connecting batteries in parallel or series, myth and theory

[[email protected]]

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

 

[Vaughn Simon]

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).

I have been doing it for years with no ill effects, but I recognize that it
is not an optimal configuration (currently two sets of two 6-volt batteries,
formerly four 12-volt batteries). I protect against possible high circulating
currents with fuses.

My batteries are there mostly for an emergency, so they seldom see a high
DOD, and that may be why I have no problems.

Vaughn

 

[[email protected]]

| 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.

 

[[email protected]]

In alt.engineering.electrical [email protected] wrote:
| On Aug 8, 4:43 am, [email protected] wrote:
|
|>
|> 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).
|
| Series parallel batteries.
|
| First, whether you use 2V cells or batteries you end up with "A
| Battery"

Right. But there is distinction of paralleling single cells individually
versus paralleling a single battery of N cells, or a string of N cells.
The latter do not have any cross connects at each cell connection. One
consideration is whether there is any advantage to that. When I put some
thought into it, I could not see any issue with lead-acid batteries.


| The problem with parallel strings is that they do not all charge or
| discharge together.

If one discharges more, its voltage would drop, and others would take
up the slack. At least that's the way I see it. A posted paper URL in
this thread earlier suggested it's OK to parallel different strings or
batteries with different capacities and they would discharge in proportion
to their capacity. I'm guessing that is because of the voltage balance
effect (the stronger string with the slightly higher voltage carriers
more of the load).


| When I was getting my accreditation for solar design and installation
| we were shown the results of a series parallel bank, if memory serves,
| of 36 x 2V cells. That is six parallel strings of six cells.
|
| The up shot was that under charge or discharge the strings did not
| operate as a single battery. i.e. Under charge the strings would
| charge one at a time.

So from a deep discharge position (20-50%) a recharge would not bring
each string back to 100% at the same rate, and if a discarge was needed
before all of them are fully recharged, it would present an imbalance
not in capacity, but in charge level.

Does that apply to both slow and fast recharge?


| The same for discharge. There were also very high transient voltages
| across the array.

What would be causing a transient?


| Parallel string should be avoided wherever possible.

Why?

 

[[email protected]]

In alt.engineering.electrical clare wrote:

| Definitely an advantage using one big cell over 2 smaller parallel
| connected cells. I'm no scientist so I cannot explain why - but they
| will last a LOT longer.

Can you tell me where you get this information? Have you tried both? Or you
just heard this somewhere?

 

[m II]

Right. But there is distinction of paralleling single cells individually
versus paralleling a single battery of N cells, or a string of N cells.

I have never seen single cells paralleled. They are always connected in
series to get the desired voltage. Then, another group of identical
series cells may be paralleled with it.



mike

 

[Johnny B Good]

On 7 Aug 2008 18:43:07 GMT, [email protected] wrote:
====snip====

ALL Batteriea are series connected cells.
A "flashlight battery" is not a battery - it is a single cell.

That seems to be the case today, but a few years back in the fifties
and sixties, Eveready used to sell "torch batteries" that _were_
batteries. These were 3 volt batteries made up from a pair of, afaicr, C
sized zinc/carbon cells mounted in a cardboard tube.

A 9 volt battery IS a battery, as is a 6 volt camera battery, or a
lantern battery. Car batteries are too.

However, a 3 volt watch 'battery' isn't, it's simply a lithium coin
cell that happens to have a cell voltage twice that of a zinc/carbon
cell (or its modern alkaline equivilent). The 6 volt lithium camera
battery is a 2 cell battery but the C3V camera 'battery' designed to fit
cameras that can also use a pair of AA sized cells (NiMH or Alkaline) is
simply a single lithium cell shaped to fit the two AA cell battery
compartment of such cameras.

The problem is that joe public needs a 'Catch All' name to describe
such electrochemical sources of portable power regardless of whether
they're buying a ready made up battery or a collection of cells to
create a battery within the 'battery powered' device itself. To them, a
ready made battery of cells in the form of a PP3 or each AA cell of a
pack of two or four is a battery just as much as a vacuum cleaner is a
"Hoover", regardless of whether it was manufactured by that company or
by Electrolux or Dysan.

On reflection, I think most zinc/carbon cells were sold either ready
made up into a 3 volt 'Torch Battery' or as 'lantern batteries' in the
thirties through to the sixties, so the name 'battery' was being
correctly applied for the most part back in those days.

The advent of the 'leakproof' cell marked the departure from the "2
cell in a cardboard tube" battery since each cell had to be enclosed in
its own individual steel leakproof cladding which also provided the
insulation which allowed them to be slid into the (typically) metalic
tube of the torch without shorting the negative zinc electrode of the
zinc/carbon type or the positive electrode in the case of the alkaline
type.

The marketing to the general public of C and D cells to fit 3, 4 and 6
cell battery compartments in electronic gadgets simply didn't exist at
that time so most 'battery sales' were exactly that and rarely included
sales of individual cells (in whatever 'pack size' marketing would have
deemed 'profitable').

By the time the 'battery' manufacturers' started to sell more cells
than batteries, the name 'battery' had become well and truly entrenched
in the public's mind and has remained so ever since.

Although it might 'grate' to hear the word 'battery' being
inappropriately applied by the general public, we have to keep in mind
that it was a word already borrowed from a previous (and more
appropriate) usage, relating to a collection of shore based artillary
designed to 'batter' the enemy.

The more guns, the bigger (or stronger) the battery. In the case of its
appropriation for a collection of series connected cells to produce
higher voltages, I suppose the high voltage 'kick' due to bodily contact
could be construed as a form of 'battery' in the sense of "Assault and
Battery". The more cells, the bigger (or stronger) the battery, just as
in the case of a gun battery.

As far as the general public are concerned, any self contained source
of electrochemically produced power, no matter whether it's in the form
of individual cells or a monolithic block of such cells connected in
series to produce the required voltage, is going to called a 'battery'.
It's simply another example of the evolving usage of words away from
their original strict meaning.

 

[Daniel Who Wants to Know]

That seems to be the case today, but a few years back in the fifties
and sixties, Eveready used to sell "torch batteries" that _were_
batteries. These were 3 volt batteries made up from a pair of, afaicr, C
sized zinc/carbon cells mounted in a cardboard tube.


However, a 3 volt watch 'battery' isn't, it's simply a lithium coin
cell that happens to have a cell voltage twice that of a zinc/carbon
cell (or its modern alkaline equivilent). The 6 volt lithium camera
battery is a 2 cell battery but the C3V camera 'battery' designed to fit
cameras that can also use a pair of AA sized cells (NiMH or Alkaline) is
simply a single lithium cell shaped to fit the two AA cell battery
compartment of such cameras.

The problem is that joe public needs a 'Catch All' name to describe
such electrochemical sources of portable power regardless of whether
they're buying a ready made up battery or a collection of cells to
create a battery within the 'battery powered' device itself. To them, a
ready made battery of cells in the form of a PP3 or each AA cell of a
pack of two or four is a battery just as much as a vacuum cleaner is a
"Hoover", regardless of whether it was manufactured by that company or
by Electrolux or Dysan.

On reflection, I think most zinc/carbon cells were sold either ready
made up into a 3 volt 'Torch Battery' or as 'lantern batteries' in the
thirties through to the sixties, so the name 'battery' was being
correctly applied for the most part back in those days.

The advent of the 'leakproof' cell marked the departure from the "2
cell in a cardboard tube" battery since each cell had to be enclosed in
its own individual steel leakproof cladding which also provided the
insulation which allowed them to be slid into the (typically) metalic
tube of the torch without shorting the negative zinc electrode of the
zinc/carbon type or the positive electrode in the case of the alkaline
type.

The marketing to the general public of C and D cells to fit 3, 4 and 6
cell battery compartments in electronic gadgets simply didn't exist at
that time so most 'battery sales' were exactly that and rarely included
sales of individual cells (in whatever 'pack size' marketing would have
deemed 'profitable').

By the time the 'battery' manufacturers' started to sell more cells
than batteries, the name 'battery' had become well and truly entrenched
in the public's mind and has remained so ever since.

Although it might 'grate' to hear the word 'battery' being
inappropriately applied by the general public, we have to keep in mind
that it was a word already borrowed from a previous (and more
appropriate) usage, relating to a collection of shore based artillary
designed to 'batter' the enemy.

The more guns, the bigger (or stronger) the battery. In the case of its
appropriation for a collection of series connected cells to produce
higher voltages, I suppose the high voltage 'kick' due to bodily contact
could be construed as a form of 'battery' in the sense of "Assault and
Battery". The more cells, the bigger (or stronger) the battery, just as
in the case of a gun battery.

As far as the general public are concerned, any self contained source
of electrochemically produced power, no matter whether it's in the form
of individual cells or a monolithic block of such cells connected in
series to produce the required voltage, is going to called a 'battery'.
It's simply another example of the evolving usage of words away from
their original strict meaning.

--
Regards, John.

Please remove the "ohggcyht" before replying.
The address has been munged to reject Spam-bots.

Where it gets really funny is when you start to refer to your
cellular/mobile phone. Since most people simply call it a cell phone and
since the adoption of Li-Ion the phones have been using a single prismatic
cell it could be "Sorry I gotta go my cell's cell is low I gotta go charge
it." or the store could "Sell you a new cell for your cell at the yearly
cell sale."

 

[Vaughn Simon]

On 7 Aug 2008 18:43:07 GMT, [email protected] wrote:
My house's UPS has a wide variety of sizes and brands, connected in
series/parallel to produce 24 volts at close to 1000 amp-hours. Every time I
find a decent-looking* deep cycle battery, I toss it on.

Except that I use 12 volts, this has been remarkably close to my own past
strategy. A minor part of my job was to change out strings of batteries on our
various UPS systems. The object of that game is to replace just BEFORE the
first battery in any given string goes bad, so it was a minor deal to test a
batch and then bring home the better used batteries.

Now that I am retired and may actually have to BUY batteries, my strategy may
need to change.

Vaughn

 

[krw]

| 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.

Starting batteries are often paralleled (though have isolation
diodes) for higher current. Most large trucks have such a setup.

 

[Vaughn Simon]

Starting batteries are often paralleled (though have isolation
diodes) for higher current. Most large trucks have such a setup.

I have often seen truck batteries connected in parallel, particularly on
diesel pickups, but have never noted isolation diodes.

I have also seen one at least one near-truck fire that was apparently caused
by shorted cells in one of the paralleled batteries on a truck, which led to the
good battery forcing a high charge current through the bad battery. Ironicly
enough, it was a fire truck.

Vaughn

 

[[email protected]]

Accreditation?

Presumably he's talking about the course he took titled "Introduction
to Renewable Energy Technologies". Which he quoted: "Lead Acid) are
suitable for use in solar power systems, but AGM batteries are
generally not".
http://groups.google.com/group/alt.solar.photovoltaic/msg/77d8d63366a6ff9e
But then later contradicted by writing "AGM and Gell batteries can be
very effective. such batteries can offer good life expectancies."
http://groups.google.com/group/alt.solar.photovoltaic/msg/4cbc1e896cfd71a6
So he doesn't take the course's gospel very seriously himself, yet for
some reason expects that others are interested in his hearsay
remembrances.

What organization has given you this accreditation?

It's an Australian organization designed to prevent an unknowing
public from being BSed by nitwit PV installers. So of course he's not
a member.

Or is
this just something else you've made up?

He's complained several times that the organization isn't up to his
high standards. <snorf> The two things I know about them are that
the ghinius doesn't like them, and they put him out to pasture. Which
means that they're obviously on the right track.

Wayne

 

[[email protected]]

| On 8 Aug 2008 02:43:39 GMT, [email protected] 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).

 

[[email protected]]

| [email protected] wrote:
|
|> Right. But there is distinction of paralleling single cells individually
|> versus paralleling a single battery of N cells, or a string of N cells.
|
|
| I have never seen single cells paralleled. They are always connected in
| series to get the desired voltage. Then, another group of identical
| series cells may be paralleled with it.

So the "reason" is "everyone else does it".

Aren't all the plates within one cell already parallel? By extension of that,
paralleling individual cells would make sense because it retains the very same
concept.

 

[[email protected]]

In alt.engineering.electrical [email protected] wrote:

| Yes, I've done some anlalytical work in this area. And you are right,
| if one cell
| in a series-parallel setup fails for some reason. The string in
| parallel will discharge
| itself into the defecitive cell and in fact reverse charge the other
| good cells in the
| series string with the defective cell in it. Depending upon the energy
| content
| of your cells, you could really have a nice fire. Yes, a diode in each
| string that
| is then connected in parallel with another string would prevent this.
| The added
| burden is that of added cost for the heavy duty diode you might need
| and of
| the voltage drop you would experience from that diode while
| inoperation. And,
| of course, you wouldn't be able to charge the string.

Paralleled strings mean "-" connected to "-" and "+" connected to "+".
That is the correct charging polarity. If one string is longer by one
cell than another, the shorter one won't be reverse charged. But it
can be _over_ charged. But you face that risk of overcharging even if
your charger applies the voltage for N cells when the string only has
N-1 cells.

The current flow during charging is reverse of that during use. So it
is heavy usage that has the possibility of reverse charging a weak cell.


| My work was with a battery pack that consisted of mutliple series-
| parallel D
| cells set up as a back-up for a medical device. Yikes! I hope they
| took my
| advice and added the diode to each series string.

For alkaline cells, which might be what gets put in such a pack, charging
them at all could be a major hazard. One string in parallel with another,
especially if one is weaker, could lead to that. So with this battery
technology, I'd say the diodes are essential.

But my question is focusing on lead-acid cells/batteries intended for power
reserve, as typically seen in off-grid systems and in backup power systems.

 

[[email protected]]

| I've been running paralleled 12 volt batteries in my motorhome for a decade.

Maybe it is the case that any issues that might exist for paralleled batteries
(or strings) increases with the length of the string. One of the things I am
considering is what voltage. From that, then, what kind of system. I am
mostly centered on 48 volts as there are inverters available for that, and
it is also the DC rated voltage for common circuit breakers. This would be
for a backup system that may in time become an off-grid system.

 

[[email protected]]

| On 8 Aug 2008 18:32:00 GMT, [email protected] wrote:
|
|>If the effect is that the _older_ strings gets _older_ faster,
|
| And if it is the newer string that gets older faster? ... Well, maybe you
| won't get the longevity you thought you'd paid for.

Right. So we need to know which it is ... which string gets older faster.


| In any event, the "best" setup does depend to some extent on the
| application and goals.

How about a power backup system (charged by the grid) that gradually shifts
to a renewable power system (charged by solar, wind, etc) and then eventually
to a completely off-grid system (or at least a sell-only grid system).

 

[danny burstein]

Mine has 4. No isolation diodes, just short jumper cables between like poles.

Not compression start? I'm disappointed.

 

[m II]

| I have never seen single cells paralleled. They are always connected in
| series to get the desired voltage. Then, another group of identical
| series cells may be paralleled with it.

So the "reason" is "everyone else does it".

Not at all. If you want 48 volts and have two volt cells to play with,
that is 48 jumpers for the paralleling the 48 cells. Add another 24 for
the series portion. That is a total of 72 jumpers. It's easier to make
two batteries first, then parallel them with two jumpers.

Aren't all the plates within one cell already parallel? By extension of that,
paralleling individual cells would make sense because it retains the very same
concept.

No. They are each in series with the one next to it. The power comes in
on one terminal, through the electrolyte and out the other plate. There
is no chance of any circulating currents within one cell. They all share
the same electrolyte bath. If there were only two large plates in a
battery, we wouldn't call them paralleled. Take those two plates and
roll them up in a cylinder shape. It may look a lot different, but
they're still not paralleled.

Now, there *are* multiple plates on each polarity because of space
constraints. There's no room for two huge plates with the same surface
are. Changing the shape of each polarity plate won't make it parallel.


mike
--

Densa International©
'Think tanks cleaned cheap'

Due to the insane amount of spam and garbage,
I block all postings with a Gmail, Google Mail,
Google Groups or HOTMAIL address.
I also filter everything from a .cn server.

http://improve-usenet.org/

 

[m II]

Not compression start? I'm disappointed.

Larger oil patch diesels often have hydraulic starters. Huge electric
ones are too hard on the ring gear and assorted fittings. A hydraulic
motor can be eased on slowly to full power.

There is a smaller auxiliary engine that first starts up to provide the
hydraulic pressure. That engine usually drives the alternator also. In
nicer set ups, the coolant for the large engine is also warmed up a bit
before start up. They have to, as in cold weather, the lubricating oil
is like molasses and 12 or 16 pistons don't like moving in it.


mike

--

Densa International©
'Think tanks cleaned cheap'

Due to the insane amount of spam and garbage,
I block all postings with a Gmail, Google Mail,
Google Groups or HOTMAIL address.
I also filter everything from a .cn server.

http://improve-usenet.org/