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[Keith]

How to stop charging below 100%?

Assuming you don't want to top up your bike and would rather charge it to some lower SOC, what can you do?

There are some manual methods. You can watch the dash SOC indicator during charging and disconnect anytime. You can ride until you reach some desired charge level and then don't charge. You can calculate the time it will take to reach a desired charge level, go away and come back to disconnect when the time is up. There are obvious problems with all of these choices.

How can this be done automatically? I will attempt to explore all of the possibilities and maybe I'll do something myself. Others are welcome to use my ideas. Here goes:

First there are a many ways to charge so that creates multiple solutions. In any case charging can be stopped either by disconnecting the AC to the charger or by controlling the charge enable logic. Deciding when to stop charging can be based on time, battery voltage, or some other SOC reading if available.

The simplest solution appears to be a settable timer on the AC to the charger. A calculation based on the current SOC, charging rate, and desired SOC is needed. That's a fairly easy web page to create, maybe I'll do that. Given the time it will take to reach the desired SoC, you set the timer and done. Complications include what type of AC connection is being used, and the accuracy of the charge prediction given variables like temperature, line voltage, pack condition etc. Huge advantage of this approach is it uses off the shelf components, no design needed, no warranty worries.

An existing, smart external charger with user input to select a desired stopping point would be great, but this choice doesn't seem to be available. Adding or modifying charger firmware requires proprietary knowledge so it probably isn't feasible. So it seems that some custom design may be required if the timer method isn't attractive.

Next up the ladder of complexity and design effort would be a pack voltage sensing AC power control device. This could be set to stop charging at some desired level by switching off the AC to the charger at a desired cutoff voltage. There are a few drawbacks to this approach. First it requires an AC power switching device rather than using existing contactors. Next it depends on a voltage reading that is going to be different than the final SOC voltage after the charging current stops. Some higher charge levels may not be settable because the cutoff voltage will be higher than the fully charged voltage. However this approach could be adapted to any bike and charger configuration. Voltage for sensing is available at the external charge connection and AC control is external to the bike. User input is simply what voltage to stop charging and that could include don't stop until the bike stops at 100% SOC.

It is possible to control the pack contactor using the enable line. Again pack voltage sensing could be used, or possibly some other SOC value obtained from the bike. In the case of external chargers the enable line is accessible and used in the connection to the bike. This approach looks pretty simple once the hurdle of an arduino type project is undertaken. The processor would have three inputs, user setting for the desired charge, voltage of the pack, and the enable line from the charger. The only required output is the enable signal to the bike.  A pair of Anderson SBS 75X connectors puts the charge control device in series between the external charger and the bike. Power for the arduino could be from a battery so connection is simple. This idea might be a winner except for the programming piece.

Controlling the on board charger enable logic gets into some trouble with hardware, by modifying the bike wiring, or software, since communication with the MBB, BMS, CAN bus and charger gets complicated, bike model specific and is probably not feasible for development except by Zero. So the only practical way for riders to control on board charging seems to be AC power switching as already discussed.

That's it as far as I can come up with on a Sunday morning. Did I miss anything? Is this worth pursuing?

[MostlyBonkers]

Hi Keith, I think there is only one reason to stop charging below 100% and that's before storing the bike for a long time.  It's probably not worth it even if you're going on holiday for a couple of weeks.

I'm pretty sure the battery is going to be good for at least 10-15 years before it drops its health by any significant amount.

For that very rare occasion that you won't be riding for more than a month, I think there's very little effort to take it for a ride down to 60%. Or set a timer on your phone to remind yourself to switch it off after a couple of hours.

I'm more interested in why you think it's  worth the bother to find a solution to a problem that doesn't exist. I don't want that to sound facetious, I just feel that people spend far too much time worrying about charging when they don't need to.

[Fred]

I agree. You'll spend more time solving the problem automatically than you would doing it manually. Unless you're just up for the challenge for the fun of it of course.

[Keith]

My situation is unique since I have four packs for my FX. That means some packs are always not in use, who knows for how long. And I don't commute, I ride off road whenever, no schedule. So while you are probably right, charge to 100% and ride is no problem, it might be for me. And while I have faith in the warranty and Farasis, I'd like to make my packs last forever. They may get repurposed long after my FX is scrap metal.

Anyway, it is a fun problem. If it isn't too difficult, I'd like to change my ways and not keep all four packs at 100% all the time. The benefit of doing that by any method may be small or even insignificant, but I don't think anyone really knows that with certainty. I'm not worried, just want to do the best for my investment. If they lose 5% in ten years instead of 10%, that's a win.

[Doug S]

I'd agree with others that this is probably not worth doing for most people, but it might be for some, as Keith points out. And it is an interesting thought exercise.

As I understand it, most if not all of the chargers for our bikes are CC/CV chargers, meaning they maintain constant current for the bulk of the cycle, switching over to constant voltage near the end, when the battery can't handle as much charging current. I'm also thinking most of them have some means of adjusting the ultimate voltage, for setting at the factory if nothing else. I'd think it would be as simple as adjusting the charger to put out a bit lower final voltage.

[MostlyBonkers]

Ahh, that's a bit different. I presume the FX tells you the state of charge of each pack, so you know where they're at when you take them out. It should be simple to work out how long each one needs on a charger to get to 50%, so you just need to find a timer that will cut the power after a set time. Something with an analogue knob that you twist for however many hours it needs would be convenient. I've never seen one though. Like an egg timer but with longer time periods.

[Keith]

Actually there is no separate charge indication for the two packs but I believe they are kept equal by the bike when possible, which is usually. A twistable mechanical timer would work but I've only seen the ones with little flags designed for daily cycles, that would not be easy to set. A reminder timer would work but might not be convenient if you leave the bike. And I will do something to get the time calculation simply.

[Lenny]

Keith I want to do the same thing for the exact same reasons. Why charging my pack to 100% and potentially harming it, when 85 or 90% is more than enough for my weekly ride needs?

I already have some stuff laying around, i.e. a wemos board, a raspberry, arduinos, a sms module and can module for arduino and a ELM237 Bluetooth ODB connector. I think I will solve it with a relay on the ac side, which is switched by one of those components. I will try to read out voltage/soc/range out of the CAN while charging (someone in another thread deciphered some CAN already) with the ELM327, connect to it with the raspberry, which at the same time is in the wifi and might be controlled by an app or something. But an arduino with an sms module placed onboard the bike might also do the job, it could even measure voltage and be powered by some 12v supply. I'll keep you updated, but it will still take a while until I find time to realize this project.

[togo]

We know SoC can be wildly inaccurate for these batteries, so let's target a voltage rather than a percentage.

[Keith]

Voltage is my thought too, simple to measure, just set a target range for storage. Maybe 105-110V is good. Easy to check, easy to control.

[Fred]

Will cell balancing be affected as this seems to happen at the end of the charging cycle?

[Erasmo]

Cell balancing happens all the time.

[Electric Terry]

I believe sometime in the next year, perhaps much sooner (just don't want to rush those working on the project) that the Diginow will have target voltage to be controlled and settable by the phone app.  You just punch in 110 volts and it charges to 80%.  Also if you are on a weak or shared outlet (garage door or fridge) you can set the amperage to charge at less than 1600 watts like 1200 watts, 800 watts or even 100 watts if you like or anything in between.

[Keith]

That sounds really great, I'm glad to know that this flexibility in charging has been recognized as a desirable feature set. But I'd rather have controls right on the charger than use a phone. I guess it is cheaper to use another device with a wireless connection than local hardware for the UI. I carry a burner on the trail so my "smart phone" is packed away, not convenient. But I'm not typical, never was, never will be! 

[Keith]

The simple timer method has some drawbacks. Digital timers may have a countdown function but it could take a lot of button pushing to set. There are simple push button timers but they have limited precision, 1, 2, 4, 6 hours. Mechanical 12 hour timers are available and cheap, might be ok. But almost everything is 15 amps, not enough for many of us. And even within rated current, sometimes they fry. Getting higher current AC power switching seems to require electrician level components. Not so cheap and still needs a control timer. Using the DC contactors to control charge stopping seems like a better idea right now. Is it? Can the contactor be damaged by opening under charging current load? Welding due to arcing on closing can happen but that seems like a different condition. Anyone know?