meier
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Power consumption for balancing the battery ??

Sat Jan 21, 2017 1:14 pm

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 ??


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Don
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Re: Power consumption for balancing the battery ??

Sat Jan 21, 2017 1:36 pm

'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
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meier
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Re: Power consumption for balancing the battery ??

Sat Jan 21, 2017 2:20 pm

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
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PV1
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Re: Power consumption for balancing the battery ??

Sat Jan 21, 2017 3:42 pm

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.
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kiev
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Re: Power consumption for balancing the battery ??

Sat Jan 21, 2017 4:41 pm

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...?
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Don
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Re: Power consumption for balancing the battery ??

Sat Jan 21, 2017 6:21 pm

meier wrote: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 ;-)
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
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wmcbrine
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Re: Power consumption for balancing the battery ??

Sat Jan 21, 2017 6:27 pm

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?

Don
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Re: Power consumption for balancing the battery ??

Sat Jan 21, 2017 8:57 pm

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
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kiev
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Re: Power consumption for balancing the battery ??

Sun Jan 22, 2017 8:27 am

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.
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Don
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Re: Power consumption for balancing the battery ??

Sun Jan 22, 2017 9:37 am

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
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