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haasman · #3 11-10-2003, 01:44 AM

Probably more than you would ever want to know .....

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How To Use a Hydrometer

A hydrometer is an inexpensive a float-type device used to measure the concentration of sulfuric acid (Specific Gravity) of battery electrolyte ("battery acid"). From this reading you can easily and accurately determine a non-sealed battery's State-of-Charge. A hydrometer is a glass barrel or plastic container with a rubber nozzle on one end and a soft rubber bulb on the other. Inside the barrel or container, there is a float and calibrated graduations used for the Specific Gravity measurement. The following is a list of instructions on how to correctly use a battery hydrometer:

BATTERY HYDROMETERS

[Source: Popular Mechanics]

If the battery has been charged within the last four hours, remove the Surface Charge. If the battery has been discharged within the last 15 minutes, wait for at least 15 minutes before testing it.

While holding a clean hydrometer vertically and wearing glasses, squeeze the rubber bulb, insert the nozzle into the electrolyte in the cell, and release the bulb. The electrolyte will be sucked up into the barrel or container allowing the float to ride freely. Start with the cell that is closest to the POSITIVE (+) terminal.

Squeeze the rubber bulb to release the electrolyte back into the battery's cell.

To increase the accuracy of the measurement, in the same cell, repeat this process several times so the float will reach the same temperature as the electrolyte. If you are measuring a large battery, stratification can occur when the more concentrated electrolyte settles to the bottom. If you notice a difference in the readings between the top and bottom of the cell, average the two readings.

At eye level and with the float steady, read the Specific Gravity at the point the surface of the electrolyte crosses the float markings. The Specific Gravity reading should be between 1.100 and 1.300.

Release the electrolyte back into the cell from which it was taken and record the reading. Be sure to avoid spillage.

If the hydrometer is not temperature compensating, measure the electrolyte temperature. If the electrolyte temperature is not 80° F (26.7° C), then compensate using the Temperature Compensation Table and examples in Section 4.4.

Repeat the process for each individual cell. The Specific Gravity reading should not have a difference of more that 30 "points" (.030) between the lowest and highest reading or 10 "points" (.010) below the battery manufacturer's recommended temperature value with the battery fully charged. If so, try and equalize the the battery by following the battery manufacturer's procedures. If equalizing does not help, replace the battery.

You can determine the battery's State-of-Charge by taking the average of the temperature compensated cell readings.

Throughly rinse the hydrometer with water after using it.

Haasman