[brian_]

This needs to be engineered and is not a home project.

All EV conversions are engineering exercises, and they're almost all done by unqualified hobbyists. The size of the vehicle doesn't change any of the technical issues, but it does escalate the cost (which will be huge).

So forget that it's a bus, except for using the specifications of the bus (weight, tire size, axle gearing, etc) and go through the same options that everyone else does. All three options listed are potentially viable, each with a suitable motor. I think when a motor, controller, transmission, and battery are all chosen, the costs of those components will add up to an unworkable project... unless you're very wealthy and this is where you choose to throw away your money.

 

[brian_]

For anyone wondering about the bus, it looks like a typical modern high-floor (floor run over the wheel wells) intercity highway coach, but it uses a ladder frame instead of the unibody construction of most modern buses of this type used in North America and Europe. It has a rear engine and of course rear wheel drive, with one drive axle (no tag axle). Curb weight is around 5,000 to 6,000 kg, and axle capacities are 5,000 kg (front) and 10,000 kg (rear) and up, depending on model. Essentially, in North American terms, the chassis is like a rear-engine school bus or Class A motorhome... but it's a bus in Indonesia.

 

[brian_]

~40:1 total reduction in first gear.

Yes, big vehicles with big tires have a high first-gear reduction. A small car might only be 15:1, but the tires are half the diameter. A current Ford F-150 pickup has a 4.69:1 first gear, multiplied by torque converter ratio (because it's a torque converter automatic, but the bus is a manual so 1:1), multiplied by a 3.55 or 3.73 axle ratio, for 17:1 or so, but it still has little tires compared to the bus. As I said, it's the same design challenge as any other conventional vehicle (especially like a truck with live beam axle), with appropriate specifications used. The solution will be a huge battery, large controller, large motor, and substantial reduction gearbox (or skip the reduction and use a huge motor from TM4)... which will be no more difficult to design and build than a conversion of an MG Midget, but vastly heavier and more expensive.

Every discussion that I have seen in this forum of conversion of vehicles as large as this has fizzled out without a project done, because it is not economically viable, or because the vehicle would not have enough range to suit the prospective builder. I haven't seen any technical problems, and indeed there are production EVs this large commercially available... including from Mercedes, which built this bus.

 

[brian_]

Engineering is much more than technical, Brian. It includes working within constraints to solve the problem and complete the project. Much of that is economics...

Yes, and that is true of any conversion; being large or a bus doesn't change that. Requirements for commercial licensing and business profitability would be significant, just as they would be for someone wanting to convert their car and use it in a place with stringent licensing requirements or use it as a taxi. DIY converters make economically-driven decisions which compromise the safety and performance of their conversions every day.

 

[brian_]

I seriously doubt any insurance company would cover a DIY conversion for use as a taxi.

In Canada, that's probably true. In Indonesia you can get a taxi ride on a scooter.

Again - a DIY bus conversion is not "engineering" and, in most countries, practicing engineering where public safety design is being decided/approved without a license to do so will get you fines and a jail sentence. Even in Canuckistan.

A public bus has to be competently engineered in every sense of the word. SE Asia has enough highway carnage from buses without sprinkling in cowboy design mods.

So you agree: it's just like any car conversion used as a taxi - the size doesn't change the design process, but commercial service likely brings additional regulations. My guess is that in Indonesia if it looks like a bus on the outside and you pay the appropriate official, it doesn't matter what's under the skin... or maybe it's only school buses that are allowed to have passengers riding on the roof. More importantly, there is no reason for any aspect of the conversion to be unsafe, if the builder is willing to pay enough.

I suggest not considering regulation of engineering too carefully, as any car conversion (even for private use) is clearly engineering and illegal for anyone other than a registered professional engineer to do in Canada and probably most first-world countries. Maybe "I didn't realize that I wasn't allowed to do this" is the best attitude.

 

[brian_]

I'd keep the transmission for both up and downhill purposes as it can give you greater speed in the flats and lets you use a smaller motor.

I agree, even some EVs from serious manufacturers (such as Volvo/Mack) use at least a two-speed transmission for this reason.

Remember that you have ZERO "engine braking" down"hill" with a fully charged battery, so you might consider using some huge resistors (possibly boil water with them) to dump the energy into (Toronto's street cars did this in winter & heated the passenger compartment) brake fade (they call it "failure" when it's the driver going too fast downhill riding the friction brakes) downhill has killed a lot of bus passengers in SE Asia.

Or just don't fully charge the battery, leaving room for the energy of a full stop from highway speed for the amount of regenerative braking needed on a long descent. Yes, resistors are used to dissipate energy for braking in some cases, but that's typically in a vehicle with no battery (such as a traditional diesel-electric train, or those streetcars).

Regenerative braking for speed control in grade descent is typically more of an issue for vehicles like this than for cars (because they have relatively high mass to drag and relatively small brakes for the mass).

 

[brian_]

That won't keep you out of fines and a prison sentence. Pretty standard to use your suggested reckless defense in the courts, Brian, which just pisses the judge off because you easily could have had a PE sign off on some safety design aspect (like sufficient braking down mountain grades).

So I assume that you're doing that in your own conversion, since it will be used on public roads... right?

 

[brian_]

Some of the electric school buses here used liquid sodium batteries.

There's a warmup time to use them - not sure SE Asians would have the patience 😂

Sure, and some cars ran on coal... over a century ago. Would anyone use a liquid sodium battery today? None of the current manufacturers of battery-electric buses do, as far as I know.

 

[brian_]

https://cleantechnica.com/2017/09/07/motiv-power-provides-electric-school-buses-california-communities/amp/

The bus in the article's illustration is too small, but larger commercially available school buses are good examples of workable components.

This thread started years ago but has more recently included an example of a recent design for a bus of this size and chassis type:
Making a school bus electric?