# how to use an ampmeter in a simulator ?

Discussion in 'General Electronics Chat' started by mikelynch, Aug 7, 2014.

1. ### mikelynch Thread Starter Member

Jun 30, 2007
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can I use an ampmeter when I only have a single resistor in the circuit. I just blow up the circuit when I try ? I can only do it using a voltage divider. I use

I use LTspice but am still learning it. so I've used Yenka for this pic

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2. ### DerStrom8 Well-Known Member

Feb 20, 2011
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The first lesson you should have learned when learning about measuring circuits is that you need to measure current in series with the load, not across it. I realize you want a voltage divider, but that means you need a load resistor, and put your ammeter in series with it.

3. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,922
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What DerStrom8 said.

Current is measured in series.

Voltage is measured in parallel.

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4. ### mikelynch Thread Starter Member

Jun 30, 2007
23
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can you tell me another name for a load resistor, I've gone through the list of components trying to find one ?

5. ### shteii01 AAC Fanatic!

Feb 19, 2010
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Load resistor is a function, not name.

6. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,922
601
Here is demonstration for you.

I am measuring current through target resistor by placing ammeter in series with the target resistor. In the demonstration I measured 0.012 A of current, or 12 mA.

I am measuring voltage across target resistor by placing voltmeter in parallel with the target resistor. In the demonstration I measured 12 volts across the target resistor.

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7. ### mikelynch Thread Starter Member

Jun 30, 2007
23
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thank you. I appreciated that diagram a lot. one last question please, if I use a car battery or a watch battery both 12volts, would the ampmeter not care, will I still see the same current though the watch battery would run down to 0 volts much much sooner ?

8. ### crutschow Expert

Mar 14, 2008
16,203
4,329
In Ltspice you just put the cursor over the component after the simulation is complete and left click when you see the clamp-on ammeter symbol. That will plot the current through the component.

Not sure what you mean about a watch battery versus a car battery of the same voltage. In real life the car battery will deliver orders of magnitude more current but a virtual ammeter in a simulation doesn't care.

9. ### mikelynch Thread Starter Member

Jun 30, 2007
23
0
ok can I ask then if in your demonstration, if that 12vots is a car battery and you use the same resistor will you still get the same reading on the ammeter ?

10. ### DerStrom8 Well-Known Member

Feb 20, 2011
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If both batteries supply 12 volts to a circuit with a constant resistance, then the current will remain the same. But in real life the car battery will probably last much longer.

11. ### mikelynch Thread Starter Member

Jun 30, 2007
23
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well thanks for clearing that up , DerStrom8, I started to wonder how big the volts were in the battery whereas T now think it will only retain its volts longer because it is holding more current. it cant hold more volts !

12. ### mikelynch Thread Starter Member

Jun 30, 2007
23
0
but it would be interesting if I powered my motor controller with a 12v car battery instead of AA batteries

13. ### crutschow Expert

Mar 14, 2008
16,203
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Batteries don't hold current, as such, they hold charge. The charge is converted to current when it flows from the battery.

If they both provide the same voltage, it won't make a difference, other than how long it runs before the battery discharges. The controller only takes the current it needs.

14. ### mikelynch Thread Starter Member

Jun 30, 2007
23
0
Thanks, I knew a battery must be holding something., i guess if Id thought more I may have realised its only current when it flows. A bit like if I had said to you that dam of water holds a lot of current... you'd decide to hang out with me a little less often

So the charge you speak of that is made up of electrons ? Can you speak about the capacity of a battery in electrons instead of amphours ? eg. this pattery has 500 grams of electrons, or this battery has 10 to the power of ? electrons ?

Ridiculous question but I would like to listen to any thing else you mhave to say about charge .

15. ### crutschow Expert

Mar 14, 2008
16,203
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Perhaps the use of charge is not the best way to describe battery capacity. The number of electrons in a battery are basically fixed. The energy is stored chemically which generates the force (volts) to move the electrons in a loop from the negative to the positive terminal. Sort of like a pump moving water in a closed loop where the pump moves the same water around and around. So the battery capacity is given in ampere-hours which is a measure of how long the chemical energy lasts to keep the electrons moving.

Some compounds store chemical energy better than others. Thus a lead-acid battery doesn't store as much energy per pound as a lithium-ion battery, which is among the best at storing energy.

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