Leaf Battery Or general Li Battery information.

[o00scorpion00o]

Hi everyone,

I'm having a discussion on another forum about charging observations on the Leaf while using the DC charger.

I got a few questions and I appreciate your time and efforts put into this.


1: Is charging controlled solely by the Charger, BMS or both ? what I mean is, I know the ramp down phase in the transition from CC to CV is controlled by the charger/BMS however , we were discussing why the 30 Kwh charges in the same time to 80% as the 24 Kwh and my interpretation of it was that the larger battery takes longer to get from CC to CV and that it's not controlled by Nissan tweaking the BMS instructions for the new battery to the charger and allowing more power to be sent to the battery.

You can clearly see the power reduce gradually as the battery % increases, is this because as the voltage rises in the battery it no longer demands the power from the charger ? Or is it completely controlled by the charger ?

2 : we know heat and cold have an effect on charge times and this can increase/decrease the internal resistance. I have read in a paper from the University of University of Wisconsin Milwaukee via this link http://dc.uwm.edu/cgi/viewcontent.cg...46&context=etd that it's the internal resistance that causes the reduced current that can flow to the battery caused by this increased IR, so this I assume is not controlled by Nissan or the charger/BMS and a result of the effects of cold on the chemistry ? or is the battery temp data sent to the charger and this tells it to reduce the power because of the cold battery ? There are other sites/studied done on this which conclude that increased IR increases charge times.

I have observed reduced current that could be pulled when I was riding my high powered E-Bike on LiPo and much increased voltage sag and poorer acceleratuion in cold weather compared to warm. I did not notice effects of charging because my charger was pretty low powered in the first place. A similar effect I observed when the battery was worn only this time I could continue to pull the max current but the voltage sagged horribly and I could not get the capacity from the pack unless riding very gently.

So my LiPo pack had no BMS and all that was between that and the battery was the motor controller which did have a LVC but obviously no cell monitoring.

3 : An effect people are noticing with older leafs is increased charge times on the fast charger due to an ageing battery and reduced regen, one person on this forum with a 2012 leaf and 30 odd K miles noticed he can't get more than 35 Kw from the DC charger compared to mine pulling 50 Kw on my 2015 Leaf (charger KW display). He has noticed some loss of capacity around 10% compared to 0 loss reported by leaf spy for me over 14,000 Miles.

So is this internal resistance the cause of the battery not demanding the power because the power simply can't be delivered to the battery as has been reported on other sites and University papers or is it the charger controlling the current sent to the battery by monitoring the internal resistance of the battery as it ages and adjusting the current accordingly ?

I appreciate your replies .

 

[RegGuheert]

1: Is charging controlled solely by the Charger, BMS or both ? what I mean is, I know the ramp down phase in the transition from CC to CV is controlled by the charger/BMS however , we were discussing why the 30 Kwh charges in the same time to 80% as the 24 Kwh and my interpretation of it was that the larger battery takes longer to get from CC to CV and that it's not controlled by Nissan tweaking the BMS instructions for the new battery to the charger and allowing more power to be sent to the battery.

You can clearly see the power reduce gradually as the battery % increases, is this because as the voltage rises in the battery it no longer demands the power from the charger ? Or is it completely controlled by the charger ?

The DC quick charger has a maximum power capability that it will put out. I've used two different chargers, one with a 48-kW limit and one with a 24-kW limit. Below that level, the BMS controls the charging.

2 : we know heat and cold have an effect on charge times and this can increase/decrease the internal resistance. I have read in a paper from the University of University of Wisconsin Milwaukee via this link http://dc.uwm.edu/cgi/viewcontent.cg...46&context=etd that it's the internal resistance that causes the reduced current that can flow to the battery caused by this increased IR, so this I assume is not controlled by Nissan or the charger/BMS and a result of the effects of cold on the chemistry ? or is the battery temp data sent to the charger and this tells it to reduce the power because of the cold battery ? There are other sites/studied done on this which conclude that increased IR increases charge times.

I have observed reduced current that could be pulled when I was riding my high powered E-Bike on LiPo and much increased voltage sag and poorer acceleratuion in cold weather compared to warm. I did not notice effects of charging because my charger was pretty low powered in the first place. A similar effect I observed when the battery was worn only this time I could continue to pull the max current but the voltage sagged horribly and I could not get the capacity from the pack unless riding very gently.

So my LiPo pack had no BMS and all that was between that and the battery was the motor controller which did have a LVC but obviously no cell monitoring.

The BMS is what limits the current, not the resistance of the battery.

3 : An effect people are noticing with older leafs is increased charge times on the fast charger due to an ageing battery and reduced regen, one person on this forum with a 2012 leaf and 30 odd K miles noticed he can't get more than 35 Kw from the DC charger compared to mine pulling 50 Kw on my 2015 Leaf (charger KW display). He has noticed some loss of capacity around 10% compared to 0 loss reported by leaf spy for me over 14,000 Miles.

So is this internal resistance the cause of the battery not demanding the power because the power simply can't be delivered to the battery as has been reported on other sites and University papers or is it the charger controlling the current sent to the battery by monitoring the internal resistance of the battery as it ages and adjusting the current accordingly ?.

The internal resistance is NOT enough to limit the power in the battery to 35 kW. You can see this by noting that you can accelerate using over 80 kW even though the cell voltage is lower than when charging. Any differences seen will have to do with the BMS (or possibly limits of the capability of the quick chargers used).

 

[o00scorpion00o]

The DC quick charger has a maximum power capability that it will put out. I've used two different chargers, one with a 48-kW limit and one with a 24-kW limit. Below that level, the BMS controls the charging.

All our DC chargers are 45-50 Kw.

The BMS is what limits the current, not the resistance of the battery.

The internal resistance is NOT enough to limit the power in the battery to 35 kW. You can see this by noting that you can accelerate using over 80 kW even though the cell voltage is lower than when charging. Any differences seen will have to do with the BMS (or possibly limits of the capability of the quick chargers used).

Most batteries are able to discharge at far higher C rates than they can charge. Hence acceleration will always mean you pull more from the battery than you can dump back in.

 

[RegGuheert]

Most batteries are able to discharge at far higher C rates than they can charge. Hence acceleration will always mean you pull more from the battery than you can dump back in.

That's only because the BMS limits the charging voltage as well as the current. Without those limits placed by the BMS, the battery could be charged at much higher currents. The maximum charging voltage from Chademo chargers is 500 V but the LEAF's BMS specifies a limit closer to 400V.

 

[madscientist]

I'm glad mad_lad ( Scorpion) , you're seeking and getting a better understanding of li battery charging.

 

[o00scorpion00o]

I'm glad mad_lad ( Scorpion) , you're seeking and getting a better understanding of li battery charging.

Thanks Boat-Mad it's nice to do more research and to find out what's actually gong on because it's driving me mad lol but rest assured we will continue this topic.

 

[o00scorpion00o]

So basically the university papers that suggested the internal resistance was/is the cause for the increased charge times is wrong ? this has cropped up on various sites though which doesn't indicate the BMS/Charger is sorely responsible for adjusting charge currents.

So another question, the point where the charge current starts to reduce when fast charging is also controlled by the charger yes ? then what allows the 30 Kwh to charge in the same time ? the fact it can stay in this constant current stage longer, right ? it's not that it gets more power it just takes longer to reach this CV stage so it can take a higher rate of current for longer ?

 

[madscientist]

That university paper you refer is , is incredibly flawed. Not only does it pull assumptions for the air , it arrives at incorrect conclusions. Quite frankly it's a typical post grad master thesis and very poor to boot. It just not a good reference

Remember the internal resistance of a battery is a complex , multi variant function , what you see in various circuits is merely a model and often a poor one. There are still many doctoral thesis on the development of accurate battery models.

 

[madscientist]

So another question, the point where the charge current starts to reduce when fast charging is also controlled by the charger yes ? then what allows the 30 Kwh to charge in the same time ? the fact it can stay in this constant current stage longer, right ? it's not that it gets more power it just takes longer to reach this CV stage so it can take a higher rate of current for longer ?

The charging strategy could be either. I notice on another thread , it's claimed the Nissan have move the CC/CV transistion further up the curve for the 30 kW battery. However I doubt that , given the safety orientated aspects of nissans charging strategy. ( and the lack of slope of voltage change on large capacity li cells too ) so if they used the same power but moved the CC transistion from 65% to say 80 % , then it would be as you say. Personally I don't think so however

If Nissan were happy to charge the 24 kW at around 1.5-1.7 C , it follows they are happy charging the larger battery at the same C rate. This would suggest merely programming the charger to deliver a higher current , assuming it has headroom to do that.

Without some charging data from the new battery , we won't know what strategy has been adopted

 

[o00scorpion00o]

If Nissan were happy to charge the 24 kW at around 1.5-1.7 C , it follows they are happy charging the larger battery at the same C rate. This would suggest merely programming the charger to deliver a higher current , assuming it has headroom to do that.

Or simply because it's larger they don't need to adjust anything , it will taper back the current when it reaches the same voltage as the smaller battery it just takes longer to get there at the same current because it's a larger battery but because it's charging at the higher rate for longer it turns out that it charges in the same time as the 24 kwh.

The new chemistry will have a new BMS so I'm sure there will be different parameters.

 

[madscientist]

Or simply because it's larger they don't need to adjust anything , it will taper back the current when it reaches the same voltage as the smaller battery it just takes longer to get there at the same current because it's a larger battery but because it's charging at the higher rate for longer it turns out that it charges in the same time as the 24 kwh.

The new chemistry will have a new BMS so I'm sure there will be different parameters.

you do realise the contradiction in what you said

(a ) it will taper back the current when it reaches the same voltage as the smaller battery it just takes longer to get there at the same current because it's a larger batter

(b ) but because it's charging at the higher rate for longer it turns out that it charges in the same time as the 24 kwh.

if its charging at the same current, it cannot be equally charging at a " higher rate " , a higher rate of what , voltage is fixed so the only variable current, hence a " higher rate " is more current . it clearly cant be the " same current " and also a " higher rate "


In Li , the time in CV is fairly independent of battery size, assuming the charger can supply the maximum demand in CV mode. you can in effect regard all the battery cells as being in parallel conceptually

There is only two ways to charge a bigger battery in the same time, (a ) more current and hence more power during CC and/or a later transition point from CV to CC .

 

[GRA]

This article here: http://dailykanban.com/2015/10/2nd-gen-leaf-expected-2018-60kwh-nmc-battery-300-mile-range-autonomous-cfrp/

indicates that the internal resistance of the 30kWh battery is lower allowing a faster charge, presumably involving a later shift from CC to to CV. That's in addition to its greater capacity.