Battery Balancing

[mgilbert]

As an RC pilot, I'm quite familiar with lithium based batteries. Our chargers contain our battery monitoring systems, and those systems monitor each individual cell in our batteries. We frequently do balance charges, which involves fully charging the battery, and then letting the BMS charge individual cells independently, until all cells are within hundredths of a volt of each other. We usually charge this way, because we need all the charge we can get - a typical RC helicopter can drain a battery in three to six minutes.

Our bike batteries have built in battery monitoring and balancing systems. Problem is, no two manufacturers seem to recommend the same methods for caring for their batteries. Rad says to fully charge a new battery, then leave it on charge for several extra hours, so the BMS can balance the 12 or 13 parallel cell packs. In fact, they recommend doing this for the first three uses, and occasionally thereafter. But, Ride1UP says not to do that. They say to only fully charge occasionally, and disconnect the charger as soon as the battery is fully charged.

If I could find out who manufactures these packs, I'd ask them, but there is no way to know, and even then, I'd expect to get even more conflicting recommendations. I do know this: an out of balance battery can ruin cells.

I know that it is best to charge our batteries to only 80%, and to never discharge them below 20% to 30%, but beyond that, I'm not sure how often, if at all, we should do a balance charge, and if so, exactly how we should go about it. Are bike batteries different than RC batteries, because of the somewhat different chemistry? Do the BMS systems keep our batteries in balance, even when we aren't charging beyond 80%???...

Any experts out there???

 

[AHicks]

Another long time RC'er here. I currently fly 60" 3D planes on 6 cells. Been flying RC since the 70's.

Here's a new concept for you regarding bikes, that I had beat into my head a while back when asking similar questions. There are a lot of differences with the chargers used and different BMS (battery management systems) in use. The BIG difference though, is regarding the discharge rate on our bikes. It's WAY less than what we would mess with in RC.

Our concern in RC is regarding how any low cells might affect out battery performance and capacity. On bikes, the discharge rate is actually lower than the lowest cell in the pack can support. Meaning all the concern we have in RC is a moot issue when it comes to bikes. A long way around to the fact the bike packs don't really need to be balance charged. The packs stay balanced pretty much by themselves.

That said, any bike battery charger I've ever used shuts down completely at the end of a charge cycle. There's no turning back on automatically if you leave it plugged in charge potential. You would literally have to unplug the charger, then plug it back in to get it to charge any further than when it shut off. Even then, as soon as the pack reads 54 and change, the charger is going to shut down again.

If you look into RAD's suggestion, where they want you to ride the bike around the block a couple of times then recharge 3 times when you first get it, their concern is over initial balance charging. No big deal.... I doubt it could hurt anything.

R1U's process represents more current thinking I believe. Rest assured though, I have NO plans of waiting half the night to rush out and unplug my charger at the end of a charge cycle. It will sit right where I turned it on until I get to it the next day to unplug it. This seems like total heresy to some, but that's their issue.

There's a bunch of "best practices" similar to the 80/20 rule you can follow if you like for max battery life. Personally, I follow a lot of it, but I'm not following religiously. For instance, when I charge, I frequently charge to 100%. That said it's a rare day when I don't go for a ride, so the bike is never more than a few hours at 100%. I would NOT store the batttery at 100%, nor would I store it completely depleted. I generally charge at 45-46 volts, so it's never cycled very low. I have bigger motors (1000w+) in my bikes, and a big fear that if ridden to a much lower voltage, the BMS is going to shut the battery down due to a big voltage sag while crossing a busy road or climbing that last hill prior to getting home... -Al

 

[mgilbert]

Another long time RC'er here. I currently fly 60" 3D planes on 6 cells. Been flying RC since the 70's.

Here's a new concept for you regarding bikes, that I had beat into my head a while back when asking similar questions. There are a lot of differences with the chargers used and different BMS (battery management systems) in use. The BIG difference though, is regarding the discharge rate on our bikes. It's WAY less than what we would mess with in RC.

Our concern in RC is regarding how any low cells might affect out battery performance and capacity. On bikes, the discharge rate is actually lower than the lowest cell in the pack can support. Meaning all the concern we have in RC is a moot issue when it comes to bikes. A long way around to the fact the bike packs don't really need to be balance charged. The packs stay balanced pretty much by themselves.

That said, any bike battery charger I've ever used shuts down completely at the end of a charge cycle. There's no turning back on automatically if you leave it plugged in charge potential. You would literally have to unplug the charger, then plug it back in to get it to charge any further than when it shut off. Even then, as soon as the pack reads 54 and change, the charger is going to shut down again.

If you look into RAD's suggestion, where they want you to ride the bike around the block a couple of times then recharge 3 times when you first get it, their concern is over initial balance charging. No big deal.... I doubt it could hurt anything.

R1U's process represents more current thinking I believe. Rest assured though, I have NO plans of waiting half the night to rush out and unplug my charger at the end of a charge cycle. It will sit right where I turned it on until I get to it the next day to unplug it. This seems like total heresy to some, but that's their issue.

There's a bunch of "best practices" similar to the 80/20 rule you can follow if you like for max battery life. Personally, I follow a lot of it, but I'm not following religiously. For instance, when I charge, I frequently charge to 100%. That said it's a rare day when I don't go for a ride, so the bike is never more than a few hours at 100%. I would NOT store the batttery at 100%, nor would I store it completely depleted. I generally charge at 45-46 volts, so it's never cycled very low. I have bigger motors (1000w+) in my bikes, and a big fear that if ridden to a much lower voltage, the BMS is going to shut the battery down due to a big voltage sag while crossing a busy road or climbing that last hill prior to getting home... -Al

I've been flying RC since the eighties. Helicopters back then were my undoing. They were impossible to learn! I tangled with one once, and wound up with stitches, and was lucky that was all it was... Anyway, thanks for the most informative post! You are correct in saying we shouldn't leave our batteries at 100% for very long, as that is indeed harmful. The same is true for deep discharging. The 80/20 rule is the real deal, too. I have a phone, which I keep in the 70/30 range. To date, it has been charged/discharged over 1,200 times (I use AccuBattery to keep up with it), and the battery capacity has not changed at all. More wear happens when charging from 80% to 100%, than from 20% to 80%. Staying consistently below 80% can double the lifespan of the battery.

 

[AHicks]

Staying consistently below 80% can double the lifespan of the battery.

As mentioned, I have sort of a performance bike with some history on it. It's a RAD City that was modified with a 35 amp controller and 1000w MAC 12t geared hub motor (torque monster). It's powered by a stock RAD battery, which is nothing special. We're at 4 years now, with countless 100% charges, and no performance or range reduction to date.

I REALLY struggle with the idea that if I were to have cut the charge at 80% this past 4 years, which would have increased the number of charge cycles by quite a few, that I would get 8 years from this battery. I say not likely. We'll see where we end up. My thought is, that "doubling" may work out well on paper, but maybe not so much from a practical standpoint. -Al

 

[harryS]

Everyone has to make their own decisions on this topic. Most of my batteries are small 36V packs, and performance would be awful if I started at 80%. I charge mine to 100% after a ride, and run them down halfway. I still use only 50% of the battery, but am running it in the sweet spot near full voltage. I'll have to do a full cycle on some of my older batteries to see what capacity they still have after 4 years. I use RC wattmeters for that purpose.

 

[AHicks]

Everyone has to make their own decisions on this topic. Most of my batteries are small 36V packs, and performance would be awful if I started at 80%. I charge mine to 100% after a ride, and run them down halfway. I still use only 50% of the battery, but am running it in the sweet spot near full voltage. I'll have to do a full cycle on some of my older batteries to see what capacity they still have after 4 years. I use RC wattmeters for that purpose.

Exactly. Familiarize yourself with "best practices" and use the ones that work for you. Then go RIDE!

 

[GenXrider]

I forgot to set my alarm and accidentally charged my battery to 100% before going to bed one night and didn't realize until after midnight. I didn't get a chance to ride it until about noon to get the battery down to 80%. I'll be extra careful not to do that again.

 

[mgilbert]

That won't really hurt anything, if it only happens once in a great while. I always set a timer on my phone, for approximately how long I think the battery needs to charge, to reach about 50%, if I won't be riding soon. I do the same thing before a ride, for 70% to 80%, depending on how long I intend to ride.

 

[Gionnirocket]

As mentioned, I have sort of a performance bike with some history on it. It's a RAD City that was modified with a 35 amp controller and 1000w MAC 12t geared hub motor (torque monster). It's powered by a stock RAD battery, which is nothing special. We're at 4 years now, with countless 100% charges, and no performance or range reduction to date.

I REALLY struggle with the idea that if I were to have cut the charge at 80% this past 4 years, which would have increased the number of charge cycles by quite a few, that I would get 8 years from this battery. I say not likely. We'll see where we end up. My thought is, that "doubling" may work out well on paper, but maybe not so much from a practical standpoint. -Al

What makes you think that it only works on paper?
Perhaps you're stuck again as on the balancing compared to RC?
Have faith my friend as it is well documented.

... and I wouldn't word it as Li ion balance themselves.. it's more that a bike battery is not stressed to the same level and less heat is generated, thus falling out of balance is less likely.

 

[AHicks]

Documentation be damned. Show me....

 

[highbids]

My 2019 36V 350W Rattan Challenger shuts off when it's down to three bars.

The newer one is a 48V

Anyone else have this problem if you did how did you fix it.

The e-bikes only got 600 miles on it

 

[tomjasz]

Useless to judge by bars. Give us some multimeter voltage readings!

 

[highbids]

Thanks I'll do that,

 

[harryS]

I think three bars out of five indicates about 45-48 volts, enough to tell him the battery is not healthy.

Let's see what highbids comes up with. Doesn't hurt to have numbers.
Whoops. I misread and thought it was a 48V battery.

Let me make a new prediction, 36-38V.

 

[tomjasz]

I think three bars out of five says about 45-48 volts, enough tp say the battery is not healthy.

Let's see what highbids comes up with.

Sadly those $1 INDICATORS are notoriously inaccurate.

 

[Gionnirocket]

I try to stay away from bars when riding...
But if I do hit 3.. I'm definitely shutting down

 

[highbids]

I think three bars out of five indicates about 45-48 volts, enough to tell him the battery is not healthy.

Let's see what highbids comes up with. Doesn't hurt to have numbers.

I'l going check it with a voltage meter, here's what one guy said to look for

Step 1 would be to read the battery voltage when it shuts down using a digital voltmeter. If it is under 31.5v the problem is the meter calibration. If it is over 31.5v then you have a setting wrong or defective controller or BMS.

 

[tomjasz]

3.2V for a 10S (36V) battery or 32V pack voltage is a bit lower than I prefer. But it's still higher voltage than the drop-dead specification of typicallt 2.7V.

 

[harryS]

First put your meter on the charger, if it's easy to do without short circuiting the plug, That would read 42.0 if everything is perfect on both meter and charger. My chargers typically read 41.7-41.9 volts. For reference, a 50% charge is nominally 36-37 volts on a 36V battery,
,
As far as shutdown, your bike controller is probably set for 30-31 volts. Your battery BMS can also shut down the battery, and it will do so if any of the ten series cell groups goes under about 2.9V, The actual varies a bit depending on the BMS.

Unless you have a really strong battery, the BMS usually triggers first. While it's set lower, the battery is often so depleted at this level that any high demand for current like using throttle or climbing a hill will induce enough voltage sag that an individual cell may briefly hit the 2,9V limit and trigger shutdown. Voltage sag is transient. As soon as you remove the load, voltage returns to previous level.

I've had bad batteries that shut down at four bars, in one case that was 39 volts on a 36V battery. It had an internal cell sitting at 3.3V when the rest were like 4.0V, Bad news.

 

[Lightning P38]

Exactly. Familiarize yourself with "best practices" and use the ones that work for you. Then go RIDE!

Hi, I have a 36 volt battery that I have used for two years, from ebikekit.com . About 50 discharge cycles from 100% down to 50% or 60% typically. Today I topped off the battery, but this time it seemed it was taking longer than usual, and the charger was warm to the touch, so I checked the voltage with my voltmeter, and the battery was at 41.8 volts. The charger light was still red, so it was still charging. I was thinking it should reach 42 volts.

This is the first time I checked the voltage this year, because things have been humming along.

Am I seeing a slight reduction in battery capacity?
Is there anything I should be watching?

thx.