Very very elementary electronics questions

[nuevallorker]

Hello,

As the group name contains the word "basic" in it, there must be a level below basic which I am at, since most of the posts are beyond my understanding. So.. be gentle

I'm a tinkerer, have been my whole life. For the first time ever though, I've built myself a little workshop in a walk-in closet in my apartment and i have the room and the tools to do more interesting things. I've always wanted to learn about circuitry and electronics and so i'm starting now.. in my 30's. I would say I have a pretty well rounded set of skill at fixing things, taking them apart and knowing how they work but certain electronic concepts have eluded me. There is so much electronics info on the net that its overwhelming and I never know where to start. So, I think the best way for me to start is by asking a series of questions that I come across as i tinker with things at home and then try to understand some basic principles from there.. so here goes:

1. if the dc power requirement on a device is 9v 1amp, could you also use a 4.5v 2amp supply?
2. I have a set of speakers which take 4 AA batteries or 6V but the DC charger is 9V, how come the two voltages work? why wouldnt the 9V fry the circuit board?
3. Whats the difference between smaller / larger batteries with the same voltage? for example, lets say a 12v car battery and a much smaller 12v battery. More / Less amps? (i assume obviously there are greater capacities)
4. What determines how much any given device can handle in terms of charge? for instance, why is it that some devices I have can work with less or more (DC) voltage? how do i know whether a higher voltage / higher amp charge will ruin my device?

Thanks in advance for your answers.

 

[John Fields]

On Wed, 4 Jan 2012 08:08:40 -0800 (PST), nuevallorker
<asaf.peled@gmail.com> wrote:

Hello,

As the group name contains the word "basic" in it, there must be a level below basic which I am at, since most of the posts are beyond my understanding. So.. be gentle

I'm a tinkerer, have been my whole life. For the first time ever though, I've built myself a little workshop in a walk-in closet in my apartment and i have the room and the tools to do more interesting things. I've always wanted to learn about circuitry and electronics and so i'm starting now.. in my 30's. I would say I have a pretty well rounded set of skill at fixing things, taking them apart and knowing how they work but certain electronic concepts have eluded me. There is so much electronics info on the net that its overwhelming and I never know where to start. So, I think the best way for me to start is by asking a series of questions that I come across as i tinker with things at home and then try to understand some basic principles from there.. so here goes:

1. if the dc power requirement on a device is 9v 1amp, could you also use a 4.5v 2amp supply?

No.

Voltage is like water pressure and amperage is like quantity of water,
so if you had 1 gallon per minute of water flowing out of a hose and 9
PSI on the other end of it, only 1/2 gallon per minute would flow if
the pressure was 4.5 PSI.

2. I have a set of speakers which take 4 AA batteries or 6V but the DC charger is 9V, how come the two voltages work? why wouldnt the 9V fry the circuit board?

---
If the speakers work with the charger connected but no batteries
installed, then the circuitry is designed to operate with as much
voltage as the charger can put out.

3. Whats the difference between smaller / larger batteries with the same voltage? for example, lets say a 12v car battery and a much smaller 12v battery. More / Less amps? (i assume obviously there are greater capacities)

---
A larger battery using the same chemistry as a smaller one will be
able to provide more current over the same time period, or the same
current for a longer period than the smaller one.

4. What determines how much any given device can handle in terms of charge? for instance, why is it that some devices I have can work with less or more (DC) voltage?

The choice of voltage and current is made during the design process
and depends on the power the device needs to supply, how long it has
to supply it, and how much it costs.

how do i know whether a higher voltage / higher amp charge will ruin my device?

---
RTFM.
---

Thanks in advance for your answers.

---
Yer welcome.

--
JF

 

[Ecnerwal]

In article
<11692396.562.1325693320708.JavaMail.geo-discussion-forums@vbmq3>,
nuevallorker <asaf.peled@gmail.com> wrote:

IMHO John F. answered your numbered questions well, so I'm just going to
address this one.

but certain electronic concepts have
eluded me. There is so much electronics info on the net that its overwhelming
and I never know where to start.

If it doesn't scare you off to delve into a real textbook (as it
happens, a very well written one) try _The_Art_of_Electronics_ - first
or second edition will get you a long ways, third edition is still being
worked on and you shouldn't wait for it. The first few chapters drag you
rather quickly up from zero, more or less. Quite possibly the best
(certainly the most readable) textbook in a rather large (and expensive)
pile of them from my college career.

Our EE program used in-house "textbooks" that taught circuits by the
memorize and barf-back approach. The electronics for physics (aimed at
being able to do experiments and use electronics to make them happen and
collect data from them) used AoE, and suddenly I could understand WHY
and HOW the things that had been memorized, barfed back, and largely
forgotten shortly thereafter worked - which was a lot more useful.

Depending on your personal mindset, signing up for an actual course may
work better for you, if you can find such a thing at a local community
college or adult ed program (assuming any are left in your area.) But
you can teach yourself a great deal if you put your mind to it and set
aside time for it.

See what your local library has, or can get via inter-library loan for
basic or inroductory electronics, also. A lot of the "so much
electronics info on the net" consists of umpteen different versions of
"I built this neat circuit I don't understand, isn't it neat" sometimes
with a cockamamie "explanation" attached. Sorting the wheat from the
chaff when you don't know anything to start with is rather hard in that
environment. Real books often win simply because they have to actually
pass by editors and the like, and/or because they are written by folks
who get paid for it.

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.

 

[Tim Wescott]

On Wed, 04 Jan 2012 08:08:40 -0800, nuevallorker wrote:

Hello,

As the group name contains the word "basic" in it, there must be a level
below basic which I am at, since most of the posts are beyond my
understanding. So.. be gentle

I'm a tinkerer, have been my whole life. For the first time ever though,
I've built myself a little workshop in a walk-in closet in my apartment
and i have the room and the tools to do more interesting things. I've
always wanted to learn about circuitry and electronics and so i'm
starting now.. in my 30's. I would say I have a pretty well rounded set
of skill at fixing things, taking them apart and knowing how they work
but certain electronic concepts have eluded me. There is so much
electronics info on the net that its overwhelming and I never know where
to start. So, I think the best way for me to start is by asking a series
of questions that I come across as i tinker with things at home and then
try to understand some basic principles from there.. so here goes:

1. if the dc power requirement on a device is 9v 1amp, could you also
use a 4.5v 2amp supply?

Almost certainly not (although some devices will be able to limp along on
way low voltages). Everything in that device is designed to work at 9V,
giving it half of that is going to make everything be off.

You could, if you knew enough, make a 9V, 1A supply that took in 4.5V and
a bit over twice the output current. Power must be conserved, but
voltage can be stepped up (and current down).

2. I have a set of speakers which take 4 AA
batteries or 6V but the DC charger is 9V, how come the two voltages
work? why wouldnt the 9V fry the circuit board?

Because the circuit either steps the 9V down to 6V before it uses it, or
the circuit is designed to work with anything from 9V down to whatever (a
well-discharged AA cell will deliver a useful 1V, depending on the
current).

3. Whats the difference
between smaller / larger batteries with the same voltage? for example,
lets say a 12v car battery and a much smaller 12v battery. More / Less
amps? (i assume obviously there are greater capacities)

Generally the bigger battery will have more capacity and higher current
capability. It may, however, just have more capacity, or just higher
current capability, or it may just be a cheap piece of s**t that's big
and not any more useful.

4. What
determines how much any given device can handle in terms of charge? for
instance, why is it that some devices I have can work with less or more
(DC) voltage? how do i know whether a higher voltage / higher amp charge
will ruin my device?

What determines the voltage that a device needs is the design. The way
you can know for sure what voltage will ruin your device is to give it
progressively higher voltages until it dies -- then you'll know.

(Circuit designers don't necessarily know just at what point their
circuits will die, either -- you design for a nominal voltage, you make
sure it'll work at that voltage, if you're good you'll think about making
sure it'll work at higher and lower values -- but rarely do you do the
analysis and measurements necessary to confirm life or death at a
particular supply voltage).

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

 

[Ecnerwal]

On the web - not quite as good as AoE in my opinion, but handy and not a
crock...or spam-laden ad site. Obviously it's eventually focussed on the
stuff used in the related course, but seems pretty decent on a quick
skim-through.

http://www.clear.rice.edu/elec201/Book/basic_elec.html

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.

 

[Rich Webb]

On Wed, 04 Jan 2012 13:18:07 -0500, Ecnerwal
<MyNameForward@ReplaceWithMyVices.Com.invalid> wrote:

In article
11692396.562.1325693320708.JavaMail.geo-discussion-forums@vbmq3>,
nuevallorker <asaf.peled@gmail.com> wrote:

IMHO John F. answered your numbered questions well, so I'm just going to
address this one.

but certain electronic concepts have
eluded me. There is so much electronics info on the net that its overwhelming
and I never know where to start.

If it doesn't scare you off to delve into a real textbook (as it
happens, a very well written one) try _The_Art_of_Electronics_ - first
or second edition will get you a long ways, third edition is still being
worked on and you shouldn't wait for it. The first few chapters drag you
rather quickly up from zero, more or less. Quite possibly the best
(certainly the most readable) textbook in a rather large (and expensive)
pile of them from my college career.

Another vote for AoE and to add a suggestion that the OP consider
picking up the companion "Student Manual" if he opts for the self-study
approach. This is the hands-on complement to the main text and will
require some investment in components and test equipment. However, it's
really helpful to have guide in "making the theory work" and to get the
occasional Aha! moment when, e.g. the diode I-V curve really does plot
out as logarithmic.

--
Rich Webb Norfolk, VA

 

[fungus]

On Jan 4, 5:08 pm, nuevallorker <asaf.pe...@gmail.com> wrote:

1. if the dc power requirement on a device is 9v 1amp, could you
also use a 4.5v 2amp supply?

No, volts and amps are completely separate things
and can't be mixed up like that.

If you want a car anaology: It's like speed vs. carrying
capacity. A racecar can't carry 50 people, a bus can't
reach 150mph.

2. I have a set of speakers which take 4 AA batteries or 6V but
the DC charger is 9V, how come the two voltages work?
why wouldnt the 9V fry the circuit board?

The speakers must be designed for 9V. Some things will
work with less volts, eg. light bulbs, but they won't be as
bright as if you run them at full voltage.

nb. Not many things will work with more volts than designed
for. They usually overheat and burn out.

3. Whats the difference between smaller / larger batteries
with the same voltage?

Think of them as things filled with electrons. A bigger battery
can hold more of them so it will take longer to empty.

It might also be able to empty faster (more current), think
of it as having a wider spout than a small battery.

4. What determines how much any given device can handle
in terms of charge? for instance, why is it that some devices
I have can work with less or more (DC) voltage? how do i know
whether a higher voltage / higher amp charge will ruin my device?

Lower voltages will make bulbs dimmer, motors slower,
speakers quieter, etc. Most 'analog' devices fit into this
category.

Some things require a minimum voltage to do anything
at all. There's no gradual dropoff, they do absolutely
nothing if the voltage is too low. Most 'digital' devices
are in this category.

(nb. I use the words 'analog' and 'digital' in a very, very
loose sense here...)

Higher voltages will almost always ruin a device. Don't
do it. Your bulb will burn out, your motor will spin too
fast, get hot, and burn out, etc. Some things will fail
instantly (a LED), others will take time, but eventually
they'll fail.

 

[JeffM]

Ecnerwal wrote:

nuevallorker wrote:
There is so much electronics info on the net that [it's] overwhelming
and I never know where to start.

[...]try _The_Art_of_Electronics_

....by Paul Horowitz and Winfield Hill.

We rarely see Win Hill posting these days,
so he must be hard at work (on the 3rd edition?).

All electrical/electronic topics start with arithmetic.
The 4.5V question shows that the OP did *not* start there.

He obviously has a 'Net-connected computer,
so, as with so many topics, Wikipedia is an apt starting point.
Fields pointed to the usual water-based model.
Here's Page 1 for this topic, indexed to that point:
http://en.wikipedia.org/wiki/Ohm's_law#Hydraulic_analogy
Plenty of links to follow there and an "Electronics portal" at the
bottom.

For the battery volume question,
look up the "milliAmp Hours" spec for the ones you have.
http://google.com/search?q=site:en.wikipedia.org+battery+%22.Ampere-Hour%22

 

[Phil Allison]

"nuevallorker"

1. if the dc power requirement on a device is 9v 1amp, could you also use a
4.5v 2amp supply?

** The device is unlikely to work well ( or at all ) with only half the
needed supply voltage.

2. I have a set of speakers which take 4 AA batteries or 6V but the DC
charger is 9V, how come the two voltages work? why wouldnt the 9V fry the
circuit board?

** The device is designed to work with a 9V supply but will tolerate a lower
voltage and give less output power.


3. Whats the difference between smaller / larger batteries with the same
voltage? for example, lets say a 12v car battery and a much smaller 12v
battery. More / Less amps? (i assume obviously there are greater capacities)

** Physically larger batteries can deliver higher currents if needed and
have longer run times.

4. What determines how much any given device can handle in terms of charge?
for instance, why is it that some devices I have can work with less or more
(DC) voltage? how do i know whether a higher voltage / higher amp charge
will ruin my device?

** The components used to make any electronic product all have max voltage
ratings and heat dissipation limits too. Keep increasing the DC supply
voltage and you will exceed the ratings of one of more components and then
it will fail.

The maker knows what supply voltage gives reliable operation and a long
ife - you can only find out the hard way just where the upper limit is.


.... Phil

 

[krw@att.bizzzzzzzzzzzz]

On Wed, 4 Jan 2012 08:08:40 -0800 (PST), nuevallorker <asaf.peled@gmail.com>
wrote:

Hello,

As the group name contains the word "basic" in it, there must be a level below basic which I am at, since most of the posts are beyond my understanding. So.. be gentle

I'm a tinkerer, have been my whole life. For the first time ever though, I've built myself a little workshop in a walk-in closet in my apartment and i have the room and the tools to do more interesting things. I've always wanted to learn about circuitry and electronics and so i'm starting now.. in my 30's. I would say I have a pretty well rounded set of skill at fixing things, taking them apart and knowing how they work but certain electronic concepts have eluded me. There is so much electronics info on the net that its overwhelming and I never know where to start. So, I think the best way for me to start is by asking a series of questions that I come across as i tinker with things at home and then try to understand some basic principles from there.. so here goes:

1. if the dc power requirement on a device is 9v 1amp, could you also use a 4.5v 2amp supply?

No, but you could use 9V at 2amps. The voltage is the critical number. The
current delivered by the supply must be equal to or more than required by the
widget
..

2. I have a set of speakers which take 4 AA batteries or 6V but the DC charger is 9V, how come the two voltages work? why wouldnt the 9V fry the circuit board?

There is a regulator that drops the 9V to 6V (or steps up the 6V to 9V, or
both are changed to some other...).

3. Whats the difference between smaller / larger batteries with the same voltage? for example, lets say a 12v car battery and a much smaller 12v battery. More / Less amps? (i assume obviously there are greater capacities)

At the same voltage, yes. A physically larger battery may have more cells,
and thus a higher voltage.

4. What determines how much any given device can handle in terms of charge? for instance, why is it that some devices I have can work with less or more (DC) voltage? how do i know whether a higher voltage / higher amp charge will ruin my device?

It depends on what you're doing. In your situation above, you have a device
that needs 9V at 1A. A higher (or perhaps lower) voltage will damage it. It
will want to draw 1A. If that isn't available, it will draw too much from the
supply, possibly damaging the supply or the voltage will drop, possibly
damaging both. If you can supply more than 1A, great, the load only needs 1A.
Higher won't hurt anything.

There are other situations, like in a home, where the current matters too. For
instance, a 120V circuit may be 15A or 20A. You never want to replace a 15A
fuse with a 20A fuse because the wiring will likely only handle 15A safely. A
15A widget will still work on a 20A fuse (see above) but it's not safe.

Thanks in advance for your answers.

 

[Kaz Kylheku]

On 2012-01-04, nuevallorker <asaf.peled@gmail.com> wrote:

Hello,

As the group name contains the word "basic" in it, there must be a level below basic which I am at, since most of the posts are beyond my understanding. So.. be gentle

I'm a tinkerer, have been my whole life. For the first time ever though, I've built myself a little workshop in a walk-in closet in my apartment and i have the room and the tools to do more interesting things. I've always wanted to learn about circuitry and electronics and so i'm starting now.. in my 30's. I would say I have a pretty well rounded set of skill at fixing things, taking them apart and knowing how they work but certain electronic concepts have eluded me. There is so much electronics info on the net that its overwhelming and I never know where to start. So, I think the best way for me to start is by asking a series of questions that I come across as i tinker with things at home and then try to understand some basic principles from there.. so here goes:

1. if the dc power requirement on a device is 9v 1amp, could you also use a
4.5v 2amp supply?

No. Generally speaking, you must respect the minimum and maximum voltage
ratings of a device.

You can double DC voltage inexpensively, without any inductive component
(transformer).

This is done by generating an oscillating signal and driving a voltage
double based on diodes and capacitors.

You don't have to build this yourself because off the shelf "charge pump"
integrated circuits exist for this. These typically require a few
external components, such as, notably, the large capacitors that
can't be fabricated on a chip.

2. I have a set of speakers which take 4 AA batteries or 6V but the DC
charger is 9V, how come the two voltages work? why wouldnt the 9V fry the
circuit board?

Not necessarily. It's designed that way. Lots of electronic components
have a safe operating voltage range that is quite wide, and circuits made
up of those components can be designed to have a wide voltage range.
For instance some integrated circuits can operate on anything as low as 3V
or as high as 18V.

Note that "wall wart" devices only have nominal voltages. They are unregulated
devices whose voltage depends on the load. If you just plug one into the wall
and read its voltage without any load plugged in, you will read a higher value
than when current is being drawn.

3. Whats the difference between smaller / larger batteries with the same
voltage?

Usually, how much charge they store: how many mAh (milli-Ampere-hours).

for example, lets say a 12v car battery and a much smaller 12v
battery. More / Less amps? (i assume obviously there are greater capacities)

A car bettery can not only deliver lots of amps instantaneously (to turn a
starter motor) but it has a greater storage capacity. In simple terms, it
contains more electrons at the 12V potential than a small battery.

Voltage is: how high is the waterfall?
Capacity is: how big is the body of water behind the waterfall?
Amps is: how wide is the waterfall: trickle or torrent?

4. What determines how much any given device can handle in terms of charge?
for instance, why is it that some devices I have can work with less or more
(DC) voltage? how do i know whether a higher voltage / higher amp charge will
ruin my device?

To understand that, you have to know about components like semiconductors,
resistors and capacitors. All electronic devices have certain limits about how
much voltage can be applied, how much current they can carry or how much heat
they can dissipate. This is for various reasons. Sometimes the reasons have to
do with power dissipation: the more current that flows through a device, the
hotter it gets, until it fails from excess heat (explodes, melts). Wattage
ratings often depend on the environment: is the device connected to an
efficient heat sink or not, and what is the ambient temperature.

Some components have very little current flowing through them when a voltage is
applied within the safe range, but when a certain threshold voltage is
exceeded, there is suddenly a massive leakage of current which destroys them.
The voltage depends on the construction of the components: what materials are
used, how thick they are, how they are put together, their electronic
properties (especially if they are semiconductors).

When these things are put together in circuits, it becomes more complicated
because some components serve to protect others. A component that fries
at 3V can be easily be designed into a circuit that runs off 40V power rail,
because it occurs in a sub-circuit where the full 40V does not appear.

Some circuits don't perform well with excess voltage or undervoltage, even if
they don't fail. Their designs are calibrated to work in a certain range and
things go wrong outside of that range. Some part of a circuit may fail to
activate properly, or a signal may become distorted, etc.

 

[nuevallorker]

Wow, that was a bigger response turnout than i expected. Glad to see
unanimously consistent and clear responses. These all make sense to me
so far. Thanks very much for the answers and for the book suggestion
(just ordered it).

One follow up question about current since the last poster mentioned
that an excess of amps wouldnt hurt. So does that mean that current is
"pulled" rather than "pushed" ? In other words, if my widget needs 3v
and 500mA and i use a 3v supply at say 5amps its only going to "pull"
the current it needs?

 

[Kaz Kylheku]

On 2012-01-05, nuevallorker <asaf.peled@gmail.com> wrote:

Wow, that was a bigger response turnout than i expected. Glad to see
unanimously consistent and clear responses. These all make sense to me
so far. Thanks very much for the answers and for the book suggestion
(just ordered it).

One follow up question about current since the last poster mentioned
that an excess of amps wouldnt hurt. So does that mean that current is
"pulled" rather than "pushed" ?

The amount of current flowing depends on the voltage of the device
and its resistance. This is called Ohm's Law.

(Some devices have a voltage-dependent resistance; they are called "non-ohmic"
though, of course, Ohm's Law is a law and as such is never violated!)

One form of Ohm's Law isolates the current on the left hand side:

I = V/R (current is voltage divided by resistance)

Devices pull current in the presence of a voltage by exhibiting a given
resistance.

A good ("stiff") voltage source maintains the same voltage to the device
over a wide range of current pulls.

In other words, if my widget needs 3v
and 500mA and i use a 3v supply at say 5amps its only going to "pull"
the current it needs?

That is correct. In fact 3V supply will not deliver any current at all when
its output is an open circuit (but a voltage still exists).

There do exist "current source" power supplies which effectively push current.

These devices assert: "so much current (so many milliamps or amps) must flow,
no matter what!" (Well, *ideal*, current sources used to model real ones
work "no matter what"; real ones have limitations!)

Since Ohm's Law cannot be broken, current sources actually push current by
changing their voltage in response to the resistance of the device
(I stays the same and since I = V/R, V has to stay proportional to R!)
Thus they develop a greater voltage across a greater resistance, and a smaller
voltage across a smaller resistance.

Ordinary power supplies for consumer electronics and such are rarely,
if ever, current sources. You won't see that.

 

[Phil Allison]

"fungus = retarded fuckhead

nuevallorker

One follow up question about current since the last poster mentioned
that an excess of amps wouldnt hurt. So does that mean that current is
"pulled" rather than "pushed" ? In other words, if my widget needs 3v
and 500mA and i use a 3v supply at say 5amps its only going to "pull"
the current it needs?

Your conclusion is right but the reasoning is wrong.


** His reasoning is 100% spot on - you asinine POS.

Fuck OFF !!!

 

[fungus]

On Jan 5, 1:33 am, nuevallorker <asaf.pe...@gmail.com> wrote:

One follow up question about current since the last poster mentioned
that an excess of amps wouldnt hurt. So does that mean that current is
"pulled" rather than "pushed" ? In other words, if my widget needs 3v
and 500mA and i use a 3v supply at say 5amps its only going to "pull"
the current it needs?

Your conclusion is right but the reasoning
is wrong.

Try to think of electricity like water going
through pipes.

Imagine your power supply is a big tank of
water on your roof. The water pressure depends
on the height of the tank, this is the like voltage
in the circuit.

How much water will flow when you open a
tap/faucet/valve? That depends on the diameter
of the water pipe. If the pipe is only 1mm diameter
then it'll take a long time to fill a bucket no matter
how much water pressure you have. If the pipe
is a foot in diameter you'll fill a bucket almost
instantly even with very little pressure.

The diameter of the pipe is like the resistance
of a circuit and the flow is like the current (amps).

The amps that will pass through a circuit depends on
the voltage and the electrical resistance in exactly the
same way that the water flow through a pipe depends
on the water pressure and the diameter of the pipe.

 

[Phil Allison]

"fungus = retarded fuckhead


Your conclusion is right but the reasoning is wrong.


** His reasoning is 100% spot on - you asinine POS.

Fuck OFF !!!

LUNATIC !!!!!

 

[fungus]

On Jan 5, 11:10 am, "Phil Allison" <phi...@tpg.com.au> wrote:

"fungus = retarded fuckhead

 nuevallorker

One follow up question about current since the last poster mentioned
that an excess of amps wouldnt hurt. So does that mean that current is
"pulled" rather than "pushed" ? In other words, if my widget needs 3v
and 500mA and i use a 3v supply at say 5amps its only going to "pull"
the current it needs?

Your conclusion is right but the reasoning is wrong.

When you drink through a straw are you pulling
the liquid upwards or is the atmosphere pushing
it towards your mouth?

I learned the answer to that in first year physics,
maybe you were asleep...?

** His reasoning is 100% spot on   - you asinine POS.

    Fuck OFF  !!!

 

[amdx]

My post didn't show up, so here it is again.

1. if the dc power requirement on a device is 9v 1amp, could you also
use a 4.5v 2amp supply?

This requires you to know and understand "Ohms Law". The voltage is the
pressure that pushes the current through your
load (device). If you drop the voltage in half it will not push enough
current through your device to make it work properly.

2. I have a set of speakers which take 4 AA batteries or 6V but the
DC charger is 9V, how come the two voltages work?

Why wouldn't the 9V fry the circuit board?

There could be a regulator in the speaker that drops the voltage down
to 6 volts. Or the amplifier could just work from 6 to 9 volts, the
power output would be higher with higher voltage.

3. Whats the difference between smaller / larger batteries with the
same voltage? for example,

lets say a 12v car battery and a much smaller 12v battery. More / Less
amps? (i assume obviously there are greater capacities)

Assuming the same chemistry, a larger battery would be able to deliver
the same amperage for a longer time and/or more current without having
it's voltage drop below it normal voltage. The larger battery would also
have a lower "Internal Resistance".

4. What determines how much any given device can handle in terms of
charge? for instance, why is it that some devices I have can work with

less or more (DC) voltage?

Many factors, a tv remote control has to turn on an LED with maybe
15ma of current and needs to fit in your hand, so 3 volts, 2 AAA
batteries will work great. Although for a longer life I like AA.
If you have an amplifier supplying 10 Watts instead of 3 volts you
might want 12 volts or even 15 volts as a supply voltage, this higher
voltage allows you to push enough current through the speaker to get
10 watts. If you only had 3 volts it would take additional circuitry to
get 10 watts. The current from the 3 volts would also be 5 to 10 times
higher also.
Devices are designed around a specific voltage, if you exceed that,
something will probably get hot.


how do i know whether a higher voltage / higher amp charge will ruin
my device?

You don't want to exceed the voltage that a device is designed for,
you can have a power supply that will deliver higher current than the
device is rated for. The device will only use the current it needs when
supplied the proper voltage.

Note: a wallwart will measure a higher than rated voltage until the
current output is at it's rated current.
Example: A specific 12 Volt wallwart measures 16.5 volts until it has
a 1.5 amp load applied, then the voltage measures 12 volts.
This goes back to question 3 and "internal resistance"

Thanks in advance for your answers.

Your welcome.
Mikek

 

[Tim Wescott]

On Wed, 04 Jan 2012 16:33:31 -0800, nuevallorker wrote:

Wow, that was a bigger response turnout than i expected. Glad to see
unanimously consistent and clear responses. These all make sense to me
so far. Thanks very much for the answers and for the book suggestion
(just ordered it).

One follow up question about current since the last poster mentioned
that an excess of amps wouldnt hurt. So does that mean that current is
"pulled" rather than "pushed" ? In other words, if my widget needs 3v
and 500mA and i use a 3v supply at say 5amps its only going to "pull"
the current it needs?

Well, mostly yes.

In general, if a supply says "3V, 500mA" that means that it is _rated_ to
supply 500mA at 3V -- it doesn't mean that it will push 500mA out of its
terminals while delivering 3V. In fact, it can't -- to get 3V at 500mA
requires a load that will consume 500mA when it has 3V on it.

If you had a source that would deliver 3V no matter what, and a load that
wants to take 500mA at 3V, then 500mA will flow regardless of whether
that source is capable of delivering barely 500mA, or 500A.

Life is complicated by wall warts. If you have an older wall wart that
says "3V at 500mA", it might deliver 4V at no current, and more than 500mA
at less than 3V. So unplugging from a "3V, 500mA" wall wart and plugging
into a "3V, 5A" wall wart might get you more voltage, although usually
things would still work.

Newer wall warts (the slim, light weight ones) have switching supplies in
them, and are better regulated (although I'm sure that not all of them
are perfectly regulated). So you can at least hope that if it says 5V,
it'll be 5V over a large range of currents.

My advice is to -- for the most part -- treat the voltage on a wall wart
as gospel, and treat the current rating as a "do not exceed". So if you
have ten 12V, 100mA devices, then feel free to connect one or all of them
to a 12V, 1A wall wart. But if you have a 12V, 1A device, expect it to
make your 12V, 100mA wall wart fall to its knees.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

 

[Phil Allison]

"fungus = retarded fuckhead


** His reasoning is 100% spot on - you asinine POS.

Fuck OFF !!!

FUCKING LUNATIC !!!!!