Low volts high volts big amps little amps

[ohdearme]

Hello All

I am trying to understand this so could a kind someone show me a diagram, a simple circuit where I could use say a 1.5 and a 9 volt battery to explain the principle of high and low voltage against big and little amps. I have a set of 1.5v batteries, showing full voltage but little or no current is passing. Not to tecky please, I have a multimeter, some leds, resistors and a few other bits and pieces.

Regards

 

[motorbiking]

I'm not sure I fully understood you.. but here goes

A battery has an Ah for a given A load. e.g. 2500mAh at 300mA, with voltages say 4.7v, They also have a maximum discharge e.g. 2A. So if you need 10A current with 4.7v you will need 5 cells in parallel. If you want 8.4v you need 5 parallel pairs of two series. A typical AAA has a max output of about .45A. A high quality 18650 can manage 5A no problems.

How are you measuring the Current being drawn? Its possible your LEDs are consuming very little current, hence you are outputting very little current.

High end LEDs must be driven, to manage the Amps, otherwise they will fry very quickly unless cooled.

 

[SFK]

Also not sure I understand your question to "Explain principle of Low voltages, high voltages, big amps, little amps".

Assuming you want knowledgeable about relationship between Voltage (V), Amps (A) and Power (W) I would start with this
https://science.howstuffworks.com/environmental/energy/question501.htm
and then look at something like this:
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elepow.html

But as you have batteries, resistors and LEDs, this this is a good link to get some immediate hands on and theory experience of volts and amps:
http://www.instructables.com/id/Choosing-The-Resistor-To-Use-With-LEDs/


sfk

 

[JohnW2]

I am trying to understand this so could a kind someone show me a diagram, a simple circuit where I could use say a 1.5 and a 9 volt battery to explain the principle of high and low voltage against big and little amps. I have a set of 1.5v batteries, showing full voltage but little or no current is passing. Not to tecky please, I have a multimeter, some leds, resistors and a few other bits and pieces.

See my attempt at an explanation of your original question for you in ( this thread - click here )

As for your above question, take one of of your duff 1.5V batteries mentioned above, connected a voltmeter across it, and then connect a low value resistor (less than about 5 ohms, if you have one, but 10 ohms or more would probably do) and observe what happens to the voltage across the battery terminals.

As I wrote to you in the other thread thread, it's just like a high-up water tank connected to a long and almost completely (but not totally) furred-up pipe (an analogy for a duff battery). With no water flowing through the pipe, teh pressure at the bottom (c.f. voltage) will be more-or-less 'as expected' from the height of the tank. Try to draw water out the bottom of that pipe (c.f. electrical current') and the pressure (c.f. voltage) at the bottom of the pipe will fall considerably, and little water (c.f. current) will flow.

Kind Regards, John

 

[flameport]

Voltage / volts = how much force applied
Current / amps = how much electricity can pass
Resistance / ohms - restricting the amount of current.

 

[JohnW2]

Voltage / volts = how much force applied ... Current / amps = how much electricity can pass ... Resistance / ohms - restricting the amount of current.

A bit more graphic than my water tank/pipe analogy

However, I think what the OP needs to understand, but may not yet have grasped, is that a duff battery has an appreciably increased internal resistance, which has the same effect (in restricting current) as it would if it were external to the battery.

Kind Regards, John

 

[Diver Fred]

Watts 'triangle'

Volts x Amps = Watts

or

Watts
Volts x Amps

So

1.5 Volts x 5 Amps = 7.5 Watts
or
5 Volts x 1.5 Amps = 7.5 Watts


Conversely

7.5 Watts / 1.5 Volts = 5 Amps
or
7.5 Watts / 5 Amps = 1.5 Volts

 

[big-all]

ok lets try a different tack
volts= engine
amps =fuel tank
watts=throttle with a restricter [battery output ability]

a battery can be rated at say 18v 2ah this means thats the amount off power it contains
it may be able to give you 0.5ah for 4hrs max or even 50amps for about 2 mins all depends on battery type but you wont get above the maximum it can give out apart possibly from overload[dead short ]but we will put that to one side

if you still confused
a dripping tap is connected to reserviour but you wont get the full capacity when you open the tap

 

[ohdearme]

Thank everyone, thanks for your patience JohnW2, I am reading around this and getting the idea. The analogies are very helpful
Best

 

[ericmark]

Many years ago when I was an apprentice at collage we were given some home work. Very simple question "Why does a batteries volts go down?" this was in reference to lead acid batteries.

My first thought was the simple answer "Because it is discharged" however that answer may be OK for a mechanic, but I was an electrician. No internet then so it was to the collage library I went. There was some info about other cells, but Pb(s) + PbO 2(s) + 2H 2SO4(aq) → 2PbSO 4(s) + 2H 2O(l) is the formula. don't bother to work it out, the main point is the formula is true for nearly fully discharged and fully charged there is nothing to show why the voltage drops or why the current that can be draw reduces. With the old nickel iron battery the current did not seem to reduce as it became discharged, it just stopped. And with a Daniel cell the voltage does not vary that is why they are used as a reference for voltage.

I could only guess at the answer, in real terms it was a load of waffle. Even today can't really say why the volts go down on a lead acid battery, I know it does, and I know the volts are a good indication as to how charged it is. The home work got me 9/10 and everyone who answered "Because it is discharged" got 1/2 a mark, I was told my answer was not quite right hence only 9 marks, but never told where I got it wrong. I will guess the lecturer never really thought about the question before setting it. And also did not really know the answer. Rest of class felt had I not wrote an essay they would have got better marks.

However today with such high tech batteries the question is even harder. You can buy rather small batteries that will jump start your car, small enough to fit in your pocket, and if they go wrong can burst into flames even when fully discharged.

We can talk about the internal resistance and ohms law, but that is only part of the answer. We are told to relate to water, however having worked with pumps that is not easy either, the resistance to flow in a pipe, and especially if it goes around a bend, is complex.

Some times we just have to accept because it is. What we need to remember is time, an amp is one coulomb of charge per second, a watt is a Joule per second, the odd one out is the Kilowatt/hour which in spite of having hour in the name, has nothing to do with time. 360 Joules = watt/hour i.e. 60 seconds times 60 minutes so 360 seconds in an hour so the second in the watt is cancelled out by the hour in KWh so 360 KJ = 1 kWh another example of how metric does not work.

 

[JohnW2]

...the odd one out is the Kilowatt/hour which in spite of having hour in the name, has nothing to do with time. 360 Joules = watt/hour i.e. 60 seconds times 60 minutes so 360 seconds in an hour so the second in the watt is cancelled out by the hour in KWh so 360 KJ = 1 kWh another example of how metric does not work.

3,600, actually (60 x 60), not 360

I also think you may confuse some people by talking about "watt/hour", implying that you mean "watts divided by hours", whereas to get energy you have to multiply power (e.g. watts) by time (whether seconds, to get Joules, or hours, to get kWh).

Kind Regards, John

 

[ban-all-sheds]

http://www.the12volt.com/ohm/ohmslaw.asp

 

[ericmark]

3,600, actually (60 x 60), not 360

I also think you may confuse some people by talking about "watt/hour", implying that you mean "watts divided by hours", whereas to get energy you have to multiply power (e.g. watts) by time (whether seconds, to get Joules, or hours, to get kWh).

Kind Regards, John

Ups what a nought between friends.

 

[durhamplumber]

Easiest diagrams i have ever seen on the above topics are using the analogy of water containers

 

[ban-all-sheds]

TBH I don't think that anybody who needs laboured analogies explained in depth is ever going to get it.