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What is the efficiency of a battery recharging system?

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Posted by Gary Helfert on August 11, 2005, 4:12 am

When charging a battery both the charger & battery get warm (lost energy).
I am curious to know:

If you pump 100 Watt-Hours of electricity into a bank a Lead Acid batterys,
what can I expect to get out?

Do Ni-Cads recharge with more/less/same loss?

Posted by Robert Morein on August 11, 2005, 6:04 am

This is a complicated question, because it depends upon the design of the
For example, if the charging current is too low, the answer to your question
is 0, because the battery does not charge at all.
The following document,
http://www.vicr.com/documents/design_articles/pb_battery-charger.pdf  gives
calculated efficiencies of between 77% and 85%, depending upon the depth of
discharge of the battery.

No, claims vary between 85% - 90%. The faster, the more efficient. On the
other hand, very fast charging is harmful to the cell.

Currently, the most efficient cell is lithium, because the cell does not
heat up during charging; hence, minimal thermal loss.

Posted by BobG on August 11, 2005, 1:07 pm

The charger CAN be very efficient just like a switching power supply...
90% or more. The efficiency of the lead-acid charging process is also
know, but I cant remember it so I wont guess. RMs number of 77-85%
sounds familar

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