Going Electric.. present small car options.. confusing

[puntofan01]

This is kind or relevant and does affect motorway range but the added weight/complexity almost outweighs the pros, also EVs are expensive and adding more R&D to the costs to create a 2 speed gearbox that the computer controls will only make an already expensive car more expensive.


Not entirely true, my Ampera has a sort of gearbox to engage the ICE when the batteries are depleted or when you ask it to so you can reserve your battery for later use, obviously this is far from a traditional gearbox and more a series of clutches but it does add significantly more efficiency to the electric motor at the cost of much more complexity.

The car has 2 electric motors, one is the primary drive motor and the other motor acts as the generator for the ICE but can also drive the car (as motors can act as generators or motors depending on which way the current is going)
When you're accelerating on purely electric the 111kW primary motor accelerates you through one fixed ratio to the limited top speed of 100mph where the motor is at around ~8500rpm iirc, this is not as efficient as running the electric motor at a lower RPM even discounting wind resistance etc
Given my car has the second motor generator, when cruising at a set speed the car clutches in the secondary motor and reduces the rpm of the primary motor instead using both motors at a low RPM (something like 3000rpm at 70mph). As a result the Ampera is capable of very high efficiency when operating at a constant speed despite being a very heavy car lugging around an ICE and fuel tank etc. 4.5mi/kWh is achievable in good weather in an Ampera which is very impressive and it is down to this dual motor low rpm setup.
It adds a lot of complexity and only really made sense to implement on the Ampera because it already needed that second motor/generator for the range extender to work but it does prove a lower RPM motor is more efficient than high RPM, don't ask me the technicalities because I don't understand exactly how. I will also point out to avoid confusion this is all without the ICE running, adding the ICE into the mix changes all of this considerably given you are then using two fuel sources.

I'm glad that someone actually understood what I was meaning.

 

[StevenRB45]

Thought for the day..

If you have a dual or tri motor setup can you run different gear ratios on each motor?

Probably a stupid thought but this is not reciprocating motion we're talking about so if one motor drops out of it's power band doesn't necessarily matter if the bearings could take it as long as it doesn't become drag.

Acceleration the lower geared motor does the work, top speed the other one does, at a cruise they both chip in.

No idea if this is a thing..just a thought on my lunch time walk.

 

[AndyRKett]

Thought for the day..

If you have a dual or tri motor setup can you run different gear ratios on each motor?

Probably a stupid thought but this is not reciprocating motion we're talking about so if one motor drops out of it's power band doesn't necessarily matter if the bearings could take it as long as it doesn't become drag.

Acceleration the lower geared motor does the work, top speed the other one does, at a cruise they both chip in.

No idea if this is a thing..just a thought on my lunch time walk.

If you have two motors you can design the motors for different applications, so have one that’s more efficient running at a high speed and one that works best at a lower speed, the. You can combine/blend the two motors to result in best performance you don’t generally bolt the output of your motor to the wheel you’ll have some sort of gearing normally, even if you did bolt the output of the motor to the wheels the gearing is one to one.

I think Tesla do this with there dual motor set ups, one is best suited to setting off and low speed acceleration and the other motor is better suited to carrying speed. Electric motors are not like engines they don’t have a narrow power band you have to sit in the middle of, but if you have an electric motor that works best between 0-16,000 rpm, obviously your wheels won’t be doing 16,000 rpm so you design your gearing to match the desired speed of the car compared to the output speed of the motor.

You might have one motor that is 70kw for doing most of your acceleration and stopping, then you have a second motor that is also 70kw which is geared to kick in over 50mph to provide extra power and acceleration when needed, this is more efficient to use two smaller motors that you can switch on and off, than having one massive 140kw motor than would use much more battery power at 20 - 30mph.

If you have two motors it’s more efficient to have one geared lower and one geared higher then you can run your second motor at lower rpm using less power but you still have your other motor geared lower for when you slow right down or stop and start.

As I said it’s a bit like having a V8 engine and all the power of a powerful V8 but then you turn off half the cylinders when you’re doing 20mph and in essence have a standard 4 pot. The gearing on the motor is for energy efficiency rather than keeping anything in a power and because as an electric motor gets faster the power (BHP) increases and the torque stays the same.

If you put a gearbox in an electric car the benefits of the gearbox would need to be outweighed but the weight gain, if you’ve got two motors you’ve got two gears and your then not adding any weight.

 

[StevenRB45]

Public fast chargers had been free in my area until recently noticed a sign go up saying from April 1st they would be charging 35p per KWH.

Making your average electric car powered (somewhere between 3 and 4 miles per kwh) off that charger have a cost per mile in fuel of 10-15p..Good job lads it costs as much as a petrol in fuel nevermind a diesel.

 

[DaveMcT]

A Sturmey Archer style three speed gearbox (does not have to be a hub gear) would be very efficient and relatively cheap to manufacture. It's just one set of straight cut planetary gears that give two speeds plus 1:1.

 

[AndyRKett]

A Sturmey Archer style three speed gearbox (does not have to be a hub gear) would be very efficient and relatively cheap to manufacture. It's just one set of straight cut planetary gears that give two speeds plus 1:1.

Still not needed on an electric car.

As previously noted above, the cars that multiple gears usually have multiple motors. With a powerful motor having one gear and a less powerful motor having another gear.

 

[Most Easterly Pandas]

Not entirely true, my Ampera has a sort of gearbox to engage the ICE when the batteries are depleted or when you ask it to so you can reserve your battery for later use, obviously this is far from a traditional gearbox and more a series of clutches but it does add significantly more efficiency to the electric motor at the cost of much more complexity.

The car has 2 electric motors, one is the primary drive motor and the other motor acts as the generator for the ICE but can also drive the car (as motors can act as generators or motors depending on which way the current is going)
When you're accelerating on purely electric the 111kW primary motor accelerates you through one fixed ratio to the limited top speed of 100mph where the motor is at around ~8500rpm iirc, this is not as efficient as running the electric motor at a lower RPM even discounting wind resistance etc
Given my car has the second motor generator, when cruising at a set speed the car clutches in the secondary motor and reduces the rpm of the primary motor instead using both motors at a low RPM (something like 3000rpm at 70mph). As a result the Ampera is capable of very high efficiency when operating at a constant speed despite being a very heavy car lugging around an ICE and fuel tank etc. 4.5mi/kWh is achievable in good weather in an Ampera which is very impressive and it is down to this dual motor low rpm setup.
It adds a lot of complexity and only really made sense to implement on the Ampera because it already needed that second motor/generator for the range extender to work but it does prove a lower RPM motor is more efficient than high RPM, don't ask me the technicalities because I don't understand exactly how. I will also point out to avoid confusion this is all without the ICE running, adding the ICE into the mix changes all of this considerably given you are then using two fuel sources.

Your ampera is also far more complex than a BEV having and ICE also, and as such needs a gearbox.

Try not to compare your Ampera with a full BEV. As amazing as the Ampera is (Vauxhall made a massive mistake pulling it IMO) its underpinnings are still essentially a Hybrid. It’s not really any different to how and why the Prius as a transmission system.

 

[Most Easterly Pandas]

Public fast chargers had been free in my area until recently noticed a sign go up saying from April 1st they would be charging 35p per KWH.

Making your average electric car powered (somewhere between 3 and 4 miles per kwh) off that charger have a cost per mile in fuel of 10-15p..Good job lads it costs as much as a petrol in fuel nevermind a diesel.

35p seems steep for a fast charger, unless that also covers parking charge while charging for a few hours.

35p a unit is normally the price of rapids, where by you’re also paying for the convenience of rapid charging speeds.

 

[varesecrazy]

I see that PHEV is becoming a dirty word..

BMW are having to advertise theirs to shift stock before they are taxed 'properly'

I was amused the ad. Stated
'Carbon Neutral in Manufacture'
Once in use this may not remain the case

Shock..horror !!

 

[Most Easterly Pandas]

I see that PHEV is becoming a dirty word..

It is with some. I’ve no issue with them myself, an EV mile is an EV mile IMO, and even if only purchased for tax reasons by a fleet, they’ll be off fleet within a few years and then filter into the used market where they’ll likely be used properly.

 

[DaveMcT]

As previously noted above, the cars that multiple gears usually have multiple motors. With a powerful motor having one gear and a less powerful motor having another gear.

Motors have their most efficient speeds so it depends which offers the least cost. For some reason the auto industry seems to hate epicyclic gears (unless found in a slush box automatic). Yet it's been proved time and again they are less costly to make and are more efficient than parallel shaft gears.

Another option is switchable multi pole motors. These can have any number of poles (subject to speed limitations and space inside the casing). The poles/coils can be switched to give a gearing effect.

At 50Hz a.c. two-pole motors operate at 3,000 rpm unloaded, and approximately 2,900 rpm under load.

Four-poles gives 1,500 rpm and about 1,425 rpm under load.

Six-pole motors run at 1,000 rpm unloaded and around 900 rpm loaded.

We can go to 12-poles, 16-poles, etc, though larger pole counts usually mean a large diameter casing which limits the max speed.

 

[AndyRKett]

Another option is switchable multi pole motors. These can have any number of poles (subject to speed limitations and space inside the casing). The poles/coils can be switched to give a gearing effect.

At 50Hz a.c. two-pole motors operate at 3,000 rpm unloaded, and approximately 2,900 rpm under load.

Four-poles gives 1,500 rpm and about 1,425 rpm under load.

Six-pole motors run at 1,000 rpm unloaded and around 900 rpm loaded.

We can go to 12-poles, 16-poles, etc, though larger pole counts usually mean a large diameter casing which limits the max speed.

What you’re saying doesn’t make very much sense here.

This doesn’t make a lot of sense to anyone who has designed or worked on electric motors, you don’t just add more poles to the motor for “gearing” and you can’t just turn off poles in a motor, without there being consequences to that.
Assuming an electric car even uses an AC motor as a lot of them don’t.

The motor in a Tesla model S capable of 155mph is able to rotate at about 18,000 rpm so bearing that in mind 3000rpm is a touch over 25mph. Non of your maths above is applicable.

 

[DaveMcT]

My maths as you "politely" put it is talking about multi pole induction motors. They are simple machines that do not need fancy are earth magnets. As you well know they create a rotating field inside the casing. The number of magnetic poles defines the speed that field rotates. The numbers given assume 50Hz. Multiply that frequency by 5 and 3000rpm becomes 15,000 rpm. So what's your problem?
Switching the poles allows one motor to have two or four or eight etc and so run at different synchronous speeds. Again what's your problem?

 

[AndyRKett]

I literally have no idea what you’re trying to explain here or why!? Are you saying that you should packs motor with 12 poles then just turn off the poles you don’t want to slow down/speed up the running of the motor ?? The comparison is to build a 12 cylinder car and turn the spark plugs to the pistons on and off to increase or decrease speed? To do that would not alter the “gearing” of a engine so why would having more or less poles alter the “gearing” of the motor?

If you turn off pistons on an engine you create a lot of internal drag it’s weight that’s not then needed. In an electric motor what would you be doing with the switched off poles? They would generate current. And unless plugged into anything the current could circulate in the windings and damage them. If connected to a load then it would create a back emf that resists the turn of the motor. What you’re saying isn’t how motors work it’s not how they are wired and you can’t gain any gearing effect by altering the number of poles because once you’ve built your motor you can’t then change the number of poles.

My original comment the comment you replied to was simply put that a powerful motor would have one gear a less powerful motor would have a different gear and both motors with both different gears can appear in the same car, and do different jobs depending on the speed of the car.
I’m not sure therefore why you started talking about gearing a motor by the number of its poles?

 

[Didge3]

I see that PHEV is becoming a dirty word..

BMW are having to advertise theirs to shift stock before they are taxed 'properly'

The problem with most PHEVs is they are an electrified version of an existing petrol/diesel car and usually they only have full power/functionality available under ICE power. This applies to the Outlander PHEV, 330e and Golf GTE's, the Outlander and 330e have relatively big (for what is supposed to be a fuel saving car) 2.0L petrol engines that are required to give the cars full acceleration where they usually use a relatively small electric motor (something like 70hp).
If used properly and kept in electric mode for driving around town you're still getting emission free driving which in city centres is a win either way.
The dirty word/term for me is, self-charging hybrid :yuck:

It is with some. I’ve no issue with them myself, an EV mile is an EV mile IMO, and even if only purchased for tax reasons by a fleet, they’ll be off fleet within a few years and then filter into the used market where they’ll likely be used properly.

Precisely! Nobody is going to spend the extra cash on a PHEV second hand versus regular ICE if they have no intention of plugging it in, well not until ICE is banned and you'll be forced to at bare minimum buy a PHEV by which point I'm hoping BEV's will make more sense and can meet range requirements of most everyone.
Cars like Volt/Ampera/i3 Rex, which are more EREV's should've been the norm for PHEV's, the Ampera sort of discourages driving on the range extender around town just because it'll rev hard to keep up demand, you're much better off using it on the motorway where cruising it stays tame and switching to EV power in town, I believe the i3 Rex is pretty similar in behaviour

 

[Most Easterly Pandas]

The problem with most PHEVs is they are an electrified version of an existing petrol/diesel car and usually they only have full power/functionality available under ICE power. This applies to the Outlander PHEV, 330e and Golf GTE's

And any other PHEV like you say. We are talking full power however like you say, which for some will never be called upon.

the Outlander and 330e have relatively big (for what is supposed to be a fuel saving car) 2.0L petrol engines

Or a tiny engine in the case of the Outlander for whats a 2300kg+ vehicle.

Engine size is relatively irrelevant however as most are normally Atkinson Cycle engines, as such the engine would be gutless on its own if not working along side the electric motors in a Hybrid / PHEV.

The dirty word/term for me is, self-charging hybrid :yuck:

Oh you're one of them

Don't like factual phrases

Cars like Volt/Ampera/i3 Rex, which are more EREV's should've been the norm for PHEV's

Not at all. A PHEV is far more economical than any REX when driven using Petrol. A PHEV has the ability to directly drive the vehicles wheels where as a REX doesn't, and only has the capability of charging the battery and the car is then driven by the electric motor only. Every time you convert energy you incur losses, as such a PHEV which converts the Petrol straight to kinetic energy of the vehicle, rather than a REX which changes it from Petrol, into a battery, and then into the motor, suffers far higher losses.

From memory the i3 REX for example only does circa 30MPG on petrol! My previous Prius PHEV when not plugged it and only propelled fully by Petrol was capable of an easy 70MPG (real world calcs) at motorway speeds.

A REX is only something made to help those with range concerns, and is certainly far from cost effective.

 

[StevenRB45]

Oh you're one of them

Don't like factual phrases

It's also disingenuous...my Mazda is self charging...it has an alternator.

 

[Most Easterly Pandas]

It's also disingenuous...my Mazda is self charging...it has an alternator.

I don't agree. Your Mazda isn't a hybrid and its alternator charges a 12v auxiliary battery. This doesn't in itself drive the vehicle, the ICE and only the ICE does

 

[StevenRB45]

I don't agree. Your Mazda isn't a hybrid and its alternator charges a 12v auxiliary battery. This doesn't in itself drive the vehicle, the ICE and only the ICE does

Erm...it doesn't need to be plugged it into the mains to charge the battery.

So factually it is self-charging.

I understand the whole process is different, reclaiming energy that is lost into the environment in a normal car to charge the battery..but the point I was making is..it's a stupid tagline.

 

[Most Easterly Pandas]

but the point I was making is..it's a stupid tagline.

Aren't most? It's a stupid / wacky tagline that get remembered and discussed, exactly what advertising strives to achieve really.