Electric Motorcycles

So far I'm thinking:

• Electric motor with 10-20hp peak and maybe 1-2hp continuous.
• Simple chain drive to rear wheel.
• About 80kg of sealed batteries in case it falls over -- maybe Optima Yellow Top? Either a 48V or a 60V system.
• Some kind of twistgrip controller. Are regenerative ones available in this power range?
• Some kind of onboard charger, so the bike can just be plugged in to the 240V mains and left overnight / at work / etc.
• All shoehorned into a rolling chassis from a streamlined 250-400cc commuter would be about right ... kerb weight about 160kg before, less than 200kg after I hope.

Does this sound reasonable?

I've gone through the bikes in the photo album and going by the stated ranges and battery configs, the efficiency seems to vary enormously ... between 50 Wh/km and 400 Wh/km! Anyone know a good rule of thumb for a two-wheeled electric beastie?

I'd need to get a 'regular' range of maybe 40km (25mi) and a 'regular' speed of 60km/h (38mi/h) out of it to make it a practical bike, and maybe occasionally a 60km (38 mi) range or a 80km/h (50 mi/h) top speed.

Is this practical with the available tech, or will I just have to wait for fuel cells or unobtainium batteries or something?

Thanks!

-----Nick 'sharks' Moore

One way around this is to use a "Contactor controller", or series-parallel switch. Put simply: split the pack in half, and wire these halves up so that they can be connected in series or parallel. This provides two 'gears' ... in parallel, maximum current is increased for more torque, and in series maximum voltage is increased for more top speed.

Pretty obviously, fuses would be needed to prevent the batteries exploding if a contactor stuck or was closed at the wrong time.

And, of course, dropping down into Parallel reduces the battery voltage, so if you've sped up to top speed in Series and then shift into Parallel, there's sufficient voltage to regeneratively charge the batteries. It's not exactly sophisticated, but it's a start. The idea can be extended:

Num Batteries	Num Gears.	Gears ( Nseries * Nparallel )				Top Speeds With top gear top speed = 100
2	2	1 * 2	2 * 1			50	100
4	3	1 * 4	2 * 2	4 * 1		25	50	100
6	4	1 * 6	2 * 3	3 * 2	6 * 1	17	33	50	100
8	4	1 * 8	2 * 4	4 * 2	8 * 1	12	25	50	100

The complexity gets out of hand pretty rapidly. Six is probably the largest useful number ...

Just as the selection of series vs. parallel is a bit like the selection of gears in a gearbox, the two likely strategies are manual or automatic switching. For manual switching, a control would select which contactors to close, giving a selection "Parallel-Neutral-Series" just like 1-N-2 on a motorcycle gearbox. The throttle setting would provide PWM control over power and regen. For automatic switching, a controller would monitor throttle position, battery voltage and motor voltage, and select the appropriate 'gear' and PWM setting.

Someone on the list pointed out that this would be a Bad Idea with most controllers: the input stage capactitors need 'precharging', generally done by a resistor in parallel with the contactor. Switching voltages would be messy. Instead, if you wanted to do S/P switching, you'd need a controller designed for the job, with input stage capacitors _before_ the switch. Since the S/P switching is mostly there to do regeneration, and since the controllers people are talking about don't do regen anyway, it's not a big deal -- I'd need to build my own controller anyway!

TS-LCP50AHA	3.6V	50Ah	1600g	190x116x46	US$98.
TC-LCP100AHA	3.6V	100Ah	3000g	220x145x61	US$200.

To get to a nominal 48V (for the Etek) it'd need about 14 cells in series: so that'd be 42kg / US$2800 for the 100Ah pack.

One limitation of these cells is that they become quite inefficent past 2CA discharge, eg: you shouldn't try to get more than 100A out of a 50Ah cell. This makes a series/parallel setup essential to run an Etek motor ... with two banks in parallel, you could source 200A without sagging much. Another possibility is to use UltraCapacitors as an intermediary.

The other problem is that LiIon batteries need a per-cell Battery Management System. Mostly what this seems to be is a method for making sure that the voltage across a 3.6V nominal cell never gets above about 4.3V. The easiest way to do this is to shunt current past the cell, with a circuit which is more-or-less a 'sharper' version of a Zener diode.

Simple charging system: A power supply capable of 32V 10A sits across a bank of 7 Lithium cells, each of which is clamped to 4.3V. While they're charging, the bank voltage will be <30V. When all shunts are shunting, bank voltage will have risen to 30.1V, at which point the charger can turn itself off.

These batteries apparently like to be variable current charged, so the one power supply can switch once a minute between the two banks. Now, admittedly, that's a 320VA PSU we're talking about, so it's still no lightweight. But it's not a welder either, and it doesn't have to be too sophisticated since the clampers do almost all the regulation.

They also have integrated packs with built-in charger at very good prices. Two of the 24V packs seem the obvious easy solution to my e-bike's power needs, but I'd like something which could handle regeneration ...

TS-IC36V18AH    36V	18Ah	7200g	415x97x132	US$300.
TS-IC24V50AH    24V	50Ah 	18kg 	405x122x202	US$700.
TS-IC24V90AH    24V	90Ah	24kg 	490x120x217	US$1000.