PHEV traction battery charge query

[Flatcoat]

We know The traction Battery capacity is circa 18kw. I understand the traction system is designed to reserve 30% of the charge for ‘back up’ to the ICE. So, does that mean when the range is down to zero and the ICE cuts in there is actually about 5.5kw left? And if so when the car is plugged in to charge it is charging up a theoretical 12.5kw (assuming a 100% charge)? I am also guessing in practice and due to the charge rate taper the Battery will only get to 90-95% charge? Or is the Battery actually around 25/26kw and the 18kw is the usable element of the battery? 

[philip42h]

50 minutes ago, Flatcoat said:

We know The traction battery capacity is circa 18kw. I understand the traction system is designed to reserve 30% of the charge for ‘back up’ to the ICE. So, does that mean when the range is down to zero and the ICE cuts in there is actually about 5.5kw left? And if so when the car is plugged in to charge it is charging up a theoretical 12.5kw (assuming a 100% charge)? I am also guessing in practice and due to the charge rate taper the battery will only get to 90-95% charge? Or is the battery actually around 25/26kw and the 18kw is the usable element of the battery? 

Have you still not got your car Adrian? Or have you just not updated your profile?

Either way ... as I understand it is an 18.1 kWh Battery - I don't think we know exactly how much of that is 'useable'.

If I understand correctly the 30% reserve is simply that the car switches into hybrid mode when there are 3 bars (out of 10) left on the Battery meter. Just like the average fuel gauge that may or may not be terribly accurate.

I've no idea where in the range 90% - 99% full it will register 10 bars and full but we can be pretty sure that it won't be 100% (exactly as you suggest above). IIRC some of the PHEV owners, probably Ernie, have reported overnight charges of around 12kWh.

The important figure at the end of the day is the 75km / 47 miles WLTP combined EV range ... 😉

[Lawnmowerman]

When charging from zero EV available, the figures I have recently for a 'full charge' have been:

14.81kwh

14.97kwh

15.23kwh

14.92kwh

14.83kwh

14.47kwh

14.77kwh

The highest figure is when I have not used cabin pre-heating before departure.

 

[Nick72]

2 hours ago, Flatcoat said:

We know The traction battery capacity is circa 18kw. I understand the traction system is designed to reserve 30% of the charge for ‘back up’ to the ICE. So, does that mean when the range is down to zero and the ICE cuts in there is actually about 5.5kw left? And if so when the car is plugged in to charge it is charging up a theoretical 12.5kw (assuming a 100% charge)? I am also guessing in practice and due to the charge rate taper the battery will only get to 90-95% charge? Or is the battery actually around 25/26kw and the 18kw is the usable element of the battery? 

According to my wall box app, from empty (top of the blue reserve line) it puts in 14.4kWhr of energy on average. Most it ever put in was 15.5. Least was about 13.4. 

 

 

 

 

[philip42h]

So, about 15kWh for a 'full charge' - that starts to sound like a 15% - 20% 'reserve', or, at least, the reserve can be 'dipped into' - which sounds reasonable. Obviously this 15kWh will also includes any energy expended in cabin conditioning, climate control for the traction Battery and losses in the charging system itself ...

[Flatcoat]

Where are you getting that charge data from? 

[Lawnmowerman]

From the wall charger app. Adrian.

[ernieb]

Very different to what I've seen, I use a granny cable and I have sometimes connected it via a mains power monitoring adapter this consistently showed a energy usage from zero% SOC of around the 12.5 to 13.2kWh.  This would then show a SOC of 100%, I've never seen number anywhere approaching 14kWh and above. 

The traction Battery is as far as I know, 96 cells @ 3.7volts, 355.2volts total rated at 51amps, 18.1kW.

[Mike2222]

All modern BEVs are quoted as Battery capacity & usable Battery capacity, because it utterly knackers a Lithium-ion Battery if you genuinely cycle it from 100% full to 0% empty (from what I've read, different battery chemistries can be more resilient, eg Lithium-Iron-Phosphate, which can be found in some 'made in China' Tesla Model 3s, as well as commonly found in newer home battery set ups which permit a full depth of discharge). 

 

Considering the reputation for over-engineering their vehicles, so as to be otherworldly reliable, plus being happy to warranty their hybrid batteries to 15yrs (with the annual dealer checkup), it would not surprise in the slightest if Toyota have also designed a relatively large upper buffer that can never be charged (ie a software restriction), which would mean the total battery size is >18.1kwh and 18.1kwh is simply what is quoted as the "usable" capacity (albeit with the last ~30% software-partitioned for HEV use, meaning total battery size could be approx 20kwh.

 

Although considering battery pack costs, perhaps more likely, they have split the buffer to both ends of the system. IIRC, the regular HEV Rav4 has a 1.6kwh hybrid battery (albeit last I read was different chemistry - NiMH - so engineering principles may be different), so if ppl are able are able to charge their PHEVs with 14-15kwh up to 100%, logically/back-of-a-coaster-man-maths tells me that would equate to roughly 1.6kwh at both ends...ish.

[nlee]

Don't forget charging losses. The charger app, or energy monitor will show energy supplied not what gets into the Battery. I don't see a way of seeing what gets into the Battery on the RAV but you can see figures for other cars across the web. It can vary massively from brand to brand but 10% is a reasonable assumption. I get similar 14.5kwh figures so about 13kwh going into the Battery.

Supposedly a 7kw charger should have less losses than a 3kw charger but Ernie's figures suggest otherwise.

[Flatcoat]

10 hours ago, Lawnmowerman said:

From the wall charger app. Adrian.

I don’t have a wall charger, yet…… Mike2222 thoughts are similar to mine however where does this lower end 30% buffer come in? I am simply intrigued and I suppose a better way of putting my initial question is the quoted Battery capacity net or inclusive of the 30% lower buffer and whatever top buffer? In terms of longevity I am not in the least concerned given the experience and over engineered reliability Toyota tend to apply to most drive trains (their diesels are probably the exception). 

[ernieb]

The 30% comes from the MyT (blue section), on the Home page gives you the %age.

I recall that when I was waiting for my car I looked a lot at the US forums and guys there were connecting monitors to the OBD port and demonstrated that the reserve and also that even if the app says it’s 100% it’s between 95-98%.  The comments were that this was to extend Battery life which makes sense.

 

[Nick72]

12 hours ago, Flatcoat said:

Where are you getting that charge data from? 

Wall box. 7.4kW charger. Has an app with all the history.

[IanML]

The wall box will measure what it supplies, but that energy is subject to heating losses in the on-board charger and the Battery itself.  You can expect the actual energy stored to be something like 85 to 92% of that supplied.

[kucyk]

FYI, this is the official info from Toyota Førde regarding plug-in Battery.

0 – 1,6kWh: reserved space protecting Battery from over-discharge
1,6 – 2,5kWh: reserved space for hybrid operation (you are within this range when your EV distance is 0)
2,5 – 16,0kWh: working area of plug-in hybrid
16,0 – 18,1kWh: reserved space protecting Battery from overcharging

[ernieb]

Very interesting, thanks Luke.

[Hayzee]

1 hour ago, kucyk said:

FYI, this is the official info from Toyota Førde regarding plug-in battery.

0 – 1,6kWh: reserved space protecting battery from over-discharge
1,6 – 2,5kWh: reserved space for hybrid operation (you are within this range when your EV distance is 0)
2,5 – 16,0kWh: working area of plug-in hybrid
16,0 – 18,1kWh: reserved space protecting battery from overcharging

Seems to pretty much back up Ernie's figures (12.5-13.2kwh) regarding power used charging the traction Battery from 0 to 100% 

[Flatcoat]

3 hours ago, kucyk said:

FYI, this is the official info from Toyota Førde regarding plug-in battery.

0 – 1,6kWh: reserved space protecting battery from over-discharge
1,6 – 2,5kWh: reserved space for hybrid operation (you are within this range when your EV distance is 0)
2,5 – 16,0kWh: working area of plug-in hybrid
16,0 – 18,1kWh: reserved space protecting battery from overcharging

Thanks, very useful and about what I anticipated. 

[Centaur]

That is indeed very interesting.  Presumably it also means that, when charging, the Battery will accept its maximum charge current up to ~14.5kWh (80% of 18.1kWh) and then tail off as it approaches 16kWh.  The last 1.5kWh only represents ~10% of the 13.5kWh usable capacity for EV operation (between 2.5kWh and 16kWh).  Effectively, this allows a full charge current over ~90% of the battery's EV capacity.

Assuming that to be the case, from the 2.5kWh lower end of the EV operation to 14.5kWh (90% usable EV / 80% full), it should only take the 6.6kW charger around a couple of hours, allowing for some losses.  That sounds reasonable, given that the brochure says that a full charge takes 2.5 hours.  Put another way, you should get around 41 EV miles in the first couple of hours and only another 5 in the extra half hour.

[Flatcoat]

My take on it is the Battery never fully discharges so will typically still have around 2/2.5kw charge when showing zero and in practice be around 90-95% charged when showing full. I have noticed with milder weather over the weekend the range is increasing. 

[Mike2222]

31 minutes ago, Centaur said:

Presumably it also means that, when charging, the battery will accept its maximum charge current

In practice, this doesn't necessarily happen. I can only speak from experience with my Leaf, as I haven't received my Rav4 PHEV yet (should be in next 1-2wks tho, 🙏, as its arrived at dealer 😁), but the rate of charge etc is 'decided', if you will, by the BMS (Battery management system). The max possible charge current is obviously a combination of the tech specs of the supply (eg chargepoint vs 3pin etc) and the onboard charger, but generically the biggest factor I have noted in charging speed/rate is battery pack temp, too low & too high are a problem. 

 

Also, worth noting other things that interfere with this is I think the car has a charge timer, which is usually designed as "when do you want the car ready and 100% for", which is a pain in a full BEV as day to day you should aim to charge no more that 80% unless you actually need it, for Battery health/longevity, however the design purpose of this as I understand it is that charging warms the Battery (aforementioned charging losses), making it more efficient when you then jump in and set off at the predetermined time, counterbalanced with fact you should try to avoid leaving a battery fully charged and idle for long periods. Doesn't seem any consideration was given in the design for overnight time-of-use tariffs! 

 

Also, chargepoint software usually does the same. The one I have for the Leaf seems to throttle the charge rate initially if it knows it has a longer time to play with (it shows you the predicted charge on a graph in the app when you plug it in), ie if the temps are good and you hit max charge, it'll go at 6.6kw front the off, which would take in the region of 2.5hrs as you say, but if you ask it to stick to the cheap rate period, which is eg 4hours long, it might aim to take 3.5-4hrs and charge at a slower rate intentionally, which is better for the battery. Only issue with that being that if your plans change and you need to jump in car at short notice halfway thru, you'll be less charged than you thought. But I don't often do that at 2am!

[nlee]

15 hours ago, Centaur said:

That is indeed very interesting.  Presumably it also means that, when charging, the battery will accept its maximum charge current up to ~14.5kWh (80% of 18.1kWh) and then tail off as it approaches 16kWh.  The last 1.5kWh only represents ~10% of the 13.5kWh usable capacity for EV operation (between 2.5kWh and 16kWh).  Effectively, this allows a full charge current over ~90% of the battery's EV capacity.

Assuming that to be the case, from the 2.5kWh lower end of the EV operation to 14.5kWh (90% usable EV / 80% full), it should only take the 6.6kW charger around a couple of hours, allowing for some losses.  That sounds reasonable, given that the brochure says that a full charge takes 2.5 hours.  Put another way, you should get around 41 EV miles in the first couple of hours and only another 5 in the extra half hour.

This is the typical charging profile according to my charger app.

[kucyk]

2 hours ago, nlee said:

This is the typical charging profile according to my charger app.

Hello Hypervolt owner 😀

[Centaur]

Those are both very interesting graphs and tend to confirm what kucyk was told by Toyota about Battery capacity.  Were the Battery to be charged closer to the full 100%, the tail current would be expected to drop away rather more gradually and the total kWh supplied to be higher.