Power consumption for balancing the battery ??

Hi guys -

Have googled and looked every where - no result :-( ...


I have noticed my 10amp charger goes from 2400w down to around 1000w when the battery is full. - It continues to use aprox 1000w for some time actually quite some time - I assume it is for balancing the cells -

I noticed it because i had a short drive aprox 20km / 12,5m and wanted to charge to test what kw i had used for that tour - the result was depressing ... because of the balancing process...


If i run the car empty i can charged somehow around 15-16kw ...

So is it stupid to "small" charge the car - does it use a certain amount of kw in the balancing process - then obviously its smarter to use most of the juice before charging ??


Cheers from denmark ( all winter aprox +5 degress celsious / 41 f ) so webasto is NOT yet installed

'Small charging' to 100% isn't recommended, but plugging in and 'small charging' from 50% to 75% is fine. Lithiums don't really like spending time at a 100% charge, so if you don't need a full charge for your trip, partial charging is best. The battery pack doesn't need balancing every day - Once every 3 to 6 weeks is fine

IMO, the best way to charge is to put as much juice in as you need for your travel (plus a little extra just in case) and not charge to 100% SOC unless you really need a full charge. If you do this every day, then a charge to 100% to balance the cells every month or so is a good idea

Don

I know the LiIon cell chemistry - also know that the Mitsu engineers actually doesent let the battery become charged to 100%

So i dont believe there will be any or at least very very little diffference in charging the car to 100% - it would make no sense to me to charge it only to 80...I have range anxiety enough already ;-)



Anyway thats not at all my point - it is whether or whether not people have recorded how much usage there is for the balancing process -

Inorder to determine if it is way to expensive in electricity to recharge the battery after fx 20-30km/10-20m

Forum member KiEV recently found the data on the CANBus that tells which cells have balancing enabled, so we might be able to get more information on the balancing process soon.

Not all of the power going into the car goes into the pack. The car itself has between 100-200 watts of self-consumption while charging.

i don't know if 1000W is reasonable for the charger in active topping-off (CV) mode as i haven't measured it directly, but i'll take an action item on it. My EVSE is supplying 240 VAC, so that would be about 4 amps.

The charger is a boost-type switching power supply that would need to maintain current on the front end in order to rectify, boost and regulate the voltage up to pack-level.

There are 88 balancing circuits that can bleed or partially bypass voltage at about 0.1 Amps each--so if they were all on there would be 8.8 Amps total in the bleed or by-pass circuits.

Each cell is controlled separately and cycled on-off frequently. If the cell voltage exceeds the setpoint, then balancing is turned on for that cell. Charging is still occurring but at a slightly lesser rate for that cell. When the cell voltage is below the set point, then full charging occurs. When the entire pack reaches the "full" set point, then the charger is turned off. From the scans i made it appeared that balancing was turned off at the same time.

My guess is that the overall pack voltage is used to regulate the charger output and it can be throttled back as the pack fills. The Canion app would show this in the current time history, but who wants to sit in a cold car waiting for the last bit of balancing to occur...?

meier said:

So i dont believe there will be any or at least very very little diffference in charging the car to 100% - it would make no sense to me to charge it only to 80...I have range anxiety enough already ;-)

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After 5 years, I still don't understand the 'range anxiety' thing I guess

We leave home at least 80% of the time with only a partial charge, many times with less than half a charge and we've never ever ran out of power and failed to make it home. If my trip is only 10 miles out and 10 back and I have 5 or 6 bars showing, I don't think twice about it. If I was the slightest bit worried, I'd plug it in for half an hour before we were due to leave

I try to only fully charge once a month or so (finishing just before we leave) but sometimes we slip up and forget to unplug it in time, so occasionally we end up getting a full charge more often than once a month, but that's what we try for

Don

Range anxiety aside, is it not true that the car doesn't really charge to 100%, and there's no real reason to withhold the "full" charge?

The car charges to 100% of the voltage that Mitsu engineers decided to use - True, this is not the full maximum voltage that the pack could be charged to. When I mention a '100% charge' that to me is where it shuts off and no more charging is possible - 100%. I don't understand why we would refer to that as a 96.5% charge or whatever, based on the fact that more energy could be put in the battery if Mitsu had decided to allow it to be charged to a higher voltage? If it's not possible to charge any higher, that's a 'full charge' or a 100% charge to me - 100% of what's allowed. The car also shuts off before the battery is completely discharged, for the same reason - Doing so protects the battery from damage. There is a bit of possible energy reserved and not used at both ends, but when the car stops moving, that would be a 0% charge, at least in my book and when it stops charging, that would be 100%

Ideally, if we never went below 20% and never above 80%, the battery could probably be made to last twice as long, or at least I'm led to believe that's true from everything I've read on the subject, *but* Mitsu would probably never publically admit to that because that would be giving away 40% of the cars usable range. But still . . . . if your daily usage doesn't require you to go below 20% or above 80%, why not stick to what's best for the battery? The only 'anxiety' with a BEV's range is caused by the operator not knowing what's needed for the trip at hand. Planning ahead relieves the anxiety

Don

i think the 100% charging myth is like an urban legend.

The only scientific test data that i've seen available on the web about battery life versus charge level, was a test study in which cells were STORED FOR A ONE YEAR PERIOD WHILE HELD AT 100%. At the end of that time the cells were cycled to determine capacity, and a reduction of capacity was measured. This has nothing to do with how the cells in a car are typically used, especially with daily driving.

There is no evidence that daily charging to full is harmful.

From the Battery University website: "Most Li-ions charge to 4.20V/cell, and every reduction in peak charge voltage of 0.10V/cell is said to double the cycle life. For example, a lithium-ion cell charged to 4.20V/cell typically delivers 300–500 cycles. If charged to only 4.10V/cell, the life can be prolonged to 600–1,000 cycles; 4.0V/cell should deliver 1,200–2,000 and 3.90V/cell should provide 2,400–4,000 cycles."

This would seem to be saying that if we stop charging at about 80% (3.9 volts) instead of going all the way up to 4.1, we could expect our battery to last about 4 times as long. If cycling every day to 4.1 will only yield a lifespan of 600 to 1,000 cycles, that's not a very reassuring number for those of us who hope to drive the car for 10 years which might require 3,000 cycles or so

It's pretty universally recognized that the so called 'sweet zone' for lithiums (you can Google 'Lithium sweet zone or sweet spot and read for hours) is to operate them between 40% and 80% SOC as much as is practical which extends their life as much as possible and then for those times when you do need to charge to 100%, do that just before use and not the day/week/month before you begin the discharge

If you need to drive about 20 miles every day, the smart way to do that would be to cycle the battery from 75% down to 50% and then recharge to 75% - Not from 100% down to 75% and then fully recharge every night

I do pretty much the opposite of every recommendation I've ever read with my cel phone - I plug it in every night even though it says I'm at 75 or 80% and it's probably recharged to 100% before I even get to sleep, but I leave it plugged in all night and only unplug it in the morning. I like having 100% every morning because I never know when I'm going to use every bit of it's capacity. When it begins losing capacity after a year or 18 months, I buy a new battery for $6 or $8 and begin anew. For my car, I seldom need 100% - I have a pretty good idea each day of what I'll need for my trip(s) and I don't ever want to have to buy a battery, so I do things very differently

Maybe I'm not going to get any more life from my car battery than anyone else, but from everything I've read I *think* my practices are going to extend it's life a bit and I'm pretty sure I'm not hurting anything, so why not? Most of the time I fully recharge only when I need to

Don

Found some info on the German site that Martin updates the Canion app.

a charging power curve showing the length of taper/balancing phase


Some discussion about the missing power:

When I load [aka charge], so messe z.b. 220V and 14.2A, gives 3.1kW. On Canion are displayed 356V and 6.7A, makes 2.4kW.
Where are now the 0.7kW difference?

1. The charger in the i-MiEV has an efficiency of 90%. Of the 3.1kW remain 2.8kW (-0.3kW) remain.

2. The i-MiEV has a standstill (ignition on, without charging cable) of 1.1A or 0.4kW for the operation of all control units and the charging current for the 12V battery. Control units and charging the 12V battery (300 ~ 360V -> 14V converter) remain in operation when charging the 360V battery.

Of the remaining 2.8kW (point 1) thus still another 0.4kW away. This leaves 2.4kW.

First, addressing meier's original query -

meier said:

...I had a short drive aprox 20km / 12,5m and wanted to charge to test what kw i had used for that tour - the result was depressing ... because of the balancing process...

Click to expand...

Yes, the variability due to balancing (and other factors such as temperature) over a short drive won't really tell you much. For myself, I kept meticulous records for 8000 miles and came up with an average of my own consumption for my i-MiEV but then gave up any more datataking because I realized that external influences (such as running the heater) have a ridiculously-high impact on the numbers.
Ref: http://myimiev.com/forum/viewtopic.php?f=28&t=403&start=20#p5744

meier, I was mulling over your question and kiev's response is probably as good as you're going to get.

If it's of any help, I dug up an old TED graph from 2012 so you can see what the power draw looks like when the charging starts tapering off and does its cell balancing. The voltage shown (red line) must be doubled (TED was only looking at one leg of the split-phase 240vac line). The drop in the curve soon after charging starts is the usual 'timeout' that the charger does, which I speculate is to determine if there is an abnormal sag in the battery's voltage and is a safety feature built into some chargers.



Regarding charging to 100%, car manufacturers are very careful with their wording, as Nissan found out when they were penalized when they were forced to post the car's range at 80% SOC rather than 100% because they were recommending that for everyday normal use people should charge to 80%. As another visual datapoint, here's a photo of the latest Tesla screen I took today (note that I am 'storing' the car and keep it at 50%SoC until I need it next). Tesla provides a simple programming option of stopping charging anywhere between 50% and 100% (I have yet to charge mine to 100%, but perhaps should do so one of these days to ensure the cells are balanced).



I won't get into this off-topic debate other than say that I support Don's comments. On the Tesla Motor Club website there are many well-informed in-depth discussions on this subject, which has been beaten to death on just about every EV forum out there. For my own i-MiEVs, I rarely charge over 13 bars (and immediately drive the car if I do), almost never go below two bars, and hope that my battery pack rewards me with a long life for treating it this way. I'll never know if there will be a difference compared to simply having charged it to 100% every time. Anecdotally, there have been at least two battery replacements on this forum after people repeatedly charged to 100% in a hot climate.

JoeS said:

Tesla provides a simple programming option of stopping charging anywhere between 50% and 100% (I have yet to charge mine to 100%, but perhaps should do so one of these days to ensure the cells are balanced)

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That's a feature I really, really wish we had on the iMiEV. I would use it every day

For those who don't recall, Joe took a 10,000 mile trip around the USA in his Tesla yet he's still never fully recharged to 100%

Don

Don said:

JoeS said:

For those who don't recall, Joe took a 10,000 mile trip around the USA in his Tesla yet he's still never fully recharged to 100%

Don

Click to expand...

Click to expand...

If I had the range to spare on a daily driver, then I wouldn't charge to 100% either. However, during the winter months, I have used as much as 85-90% of my 36 mile round trip commute. I don't have the ability to plug in at work so I pre-heat in the morning, drive gingerly to work - about 20-25 min, and use about 4-5 bars - so that is 12 bars left.
Sometimes, on my trip home, traffic is so bad that I am sitting in the car for over an hour - with the heater on, even as minimal as possible. And the return route is mainly uphill, so there have been times when I have gotten home with only 2 bars showing.
During the summer months, I usually have between 7-9 bars remaining when I get home.
But I always charge to 100% over night b/c I never know when I am going to need to make an extra trip, run an errand, etc. Remembering my reading when Mitsu was asked why they developed a car with such a small battery, the response from Mitsu was that the car would be recharged every night at home. There was no need for a larger battery. I can't find the quote now, but that is what I remember reading.

And with their 8 year/100,000 mile warranty - my hope is that the Mitsu engineers planned on the battery going to 100% every night.
I understand folks squeezing the most life out of their battery, and wanting to stay in that sweet spot. However, with my commute, especially during the winter months, that would prove to be a very short range car and not very usable.
(my 2 cents)

I'll offer MR BEAN as the extreme example- he's being run for maximum economic utilization. The car sat unused for a year after manufacture (likely at a high SOC) and has been charged to 100% just about every night since, with 100% midday charges about 3x per week, plus many CHAdeMO sessions. My recent 6 miles on the turtle 'till involuntary shutdown shows that the battery degradation has been minimal after 65,000 hard miles.

-Jay

kiev said:

Of the remaining 2.8kW (point 1) thus still another 0.4kW away. This leaves 2.4kW.

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So if you use regular mitsu L1 charger you are getting only 0.4kW charging rate. Not much.

Thanks alot for this comprehensive reply - Im not sure i understand the graph though - it seems that there is a very little period around 1 minute only in the end with balancing I have experienced i gues more than 1 hour i think - - BUT i will monitor it and make some testing when i have the time

meier said:

Thanks alot for this comprehensive reply - Im not sure i understand the graph though - it seems that there is a very little period around 1 minute only in the end with balancing I have experienced i gues more than 1 hour i think - - BUT i will monitor it and make some testing when i have the time

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meier, we are on the same page. If you'll look at the abscissa of the graph it is time using a 24-hour clock in one-hour intervals; thus, the balancing point starts at around 21:20 and continues for at least an hour. BTW, you had included a repeat of my entire post which I took out to keep things simple.

JoeS said:

meier, we are on the same page. If you'll look at the abscissa of the graph it is time using a 24-hour clock in one-hour intervals; thus, the balancing point starts at around 21:20 and continues for at least an hour. BTW, you had included a repeat of my entire post which I took out to keep things simple.

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Ahhh of course i must have been tired - yes I see its almost an hour

Hello: I just joined because I am inching closer to purchase of a 2012 i-MiEV with 17K miles on it. I would like to know exactly how many kWh it will use to go from no charge to full charge on the included 120VAC small charger. I have a Kill-A-Watt device that will show accumulated draw over a specified time; has anyone use one of those to determine this? I am assuming the car would pull more current at the beginning then taper off toward the end of the charging period; just trying to quantify that. I realize the charge time is long for this included device but I cannot afford to add fast 240VAC charger to my house right now.
Also, exactly how is the battery warranty transferred to a subsequent owner? Is there a transfer fee or registration procedure or does mitsubishi track it via VIN? THank you from Tom in Tucson AZ.