trying to understand golf catr batterys

[speedgolfer]

Ok in one place they say a 6 volt battery fully charged is 7.2 volts and another palce it says 6.37
so at 7.2 x 6 is 43.3 pack voltage but he site says 38.2 to 38.9 is fully charged pack voltage
could somebody give what numbers are right

thanks Mike

[wildbillw]

Take a look at the "state of charge" sticky under the "Club Car - Electric" forum.

Wildbillw

[kab69440]

7.2 may be what they read immediately after charger shutoff. Four of mine read 6.5 and two read 6.4 after a 12 hour post charge rest. I usually have 38.7-38.8 at the 12 hour rest mark. 38.2 is considered "100%".

[JohnnieB]

Originally Posted by speedgolfer

Ok in one place they say a 6 volt battery fully charged is 7.2 volts and another palce it says 6.37
so at 7.2 x 6 is 43.3 pack voltage but he site says 38.2 to 38.9 is fully charged pack voltage
could somebody give what numbers are right

thanks Mike

There are three set of numbers associated with cart batteries, On-Charge, At-Rest and Under-Load. These three sets of voltages vary with the brand of batteries, age of the batteries and the temperature of the electrolyte in the batteries. In addition, the voltage sets for the same batteries may vary for different applications of the same batteries, (IE: the same deep-cycle battery used in golf carts can be used in solar/wind applications, but the voltage sets may be different)

The 7.2V for a 6V battery is 2.4VPC (Volts per Cell) and is an On-Charge voltage well into the gassing range, but too low for a charger cut-off voltage and too high for a float charge voltage for golf cart applications, so the author of the article may have been speaking in terms of other applications.

The 6.37V is 2.122VPC (6.366 rounded), which is the typical 100% SoC voltage for a Trojan T-105 battery that is properly broken in, about a year old and the electrolyte temperature is 80°F. This is the At-Rest voltage, which means the battery has been neither charged nor discharged for at least 12 hours since the charge was terminated at an On-Charge voltage in the 44.1V to 50.2V range.

The Voltage vs State of Charge charts seen on this forum tend to be based on the T-105, as described above, so newer or older batteries, different brand batteries and voltages taken at different temperature won't match the charts precisely.

Fortunately, the deep-cycle, lead-acid, wet-cell batteries used in golf carts are very forgiving and their discharge curves are fairly linear, so approximate is usually close enough, but if you want a specific SoC chart for your battery pack, average the At-Rest voltage after at least three consecutive charge cycles and add (or subtract) the 100% voltage from the T-105 based chart, then offset the voltages on the T-105 base chart by that amount.

Basically, If your 100% charged 36V battery pack measures 0.7V higher than 38.2V, the 90% voltage should also read 0.7V higher, etc.
-------------

The On-Charge voltage will vary from whatever the pack voltage is when the charger was attached, up to whatever voltage the charger shuts off at. Most automatic golf cart chargers simply turn off when the On-Charge voltage climbs into the 44-46 volt range, but some of the more sophisticated chargers monitor the the On-Charge voltage rise over time and don't shut off until is stops rising, or at least rises slower than a predetermined rate.

Technically, a battery isn't "Fully" charged until the specific gravity of the electrolyte ceases to increase, but the terminal voltage tracks the SG pretty well, and is much easier to monitor.

---------------

Under-Load voltage is measured while discharging the batteries.
If you have a dash mounted Digital SoC meter, you should strive not to load your batteries below 1.75VPV (31.5V for a 36V pack) and avoid loading them below 1.5VPC (27.0V for a 36V pack) except in the most dire emergencies. (IE: Getting the cart off the railroad tracks when a fast moving freight train is blowing its horn at you.)

-----------

Note: Most of the battery information on-line is for applications other than Golf Carts.