Thank you Jerry! Very informative. This information is new to me. Is it consistent with the Dahl lecture?
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What should my ideal charge percentage be?
- Thread starter Al Sherman
- Start date
That is not correct. The car will not draw power from the grid (when plugged in) to power 'housekeeping'. It will only draw power from the grid if you turn on the heater/AC or when the battery is charging. If the battery level (from vampire drain) drops below the set charge level the car will initiate the charger and bring it up to the set level. Depending on how much your vampire drain is it usually takes 2 to 3 days before the battery level drops enough below the set value to initiate the charge again.
It does not draw power randomly for other reasons. It does not draw power constantly to maintain the battery level. If the battery level is higher than the charge limit, it will not draw power from the grid until the battery level has dropped below.
I keep Teslafi.com log my car 24/7 and I have never see the car draw power from the grid for any other reasons other than to charge the battery or run the heater/AC.
brucet999
Active Member
I think you may be conflating two things with that answer. The charge cable can only deliver 240V or 120V AC power from your wall outlet. The onboard charger can only convert that AC power to high voltage DC and feed it to the main battery. All of the accessories, including onboard electronics work off the 12V battery, which in turn is periodically re-charged from the main battery via a DC to DC voltage converter.
Plugged in or not, the accessories still pull power from the 12V battery. The periodic re-charging of that 12V battery is what causes "vampire drain" from the main battery and, due to its small size and frequent charge/discharge cycles, early failure of said 12V battery.
Very interesting. So I should open my garage, pull in both Teslas, and hook them both up, every night? I'll need to Summon them in, as they are so big.
Or as David said, only every 2 or 3 days? Irrespective of whether we need to charge the batteries?
I'm thinking this is a lot of extra hassle, and maybe if you all are right about this, that Tesla should just design a better 12 volt battery. Maybe a 24 volt, or 40 volt battery? I have a Ryobi leaf blower that has a 40 volt battery ....
Or as David said, only every 2 or 3 days? Irrespective of whether we need to charge the batteries?
I'm thinking this is a lot of extra hassle, and maybe if you all are right about this, that Tesla should just design a better 12 volt battery. Maybe a 24 volt, or 40 volt battery? I have a Ryobi leaf blower that has a 40 volt battery ....
I never said it will draw power constantly to maintain the main battery level. I also didn't say it would draw from the grid if the battery level is higher than the desired limit. I have seen the HVAC turn on while parked and not plugged in on hot days. Whether that's drawing from the main battery or 12v I'm not sure. What I'm saying is there's a couple of good reasons to always keep the car plugged in which also is what Tesla advises. I was incorrect in stating that the grid is directly charging the 12v. The battery does that as you and @brucet999 state.
mknox
Well-Known Member
Nope not correct. I have had my car for over 4 years and my charging circuit in the garage is on it's own sub-meter so I can see everything that goes on. The only time my car draws wall current is when it is actively charging, if I get in and the HVAC comes on or if I remotely turn the HVAC on. And when it does draw wall current, it draws it at the full amperage that it is capable of, or else at the level I've set it to in the car. When the HVAC runs, the amperage may start to lower as the car heats up or cools off.
All other loads are powered from the 12v battery, and the DC-DC converter will come on from time to time to keep the 12v topped up from the main pack, but when this happens it does not draw shore power. If the main pack drops approximately 2 or 3% SOC from the set point, a charging cycle will initiate, but if you have a timer set, it will respect the charge time and not come on until that time.
Mike, are you saying it does not need to be plugged in for the DC converter to come on to top off the 12v?
Exactly. The DC-DC converter is using the main battery pack as a source and as it's only source. The 12 Volt battery is entirely charged/maintained by the DC-DC converter that is drawing from the main battery. There is no separate or dedicated charger that draws from the grid and charges the 12 Volt battery.That's why it doesn't matter for the 12 Volt system weather the car is plugged in or not. It's getting it's power from the main battery whenever it needs. This is the main cause for the so called 'vampire drain'.
The heater and AC is also using only the main battery as it's power source. (It runs on the same voltage as the main battery so no DC-DC converter is necessary). When you turn on the AC/heater even while the car is plugged in, the power comes from the main battery. When the car is plugged in, the car will turn on the charger and recharge the main battery at the same power rate that is taken by the AC/heater. In other words, it is making up exactly what the AC/heater uses, so there is no net loss. Still there is never a direct connection from the grid to the AC/heater or any other system in the car. Everything the car needs is taken from the main battery and the chargers recharge the main battery as needed.
The reason is that you can build a heater/AC system only to run from either DC or AC, not both. So everything in the car is made for DC current as it is provided by the main battery. The car's chargers are taking the AC current from the grid and convert them to DC current to charge the main battery.
I hope that clears up some of the confusion.
Got it, however it does make me question why Tesla advises owners to plug in everyday unless you need the electrons the next day. I can go a week without charging as long as I know it's not hurting anything.Exactly. The DC-DC converter is using the main battery pack as a source and as it's only source. The 12 Volt battery is entirely charged/maintained by the DC-DC converter that is drawing from the main battery. There is no separate or dedicated charger that draws from the grid and charges the 12 Volt battery.That's why it doesn't matter for the 12 Volt system weather the car is plugged in or not. It's getting it's power from the main battery whenever it needs. This is the main cause for the so called 'vampire drain'.
The heater and AC is also using only the main battery as it's power source. (It runs on the same voltage as the main battery so no DC-DC converter is necessary). When you turn on the AC/heater even while the car is plugged in, the power comes from the main battery. When the car is plugged in, the car will turn on the charger and recharge the main battery at the same power rate that is taken by the AC/heater. In other words, it is making up exactly what the AC/heater uses, so there is no net loss. Still there is never a direct connection from the grid to the AC/heater or any other system in the car. Everything the car needs is taken from the main battery and the chargers recharge the main battery as needed.
The reason is that you can build a heater/AC system only to run from either DC or AC, not both. So everything in the car is made for DC current as it is provided by the main battery. The car's chargers are taking the AC current from the grid and convert them to DC current to charge the main battery.
I hope that clears up some of the confusion.
I think it's just to get the owners to make it a habit to plug in. Nothing worse than forgetting to plug in before you go to sleep. There is also the issue that keeping a battery connected to a charger is actually bad and phone manufacturers actually recommend to unplug the phone when done charging and not leaving it plugged in. A Model S/X has a sophisticated battery management system and it's fine to keep it plugged in. Last but not least, we have in our heads that we drive cars for days and then fill it up when near empty. An EV is different. You plug it in and top it off every day. So people need to be reminded to do things differently with an EV.
mknox
Well-Known Member
That is correct. The DC-DC converter will come on from time to time to keep the 12v topped up even if the car is off and not plugged in. There are a number of things (like the 3G / LTE radio) that are constantly taxing the 12v system and so it needs to be maintained.
The DC-DC converter converts high voltage DC from the main pack to 12v DC for the 12v battery.
I have read these forums extensively. I have also read the Dahl study, which contradicts this somewhat. Dahl's main theory is that it is the amount of time at high SOCs as well as the temperature are the two factors, taken together, that lead to battery wear. There is a section in there were he talks about "beating the clock" by cycling to 100% and immediately discharging. He also told another member, in a follow up question, that there is a charge state where being over a certain voltage could cause harm. I believe that state is over 80%.
Yours is the only place I have seen this theory about size of the cycles. Where do you get your info?
Jerry thank you for the informative posting!
Might I ask --
>>> Today, Li-ion meets the expectations of most consumer devices but applications for the EV need further development before this power source will become the accepted norm.
What are the authors saying here-- is this the typical CYA? Or what? Any thoughts? It's not Nickel-water (Jay Leno's Baker Electric); it is not lead-acid, not nickel-cadmium or nickel-hydride or nickel metal hydride (?) so what exactly gives with this oddly-worded hedging? That they are not on board with Elon? That they think PanaSanyo with come out tomorrow with the next new thing? Just wondering what your thoughts are.
>>> cycling, elevated temperature and aging decrease the performance over time. Manufacturers take a conservative approach and specify the life of Li-ion in most consumer products as being between 300 and 500 discharge/charge cycles.
Is that also true with our Tesla car batteries? Any reason to think otherwise?
>>> A battery may fail within the allotted time due to heavy use or unfavorable temperature conditions; however, most packs last considerably longer than what the stamp indicates.
I'm not recalling what I was expected to believe about my S90D's battery's life. But I'm good. I plan to never ever sell it. I plan to drive it forever. I'm confident it will be there as long as I need it.
>>> Although a battery should deliver 100 percent capacity during the first year of service, it is common to see lower than specified capacities, and shelf life may contribute to this loss.
Seems like this has been the root of much discussion here.
>>> In addition, manufacturers tend to overrate their batteries, knowing that very few users will do spot-checks and complain if low.
Not a complaint I've seen on the boards about anything from Tesla, at least not by those who own them.
>>> The smaller the discharge (low DoD), the longer the battery will last. If at all possible, avoid full discharges and charge the battery more often between uses.
Not what I've been reading here-- this indicates I should plug it in every night and charge from 80 to 90 or 70 to 80 or whatever. Never let it drop much. RIght?
>>> There is no memory and the battery does not need periodic full discharge cycles to prolong life. The exception may be a periodic calibration of the fuel gauge on a smart battery or intelligent device.
Now I'm wanting to ask how old this report is. Surely my S90D has a battery with memory?
>>> Most chargers for mobile phones, laptops, tablets and digital cameras charge Li-ion to 4.20V/cell. This allows maximum capacity, because the consumer wants nothing less than optimal runtime. Industry, on the other hand, is more concerned about longevity and may choose lower voltage thresholds. Satellites and electric vehicles are such examples.
We have the lower voltage threshold, don't we?
>>> HIgh voltages and exposure to elevated temperature is said to degrade the battery quicker than cycling under normal condition. (Nissan Leaf case)
Is this anything we need worry about?
>>> Lower charge voltages prolong battery life and electric vehicles and satellites take advantage of this. Similar provisions could also be made for consumer devices, but these are seldom offered; planned obsolescence takes care of this.
We have lower charge voltages? What is the reference to "planned obsolescence?" I'm not thinking that Elon is hip with that. Just my gut on that call.
>>> Avoid so-called ultra-fast chargers that claim to fully charge Li-ion in less than one hour. Last updated 2017-03-03
Hmmm.
I'm guessing that my last trip to the Hawthorne Supercharger was on an "so-called ultra-fast charger" ... what are we missing here?
Thanks for any answers-- Sorry for the rant-- Vern
Might I ask --
>>> Today, Li-ion meets the expectations of most consumer devices but applications for the EV need further development before this power source will become the accepted norm.
What are the authors saying here-- is this the typical CYA? Or what? Any thoughts? It's not Nickel-water (Jay Leno's Baker Electric); it is not lead-acid, not nickel-cadmium or nickel-hydride or nickel metal hydride (?) so what exactly gives with this oddly-worded hedging? That they are not on board with Elon? That they think PanaSanyo with come out tomorrow with the next new thing? Just wondering what your thoughts are.
>>> cycling, elevated temperature and aging decrease the performance over time. Manufacturers take a conservative approach and specify the life of Li-ion in most consumer products as being between 300 and 500 discharge/charge cycles.
Is that also true with our Tesla car batteries? Any reason to think otherwise?
>>> A battery may fail within the allotted time due to heavy use or unfavorable temperature conditions; however, most packs last considerably longer than what the stamp indicates.
I'm not recalling what I was expected to believe about my S90D's battery's life. But I'm good. I plan to never ever sell it. I plan to drive it forever. I'm confident it will be there as long as I need it.
>>> Although a battery should deliver 100 percent capacity during the first year of service, it is common to see lower than specified capacities, and shelf life may contribute to this loss.
Seems like this has been the root of much discussion here.
>>> In addition, manufacturers tend to overrate their batteries, knowing that very few users will do spot-checks and complain if low.
Not a complaint I've seen on the boards about anything from Tesla, at least not by those who own them.
>>> The smaller the discharge (low DoD), the longer the battery will last. If at all possible, avoid full discharges and charge the battery more often between uses.
Not what I've been reading here-- this indicates I should plug it in every night and charge from 80 to 90 or 70 to 80 or whatever. Never let it drop much. RIght?
>>> There is no memory and the battery does not need periodic full discharge cycles to prolong life. The exception may be a periodic calibration of the fuel gauge on a smart battery or intelligent device.
Now I'm wanting to ask how old this report is. Surely my S90D has a battery with memory?
>>> Most chargers for mobile phones, laptops, tablets and digital cameras charge Li-ion to 4.20V/cell. This allows maximum capacity, because the consumer wants nothing less than optimal runtime. Industry, on the other hand, is more concerned about longevity and may choose lower voltage thresholds. Satellites and electric vehicles are such examples.
We have the lower voltage threshold, don't we?
>>> HIgh voltages and exposure to elevated temperature is said to degrade the battery quicker than cycling under normal condition. (Nissan Leaf case)
Is this anything we need worry about?
>>> Lower charge voltages prolong battery life and electric vehicles and satellites take advantage of this. Similar provisions could also be made for consumer devices, but these are seldom offered; planned obsolescence takes care of this.
We have lower charge voltages? What is the reference to "planned obsolescence?" I'm not thinking that Elon is hip with that. Just my gut on that call.
>>> Avoid so-called ultra-fast chargers that claim to fully charge Li-ion in less than one hour. Last updated 2017-03-03
Hmmm.
I'm guessing that my last trip to the Hawthorne Supercharger was on an "so-called ultra-fast charger" ... what are we missing here?
Thanks for any answers-- Sorry for the rant-- Vern
Let me answer some of your questions. I had my Model S for 3 years and 115,000 miles. I also have access to the battery data thought the CAN bus so I was able to learn what the battery does and what the car does. I also bought my first EV back in 1992 and kept up with battery development all those years.
Lithium batteries age (degrade) faster with higher temperatures and with higher state of charge. So it's not good to keep the batteries hot nor is it good to keep them fully charged all the time. Neither is the case in an EV, especially not with a Tesla as it keep the battery temperature within a healthy level without us having to do anything. And if you keep the charge level to 90% or lower you are totally on the save side. Charging to 100% is not bad. Keeping the battery at 100% for longer is bad. So no worries about charging fully and then start driving. That's fine.
Lithium batteries have no memory effect. Battery capacity is not measurable like say water in a glass. How much capacity is left is a combination of voltage and temperature and measuring how much energy was added in and how much was taken out. It's not 100% accurate and it gets especially difficult to calculate the exact capacity when the battery is charged and discharged partially for a while. The calculations errors just add up. It can easily be calibrated by charging to 100%. It's not memory effect.
Balancing is another one of these myths that are overly discussed and misinformation is spread. When batteries are connected in series, they need to have the same capacity or else the one cell with the lowest capacity will limit all the other cells to the same. Again, that is something that Tesla takes care of in a very sophisticated way without needing any attention or us doing anything. My battery pack is over three years old and has 115,000 miles on it and the differences between the modules is less than 0.1%. That is amazingly good and for such an 'old' and much used battery. My battery has aprox 460 full cycles on it and lost about 7% capacity. But keep in mind that most of the capacity loss (degradation) happens in the beginning and then slows down over time/age. In other words, in another 3 years from now my battery won't have lost 14% but probably much less because degradation slows down.
Fast charging does not hurt the battery. I have used Superchargers for more than half my miles driven and my degradation is above average. I also live in a rather warm climate and drive a lot in hot climates (California, Arizona, Nevada).
Outstanding information! I'm going to quit worrying about a lot of battery issues that I've been worrying about. Thank you.
David have you written elsewhere about your history with EVs? I'd like to read it.
Edit: I see that you have 7 videos on YouTube (looking at your YouTube: Sharkcookie.ev). I'm going to look at all of them before I pester you (or anyone else here) with questions. Many thanks.
David have you written elsewhere about your history with EVs? I'd like to read it.
Edit: I see that you have 7 videos on YouTube (looking at your YouTube: Sharkcookie.ev). I'm going to look at all of them before I pester you (or anyone else here) with questions. Many thanks.
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Why do you say balancing is a myth? Every two or three months my 90D will lose a couple of miles that is easily recalibrated by driving it down to 10-20% and then charging up to 93-100%. This was all very well documented in wk057's research. It seems to be more a software algorithm thing in the BMS than a battery issue.
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