Electric vehicles-Conversions

[harryp]

however to reach those high power levels without ridiculously high current through the cable it is done at 800 volts, 440 amps

Simon, I would have to say that 400 amps is already " ridiculously high " and from a safety point at least, so is the voltage. It begs a new beginning in Darwin Awards; the general run of the public, being like the general run of pedestrians involved in road traffic accidents, as just a little too slow.
Having done my apprenticeship with a manufacturer of 400Kv switchgear and tested same, the repercussions do not bear thinking about

[Mandrake]

Currently in use 50kW CCS and Chademo rapid charge standards which have been around for years now (since 2009 for Chademo) are already 125 amps at 400 volts DC.

The cables are about 30-40mm in diameter. There are a lot of safety features and interlocking - the plugs are purpose designed for ev charging, are water proof when plugged in and safe to plug in and disconnect in the rain, are physically locked while charging is occurring so you can't yank them out in the middle of a charge, and are not live until after the plug has been plugged in, physically locked, data communication has been established with the car, and safety checks such as earth resistance tests have been completed. Only then does the contactor in the charge close to apply power.

Tesla Superchargers have been around since 2013 and they are 125kW so about 312 amps at 400 volts DC.

The charging standards are very safe with multiple layers of safety almost to the point of paranoia. That also applies to the lower power household AC charge points.

For example in my 7kW charger installation at home a separate mini-consumer unit has been fitted connected directly to the meter separate to the main consumer unit, it has a 63 amp circuit breaker and an RCB, the cable from there under the house out to the charge point is heavy 40 amp armoured cable, the charge point itself on the wall has another circuit breaker and another RCB, the charge point has a contactor that does not apply any high voltage to the plug until after it is connected to the car and has communicated with the car.

If you pull the plug out while charging the pilot signal breaks first and immediately triggers the contactor in the charge point to open and charging to end before the line pins break contact preventing arcing and any chance of shock. The plugs are completely water proof when plugged in and are also safe to plug in and unplug in the rain. (I've done it loads of times...)

It's all very well thought out and has heavily regulated safety standards, and is infinitely safer than an overloaded dodgy 13 amp ring circuit so I don't have any worries about it. I also haven't heard of any electric shocks fatal or otherwise from electric car charge points in the media or on EV forums - I'm sure it will happen one day probably due to someone tampering with the wiring of their home charge point, but as installed they are very safe and certainly far safer than typical 240v internal home wiring.

The sky is not falling on our heads.

[Hell Razor5543]

The way I would do this (as well as the monitoring circuits) is to start charging at a nice safe level, and then, constantly monitoring things, steadily ramp up the available charging current. Once it started to become unstable I would then drop it down a few percentage points (5 - 10%) to keep things safely in tolerance.

[CitroJim]

Simon, clearly well thought out then. Good. They seem almost idiot-proof...

I wonder if the same conversations were had when self-service petrol pumps were first mooted and the potential dangers therein...

I suppose they're safe in normal use and only dangerous if tampered with...

The only worry I have is that however idiot-proof something is made, all that happens is that sooner or later a better quality of idiot comes along to defeat it...

[Hell Razor5543]

I remember somebody saying something like "When mankind manages to make something fool proof somebody else breeds a bigger fool!".

[Mandrake]

Well that crazy Bjørn Nyland is at it again. Not content with tugs of war with a Toyota Landcruiser or Hummer in the snow, this time he wanted to find out if he could tow a 43 ton lorry in the snow...



Interesting to see how the front and rear traction control is completely independent since there is no mechanical link between front and rear on an AWD electric car. Even when the front spins for a moment the rear is still gripping and keeping up momentum and vica versa.

[Mandrake]

Ok here's one I don't believe I've seen before - an EV conversion of the 2CV



Skip ahead to 3:30 if you just want to see the 2CV.

[Mandrake]

For those of you who like to pour over the small details of how a car is put together, especially in the plumbers nightmare of an engine bay, here is a nice video of a guy showing the insides of the front of a Tesla Model 3 with the "frunk" removed, which is normally hides all the gubbins. The first video is the top side the second is from underneath:





Looks relatively complex, but well laid out. A few of things of note - despite what I said earlier (possibly in another thread) it still does in fact have a lead acid 12v battery! Rumours were that it had been eliminated in favour of an always-on DC-DC inverter, but nope!

The second is that the car is clearly designed to be all wheel drive with the one chassis design right from the beginning because in this RWD car there is a massive hole where the front motor and differential would be, complete with mounting brackets for the non existent motor! Makes perfect sense but it does look kinda funny... You could literally smuggle a body bag in the space left under the front in the RWD model.

There is an interesting mixture of steel and aluminium in both the chassis and body panels, for example the doors are aluminium but the quarter panels are steel. The main chassis rails under the front are steel but the crumple rails in front of that are aluminium.

There is a conventional looking oil filter screwed onto the side of the motor/differential assembly at the back! And what looks like an electric oil pump. Interesting, and not something I have seen on other EV's.

[Mandrake]

Remember the Rimac Concept One EV Hypercar that Hammond crashed recently ? That has been out for a couple of years now, and here is their new model, just announced. Yowzers! Some unbelievable performance figures there. Who said electric cars were slow milk floats ?

https://newatlas.com/rimac-c-two-electr ... car/53703/

[MikeT]

The police are going to have to up their game to match these rapid EV's. Trade-in their eurocopter for a Typhoon, perhaps?

[bobins]

A highly accurate EMP gun should do the trick

[Mandrake]

The police are going to have to up their game to match these rapid EV's. Trade-in their eurocopter for a Typhoon, perhaps?

Or just buy said EV ?

[MikeT]

This is where the push to have internet connectivity comes in - remote kill.

[Mandrake]

Another mini video by Bollinger, this time going into more detail about the suspension.



This video answers the question we had of why is the sphere mounted on the side of the ram ? It turns out that there are actually two spheres per wheel, and it is a double acting ram!

Previous videos did not show inside the ram nor did they show what turns out to be the main sphere for each wheel, which is mounted separately with a flexible hose.

All Citroen Hydropneumatic strut rams are single acting pistons. That means on the compression stroke the piston forces oil into the sphere through the damper, however on the rebound it relies on the gas pressure in the sphere to push the oil back out through the damper and follow up the piston. The only use of a double acting ram on the Citroen system is for the Activa anti-roll rams, which need to be double acting to allow the roll bar to be twisted in either direction.

On the Bollinger system they have a double acting ram for the strut rams for each wheel - the top end with the large piston area is connected via a flexible hose to a much larger sphere than we have not previously seen depicted, but which is shown in this video. In addition the smaller sphere mounted on the side of the ram is connected to the "back" side of the piston at the bottom - because there is reduced cross sectional area on the back of the piston, (like on a power steering rack) the sphere connected to this side has to be smaller for the same springing rate.

So why go to this extra trouble of two spheres per wheel and a double acting ram ? One reason is shown in the video - making the springing rate very linear over a very wide range of loads and suspension travel.

Normal hydropneumatic with a single acting piston is non-linear when considered over a wide range of oil displacement in the sphere - as you compress the gas further you reach a point where the gas volume is small relative to the oil displacement and it rapidly gets stiffer in a non-linear way.

Normally you don't notice this effect because in an unladen Citroen the entire suspension travel is only a small proportion of the total possible diaphragm displacement inside the sphere, so over this reduced operating range the suspension approximates a linear springing rate. However if the spheres are low on gas and you load the car up you'll notice it gets hard and suspension travel becomes limited very quickly.

In the two sphere double acting ram scenario used in the Bollinger when the suspension is compressed oil is pushed into the larger top sphere by the large piston, and simultaneously pulled out of the smaller bottom sphere by the gas in the bottom sphere following up the smaller back side piston. Total springing stiffness at any given point of travel is the sum of these two spheres which are operating in opposite configuration.

The beauty of this is it would make the springing rate very linear over a very wide suspension travel and load range. When the gas in one sphere is being compressed and reducing in volume and is starting to become non linear, the expanding large volume of gas in the opposite sphere will provide the dominant compliance, and vica versa. I haven't studied it enough to work out whether it makes the springing rate perfectly linear over the entire range, or whether it just becomes a much better approximation than a single acting system, but looking at the graph they show in the video tends to suggest that it makes the springing rate almost perfectly linear. Bravo!

I can see a second major potential benefit of using a double acting ram for the suspension which they don't talk about at all, and that is avoiding cavitation on the piston under rapid large suspension movements, especially if you have stiff damping.

In one of the mega long harsh Hydractive 2 ride threads I remember discussing the possibility of cavitation at the piston being a source of ride harshness under extreme conditions. With a single acting piston you have no problem on the compression stroke as the oil between the piston and damper valve, and from damper valve to gas interface at the diaphragm will always remain compressed no matter how hard or sudden the movement is.

However there is a potentially significant problem with rapid rebound movements because when the piston moves away from the sphere the only thing pushing the oil out to follow up the piston is the spring rate of the gas pressure in the sphere. Furthermore it is trying to push it through the damper valve, which will restrict the flow of oil trying to follow up the piston. The stiffer the damper valve is the more it will restrict that flow.

If the damper valve is sufficiently stiff and the rebound movement is sufficiently large and abrupt, it's possible that the oil can't follow the piston and a void will form in the oil between the damper valve and the piston, and then momentarily later it will catch up and "crash" into the piston harshly, in essence a kind of cavitation as it would cause a large shockwave. This places an upper limit on how stiff you can tune the damping without risking cavitation, and I suspect Hydractive 2 comes close to that limit under certain conditions.

On the double acting ram design this can be avoided completely because no matter which way the ram moves one sphere always has oil going into it, and thus the damper valve for that sphere in that direction can restrict movement without risking cavitation. So you would use asymmetric damper valves in each sphere which provide most of their damping on the "in" direction. So your compression damping would be set primarily by the damper valve to the top sphere and the rebound damping by the damper valve for the bottom sphere. The damping for the outflow direction for each sphere would be kept to a minimal level to avoid cavitation occurring.

Clever design using two spheres and a double acting ram for each wheel - I don't think this has been done before anywhere else ? Certainly not by Citroen.

[RichardW]

Interesting stuff on the Bollinger. Wonder if they will get it type approved and into production, or maybe they will just be niche cars built as one offs and IVAd.

Seems that the pure EV companies are involved in a race to the top rather than the usual race to the bottom. It seems that if money is no object then you can make the range problems go away, and have some hysterical performance into the bargain. Hopefully there will be continuing improvements in the cost / capacity balance of batteries in mainstream cars that will bring prices into line with ICEs and range into the 200-300 miles arena that will make them acceptable for the majority of people.