Speak EV - Electric Car Forums banner

1 - 14 of 14 Posts

·
Registered
Joined
·
8 Posts
Discussion Starter #1
I have a 2021 eNiro on order and hoping it turns up Oct/November

as a bit of prep I have been looking at home charging options. Would love to hear about others experiences what’s good etc.

i am also interested in bidirectional charging but can‘t see if that is dependant on the car also. Any ideas of info about this?
 

·
Registered
Joined
·
4 Posts
By bidirectional charging, do you mean the ability to return power to the home (vehicle-to-grid)?
If so, then my understanding is that the Leaf is the only car with that capability - because it uses Chademo, which is required by the current application.
 

·
Registered
Joined
·
4,079 Posts
Useless :devilish: European standard (not an EU issue) of CCS will not have bi-directional charging until 2025 at best. But it is the future apparently .... ;)
 

·
Registered
Joined
·
153 Posts
You can add around 50 miles a night in 7h off-peak using the granny charger, so if that's going to be enough there's no need to rush into anything. That said, the charging loss at the trickle charge rate of 10A is around 25%. A 7kW home charger obviously whacks in a lot more miles in the same time, and is more efficient - typically around 15% loss and even as low as 10% in the present warm weather. I'll be pushing up the daisies long before my home charger pays for itself financially though.
 

·
Registered
Joined
·
169 Posts
I’ve read this poor efficiency granny “charger“ thing on here a few times. I am not doubting this info but as a retired EE engineer I would certainly like to understand just why it should be so. Neither the granny lead nor the home wall box is actually a charger strictly speaking. The actual 240V AC charger is common to both charging methods and is built right into the car itself. The granny lead and wall box units are both simply switch gear, connectors and comms interface units. The 240V AC power going to the car is exactly the same stuff in both cases. The different cable and connector losses can’t account for it surely?

I would love to see a link to the source of this relative efficiency data if there is one please.

The only possible explanation I can think of is that during AC charging there might be so much of the car residual systems powered on, that it absorbs a more significant chunk of the available charging power. So then when charging at a lower ”granny” rate, this residual power draw could be a larger proportion of the total AC power in.

Thanks for any detailed info.

Peter
 

·
Registered
Joined
·
3,743 Posts
You can add around 50 miles a night in 7h off-peak using the granny charger, so if that's going to be enough there's no need to rush into anything. That said, the charging loss at the trickle charge rate of 10A is around 25%. A 7kW home charger obviously whacks in a lot more miles in the same time, and is more efficient - typically around 15% loss and even as low as 10% in the present warm weather. I'll be pushing up the daisies long before my home charger pays for itself financially though.
Not sure I understand why folk paying heaps per month for a fancy BEV skimp on the convenience and safety of a proper home charger.
 

·
Registered
Joined
·
4,079 Posts

·
Registered
Joined
·
8 Posts
Discussion Starter #8 (Edited)
By bidirectional charging, do you mean the ability to return power to the home (vehicle-to-grid)?
If so, then my understanding is that the Leaf is the only car with that capability - because it uses Chademo, which is required by the current application.
Yes sorry, by bidirectional charging i mean vehicle to grid. This this could be useful feature to also act as a home battery like the power wall (invested in those battery in the car so can make use of them)
 

·
Registered
Joined
·
8 Posts
Discussion Starter #9
You can add around 50 miles a night in 7h off-peak using the granny charger, so if that's going to be enough there's no need to rush into anything. That said, the charging loss at the trickle charge rate of 10A is around 25%. A 7kW home charger obviously whacks in a lot more miles in the same time, and is more efficient - typically around 15% loss and even as low as 10% in the present warm weather. I'll be pushing up the daisies long before my home charger pays for itself financially though.
Hi john, I regularly travel 100 a day so would need to add more over night sometime, hence the need for home charging (don’t fancy relying on public network yet). Also like the idea of plug in at night ready to go in the morning, no more waiting in line at the petrol station
 

·
Registered
Joined
·
1,079 Posts
I’ve read this poor efficiency granny “charger“ thing on here a few times. I am not doubting this info but as a retired EE engineer I would certainly like to understand just why it should be so. Neither the granny lead nor the home wall box is actually a charger strictly speaking. The actual 240V AC charger is common to both charging methods and is built right into the car itself. The granny lead and wall box units are both simply switch gear, connectors and comms interface units. The 240V AC power going to the car is exactly the same stuff in both cases. The different cable and connector losses can’t account for it surely?

I would love to see a link to the source of this relative efficiency data if there is one please.

The only possible explanation I can think of is that during AC charging there might be so much of the car residual systems powered on, that it absorbs a more significant chunk of the available charging power. So then when charging at a lower ”granny” rate, this residual power draw could be a larger proportion of the total AC power in.

Thanks for any detailed info.

Peter
There are also losses on places like the input filtering on the charger, and quiescent draw of the charger electronics, which will be a higher percentage at lower currents. The OBC will have been designed for max efficiency at full load (7kw).
The actual figures will vary by make/model, in some cases differences may be marginal.
 

·
Registered
Joined
·
169 Posts

·
Registered
Joined
·
153 Posts
I’ve read this poor efficiency granny “charger“ thing on here a few times. I am not doubting this info but as a retired EE engineer I would certainly like to understand just why it should be so. Neither the granny lead nor the home wall box is actually a charger strictly speaking. The actual 240V AC charger is common to both charging methods and is built right into the car itself. The granny lead and wall box units are both simply switch gear, connectors and comms interface units. The 240V AC power going to the car is exactly the same stuff in both cases. The different cable and connector losses can’t account for it surely?

I would love to see a link to the source of this relative efficiency data if there is one please.

The only possible explanation I can think of is that during AC charging there might be so much of the car residual systems powered on, that it absorbs a more significant chunk of the available charging power. So then when charging at a lower ”granny” rate, this residual power draw could be a larger proportion of the total AC power in.

Thanks for any detailed info.

Peter
With regard to charging losses I can only give you data from my own experience, so I’ve been diving into my charging history. I hope you find the following interesting

Early on in the ownership of the e-Niro, our first EV, I was puzzled by the fact that a manual calculation of miles/kWh was sometimes wildly at odds with the figure reported by the car and at other times the same, e.g. my wife did 100 miles on 100%-70% (30% of 64 = 19.2kWh = 5.2miles/kWh) but the car reported 4.8. Yet on a motorway test I calculated 3.7 and the car said the same. I subsequently got a Bluetooth OBD dongle and started using the Soul EV Spy app and discovered all the charge/discharge data that the BMS accumulates, in kWh and Ah. It quickly became apparent that the SOC% represents Ah and not kWh – battery capacity = 180Ah. Therefore there is much more energy in the top end of the battery, at higher voltage, than there is lower down. My motorway test just happened to be around 40-50% SOC, where 10% = 6.4kWh. So I set about recording the battery voltage at different states of charge, then plotted the results and calculated the energy stored in each 5% (with subsequent refinement to the 0.5% that the BMS records, readable via the dongle, q.v.


You’ll see that the kWh add up to more than 64 but I now think that I’ve overestimated the bottom 5-10% -- I don’t go there so I have no actual voltage data. Calculations based on the rest of the curve tally very closely with the car’s efficiency figures. Anyway, back to charging…..

The last time I used the granny lead was back at the end of February/beginning of March. The charge rate reported by the car was 2.3kW. The voltage at our son’s house is quite high – 2.2kW is more common, and seems to equate to higher losses.

The figures, in order, are a) added to battery, as calculated from my graph; b) BMS charge; c) energy ex wall socket/50kW rapid charger/7kW home charger:

Granny 1) 32.5%-79.5% = 30.9 v. 32.1 v 39.7kWh = 22% loss overall

Granny 2) 58%-100% = 29.25 v 29.6 v 36.9kWh = 21% loss

50kW rapid 1) 34%-97.5% = 41.23 v 45.2 v 50.2kWh = 18% loss*, battery temp** 20/24°C --> 24/31°C

50kW rapid 2) 53%-79% = 17.5 v 18.5 v 20.54kWh = 15% loss, 15/16°C --> 20/21°C

50kW rapid 3) 34%-97.5% = 41.23 v 45.2 v 50.2 = 18%, 20/24°C --> 24/31°C

7kW home charger 1) 33.5%-79.5% = 30.33 v 31.8 v 36kWh = 15% loss

7kW home charger 2) 58%-100% = 29.25 v 29.5 v 32kWh = 9% loss***



* This rapid charger loss is on the high side – 12-15% is more common.

** Battery temperatures before and after for the granny lead/home charger are meaningless because of delay before unplugging/recording data.

*** This is the most recent charge and a record low loss – very low between BMS and battery – due to high ambient temperature (22°C before and after, and not long after when unplugged)? This might also be a factor in greater vehicle efficiency in warm weather, i.e. minimal regen losses on actual charging of battery?
 

·
Registered
Joined
·
169 Posts
Thank you Richard so much for reporting the detail of your testing. All very interesting stuff. I haven’t even got an EV (yet!), so I do find this fascinating.

I do have some considerable experience with LiIon cells generally (not in EVs) though. One crucial thing is their very significant internal resistance V cell temperature curve. Charging (and indeed discharging) is hugely more efficient at say 30° battery core than it would be at say 10°. The internal resistance energy losses increase dramatically as temperature is reduced. So I wonder if a fairly significant part of your granny charging efficiency deficit could be due to doing the granny tests back in February? to make the comparison, ideally wall connection and granny lead comparisons should be done at near identical battery core and ambient temperatures.

I know this is difficult, as apart from anything else, the thermal mass of the battery is very large so it will have a very long time constant Of many hours. Recent driving, charging (or lack Thereof) will have an effect on the battery core temperature compared to ambient air. Add to this, the battery temperature management system doing its thing too. Interesting stuff.

cheers
Peter
 

·
Registered
Joined
·
153 Posts
Thank you Richard so much for reporting the detail of your testing. All very interesting stuff. I haven’t even got an EV (yet!), so I do find this fascinating.

I do have some considerable experience with LiIon cells generally (not in EVs) though. One crucial thing is their very significant internal resistance V cell temperature curve. Charging (and indeed discharging) is hugely more efficient at say 30° battery core than it would be at say 10°. The internal resistance energy losses increase dramatically as temperature is reduced. So I wonder if a fairly significant part of your granny charging efficiency deficit could be due to doing the granny tests back in February? to make the comparison, ideally wall connection and granny lead comparisons should be done at near identical battery core and ambient temperatures.

I know this is difficult, as apart from anything else, the thermal mass of the battery is very large so it will have a very long time constant Of many hours. Recent driving, charging (or lack Thereof) will have an effect on the battery core temperature compared to ambient air. Add to this, the battery temperature management system doing its thing too. Interesting stuff.

cheers
Peter
Actually, the February granny charge losses were atypically low - 25% is more usual, even in summer. I put them down to a slightly higher charge rate due to higher local mains voltage (245-250V), giving 2.3kW rather than typical 2.2.
 
1 - 14 of 14 Posts
Top