Maybe a bit of a dumb question, but I thought I'd ask because I'm
interested!

You can buy various tools which are operated with rechargeable
batteries. And there is quite a range of battery voltages to choose
between - 7.2, 12, 18, 20, 24, etc.

Question is, is a higher (or lower) voltage better (or worse)? Higher
voltage implies lower current to achieve the same power rating.

Andrew

Do you need a handyman service? Check out our
web site at http://www.handymac.co.uk

On Wed, 20 Aug 2003 21:38:45 +0100, Andrew McKay
wrote:

Maybe a bit of a dumb question, but I thought I'd ask because I'm
interested!

You can buy various tools which are operated with rechargeable
batteries. And there is quite a range of battery voltages to choose
between - 7.2, 12, 18, 20, 24, etc.

Question is, is a higher (or lower) voltage better (or worse)? Higher
voltage implies lower current to achieve the same power rating.

Andrew



Broadly, yes, although there is appropriateness.

For example a 9.6v screwdriver may be fine but not a 9.6v SDS drill
:-)

More to the point is the battery technology and quality (they are not
all the same) , the electronic control of the motor if used, the
charging arrangements for the batteries and the mechanics of the tool.

In other words this can be a marketing scam. It's possible to put
together a tool with crappy battery packs of 24v, a cheap charger that
overcharges or doesn't charge quickly enough and a junk motor and
mechanics.

I've found that this is definitely an area where buying cheap
unbranded tools based on battery voltage is an unwise move.

One of my most used tools is a Makita 6228, which is a 14v drill.
This has superb electronic speed control and torque with two geared
ranges. The charger will recharge the battery packs in an hour, and
most deals for these (at around £140 inc.) come with 3 batteries.
This means that you can keep going continuously in any practical work
that I've ever done.


..andy

To email, substitute .nospam with .gl

In message ,
Andrew McKay wrote:

Maybe a bit of a dumb question, but I thought I'd ask because I'm
interested!

You can buy various tools which are operated with rechargeable
batteries. And there is quite a range of battery voltages to choose
between - 7.2, 12, 18, 20, 24, etc.

Question is, is a higher (or lower) voltage better (or worse)? Higher
voltage implies lower current to achieve the same power rating.


You've three variables really:

1: the instantaneous power requirement of the tool

2: the Voltage of the battery pack

3: the "Ampere-hour" rating of the battery pack.

Put simply, 2*3 is the "power available" in the pack, so it can be seen
that increasing either 2 or 3 will result in more power being available
to the tool. So, two tools of a similar power useage but different
battery ratings will be able to be used for differing lengths of time
before requiring a recharge, likewise two tools with different power
useage but similar battery ratings.

The only other thing to worry about is that - in theory - the higher the
battery voltage, the more "torque" can be available at the motor, so an
18V combi drill *should* find making a hole in a masonry wall easier
than a 12V combi drill. In practice there are other factors which affect
this ability which include the quality of the cells in the battery pack
(particularly their "internal resistance"), the quality of motor, of
control electronics and especially of the mechanical design of the tool;
the gearbox for example.

The main problem I've found when comparing battery tools is that factor
1: is very rarely quoted in the literature available, and the factors
mentioned in the above paragraph are only known when you have used the
tool for a while. The only info to go on (in the absence of
reccommendations or otherwise from places such as uk.d-i-y) is therefore
the battery ratings and, generally, the higher the Voltage, the higher
power the tool. Some cheap brands manage to do this by compromising on
the quality of the cells, or perhaps by fitting cells with lower
Ampere-hour ratings so that you have to recharge them more often.

Bit convoluted, and undoubtedly someone will come up with a more lucid
explanation, but I hope this has helped a bit :-)

Hwyl!

Martin.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Don't fight technology, live with it: http://www.livtech.co.uk/
.... I Have To Stop Now, My Fingers Are Getting Hoarse!

In article ,
Andrew McKay wrote:
You can buy various tools which are operated with rechargeable
batteries. And there is quite a range of battery voltages to choose
between - 7.2, 12, 18, 20, 24, etc.

Question is, is a higher (or lower) voltage better (or worse)? Higher
voltage implies lower current to achieve the same power rating.

They all seem to use the same sized cells - called sub C size. So the only
way to increase capacity is to increase the voltage - you can't parallel
these types of cells.

--
*Errors have been made. Others will be blamed.

Dave Plowman London SW 12
RIP Acorn

Dave Plowman wrote:

They all seem to use the same sized cells - called sub C size. So the only
way to increase capacity is to increase the voltage - you can't parallel
these types of cells.

The capacity of the sub c cells can vary by quite a margin however.
Cheap and nasty ones as found it the budget tools may only be good for
1.2Ah. The better end of the market can offer twice that capacity not to
mention closer cell matching, and lower internal resistance, better
cycle life and discharge characteristics.

Not all battery packs are equal - and to an extent you get what you pay
for.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

more volts equal more power if all the other factors are the same.
the most used drill I have is a 9,6volt hitachi (brilliant for
screwdriving and holes in wood) second most used is a 12volt elu
impact screwdriver, 7.2makita then come the also rans 18v cheapie,
24volt cheapie, 12v b&D 12vbosch. So you can see the quality and
usability are the most important factors, then when you have a make
that works well, get the highest voltage that does what you need with
the most practical weight.

mrcheerful

In article ,
John Rumm wrote:
They all seem to use the same sized cells - called sub C size. So the
only way to increase capacity is to increase the voltage - you can't
parallel these types of cells.

The capacity of the sub c cells can vary by quite a margin however.
Cheap and nasty ones as found it the budget tools may only be good for
1.2Ah. The better end of the market can offer twice that capacity not to
mention closer cell matching, and lower internal resistance, better
cycle life and discharge characteristics.

Not all battery packs are equal - and to an extent you get what you pay
for.

Absolutely. I've re-celled several cheapo packs, and the difference in the
tool performance is noticeable.

--
*Learn from your parents' mistakes - use birth control

Dave Plowman London SW 12
RIP Acorn

Dave Plowman wrote:

In article ,
Andrew McKay wrote:

You can buy various tools which are operated with rechargeable
batteries. And there is quite a range of battery voltages to choose
between - 7.2, 12, 18, 20, 24, etc.


Question is, is a higher (or lower) voltage better (or worse)? Higher
voltage implies lower current to achieve the same power rating.


They all seem to use the same sized cells - called sub C size. So the only
way to increase capacity is to increase the voltage - you can't parallel
these types of cells.




Actualy you can for discharge, but not for charge Well even then...Oh
well. Its not practicable for power tools.


Otherwise you are totally correct.

Sub 'C's are rated for something like 30-100A peak discharge rate, for
Nicads, and maybe 30A only for NiMh.

So in practice power available is very much a function of the number of
cells assuming the motor is rated to take the correct current draw.

SUB 'C's come in various capacities too - the originals were something
like 1.2A/h but modern NiMh cells are pushing 3A/h.

With a motor efficiency (these are real cheapo motors) in the 50-60%
range a 10 cell unit (12V) at 30A is roughly 360W in and about 200W out.

Or a bit more than 1/4bhp. Of course at this current the pack will last
only 6 minutes flat out

John Rumm wrote in message ...
Dave Plowman wrote:

They all seem to use the same sized cells - called sub C size. So the only
way to increase capacity is to increase the voltage - you can't parallel
these types of cells.

The capacity of the sub c cells can vary by quite a margin however.
Cheap and nasty ones as found it the budget tools may only be good for
1.2Ah. The better end of the market can offer twice that capacity not to
mention closer cell matching, and lower internal resistance, better
cycle life and discharge characteristics.

Not all battery packs are equal - and to an extent you get what you pay
for.

Got it in one.

Cheap battery tools equals cheap battery and cheap charger. Either the
charger fails to charge or boils the battery, sooner or later. More
expensive tools tend to work until battery fatigue.

Either way though buying a complete new machine is cheaper than
replacing parts.

On Wed, 20 Aug 2003 21:38:45 +0100, Andrew McKay
wrote:

Question is, is a higher (or lower) voltage better (or worse)?

Judge it by weight of the pack. Given the variation in cell quality,
weight is as good a guide as any.

In message , Michael
McNeil writes
John Rumm wrote in message
.. .
Dave Plowman wrote:

They all seem to use the same sized cells - called sub C size. So the only
way to increase capacity is to increase the voltage - you can't parallel
these types of cells.

The capacity of the sub c cells can vary by quite a margin however.
Cheap and nasty ones as found it the budget tools may only be good for
1.2Ah. The better end of the market can offer twice that capacity not to
mention closer cell matching, and lower internal resistance, better
cycle life and discharge characteristics.

Not all battery packs are equal - and to an extent you get what you pay
for.

Got it in one.

Cheap battery tools equals cheap battery and cheap charger. Either the
charger fails to charge or boils the battery, sooner or later. More
expensive tools tend to work until battery fatigue.

Either way though buying a complete new machine is cheaper than
replacing parts.

CPC are doing a 24v hammer drill with two batteries for less than £30 -
cheap enough to discard it when the batteries go
--
geoff