[RE-wrenches] Still walking it back

[Larry Crutcher, Starlight Solar Power Systems]

Dan is correct if the discussion is about the open circuit test of a charged battery: resistance is lower than when discharged.

However, the resistance I was describing to Mick was the effect of a battery under charge. The "resistance" to current flow increases because the electrochemical process slows down as active material is converted back to it's original state. I believe this is what Dan meant by "equilibrium", PbSO4 is converted to PbO2, Pb and H2SO4 increasing specific gravity, reducing current flow. 

A common question I am asked is "why can't I force my charger (PV solar or otherwise) to put out full power?" The reason is the battery simply can't absorb any more current as described above.

Larry Crutcher
Starlight Solar Power Systems



On Nov 2, 2012, at 8:41 AM, Mick Abraham wrote:

Hi, Mechanix~ I'm sorry to add more "noise" to the List but I sort of
mis-spoke again.

Dan Lepinski @ Exeltech sent a mail to me Off List; below I am posting
the part of his
mail which addresses my latest faux pas:

+++++++++++++++++++++++++++++++++

"As battery state of charge increases (toward 100%), the internal resistance
actually goes *down* -- which is why you can get a very high short-circuit
current from a fully charged battery .. and a much less current from a
nearly dead one.

"What is happening instead is a voltage equilibrium -- that of the battery
becoming more equal with the voltage of the charging source.  This is
what reduces the charge current flowing from a constant-voltage source
into the battery.

"Think of it this way: If you're adding air to a car tire, and have a compressor
that produces a maximum of 35 psi, as the tire pressure approaches 35 psi,
the air flow from the compressor to the tire will slow, and then eventually stop
when the two pressures become equal."