Experiencing regenerative braking issues after 1 year

[1.21GW]

As the weather turns colder all the new Model 3 owners are worrying about the regen... lol. If you live in the northern states, say goodbye to regen for a few months.

Also, if you charge to 100% you will lose regen. Nothing to do with software updates.

 

[Amyshubby]

If you live in the northern states, say goodbye to regen for a few months.

I'm a little confused as to why this would happen. I fully understand why a car at 100% has nowhere for the energy to go, and I also know the battery is less efficient in the cold. However, it I'm charged to 70% and the car is producing energy, why can't it go into the battery? Is it just producing energy at a faster rate than the battery can absorb?

 

[1.21GW]

I'm a little confused as to why this would happen. I fully understand why a car at 100% has nowhere for the energy to go, and I also know the battery is less efficient in the cold. However, it I'm charged to 70% and the car is producing energy, why can't it go into the battery? Is it just producing energy at a faster rate than the battery can absorb?

yes. Batteries can discharge faster than they can recharge. When they are cold, this is even more pronounced. It takes quite a bit of driving to warm the batteries to get full regen back.

 

[ajdelange]

... it I'm charged to 70% and the car is producing energy, why can't it go into the battery? '

Please see No. 5

Is it just producing energy at a faster rate than the battery can absorb?

No, no, no. It (the dynamo) is not producing energy because if it did and passed that to the battery the battery would be damaged. As I keep repeating here the dynamos are 4 quadrant machines. They can absorb or generate torque in controlled amounts by supplying or producing controlled amounts of energy. If the battery condition is such that absorbing energy at above a certain rate would damage it the controller sets the dynamo field such that less than that amount of power is generated. This, of course, limits the amount of torque that is absorbed and regen braking is less effective. I am amazed at how hard it is for people to grasp this simple concept so perhaps I am not explaining it very well.

 

[camalaio]

Please see No. 5

No, no, no. It (the dynamo) is not producing energy because if it did and passed that to the battery the battery would be damaged. As I keep repeating here the dynamos are 4 quadrant machines. They can absorb or generate torque in controlled amounts by supplying or producing controlled amounts of energy. If the battery condition is such that absorbing energy at above a certain rate would damage it the controller sets the dynamo field such that less than that amount of power is generated. This, of course, limits the amount of torque that is absorbed and regen braking is less effective. I am amazed at how hard it is for people to grasp this simple concept so perhaps I am not explaining it very well.

Besides the fact there is no dedicated "dynamo" in this car, so that word is innaccurate...

Don't hold your knowledge over others (like I just did one sentence ago, see?) and act like it's so simple.

Batteries, despite them being a core part of our vehicles and even phones, are not well understood by the general population. And they don't need to be. Just like no one needs to understand why their gas engine doesn't produce heat immediately, why no one needs to understand how LCDs work, and no one needs to even understand how brakes on their car work. They wait for heat. They look at a display. They stop their vehicle.

So when someone asks a question you know something about, perhaps offer your knowledge a bit more tactfully than expressing your wonder at how people can't understand the relatively esoteric topic.

Here's my take:
The motor/generator in the car can use or produce any amount of electricity asked of it. When the battery is cold it's detrimental to charge it quickly, and regenerative braking actually produces a lot of power (you're slowing down a 4000lb car!). So in this case, the car limits charging of the battery in order to preserve its long term health. After driving a bit and the battery is warmer, it's able to apply more power without battery health impacts.

 

[Sophias_dad]

One way, albeit silly, for the car to do regenerative(or at least not-friction) braking with the battery at 100% would be to intentionally(and automatically) enable the electrical accessories(resistive heater >and< AC for the cabin, seat heaters, defrosters, and so on). Diesel electric locomotives have entire panels of electric resistance heaters to dissipate the energy generated as they slow down.

I imagine the scale of the slowdown for a 3 with all its electric accessories enabled would still be pretty dismal, IIRC, the heaters are like 6kw. I don't know what the regeneration-side of the power graph is, but I'd be surprised if 6kw was more than 1/3 of the usual regeneration.

Way simpler to just charge to 90-95%...

 

[Fredneck]

One way, albeit silly, for the car to do regenerative(or at least not-friction) braking with the battery at 100% would be to intentionally(and automatically) enable the electrical accessories(resistive heater >and< AC for the cabin, seat heaters, defrosters, and so on). Diesel electric locomotives have entire panels of electric resistance heaters to dissipate the energy generated as they slow down.

I imagine the scale of the slowdown for a 3 with all its electric accessories enabled would still be pretty dismal, IIRC, the heaters are like 6kw. I don't know what the regeneration-side of the power graph is, but I'd be surprised if 6kw was more than 1/3 of the usual regeneration.

Way simpler to just charge to 90-95%...

Regen on my car is indicated to be over 50kW. When the car is charging it gets down in the 6 kW range as I approach 100%. So turning on the 6 kW heaters won't add much. Not really much point. If you want to burn energy to slow the vehicle, that's what the brakes do. They could simply use them to give the "feel" of regen.

 

[Fredneck]

Energy from regen can and will go to a fully charged battery. The problem is that the battery can't store it without becoming damaged. Therefore regen is turned off when the battery is "full".

I'm not sure what you are trying to say. The energy from regenerative braking will not go to the battery when it is fully charged. The controller won't allow it which is what you also say. So your first statement is in contradiction to your last.

 

[Fredneck]

One more point. When I say, “strain the brakes” I obviously don’t mean somethings going to be damaged or fail. It only feels like it LOL. When you use regenerative braking all the time and then it’s not there, it is so very noticeable. No doubt in my mind that brake pads would wear faster without regenerative braking. That’s all I meant.

I agree, you get used to the "feel" of regenerative braking. When it is gone (happens a lot here because of the cold) you have to be on your toes to be safe and also to try to not waste energy.

That's the other problem with not having the actual regen. When you need to slow faster than partial regen will do or any slowing with no regen, all that power is lost as heat. So charging to 100% won't give you the same range extension you will get from the 80% to 90% part of your charge.

BTW, I think you will see the same regen limitation at the very low end as well. It may have to be around 2 or 3% before it cuts back on regen, but the charging rate is similarly slowed at those low state of charge numbers. I just don't recall the exact numbers.

 

[Fredneck]

I'm a little confused as to why this would happen. I fully understand why a car at 100% has nowhere for the energy to go, and I also know the battery is less efficient in the cold. However, it I'm charged to 70% and the car is producing energy, why can't it go into the battery? Is it just producing energy at a faster rate than the battery can absorb?

Like 1.21GW said, the batteries can't charge as fast as they discharge. There is an effect where the lithium in solution plates onto the anode if the charging is too fast. "Too fast" is determined by both the state of charge and even more so by the temperature. As 1.21GW said, the battery is big and it takes a lot to change it's temperature. When I start out with a battery temperature around 50°F, it isn't fully up to temp and the regen fully back for some 40 miles and nearly an hour of driving. At lower temps it's even worse.

 

[Amyshubby]

Thanks for the responses. I'm in NY so I guess I'll experience this soon enough.

 

[ajdelange]

I'm not sure what you are trying to say. The energy from regenerative braking will not go to the battery when it is fully charged. The controller won't allow it which is what you also say. So your first statement is in contradiction to your last.

What I was trying to say is that a "full" battery will accept current but that to allow it to do so will damage it and that, therefore, the controller will not allow a "full" battery to get any from regen.

 

[Fredneck]

What I was trying to say is that a "full" battery will accept current but that to allow it to do so will damage it and that, therefore, the controller will not allow a "full" battery to get any from regen.

Yes, so it is meaningless to talk about the battery "accepting" a charge it will never get. Why not just be clear about the fact that when regen doesn't happen it's because the BMS won't allow it to protect the battery? Going into four quadrant dynamos just seems inordinately complex. Also, your response doesn't really address the question being asked.

 

[Fredneck]

Thanks for the responses. I'm in NY so I guess I'll experience this soon enough.

I'm surprised you haven't seen it yet. It has been getting below 50°F for a few weeks here.

 

[ajdelange]

Why not just be clear about the fact that when ...

It's clear that what is clear to me isn't clear to you so suggest you just add me to your "ignore" list.

 

[Amyshubby]

I'm surprised you haven't seen it yet. It has been getting below 50°F for a few weeks here.

I've started to see it for really short periods when I first start my day but it goes away pretty quickly.

It might have something to do with the fact the car is garaged and I warm it up before I leave (at 80%).

 

[Fredneck]

I've started to see it for really short periods when I first start my day but it goes away pretty quickly.

It might have something to do with the fact the car is garaged and I warm it up before I leave (at 80%).

Garage keeping it likely helps when at border line temps. The battery does not warm up fast, so the time it takes to heat the cabin is nothing compared to the time it takes to warm the battery. Keeping it warm from the previous day is much more effective. For example, you can't even warm the battery from a 1.4 kW, 120 volt connection. The cabin uses all of that. lol