Quiz question

In article ,
Roderick Stewart wrote:
On Fri, 11 Oct 2013 16:32:01 +0100, "Max Demian"
wrote:

What I want to know is, what *exactly* have they done to car batteries
so that they don't need to be topped up any more. I know that they are
supposed to use a different lead alloy for the electrodes, which
supposedly reduces the amount of 'gassing' (conversion of water to
hydrogen and oxygen by electrolysis) during charging, but what about
loss by evaporation?

Probably the same as anything else these days that is regarded as
"maintenance free". You just throw it away before it needs any.

Not so - I've just replaced an 11 year old battery which never had any
attention. Some years ago that would have been unthinkable.

--
*If you remember the '60s, you weren't really there

Dave Plowman London SW
To e-mail, change noise into sound.

Roderick Stewart wrote:

If I had found that our nominal 15Ah batteries
which had only tested at about 9.5Ah on the 4.8A test load gave
something like the full 15Ah at the lower test current, I'd still have
been disappointed but I'd have understood, but it was nowhere near,
maybe about 0.5Ah to 1Ah higher at the most.

I was just wondering how they'd fare at 150mA, which would be the 100
hour rate. From what you've said, it doesn't sound like they'd manage
15Ah even then, which strongly suggests the claimed capacity is simply
bogus.

I'd have thought a 10-12
hour discharge time to cover a working day was reasonable though; it's
no more than we expect from our computers and phones.

What are these small lead acid cells intended for, anyway? I'm not
talking about 15Ah motorcycle batteries, which are more like car
batteries in being designed for high starting currents. Rod was
describing those lead acid batteries you can buy from Maplin and the
like. Does anyone know of a real-world application for them? Is a
10-12 hour discharge time realistic?

I personally know of only one such application: as the standby supply
for an industrial clock system. The mean current when operating the
clocks was well below 150mA, so a 0.01C (150mA) discharge rate would be
relevant.

We also used them to power PMBXs, but I've no idea what kind of run
time they were expected to manage. The bigger PABXs used wet batteries
which is not what Rod was talking about.

According to this, sealed lead acid batteries are normally quoted at
the 20 hour rate:


One battery that does not perform well at a 1C discharge rate is the
SLA. To obtain a practical capacity reading, manufacturers commonly
rate these batteries at 0.05C or 20 hour discharge. Even at this slow
discharge rate, it is often difficult to attain 100 percent capacity.
By discharging the SLA at a more practical 5h discharge (0.2C), the
capacity readings are correspondingly lower. To compensate for the
different readings at various discharge currents, manufacturers offer a
capacity offset.

Applying the capacity offset does not improve battery performance; it
merely adjusts the capacity calculation if discharged at a higher or
lower C-rate than specified. The battery manufacturer determines the
amount of capacity offset recommended for a given battery type.


See http://www.buchmann.ca/chap5-page1.asp for the full article.


--
SteveT

In article ,
Steve Thackery wrote:
Roderick Stewart wrote:

If I had found that our nominal 15Ah batteries
which had only tested at about 9.5Ah on the 4.8A test load gave
something like the full 15Ah at the lower test current, I'd still have
been disappointed but I'd have understood, but it was nowhere near,
maybe about 0.5Ah to 1Ah higher at the most.

I was just wondering how they'd fare at 150mA, which would be the 100
hour rate. From what you've said, it doesn't sound like they'd manage
15Ah even then, which strongly suggests the claimed capacity is simply
bogus.

I'd have thought a 10-12
hour discharge time to cover a working day was reasonable though; it's
no more than we expect from our computers and phones.

What are these small lead acid cells intended for, anyway? I'm not
talking about 15Ah motorcycle batteries, which are more like car
batteries in being designed for high starting currents. Rod was
describing those lead acid batteries you can buy from Maplin and the
like. Does anyone know of a real-world application for them? Is a
10-12 hour discharge time realistic?

Security alarms often use smallish lead acid batteries

--
From KT24

Using a RISC OS computer running v5.18

"Peter Duncanson" wrote in message
...
On Fri, 11 Oct 2013 16:32:01 +0100, "Max Demian"
wrote:

"Dave Plowman (News)" wrote in message
...

Sealed lead acid is the correct name. Although it has been hijacked by
some for use with semi-sealed wet types. Which still have a means of
filling concealed beneath a sticker or whatever.

What I want to know is, what *exactly* have they done to car batteries so
that they don't need to be topped up any more. I know that they are
supposed
to use a different lead alloy for the electrodes, which supposedly reduces
the amount of 'gassing' (conversion of water to hydrogen and oxygen by
electrolysis) during charging, but what about loss by evaporation?

Try this article for a start:
http://en.wikipedia.org/wiki/Car_battery

Lead-acid batteries for automotive use are made with slightly
different construction techniques, depending on the application of
the battery. The "flooded cell" type, indicating liquid electrolyte,
is typically inexpensive and long-lasting, but requires more
maintenance and can spill or leak. Some flooded batteries have
removable caps that allow for the electrolyte to be tested and
maintained.

More costly alternatives to flooded batteries are valve regulated
lead acid (VRLA) batteries, also called "sealed" batteries. The
absorbed glass mat (AGM) type uses a glass mat separator, and a "gel
cell" uses fine powder to absorb and immobilize the sulfuric acid
electrolyte. These batteries are not serviceable: the cells are
sealed so the degree of charge cannot be measured by hydrometer and
the electrolyte cannot be replenished.

More information about AGM and gel cell types he
http://en.wikipedia.org/wiki/Lead%E2...rbed_glass_mat

I think I must have looked at that article befo Wikipedia would usually
be my first port of call. It seems to be rather old-fashioned/generalised. I
haven't seen a car battery with removeable caps for years, and the ones I
have looked at don't seem to be 'sealed' in the sense of being able to be
mounted in any orientation, and they do appear to have liquid electrolyte,
but just no way to top them up.

I suppose it must just be part of a gradual improvement in design rather
than anything radical.

--
Max Demian

"Steve Thackery" wrote in message
...
Roderick Stewart wrote:

If I had found that our nominal 15Ah batteries
which had only tested at about 9.5Ah on the 4.8A test load gave
something like the full 15Ah at the lower test current, I'd still have
been disappointed but I'd have understood, but it was nowhere near,
maybe about 0.5Ah to 1Ah higher at the most.

I was just wondering how they'd fare at 150mA, which would be the 100
hour rate. From what you've said, it doesn't sound like they'd manage
15Ah even then, which strongly suggests the claimed capacity is simply
bogus.

I'd have thought a 10-12
hour discharge time to cover a working day was reasonable though; it's
no more than we expect from our computers and phones.

What are these small lead acid cells intended for, anyway? I'm not
talking about 15Ah motorcycle batteries, which are more like car
batteries in being designed for high starting currents. Rod was
describing those lead acid batteries you can buy from Maplin and the
like. Does anyone know of a real-world application for them? Is a
10-12 hour discharge time realistic?

Well I've got a hand held vacuum cleaner with a 6V lead acid battery if
that's any help. (Vax Libretto)

--
Max Demian

On Fri, 11 Oct 2013 12:07:24 -0500, "Steve Thackery"
wrote:

I'd have thought a 10-12
hour discharge time to cover a working day was reasonable though; it's
no more than we expect from our computers and phones.

What are these small lead acid cells intended for, anyway? I'm not
talking about 15Ah motorcycle batteries, which are more like car
batteries in being designed for high starting currents. Rod was
describing those lead acid batteries you can buy from Maplin and the
like. Does anyone know of a real-world application for them? Is a
10-12 hour discharge time realistic?

It was some time ago now, but the 15Ah ones were built into flight
cases with small video monitors that drew about 1.75A, in the hope
that they would run for a full working day without the nuisance of
recharging. Unfortunately they tended to conk out towards the end of
the afternoon, which is what prompted the investigation into the true
capacity as opposed to what was printed on the side.

We used a lot of smaller nicad batteries that clipped onto the backs
of cameras, or fitted into video recorders and sound mixing desks,
either 1.6Ah or 3.5Ah. These deteriorated after a year or so, but what
affected them most was cold weather. On a winter's day some of them
only lasted about half as long as they should. They also cost a
fortune; a Sony or PAG 3.5Ah nicad battery would cost about £200,
whereas a biggish car battery of about 60Ah would cost about a quarter
of that, and didn't suffer so much in the cold. We tended to use car
batteries or Dryfits in homebrew carry cases except where portability
was an issue, because although they were heavy we didn't have to
change them so often.

Rod.

In article ,
Max Demian wrote:
I think I must have looked at that article befo Wikipedia would
usually be my first port of call. It seems to be rather
old-fashioned/generalised. I haven't seen a car battery with removeable
caps for years, and the ones I have looked at don't seem to be 'sealed'
in the sense of being able to be mounted in any orientation, and they
do appear to have liquid electrolyte, but just no way to top them up.

They usually have normal caps under some sticky back plastic. But simply
don't need topping up - unless you have a faulty alternator. Even on my 30
year old Rover.

--
*I can see your point, but I still think you're full of ****.

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Roderick Stewart wrote:
We used a lot of smaller nicad batteries that clipped onto the backs
of cameras, or fitted into video recorders and sound mixing desks,
either 1.6Ah or 3.5Ah. These deteriorated after a year or so, but what
affected them most was cold weather. On a winter's day some of them
only lasted about half as long as they should. They also cost a
fortune; a Sony or PAG 3.5Ah nicad battery would cost about £200,
whereas a biggish car battery of about 60Ah would cost about a quarter
of that, and didn't suffer so much in the cold. We tended to use car
batteries or Dryfits in homebrew carry cases except where portability
was an issue, because although they were heavy we didn't have to
change them so often.

Yes. If size weight and portability wasn't a major issue, car batteries
were a very cost effective solution - provided you didn't run them flat.
Use them down to no more than half capacity, and they seemed to last as
well as in a car.

--
*My designated driver drove me to drink

Dave Plowman London SW
To e-mail, change noise into sound.

On Fri, 11 Oct 2013 12:57:20 +0100, "Dave Plowman (News)"
wrote:

In article ,
Johny B Good wrote:
On Fri, 11 Oct 2013 00:32:51 +0100, "Dave Plowman (News)"
wrote:

In article ,
Paul Ratcliffe wrote:
A 'dry charged' lead acid has a very good shelf life

Could you explain that term please. Not sure I've heard it before.

It is in a fully charged state chemically speaking but with the acid
removed. Add acid of the correct SG, and you have a battery ready to go
after an hour or so 'settling'. It's also a safe way to transport a
battery with the acid in a separate sealed container - that's how most
mail order batteries arrive.

I think you meant to say: "that's how most mail order Flooded Cell
Lead Acid batteries arrive.

No I didn't. Not in the context of talking about dry charged lead acid.
The principle doesn't exist with SLA types.

Well, a dry charged lead acid battery (or cell) is simply a Flooded
Cell Lead Acid type that has simply had the electrolyte filling stage
of its manufacture postponed so that the end user can complete this
final stage of manufacture for himself.

Transporting the required electrolyte fill in a seperate stout
polyethylene bottle reduces the risk of dilute sulphuric acid spill
considerably (presumably to the point where the parcel delivery
service deem it sufficiently safe to withstand the rigours of
transport)


The 'dryfit' types (AGM or Gel types) are,
quite obviously, supplied in a ready for service state so should be
excluded from this particular safety aspect of mail order
transportation.

Sealed lead acid is the correct name. Although it has been hijacked by

SLA was what I meant but the TLA escaped me for the moment so I used
a tradename in its stead.

some for use with semi-sealed wet types. Which still have a means of
filling concealed beneath a sticker or whatever.

This type are usually refered to as "Low Maintainance" but are
sometimes, erroneously, also described as "Maintainance Free".
--
Regards, J B Good

On Fri, 11 Oct 2013 17:56:14 +0100, "Dave Plowman (News)"
wrote:

In article ,
Roderick Stewart wrote:
On Fri, 11 Oct 2013 16:32:01 +0100, "Max Demian"
wrote:

What I want to know is, what *exactly* have they done to car batteries
so that they don't need to be topped up any more. I know that they are
supposed to use a different lead alloy for the electrodes, which
supposedly reduces the amount of 'gassing' (conversion of water to
hydrogen and oxygen by electrolysis) during charging, but what about
loss by evaporation?

Probably the same as anything else these days that is regarded as
"maintenance free". You just throw it away before it needs any.

Not so - I've just replaced an 11 year old battery which never had any
attention. Some years ago that would have been unthinkable.

That, quite obviously, must have been a genuine "Maintainance Free"
design with pressure relief vent caps and catalytic materials
incorporated into each cell to recycle the hydrogen/oxygen mix back
into water (and low grade heat).

I bet you were taking full advanatage of an engine that could fire up
within one revolution of being cranked on the starter to minimse wear
and tear on both battery and starter motor. Some (most?) people will
keep the starter running for a second or so after the engine has
actually fired up which puts additional stress on battery and starter.
--
Regards, J B Good