Keeping it plugged in - 2018 Honda Clarity Forum
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post #1 of 15 (permalink) Old 02-22-2020, 10:51 AM Thread Starter
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Keeping it plugged in

About to take delivery on mine (finally).
What are the collective wisdom of keeping it plugged in? I do know that for small consumer equipment like cell phones and laptops using Lithium Polymer cells, keeping them plugged in when they are already fully charged is not a good thing as the short cycle at high charge state reduces the total charge capacity and cells to swell. Some equipment has protection against this by reducing the total charge if it sees constantly plugged in behavior.


How does Clarity manages the battery? If I keep it plugged in after charging is completed, I would expect the charging to stop as the car has charge controller onboard. However, as the car sits, the charge will naturally drain. Would the charger in the car short cycle the battery keeping it topped off? (Bad for the cell longevity.) Or will it "cut the top" to prevent short cycling but reduces the available EV range?


For the sake of argument, let's assume that the car is used daily during the week for 25 mile commute, and it is plugged into Level 2 EVSE when parked overnight.
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post #2 of 15 (permalink) Old 02-22-2020, 11:29 AM
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It's safe to leave it plugged in.

The Clarity has an automatic power cut off built in.

If you were to leave the Clarity plugged in when you left it unattended for days, weeks or months the car would still maintain charge.
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post #3 of 15 (permalink) Old 02-22-2020, 01:56 PM Thread Starter
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Yes, I understand it will stop charging automatically. The concern is that if the charge control circuit will allow short cycling or "cut the top" to prevent short cycling.

Here is a bit more detailed explanation on what I am talking about.
https://electrek.co/2018/05/04/are-y...ium-batteries/


In essence, if the charger keeps the charge levels at high charge levels for a long time by continuously cycling between above 80% and 100%, it dramatically shortens the life of the battery. Most commonly, this happens when the equipment is constantly left on the charger where the charger will cycle on frequently to keep the charge at near 100% level.


To combat this, certain manufacturer implements what they call "cut the top" where if they detect that user has a habit of leaving stuff continuously on charger, they force a discharge to 80% level to prevent cycling at above 80% levels.


Lithium chemistry being what it is, there is no perfect answer but knowing how Honda manages the battery and the charge levels will help me adapt my own behavior so that I am not prematurely wearing out the battery on a car that I am planning to keep for a long time.


For example, I would plug it in when I come home. Should I remove it from charger before I go to sleep? Or should I just leave it until when I go to work in the morning.
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post #4 of 15 (permalink) Old 02-22-2020, 03:46 PM
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The Clarity isn't the Leaf. There is a computer controlled buffer at both the top and the bottom of the Clarity's battery that is kept empty to avoid the chemical changes that occur in LiON batteries that are fully charged or discharged. (The Leaf doesn't have these buffers.)

Leave it plugged in.

2018 Honda Clarity Touring PHEV - Forest Green w/Tan interior (wife's car)
2017 Volt LT - Heather Gray; black bow ties, Charcoal VoltShelf
2012 Cruze ECO MT (hail totaled 5/8/17 103,600 miles @42.5 MPG)
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post #5 of 15 (permalink) Old 02-23-2020, 05:56 PM
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Originally Posted by N21HV View Post
What are the collective wisdom...
Now, THERE'S an assumption...

Once the Clarity is charged it stops accepting current and signals the EVSE to stop sending it. There are no background processes running once the car is shut-down - it's not a Tesla - so there's no "phantom drain" occurring - and the amount of power that a small Li battery like this loses while resting is so insignificant that it doesn't even register. Plus Honda has selected a very stable battery chemistry, locked-off both upper and lower buffer capacity and liquid-cooled (and heated) the battery to maintain its optimal temperature.

That said, when the weather is cold or hot I keep the Clarity plugged into the EVSE so that I can pre-condition the cabin when necessary. When the weather is mild I don't bother charging until the charge is depleted.
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post #6 of 15 (permalink) Old 02-23-2020, 10:57 PM Thread Starter
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"locked-off both upper and lower buffer capacity"


Ah, there's the key nugget there. That implies (not sure if I can find the technical documentation on that somewhere) that they already implemented "CTT (Cut the Top)" from get-go and therefore, that is already factored in (maybe out in this case?) the capacity claims and computations.


Good to know. Thank you.
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post #7 of 15 (permalink) Old 02-24-2020, 09:22 AM
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Quote:
Originally Posted by N21HV View Post
"locked-off both upper and lower buffer capacity"


Ah, there's the key nugget there. That implies (not sure if I can find the technical documentation on that somewhere) that they already implemented "CTT (Cut the Top)" from get-go and therefore, that is already factored in (maybe out in this case?) the capacity claims and computations.


Good to know. Thank you.
It's factored into the EV mileage claims and computations. Honda reports "usable" battery size and not the actual battery size. Chevy and Tesla report actual and not usable, leaving people to determine usable by observation.
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2018 Honda Clarity Touring PHEV - Forest Green w/Tan interior (wife's car)
2017 Volt LT - Heather Gray; black bow ties, Charcoal VoltShelf
2012 Cruze ECO MT (hail totaled 5/8/17 103,600 miles @42.5 MPG)
2010 Mit Lancer GT MT (traded for ECO @31K miles)
2002 Pont Montana AWD - title to son at college graduation
1990 Pont Transport (traded for Montana @240K miles)
1986 Fiero GT MT (traded for Transport - needed more seats)
1985 Fiero 2M4 MT (traded for Fiero GT @8K miles)
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post #8 of 15 (permalink) Old 02-24-2020, 12:38 PM
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Originally Posted by obermd View Post
It's factored into the EV mileage claims and computations. Honda reports "usable" battery size and not the actual battery size. Chevy and Tesla report actual and not usable, leaving people to determine usable by observation.
Tesla doesn't quote or make available any info on battery capacity.
The old 60, 70, 85, 90, 100 nomenclature had only a nominal relationship to battery size, and the now only use "Standard Range" "Land Range" and "Mid Range" (no current model offerings for Mis Range but they do have EPA test ratings for them).

Although I lean towards less regulation, I think the consumer needs to have both the total and usable pack numbers clearly stated. It is unlikely that they will do this voluntarily.
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post #9 of 15 (permalink) Old 02-25-2020, 11:41 AM
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Originally Posted by DucRider View Post
Tesla doesn't quote or make available any info on battery capacity.
The old 60, 70, 85, 90, 100 nomenclature had only a nominal relationship to battery size, and the now only use "Standard Range" "Land Range" and "Mid Range" (no current model offerings for Mis Range but they do have EPA test ratings for them).

Although I lean towards less regulation, I think the consumer needs to have both the total and usable pack numbers clearly stated. It is unlikely that they will do this voluntarily.
I missed that the M3 and MY don't show battery capacity anymore, but they're easy to calculate from www.fueleconomy.gov. The M3 standard is a 60 KWh usable battery and the M3 long range is an 85.8 KWh usable battery. Assuming a 10% buffer this would be a 66 KWh and a 95KWh battery, respectively.

The initial Model Y also has an 85.8 KWh usable battery.

The calculation is relatively simple: Range * KW / miles = usable battery size in KWh.

2018 Honda Clarity Touring PHEV - Forest Green w/Tan interior (wife's car)
2017 Volt LT - Heather Gray; black bow ties, Charcoal VoltShelf
2012 Cruze ECO MT (hail totaled 5/8/17 103,600 miles @42.5 MPG)
2010 Mit Lancer GT MT (traded for ECO @31K miles)
2002 Pont Montana AWD - title to son at college graduation
1990 Pont Transport (traded for Montana @240K miles)
1986 Fiero GT MT (traded for Transport - needed more seats)
1985 Fiero 2M4 MT (traded for Fiero GT @8K miles)
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post #10 of 15 (permalink) Old 02-25-2020, 04:48 PM
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Quote:
Originally Posted by obermd View Post
I missed that the M3 and MY don't show battery capacity anymore, but they're easy to calculate from www.fueleconomy.gov. The M3 standard is a 60 KWh usable battery and the M3 long range is an 85.8 KWh usable battery. Assuming a 10% buffer this would be a 66 KWh and a 95KWh battery, respectively.

The initial Model Y also has an 85.8 KWh usable battery.

The calculation is relatively simple: Range * KW / miles = usable battery size in KWh.
Even the S and X no longer have any number associated with them.

Your calculation method could be correct if charging was 100% efficient (assuming you meant kWh and not kW and are deriving that from the kWh/100 miles on the Monroney). The kWh/100 miles calculation is "from the plug" and includes charging losses.

In reality, the M3 LR took 89.406 kWh to fully recharge on both the hwy and UDDS portions of the EPA application. At 90% charging efficiency (unless Tesla is vastly different than any other manufacturer, this is a good number +/- ~1%) the usable capacity would be 80.5 kWh. This is very close to the capacity that can be derived from the 350V and 239 Ah reported in the EPA data. If their charging efficiency was closer to 88%, the usable battery would match the 78 kWh reported by other sites

Tesla has a buffer much smaller than 10% and recommends that owners not charge to 100% on a regular basis, but only when needed for long trips. The have a slider that allows you to select any charging % (virtually every Turo Tesla rental will charge you an extra fee if you mess with the "standard" 90% setting)

https://iaspub.epa.gov/otaqpub/displ...d=48706&flag=1

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