Hi Don-
I can see it at least partially from the physics & electricals of this.
Say you had two cells in parallel, and then another cell in series with
this parallel combination. Now connect this battery to a load. The load
will eventually exhaust the single series cell, while the two parallel
cells will still have 50% of their energy left. At his point, the single
series cell will start being reverse charged by the two parallel cells via
the electrical path through the load. This reverse charging risks explosion
of the single series cell.
I would even be cautious about connecting two cells in parallel. If their
terminal voltage characteristics are not well matched, and especially if
they have low internal resistance, one cell could end up charging the other
quite quickly, possibly to bad effect, e.g., primary lithium cells have
been know to explode during attempts to recharge them.
The other Don
"MacArthur, Don"
<Don.MacArthur@gd
-itronix.com> To
Sent by: <[email protected]>
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Subject
08/13/2007 12:11 ATEX Requirement for Cell
PM Connection
EN 60079-15: 2005 which is titled Electrical apparatus for explosive gas
atmospheres – Part 15: Construction, test and marking of type of protection
“n” electrical apparatus, and other hazardous locations standards have cell
connection requirements which are as follows:
“Cells shall be connected in series except for the specific case where two
cells are connected in parallel with no further cells connected in series.”
My questions to the group are:
1. Why is the above statement a requirement? Worded another way…
2. What is the safety issue when cells are connected in series with some
in parallel when the cells are used in an explosive gas atmosphere?
I’ve asked around various safety agencies and have not received a response
let alone any response that makes sense.
Kind Regards,
Don
Don MacArthur
Compliance Engineer
General Dynamics - Itronix Corporation
12825 E. Mirabeau Parkway
Spokane Valley, WA 99216
ph: 509-742-1342
fax: 509-742-1672
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