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I am all for a test but not if you cannot afford a failure.
Before you buy anything, note what type of vehicle platform you intend to convert to an EV.
Then locate the car on diyelectriccar (or one very similar) and find out how much current the thing takes to drive in your goal speed.
Then locate your goal generator and find out how much gas it uses at a given wattage (most will give you this now days as part of the spec)
This will give you a rough estimation of your FE because you will know how many watts makes you go what speed and how much gas it takes at a minimum to make the watts. Now how closely this estimation is will depend on if you plan on converting to a dc generator wound to mechanically control current flow (most efficient and within 10% of calc) or an AC genset with full electronic regulation which is not efficient which may be up to 30% less than calculated.
The main trouble will be finding someone who converted to 48v and drives 30mph. I will say even electric has losses that many seem to ignore, a 48v EV is much more efficient at WOT going 25mph than a 144v EV running 33% throttle at 25mph due to controller issues, assuming of coarse the vehicle weight is within normal design limitations and not way over driven at 48v.
When I ran through the calculations for a Leaf using the "Standard" current draw I ended up with a 16mpg-37.4mpg fuel economy range to drive a leaf down the road depending on which genset and parameters I chose out. Of coarse many can drive more efficiently than the standard and a lower set of speeds make that number more up rapidly but it is worth remembering aero, weight and speed are more critical than ever in your choice on a vehicle of this type.
So your first step is more research. Be very carefull to choose a car that once converted real world uses a frugal amount of watts. Then take great care on the genset because there are many inefficient duds out there.
A Miles ZX40 although not paticularly light or aero but generally comes with a more efficient than average motor and drivetrain than most converted cars generally will have. If you have the bank these are road legal and relatively cheap ($1k-$6k) and best of all their design parameters are known and current requirements are known. They also have lots of people room (7ft tall and still room to go) but seat 4. Then it would just be a matter of choosing a decent genset to match.
This same story is true of any conventional EV on the road even the prius since the current requirements are well known. Which makes it much easier and fruitfull to be able to determine real world what you will get for FE without actually assembling it.
If you choose a car in the wild there are many places that you can loose efficiency due to how you convert resulting in a potentially excessive watt draw to drive down the road.
So choose carefully and do lots of research because the convert to EV is a whole animal in of itself. Only if you exceed exceptionally on that regard will the genset step work out well.
Cheers
Ryan
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