[Duncan]

Hi Guys

I have a problem,
I have my "Device" - which is short ranged but high performance

Many years ago back in the 80's one of my friends had a kit car - a Marlin Roadster

This was great and I thought it looked lovely

My friend has now retired and is living in a canal boat - a Narrow boat

So I asked him about the Marlin - which has been off the road for a long time
He decided to keep his Marlin - but revealed that he had bought a "spare" which was no use as a spare as it was a Mk2

Anyway I got his spare shipped out here so it's now a project for me

But it's tiny - much smaller than my device with Marina suspension

I just don't think that I can fit enough batteries to be any good

With the Marina suspension it is not going to be a high performance machine like my Green one so it needs to be able to cruise a decent distance

I just don't think I'm going to be able to fit enough batteries

Any ideas or am I just going to have to fit a petrol engine - probably a Ford crossflow??

 

[Emyr]

Aerodynamically, retro roadsters and 7esques all suck, so how much weight and space do you think that chassis has for batteries while keeping a decent weight distribution?

 

[puddleglum]

Maybe you can get a hold of some Tesla modules. They are more compact than the Volt ones. Smaller, car with modest power should have lower energy consumption so you might get better range/kwh. the bad Aero will be a problem though. Cool little car, hope it works out.

 

[MattsAwesomeStuff]

I think you answered your own question. None of us can tell you what you'd want to do.

It's not good enough to race.

If you don't race it, you want it to have long range.

It's too small to have decent range with the battery storage you could fit.

...

It's a cute car. Put a petrol engine in it.

You don't have to be religious about EVs.

 

[brian_]

If I understand this correctly, this is the later (so Marina rather than Spitfire) Marlin Roadster (Marlin has built a few similar car kits).

I assume that the seats are essentially on the floor, so there is no space under them.

You could fill the passenger side with battery, but I wouldn't want a cruising machine which can only be used solo.

Although the Device has all of the battery in the front, which works for that design, a pack could be placed in the back as well. Of course there's not much space for that - presumably no trunk at all - but there must be a fuel tank and it's probably even a simple rectangular shape.

A radical change would be to put a complete drive unit in the back (which would involve replacing the rear suspension), leaving the tunnel for additional battery space.

 

[Duncan]

Hi Guys

More details
The battery bay in my device is
- 600 wide - 900 long and 450 high at the low end
The battery is 550 wide - 800 long and 350 high - not including the pipes

The engine bay on the Marlin is
700 wide at the back, 440 wide at the front - 740 long and 450 high at the front

Fitting a rear motor would not help as the transmission tunnel is only 125 wide between the seats

I had a thought last night that I could stack the batteries two deep - but nowhere near enough height for that

I could move the "firewall" back a bit - but not far enough

I could stuff in a total of 42 Leaf modules - from the measurements I have - that would be 18 Kwh - but with the aerodynamics that might - just might get me about 60 km

Looks like I am going back to the dino age for this one!

 

[puddleglum]

If you could fit the motor in the rear, you should have room for 6-8 tesla modules in the engine bay. That's 31-41KWH. Might be enough.

 

[Duncan]

The Tesla modules are
685 long 304 wide and 76 thick
So I should be able to fit six

30 kwh - that is tempting

I intended fitting the motor - I've got a 9 inch - in the transmission tunnel

I wonder about getting my hands on some of those modules

 

[brian_]

The battery bay in my device is
- 600 wide - 900 long and 450 high at the low end
The battery is 550 wide - 800 long and 350 high - not including the pipes

So the Device has 243 L of volume under the hood, disregarding the extra height further back, filled with 154 L of battery (a reconfigured Volt pack), plus plumbing and wiring.

And wow, is that ever a long hood!

The engine bay on the Marlin is
700 wide at the back, 440 wide at the front - 740 long and 450 high at the front

So the Marlin has 191 L of volume available under the hood, assuming a motor which would fit in the transmission tunnel.

There is enough volume under the hood alone for the entire Volt pack, but the shape doesn't work, so a different battery donor is needed.

I could stuff in a total of 42 Leaf modules - from the measurements I have...

Does that include the fuel tank space? If not, why not?

42 modules at 2.4 L each is about 100 L... a bit over half the volume of the space, limited by how the fixed module dimensions fit the area. This could be at 315, 158, or 105, or 79 volts (nominal, at 7.5V/module).

... that would be 18 Kwh - but with the aerodynamics that might - just might get me about 60 km

The aerodynamics are poor, but 300 Wh/km (480 Wh/mile) for a tiny car?
Conservative estimation is good, I suppose...

 

[brian_]

If you could fit the motor in the rear, you should have room for 6-8 tesla modules in the engine bay. That's 31-41KWH. Might be enough.

The Tesla modules are
685 long 304 wide and 76 thick
So I should be able to fit six...

While you guys were posting I was working through this, and thought that four Tesla Model S/X modules could be stacked in that space, for a total of 21 kWh at 91 V. Maybe five could be stacked in there for 26 kWh at 114 volts, depending on the construction of the support frame and box. Voltages can be doubled by module modification for 12s instead of 6s.

I don't see six of them (137 V), because they need an enclosure, unless the hood rises enough to provide enough height with the stack as far back as possible in the space (which is where they should be, anyway).

There would be good space for whatever on each side of the module stack (which of course would be in a box) at the back. I have no idea if Tesla modules are economically or practically reasonable.

 

[puddleglum]

I don't see six of them (137 V), because they need an enclosure, unless the hood rises enough to provide enough height with the stack as far back as possible in the space (which is where they should be, anyway).

I think 6 would fit for sure, maybe 7 if the engine bay tapers enough, probably not 8. My thought was mount 6 on edge longitudinally, tight to the firewall and there could be room for a 7th laid flat on top. I admit I've never worked with them so I may be wrong. From pictures, the modules have plastic covers top and bottom and mount on the outside flange. That should allow them to be stacked tight together with a frame on the outside edge. All the terminals are at one end and the cells are water cooled so there shouldn't be a need for a bulky enclosure. Possibly just a plate on the bottom and a cover over the terminals. Cost and availability could make the whole thing a moot point though.

 

[brian_]

... All the terminals are at one end and the cells are water cooled so there shouldn't be a need for a bulky enclosure. Possibly just a plate on the bottom and a cover over the terminals. Cost and availability could make the whole thing a moot point though.

On the other hand, Tesla feels that it is worthwhile to house them in a complete metal box...

 

[brian_]

I think 6 would fit for sure, maybe 7 if the engine bay tapers enoug., probably not 8. My thought was mount 6 on edge longitudinally, tight to the firewall and there could be room for a 7th laid flat on top.

Additional height at the back of the area is certainly needed; Duncan can determine how much more height there is, and what will fit.

While it seems likely that they would be fine on edge, they do need to be supported from the edges (not just stacked) so there is space needed for structure.

The front two modules in 16-module cars (the higher-capacity variants of the Model S) are placed one above the other, and would serve as an example of appropriate spacing... but I don't know what that spacing is.

 

[puddleglum]

On the other hand, Tesla feels that it is worthwhile to house them in a complete metal box...

Very true but it also forms the floor pan of the car from a manufacturer who is also under more scrutiny for safety issues than probably any other carmaker out there. I'm not arguing that the pack should have some protection though. Just trying to find options.

 

[puddleglum]

Additional height at the back of the area is certainly needed; Duncan can determine how much more height there is, and what will fit.

While it seems likely that they would be fine on edge, they do need to be supported from the edges (not just stacked) so there is space needed for structure.

The front two modules in 16-module cars (the higher-capacity variants of the Model S) are placed one above the other, and would serve as an example of appropriate spacing... but I don't know what that spacing is.

If the height is 450 mm, there should be room for a mounting cage to bolt in all the vertical cells, the one flat on top and a tin cover around the whole thing. I wasn't suggesting they just be set in loose. For sure Duncan would have to see how many would actually fit.

 

[brian_]

Very true but it also forms the floor pan of the car...

Not really - the Tesla battery is mounted to the floor of the car's body; it isn't the floor. Tesla Motors likes to show the drivetrain components looking like the battery box might be a structural floor (thus the inappropriate "skateboard" description), but they're leaving out the entire body in those photos, and the battery case isn't part of the structure.

Underside of Tesla Model S without battery pack installed 1 of 2
Underside of Tesla Model S without battery pack installed part 2 of 2

Image of the model S body with the body lifted up from the battery (and drive units and suspension and subframes), showing that the body is complete with floor (from GreenCarReports):

... from a manufacturer who is also under more scrutiny for safety issues than probably any other carmaker out there.

They're only special to EV fans; they are regulated just like everyone else. And other manufacturers (e.g. Nissan, in the Leaf) uses a similar battery box under the floor.

 

[brian_]

I wasn't suggesting they just be set in loose.

I do understand that - sorry for the misunderstanding. I just meant that structure and enclosures take space, affecting what will really fit.

 

[tom3141]

Sounds like a similar dilemma to my Cappuccino. I think I’m going to use the passenger seat space in mine but I’m currently looking into the possibility of putting batteries under the floor. The reduction in ground clearance is the worry.

An ICE might be your best bet. How about an electric turbo system -https://www.autoblog.com/2018/07/20/ferrari-patents-fascinating-electric-turbocharger/

 

[brian_]

It's too bad that cells are so dense... a pack made to look like luggage could be "strapped" on the back, in the classic style for cars with this type of body. Of course, in this case it would replace the spare tire.

 

[galderdi]

Come on guys. Think outside the box......Literally.


The two key requirements here are (In my opinion):
Maintain the small /sporty performance.
But occasionally be able to handle reasonable road distances.


I come back to an old favourite of mine. The range extending trailer.
Implement as much battery as you can fit in the car proper. Enough to give you some fun on a khanacross/autocross course. But then create a second set of batteries in a trailer with a set of cables running over the hitch to the car.
So now you can drive it a reasonable distance using the trailer. Then arrive at an event, disconnect the trailer and run it in Sport mode using the in car battery. It also gives you the confidence knowing you have the trailer battery to get home again.