jtgift.blogg.se - 9v battery terminal

Additionally, 9V batteries tend to last longer than AA or AAA batteries, so you won’t have to replace them as often. They’re also relatively inexpensive, so you don’t have to worry about breaking the bank when you need to purchase new ones.

The main positive aspect of 9V batteries is that they’re small and lightweight, making them easy to carry around with you. Some devices may have a switch that allows you to choose which direction the current will flow through the device if your device does not have this switch, you must make sure that the positive and negative terminals of the battery are aligned with the corresponding terminals on the device before inserting the battery into the device.ĩV batteries come in handy for a lot of devices, but what are the positive and negative aspects of using them? Let’s take a look. It's not very useful though.When the battery is inserted into a device, the positive and negative terminals must be aligned with the corresponding terminals on the device in order for the device to work properly. It is possible to measure the potential to ground of an isolated battery with care, and a very, very high input impedance meter (often called an electrometer). You touching it (body resistance 100k) would get it to the same potential as you with a time constant of \$\mu S\$. Adding just a few nC of charge to it, as you might easily do by walking across a carpet with it, would change the potential by thousands of volts.Ĭonnecting it to another body using a resistance of 100Mohm (about the highest value of resistor whose accuracy won't be trashed by surface contamination if you touch it) would equalise the potentials with a time constant of mS. For instance, a 9v battery may have a capacitance to infinity of a few pFs. While each terminal of a 9v battery does have a potential with respect to a reference point at infinity, it's not a stable or useful potential, as it takes so little charge to change it. It's a definition of potential, but not a practical one. I do not understand how this relates to circuits. Wikipedia tells me that the electric potential of a point is the amount of energy needed to move a unit positive charge from a reference point, usually infinity, to that point. When debugging it is very often most convenient to attach the negative probe to the circuit ground and take all readings with reference to that point.

Inverting the meter so that its positive lead is grounded will also result in a -9 V reading.įor most practical electronics you just need to work out the potential between points.

Inverting the battery we now have a positive ground.

Putting a medium resistance (say 100k) across the meter terminals will cause the reading to collapse to zero. Note that a very sensitive digital meter will show random readings due to stray electric fields.

Without a reference for the voltmeter it will read 0 V.

This prevents floating of the device power supply and might be used for safety, to avoid audio hum, etc., depending on the application.

We have the option of connecting the circuit ground to earth.

One recent question on this site showed an old transistor radio circuit with the battery positive as the "ground". In most battery powered equipment this will be the DC negative supply.

In this case some arbitrary point in the circuit has been taken as ground.

In this case there is a circuit through local earth.

The voltmeter measures the battery voltage as there is a complete circuit.Various measurement and reference schemes for a 9 V battery and voltmeter. Simulate this circuit – Schematic created using CircuitLabįigures 1 to 8. For most practical applications we don't use infinity as a reference but rather something much more local. This can be the earth, the moon, the car chassis, the negative or positive terminal of the power source or even to an AC signal. Potential is always measured relative to some reference point.