1200 miles, Balance Battery time?

[santacruzpaul]

I have 1200 miles on my Radrover 5
I bought it about 4 months ago,
Is it time to balance the battery??
Probably have charged it about 100 times since balancing when it was new,
Your input is much appreciated,
Thanks, Paul

[Altema]

I have 1200 miles on my Radrover 5
I bought it about 4 months ago,
Is it time to balance the battery??
Probably have charged it about 100 times since balancing when it was new,
Your input is much appreciated,
Thanks, Paul

You won't need to balance it unless the battery is new, not used for a while, or if you notice a decrease in range. Rad warns against balancing more than once a month. If the battery is in regular use, it will maintain balance fairly well.

[santacruzpaul]

I have 1200 miles on my Radrover 5
I bought it about 4 months ago,
Is it time to balance the battery??
Probably have charged it about 100 times since balancing when it was new,
Your input is much appreciated,
Thanks, Paul

You won't need to balance it unless the battery is new, not used for a while, or if you notice a decrease in range. Rad warns against balancing more than once a month. If the battery is in regular use, it will maintain balance fairly well.

Thanks for the info Altema

[DickB]

I have studied the spec sheet for the chip that Rad uses in the BMS.  The chip uses passive balancing, and balances only during the charge cycle, and only after the Charge light turns green. If you unplug the charger immediately after the green light turns on, the chip has no opportunity to balance. If you leave it plugged in for any significant amount of time after green, the chip has the opportunity to balance the cells and will do so if needed. There's nothing special about a 12 hour charge other than it guarantees that the chip has enough time to balance. New cells from the factory are more likely to be at different voltages (unbalanced), hence the recommendation for three 12-hour cycles, to give the chip enough opportunity to balance. Unless you have baby-sat every time you charged and unplugged immediately after green, your cells are balanced.

This is a post I put on Facebook:   

A frequent topic here is the length of time to leave the Rad charger plugged in and connected to the battery.

From my Rad Owner's Manual:
"Remove the charger from the battery within one hour of the green light indicating a complete charge. The charger is designed to automatically stop charging when the battery is full, but unnecessary wear of the charging components could occur if the charger is left attached to the battery and a power source for longer than 12 hours. Detach the charger within one hour, or as soon as possible, once the green light indicates a complete charge to avoid unnecessary wear of charging components."

While this is good advice, there is no real harm in leaving the charger on for more than 12 hours. Here is why, and why Rad advises what they do.

Electronics generally follows what is referred to in the industry as a "bathtub" reliability curve. Electronics fails at a relatively higher (but still very small) rate early in its life. This is called the  "infant mortality" rate. After that, failures occur at a very small "steady state" rate. Late in life, the failure rate increases due to "wear out". (See the attached graph.)

Notice that there is no absolute time frame on the x-axis of the graph. That is because it is extremely difficult to predict the failure rate of electronics in general and even specific electronic components in particular. However, the time frame is measured in years if not decades.

Consider your alarm clock. It has many of the same types of components as the Rad charger and battery BMS – semiconductor chips, transistors, LEDs, capacitors, and resistors. What is the lifetime of your alarm clock? Certainly it is measured in years, even though it is wearing out all the while it is plugged in. In the case of your alarm clock, there is no "unnecessary wear" - it is necessary to leave it plugged in to be useful. It is not necessary to leave the Rad charger plugged in 24/7, so yes, if you do, you are causing "unnecessary wear". However, that wear is so small as to be negligible. Even if left plugged in 24/7, you are likely to remain in the very low "steady state" failure period, and never enter the "wear out" period.

The cells in the battery are a different matter. Cell wear is due to charge/discharge cycles, and each cycle causes measurable wear on the cells in the form of reduction in their capacity. Looking at the second chart for a particular Li-Ion cell, cell capacity is reduced by about 10% after 200 complete charge cycles. Rad says that the cells in my Rover 5 are Samsung 35E. The spec sheet for that particular cell lists a degradation to 60% capacity at 500 cycles. If you use your Rad a lot, you will experience cell degradation long before the battery or charger electronics will "wear out". Leaving the charger plugged in does not significantly affect cell "wear out", because cell wear is due to a charge and discharge cycle, not a trickle charge.

Note that Rad does not give any concern to "overcharge". Why not? Because, other than due to a component failure, it can't happen. While Rad does state that "the charger is designed to automatically stop charging when the battery is full", technically that is not the case. The charger does deliver current to the battery as long as it is plugged in. The charger operates in Constant Current – Constant Voltage mode. When plugged into a discharged battery, it will deliver a constant current of 2A as the battery voltage rises. As battery voltage approaches the charger's float voltage of 54.6V, the current gradually decreases. At about 200mA, the charger light switches from red to green, and the battery is essentially fully charged and can be disconnected. But current continues to flow, and diminishes until it reaches a very low rate as battery voltage reaches the charger float voltage. This small current is necessary to enable the battery BMS to balance the cells. This is why Rad advises to charge for 12 hours periodically. There is nothing special about 12 hours, other than in most cases that will be sufficient time for the BMS to balance. (New cells may be more unbalanced, hence the recommendation to balance for three consecutive 12-hour cycles.)

The BMS balances cells only during charging, and is only effective under low "trickle" charge. It balances by shunting current past fully-charged cells and only through the lower-voltage, less than fully charged cells. This may take several hours or only a few minutes, depending upon how far out of balance the cells are. Balancing is entirely managed by the BMS – the charger has no "knowledge" of what is going on and just supplies current. You can't over-balance or over-charge cells.

In summary, following Rad's instructions to the letter and using a timer is best practice, and does reduce "unnecessary wear". On the other hand, not doing so is not really harmful and does not have a significant impact on "wear" of the charger or battery.

[JimInPT]

Excellent essay, Dick; thanks very much!

[santacruzpaul]

I have studied the spec sheet for the chip that Rad uses in the BMS.  The chip uses passive balancing, and balances only during the charge cycle, and only after the Charge light turns green. If you unplug the charger immediately after the green light turns on, the chip has no opportunity to balance. If you leave it plugged in for any significant amount of time after green, the chip has the opportunity to balance the cells and will do so if needed. There's nothing special about a 12 hour charge other than it guarantees that the chip has enough time to balance. New cells from the factory are more likely to be at different voltages (unbalanced), hence the recommendation for three 12-hour cycles, to give the chip enough opportunity to balance. Unless you have baby-sat every time you charged and unplugged immediately after green, your cells are balanced.

This is a post I put on Facebook:   

A frequent topic here is the length of time to leave the Rad charger plugged in and connected to the battery.

From my Rad Owner's Manual:
"Remove the charger from the battery within one hour of the green light indicating a complete charge. The charger is designed to automatically stop charging when the battery is full, but unnecessary wear of the charging components could occur if the charger is left attached to the battery and a power source for longer than 12 hours. Detach the charger within one hour, or as soon as possible, once the green light indicates a complete charge to avoid unnecessary wear of charging components."

While this is good advice, there is no real harm in leaving the charger on for more than 12 hours. Here is why, and why Rad advises what they do.

Electronics generally follows what is referred to in the industry as a "bathtub" reliability curve. Electronics fails at a relatively higher (but still very small) rate early in its life. This is called the  "infant mortality" rate. After that, failures occur at a very small "steady state" rate. Late in life, the failure rate increases due to "wear out". (See the attached graph.)

Notice that there is no absolute time frame on the x-axis of the graph. That is because it is extremely difficult to predict the failure rate of electronics in general and even specific electronic components in particular. However, the time frame is measured in years if not decades.

Consider your alarm clock. It has many of the same types of components as the Rad charger and battery BMS – semiconductor chips, transistors, LEDs, capacitors, and resistors. What is the lifetime of your alarm clock? Certainly it is measured in years, even though it is wearing out all the while it is plugged in. In the case of your alarm clock, there is no "unnecessary wear" - it is necessary to leave it plugged in to be useful. It is not necessary to leave the Rad charger plugged in 24/7, so yes, if you do, you are causing "unnecessary wear". However, that wear is so small as to be negligible. Even if left plugged in 24/7, you are likely to remain in the very low "steady state" failure period, and never enter the "wear out" period.

The cells in the battery are a different matter. Cell wear is due to charge/discharge cycles, and each cycle causes measurable wear on the cells in the form of reduction in their capacity. Looking at the second chart for a particular Li-Ion cell, cell capacity is reduced by about 10% after 200 complete charge cycles. Rad says that the cells in my Rover 5 are Samsung 35E. The spec sheet for that particular cell lists a degradation to 60% capacity at 500 cycles. If you use your Rad a lot, you will experience cell degradation long before the battery or charger electronics will "wear out". Leaving the charger plugged in does not significantly affect cell "wear out", because cell wear is due to a charge and discharge cycle, not a trickle charge.

Note that Rad does not give any concern to "overcharge". Why not? Because, other than due to a component failure, it can't happen. While Rad does state that "the charger is designed to automatically stop charging when the battery is full", technically that is not the case. The charger does deliver current to the battery as long as it is plugged in. The charger operates in Constant Current – Constant Voltage mode. When plugged into a discharged battery, it will deliver a constant current of 2A as the battery voltage rises. As battery voltage approaches the charger's float voltage of 54.6V, the current gradually decreases. At about 200mA, the charger light switches from red to green, and the battery is essentially fully charged and can be disconnected. But current continues to flow, and diminishes until it reaches a very low rate as battery voltage reaches the charger float voltage. This small current is necessary to enable the battery BMS to balance the cells. This is why Rad advises to charge for 12 hours periodically. There is nothing special about 12 hours, other than in most cases that will be sufficient time for the BMS to balance. (New cells may be more unbalanced, hence the recommendation to balance for three consecutive 12-hour cycles.)

The BMS balances cells only during charging, and is only effective under low "trickle" charge. It balances by shunting current past fully-charged cells and only through the lower-voltage, less than fully charged cells. This may take several hours or only a few minutes, depending upon how far out of balance the cells are. Balancing is entirely managed by the BMS – the charger has no "knowledge" of what is going on and just supplies current. You can't over-balance or over-charge cells.

In summary, following Rad's instructions to the letter and using a timer is best practice, and does reduce "unnecessary wear". On the other hand, not doing so is not really harmful and does not have a significant impact on "wear" of the charger or battery.

Thanks DickB for the detailed explanation,
I am one of those that babysit my charger with a timer till it goes green,
Since I am so anal retentive about removing the battery from the charger when light goes green,
Would you suggest me balancing? Or just leaving battery changing for an hour or so after getting the green light.
Thanks, Paul

[JimInPT]

Since I am so anal retentive about removing the battery from the charger when light goes green,
Would you suggest me balancing? Or just leaving battery changing for an hour or so after getting the green light.
Thanks, Paul

Paul, FYI I keep it pretty simple; I usually recharge when down to the 2-3 bar range, on a 7-hour countdown timer that is usually at least an hour on green before it shuts down on the occasions I've checked.  I ran my scheme past the Rad techs just to see if they had any comment on this method and they were fine with it.

[DickB]

Thanks DickB for the detailed explanation,
I am one of those that babysit my charger with a timer till it goes green,
Since I am so anal retentive about removing the battery from the charger when light goes green,
Would you suggest me balancing? Or just leaving battery changing for an hour or so after getting the green light.
Thanks, Paul

Leave it on the charger for 12 hours. In the future leave it on for at least an hour or two after green; should remain balanced.

[Altema]

Yes, excellent essay indeed! I was unaware that Paul unplugged the moment it turned green, so that changes things a bit. I use a timer on mine, but if I know it's going to take five hours to top off, I'll set the timer for an hour or two more.

[santacruzpaul]

Since I am so anal retentive about removing the battery from the charger when light goes green,
Would you suggest me balancing? Or just leaving battery changing for an hour or so after getting the green light.
Thanks, Paul

Paul, FYI I keep it pretty simple; I usually recharge when down to the 2-3 bar range, on a 7-hour countdown timer that is usually at least an hour on green before it shuts down on the occasions I've checked.  I ran my scheme past the Rad techs just to see if they had any comment on this method and they were fine with it.

Thanks for the tip JiminPT,

[santacruzpaul]

Thanks DickB for the detailed explanation,
I am one of those that babysit my charger with a timer till it goes green,
Since I am so anal retentive about removing the battery from the charger when light goes green,
Would you suggest me balancing? Or just leaving battery changing for an hour or so after getting the green light.
Thanks, Paul

Leave it on the charger for 12 hours. In the future leave it on for at least an hour or two after green; should remain balanced.

Got it DickB, thanks for the knowledge,

[santacruzpaul]

Yes, excellent essay indeed! I was unaware that Paul unplugged the moment it turned green, so that changes things a bit. I use a timer on mine, but if I know it's going to take five hours to top off, I'll set the timer for an hour or two more.

Thanks for the knowledge again Altema

[santacruzpaul]

Put 22 miles on the Radrover 5 yesterday, Ran it down to 3 bars using PA 4 and throttle more than I normally do.
Just got done charging for 12 hours,
I have been charging after each ride with battery level at 5 bars on my usual 10 mile rides,
I am going to start charging only when I get 4 bars or less, And let the charger run for about an hour or so after I get the green light.
Am I on the right track?
Thanks, Paul

[JimInPT]

I am going to start charging only when I get 4 bars or less, And let the charger run for about an hour or so after I get the green light.
Am I on the right track?
Thanks, Paul

From what I've learned, that seems fine, but I only charge when at 3 bars, or as low as 2 bars (I don't let it go lower than that), unless I'm planning a long ride the next day if it's at 4 bars.  The battery pack has a finite number of charge cycles (in excess of 800 or so for Rad packs, but there is a limit), so I think dropping it lower to reduce the number of charge cycles is beneficial as long as it doesn't go below 2 bars very often.

There's a lot of rumors and black-magic advice about batteries, but I think the consensus is that the best for this battery chemistry is to charge when it hits 20% and stop charging at 80% - I always take it to 100% for maximum range and almost never let it get as low as 20% but my overall goal is to minimize the number of charging cycles over time.

[Altema]

I am going to start charging only when I get 4 bars or less, And let the charger run for about an hour or so after I get the green light.
Am I on the right track?
Thanks, Paul

From what I've learned, that seems fine, but I only charge when at 3 bars, or as low as 2 bars (I don't let it go lower than that), unless I'm planning a long ride the next day if it's at 4 bars.  The battery pack has a finite number of charge cycles (in excess of 800 or so for Rad packs, but there is a limit), so I think dropping it lower to reduce the number of charge cycles is beneficial as long as it doesn't go below 2 bars very often.

There's a lot of rumors and black-magic advice about batteries, but I think the consensus is that the best for this battery chemistry is to charge when it hits 20% and stop charging at 80% - I always take it to 100% for maximum range and almost never let it get as low as 20% but my overall goal is to minimize the number of charging cycles over time.

I bought a charger that lets you select 80, 90, or 100% charge, but still charge to 100% depending on which battery I'm using. My favorite battery is lightweight and has a 40amp BMS, but is only 12ah, so it needs to be full to make it back home from longer rides. For group rides, I formerly used both my Tesla batteries, but switched to using just one of them. Most of the bikes in the group are from Trek or Tern, and economy mode on my Rad keeps up fine with them. A 15 mile ride in eco mode leaves the battery at about 92% full.