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Thread: TwinMax accuracy is voltage dependent

  1. #1
    Registered User hjsbmw's Avatar
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    TwinMax accuracy is voltage dependent

    That is no surprise, but it won't tell you whether the battery is good or not.

    I recently used mine, it told me to make an adjustment. It illuminated the scale, and the needle pulsed with the cylinders firing. After I was done I rechecked, and it told me I needed to adjust more. This repeated 2-3 times until I got suspicious and had a closer look at the connections and so on. Didn't find a problem, but all the time the TwinMax was on, and by now long enough to finally drain its 9V battery to the point where the light on the scale went out. That gave it away. Installed a new battery, and had to undo all the adjustment back to where I started.

    I thought it would be nice to be able to use a 9V adapter. I didn't want to drill and insert a socket in the tool, so I came up with this: get a 9V terminal and female barrel plug at Radio Shack and solder them together to make an adapter (marked). The polarity matters, but with a multimeter it is easy to figure out the order of wires.
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    Harald
    2007 R1200R

  2. #2
    Registered User hjsbmw's Avatar
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    Here is a picture with the wires connected. It provides a stable power source. I can leave the adapter on the TwinMax and tug it into the battery compartment to store the tool away. I only remove the power supply.
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    Harald
    2007 R1200R

  3. #3
    RK Ryder
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    Great idea. Why didn't the manufacture come up with an alternate power source?
    Paul
    Retired and riding my RTs, the '87 K100 & the '98 R1100 !
    Treasurer of the Forest City Motorrad Club #159
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  4. #4
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    Too cheap.

    They *should* have designed the thing with its own LDO voltage regulator to provide a stable power rail for the op amps, but didn't do that either.

    It isn't a terrible design, but it could be much improved, though that would cut into the profit margin or force a bump upwards in price by a couple bucks.
    BMWs in my garage: 1982 R65LS, 1978 R100/7

  5. #5
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    Thanks!

    Great job hjs.

    Kurt linked this thread over on Airheads.

    Excellent tip, as the 9V's don't stay above the required 8.5V for very long.

    Walking Eagle

  6. #6
    Cam Killer marchyman's Avatar
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    A common Twinmax mod was to open the case and disconnect power to the bulb providing meter illumination. At least that was the thing to do on the older model Twinmax... I haven't looked inside a current model. The battery lasts much longer that way.

  7. #7
    got, got, got no time... rguy's Avatar
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    My balance rarely changes dramatically and usually just requires some minor tweaking every few thousand miles. If the Twinmax doesn't seem right I switch the vacuum lines to test the battery condition. If the needle doesn't flip to the other side I know the battery is bad. It just takes a minute to test it. I usually check it every time I use it because it is such an simple test.
    Neal - '09 R1200GS / '81 R65
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