Report: Measuring Specific Gravity with a Refractometer

Discussion in 'Home Power and Microgeneration' started by William P. N. Smith, Jun 22, 2005.

  1. In a previous thread, in a response to a query about (expensive)
    refractometers for measuring lead acid battery specific gravity, Wayne
    pointed out a $40 version:

    http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=90716

    http://www.harborfreight.com/manuals/90000-90999/90716.pdf

    I bought one, and have since had a chance to try it out, and have been
    very impressed. It's clear, easy to read, doesn't require any great
    skill to use, and takes very repeatable readings.

    I was going to compare it to my float-style SG tester, but (as always)
    I couldn't get a stable reading, the float stuck to the side of the
    glass tube, and a small leak in the rubber bulb caused the liquid
    level to drop slowly, giving me a limited time to make my measurement.
    After a set of measurements with the refractometer I heaved the
    float-style one in the trash. 8*| Since I really care about
    differences between cells, the absolute accuracy of the readings isn't
    important, and I can't say my float-style tester was 'accurate', so
    I'll leave the accuracy discussion to the 'professionals'.

    The refractometer is really easy to read, there's a reticule on a
    screen (see the instruction manual), the top part of the screen is
    blue and the bottom is white, and the reading is the dividing line
    between the two.

    A drop of water is used as a calibration, and there's a line at the
    bottom of the screen for 1.000 SG. There's an adjustment screw, but
    mine was properly calibrated from the factory, so I didn't have to
    twiddle it at all.

    A single drop of electrolyte is enough to cover the stage and give a
    good reading, so you are losing less electrolyte per reading than with
    a float-style SG tester (IME).

    Markings are 1.15 to 1.30 in steps of 0.01, ,and are very clear and
    easy to read (the picture in the manual is pretty awful looking, but
    that's scanning and compression artifacts). There's a focus
    adjustment, which I was able to crank down to where I could see
    clearly without my glasses, which was helpful. Readings to 0.005 are
    trivial, 0.0025 are easy, and if you are good (or arrogant) enough you
    can read to 0.001. I did find that there was a bit of parrallax
    error, so I could get the line to move around a bit (0.001 or so) by
    moving my eye up and down, but since battery failure is usually
    defined as a delta of 0.05 between cells, this is plenty of resolution
    for me.

    The only real problems I had with it was keeping everything in focus
    (cheap optics, probably better with more expensive units), and the
    fact that the scale doesn't go any lower than 1.15. Some of the cells
    in my small boat batteries were well below 1.15, but they hadn't been
    charged in quite a while, so I put them on charge and will retest them
    this morning.

    I kept a small container of water to rinse the stage off between
    readings, and a dry cloth to ensure it was clean and dry between
    cells, and had no trouble at all. You don't need a lot of light to
    read the meter, if you can see what you are doing with the batteries
    you can read the scale.

    All in all, if you are measuring a lot of batteries on a regular
    basis, I'd really recommend this tool. I'm in charge of battery
    maintenance for 6 golf carts, 4 boats, and a couple of golf cart
    batteries on a weather station, and this is the neatest toy to come
    along in quite a while! Many thanks again to Wayne for pointing it
    out!
    William P. N. Smith, Jun 22, 2005
    #1
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  2. Ron Rosenfeld <> wrote:
    >William P. N. Smith wrote:
    >>I bought one, and have since had a chance to try it out, and have been
    >>very impressed. It's clear, easy to read, doesn't require any great
    >>skill to use, and takes very repeatable readings.


    >Thank you for that report, Wayne.


    You're very welcome, Fred. 8*)
    William P. N. Smith, Jun 23, 2005
    #2
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  3. William P. N. Smith

    wmbjk Guest

    On Wed, 22 Jun 2005 08:12:53 -0400, William P. N. Smith wrote:

    >In a previous thread, in a response to a query about (expensive)
    >refractometers for measuring lead acid battery specific gravity, Wayne
    >pointed out a $40 version:
    >
    >http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=90716
    >
    >http://www.harborfreight.com/manuals/90000-90999/90716.pdf


    <snipped favorable report>

    >All in all, if you are measuring a lot of batteries on a regular
    >basis, I'd really recommend this tool. I'm in charge of battery
    >maintenance for 6 golf carts, 4 boats, and a couple of golf cart
    >batteries on a weather station, and this is the neatest toy to come
    >along in quite a while!


    Excellent report, thanks for taking the time to write it up. I've
    always liked the concept of that device, and now that I know it works,
    I'm going to order one. Affordable gadgets are one of my favorite
    investments. Now all we need is a design for something useful that can
    be built from HF catalogs and AOL discs. :)

    Wayne
    wmbjk, Jun 23, 2005
    #3
  4. William P. N. Smith

    wmbjk Guest

    On Wed, 22 Jun 2005 21:14:57 -0400, Ron Rosenfeld
    <> wrote:

    >On Wed, 22 Jun 2005 08:12:53 -0400, William P. N. Smith wrote:
    >
    >>In a previous thread, in a response to a query about (expensive)
    >>refractometers for measuring lead acid battery specific gravity, Wayne
    >>pointed out a $40 version:
    >>
    >>http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=90716
    >>
    >>http://www.harborfreight.com/manuals/90000-90999/90716.pdf
    >>
    >>I bought one, and have since had a chance to try it out, and have been
    >>very impressed. It's clear, easy to read, doesn't require any great
    >>skill to use, and takes very repeatable readings.
    >>

    >
    >Thank you for that report, Wayne.


    Always happy to be of service. :) But it was William P.N. Smith
    who took the time to write up the report. My own crafty plan was to
    wait for him to try it out before ordering one.

    Wayne
    wmbjk, Jun 23, 2005
    #4
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