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Thread: I'm looking for a voltmeter & ammeter that measures the max amps

  1. #1
    Senior Member+ MichaelMeissner's Avatar
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    Question I'm looking for a voltmeter & ammeter that measures the max amps

    I've been looking at the various low cost voltmeters and ammeters, and many can measure the total watts that goes through the circuit, such as:


    But what I'm curious about is in addition to the total watts, what is the maximum amps (or watts since the voltage is usually constant) that was used at any particular point of time. In particular, I'm looking at powering cameras using either 9v batteries or USB batteries using a 9v boost, and I'm wanting to get a handle on how much power the camera needs, when I'm doing an operation (focusing, shooting 4K video, etc.), and also for sizing of batteries and voltage boosters. Right now, I'm just looking at the display and mentally seeing what the number is, but I can miss some peaks.

    There is a new monitor that I just noticed that seems to have a bluetooth function, and it can send data to an app on the phone, and it has a graph. However, it is only USB, and ideally, I would like to run it on other batteries as well:


    It is kind of hard to tell from the sales page exactly what kind of measurements are done.

    So am I missing something? Ideally there is a unit that can handle 3-12 volts, with a optional 5v input for the display, and fairly cheap (preferred to be under $20, I might settle if it is under $30).

  2. #2
    Senior Member+ defragster's Avatar
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    The first one tracks power over time? both watt and amp hr's.

    If you measured 10 seconds of steady state 'idle' power. Then during that same 10 seconds [time longer than any operation but easy to tabulate] you exercised some high current draw operation you might catch the added power used over the time that operation was in effect. And during that operation the current might track fast enough to get an idea of a momentary current and one that was max. Depending on the sample rate I suppose the peaks might show in the total power if they have any sustained value.

  3. #3
    Senior Member+ MichaelMeissner's Avatar
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    Quote Originally Posted by defragster View Post
    The first one tracks power over time? both watt and amp hr's.

    If you measured 10 seconds of steady state 'idle' power. Then during that same 10 seconds [time longer than any operation but easy to tabulate] you exercised some high current draw operation you might catch the added power used over the time that operation was in effect. And during that operation the current might track fast enough to get an idea of a momentary current and one that was max. Depending on the sample rate I suppose the peaks might show in the total power if they have any sustained value.
    The problem is I'm trying to measure the watts used by a digital camera over time, where I want to do various things on the camera and see what the peak power needed along with the total power. While I'm operating the camera, I can't always see the meter and record the peaks. In particular, some of the voltage boosters (from USB/5v to 7.5-9v) just can't deliver enough amps and the camera shuts down. I've seen complaints that one version worked on earlier cameras by when the user upgraded the camera, it no longer worked. I've also noticed new warnings on the sites selling the boosters and new devices that have 2 USB plugs so they can use two separate USB batteries.

    I have one voltage booster (HQRP) that seems to work with my current cameras (roughly 9v and 0.75a), but I would like to be able to measure exactly what the current draw is, so if I upgrade, I can realize if I need to upgrade batteries or voltage boosters.

    After reading a lot of the ads and watching videos after posting the query, I just ordered one of the UM34C devices (USB 3.0 A input/output, USB C input, micro-usb output, with a bluetooth connection). The second generation (UM25C/UM34C) now shows both volts and amps on the same graph (earlier ones had separate V/A graphs). The bluetooth connection would allow me to display a longer graph on my cellphone and there are opensource Linux readers also. It looks like it probes the power once a second, which is probably fine with my usage. The UM25C devices tend to have USB 2.0 A input/output, USB C input/output, and micro-usb output -- I don't have any USB C plugs at the moment, so I opted for USB 3.0 A which I do have.

    I realized I could use it on 9/12v power supplies by using a 5.5mm/2.1mm connector to USB plug. I can't use it for single cell lipos, but there I will use the meters I have which have a separate port to power the meter. Typically for powering a teensy, it is more steady state usage.

  4. #4
    Senior Member+ KurtE's Avatar
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    I am not sure if something like the ODroid Smart Power 2 unit might work for you? https://wiki.odroid.com/accessory/po...ry/smartpower2

    It is a power supply for 4-5.3v and measures voltage and amps. It is also setup to use wifi and creates a page showing things like Amps and Amp hours. But it is programmable and there are instructions on how to build and download firmware on the wiki

    I have one sitting around here, don't remember if it had any options to show peak values or not...

    I ordered mine through Ameridroid: https://ameridroid.com/products/smar...c-power-supply
    At the time they were the only American distributor, which saved a lot on shipping costs. There are other distributors now, which you can see on the page: https://www.hardkernel.com/main/distributor.php

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