Battery never big enough?

[Davall]

Prompted by seeing petrol engine kits for sale to convert one's mountain bike into a moped, I was just wondering about the legal position in the following hypothetical case.

If a small petrol engine were used purely to keep the battery topped up on the move, with no link between the petrol engine and the bicycle drive (i.e. the engine is solely used as a mobile battery charger, replenishing the juice as it gets used up), would the authorities consider that an electric bike or a moped?

I suppose it's the principle used in the Toyota Prius, but has the idea ever been put into practice on a bike?

Sorry.....just idle musing really!

 

[flecc]

It would be a moped.

This would be defined by the fact that it's impossible to separate the electrical flows, the current from the generator could be powering the bike motor, leaving the battery comparatively resting. In fact that's very likely to happen in practice since the state of inertia of the battery could be dictating what happens, and that would be even more likely in cold weather when the chemical reaction necessary for charging would be impeded by the low temperature.

It might appear that charging a second and unconnected battery would be ok while riding, but even that can fall foul of the law since manufacturing on the public roads is an offence, and the generator is doing just that. I first learnt of this strange law when the readymix concrete trucks first appeared many decades ago and a legal provision had to made for them. In this connection, I've often wondered about ice cream vans since they actually manufacture ice cream from the ingredients while on the road.
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[Davall]

I would imagine that clever and tamper-proof electronics could be used to isolate the engine power and ensure the electric motor can only draw from the battery, or never draw more than x watts, but this is well beyond my knowledge so it's only speculation.

Fascinating reply though, thanks.

 

[flecc]

I would imagine that clever and tamper-proof electronics could be used to isolate the engine power and ensure the electric motor can only draw from the battery, or never draw more than x watts, but this is well beyond my knowledge so it's only speculation.

Fascinating reply though, thanks.

It is impossible to isolate the two, since the point of entry and take off from the battery are identical, the cathode and anode. Therefore, no matter how complex the charging electronics (BMS), charge current could and would divert from input to output at the common cathode and anode without entering a chemical conversion into charge. And as I explained, that would be the physically preferential route for charge current to take.
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[Davall]

I do follow your line of reasoning, and I'm no electronics buff, but isn't this analagous to a car battery being continually charged by the alternator?

The car headlamp will draw 55 watts from the battery (and/or the charging circuit) and the battery will remain topped up, thus giving a very long duration for the bulb to operate without ever flattening the battery. It doesn't really matter whether the charge has come from the battery or the generator, provided no more than 55 watts is being drawn.

If a power limiter were built into the e-bike electronics to ensure there's a limit on what the electric motor is capable of drawing, and that limit is the same limit as the donor e-bike in non-petrol-engined form, I'm not sure where the legislators could really find fault. In effect the petrol engine is only being used to keep the battery continually topped up.

However, I suppose the logical next step is then to do away with the battery, in which case the petrol engine would become the sole motive source and it might then become a moped....

...I can see the legal wrangling this idea might generate!

 

[Orraman]

Some years ago I spoke to a man in the DFT wanting to know the legal position on the possibility of using a small generator to charge one battery while another electrically isolated battery provided the motive power.
I had a spare 10cc water-cooled model engine rated at 1hp and fancied knocking up a geni.

A double pole double throw relay could provide the isolation and the batteries could be relatively small. The sub-C size nicads could deliver more than 80 A for the short time that it took to propel an electric powered 'glider' to altitude. Change over time and charge rate cold be automatic.

The DOT chap entered into the spirit of the thing being willing to look for regulations.
"Only one motor to be on the bicycle". Could I put the geni in the trailer?
If electronics could be proved to provide the isolation then capacitors might be used in place of batteries, they weigh very little?

His unofficial response was that while there was no direct legislation denying this idea, it ran very close and only a court could make the decision. While he doubted that any penalty would be large it would result in a criminal record.

Dave

 

[Davall]

I was pretty convinced I wouldn't have been the first to dream up this idea, and you've just proved it Orraman!

Thanks for the reply. I guess one day somebody is bound to have the precedent tested in court. (Won't be me - I'm not skilful enough to design such a thing!)

 

[flecc]

I do follow your line of reasoning, and I'm no electronics buff, but isn't this analagous to a car battery being continually charged by the alternator?

The car headlamp will draw 55 watts from the battery (and/or the charging circuit) and the battery will remain topped up, thus giving a very long duration for the bulb to operate without ever flattening the battery. It doesn't really matter whether the charge has come from the battery or the generator, provided no more than 55 watts is being drawn.

If a power limiter were built into the e-bike electronics to ensure there's a limit on what the electric motor is capable of drawing, and that limit is the same limit as the donor e-bike in non-petrol-engined form, I'm not sure where the legislators could really find fault. In effect the petrol engine is only being used to keep the battery continually topped up.

The crucial factor is that if any of the generator current supplied the bike motor, it would most definitely be illegal. Since that definitely would be the case on the technical facts, a conviction would result. English law, like most law, doesn't work by negotiation, doing "deals" on a quid pro quo basis of the type you describe. Interpretations are always of the simple facts, guilt or no guilt. In the proposed case of a generator inevitably jointly supplying both battery and motor, the vehicle becomes a petrol-electric driven one, subject to motor vehicle law. I'm confident that would be the ruling if a court went as far as to seek the guidance of a Master on this point of law.
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[monster]

unless you can some-how make the engine completly silent then your going to get legal hassles from the police on a regular basis. the laws the law, but on the streets its only a bicycle if it looks and sounds like a bicycle. i once installed a 50cc bicycle engine. i only dared ride it a few times on the road. the second time i rode it i got tailled by cops for two blocks. they didn't stop me but the experience was enough for me to sell the bike. someone on a remote scotish island bought it. it's much more convenient to plug in than to queue up at a filling station with a bicycle. the petrol station probably would not let you fill up.

it was slower than an electric bike and sounded like a lawnmower. complete waste of time.

 

[monster]

just buy a bigger battery. unless you want to cycle 100 miles a day a petrol genset would be heavier than the equivilent energy in batteries anyway. genset=12kg
12kg battery=60miles

 

[flecc]

i once installed a 50cc bicycle engine. - - - - - - - -
- - - - - - - the petrol station probably would not let you fill up.

Even in the mid 1950s when there were a million of these on the road and car customers were few and far between, filling stations regarded the petrol assist bikes as a pest, taking barely a pint or so of petrol in most cases and the owners messing about mixing in lubricating oil at the same time.

Most owners soon learnt to use a gallon can to buy the petrol in bulk (!) and make a premix with oil at home.

As you say, an e-bike is very much easier and better than a cyclemotor in all respects, but doesn't compare so well with mopeds on speed, weather protection, reliability, running costs and sometimes even capital costs.
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