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TomT
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Re: Electrical charging - measured results, 120v vs. 240v

Mon Jan 17, 2011 10:48 am

Interesting since, depending on local topographical conditions and SOC requirements for a given driver, the brakes on the Leaf could actually wind up being used more than those on an ICE vehicle, and perhaps lasting less long...

garygid wrote:Since, in high-SOC, long-downhill situations, the disc brakes are your ONLY speed-regulating mechanism, they will need to be very heavy duty discs and pads, and the brake assembly will get, most likely, VERY hot.
Leaf SL 2011 to 2016, Volt Premier 2016 to 2019, and now:
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DaveEV
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Re: Electrical charging - measured results, 120v vs. 240v

Mon Jan 17, 2011 11:38 am

garygid wrote:Since, in high-SOC, long-downhill situations, the disc brakes are your ONLY speed-regulating mechanism, they will need to be very heavy duty discs and pads, and the brake assembly will get, most likely, VERY hot.
We covered this months ago... do we really need to do this again?

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garygid
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Re: Electrical charging - measured results, 120v vs. 240v

Mon Jan 17, 2011 12:03 pm

Sorry, I thought that we were discussing newly-discovered details if Regen, and how they will impact us. Maybe I was confused.
See SOC/GID-Meter and CAN-Do Info
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AndyH
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Re: Electrical charging - measured results, 120v vs. 240v

Tue Jan 18, 2011 4:19 am

DaveinOlyWA wrote:80% provides a maximum level of safe reliable charging. Now that does not mean that 100% is not safe or risky. But as much as we would like to think we have battery management down, in actuality there are several things that are not completely understood.
I'm sorry Dave, but I have to respond here. I build battery packs with lithium cells, and do custom battery management system builds/installs for LiFePO4, LiMn, and LiPo packs. What I'm trying to say is coming from the cell-level looking 'up' the complexity scale, if that makes any sense.

In general, rechargeable lithium cells do give a very long life when 80% of capacity is used. No argument here at all. But this is 80% of the TOTAL capacity of the cell. It can be difficult for the general public to find total capacity numbers, because many manufacturers report consumer max/min voltages or consumer capacity rather than 'ultimate'.

Let's design a battery - we want to use 80% capacity for long life and want to set the max and min voltage for our new pack. Let's use A123-Systems LiFePO4 cells.

Our first stop is the publically-available datasheet from the A123-Systems website:
http://www.a123systems.com/cms/product/ ... 650M1A.pdf
Recommended standard charge method 3A to 3.6V CCCV, 45 min
Recommended fast charge current 10A to 3.6V CCCV, 15 min
Maximum continuous discharge 70A
Pulse discharge at 10 sec 120A
Recommended pulse charge/discharge cutoff 3.8V to 1.6V
We see two 'end of charge' voltages - 3.6V for standard 'continuous input' charging and 3.8V for pulse charging. We'll use continuous, so will set the BMS to 3.6V.
The pulse discharge low voltage point is 1.6V, but we notice that their continuous load charts use 2.0V for the low voltage point. We'll use 2.0V for the 'empty' but will make sure our cells don't drop under 1.6V when loaded. So far so good.

Now we start to think/worry/analyze/what-if. We believe that using 80% of total capacity will give us a longer life - but are our numbers 100% or 80%? Should we contact A123-Systems and get a capacity chart and select more conservative numbers for our management system?

(Here's where we'd likely register with A123-Systems as a developer and get access to the ultimate numbers. We're not doing that, so let's see what else we can find from public sources.) Here's a report from a June 2006 Plug-in Prius conversion fire that includes developer-level info from A123-Systems:
http://www.evworld.com/library/prius_fire_forensics.pdf
Maximum cell voltage 3.85 volts recommended; 4.20 volts absolute
Minimum cell voltage 1.60 volts recommended; 0.50 volts absolute
Our public datasheet max is 3.6V, yet 3.85V is the 'recommended' max and ultimate is 4.20V
Same for minimum - 2.0, 1.6, and 0.5.

All Right! The numbers we've selected - 3.6V and 2.0V are 80% of ultimate capacity - we don't have to restrict any further because we're ALREADY at the desired 80% point.

Bottom line for us Leafers is that we do not have to second, third, or fourth guess the cell or pack voltages or charge level because Nissan has already included a capacity buffer top and bottom for their pack. We do not have access to the ultimate 100% of the capacity the way RC modelers or DIY-Ebikers or DIY EV builders do - Nissan has designed and delivered a consumer-grade product that we can simply plug-in and use.
DaveinOlyWA wrote: Add to that he changing capacities of the pack based on temperature age, depth of discharge, etc.
We know that the car is capable of measuring capacity, temperature, cell age, internal resistance/degradation, current in and out, and depth of discharge. We also know that this info is reported thru the car on the network. We also know that Nissan's been at this 'lithium' thing for a very long time. I don't expect there's a chance in the world that they'd field a car without knowing absolutely how to manage the battery - and it appears from the info we have that Nissan is properly managing the pack.
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DaveinOlyWA
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Re: Electrical charging - measured results, 120v vs. 240v

Tue Jan 18, 2011 6:12 am

AndyH wrote: We do not have access to the ultimate 100% of the capacity the way RC modelers or DIY-Ebikers or DIY EV builders do - Nissan has designed and delivered a consumer-grade product that we can simply plug-in and use.
therein lies the confusion and i guess we have to either ignore Nissan's warning (recommendation) to not use 100% on a regular basis. my comment above is an attempt to explain that statement.

what i said is NOT my personal belief. i personally do not think 100% or QC hurts the longevity of the pack in anyway. and i agree that Nissan would not allow access to the true 100% level. i wish i had the time and money (would need two cars) to do a side by side. one ONLY charged at QC and the other normally. i be willing to bet the long term battery life differences would be neglible

many here report brief spikes after charging which is most likely the pack self balancing itself which is something that really cant happen if the pack is truly at 100%
2011 SL; 44,598 mi, 87% SOH. 2013 S; 44,840 mi, 91% SOH. 2016 S30; 29,413 mi, 99% SOH. 2018 S; 25,185 mi, SOH 92.23%. 2019 S Plus; 2640.9 mi, 99.37% SOH
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AndyH
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Re: Electrical charging - measured results, 120v vs. 240v

Tue Jan 18, 2011 6:58 am

Right. I'm not sure what the spikes represent. It's more likely that the BMS balances regularly rather than waiting for end of charge, but I don't know that for sure.

I've been thinking about Nissan's recommendation that 80% is better when it gives us the range we need. The best I can come up with this morning is that it may be a combination of minor factors.

If an owner drives 30 miles every couple of days, it's going to be easier on the battery to charge to 80% every couple of days rather than keeping the car on the charger and continually topping it off to 100%. The two very slight negatives are constant topping and 'storing' the pack fully charged. Another factor is time-based degradation. This type of use is closer to storage, so 40-60% SOC may be best for longest life.

If an owner drives 80 miles a day every day, then charge to 100% and cycle the battery. The daily use minimizes the 'storing at 100%' negative, and gives us more miles per unit of time-based degradation. ;)

I can't quantify the small effects of these choices as I don't have all the gory details of the battery, so don't bet anything on this. I'm very comfortable that Nissan's taken care of the major pack killers, and expect the rest of these choices to result in numbers too small to pick out of the noise of real-world vehicle use.
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DaveinOlyWA
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Re: Electrical charging - measured results, 120v vs. 240v

Tue Jan 18, 2011 7:18 am

the pack does balance continuously but at a much slower rate than the charger.

take a bowl of water. use the analogy that water seeks its own level equating to charge balancing

drop a pebble into the water. the water level rises but because of the waves created by dropping the pebble into the bowl, a truly accurate reading cannot be made until the waves stop.

Andy; to be honest with ya, we are on the same page and its probably my inability to say what i know clearly and a printed forum is the toughest way to get a point across. i have spent years discussing my Zenn with other people who know nothing or have major misconceptions about EVs.

this requires creating analogies they are familiar in an attempt to give them some understanding. not always an easy job
2011 SL; 44,598 mi, 87% SOH. 2013 S; 44,840 mi, 91% SOH. 2016 S30; 29,413 mi, 99% SOH. 2018 S; 25,185 mi, SOH 92.23%. 2019 S Plus; 2640.9 mi, 99.37% SOH
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garygid
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Re: Electrical charging - measured results, 120v vs. 240v

Tue Jan 18, 2011 9:42 am

In spite of AndyH's best design, and confidence in Nissan, we do not yet KNOW what they ACTUALLY implemented, or why Nissan has made seemingly contradictory statements about how to use THEIR battery.

Comparisons to other similar battery chemistries or conjecture as to what Nissan MIGHT or SHOULD have done get us closer to understanding, and are a GREAT education for what is possible, but does not tell us WHEN or HOW Nissan attempts to "protect" and "equalize" their cells.

Further, we do not know how the cells WILL AGE, and Nissan does not yet display enough information to help us extend the useful life. It appears that the estimated capacity has to drop 17% (to 83%) BEFORE there is any displayed indication (one bar capacity loss). By then, it might be too late to change usage patterns to "preserve" the battery better.

Basically, we have a LOT of guesses, and LITTLE really helpful information, for example: frequent QC should be avoided, but it is OK to do QC occasionally, even 3 or 4 times a day.

But, this is probably the way it will be for early adopters. We will learn a lot more as we use, observe, and measure. The reports of experiences and observations will help guide the rest of us. Keep up the good work.
See SOC/GID-Meter and CAN-Do Info
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2011 LEAF, sold in 2015
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Re: Electrical charging - measured results, 120v vs. 240v

Tue Jan 18, 2011 10:17 am

Gary; its easy to understand your apprehension especially when there is so little information to go on. but in defense of Nissan; i can understand them providing limited information simply because we as a society hasnt a clue as to battery management, charge cycling, SOC or anything else.

look at the hoopla over range. that is a perfect example. EVERYONE has something to say about it, but at the same time, 80+% are two family household who need more than 100 miles at once only 5-15 times a year. iow; most people dont know what their needs are.

the only ammunition they have is the annual trip to Grandmas house for Thanksgiving that is 150 miles one way.

so we have to look at Nissan's motivation; if they cannot back up their product, we will pretty much know it in 3-4 years. that is not enough time to "bait and switch" its also no where near enough time to make their money back and run.

so they have 2 real options;

1) the batteries will actually last, meeting or exceeding the warranty period easily

2) Nissan knows the batteries will not last and already have a free warranty upgrade program sitting and waiting ready to launch as soon as the better technology is ready which would have to be within the next 2 years or so.

now with Nissan controlling battery manufacturing here in the US, they are poised to offer a pretty good warranty program for battery exchanges down the line. $5,000 for a battery replacement/exchange program would be a good deal since i expect to save more than double that on gas savings alone.

implement a prorated cost structure for the people who dont make the 150,000 mile period and so on.
2011 SL; 44,598 mi, 87% SOH. 2013 S; 44,840 mi, 91% SOH. 2016 S30; 29,413 mi, 99% SOH. 2018 S; 25,185 mi, SOH 92.23%. 2019 S Plus; 2640.9 mi, 99.37% SOH
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Smidge204
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Re: Electrical charging - measured results, 120v vs. 240v

Tue Jan 18, 2011 10:22 am

DaveinOlyWA wrote:this requires creating analogies they are familiar in an attempt to give them some understanding. not always an easy job
Someone need an analogy? :lol:

"It's like a guardrail at the Grand Canyon, right? You got that cliff there, and nobody wants anyone to fall off the cliff. So they put a guardrail up. Now they know the very edge ain't the best place for that guardrail, so they set it back a little bit for extra safety. When you charge your EV to 80%, you're basically staying even further back from that guardrail - because there is already a safety margin beyond the guardrail you can't get to anyway. That's fine, because it's just safety on top of safety, but it's okay to go right up to the guardrail if you want to."

=Smidge=

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