the law
1. ‘The electric motor must not be able to propel the machine when it is travelling at more than 15mph’.
Believe me, 15 mph is plenty for off road riding. Sure there are times it would be nice to go faster but not many. Heinzmann motors use a spragg clutch to avoid drag from the motor if you exceed 15 mph so downhill is just as fast as you like.
2. ‘Maximum kerbside weight (including batteries but without rider) shall not exceed 40 kg’.
With Lithium batteries; dead easy to do.
3. Maximum continuous rated power output of the motor shall not exceed 200W
Now this is a good one. You may think 200 Watts is nothing but I was told the average cyclist will put out 150 watts, go to the gym and try to keep up 200 watts for 10 minutes on anything that has a screen on it, it’s not easy. The law also says ‘continuous’, most motors will run continuously at 200 watts, however they often have a ‘boost’ which will give you extra power for short periods of time which is usually just enough to get up that tricky hill. You develop a skill or knowledge to get the most out of what you have got.
4. Minimum age is 14 years
Are you?
the electrics
I’m no expert on electronics, I can only tell you what I have learnt in layman’s language, but this is the gist of ‘electric bike world’ as I see it:
batteries:
The batteries used now are lithium, very similar to the ones in battery powered hand tools. Lead acid jobs are far too heavy for the power you can get out of them.
Lithium-ion (LiFe) batteries tend to be a bit tricky; if they are charged or discharged too quickly they can over heat and even burst into flames and burn like a Roman candle or explode!
Other materials can be added. In my own batteries (LiFePO4) phosphate is included , which gives stability to the chemical process so they don’t burst into flames. The battery consists of a group of cells similar to torch batteries; they can be round, flat, square, whatever. They are connected together in series to get the appropriate voltage.
With rechargeable clusters of cells like this a ‘Battery Monitoring System’ (BMS) is added. This is a circuit board with small cables running to each cluster of cells. The BMS is monitoring the voltage between each cluster of cells to keep them balanced and will shut down the battery if it is being overcharged or discharged too fast.
The battery is like the fuel tank of a motor bike but instead of measuring in litres it is measured in amps per hour (Ah), therefore a 10 Ah battery (pretty average electric cycle battery) has the ability to give you up to 10 amps for one hour. I use on average 6 Amps per hour with a 36volt battery which is 1 amp every 10 minutes so a 10Ah battery would in theory give me 1 hour and 40 minutes riding.
Generally battery voltage ranges from 12 V to 48V. Although there are some using 60V and 70V and in the US even over 200 Volts! I have been told 50V is the legal limit over here. The higher the voltage the less resistance there is in the cable therefore a smaller lighter cable as well as components can be used. However, extremely high voltage also tends to kill you!
I think the batteries have been the weak link in cycling. I originally bought a Heinzmann kit for my mountain bike which included their battery. Heinzmann’s 9.8 Ah battery would last about 1 ¼ to 1 1/2 hours if I was careful. To extend this time, a rack or saddle bags to stick extra batteries in is available.
I could not see a flimsy little rack or bouncing batteries in saddle bags lasting very long on green lanes so I decided to build my own.
We packed in as many battery cells as we could without becoming bulky or over weight. It is a 28Ah capacity unit producing 36 Volts and is bolted below the frame.
I was hoping to get at least 3 ½ hours use out of one battery and change at lunch time. In reality; with sensible use of the economy switch, the battery will last between 3 1/2 to 5 hours depending on ground conditions. Soft ground in winter tends to cause a fair bit of drag. Our best ride so far is 50 miles on bridleways in about 5 1/2 hours in the summer.
motors:
We are after power.
Power is measured in Watts. One simple equation is:
Volts x Amps = Watts.
Motors come as bolt on, built in, hub, geared not geared, brush and brushless, regenerating, lots to choose from.
I use a Heinzmann rear hub motor (you really do need a rear motor if you’re planning to ride in the mud), it’s German and well made. I keep asking people in the know and they all think that Heinzmann is the dog’s doo daas. It is expensive mind and there are plenty of nice cheap Chinese and Asian motors around. Heinzmann have been in the business of electric motors since 1897. They are used in fans, pumps, handling and robotics as well as for transportation, moving/positioning and in light electric vehicles. They do seem to know what they are doing.
They do now use regenerative systems in their latest hub motor but I suspect it is more a marketing ploy as everyone else is doing it. I don’t think it is worth the trouble. The only time you would want to recharge would be when braking. I rarely use the brakes and when I do it is usually down a very steep tricky hill and I’m going very slowly, not the sort of energy requirement needed to get amps back into the battery. Although batteries are always improving and charging times are coming down my own batteries will not take more than 2 amps per hour charge, my average use is about 6 amps per hour. So if I could find a hill that took one hour to go down and it was steep enough to engage regenerating without slowing me down too much, after one hour of decent I would have gained 20 minutes of battery life. Get the picture?
I know you think you need a 4KW, 6KW, 8KW motor but you don’t……………... It is a whole different form of riding skill. The bigger the motor the faster the Ah’s get used up, the less distance you can travel.
Incidentally, Heinzmann motors are used in cross country racing wheel chairs! No kidding.