Is anyone here converting a really small car to electric and using modern batteries such as Lithium Ion/Polymer? I’m toying with the idea of taking a 2000 model Toyota Echo or Daihatsu Charade and replacing the engine.
Lead Acid batteries, and even NiMH, would be very heavy. An LiPo pack
capable of supplying 17kW continuous would only weigh 100kg. It looks to be expensive though.
The problem I’ve run into with converting small cars is finding enough room for the batteries. I converted a '92 Tercel, and it took the whole engine compartment and half the trunk as well. Granted, I used Lead Acid batteries, but an Echo is tiny!
Might work though. 
dexx, hi,
i’m new to this forum but not new to EVs. the first thing i’d say is: what do you classify as “small”? you see, because i classify Category L7E aka “Quad-Bike” which is 350kg, as “small” 
there are two critical issues for EVs: weight (which influences rolling resistance, acceleration and hill climbing), and aerodynamics (which influences top speed). weight is a square law, gravity’s a *****, and aerodynamics are a cubic law.
so those issues should be defining your priorities.
in 2005 i did an EV conversion on what i considered at the time to be a “small” vehicle - i selected a Citroen 2CV as the basis, but i did not even remotely consider sticking with the original 2CV bodywork - i went for an “inline” 2-seater, with a narrow look, like the Carver One (but on a wide 4-wheel base of course).
anyway, now i would use something like a Suzuki Swift (aka Geo Metro), an Aixam Diesel 500 etc. but even there i would not use the same bodywork, and the reason is that these vehicles all have a Drag Coefficient of about 0.35 and a Frontal Surface Area of 2sqm. at 60mph, well, you can plug the numbers into here:
Vehicle Simulator
or if you prefer a libreoffice spreadsheet, grab it from here:
Yes Another EV Calculator - Page 8 - DIY Electric Car Forums
you’ll see that the numbers, thanks to the combination of those cubic and square laws, quickly run away, but the good news is that if you keep well below the radar, you can get absolutely stunning performance…
… and, importantly, that means you do not need a huge battery pack. but there is no way in hell that you will find an off-the-shelf vehicle with a highly efficient aerodynamic bodywork shell. that’s why, for example, there was a guy who chopped the entire left side above 2ft off a Geo Metro, replaced the windscreen with glass only 2ft wide, and moved the passenger windows to be down the middle of the car!
i’m researching this stuff at the moment - right back to the older car styles where the engine performance was so poor they had to get as much out of the aerodynamics as possible.
anyway, good luck
l.
Ultra-Efficient Category L7E Hybrid Electric Vehicle: 200mpg+ - micro-fund a prototype ultra-efficient (200mpg+) hybrid
i’ve been asked by someone on this forum to help them evaluate a “Microcar Virgo” as the basis for an EV conversion: he’s considering to put in a 90Ah LiPo battery pack in.
it’s similar to what you’re asking here so i’ll discuss it here.
first, specs:
so, the front surface area is 1.78sqm, and it looks (very roughly!) like a 0.35 drag coefficent vehicle.
now, the person who contacted me wanted to use a single-geared Lynch Electric Motor (LEMCO) which is a damn good “simple” choice, at 48V. the table from here:
L.M.C. Manufacturers of Permanent Magnet DC Motors - L.M.C Ltd Motors and Generators
says that at 48V the LEM-200 does 2500 RPM, and is rated torque of 35Nm.
also it says peak efficiency of 88%, so, knocking off a bit, let’s say it’s 85%.
tyres are R13 so that’s 0.33 metres radius.
weight is, let’s say… net weight is 400kg, 2 passengers 150kg, that’s 550kg.
ok! let’s plug those in, here:
Vehicle Simulator
Weight 550
Drivetrain Efficiency .85
Drag Coefficient .35
Surface Area 1.78
Rolling Resistance 0.007
Gear Ratios [1.0]
Axle Ratio 4.5
Max Rpm 2500
Max Accel 6
Max Power 10000
Max Available Power 10000
Peak Torque 35
Wheel Radius .33
and you get: max speed of 46mph, in 30 seconds, needing a peak power of 3.4kW to sustain 46mph. which is quite cute.
if you then plug that into the estimated “efficient” fuel economy figure of 0.28 litres per kilowatt per hour, that would work out aaaaat… 46 / (0.28 / 4.6 * 3.4) assuming imperial gallons 4.6 not hectares per potato U.S. gallons of 3.8 that’s a whopping 222mpg!
so yeah for goodness sake consider dropping in a 4kW small Diesel Generator in the back as well as a fast charger: don’t waste your money on a 90Ah LiPo battery pack, get a much smaller, lighter one and then you’ll no longer be limited on the range of the battery pack!
but yes: remember i’m guessing on that Drag Coefficient. absolute worst case it’s going to be 0.45 (most cars are between 0.25 and 0.45), which would put the car up to about 4.5kW.
for reference, the Aixam “NICE” Mega City Car uses 4kW @ 40mph and is pretty similar to what you want, similar drag coefficient etc. etc. in some ways, if 40mph is the target, you might as well just buy one of those
[quote=Dexx;9137]Is anyone here converting a really small car to electric and using modern batteries such as Lithium Ion/Polymer? I’m toying with the idea of taking a 2000 model Toyota Echo or Daihatsu Charade and replacing the engine.
Lead Acid batteries, and even NiMH, would be very heavy. An LiPo pack
capable of supplying 17kW continuous would only weigh 100kg. It looks to be expensive though.[/quote]
Dexx, Check out my two White Papers on batteries. LiPo is definitely lighter than LiFePO4, but - could eat you up in cost terms. Prismatic or Cylindrical Lithium Iron Phosphate is more affordable. A123 Pouch Cells might be a choice too - see Jan. 20, 2012 Video on EVTV Motor Verks | Electric Car Conversion Videos
I have seen Electric Aircraft using RC LiPo Packs Custom Wired for Series Parallel Arrangement’s of their own, lots of work there though!
Lazair designer Dale Kramer was at Oshkosh Air Venture 2011, and I saw this aircraft there: [ame=“http://www.youtube.com/watch?v=Se7bQ16bph4”]Lazair[/ame].
Charging Required reaching into the system and changing from Series to Parallel Connections. Flies nice, and has enough power to fly on Floats, too!
If you want to go with Automotive Level LiPo - check out the people who have done it already on EV Album (Search - Component type - Kokam).
That should give you some ideas to work from!
Thanks to those who have replied. The likes of the “Virgo” are a bit too small for my needs. I’m looking at 4 seater cars weighing in around 900kg (pre conversion). The cost of LiPo batteries is coming down. But is still the major factor. However they seem eminently superior to Lead Acid and NiMH.