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Monitoring battery charge with an osciloscope

Discussion in 'Power Electronics' started by cyberwasp, Dec 29, 2019.

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  1. cyberwasp


    Feb 26, 2013
    I recently purchased an oscilloscope and have been watching video tutorials on using them. I used one when I was in school 40+ years ago. So I'm playing catchup as I'd like to get into it again.

    Recently I built a few lithium chargers using TP4056 modules which I power off of an Anker powerport 4 usb power brick. I heard not to use one that has a ground plug as it can damage an oscilloscope as they are also earth grounded. (don't want to blow up my new scope!)

    I would like to connect the scope to the tp4056 to monitor the charge current. I've seen this done in several videos. The scope ground lead is of course put to the tp4056 output ground, However I can't see in the video exactly where the probe is attached but from what I could see, the probe was on R3 as the red arrow indicates in my image. TIA
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    There is likely to be a current sense resistor somewhere. Typically you would want to monitor the voltage across it.

    A current sense resistor is unlikely to have one end grounded. The answer is to use both channels on your scope. Measure the voltage from ground to each end of the resistor (one on each channel) then use the Oscilloscopes math functions to subtract one channel from the other.

    The problem you may face with this technique is that you will have lowered resolution, but it may be sufficient.

    I assume you're also using a very slow sweep rate (10 minutes per division?) In order to essentially create a graph of current over time.
  3. cyberwasp


    Feb 26, 2013
    You've just confirmed what I found about a minute ago in a video. According to the data sheet, the resistor I pointed to in my attachment goes to the charge current monitor pin of the 4056. So if I put the probe on that using ch-2 I can also monitor the current.
    I just want to get as much info as I can so I don't blow myself up., or worse my new scope
    Cool! Thank you very much!
  4. davenn

    davenn Moderator

    Sep 5, 2009
    there was no attachment in your first post
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