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.
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.
This is valid for 0-130ºF or -17.8- 54.4ºC
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