LTspice: need to see currents when clicking nodes - Page 1
Forum section: electronics / general

author: eti
author_rank: Super Contributor
timestamp: November 15, 2022, 06:13:35 am
content: In “LTspice” once I’ve run a simulation and I click on the nodes, I can see the voltage of that node. Please, is there a simple way to do this for current too?Thank you

author: RoGeorge
author_rank: Super Contributor
timestamp: November 15, 2022, 07:01:47 am
content: LTspice will not show the current of a node. It can only show the current flowing through a component in the circuit.A node is a place where many wires are put in electrical contact together. Each wire tied at the same node node will carryits own currentm they do not carry each the same current. The currents from all the wires in a given node will sum zero (Kirchhoff's law). So the current of a node, any node, is always zero, because of physics laws.To probe the current through a specific wire, insert a voltage source of zero volts, and display the current through that 0V voltage source.

author: eti
author_rank: Super Contributor
timestamp: November 15, 2022, 07:24:24 am
content: Quote from: RoGeorge on November 15, 2022, 07:01:47 amThank you for your help, that’s what I actually meant, so how do I automatically show the current going through a component when I click it?

author: tooki
author_rank: Super Contributor
timestamp: November 15, 2022, 07:38:16 am
content: Run the simulation. The mouse pointer changes to show a current arrow, then click on the component. Note that LTspice often draws the current arrow in the opposite direction of what you want. If that happens, and you need the current in the plot window to show the opposite way, you can edit the trace’s formula to add a minus sign in front of it.If you want a simulation to display the voltages and currents on the schematic, I don’t think that’s something LTspice does. But other simulators, like Tina and Falstad, do.

author: RoGeorge
author_rank: Super Contributor
timestamp: November 15, 2022, 07:39:48 am
content: Don't know what you mean by automatically display the current. Post a capture of the schematic, and attach the .asc file together with the question(s).First result when searching for "LTspice 101 youtube" was this:It happens to show how to probe the current through a resistor.Side note, never draw the GND touching the wire, like the dude in the video.

author: eti
author_rank: Super Contributor
timestamp: November 15, 2022, 09:17:58 am
content: Quote from: RoGeorge on November 15, 2022, 07:39:48 amThanks mate. I'll have a look.That poor bloke having to use a Mac for Ltspice

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: November 16, 2022, 03:58:30 am
content: Hi,There is a list of shortcuts here:https://www.analog.com/media/en/news-marketing-collateral/solutions-bulletins-brochures/ltspice_shortcutflyer.pdfTo look at the current in a trace,  [LEFT-CLICK].To measure the voltage between two nodes, click on the first node, keep the button pressed and release on the second node.Regards,Jay_Diddy_B

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: November 16, 2022, 05:59:52 am
content: Quote from: tooki on November 15, 2022, 07:38:16 amThis will show you the current through a 2-terminal device like a resistor, if you have a (N>2)-terminal device then where each wire contacts a pin then the icon will change also and you can click on the individual pin to see the current flowing.

author: tooki
author_rank: Super Contributor
timestamp: November 16, 2022, 07:05:10 pm
content: Oh yeah, that’s right, and I’ve even used that capability before, come to think of it!

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: November 17, 2022, 07:42:55 am
content: Quote from: tooki on November 16, 2022, 07:05:10 pmThat's called "too many beers ago" for me

author: tooki
author_rank: Super Contributor
timestamp: November 17, 2022, 09:10:40 am
content: Quote from: Geoff-AU on November 17, 2022, 07:42:55 amToo many… or too few?

author: iMo
author_rank: Super Contributor
timestamp: November 17, 2022, 09:11:14 am
content: Simply place the probe at the wire such it shows "voltage". Then click at that voltage value and you will get a window with all the voltages and currents in your circuit. Do select a current flowing through that wire. It will show you the current then. You may have current as well as voltage probe set at a wire.. See below..

author: tom66
author_rank: Super Contributor
timestamp: November 17, 2022, 09:37:09 am
content: In the past I've added a 1uohm resistor into a circuit to measure current where it was not otherwise possible to measure current through a specific net. LTSpice does not allow you to use a zero ohm resistor but a micro-ohm is a close approximation to one.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: November 17, 2022, 02:10:24 pm
content: Quote from: tom66 on November 17, 2022, 09:37:09 amHi, if you need to do this, use a 0V voltage source as the sensing element.Jay_Diddy_B

author: Zero999
author_rank: Super Contributor
timestamp: November 17, 2022, 04:30:44 pm
content: Quote from: tom66 on November 17, 2022, 09:37:09 amPressing Alt whilst the mouse cursor is over the net works for me. Under WINE I need to hold both Alt keys, or the Windows+Alt. Failing that, manually enter the components in, for example if it's three resistors I(R1)+I(R2)+I(R3).