Electrical charging - measured results, 120v vs. 240v

For anyone that is interested, my TED screen is available for anyone to look at. You can interact with it and view as much of the data as you want.

The main screen shows 3 MTU's. MTU1 is the house main. MTU2 is solar production, MTU3 is the EVSE. If you go to the graphic display, the ONLY MTU ON IT WILL BE THE EVSE!!

http://jjhamilton.dyndns-ip.com:50000/
(the page is slow to load, so be patient)

I generally keep a data sheet on my mileage, so if you see a day you want specific info on, let me know.

DaveinOlyWA said:

Balancing is something that should be working all the time even at 80%. If not then overcharging of high cells would be nearly unavoidable if charging to 100% which is one reason why 100% charging can be problematic.
Something I thought about was setting charge to 80% then letting it sit a bit then charging to 100% but not sure if the times would work with 110 volt charging being so slow

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We don't have to think about this, Dave, because Nissan's got it all figured out and completely automated. The car monitors all cell voltages, current in and out, and cell internal resistance -- the car knows what's happening with the pack. Because of the full-time computerized monitoring and balancing, charging to "consumer 100%" (actual 90%!) is not problematic in the least.

We really do not need to think 'lead acid' or 'I must manage my pack' or 'I hope I didn't leave the charger on too long' or any of the other fears we have with DIY EVs because this car is in a completely different league.

If charging to 100% (of usable capacity) is not problematic in the least, why is charging to 80% suggested?

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. Add to that he changing capacities of the pack based on temperature age, depth of discharge, etc.

Its reallynothing more than covering your bases. Its like a game of zenga. It will not go on forever and that is the same with running anything all out, full bore or .....100%

Sorry, that 80% is maximum safe, and 100% is also safe and not risky ...
to me, this "does not compute"!

I hadn't noticed this much with my work commutes, but I took a longer drive on Saturday. I left home at 100% charge, and all of a sudden I noticed that I wasn't getting any regen action (I was in ECO mode). Then it hit me that the pack was charged to 100%, so that must have been the reason...

I drove almost 10 miles before I saw any regen occurring, but it would only go on at 1 or 2 dots. I didn't see the whole amount of regen I'm used to until I had gone many more miles.

Since I live on a slight hill going down to work everyday, it probably makes sense to only charge to 80% for battery health as well as regen possibilities...

sparky, evnow, and LEAFer have been talking about this over on ECO Mode Impressions. It begins to sound as if ECO mode only includes heavier regen if the charge level is below 80%.

Is there any warning that Regen is not available (when in the higher SOC conditions)?

garygid said:

Is there any warning that Regen is not available (when in the higher SOC conditions)?

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No, gary, and I can't tell a difference in braking action with/without regen. The only notice you get is if you happen to be looking at your energy meter you'll either see a regen indication or not.

Once you break barrier for no-regen (80-90%), the regen comes on slowly and eventually will be fully enabled. But as I said, from a purely feel standpoint when brakeing, Nissan did a great job of making the regen and mechanical brakes seemless.

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.

But, hopefully, Nissan has designed for that (yes, infrequent) use.

Is there any special mention or caution about hot brakes in the manuals?

Clearly, this is an area where some planning ahead (to have less SOC at the top if the grade) would help.

In an emergency, turning ON the heater full blast, and opening all the windows to increase drag (and cool the car), are options to use.

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 said:

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.

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garygid said:

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.

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We covered this months ago... do we really need to do this again?

Sorry, I thought that we were discussing newly-discovered details if Regen, and how they will impact us. Maybe I was confused.

DaveinOlyWA said:

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.

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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/pdf/1/_ANR26650M1A.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

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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

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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 said:

Add to that he changing capacities of the pack based on temperature age, depth of discharge, etc.

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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.

AndyH said:

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.

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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%

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.

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

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.

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.

DaveinOlyWA said:

this requires creating analogies they are familiar in an attempt to give them some understanding. not always an easy job

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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=