Thinking of a project and how to get constraints

[roundcrisis]

Hi there

I am starting to think about a potential project. My background is not mechanical (please bear with me). So I have a few questions :

1) Can it be an automatic? why not? What are the challenges of one and the other?
2) Does the size of the car matter? I am aiming to have a 200 mile range, so I need to fit a decent size battery, I assume this affects the car choice.
3) How can I price the parts that I would need for the conversion? (besides the battery)
4) How do I go about getting a battery , is the best option getting a battery off of another donor EV?

If these are all obvious questions and there is somewhere I should start reading instead, please point me there.

Cheers

[arber333]

Auto transmission is not necessarily a good thing. But maybe not bad either. Certainly old atx with oil wedge clutch are power hungry monsters.
Maybe modern dsg atx are more efficient today. Maybe if you use robotic atx... I haven't tried. My pug had atx but I pulled it out and I use Leaf motor and gearbox together with driveshafts. I spliced driveshafts to Pug ones on lathe. I needed to spin them and balanced them.

Now it works good in direct drive 8:1.

Generally size matters when accelerating and climbing hill. On level road frontal cross section matters. For 200miles you need 40kwh battery at least.

Yes I believe best option is to get battery from EV. Its modules are in tune and you get BMS with it usually.

[celeron55]

1) Can it be an automatic? why not? What are the challenges of one and the other?
2) Does the size of the car matter? I am aiming to have a 200 mile range, so I need to fit a decent size battery, I assume this affects the car choice.
3) How can I price the parts that I would need for the conversion? (besides the battery)
4) How do I go about getting a battery , is the best option getting a battery off of another donor EV?

1) For your first conversion you probably want a manual. A manual is generally more efficient and you don't need to control it electrically in any way. UNLESS you're going to replace the transmission with something else, then you might just as well sell the automatic and have a nice PRND display on the dash that you could integrate into your system. Haven't seen many doing this though.

2) Smaller car is cheaper because you need less batteries for the same range. I think (Cross-sectional area) * (drag coefficient) will mostly determine your highway energy consumption, so something aerodynamic, narrow and low will allow you to have the smallest cost per highway range. For slow city driving weight will become important also.

3) What I do is browse online marketplaces and shops like crazy to figure out what's available and at what price, and at the same time try to make a list of what's needed and what fits together. There's always a market value for everything and you can find better deals if you're patient or flexible. If you have a salvage yard nearby, you could get better prices there if you know what you're looking for.

4) An EV battery is the most straightforward and reliable choice. A PHEV battery can also work but paralleling them to get enough capacity might be tedious and even risky. Consider the BMS - if you can use the original BMS of an EV or PHEV battery, that saves you lots of time, money and potentially burned wires.

If you want lots of range (200 miles is absolutely huge in a conversion) I think an important factor in car choice is making sure it has enough load capacity to carry the batteries. In any 5-seater you might be losing the rear seat and a 2-seater might be impossible, a van is easy of course, just dump any amount of batteries in. Personally I wouldn't even consider anything other than Tesla battery modules for such an attempt in range, but some of the more recent EV batteries could also work. This is definitely not a use case for PHEV batteries, too much weight per stored energy.

A consideration that will propagate to much of the system is what voltage battery pack you're going to use. If you use a partial pack from a high range EV, you're going to have less voltage and some systems don't like much smaller voltages. On the other hand if you're considering skipping the scrappers and buying a brand new hobbyist friendly inverter and motor combo, those might be designed specifically for a lower voltage. Of course given you have that manual transmission, you can work around any rpm or torque deficiencies by switching gears.

[roundcrisis]

Thanks for the replies. I really appreciate it.

I think I got much more to learn before I start seriously considering a conversion. I guess my list of things to learn would be:

a) Batteries and BMS systems . At the moment I'am reading DIY Lithium Batteries by Micah Toll but I wonder if there is anything else I can learn from ? I see the BMS section is a bit light, but I didn't get there yet. However it seems clear that relying on donor cars would be simpler but it would be useful to understand what I am dealing with here
b) Points 1 and 2 really show how much I don't know about cars, I don't have a garage at the moment (it's something I might be able to fix in a few months) meanwhile tho but I am sure there are books or videos where I can learn about basic car mechanics and custom car work, any suggestions?

Regarding the paragraph below: I would have thought that some room would become available because removing the ICE

If you want lots of range (200 miles is absolutely huge in a conversion) I think an important factor in car choice is making sure it has enough load capacity to carry the batteries. In any 5-seater you might be losing the rear seat and a 2-seater might be impossible, a van is easy of course, just dump any amount of batteries in. Personally I wouldn't even consider anything other than Tesla battery modules for such an attempt in range, but some of the more recent EV batteries could also work. This is definitely not a use case for PHEV batteries, too much weight per stored energy.


Thanks again

[celeron55]

Yes, you will have room. But not 200 miles of room, so to say.

I recommend watching people repair and modify cars on Youtube, if you have the time. It's the closest you can get to hands-on experience without actually touching a car. For example, go find a couple clutch replacement videos for starters, and then something where someone pulls out an entire engine.

[roundcrisis]

Thanks. Will start there