Charge Strategy for Max Battery Life

Discussion in 'Clarity' started by Steven B, Apr 18, 2018.

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  1. Viking79

    Viking79 Well-Known Member

    That SAE paper probably clues into why the engine runs so much in extreme cold, as it is heating the battery with engine coolant as I was guessing. If car is parked in attached garage it takes very cold days of around 0F or less ambient to start the engine. Looking at that paper the trigger is 32 F battery temp which triggers it, which is about right for my garage temperature (garage is maybe 25 F on those cold days, but battery is insulated and takes time to drop after charging, etc).

    The paper also shows the worst charging efficiency at 88% for 240V (assuming all energy lost is in the form of heat, maybe that isn't a valid assumption for the battery), which is better than my pessimistic self gives it (I usually say 80%). It shows max heat rejection as 860 W for Battery, DC-DC, and Charger. It also shows most of the losses in the charger, I figured it would be the battery.

    The Clarity only is 311 V Nominal (168 cells in 84s2p format, so this puts it at a pack size of 12.4 kWh usable, which is more inline with what I expected if it is 20 Ah for each cell usable, of 27.3 Ah rated, which would be ~17 kWh at 311 V).

    I love all these technical papers you are dragging up specific for the Clarity, keep up the great work :)
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  3. AnthonyW

    AnthonyW Well-Known Member

    What throws me is the watts heat rejection. What does that translate into in terms of degrees temperature cooling. For instance, with you houses heat pump you are told that if the the conditioned air is 20 degrees cooler than the return duct air you are good. Can the watts heat rejection be translated into a similar example. And the battery portion only has 30 watts of heat rejection specifically. So if the coolant is hotter than the battery’s upper limit while charging, the coolant will bypass the battery which is not good for long term life. Just wondering if I should skip charging at work when it is really hot out?

    Sent from my iPhone using Inside EVs
  4. ab13

    ab13 Active Member

    Figure 6 tells me the battery pack dissipates 30 W during charging. Figure 5 says at max battery use it could be 400 W during driving. The target max battery temp is 35 C, so if it's 40 C outside, it may be better not to charge.

    K does stand for Kelvin, which is equivalent to Celsius, the starting number is different, 0 K is absolute zero.

    The thermal resistance is what indicates the change in temperature to heat removed. I need to look at this a little more to see what it says, the battery and system information are mixed together.
    Last edited: Jun 25, 2018
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  5. KentuckyKen

    KentuckyKen Well-Known Member

    I’m just thankful it’s cooled at all unlike a friend’s Leaf that is on its second battery and that one is losing capacity as well. With garaging to buffer the worst temperature swings much of the time, I’m not expecting to have any problems. But I am using some of the charging tips from this thread. Many thanks to those who shared them.
    Viking79 likes this.
  6. Steven B

    Steven B Active Member

    I don't think we have enough information from this to make decisions on an ambient temperature limit above which charging should be avoided. As time goes by with the vehicle parked in the heat, the water temperature should approach the ambient temperature and given adequate time would be greater than their stated optimum battery temperature max of 35C. However, based on the tone of the article, it appears that the most stressful scenario is "high-load CS [Charge Sustaining] driving" rather than battery charging.

    I'd instead point you back to an earlier link. Take a look at slides 24 and 26 of this to see the effects of charging at 45C, 25C and 5C:

    Slide 26: The x axis is number of cycles and the y axis is percentage of nominal capacity, so as the charge cycles add up, charging at elevated ambient temperatures will cost you. At 25C, your battery will lose 15% of its capacity after around 3000 cycles, but it will take only 1400 cycles to lose the same amount of capacity at 45C.

    One thing I noted was that when charging at 45C, degradation happened twice as fast if you charged all the way to 100% than if you stopped at 90%. That's one reason I wanted Honda to tell us what the margins are on the top end and on the bottom end. WE DON'T ACTUALLY KNOW HOW CLOSE TO THEORETICAL 100% CAPACITY WE HAVE CHARGED THE CAR WHEN IT STOPS CHARGING AND THE APP SAYS 100%. I've been adjusting my charge schedule daily to stop just prior to app 100% just in case.
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  8. ab13

    ab13 Active Member

    That's probably why I see people with BEV recommended charging to 80 or 90%. The app should have that feature, which would also fix the downhill battery full situation.

    In the battery pack degradation pdf, it gives a temp of 56 C for max battery operation.
    Last edited: Jun 25, 2018
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  9. ab13

    ab13 Active Member

    After looking at it a little more the important details are from the batter pack deterioration PDF, which indicates the MAX battery pack temperature should be 56 C in operation. On the SAE paper, page 4, section 2 says the battery upper limit temperature should be within 15 degree C at the high temperature condition, which I conclude is 40 C ambient from table 2. That makes sense in that it would be 55 C, so it's about the same limit as the 56 C given in the degradation document.

    On page 5, it says they will target a 12 degree temperature difference, so they are giving a 3 degree margin under the 15 degrees that is the upper limit. Figure 12 is showing contributions to temperature change by the components. The main one to look at is the radiator out, which results in the cooling fluid being 4 degrees above ambient, which means the 12 degree difference over ambient the battery temperature is allowed is reduced to 8 degrees. So the cooling system has to remove the battery heat with only an 8 degree rise going across the battery. The other components, charger and DC-DC converter are cooled after the battery and can take higher temperature changes.

    They used this to determine the flow rate needed for the cooling fluid. They determined there should be a 2.3 K/W thermal resistance per cell to the cooling jacket. This number doesn't help understand the figure 12 though, because you'd need to know the number of cells and a little better detail on the flow path. I estimated the number of cells at 168 by the battery pack size and battery specs, but I don't know if that's accurate. If it's 168, then for 400 W heat rejected by the pack, it's 2.38 W per cell. This is still an average, assuming the battery pack is uniform, etc... That means if a cell has a 2.3 K/W thermal resistance, and it dissipates 2.38 W, then the temperature rise of the cell would be 5.47 degrees (2.3 K/W * 2.38 W). So that does stay within the range of 8 degree that are allowing for the design. Although the cells at the end of the cooling would see some higher fluid temperatures, so I don't think the gap between 8 and 5.47 isn't as big a margin as it appears.

    The curious part is what goes on in the EV, which isn't seen from the preview document. The EV appears to have 3 battery banks instead of 2 on the PHEV.
  10. insightman

    insightman Well-Known Member Subscriber

    The Clarity PHEV review by The Drive confirms your 168-cell calculation: "a 17-kWh, 168-cell lithium battery." Calculating based on 168 cells/17 kWH, the 25.5 kWH Clarity Electric battery pack would have 252 battery cells.
  11. Steven B

    Steven B Active Member

    In my wish list for app improvements, I listed being able to schedule the charge to stop at a percentage:
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  13. KentuckyKen

    KentuckyKen Well-Known Member

    StephenB and ab13, you are now officially members of the Clarity Brain Trust. Some other posters here are already on it. Thanks for making the technical information understandable.

    PS: I’m not smart enough to be a member of this august body; I’m just the unofficial Recording Secretary.
    Steven B likes this.
  14. AnthonyW

    AnthonyW Well-Known Member

    Yes, StephenB and ab13, very helpful in making sense of all this. It is comforting to know that 25% to 27% of the battery is reserved and not usable. It would be awesome to know how much is allocated to the top and bottom of the SOC.

    I sent feedback on the Hondalink app asking for the option to stop charging at a certain percentage. In the meantime, I have created a spreadsheet to calculate how much time it takes to charge to a certain percentage target from a certain starting percentage, ambient temperature, a defined starting time, and specific power source (120v/15a, 120v/20a, or 240v/32a). That way I can set the timer on my Wifi Smart Plug at home and track the timer on Level 2 chargepoint at work. Been able to consistently hit my percentage charged target (usually 80%, 90% or 50%) very consistently so far.
    KentuckyKen likes this.
  15. KentuckyKen

    KentuckyKen Well-Known Member

    AnthonyW, that’s a great idea. Would you be willing to share your spreadsheet?
  16. Clarity 4 life

    Clarity 4 life New Member

    I agree with this statement.
    Invest in your time to enjoy life!!!
    MPower likes this.
  17. thecompdude

    thecompdude Member

    I still don't see the option to stop at a specific percentage. Is there a way to achieve this.

    I want to limit my battery charge to 90%, as I live at the top of a hill. The moment I leave my driveway, I am going down a steep incline and the car starts the ICE to absorb the Regen braking energy. I would like to avoid it!
  18. PHEV Newbie

    PHEV Newbie Well-Known Member

    Because I run a lot of errands and have time to charge in between, I keep my battery between 50-80%. On my OEM 120v charger, it's very consistent that I get 8% charge per hour so I just set a timer and then shut off the charge from my Honda App. I charge to full once or twice a month for cell balancing. For battery longevity, Tesla recommends that you charge their cars to 80% maximum for every day use and then charge to full at least once every 3 months for cell balancing.
  19. Mowcowbell

    Mowcowbell Well-Known Member

    While there is not a stop at a specific percentage option in the HondaLink app, there is a option to start and stop at a specific time. I have figured out with my 16amp Level II EVSE, I get about 11 miles per hour of charge. Each 11 miles is roughly a 25% battery state of charge. I adjust the stop time if I need a bit more charge (or less) to put me about at 80% charge level when I start my commute each day.
  20. KentuckyKen

    KentuckyKen Well-Known Member

    While not charging completely will take care of your problem, you might try what worked for me on my slight downhill. I started avoiding using the paddles and just used the pedal. And then I don’t wait to the very end so I avoid a hard, all at once, braking and regen. That fixed the ICE start up for me. You’ll have to see if it works for you. Your downhill may be too steep for it to work for you.
  21. MNSteve

    MNSteve Well-Known Member

    Do you think that your braking pattern was different based on whether you were using the paddles or the pedal? I can understand this technique working if by using the pedal you were spreading out the braking over a longer period, but otherwise I don't understand how it would matter whether you invoked the braking using the paddles or the pedal. Just trying to understand the difference.
  22. KentuckyKen

    KentuckyKen Well-Known Member

    I see what you mean. I use the paddles but end up in 4 chevron regen and that’s when the ICE would come on (and once when I had to panic brake for an idiot driver). Using just the pedal, I seem to be better at spreading out the regen over a longer interval. Like you say, that’s probably the reason since it avoids a high peak of regen in a short time and anyway of accomplished that would work.
    Or it could be that after 6 months, my battery has mellowed out
    I’ll have to try all paddle after charging and see if it goes back to its old ways.
  23. MNSteve

    MNSteve Well-Known Member

    The reason that I asked is that I am trying to convince folks, myself included, that there is no magic in the paddles - that if you change the speed from X to Y in Z feet, that the amount of regeneration you get is the same whether you use the paddles or the pedal. The caveat is that you have to keep the amount of braking required below what triggers the friction brakes, which isn't an issue for the paddles. You have illustrated another difference in the sense of triggering the ICE.

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