Alternative Power sources - Report: Measuring Specific Gravity with a Refractometer

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Report: Measuring Specific Gravity with a Refractometer

William P. N. Smith

2005-06-22, 12:25 pm

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/ct...temnumber=90716

http://www.harborfreight.com/manual...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!

Ron Rosenfeld

2005-06-22, 11:25 pm

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

quote:

>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/ct...temnumber=90716
>
>http://www.harborfreight.com/manual...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.

-- ron (off the grid in Downeast Maine)

William P. N. Smith

2005-06-23, 12:25 pm

Ron Rosenfeld <ronrosenfeld@nospam.org> wrote:

quote:

>William P. N. Smith wrote:
[vbcol=seagreen]
>Thank you for that report, Wayne.

You're very welcome, Fred. 8*)

wmbjk

2005-06-23, 6:25 pm

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

quote:

>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/ct...temnumber=90716
>
>http://www.harborfreight.com/manual...90999/90716.pdf

quote:

>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

2005-06-23, 6:25 pm

On Wed, 22 Jun 2005 21:14:57 -0400, Ron Rosenfeld
<ronrosenfeld@nospam.org> wrote:

quote:

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

Ron Rosenfeld

2005-06-24, 12:25 pm

On Thu, 23 Jun 2005 07:52:29 -0400, William P. N. Smith wrote:

quote:

>Ron Rosenfeld <ronrosenfeld@nospam.org> wrote:
>
>
>You're very welcome, Fred. 8*)

Sorry about that, William.

-- ron (off the grid in Downeast Maine)

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