I’ve seen this mentioned, but I don’t think I’ve heard a proper explanation. Are there some expected complications with integrating an automatic that should be avoided? I’ve never driven a manual car so if I’m gonna buy a car to convert it’d probably be my first manual drive vehicle.
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Acting on the assumption that you’re going to replace the gas engine with an electric one, and preserve the transmission, this is true. And commonly, you do want to.
The hydraulic systems in an automatic will require constant power. An idling engine can provide this, but one of the advantages of an electric engine is that it shuts down when stopped. Without this engine power, there’s no hydraulic power to change gears in the transmission mechanics, and you’d be stuck in neutral. Furthermore an automatic is just generally heavier and less efficient compared to the equivalent automatic, so given the choice, it seems like a no-brainer.
Whereas in a manual, there’s no such need. When driving you’d likely still change gears, but much less frequently. For city driving you could just leave it in 3rd gear or so. The transmission has no energy needs and the driver directly moves the parts inside it with the gear lever.
Especially for front wheel drive, the differential – which turns 1 spinning power source into 2 for your two driven wheels – is part of the transmission itself. So separating it out as a discrete component and just having electric power feed into it isn’t an option. Besides, the electric motor generally does well with some gearing lower than 1:1 (approximately 4th gear in a typical manual). The transmission is still functionally useful for having a neutral (safety) and reverse gear.
An alternative design would be to put an electric motor on each wheel, but there are concerns with that design, like uneven power to each wheel. Using the original differential would be better.
The majority of EVs have fixed ratio gears. They might be listed on AutoTrader as automatic but that’s not really the case. This is because the electric motors have such wide torque and efficiency curves there wouldn’t be a benefit, and a changeable ratio box would add complexity and losses and potentially require maintenance.
Thus, when converting a fossil car, you can replace the engine with the electric motor and simply leave the manual gearbox in a fixed ratio. That said, some conversions have kept the gearstick as much for driver satisfaction as anything.
Less to go wrong. An automatic is a whole extra system to integrate that is mostly unnecessary based on how electric motors work and their efficiency. Usually the main gears you shift into with an electric conversion is neutral, reverse, and often 3rd gear is the best balance of usability for your forward gear. Once it’s in forward you can just leave it and act like it’s an automatic. With a manual gas engine you can’t come to a stop and not stall without shifting into neutral or just holding the clutch, but with an electric motor that is a non-issue.
ICE cars have access to several forms of energy transmission from the engine, including hydraulic pressure, air pressure, and vacuum power, all produced by gasoline engines as part of their function. Electric motors don’t produce any of these so an ideal EV conversion minimizes the number of systems that require these alternate forms of power.
Presumably you aren’t going to keep the transmission if you convert to EV. Transmissions solve an issue that’s specific to gas/diesel cars – i.e. the efficiency of the engine at a specific RPM range. Electric motors do not have this limitation, they can work at a wide range of RPM.
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