All EV’s - Batteries & Charging | Motoring discussion | Back Room Forum

Fri 3 Dec 2021 21:05

All EV’s - Batteries & Charging - mcb100

There has been quite a bit of talk on here about EV’s and there may be folk to whom it’s all a bit mysterious, so here’s my attempt at explaining some of the basics.
We’ll start with the units, and you’ll hear talk of kWh and kW. Starting with kWh, that’s the battery size - in effect the size of the tank. It’s not an outright definition of range since vehicle size, weight, etc will impact on how far it’ll go. If you could put a 15 gallon tank in a Peugeot 108, it’ll go further than a Mercedes S-Class with a similarly sized tank.
KW next, and that’s the rate at which it will change when plugged in. This will vary enormously, depending upon what the car is plugged into, and a bit of maths is useful here. A 230V domestic socket, with a 13 amp plug plugged into it will supply a midge under 3kW. If we know a battery capacity is 75kWh, divide that by 3kW and you’ve got a 25 hour charge from empty to full.
Upgrade to a 7.4kW wall box and, in our case, it’s 75 divided by 7.4 giving just over 10 hours. It it’s a commercial property with three phase wiring, you’ve got the potential of 22kW AC charging, but cars tend to have a maximum of 11kW chargers onboard.
On a point of pedantry, the charger itself is built into the car, and it’s the charger that will alter the speed of charge, or adapt from AC to DC. The wall box is simply a source of electrons.
That’s AC charging, which will have to be converted to DC as the motor or motors are direct current.
Anything faster than 22kW will be DC, and charging speeds are up to 350kW (rare). Typically a rapid charger will be 50-150kW. The same maths apply - divide the battery capacity by the charge rate to get a time. 150kW into a 75kWH battery gives 30 minutes - however it’s not not quite linear at this point as charging speed will slow as the battery gets to 80% charged in the interest of battery management. It won’t kill a battery repeatedly rapid charging to 100%, but it’s the EV equivalent of redlining a petrol engine from stone cold every morning. No appreciable downside initially, but potential excess wear in years to come.
Cables and plugs are now pretty universal, with the exception of some Japanese stuff, and any car will plug into just about any charger. You can plug a non-Tesla into a Tesla Supercharger but you won’t get anything out of it as the car and charge point do an ‘electronic handshake’ and it’ll recognise you’re not in a Tesla.
If this is already understood, then I’m sorry for keeping you this long. If it’s answered any questions, then that’s a result.

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Fri 3 Dec 2021 21:23

All EV’s - Batteries & Charging - misar

Your tutorial seems to have a few misconceptions. I will leave the EV experts to explain but they might start with AC-DC.

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Fri 3 Dec 2021 22:42

All EV’s - Batteries & Charging - mcb100

What a peculiar response. You’re telling me I’m wrong, but going to rely on others to tell me where.
I shall await the EV experts’ feedback.

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Sat 4 Dec 2021 14:10

All EV’s - Batteries & Charging - misar

What a peculiar response. You’re telling me I’m wrong, but going to rely on others to tell me where. I shall await the EV experts’ feedback.

It was a polite hint that it is not a good idea to publish tutorials on matters you do not fully understand.

I refrained from offering any suggestions because experience of many EV threads on here warned me that no matter what I wrote somebody would be along to disagree, leaving you even more confused. Seems I was right ....

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Fri 3 Dec 2021 23:08

All EV’s - Batteries & Charging - Big John

Have you presumed battery charging is 100% efficient on the calculations? It's not by some margin.

Obviously there needs to be a conversion from AC to DC between the power socket and car charging. Never mind the motor clearly the batteries are DC. It would be a bad idea to have the AC/DC conversion pre charge cable - it'd be rather dangerous. It's one of the many reasons we moved to AC mains in the first place - A DC electric shock is much more lethal. However I think DC chargers might be a thing of the future - I still think it's a bad idea.

Edited by Big John on 03/12/2021 at 23:15

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Fri 3 Dec 2021 23:21

All EV’s - Batteries & Charging - mcb100

Losses are dependent on input voltage (higher voltage = lower loss) ambient temperature and whether the car is drawing AC or DC.
Figures vary from 99% efficiency on a 400 volt DC Tesla charge point up to approximately 15%, so 85% efficiency.

Edited by mcb100 on 03/12/2021 at 23:22

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Fri 3 Dec 2021 23:31

All EV’s - Batteries & Charging - Big John

Losses are dependent on input voltage (higher voltage = lower loss) ambient temperature and whether the car is drawing AC or DC. Figures vary from 99% efficiency on a 400 volt DC Tesla charge point up to approximately 15%, so 85% efficiency.

I don't get the 99% figure - why do hybrid / electric cars have battery cooling systems then? They generate heat being charged and depleted. Battery technology isn't my area of expertise but I do have a grounding (pardon the pun) in the laws of physics.

My worry of high voltage DC comes from my days of repairing valve TV's - the high voltage valve DC rail was something else, you had to take extreme methods to avoid potential shocks. I used to have a bespoke ( er home made) device to discharge high voltage/capacity electrolytic capacitors. The theory was with DC you couldn't let go in a shock situation - in reality don't know,

Also my late father who lived in Keighley mentioned DC mains and that shock deaths were frequent - could be down to other factors such as running irons from light fittings being the norm! I only remember AC being of early 60's vintage but I remember light fittings were robust to cope with a DC spark, Apparently my Grandfather destroyed a radio(vintage) with transformer plugging into DC mains when he moved house( DC + transformer = near short circuit).

Edited by Big John on 03/12/2021 at 23:59

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Sat 4 Dec 2021 01:36

All EV’s - Batteries & Charging - Ethan Edwards

Today's EVs are rarely powered by a thin cord plugged into a light fitting. The sockets are really well designed, safe and even water resistant IP something. In other words your ev can happily live outside in rainy Britain and be charged without you getting fried. Although I've only been an owner since end Sept , I've had many opportunities to get sizzled and I'm still here. Picking up my second ev tomorrow.

Edited by Ethan Edwards on 04/12/2021 at 01:37

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Sat 4 Dec 2021 09:36

All EV’s - Batteries & Charging - Andrew-T

<< ... my late father who lived in Keighley mentioned DC mains and that shock deaths were frequent - could be down to other factors such as running irons from light fittings being the norm! I only remember AC being of early 60's vintage ... >>

When we moved to Cardiff just after the war, parts of the city were on 230v AC, others on 200v DC. I've no idea how electrical shops coped with that. Fortunately it was sorted out quite soon.

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Sat 4 Dec 2021 06:07

All EV’s - Batteries & Charging - Brit_in_Germany

You write that the motor is dc. This is not generally true. Some will be ac like the Tesla S or Renault Zoe while others will use a permanent magnet (ie rare earth rich) dc motor.

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Sat 4 Dec 2021 09:58

All EV’s - Batteries & Charging - mcb100

You’re correct, my error.

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Sat 4 Dec 2021 09:07

All EV’s - Batteries & Charging - mcb100

My 99% quoted figure is from a respected source, quoting a Tesla 3 charging from a 400V DC source. Ideal temperature for an EV battery seems to be 20-25C, minimising the need for charging losses via having to heat or cool it.
Tesla quote for the Model Y that it takes 87.686kWh to take a 77.702kWH battery from 0-100% from a 240V source. In reality, this is a bit theoretical in that you wouldn’t get to zero unless the car had ground to a halt, and if you’re on a DC charger you’d typically stop charging at 80% to cut heat build up, and subsequent inefficiency from having to employ battery cooling. On a long, multi-stop trip it’s usually a shorter total elapsed time to make an additional ‘splash and dash’ than wait for a rapid charger to get the battery to 100%.
Regards safety, if you’re using anything other than a 3 pin plug then there’s nothing glowing until both ends of the cable are locked in and the car has said hello to the charge point.

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Sat 4 Dec 2021 09:46

All EV’s - Batteries & Charging - thunderbird

Surely all this is irrelevant. If you charge the car using the correct cable from the appropriate supply point you will be perfectly safe. No doubt there will be the usual bunch of m****s out there who believe they know better than the manufacturers and have ways of getting the car to charge faster to higher levels but if Darwin's law applies they won't be around long enough to cause the rest of us issues.

If you think about it pouring highly volatile petrol into an open tank filler at a petrol station surrounded by loads of other people doing exactly the same seems far more dangerous than plugging a properly insulated cable into the car and charging point and then starting charging however its done. How many cars have I seen burst into flames during at a petrol station in the past 65 years, total none.

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Sat 4 Dec 2021 11:00

All EV’s - Batteries & Charging - Bolt

Surely all this is irrelevant. If you charge the car using the correct cable from the appropriate supply point you will be perfectly safe. No doubt there will be the usual bunch of m****s out there who believe they know better than the manufacturers and have ways of getting the car to charge faster to higher levels but if Darwin's law applies they won't be around long enough to cause the rest of us issues.

If you think about it pouring highly volatile petrol into an open tank filler at a petrol station surrounded by loads of other people doing exactly the same seems far more dangerous than plugging a properly insulated cable into the car and charging point and then starting charging however its done. How many cars have I seen burst into flames during at a petrol station in the past 65 years, total none.

Unless they have access to the software which is likely locked no one should be able to tamper with charge control, my only thoughts are with the EMF from the cables charging at such high amps kwh as its very high compared to house usage !

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Sat 4 Dec 2021 11:30

All EV’s - Batteries & Charging - thunderbird

my only thoughts are with the EMF from the cables charging at such high amps kwh as its very high compared to house usage !

Excuse my ignorance if I am wrong but if you have a wall box professionally fitted where would the risk come from? Surely the amps and EMF would be taken into account in the specifying of cable, plugs etc.

There will no doubt be some muppets who try to wire the charging cable into existing circuits but that would be their own fault and not the fault of the car manufacturer or cable supplier. Tampering with gas services is an offence but not sure if tampering with the wiring after the consumer unit is, it didn't used to be. But if its proven that any works were dangerous there must still be the provision to prosecute.

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Sat 4 Dec 2021 12:15

All EV’s - Batteries & Charging - Bolt

my only thoughts are with the EMF from the cables charging at such high amps kwh as its very high compared to house usage !

Excuse my ignorance if I am wrong but if you have a wall box professionally fitted where would the risk come from? Surely the amps and EMF would be taken into account in the specifying of cable, plugs etc.

There will no doubt be some muppets who try to wire the charging cable into existing circuits but that would be their own fault and not the fault of the car manufacturer or cable supplier. Tampering with gas services is an offence but not sure if tampering with the wiring after the consumer unit is, it didn't used to be. But if its proven that any works were dangerous there must still be the provision to prosecute.

Its not the installation I was getting at due to the safety features, but the cables and connections to the car still have emf around them and vary due to atmospheric conditions which I think are leaving the possibility of electrical shorts a possibility and or overheating

Just my thoughts and could be wrong, but even .5 and under volts can cause a fire in the right circumstances

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Sat 4 Dec 2021 11:35

All EV’s - Batteries & Charging - mcb100

glowing = flowing

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Sat 4 Dec 2021 11:55

All EV’s - Batteries & Charging - thunderbird

glowing = flowing

I would suggest that glowing = run like the clappers and call for help.

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Sat 4 Dec 2021 12:37

All EV’s - Batteries & Charging - Andrew-T

glowing = flowing

I would suggest that glowing = run like the clappers and call for help.

Nice typo :-) I would suggest taking a second or two to pull a plug or throw a switch as a better choice than running. Anyway any decent installation would have tripped out before anything started to glow :-)

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