Confirmation of SOC vs. Voltage Chart

[Tom47]

Originally Posted by Pat911

Confirming that charging at a lower voltage (within reason) will still get the job done, albeit with the longer time trade off.

The chart that you posted Tom is correct, but what you have there is the settling voltage, not the max charging voltage. But it is also misleading in that a 100% charged pack will not stay at 58.4v for very long. It will almost instantly drop. The settling process will take time too. To get a accurate settling voltage you will need to wait 24 hours.

Your experience of replenishing 30aH with a 15A charger in 1.5 hours does not compute, no matter how you look at it. The only explanation is that your charger is able to supply greater than 15A or that your battery draw was less than 30aH. Does your SOC meter count up when charging? If so, are you able to monitor it whilst charging? Also, can you measure the open circuit voltage of your charger, that’s when it is turned on but not connected to the battery.

Cheers
Pat.

Thank you for your reply, Pat.

I thought it was unusual for the faster than expected charge. The SOC meter did count up but I didn't watch it continuously and I'm not sure where it was until I noticed the charger shut off at about 1.5 hours. At that time the SOC meter read 100 and the Ah read 72. Is it possible I was not at 100% when I reset the SOC meter and it is actually less? But then, the 42 Ah reading must have been high too if it is linear.

I will check the open circuit voltage tomorrow. It is possible it is higher than it says.

Tom

[Tom47]

Originally Posted by WalterM6

Tom, I wouldn't worry to much about the backup timer. It's just a peace-of-mind timer. I just use it so it won't stay plugged in all the time. If you think it is going to take 2 hours to charge set the timer to 3 hours.

That sounds like a plan....and is directly in line with what Pat said in another thread.

[Tom47]

Originally Posted by Pat911

Confirming that charging at a lower voltage (within reason) will still get the job done, albeit with the longer time trade off.

The chart that you posted Tom is correct, but what you have there is the settling voltage, not the max charging voltage. But it is also misleading in that a 100% charged pack will not stay at 58.4v for very long. It will almost instantly drop. The settling process will take time too. To get a accurate settling voltage you will need to wait 24 hours.

Your experience of replenishing 30aH with a 15A charger in 1.5 hours does not compute, no matter how you look at it. The only explanation is that your charger is able to supply greater than 15A or that your battery draw was less than 30aH. Does your SOC meter count up when charging? If so, are you able to monitor it whilst charging? Also, can you measure the open circuit voltage of your charger, that’s when it is turned on but not connected to the battery.

Cheers
Pat.

My resting voltage is 53.23. This is 3.33 volts per cell which is nominal operating charge. However, I think what happens is my 100% SOC is actually 80%. My battery draw was closer to 22 amps which may account for the 1.5 hour charge.

My charger is exactly 72.0 volts open circuit. But it keeps cycling on and off because there is a current sensor on the battery lead. I guess if it doesn't sense and current it shuts off.

Long story short, I feel this ECO pack/ charger combination is doing the proper charge. It does shut off at less than 55 volts. I shouldn't need to worry about overcharging the pack.

[Pat911]

3.33v resting is ok and 22A accounts for the reduced charging time. It’s all good, and I’m glad you’re satisfied with the upgrade.

Cheers
Pat.

[Tom47]

Originally Posted by Pat911

3.33v resting is ok and 22A accounts for the reduced charging time. It’s all good, and I’m glad you’re satisfied with the upgrade.

Cheers
Pat.

Thanks Pat! I'm glad I went in this direction. I came real close to buying new 8 volt batteries instead.

Yesterday I used 16Ah during a ride. I started the charger and watched the SOC meter, amps, amp-hours and voltage periodically until it shut off. The charger ran for 1 hour and 5 minutes.

The last one minute or so of charging the voltage started climbing rapidly to 57+, but it was so fast I couldn't detail the other readings and the decimal after 57 was too fast to read. The SOC and Ah were are 100 and 72 when the voltage started climbing fast from 54.65 until the charger shut off.

Thanks for all your assistance.

Have a great day!
Tom

[superfan86]

I've spoken with the techs over at BigBattery regarding the voltage range at 100% SOC. Their BMS system allows for fluctuations as high as 58.8 and as low as 53.3 to be considered at "full charge." As you see in your chart, the amount of usable energy between 53.3 and 58.8v is less than 1% of the total capacity of the battery, so I can imagine that the batteries taking in juice from the charger at that point can lead to some rapid changes in voltage while the cells try to balance.

Based on what I've seen, the SOC at 100% typically settles at 53.3/4 within 30 minutes of coming off the charger, even if on the tender it surges to 58.8. I also see slight fluctuations in voltage based on the temperature in my garage. I assume that this has to do with the chemical reaction in the battery being more or less efficient at different temperatures.

I was experiencing extremely inaccurate readings from the first battery meter I bought and swapped to one designed for this chemistry. So far it has proven to be significantly more accurate. On the advice of BB, I set "full" to 53.3v and "empty" to 45v.

That said, I have operated the cart at voltages as low as 42v, but the results were...short lived.

[Tom47]

Originally Posted by superfan86

I've spoken with the techs over at BigBattery regarding the voltage range at 100% SOC. Their BMS system allows for fluctuations as high as 58.8 and as low as 53.3 to be considered at "full charge." As you see in your chart, the amount of usable energy between 53.3 and 58.8v is less than 1% of the total capacity of the battery, so I can imagine that the batteries taking in juice from the charger at that point can lead to some rapid changes in voltage while the cells try to balance.

Based on what I've seen, the SOC at 100% typically settles at 53.3/4 within 30 minutes of coming off the charger, even if on the tender it surges to 58.8. I also see slight fluctuations in voltage based on the temperature in my garage. I assume that this has to do with the chemical reaction in the battery being more or less efficient at different temperatures.

I was experiencing extremely inaccurate readings from the first battery meter I bought and swapped to one designed for this chemistry. So far it has proven to be significantly more accurate. On the advice of BB, I set "full" to 53.3v and "empty" to 45v.

That said, I have operated the cart at voltages as low as 42v, but the results were...short lived.

That is precisely the voltage reading I have gotten in actual operation. The only difference is the shutoff voltage for the ECO charger is 57 volts.

I questioned ECO why it was 57 and not 58.4 and they explained there is little to be gained by going much over 53.33, which is 100% in practical use.

I have set my minimum operating voltage, which is set in my mind not through the BMS, at 51.2 volts. This is 20% which other users and ECO have recommended not to go below.

I charge my battery every day that I drive it more than a mile. As was explained by ECO, four 25% charges are the same as one 100% charge. 100% is one charge cycle and multiple charge cycles that add up to 100% is still one charge cycle.

There is no reason to not charge it every time is is driven from this aspect of lithium life expectancy. If I just drive it around my yard however, I do not charge it that day. But I often drive 20 miles plus on a nice day and need it to be ready to do that.

Tom

[Ronno6]

Originally Posted by superfan86

I've spoken with the techs over at BigBattery regarding the voltage range at 100% SOC. Their BMS system allows for fluctuations as high as 58.8 and as low as 53.3 to be considered at "full charge." As you see in your chart, the amount of usable energy between 53.3 and 58.8v is less than 1% of the total capacity of the battery, so I can imagine that the batteries taking in juice from the charger at that point can lead to some rapid changes in voltage while the cells try to balance.

Based on what I've seen, the SOC at 100% typically settles at 53.3/4 within 30 minutes of coming off the charger, even if on the tender it surges to 58.8. I also see slight fluctuations in voltage based on the temperature in my garage. I assume that this has to do with the chemical reaction in the battery being more or less efficient at different temperatures.

It is my understanding that the BMS basically disengages the charger once it determines that the battery has reached full charge. Based on what, exactly, I do not know. However, as the charger will run continuously if plugged in, you will see charger output voltage registering on the gauge, even if there is no charge being applied to the cells. Just as if you were running the charger with the power button switched to off.........

[Tom47]

Originally Posted by Ronno6

It is my understanding that the BMS basically disengages the charger once it determines that the battery has reached full charge. Based on what, exactly, I do not know. However, as the charger will run continuously if plugged in, you will see charger output voltage registering on the gauge, even if there is no charge being applied to the cells. Just as if you were running the charger with the power button switched to off.........

I don't understand why the BB charger continues to run after full charge. That is a good reason to use the timer as they say to unplug them when charge is complete.

My ECO charger shuts off about 15 seconds after the Ah gauge hits 72 Ah or 100%. During that 15 seconds, the voltage rises quickly from 54+ to 57 volts which is output voltage of the charger. I have my time set to shut power off 1/2 hour after the partial charge cycle.

I quess the ECO charger shuts down when the voltage to the battery equals the charger output and it shuts down. ECO told me I really don't need the timer, but it gives another safety from overcharging.

[Pat911]

That is precisely the voltage reading I have gotten in actual operation. The only difference is the shutoff voltage for the ECO charger is 57 volts.

I questioned ECO why it was 57 and not 58.4 and they explained there is little to be gained by going much over 53.33, which is 100% in practical use.

I have set my minimum operating voltage, which is set in my mind not through the BMS, at 51.2 volts. This is 20% which other users and ECO have recommended not to go below.

I charge my battery every day that I drive it more than a mile. As was explained by ECO, four 25% charges are the same as one 100% charge. 100% is one charge cycle and multiple charge cycles that add up to 100% is still one charge cycle.

There is no reason to not charge it every time is is driven from this aspect of lithium life expectancy. If I just drive it around my yard however, I do not charge it that day. But I often drive 20 miles plus on a nice day and need it to be ready to do that.

Tom

Excellent post Tom!