SOC Battery Voltage Question

[Chevota Guy]

I looked at the SOC chart on BGW and then measured my batteries and pack voltage. 2018 Trojan T1260 batteries in 2010 RXV.

It had only been about 6 hrs from the time I removed the charger, but I was surprised to see the following readings:

Pack: 52.4V
Bat 1: 13.0V
Bat 2: 13.1V
Bat 3: 13.1V
Bat 4: 13.0V

All readings quite a bit higher than the 100% full charge values in the chart at 50.9V pack and 12.73V individual.

Is this normal ?

[ThreeCW]

My Trojan pack (8 x 6 V T-125's) is at 52.0 volts fully stabilized after a full charge.

6 hours is not enough to fully stabilize ... more like 12 to 24 hours to stabilize without use.

If you can't wait that long, let them stabilize for as long as you can, then take your cart for a couple hundred yard run, then let it stabilize for 10 minutes and measure the voltage again ... that should get you a pretty accurate state of charge reading.

[JohnnieB]

The finish charge voltage for Trojan brand 12V batteries 16.2V, which equates to 64.8V for a 48V pack. (See attached chart)

While the cells in a battery are being charged, the electrolyte in intimate contact with the plates and the plate surfaces in intimate contact with the electrolyte acquire a higher state of charge than the the electrolyte and lead of the plates further away from each other. It is that "surface" charge that is read in the battery's terminals, but there is very little energy stored in it, so it is useless for estimating SoC. It takes several hours for the hyper-charged electrolyte and plate surfaces to equilibrate and pass a voltage that bater reflects the cell's true SoC.

The SoC charts are based on the average of a statistically significant population of mature batteries measured from 6 up to 24 hours after charging stops. For our purposes, 12 hours rest is typically used. New batteries may be above the voltage listed on the SoC charts, while old batteries may be below the listed voltage.

[Chevota Guy]

Thanks guys for the good information and explanations. Super helpful to a relative new comer to electric carts.

[wingnut2000]

following

[JohnnieB]

Originally Posted by wingnut2000

following

FWIW: You can click on the "Thread Tools" on the bar above the first post on the page and subscribe to the thread instead of making a post in it.

[kernal]

Originally Posted by Chevota Guy

I looked at the SOC chart on BGW and then measured my batteries and pack voltage. 2018 Trojan T1260 batteries in 2010 RXV.

It had only been about 6 hrs from the time I removed the charger, but I was surprised to see the following readings:

Pack: 52.4V
Bat 1: 13.0V
Bat 2: 13.1V
Bat 3: 13.1V
Bat 4: 13.0V

All readings quite a bit higher than the 100% full charge values in the chart at 50.9V pack and 12.73V individual.



Is this normal ?

I have a digital meter hooked directly to the batteries on my RXV and is always on. I walk by it a lot during the day. I have observed that same phenomena over the years. Now with 4+ years and ~ 430 charge cycles the observed voltage of the pack is slightly lower at any equivalent time stamp. My guess is this is a sign of the inevitable decline in battery health. But this is just one measure and by itself means nothing.

[opelikamike]

My T1275 2018 Trojan batteries on my 2015 RXV mirror Chevota Guy's observations. I'll read voltages later today after cart hasn't been charged or driven for 12 hours.

[JohnnieB]

Something to remember about the SoC charts for Trojan brand batteries. They are based on testing of 6V batteries 30 or more years ago and Trojan has tweaked their design a few times since then.

Plus, the chargers commonly in use back then were the ferroresonant transformer type and shutoff at a predetermined voltage (45V +/-1V for a 36V battery pack) instead of fully charging the batteries. Modern charger use dV/dT (change in Voltage over change in Time) technology to more fully charge batteries and the finish voltage is higher.

Also, I've been unable to find out what the battery temperature of the batteries tested were and temperature effects Voltage as well as storage capacity.

[Chevota Guy]

Originally Posted by JohnnieB

Something to remember about the SoC charts for Trojan brand batteries. They are based on testing of 6V batteries 30 or more years ago and Trojan has tweaked their design a few times since then.

Plus, the chargers commonly in use back then were the ferroresonant transformer type and shutoff at a predetermined voltage (45V +/-1V for a 36V battery pack) instead of fully charging the batteries. Modern charger use dV/dT (change in Voltage over change in Time) technology to more fully charge batteries and the finish voltage is higher.

Also, I've been unable to find out what the battery temperature of the batteries tested were and temperature effects Voltage as well as storage capacity.

The point about temperature of the original data is a good one. I keep my cart in an AC garage at 82°F, and that it is likely warmer than factory OEM tests.