Chris,
I would be interested in the reason for paralleling each pair in the string. No two batteries have exactly equal chemical/electrical characteristics, so there will be slightly different sourcing/acceptance of currents. You want the battery stack to source/accept current so that each battery shares the "load" as equally as it can. By paralleling each pair you woll be forcing each pair to the terminal voltage of the other, where when you make a series string each battery can attain the voltage per it's charge state.
So if you make up a series string for the voltage you want, then parallel another string of the same voltage/capacity then differences between the two strings will be the overall terminal voltage and each battery in the string will charge/discharge according to it's individual terminal voltage and not to the terminal voltage of it's pair. With equal size/condition batteries the terminal voltage of the composite stack will be the source voltage but each individual battery will balance to it's own characteristic.
I have been running a house bank in a sailboat for many years that consists of a pair of 6v batteries wired in series for 12v, paralleled with another of the same. There will be usually about 10mv or less difference between the terminal voltage of each 6v battery pair, independent of charge state, which to me suggests that the batteries are sharing the load according to their internal resistance. As the batteries age (I get about 10 years out of a stack of flooded cell golf cart type) they seem to have the same characteristics except that the capacity is diminished over time.
Note that when combining batteries in series/parallel strings it is important that they be all the same age and condition.
You can probably convince yourself by drawing a comparable circuit of series parallel resistors, applying a voltage to the string then calculating the current in each resistor (Kirchoff's law) . Make small differences in the resistor values. Then draw it as two resistor strings paralleled and see what the difference is.
John
Flatwater Electronics
www.flatwaterfarm.com
"Neurosurgery for computer looms."
| Reply via web post | Reply to sender | Reply to group | Start a New Topic | Messages in this topic (2) |
No comments:
Post a Comment