It's not the outside air temperature when you are driving that matters. It's the internal temperature of the battery pack. If the car was sitting overnight in low temperatures, the internal battery temperature will approach those overnight temperatures. Preconditioning will help bring the internal battery temperature up to a point where regen is less affected.
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Will regenerative braking go over 'charging limit'?
- Thread starter Oldrocky
- Start date
Hmmm, I don't understand. I get it that I may not get as much energy -stored- in a battery that is
cold ... but not that the amount of braking power is reduced. The BMS reduces the amount of
braking available when the car is cold?
Either way - I'm talking about the hill that starts, literally, just at the end of my driveway. The
car is in the garage and the outside temp in the garage (according to apps) is never below 50.
So I guess I'm back to asking "why does my MX-100D provide less braking thru regen at times?
- Jim in PNW
cold ... but not that the amount of braking power is reduced. The BMS reduces the amount of
braking available when the car is cold?
Either way - I'm talking about the hill that starts, literally, just at the end of my driveway. The
car is in the garage and the outside temp in the garage (according to apps) is never below 50.
So I guess I'm back to asking "why does my MX-100D provide less braking thru regen at times?
- Jim in PNW
Regen IS charging. When the battery is cold, the bms reduces the maximum power. If you were to go to a supercharger (without preheating) you would get very low power. As the battery heats, the power would increase.
In regen, the car will not actively heat the battery so regen will be limited.
In regen, the car will not actively heat the battery so regen will be limited.
I believe this is what takes place -
The Battery Management System reduces the amount of power allowed "into" the battery from whatever source (Supercharger, home charger or regen) when the battery pack is not within it's optimum operating temp. range. Someone more versed in this may be able to tell us what that range is.
For example, the car will "pre-condition" (bring to optimum temp) your battery when you are navigating to a supercharger, correct? This will allow for the battery, via the BMS, to be able to accept a larger amount of power quicker without doing significant harm to the battery pack. That's what the BMS is made to do and as a bonus it makes possible a quicker recharge experience while at a SC.
When starting out down your hill, the battery is probably not at it's optimum operating temp, therefore the BMS will limit the power going into the battery from any source. The regen brakes can produce a relatively large amount of power (heavy car + gravity) as it goes downhill. But the BMS has restricted the amount of juice allowed into the battery due to that optimum operating temp. thing. Where would the generated juice go?
I think the Computer makes the decision to limit the effectiveness of the regen brakes, thereby not producing more electricity than the BMS will allow to flow.
The same thing happens when you charge to 100%, The BMS does not allow any more electricity to flow into the battery (where would it go?) and will limit regen capacity just as it would shut off the flow of electricity from your charging source after reaching 100% SOC.
I've found that when at home and leaving for an extended trip, I never charge to more than 95%. Let my regen downhill "top it off"and give my brakes a brake!
I've also found that the car sometimes changes it's mind and decides to increase/decrease the regen effectiveness on the hill. Not sure why.
That's my theory on it after living at the top of a hill for over a year with a MY.
The Battery Management System reduces the amount of power allowed "into" the battery from whatever source (Supercharger, home charger or regen) when the battery pack is not within it's optimum operating temp. range. Someone more versed in this may be able to tell us what that range is.
For example, the car will "pre-condition" (bring to optimum temp) your battery when you are navigating to a supercharger, correct? This will allow for the battery, via the BMS, to be able to accept a larger amount of power quicker without doing significant harm to the battery pack. That's what the BMS is made to do and as a bonus it makes possible a quicker recharge experience while at a SC.
When starting out down your hill, the battery is probably not at it's optimum operating temp, therefore the BMS will limit the power going into the battery from any source. The regen brakes can produce a relatively large amount of power (heavy car + gravity) as it goes downhill. But the BMS has restricted the amount of juice allowed into the battery due to that optimum operating temp. thing. Where would the generated juice go?
I think the Computer makes the decision to limit the effectiveness of the regen brakes, thereby not producing more electricity than the BMS will allow to flow.
The same thing happens when you charge to 100%, The BMS does not allow any more electricity to flow into the battery (where would it go?) and will limit regen capacity just as it would shut off the flow of electricity from your charging source after reaching 100% SOC.
I've found that when at home and leaving for an extended trip, I never charge to more than 95%. Let my regen downhill "top it off"and give my brakes a brake!
I've also found that the car sometimes changes it's mind and decides to increase/decrease the regen effectiveness on the hill. Not sure why.
That's my theory on it after living at the top of a hill for over a year with a MY.
Harvey Danger
Member
OK, I think I follow. You're saying the BMS limits the battery charging - when it is "cold" (the
battery is cold) ... and that results in limited Regen braking ... and that results in my noticing
that the car isn't slowing down as much/fast at times ... and at other times the regen is "full on".
I'm not a battery theory person - but I know someone who is and I'll ask him and see if he
can uncloud the waters a bit more. If he gives me something worthwhile I'll share it here.
Thanks.
- Jim in the PNW
battery is cold) ... and that results in limited Regen braking ... and that results in my noticing
that the car isn't slowing down as much/fast at times ... and at other times the regen is "full on".
I'm not a battery theory person - but I know someone who is and I'll ask him and see if he
can uncloud the waters a bit more. If he gives me something worthwhile I'll share it here.
Thanks.
- Jim in the PNW
This is really simple, and it's this:
So the things that apply about charging and cold are the exact same issues as the recharging that comes from the motor in regeneration. That is still just charging. And the car very much monitors the temperature and will limit the charging power based on cold. When it is well below freezing, it will not allow any charging at all, because that is very damaging to the battery, so the car just won't do it. And it is actively trying to heat up the battery to get to where it can charge. Then it does operate on a gradually increasing scale, where it gets to where it's warm enough to start allowing a few amps, and as the temperature continues to rise, it can allow more recharging power.
GtiMart,
Unless they included a resistor grid to dissipate the 'extra' charging as heat. This is how the dynamic
brakes work on a modern train/locomotive. Adding a decision to the BMS would be simple. But the
cars don't have that and that may/may not be a good thing (I don't know which). I now know how it
works and that's the most important thing. Using the friction brakes (the foot pedal) works fine.
The MX often has a fan working - hard! - during supercharger sessions (something I only do while
"on the road for longer trips". Also, at times, there is steam that comes up out of the front of the
car ... which, as I understand it, is due to some moisture that is built up somewhere that the same fan is
pushing towards the front. I was at a charging station one time where another car on the charger was
putting out a literal cloud of steam (for a while) and it wasn't a time when he could have been driving
in rain or snow.
- Jim in PNW
Unless they included a resistor grid to dissipate the 'extra' charging as heat. This is how the dynamic
brakes work on a modern train/locomotive. Adding a decision to the BMS would be simple. But the
cars don't have that and that may/may not be a good thing (I don't know which). I now know how it
works and that's the most important thing. Using the friction brakes (the foot pedal) works fine.
The MX often has a fan working - hard! - during supercharger sessions (something I only do while
"on the road for longer trips". Also, at times, there is steam that comes up out of the front of the
car ... which, as I understand it, is due to some moisture that is built up somewhere that the same fan is
pushing towards the front. I was at a charging station one time where another car on the charger was
putting out a literal cloud of steam (for a while) and it wasn't a time when he could have been driving
in rain or snow.
- Jim in PNW
The car will do a few kW of regen even when the battery cannot accept it. It will use that energy to heat the cabin or make the front motor generate waste heat. You just don't feel 3-5kW. They chose not to include a waste heat generator. It would be one additional part, cost for them and maintenance for us.
I found this thread interesting, since my other electric car is a BMW i3. The i3 has no variable charging limit (though it does reserve a little in the pack) so when it's plugged in it will charge all the way to 100% and stay there, even if pre-conditioning is used.
The i3 is positively scary when driven 100% charged, since regen does not work at all! The braking dynamics are very different and even knowing this I have often came close to blowing through the stop sign on my street. I'm glad to report that the Tesla Model X has no such obvious issues!
The i3 is positively scary when driven 100% charged, since regen does not work at all! The braking dynamics are very different and even knowing this I have often came close to blowing through the stop sign on my street. I'm glad to report that the Tesla Model X has no such obvious issues!
IIRC charging to only about 80% is a good way to promote longer main battery life. When
I'm home and not taking a long trip I have my MX100D set to 80%, then when I go on long
trips where I'll be supercharging I set it up to 90% (235m range) to get more range.
I have found that using either Sentry mode or Dashcam affects range (especially if the
car is sitting for several days without being charged. About 12 to 20 miles drop - per day.
Just yesterday I drove from here to Centralia, Wa ... charged at supercharger while having
breakfast ... back to Ballard ... back to here ... charged at home for about 2 hours ... then
drove to Bellingham for dinner ... and back here. The only "wait" for charging was at the
supercharger in Centralia - but we had breakfast so no problem. The stop at home for 2
hours was always part of the plan. Arrived back home after dinner with the same margin
of range as when I got back from the longer trip to Centralia.
- Jim in PNW
I'm home and not taking a long trip I have my MX100D set to 80%, then when I go on long
trips where I'll be supercharging I set it up to 90% (235m range) to get more range.
I have found that using either Sentry mode or Dashcam affects range (especially if the
car is sitting for several days without being charged. About 12 to 20 miles drop - per day.
Just yesterday I drove from here to Centralia, Wa ... charged at supercharger while having
breakfast ... back to Ballard ... back to here ... charged at home for about 2 hours ... then
drove to Bellingham for dinner ... and back here. The only "wait" for charging was at the
supercharger in Centralia - but we had breakfast so no problem. The stop at home for 2
hours was always part of the plan. Arrived back home after dinner with the same margin
of range as when I got back from the longer trip to Centralia.
- Jim in PNW
Regen limiting can happen at FAR lower SoCs than 80%. I started out at 55% SoC and went up a steep hill. Was at around 50% SoC coming back down. Eventually, I noticed that regen was being limited. Not a lot, and not really noticeable when driving, but when I looked at the meter, the left most portion was a dotted line and if the hill got steep enough, it would hit that line and go no further. It's not only the charge level that can limit it (obviously at higher charge levels, it will always be limited, and at 100%, it will never regen at all), but if you push too much energy into the battery too quickly, it will throttle back the amount of regen. I think this is probably similar to how it throttles back the charge rate during supercharging, starting at 20% SoC and getting progressively lower and lower as the SoC rises.
