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Basic Multimeter Functions & Accessory Cables for eBike Owners

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    Basic Multimeter Functions & Accessory Cables for eBike Owners

    It has been said here many times that a multimeter is an essential tool for an ebike builder to have. Meters with the usual assortment of measurement ranges and functions are available from nearly free (Harbor Freight) to the industry standard (Fluke) at $180. I do not own the Fluke and my Harbor Freight meter was off by 20% on its readings until the probes fell off the wire after a week of use., nuff said.

    For the record, the meter I use is a Klein MM400 it was about $40 on Amazon and has done the job just fine and seems to be of decent quality.

    Desirable functions include:
    • Voltage
    • Amperage , at least charger output rating
    • Continuity, measured in Ohms Ω
    • Temperature , optional but useful
    • Backlit display , I'm old.
    • Hold, to keep a reading on screen while you do something else
    • Min-Max , nice for long term monitoring
    • Auto off, saves batteries and money because you WILL leave it on .
    I think that any ebike builder should have the ability to use their meter not just for spot testing but to monitor and cross check other meters ( chargers, battery packs, displays etc...). I would recommend that once you have a meter you assemble the following cables for it.
    • Standard test probes. These should have come with your meter. These are used for spot checking circuits and quick readings.
    • Alligator Clips. For monitoring items over a period of time it's nice to go hands free. Using a single clip with a probe is also handy when checking multiple points that have a common ground point.
    • Battery Voltage. This cable could be made in various ways. I made mine as a simple direct reading cable. It has an XT-90 on one end to match my battery packs output and banana jacks on the other end for the meter. WARNING ! If you make one of these cables you now have two floppy cables that are carrying potentially your entire output current if they short together. Think about that for a minute. I set my banana jacks into some moldable rubber (Sugru brand) while they were plugged into the meter creating a double plug that can't short on itself. It can however short on anything it comes in contact with. If you build one of these take extreme caution with it and make sure the battery end is always the last thing connected and the first thing disconnected.
    • Charger Amperage Monitor. A lot of battery issues that arise often turn out to actually be charger issues. A great place to start any kind of battery issue troubleshooting is to make sure your charger is doing what you think it is. This cable is a simple in-line XT-60 pass thru cable with the + leg run to banana jacks so that the charge can go thru the meter. *NOTE that some meters use a different port to measure amperage than they do for most other readings.
    • Optional Temperature Probe. Some meters come with a temperature probe I have not used mine but I could see where it might be useful someday.
    This short video (1:49) shows the cables listed above

    Last edited by Bicycle365; 06-28-2016, 01:54 AM. Reason: added Ω to the functions, tnx louis

    #2
    One of the features of the stock sharp needle probes is that you can insert them into the insulation of a wire to test that section of wiring, without cutting away any of the insulation.

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      #3
      I'm finding that having a multimeter with alligator clip probes is also very useful. The suggestion to buy an auto off version would have paid for a better multimeter in my case. My first, still working meter went through enough 9V to inspire me to buy a new auto off. I use it now to occasionally confirm the meters are within range. My frequent use version os the auto off and I'd be buying a 9V a week without it. So I'm old and forgetful...

      I forget to mention the continuity function is great for testing brake sensors. Another case where the alligator clips are useful when there's no third hand available.
      Last edited by Louis; 06-28-2016, 01:26 AM.

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        #4
        Does the multimeter in the OP have the "stock sharp needle probes"? I need those.

        Thanks for the recommendation. I am just about to buy a multimeter.

        I am also looking for recommendations for a nice soldering station and heat gun (for heat shrink tubing).

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          #5
          commuter ebikes Yes and they can store clipped to the back of the meter. They are sharp enough to draw blood if you're not careful, trust me on that one:eek:

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            #6
            I bought a $3 gun from the craft store. It's used to make those puffy ink cat sweatshirts you see on the old ladies at the mall...

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              #7
              I'm a huge eBay, Aliexpress, and Amazon fan. The core principle in building from kits is finding creative solutions. That's where forums are so incredibly helpful. Sharing creative solutions.
              I use my knife sharpening stone to make points on my probes.

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                #8
                There is no doubt in my mind that the Klein MM400 in the first post is worth every penny of the $40 price. However, if you can't quite swing $40 for that right now, consider the $15 sparkfun as a starter unit.

                If any tool is important for what you do, you should have two of them. A "good" one, and a cheaper one that you take when you're going where it might be broken or stolen...

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                  #9
                  Spot on. My list of two has grown. I hate being shut down and somethings, like it or not are consumables. I went two years without needing my back up display, but when I did, I was done in 20 minutes. Not shut down for a week. Or shipping poor for an overnight or two day delivery. We should maybe have a recommended "Two, One for the Pats Box" list... I agree a Multimeter is one. Also nice to keep things honest.
                  Although common wisdom, two throttles has yet to pay off. Speed sensors, sensor magnet, brake lever, battery, and thrust bearing has.

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                    #10
                    spinningmagnets Thanks for that one. I have a analog meter that I have been using. Im going to get one of these Sparkfuns as my backup..
                    Great site in general too...

                    Comment


                      #11
                      Don't forget about that auto off feature. I found 9V batteries got expensive.

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                        #12
                        we added to the luna cycle website the multi meter we figured to be the ultimate volt meter

                        Although it does not seem like much on first site it has auto ranging which makes it really simple to use and it is tiny and well made.

                        Perfect for taking along with you in a small tool bag.

                        we actually put a lot of thought into sourcing this meter....

                        and weighted through all the clones of this particular product and got in with the factory direct.

                        http://lunacycle.com/electricbike-mu...ect-for-ebike/
                        Click image for larger version

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                          #13
                          I was looking for a cheap multimeter and thus I bought Klein MM400 multimeter. After 3 weeks, it's stopped working. Cheap product means luck! Although, I ask their support about this problem. Waiting for their response.
                          I bought it after reading this review https://bestmultimeterreviews.org/klein-mm400-review/. Because,at that time I was looking for cheap option like this.
                          Last edited by dakori; 05-14-2018, 06:40 PM.
                          .

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                          • max_volt
                            max_volt commented
                            Editing a comment
                            Did you check the internal fuses? oh wait, you need another meter to do that.

                          #14
                          My greatest grief with the inexpensive meters is their accuracy is often specified around 1%. I've measured several and some meet their specifications and some don't. Regardless, if you are trying to calibrate a charger or measure battery SOC 1% is too big an error for me. Even if it's 1% of the measured value (not the full range - some mean it this way), 1% at 50V is 0.5V (1% of a 200V full scale is 2V!!!!).

                          Having said that I have an even smaller old meter that has a hinged cover that sets in my toolbag for troubleshooting. Even an inaccurate meter is good for basic stuff!

                          I take my meters and compare them to uber accurate bench meters. I haven't bothered opening them up and calibrating but then I know which ones are more trustable and how far off they are at the typical voltages. Some get pretty close but the best cheap one I have is still about 0.2V off at ~50V...

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