Inductor or coil and how to reverse engineer them - Page 1
Forum section: electronics / beginners

author: mjn2024
author_rank: Contributor
timestamp: August 04, 2021, 11:36:30 pm
content: I am new to elections and have 2 questions. I was reverse engineering a board the uses 3 1.5 volt batteries to charge a phone. The method to reverse engineer the board that seemed most obvious to me was to take a multi meter and set it to continuity and start probing. A little ways in I got to what I think is either a coil or inductor. So my first question is it a coil or inductor. My second question is one side of the coil/inductor is connected to ground and since a coil is just a wire that is looped how can I tell the difference between a connection straight to ground and a connection to ground that goes through the coil.

author: bob91343
author_rank: Super Contributor
timestamp: August 04, 2021, 11:56:58 pm
content: Your multimeter isn't the best device for this. Further, an inductor and a coil are the same; inductor is what it does and coil is how it's made.Perhaps you would do well to read up on electricity fundamentals; many of your questions will be answered.

author: radiolistener
author_rank: Super Contributor
timestamp: August 05, 2021, 01:15:33 am
content: Quote from: mjn2024 on August 04, 2021, 11:36:30 pmThis is inductor coil.Quote from: mjn2024 on August 04, 2021, 11:36:30 pmAny straight wire also works like inductor, but it's inductance smaller than coil inductor.So, the difference between straight ground connection and inductor is the inductance value. Also it may have a little resistance difference which can be detected with DMM for a large coil. But for a small coil (this is your case) DMM will be unable to detect any difference.You're needs LC meter to measure inductance value of inductor.Also you can read marking on the inductor to get it's value. In your case 3R3 means 3.3 uH.Note: switching mode power supply or charger is a bad choice to learn electronics for beginner. Try to select some other circuit which don't use DC/DC converters, otherwise it will be too hard for you to understand how it works.

author: MathWizard
author_rank: Super Contributor
timestamp: August 06, 2021, 12:39:49 pm
content: OP I remember 1 day when I was just getting back into electronics and was looking at a little solar powered LED nightlight. In the day it charges a 1.4V battery, but at night it runs a 3V LED, so I didn't know how it did that. And to do it, it uses the inductor, and 2 switches, in the form a diode, and some transistor.Just go on youtube and look up coils, inductors, and there's all kinds of videos from the common types to the serious math for it all.Yeah and with lots of inductors, they might have 0.01 Ohm's coil resistance just from the length of wire, so yeah on most DMM's it would be hard to tell the difference if the coil is actually shorted or not.In bigger DC transformers, their coils/winding, if you are lucky might have 1-2-10 ohms DC resistance, and something like a small relay coil, might have 500 Ohms DC resistance

author: RoGeorge
author_rank: Super Contributor
timestamp: August 06, 2021, 01:15:51 pm
content: That's a coil made out of a piece of isolated wire turned (coiled) around a ferrite core. Since there's not much wire in it, the multimeter will show about zero Ohms, or it will beep as it will do for a short circuit.Coils in an electric circuit act as inductors, hence sometimes they will be called coils, other times inductors.The "3R3" marking means that coil has 3.3\$\mu H\$ (3.3 micro Henry). The maximum suported current can be found in the datasheet of the coil, but can also be deduced from the destination of that circuit. Since it's a phone charger, that coil should be able to work at a few Amperes at most. There's not much else to reverse engineer.Quote from: mjn2024 on August 04, 2021, 11:36:30 pmTo distinguish for that you'll need to test the coil with AC (Alternative Current). A coil has the property that it tends to oppose to changes in the current passing through it. The faster the current wants to change, the more the coil is opposing the current variations. Because of that property of coils, the fastest the variation (the higher the frequency of the AC current, the more "resistance" the coil will measure. The word "resistance" is between quotes because its correct name for coils is impedance.A multimeter only uses DC (direct current) to measure circuits continuity and/or resistance, it does not use AC current. Therefore you can not distinguish between a short circuit and a coil with a DMM (Digital Multi Meter) alone. For that you'll need to observe there is a coil that measures that zero ohms and make assumptions, or to use an inductance-meter to measure the exact value of the coil.By the way, when you measure the exact value of components, they need to be desoldered from the circuit board, or else the measurement might be influenced by other parts connected to that circuit.The coil in the picture looks OK, those ones rarely got damaged, so if it shows about zero(Ohms), or continuity beeps it means the coil is good.See if these explanations from W2AEW helps: