Posted by phil-news-nospam on August 7, 2008, 2:43 pm
I've heard from way back that connecting batteries in parallel is a bad idea.
I've heard a couple reasons. One is that it can be hard to make sure the
batteries are loaded equally. Another reason I heard is more complex. It
says that parallel connection should be done only on a per-cell basis, and
that a series/parallel combination would thus have parallel connections at
every cell ... and therefore multi-cell batteries are bad in this regard
while single cell (2V) "batteries" are the way to go.
Some googling revealed a few web pages that seem to not have much reference
to any parallel connection issues, aside from making sure the batteries are
the same size/capacity.
I would think that self-charging (a stronger battery charging a weaker one
connected in parallel) would not be much of an issue for a batteries that
are intended to keep a float charge, anyway (lead-acid is all that I am
considering here). If any battery has a problem where it can't take a
charge and could be a hazard if charged, then it seems one would have a
bigger issue by that alone than anything related to wiring them in parallel.
Maybe there are issues when the _number_ of paralleled batteries is high?
Series connection would _seem_ to be more of a problem, but clearly isn't a
show stopper at common voltage levels (12 to 48). What I refer to when I say
this is the risk that a single weak cell in the series woould be effectively
"reverse charged" by the "brute force" of the high voltage series circuit
forcing the current in the reverse direction than a charging current. On the
face of it, this risk seems like one that, if it could happen, would happen
on even a small a voltage as 6 volts (3 cell). But maybe for lead-acid the
risk is merely depleting the bad cell to zero and destroying it and nothing
more?
What risks ... to the batteries themselves ... exists in a very high number
of cells in series wired for very high voltages (120 to 600 volts for example)?
I remember running across, a few years ago, a very large DC to AC inverter
that was designed to run from a 576 volt battery configuration (which would
be closer to 600 volts). So it might seem that such setups are possible.
That wouldn't necessarily say there are no risks, as such a setup would be
an industrial one that could be well supervised for the issues that could
happen. But I would like to know what potential issues to watch for in a
home setup that could be wired to as much as 48 volts.
Would particular sub-technologies of lead-acid batteries matter in this regard
(aside from making sure all are the same type)?
Who here thinks connecting batteries (one cell or multi-cell) in parallel is
bad ... and why (if you don't know why, I'll assume it's myth).
Is there any advantage to using a big single cell (other than it's really big
current capacity, which itself may eliminate the need to even have anything
wired in parallel)? Example: Surrette 2KS33PS
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Posted by Ron Rosenfeld on August 7, 2008, 4:29 pm
On 7 Aug 2008 18:43:07 GMT, phil-news-nospam@ipal.net wrote:
>I've heard from way back that connecting batteries in parallel is a bad idea.
>I've heard a couple reasons. One is that it can be hard to make sure the
>batteries are loaded equally. Another reason I heard is more complex. It
>says that parallel connection should be done only on a per-cell basis, and
>that a series/parallel combination would thus have parallel connections at
>every cell ... and therefore multi-cell batteries are bad in this regard
>while single cell (2V) "batteries" are the way to go.
>Maybe there are issues when the _number_ of paralleled batteries is high?
>Series connection would _seem_ to be more of a problem, but clearly isn't a
>show stopper at common voltage levels (12 to 48). What I refer to when I say
>this is the risk that a single weak cell in the series woould be effectively
>"reverse charged" by the "brute force" of the high voltage series circuit
>forcing the current in the reverse direction than a charging current. On the
>face of it, this risk seems like one that, if it could happen, would happen
>on even a small a voltage as 6 volts (3 cell). But maybe for lead-acid the
>risk is merely depleting the bad cell to zero and destroying it and nothing
>more?
>What risks ... to the batteries themselves ... exists in a very high number
>of cells in series wired for very high voltages (120 to 600 volts for example)?
>Is there any advantage to using a big single cell (other than it's really big
>current capacity, which itself may eliminate the need to even have anything
>wired in parallel)? Example: Surrette 2KS33PS
Interesting paper on the topic of parallel battery wiring here:
http://www.battcon.com/PapersFinal2002/McDowallPaper2002.pdf
For me, as someone who lives off-grid, has a 48V battery bank, and does his
own battery maintenance, the big advantage of having a single string, vs
multiple parallel strings, would be the ease of maintenance -- 1 string =
24 cells to check; 2 strings = 48 cells to check, etc.
When I purchased my batteries, I could not purchase 2V batteries in the
capacity I would have liked. So I have two parallel strings. But the 2V
cells are now available in a satisfactory size, so when my present bank
needs to be replaced, I will be using a single string.
Other advantages/disadvantages suggest themselves, but are application
dependent.
--ron
Posted by phil-news-nospam on August 7, 2008, 10:43 pm
| Interesting paper on the topic of parallel battery wiring here:
|
| http://www.battcon.com/PapersFinal2002/McDowallPaper2002.pdf
It seems from that, parallel string operation is mostly OK, with one notable
exception being parallelizing to increase deliverable current capacity (as
opposed to parallelizing to increase time capacity and reduce current per
string). If one string fails under a high current load, it could be a big
problem for the other string.
--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
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Posted by Ron Rosenfeld on August 7, 2008, 11:14 pm
On 8 Aug 2008 02:43:39 GMT, phil-news-nospam@ipal.net wrote:
>| Interesting paper on the topic of parallel battery wiring here:
>|
>| http://www.battcon.com/PapersFinal2002/McDowallPaper2002.pdf
>It seems from that, parallel string operation is mostly OK, with one notable
>exception being parallelizing to increase deliverable current capacity (as
>opposed to parallelizing to increase time capacity and reduce current per
>string). If one string fails under a high current load, it could be a big
>problem for the other string.
However, I believe they are mostly discussing systems that spend most of
their time on float charge, with occasional
But the authors also described a situation where one string would discharge
more than another. Those circumstances -- "... a system that is designed
for long discharges, but is subjected to frequent shallow discharges" could
describe many off-grid systems. The result is that one string, (in the
paper the "high-rate" battery), receives the brunt of the cycling duty, and
may age prematurely as a result.
This is probably not a significant issue with two matched strings that are
placed in service together. But this phenomenon is, I believe, the source
of the recommendation to not mix batteries of different ages in off-grid
systems.
--ron
Posted by phil-news-nospam on August 8, 2008, 2:32 pm
| On 8 Aug 2008 02:43:39 GMT, phil-news-nospam@ipal.net wrote:
|
|>
|>| Interesting paper on the topic of parallel battery wiring here:
|>|
|>| http://www.battcon.com/PapersFinal2002/McDowallPaper2002.pdf
|>
|>It seems from that, parallel string operation is mostly OK, with one notable
|>exception being parallelizing to increase deliverable current capacity (as
|>opposed to parallelizing to increase time capacity and reduce current per
|>string). If one string fails under a high current load, it could be a big
|>problem for the other string.
|
| However, I believe they are mostly discussing systems that spend most of
| their time on float charge, with occasional
|
| But the authors also described a situation where one string would discharge
| more than another. Those circumstances -- "... a system that is designed
| for long discharges, but is subjected to frequent shallow discharges" could
| describe many off-grid systems. The result is that one string, (in the
| paper the "high-rate" battery), receives the brunt of the cycling duty, and
| may age prematurely as a result.
If merely aging prematurely is the result, that may not necessarily be bad if
the other string(s) age less at the same time. This spreads out your need to
replace batteries over time. If all the strings aged identically, then your
whole battery bank will need to be replaced all at once when the time comes.
| This is probably not a significant issue with two matched strings that are
| placed in service together. But this phenomenon is, I believe, the source
| of the recommendation to not mix batteries of different ages in off-grid
| systems.
If the effect is that the _older_ strings gets _older_ faster, and the others
do not, it just means _one_ string to replace sooner and _fewer_ strings to
replace later on.
I'm still concerned about a string with a shorted cell. But I can see this
would still be a problem in general, as the effect to the stunted string is
the float voltage would be a couple volts higher (more significant the shorter
the string).
--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
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>I've heard a couple reasons. One is that it can be hard to make sure the
>batteries are loaded equally. Another reason I heard is more complex. It
>says that parallel connection should be done only on a per-cell basis, and
>that a series/parallel combination would thus have parallel connections at
>every cell ... and therefore multi-cell batteries are bad in this regard
>while single cell (2V) "batteries" are the way to go.
>Maybe there are issues when the _number_ of paralleled batteries is high?
>Series connection would _seem_ to be more of a problem, but clearly isn't a
>show stopper at common voltage levels (12 to 48). What I refer to when I say
>this is the risk that a single weak cell in the series woould be effectively
>"reverse charged" by the "brute force" of the high voltage series circuit
>forcing the current in the reverse direction than a charging current. On the
>face of it, this risk seems like one that, if it could happen, would happen
>on even a small a voltage as 6 volts (3 cell). But maybe for lead-acid the
>risk is merely depleting the bad cell to zero and destroying it and nothing
>more?
>What risks ... to the batteries themselves ... exists in a very high number
>of cells in series wired for very high voltages (120 to 600 volts for example)?
>Is there any advantage to using a big single cell (other than it's really big
>current capacity, which itself may eliminate the need to even have anything
>wired in parallel)? Example: Surrette 2KS33PS