(ET) Battery float (was E-15 not getting out of first speed)

["David Roden" <etpost drmm net>]

On 24 May 2017 at 0:33, David Tiefenbrunn wrote:

> My Soneil charger is maintaining them at 41.8V which is 13.9V per 12V
> ... They do seem to bubble a lot more than I expected. 

If you run a current through a fully charged battery, it's going to gas 
and 
generate heat.  It has to.  Once it's charged, there's nowhere else for 
the 
energy to go.  But at a reasonable float voltage, which I suspect your 
charger may be exceeding, gassing and heat should be minimal.

Assuming you're dealing with a reputable battery manufacturer, that's who 
you'd ask to get a sensible value for your battery's float voltage, at 
least 
when it's new.  But even that's not really definitive, as we'll see 
shortly.

If you look at various battery references, you'll find values around 2.2 
to 
2.3vpc, or 13.2 to 13.8v for a 12v battery.  For example, Wikipedia gives 
2.23vpc for gel, 2.25vpc for AGM, and 2.32vpc for flooded batteries.  

This is kind of misleading, though.  How the electrolyte is held in the 
cells, in itself, isn't what makes the difference.  For example, Concorde 
and Odyssey are both AGM batteries, but Concorde recommends 13.0v at 20 
deg 
C and Odyssey says to use 13.65v at that temperature.  

Float voltage comes down to more fundamental design issues.  We're talking 
about such matters as grid doping with antimony, calcium, and/or selenium 
(and other proprietary materials), paste composition, and electrolyte 
makeup 
including acid concentration and various additives. 

Float voltage also changes with the battery's internal temperature (as you 
pointed out), falling as temperature increases.  And it declines as the 
battery ages.  

So there is no one-size-fits-all magic number for float voltage.  Yea 
verily 
not even the manufacturer's number hath magic to it.

Partly for that reason, I don't think that float charging is beneficial 
for 
batteries in cyclic use (that would be our ETs).  I'd disable your 
charger's 
float stage if you can, or just pull the plug once the battery is full.  

A foolproof if somewhat coarse way to nuke an obstinate charger's 
undefeatable float stage without having to remember to pull the plug is to 
connect it to a 12- to 24-hr shutoff (countdown) timer.  You can use a 
repurposed GE charger timer, buy one at a hardware store, or modify a 24 
cycling lamp timer.


David Roden - Akron, Ohio, USA

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