fiver for a 20 minute fast charge strikes the right balance

EricMears

Martyn1981 wrote: »

Also mid 2016 sounds optimistic, unless folk are aware of these in development?

Mart.

Given that we're already half way through the 7th month of 2016, "mid 2016" might need a time machine

treemachine

Pincher wrote: »

If I was designing it, I would provide a limp home option for 100% electric vehicles. Something like a lawn mower engine, with a five litre tank. Pull the chord, charge for five minutes. £200?

I've thought that as well. I'd imagine that the waste heat from the engine could be used to heat inside the car.


I wouldn't think it too hard to design it so that the engine could be removed for local journeys or during the summer.

EricMears

treemachine wrote: »

I've thought that as well. I'd imagine that the waste heat from the engine could be used to heat inside the car.

I wouldn't think it too hard to design it so that the engine could be removed for local journeys or during the summer.

Please scroll up the page and read my post #9 !

It clearly explains that such an engine already exists but that even the smallest version that would be able to charge the car at all (at a rate of extending range by 5 miles per hour of running) would be too big and heavy to carry around in the boot . I'd suggest that something six times as big that might give you a ten mile 'boost' after 20mins running could be a viable addition but would probably mean removing the back seat or towing around in a trailer (except that no BEVs have type approval for towing).

treemachine

EricMears wrote: »

Please scroll up the page and read my post #9 !

It clearly explains that such an engine already exists but that even the smallest version that would be able to charge the car at all (at a rate of extending range by 5 miles per hour of running) would be too big and heavy to carry around in the boot . I'd suggest that something six times as big that might give you a ten mile 'boost' after 20mins running could be a viable addition but would probably mean removing the back seat or towing around in a trailer (except that no BEVs have type approval for towing).

I read your post and I was confused when you talked about 1.2 kw - the generator you refer to produces 2 kw?


Here is a generator that weighs 21kg and produces 2kw. I wouldn't see the prime purpose of a generator like this as charging the battery, I would see the prime purpose as using the electricity generated to directly power the car on long journeys.


https://www.machinemart.co.uk/p/eu20i-petrol-driven-generator/

Martyn1981

treemachine wrote: »

Here is a generator that weighs 21kg and produces 2kw. I wouldn't see the prime purpose of a generator like this as charging the battery, I would see the prime purpose as using the electricity generated to directly power the car on long journeys.

Think about it this way, a 2kW generator will take one hour to generate 2kWh.

An EV can get about 4 to 6 miles per kWh, so at best, the 2kW charger will move the car 12 miles in 1 hour. Therefore, you'd be looking at 12mph.

That's probably a dangerous speed, so if you had 12 miles to go, you'd have to stay put, generate 2kWh, then drive home at a safer speed.

Mart.

almillar

treemachine - as I said above, and as EricMears and Martyn1981 have helpfully explained, your idea vastly underestimates the amount of energy moving a vehicle requires. As Martyn1981 shows, sit for an hour with your noisy generator running on my Zoe get 2kWh of electric. I would get 4.5m/kWh driving economically (12mph isn't feasible IMO) so that's 9 miles of range. If I was in a desert I might see the point, but chargers are easy enough to find in my part of the country that it would take less time to drive to one, and charge, than to sit with a noisy generator running. A 3-pin plug will give ~3kW, many chargers are 7kW, some are 22kW and some are 43AC, 50DC kW. So you can see that carrying a 2kW generator is a waste of time between all these places.
BMW have implemented your idea, without the removable part, in the REX (range extender) i3. The engine is much bigger than what you're talking about.

EricMears

treemachine wrote: »

I read your post and I was confused when you talked about 1.2 kw - the generator you refer to produces 2 kw?

Here is a generator that weighs 21kg and produces 2kw. I wouldn't see the prime purpose of a generator like this as charging the battery, I would see the prime purpose as using the electricity generated to directly power the car on long journeys.

https://www.machinemart.co.uk/p/eu20i-petrol-driven-generator/

As I explained within that post, 5A (or 1.2kW) is the minimum charging current that my 'granny lead' will accept. It will also accept a current of 10A (or 2.4kW which is of course more than 2kW) but can't make use of just any available current.

This is a MSE site and I was quoting the cheapest machine I could find that would do the job so used an example priced at £150. The Honda generator from Machine Mart would cost £1246.80. I realise it's almost half the weight but is that really worth a premium of over £1000 ?

Having such an engine running inside a moving car really isn't a great idea ! But even if you could solve the problems of fixing it firmly in place and venting the exhaust fumes outside it wouldn't be a viable power source for driving the vehicle (as Martyn explains).

But if you're happy with a vehicle that runs a petrol engine to generate electricity that in turn drives the car, you should really be looking at a 'hybrid' rather than a 'BEV'.

EricMears

Martyn1981 wrote: »

An EV can get about 4 to 6 miles per kWh

Just one minor quibble about that. My e-Up! is one of the smaller BEVs available. There are even smaller ones around but they're ridiculously cramped and are unlikely to have room to carry a week's groceries, never mind a 20kg generator.

My average fuel consumption has been 3.86 mls/kWh. It would very likely do better than that on a long level road like a motorway but I'd hate to rely on it ever getting up to 6 mls/kWh.

But apart from that, the rest of the arithmetic makes sense. Thanks

Martyn1981

EricMears wrote: »

Just one minor quibble about that. My e-Up! is one of the smaller BEVs available. There are even smaller ones around but they're ridiculously cramped and are unlikely to have room to carry a week's groceries, never mind a 20kg generator.

My average fuel consumption has been 3.86 mls/kWh. It would very likely do better than that on a long level road like a motorway but I'd hate to rely on it ever getting up to 6 mls/kWh.

But apart from that, the rest of the arithmetic makes sense. Thanks

Cheers Eric, that's really interesting. Real world numbers always are.

I was using numbers I'd seen in discussions, and to avoid criticism was aiming high. I wouldn't particularly enjoy being stuck behind you doing 7.92mph. When I was younger and slimmer, I could have jogged alongside and had a nice chat.

Out of interest, do you have any city v's speedy numbers? I appreciate that regenerative braking isn't 100% efficient, but also assume that wind resistance affects 'fuel' economy, especially as you get into the 40mph+ range.

Mart.

EricMears

Martyn1981 wrote: »

Cheers Eric, that's really interesting. Real world numbers always are.

I was using numbers I'd seen in discussions, and to avoid criticism was aiming high. I wouldn't particularly enjoy being stuck behind you doing 7.92mph. When I was younger and slimmer, I could have jogged alongside and had a nice chat.

Out of interest, do you have any city v's speedy numbers? I appreciate that regenerative braking isn't 100% efficient, but also assume that wind resistance affects 'fuel' economy, especially as you get into the 40mph+ range.

Mart.

No reliable comparative numbers I'm afraid. I log what it does between charges and take the average of all such daily (usually - though sometimes skip a charge on a low use day) results but figures over different sorts of terrain aren't much better than guesswork.

Regenerative braking certainly isn't 100% efficient - but it's streets ahead of wearing out brake pads and can make huge differences to the indicated fuel efficiency. One regular trip we do is home to Ma-in-Laws & back @just under 4 miles each way. According to the drop in indicated range, I can often do the outward trip with no reduction (sometimes even a small increase) in range but the homeward trip usually wipes 10 or 12 miles off the range. The difference is of course caused by hills : there are a couple of steep downhill stages going and of course they're uphill coming home. Regenerative braking can easily add a mile or two to range when going half a mile downhill but alas, half a mile uphill can steal 5 miles of range.

Forget the 'milk float image' ! No chance of me ever driving along at 7.9mph. Huge torque & instant response usually gets it to speed limit within a couple of seconds