What are the volt reading for 6 volt batteries under load

[sreams11]

I just picked up a 1986 ds and not sure if the batteries are any good i get the normal 6.4 after waiting a few hours after charge then i hook the cart to a post and pressed the pedal all the way down and under load and i get a numbers around 5.5 to 4.8 is this normal, also while charging when checked they are 7.4 then when you unplug the charger they are 6.8 then 15 mins later 6.6 but after few hours they settle in at the 6.4 range

[scottyb]

Originally Posted by sreams11

I just picked up a 1986 ds and not sure if the batteries are any good i get the normal 6.4 after waiting a few hours after charge then i hook the cart to a post and pressed the pedal all the way down and under load and i get a numbers around 5.5 to 4.8 is this normal, also while charging when checked they are 7.4 then when you unplug the charger they are 6.8 then 15 mins later 6.6 but after few hours they settle in at the 6.4 range

5.9 is what I like to see the battery hold under a 300a load. More drop than that indicates a weak cell or worse.

[sunking]

What you describe sounds normal. SOC (state of charge) voltages are completely useless and meaningless on an operating system. SOC voltages only apply on a battery that is fully rested and disconnected from any load or charge. And even then they are only ball park. There is only one way to determine the true SOC of a battery and that is with a lab quality temperature compensated hydrometer. But even with a hydrometer it does not tell you the capacity.

For any Trojan flooded lead acid (FLA) battery SOC voltages at room temp are:

100% = 2.122 vpc or 6.37 volts on a 6 volt battery
50% = 2.017 vpc or 6.05 volts on a 6 volt. Don't go below 50%

As for voltage sag is very hard to answer because there are a lot of variables, most importantly Internal Resistance aka Ri. A new T-105 that has had a few cycles, at room temp, at 100% SOC will have a Ri = approx .005 Ohms. That does not sound like much but is significant. Voltage = Current x Resistance.

Cruising at normal speed on a flat surface will draw roughly 50 to 60 amps on the batteries. So if we have a 6 volt battery at 100% SOC with a 50 amp load we will see the voltage sag from 6.37 volts - (50 amps x .005 Ohms) to 6.12 volts. Using Scotty's example of 300 amps or starting current of 300 amps you will sag from 6.37 volts down to 4.87 volts on a new fully charged battery.

As the battery ages or SOC decreases battery Ri goes up, thus more voltage sag and power loss. Eventually all batteries Ri goes up to a point where the battery will no longer take or supply a charge. When you connect the charger on a dead battery it trips off very quickly because the charge ris fooled into thinkng the battery is fully charged up. You measure the voltage and it reads good with no load. Then you step on the accelerator and nothing happens and you see the battery voltage dives toward ZERO.. Take your foot off and the voltage jumps back up to normal. You know it is time for new batteries.

FWIW you now know why AGM and Lithium batteries perform better because they have significantly lower Ri than FLA batteries. A 6 volt AGM 220 AH battery has an Ri of approx .0007 to .002 Ohm's depending on the manufacture. That same 300 amp start up current sags the voltage down from 6.37 volts to only 6.37 - (300 amps x .0007 Ohms) = 6.16 volts compared to 4.87 volts for a flooded Trojan.

[sreams11]

i took it out to campground today after it sat all night the batteries were 6.37 and while riding the battery would drop to low 5's then steady out to the 5.7 range also after driving a good while the curtis gauge dropped 2 lines and the volts were 6.17 then they climbed while sitting i think maybe next year just replace batteries thanks for the replies so fast

[rib33024]

If the wheels and tires are not spinning when you push the go pedal to the floor, you are going to burn up the motor or controller or melt a battery post or a fire. Never stall the motor with the pedal to the floor

Originally Posted by sreams11

then i hook the cart to a post and pressed the pedal all the way down and under load

[Volt_Ampere]

Yikes! Good way to kill your motor.

[sreams11]

i did it in moderation while i had it tied up to check the load but ya it got hot so i stopped the hooked up way and drove it and tested it on the move