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HVB, my expectations are proving to be correct


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8 replies to this topic

#1 OFFLINE   rbort

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Posted 25 April 2018 - 07:55 PM

Today I drove my Cmax 90 miles.  I used the HVB piecemeal during the first 74 miles and the temp of the HVB reached a max of 71F.  The outside temperature was about 56F.  

 

I stopped at a 240v charger and plugged in the car to charge up the HVB.  I sat in the car while charging.  I noticed the HVB temperature going up during charging, as well as the fan inside the car was racing after some time (started out slow as usual).  I charged it over an hour from empty to 60% on the HVB.  The HVB temperature rose from 71F in front of me to 75F whiile charging.

 

Then I drove 16 miles back home 100% EV and drained the HVB back to 0%.  The temperature rose further to 80F during this drive.  When I got home the HVB was at 15.9% SOC and I always plug it in right away to recharge the hybrid battery as the charge level drops further when the battery cools and I don't want it to drop below 15%.  So I plugged in the battery to recharge on 110v to bring up the hybrid battery back over 22%.  That process on 110 took 32 minutes and during this time the HVB DROPPED from 80F down to 77F.

 

So what did I observe today?  Like I always said, charging on 240v generates more heat inside the car which in turn raises the HVB temperature.

 

Charging on 120v makes less heat in today's conditions (fan in car on slow) and in fact actually lowered the HVB temperature.  Now it could be possible the 80F is too high and while charging on either 120 or 240 and the temp was going to drop anyways to the upper limit closer to 75F given the OAT is 55F, but I still believe that 240 can warm up the battery while charging more so than 120v.

 

Edit:  Just went down to check the HV battery, now at 73F and the charge dropped from 23% SOC that I brought it up to down to 19% now, a 4% drop in SOC due to the battery cooling down.  That's why I do this, bring it back up some and then let it rest, I won't charge it up any more until tomorrow.

 

Edit #2:  I plugged the HVB back in and charged it for another 22 minutes.  The HVB went from 19% SOC to 24.3 SOC.  The temperature of the HVB dropped some more from 73 to 71F.  So what this is showing is that having the car plugged into 120v and charging is dropping the HVB temp due to the fan running, however, having it plugged into 240v earlier this evening raised the temperature from 71F to 75F.

 

This is what I am seeing with my Cmax, and this is what I expected or thought would be the case even without the tool to see it (scangage).  Then it would make some sense that if you set value charge to start charging at say 10am that during the summer months plugging the car in when I get home in the evening/night would be beneficial to having the fan run all night without charging to cool the pack down, that is, if the garage temperature is actually cooler than the battery pack.  If not its useless.

 

-=>Raja.


Edited by rbort, 25 April 2018 - 08:28 PM.








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#2 OFFLINE   SELT

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Posted 26 April 2018 - 10:32 AM

Hi Raja,

 

Thanks for sharing your charging observations. I'm starting to really see the value in acquiring a scangage.

 

Quick questions:

 

1) After you completely depleted the HVB and was using the "hybrid" battery, why didn't you want it to drop below 15% and keep it above 22% SOC?

 

2) I didn't understand your last paragraph. You mentioned setting value charge to start charging at 10am in the summer... why at 10am?

And "plugging the car in when I get home...the fan run all night without charging"... how do you have the car plugged in, without charging?

 

Sorry if these are dumb questions  =(   just trying to fully understand...

 

Thanks.

Jr



#3 OFFLINE   rbort

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Posted 26 April 2018 - 02:55 PM

On lithium batteries, typically for best life you don't want to drain them much below 20%.   The system does hybrid mode from 21.5% down to about 15%, but the battery is still hot at the moment you get home.  When the battery cools, the % charge of the battery can drop say 4%, and if you left the car at 16% when you got home a few hours later it could be down to 12%, pretty low.  This happened to me once in the first car, and when I pushed the button to power up the car the engine started right away.  I was surprised why it started, but after a second I realized the HVB was waaay too low.

 

So now when I get home I bump it up to a full hybrid battery plus a couple of %, say 1 to 5%, and then unplug it to rest.  Charge it later if I don't need it the next day.  This prevents the battery voltage from dropping too deep of a discharge.

 

#2, in the situation where the battery is hot, and the garage is cooler, you could plug the car in right away and set the value charge to start at 10am.  This assumes you arrive home at night with a dead battery that's warmed up.  Now what happens is that the fan will run while plugged in, but the car will not charge the HVB until 10am.  Running the fan will air cool the battery pack and bring the temp down faster, assuming the air temp in the garage is cooler than the battery.  If its hotter than the battery then this won't work obviously.

 

So ideally, get home, plug the car in, charge now.  Wait 1/2 hour for the hybrid battery to fill up and you're say 1 to 5% charge level indicated on the MFT screen, and then switch the car to value charge.  It will stop charging and wait until 10am to start charging.  I wake up before 10am usually, so I can unplug it if I don't want to charge the car.  You can change the 10am time earlier if you do want to charge the car for tomorrow, and then you get the benefit of cooling the battery for several hours and then charging it.

 

So let's say you need to leave the house at 10am, you can set the value charge to start at 4am.  Plug the car in at 9pm and by 9:30 switch it to value charge.  Now it will wait from 9:30 to 4am before it starts charging and will be full on departure time of 10am.

 

This is alot better than plugging it in at 9pm and having it charge right away, then the temp of the battery won't drop most likely because its charging, and you get heat soak for longer along with a higher charge level which is bad x 2 for the battery.  The less time you spend at 100% waiting to be used the better, so never charge the battery back to full and leave it sit.  Instead, charge it before you leave so its at 100% on departure.

 

Make sense?

 

-=>Raja.


Edited by rbort, 26 April 2018 - 02:56 PM.


#4 OFFLINE   Tom_NC_1

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Posted 27 April 2018 - 04:53 AM

Raja and I have completely different charging philosophies. Raja is the model for conservative gentle treatment of the HVB. Anyone taking the time to follow Raja's charging routine is likely to have a long lasting HVB.

 

I learned the hard way about the ill effects of overheating the HVB during the summer of 2015 when my HVB lost about 1kWh of capacity. The lesson learned was that to protect the HVB active temperature management was needed especially since I live in a climate with quite hot summers. This is why I got a ScanGauge. Since actively managing the HVB temperature I have have virtually no additional capacity loss.

 

I use a level 2 charger at home and do not want to take the time to manage partial charging the HVB. I never charge the car it the HVB is 95ºf or higher. I usually charge the car to full after arriving home in the evening. This allows the car the maximum amount of time for the HVB to cool before the next days drive. In the years since 2015 Charging the HVB to 100% and keeping it full all the time has not had any adverse effect. The SOC through the ScanGauge shows 95% on a full charge.

 

Generally if the overnight lows are 70ºf or below two charges per day are possible. If the overnight lows are around 80ºf the HVB will not likely drop enough overnight to charge at all. Usually there is a week or two during the summer where the outside temperature is not low enough to safely charge the car so it is only driven as a hybrid.

I don't worry about an uncharged HVB as the worst case is about 15% SOC if the Hybrid portion is also completely depleted and that would be a rare event. The lowest my depleted HVB ever gets is generally about 18% SOC. So if the HVB is hot and depleted I would not bother to plug in until later or all in the hot summer.

 

I have almost 5 years and 69k total miles with over 48k EV miles on the C-Max so far. The lesson learned for me was that managing the HVB temperature to prevent overheating is critical in maintaining a healthy HVB. Everything else is secondary. You can be very conservative like Raja or fairly aggressive like myself and it will not likely make much different as long as the HVB is not overheated.  

 

Tom



#5 OFFLINE   rbort

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Posted 28 April 2018 - 07:09 AM

Wow, I just spoke about this and it happened to me yesterday, crazy....I was driving around boston for some time, used up all the HVB and in hybrid mode.  Battery charge level somewhere between 16-17% SOC on average.  I parked the car (not at a charger like I most always do) and went in a restaurant to get some dinner.  When I got back to the car and powered it up, the engine started right away!  I quickly looked at the dash and the hybrid battery was empty!  Just a sliver of blue on the bottom the SOC showed 8.9% only, crazy low NOT good.  :(

 

So the engine started charging it and I drove immediately to a charger where I plugged the car in and gave it some time to get back to 30% SOC.  At that point I saved that charge until I was on the final stretch home.  When I got home I plugged the car in and brought the charge back up to 22.2%.  This morning it was back down to 18.9%.

 

So what's the lesson learned from this for me?  Do NOT get into the hybrid battery unless its the last trip home or to a charger.  Always go into EV later and save the last few % of charge level if the car needs to stop here and there to prevent the deep discharge drop.

 

I took a picture shortly after I saw the issue last night to show you folks, this is what I was talking about above.

 

Just one more thing to keep track of if you want to minimize the HVB capacity losses over time.  Remember folks, its not just one thing that hurts the HVB, yes some are less significant than others but they all count and are additive to the loss gap over time.

 

-=>Raja.

Attached Files


Edited by rbort, 28 April 2018 - 07:13 AM.

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#6 OFFLINE   blandman

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Posted 01 May 2018 - 02:33 PM

I may be misunderstanding the problem that has been observed. Virtually every day of my daily commute over the last 5 years I have used all the available HVB capacity (although I use the ICE to get over the low pass between Half Moon Bay and San Mateo to save electrons). I then plug in at work (L2) and at home (110v plug) with very little effect on the battery. The only precaution is the I never charge when the outside temperature is 87 degrees or above.

#7 OFFLINE   P=E/t

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Posted 11 May 2018 - 05:06 AM

There’s another thing to consider about HVB temperature.

If one charges from low SOC all the way to full (not just “topping off” the last 10-20%), then the HVB is extremely heat-labile once you start to drive. In other words, under similar ambient temps, routes and driving styles, a just-charged battery will heat up much faster than one that ended its charge 4-7 hours ago.

#8 OFFLINE   P=E/t

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Posted 11 May 2018 - 05:06 AM

There’s another thing to consider about HVB temperature.

If one charges from low SOC all the way to full (not just “topping off” the last 10-20%), then the HVB is extremely heat-labile once you start to drive. In other words, under similar ambient temps, routes and driving styles, a just-charged battery will heat up much faster than one that ended its charge 4-7 hours ago.

#9 OFFLINE   P=E/t

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Posted 11 May 2018 - 05:07 AM

And why that posted twice is totally beyond me. Sorry folks.








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