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no pause in lead-acid charging with LT3652 & Panasonic?

Question asked by r273 on Jun 7, 2018
Latest reply on Jun 23, 2018 by r273

I've now a little experience of using LT3652 with Panasonic Lead Acid batteries.

 

The problem/question is as follows.


The lowest recommended float charging voltage by this manufacturer is 13.6v (the recommended range is 13.6-13.8v).

 

If 13.6v is programmed as the Float voltage for the LT3652 then a new charge cycle will resume at 97.5% of that value:

 

0.975 * 13.6v = 13.26v

 

Now look at the graph entitled "Open circuit voltage vs. Residual capacity 77°F (25°C)" on the last but one page of this Panasonic guide:

 

https://na.industrial.panasonic.com/sites/default/pidsa/files/downloads/files/panasonic_vrla_overview.pdf 

 

I have a brand new battery that, when fully charged, shows 12.96v open circuit. That's well within the manufacturer's claims. However it is also sufficiently low that when the LT3652 comes to the end of a charge cycle (as determined by the timer capacitance) it will conclude that it should start over (because 12.96 < 13.26). 

 

That seems inefficient. Charging without a pause and when no need.

 

Moreover, a waste of a capacitor (for the timer)!

 

Should I be concerned? Have I done something wrong? Are there other battery logics available? And would they help given the other implications of that graph, that the open circuit voltage when fully charged is going to fall over time (as the battery has lived more cycles)?

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