Don't over-charge lead-acid cells, they can explode! (I) noticed 
>the exploded cell after running battery charge from Diesel generator 
>when the batteries were already fully charged from win/water 
>turbines."  (can you believe this?)

I find it hard to believe too, but it's just what Richard Perez 
exhorts us to do.  And I guess Dave's batteries were failing so he 
thought it might help.

>
>"I am glad I wasn't in the battery room when it happened. The cell 
>is still giving >2.0 volts so I presume the following occured (found 
>on the web)
>""The most probable cause of internal explosions are from a 
>combination of low electrolyte levels below the plates in the 
>battery and a low resistance bridge is formed between or across the 
>top of the plates. This is called "treeing" between the positive and 
>negative plates. When current flows in the battery, a spark occurs 
>and ignites the residual gas in one or more of the cells.""

Interesting as you say, and something we should all be very aware of.

>
>"I thought my battery bank was too large to worry about charge 
>control." (My favorite part!)

Charge control was not the problem.  Failing to top the cells up was 
the problem.  This guy has run this battery for a very long time, 
maybe five to ten years, having obtained them second hand.

Back in the 1980s, I myself and most of my neighbours had pretty big 
battery banks of secondhand cells like these and none of us had 
automatic charge control.  We would monitor the voltage and adjust 
our usage accordingly.  It is true as Dave says that a large battery 
bank combined with a small charge source does allow you to do without 
a charge controller.  If the voltage got a bit high occasionally then 
no harm was done, provided the electrolyte levels were kept up.  In 
fact it was quite beneficial for the battery to get a good gassing 
charge in a prolonged gale.

I personally find this a much better way to equalise the battery than 
to hammer it with an engine driven generator.  What's the point in 
'controlling' (wasting) your renewable energy so carefully and then 
wasting a load of fuel polluting the atmosphere to overcharge the 
battery on a particular day that you might decide to equalise them?

I suspect that what happened to Dave was that he increased his 
charging capabilities by building more wind turbines and at the same 
time his battery capacity was reducing through aging, failed cells 
etc, and so he got caught out.
-- 
Hugh
Scoraig Wind Electric
http://www.scoraigwind.co.uk/

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