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Thread: DMM monitoring, amperage, and AC/DC




  1. #1
    GiggaByte is offline Member
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    Default DMM monitoring, amperage, and AC/DC

    The DMM I ordered should be here soon, it has been marked shipped yesterday. Im thinking DC is going to be the type of power to select but I want to make sure.. and can I measure amps(at the same voltage measure points)? The amperage specification for PLL is 1.1A for the i7 900 series, would I be able to select amperage on the DMM and use the same measure point I would for the PLL voltage(as an example), or is there more to it/that doesn't work like that? This will be the first time I used a DMM for a computer and while I read some things about them already, not all was answered.

  2. #2
    Citizen Crazed is offline Junior Member
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    Default Re: DMM monitoring, amperage, and AC/DC

    You can measure voltages easily with a DMM (and yes, you will be measuring DC voltages), but measuring current (i.e. amps) is a different deal altogether, and, on the motherboard itself, probably not something someone new to this aspect of tweaking would want to attempt. Measuring current draw isn't likely to be as useful to you as voltage (and voltage fluctuations) anyway so you won't lose out much by not doing it.

    Measuring voltage to different parts of the motherboard is easy because, as you'll already have read, you just stick the probes in parallel across the part of the circuit you want to measure. To measure current draw, you need to break the circuit and insert the meter in series into the break (and obviously restore the circuit when you're done). On the mainboard this is tricky as, even if you can access a suitable track on the top or bottom layer of the PCB, breaking it, connecting the meter and then undoing it afterwards is a bit of a faff.

    Even if you can do that, you can run into issues getting accurate current measures where power supply circuits are split into multiple channels and phases, while you will also have to contend with the fact that in the CPU and graphics areas in particular, the currents involved are likely to be beyond the measurement capacity of most lower cost meters (and will thus blow the fuse and break the circuit, which is potentially undesirable on a running system).

    Given that it sounds like you're new to this aspect of tweaking, remember the KISS principle, as it's an easy way to break a good board if you do the wrong thing. If you do want to start some experimental measurements, it's far easier to start with something like disk drives before moving to the board itself. It's relatively easy to make up a Molex to Molex (or SATA power female to male) test lead configured with both voltage and current taps. You could splice into the PSU to motherboard main power lines too, but again you need to remember that when measuring current, the main supply rails (+12, +5 etc) are split across multiple wires so you'd need to tap each one via multiple meters to calculate the total current consumption. Like I said above, current draw probably isn't something you really need to know so don't worry about it too much.

    Without knowing what kind of meter you've bought, and how experienced you are working with electronics, the other thing you may have to bear in mind is that lower cost DMMs tend to have pretty slow update rates, and lack features like min/max recording or datalogging, which limits their use for detecting voltage fluctuations. Right now the best advice to give you is probably to keep reading and learning. Sticking metal test probes (or soldering test leads onto small surface mount component legs) is easy enough when you know what you're doing, but when you're learning it's important not to make any false moves. The potential safety risks are small, but they're there - as is the threat to your system. Learning good. Learning by breaking stuff, not so good. :)

  3. #3
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    Exclamation Re: DMM monitoring, amperage, and AC/DC

    +1^^ excellent post.
    If you don't know EXACTLY what you're doing, measuring amperage can cause a short circuit that can instantly destroy your motherboard and/or other components.

    You absolutely cannot measure voltage and amperage using the same measuring points.
    You need to fully understand parallel versus series circuits before you start any measurements.
    You should spend some time doing web searches and finding good tutorials that deal with electronics 101.
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  4. #4
    GiggaByte is offline Member
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    Default Re: DMM monitoring, amperage, and AC/DC

    Yes im not going to stick anything in there for amperage till I know what to do, and it is this one eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices

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    Lsdmeasap's Avatar
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    Default Re: DMM monitoring, amperage, and AC/DC

    Those are nice for the price, they originally come from Harbor Freight Tools! I have a few of them here, and I think I'm the one that suggested them for you right?

    Just check voltages with them, they're too cheap to really even think about relying on any amperage results from them anyway.

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    GiggaByte is offline Member
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    Default Re: DMM monitoring, amperage, and AC/DC

    Yes you did.

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    Default Re: DMM monitoring, amperage, and AC/DC

    I thought so, I couldn't remember because I've suggested that to a few people over the past few weeks. They measure voltage accurately, and are fairly cheap, so I always suggest to go ahead and grab two.

    The only bad thing about them is they don't automatically shut off, so you always have to remember to shut them off when you are done testing, but for the price that's to be expected.

    I need two more now, just haven't gotten around to ordering yet!

  8. #8
    GiggaByte is offline Member
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    Default Re: DMM monitoring, amperage, and AC/DC

    So the Centech DMM just arrived and im somewhat confused to which of the 3 inputs i plug in the + and - wires into, with the manual already screaming at me to not use 2 of them. I believe the proper reading setting would be DCV 20 since the highest DC line ill be measuring is +12v yes? Lets say for the VTT read point here: Gigabyte GA-EX58-UD5 X58 Motherboard Review - Page 14, would I have to put both the + and - (leads are they?) on that tiny spot in the image? Or one on each end of the resistor?

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    Default Re: DMM monitoring, amperage, and AC/DC

    Looks like from the pic if you are measuring DC volts use the top and bottom inputs. If you are measuring amps use the red led (+) in the middle input and the black led (-) in the bottom input.

    And as for where to measure. Put your red led (+) to where the tip of the red line stops at right at the solder joint. Make sure not to touch the other resister next to it.
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    Default Re: DMM monitoring, amperage, and AC/DC

    My Cen-Tech meter has the following jacks in the lower right corner (from top to bottom):
    10ADC - O ==> for 10 amp readings only, red wire
    VOma -- O ==> for volts ohms and milliamp readings, red wire
    COM --- O ==> for the ground black test wire

    Use the dial's 20 DCV setting for your DC voltage testing.
    If the red and black test leads are accidentally reversed while testing voltage, the meter will show a minus sign "-" in front of the displayed voltage.
    Always double check the selector dial's position before turning on the meter and checking voltage.
    A web search using: dmm tutorial should provide links to better understand how to use your meter.
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