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Hydrometer Method of Use
Exact
procedures are instrument dependent and this is provided as a general procedure
and assumes a hydrometer with glass float and body.
1. Do not add water at
this time.
2. Put on eye and hand
protection.
3. It is recommended you
disconnect the battery especially if on a high rate of charge / discharge.
4. Remove vent cap.
Carefully insert the hydrometer into cell, not pushing down on the top of the
plates.
5. If this is the first
battery cell you are testing today fill and drain the hydrometer 2 to 4 times
before pulling out a sample
6. Carefully draw liquid
into the hydrometer and avoid "bumping" the hydrometer. Be careful the float is
not flooded (too much liquid) or sticking to the sides of the glass tube.
7. Obtain a reading by
looking directly at the float.
8. Repeat steps 3-5 to
reconfirm reading.
9. RECORD the cell number
and result.
10. If it is very warm or
very cold correct the specific gravity for temperature. If the ambient
temperature is fairly consistent and original gravities are taken when the
batteries are put into service temperature correction is not as critical and
only necessary if problems arise. Make sure electrolyte is not hot if just taken
out of service. Let it reach room temperature.
An easy procedure is to number the cells starting with the
positive cell and move from cell to cell towards the negative terminal. As part
of a preventive maintenance program it is helpful to label the batteries & cells
with numbers and letters.
Temperature Correction
SG of acid is temperature
dependent. If the temperature is very cold or very hot this can lead to
incorrect readings. To correct for temperature use the following equations the
equations or below 70ºF subtract points (0.03 per 10ºF) and above 70ºF add
points.
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Correction factor = (0.331 x T/ºF - 23) / 100 or 0.03 pts per 10 ºF
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Correction factor = (0.595 x T/ºF - 12.5) / 100 or 0.03 pts per 5 ºC
This is valid for 0-130ºF
or -17.8- 54.4ºC
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