Battery chemistry reason enough to go for the SE SR?

[Rolfe]

.... brilliant write up Rolfe, I note that you've had your 1st service in recent weeks?, did the garage give you a state of health figure (SOH)?, or info as to why the BMS needed updating? ~ the reason of my asking is that I have a cheep dongle (combined with car scanner), and my SE (LFP) at ~10,000 miles is showing a 96.15% SOH, which seem a bit steep?

No, I took it in to get them to look at the undertray and they said there was a technical bulletin or something out for these cars to update the BMS. Considering that a couple of people with Bowfer's restricted speed/power problem have reported it cured after what seems to be the same update, I think it might be that they've found the problem and all SE SR cars are getting the fix.

 

[tsedge]

Barring some breakthrough (eg solid state), battery type is largely irrelevant these days: all battery types are good.

It is a bit like asking whether your ICE car uses single point or multi point fuel injection or whether it runs best on 97 or 95 RON fuel. It makes a small difference but 99% of people don't need to care.

The important questions are how much do you have to spend and what range do you need?

 

[lbdsg]

I’m with the author of this thread. Would much rather have an LFP battery but I need the 360 camera etc. If I could I’d pay the trophy price for the trophy spec less the battery and take the 51 from the sr. Too bad that’s not an option.

 

[Rolfe]

I don't think the risk of fire is high up on the list of reasons to prefer the LFP though.

 

[502BBC]

No, I took it in to get them to look at the undertray and they said there was a technical bulletin or something out for these cars to update the BMS. Considering that a couple of people with Bowfer's restricted speed/power problem have reported it cured after what seems to be the same update, I think it might be that they've found the problem and all SE SR cars are getting the fix.

Do you know what this update does to BMS? Did it do change any charging behavior etc..

My 23 Mk1 SR is R13, I believe I didn't get this update yet but if it's cruical for the longevity of batteries I will contact them about this. I purchased mine on 2nd of August.

So far car is at 1000 km and I haven't experienced any issues besides the charging immediately stopping after I unlock my car, not sure if this is a feature or bug I just wish I could disable it.

 

[Rolfe]

I have no idea. The car was fine when I took it in and it's still fine. My impression is that it's something they're doing to all cars when they come in, but they're not specifically calling people in to have it done.

I only noticed my charge stopping when I unlocked the car when I was using the granny lead. I don't think it happened on a rapid charger.

 

[Rolfe]

According to the paper "Peter Keil et al 2016 J. Electrochem. Soc. 163 A1872", the degradation (SOH) of LFP cells is not so different from NMC cells at 100% SOC and 25 oC storage temperature. On the other hand, the resistance of the batteries differs. The resistance does not change for LFP cells.

For daily use, I would charge NMC batteries no more than 60% and LFP batteries no more than 70%.

You do that with an LFP, and maybe I'll stop and rescue you when you're stuck on the motorway with a flat HV battery, du to the GOM telling you flat-out lies because you never let the battery balance.

 

[Rolfe]

This just dropped from Dave Takes It On. Some perspective on the EV fires issue.

 

[Tig170]

Also have a look at


& this link : Petrol and diesel cars 20 times more likely to catch fire than EVs

 

[Rolfe]

That was excellent. That guy McTurk is really good.

 

[Tig170]

... also

 

[stephenw]

I was going to buy a Trophy but changed my mind when I realised the difference in the battery tech. My reasons were as per zAndy1 at the top (10-80% equivalent range, no cobalt probably mined in Africa, not having to worry about the charge state). I also read that LFP batteries cycle ~2000 times before degrading to 80% health whereas NMC you only get ~700.

But latterly I've realised that even if you only get 700 charges that's still ~200,000 miles which should be more than enough. In theory an SR will do half a million miles, but who knows (I'm going to do my best to find out). I find long journeys are fine in an SR as your charge frequency is roughly the same as your rest stops required anyway.

One thing I still really prefer on the SR though is the efficiency. Despite it having a smaller motor it's faster than the Trophy (and LR) due to it's lower weight and slightly better aerodynamics. So a lot of the extra power on the higher models is being wasted, which would bug me. I would like that reversing camera though.

Regarding the self combustion, that was also a selection factor for me. I don't believe it is an issue day to day, but if you are involved in a serious crash such that the battery integrity is damaged then it may be a different story.

(As an aside most ICE car fires are actually caused by the brake fluid hitting a hot surface - it spontaneously combusts. If you pour petrol on a hot surface it just evaporates, but if the brake fluid goes up then the petrol is very vulnerable).

 

[Rolfe]

The ICE car fire I mentioned above wasn't the fault of the car. There was a traffic jam (due to an Orange Walk, grrrrr) and a line of traffic was stationary. The car about three in front of ours suddenly burst into flames for no apparent reason. The occupants managed to get out - this was before seat belts were compulsory. It turned out that the car had happened to come to a stop over a manhole cover, and that under that manhole cover was a leaking gas main. Enough gas accumulated within the car for a spark from the spark plugs to ignite it. I have no idea if an EV in the same situation would have ignited, but I suspect there would have been a lower chance of that happening.

 

[Rolfe]

I was going to buy a Trophy but changed my mind when I realised the difference in the battery tech. My reasons were as per zAndy1 at the top (10-80% equivalent range, no cobalt probably mind in Africa, not having to worry about the charge state). I also read that LFP batteries cycle ~2000 times before degrading to 80% health whereas NMC you only get ~700.

But latterly I've realised that even if you only get 700 charges that's still ~200,000 miles which should be more than enough. In theory an SR will do half a million miles, but who knows (I'm going to do my best to find out). I find long journeys are fine in an SR as your charge frequency is roughly the same as your rest stops required anyway.

One thing I still really prefer on the SR though is the efficiency. Despite it having a smaller motor it's faster than the Trophy (and LR) due to it's lower weight and slightly better aerodynamics. So a lot of the extra power on the higher models is being wasted, which would bug me. I would like that reversing camera though.

Regarding the self combustion, that was also a selection factor for me. I don't believe it is an issue day to day, but if you are involved in a serious crash such that the battery integrity is damaged then it may be a different story.

(As an aside most ICE car fires are actually caused by the brake fluid hitting a hot surface - it spontaneously combusts. If you pour petrol on a hot surface it just evaporates, but if the brake fluid goes up then the petrol is very vulnerable).

I bought the SR because I was looking for a bargain, and most of the extra bells and whistles on the Trophy are things I don't care about. I also seldom drive more than 100-120 miles in a day, and if I do need to go a bit further one day, or the range is particularly bad in winter, I can take on a bit of extra range at a rapid charger somewhere. Even the SR charging speed ain't that bad. I simply couldn't justify an extra £2,500 for another 60 miles range for the few occasions I'd use it. (I'm setting off on a 450 mile drive tomorrow, I'll let you know how I get on.)

But even as I was researching the car, I began to realise that the LPF battery had a lot going for it. No cobalt, charge up to 100% any time you like without worrying, and the battery is likely still to be working fine when the rest of the car falls apart. The fire thing wasn't a big issue for me because I realise that NMC fires are unusual occurrences. It wouldn't have put me off an NMC battery if everything else had been pointing that way, but it was another point.

Now, I've got so used to the LFP battery that having an NMC is one of the things that would put me off upgrading to an X-Power. Which is probably silly, but there you go.

 

[crunchy]

You do that with an LFP, and maybe I'll stop and rescue you when you're stuck on the motorway with a flat HV battery, du to the GOM telling you flat-out lies because you never let the battery balance.

Read again: "For daily use, I would charge NMC batteries...". Of course, for longer destinations I would charge it up to 100 %.

 

[Rolfe]

Read again: "For daily use, I would charge NMC batteries...". Of course, for longer destinations I would charge it up to 100 %.

It's a question of balancing. If the LFP battery isn't balanced frequently, it loses track of its state of charge and starts lying to you. One result can be that you think you have enough range for your journey, but then as the battery is nearly empty the awful truth dawns and the car recalibrates. Suddenly you don't have the range you thought you had.

 

[Richmorr]

It's a question of balancing. If the LFP battery isn't balanced frequently, it loses track of its state of charge and starts lying to you. One result can be that you think you have enough range for your journey, but then as the battery is nearly empty the awful truth dawns and the car recalibrates. Suddenly you don't have the range you thought you had.

Yep an LFP battery has the same voltage for most of the battery cycle. Say for example it’s 3.4 from full 100% to 10% this is why it’s important to balance the BMS as if there’s no start point it doesn’t know the end point and the mileage drops off.
NMC has a higher voltage and decreases as the battery discharges so the BmS knows the state of charge and its not as essential to balance the battery as frequently.
One down side to NmC at the lower voltage/charge the car can feel like it’s losing power due to the lower voltage and feel a bit sluggish. LFP doesn’t really have this problem as it keeps the higher voltage at the lower state of charge.

 

[DB00nowthen]

A couple of related observations or questions:

With the NMC, when changing to 80 percent and leaving to the car to stop the charge as it it is set to “health mode”, I notice the charge it draws slows to low wattage and stays at that for an hour or more before it stops the session. Is this balancing?

I do low annual mileage of about 6k/Yr ish and replaced my Prius with the Trophy at the start July. This includes two or three long trips from Devon to Northumberland each year, and the rest is local. So in summer the charging pattern emerging is that it is mostly 80 percent charge achieved at 2-3kw from solar via zappi. With drives taking down not much or often below 60 percent charge. Do we think it would be better to take it to lower percentage? I have noted depth of discharge as a factor in “debate”

And does this mean that the 100 percent once a month is not [as] necessary?

Note I am aware that we may be in the marginal benefit/issue territory here. But I find it interesting and satisfying to optimise such things. Gotta have a hobby ?

 

[Ian Key]

With the NMC, when changing to 80 percent and leaving to the car to stop the charge as it it is set to “health mode”, I notice the charge it draws slows to low wattage and stays at that for an hour or more before it stops the session. Is this balancing?

I believe it is but it's balancing all the cells to 80% so any underperforming cells won't be benefiting from being fully charged.

I do low annual mileage of about 6k/Yr ish and replaced my Prius with the Trophy at the stuff July. This includes two or three long trips from Devon to Northumberland each year, and the rest is local. So in summer the charging pattern emerging is that it is mostly 80 percent charge achieved at 2-3kw from solar via zappi. With drives taking down not much or often below 60 percent charge. Do we think it would be better to take it to lower percentage? I have noted depth of discharge as a factor in “debate”

I don't do a lot of mileage either but usually take it down to about 70 miles of range so I know I can get to friends houses for impromptu BBQs etc. without wondering if I have enough mileage left.

And does this mean that the 100 percent once a month is not [as] necessary?

That's my thought too. I've started to do a 100% balance charge every 6 weeks.

Unfortunately we won't know if we are right or not for many years.

 

[MoDolph]

A couple of related observations or questions:

With the NMC, when changing to 80 percent and leaving to the car to stop the charge as it it is set to “health mode”, I notice the charge it draws slows to low wattage and stays at that for an hour or more before it stops the session. Is this balancing?

Nobody knows just yet. Somebody would have to observe the voltage difference between the highest and lowest cells just before and just after this happening. I know my LEAF used to be constantly balancing the cells but I think it needed a full charge to determine which cells to balance.

I do low annual mileage of about 6k/Yr ish and replaced my Prius with the Trophy at the start July. This includes two or three long trips from Devon to Northumberland each year, and the rest is local. So in summer the charging pattern emerging is that it is mostly 80 percent charge achieved at 2-3kw from solar via zappi. With drives taking down not much or often below 60 percent charge. Do we think it would be better to take it to lower percentage? I have noted depth of discharge as a factor in “debate”

It is best to keep the charge centred around 50% so 60%-40% would be optimal in your situation. Smaller depths of discharge are better provided it does not result in the battery being at a higher average charge. 100%-95%-100% would be bad because the average charge would be very high, 50%-45%-50% would be great.

Only charging to 60% would also give you plenty of headroom for extra solar if the weather was good but predicted to be poor for some time after.

And does this mean that the 100 percent once a month is not [as] necessary?

Note I am aware that we may be in the marginal benefit/issue territory here. But I find it interesting and satisfying to optimise such things. Gotta have a hobby ?

Yes but to to what extent is unknown. The advice should really be a full charge every X number of partial cycles but that would be too complicated to explain so they go with a simple once a month.

I'm working on the assumption that they chose the worst case so somebody partially charging every time and doing high miles like 20k/year. Since I only do 7k/year I'm only going to fully charge once every 3 months. It's not been something I've had to worry about yet as I have been fully charging more frequently due to long trips anyway. My last full charge was 2nd June so I am getting close this time but no negative side effects yet.