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I live 'on-the-road' (24 years, in Australia) of the last 11 years, in a 4x4 homemade (slow-build) camper, and like everyone (in normal homes) I need more power. I'm looking for a motorbike to sling into my trailer, and ask if a mid-size (650cc~ or smaller, like an offroader 500cc) engine's alternator, idling, would be powerful enough to supply & recharge my laptop, lights, 24inch LED TV, and (next buy) a HEATER, plus stuff like recharging torch and other batteries, etc? Or, I buy whatever bike thrills me, then upgrade the alternator for more zaps. Feasibilities, please? A heater might need 100amps max. But without that, the rest would probably only need around 50-to-60amps, I guess? Best add, I have 140W~ solar panels on the roof, with another 120 Watts of sunplates, I unpack when needed (when I could be bothered), a 240VAC inverter, deep cycle HD battery and a s**tfight of a wiring system which scares me each time I look at it, about 10 cigie-liter sockets, 6+ LEDs & spotlites in and outside (for the ghosts and monsters), all of which works .... OK to great. BUT NO HEATER. I run the 3L diesel to keep the charging system working when the sun is too far away, or hiding, like at night, which is OK but killing me slowly I guess. So the bike option plus a heater soon, are on my mind, short of answers, as put. Cheers,

Jusro, .... of the Forests .... (PS; no prank answers pls. I'm old .... ish!) (PPS; hope y'all have a sense of humor?)

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    A heater burning fuel direct would be more efficient, with a generator which would also be more efficient as the engine and generator are matched while the alternator is only sized to cover the electrical loads of the bike... – Solar Mike Jul 4 at 12:03
  • Thanks Mike. Yep, agree. But I want a bike anyway and, being mechanical in daze passed, if I can buy one with a big enough alternator already onboard, or, fit a larger alternator to the bike, I'd be able to use it for two purposes. Power and pleasure. I try to have stuff that has more than one purpose. The heater is a secondary thing to having the bike as a power source and fun ride in one, but it does introduce the amps/watts question. Cheers.. – Max Jusro Cook Jul 4 at 13:05
  • If we assume the alternator produces 100A at 12V that is 1200W (large for a bike anyway) that is about 1.6hp ignoring losses... So, that is a small amount of the total power of the bike engine... You can see that running the bike engine just to get 1200W is not very efficient. You would be better making a frame and getting the rear wheel to drive a generator to make use of the larger amount of engine power available. But up to you... – Solar Mike Jul 4 at 13:11
  • Most bikes have comparitively small "alternators". I wouldn't expect more than 350w at best (~30 amps), and that produced at high revs. Fittting a larger alternator is a non trivial task for modern bikes – Kickstart Jul 4 at 13:27
  • Cool again, thanks Solar Mike. A bike motor, even a 650 or larger, idling, only for about 2 hours at a time, then relying on the 2nd car battery (HD deep cycle) for most power most of the day.night, would still be far more efficient than the 3L diesel for the same work, which is why I'm asking about the worth and ability of a bike alternator etc. And yes, the frame and back wheel idea is good too, but hard for me to sort, ATC. Thanks for the figures, I'm bad with them things. – Max Jusro Cook Jul 4 at 13:39
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Most bikes alternators are pretty much integrated with the stator on the outer engine covers, with the magnets on the flywheel on the end of the crank. As such a larger alternator is likely to require a new flywheel, and larger stator (and a spacer for the outer casing to provide space for that while keeping the engine oil tight). This close integration also stops you gearing up the alternator to spin faster at idle.

There are exceptions (eg, think some Guzzis use car type alternators, while the old oil cooled Suzuki engines and the older 20 valve Yamaha engines use piggy backed separate alternators), but that limits the choice of bike. And with the piggy back alternators you are still limited on fitment (the alternator drive is internal to the engine) and gearing, severely limiting upgrades.

At idle I suspect the standard alternators are providing barely enough power to charge the battery. Probably only a couple of amps max (with some of that being used for the ignition system, etc).

There is the further issue that the bike engine will heat up quite rapidly at idle, needing the radiator fan (which will consume electrical power).

It might be possible to rig up a large car type alternator external to the bike. Maybe running from the front sprocket with the chain disconnected. You could then gear up the alternator to spin at an adequate speed. But it would limit your choice of bike to one where the chain can be easily disconnected (so limited to smaller bikes running split link chains), and would require a bit of time fiddling to attach / detach the alternator.

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    Nice one Kickstart! Thanks again for taking the time. – Max Jusro Cook Jul 7 at 11:27
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Recharging batteries: this requires few watts if the batteries are small. No problem.

Powering & recharging the laptop: the motorcycle alternator may or may not be enough but a small car alternator will be enough. You may need as much as 100 watts if the laptop is large and is used while recharging. You need about 10 amperes for this. If you have the ability to turn the motorcycle front light off, it will help.

Lights: yes, modern LED lights can be run from an alternator. Consider this: the motorcycle probably has a halogen front light, and LEDs are more energy efficient.

24 inch LED TV: I guess these consume below 50 watts, so not a problem.

All of the above: you may run into problems if you want to do all of the above at the same time.

Consider also that lights, LED TV, battery chargers and laptop run from mains voltage. You need an inverter to convert 12 volts (or whatever the motorcycle may have) to mains voltage. Cigarette lighter inverters typically are 150 watts.

HEATER: No! no! a thousand times no! You can't use an alternator to power a heater because the wattage needs of heaters are huge. Your best bet is to somehow try utilizing the engine waste heat. Heaters require anything between 500 watts to 3000 watts, if considering single-phase AC heaters.

  • Tah! The heater advice is good, thanks. I guess I'm thinking on the line that a bike motor idling, with an improved alternator, could work like a petrol genie does. I need it all onboard for when I need to move quickly, so having a genie onboard, even on trailer, is vibration-city, likely worse than the 3L diesel. But a bike's tyres cushion any vibes nicely. All a feasibility study for now, and your advice has helped. – Max Jusro Cook Jul 4 at 13:18
  • I think you'll find that a modern, compact generator will probably be less vibration than a motorcycle engine, and will be tons more efficient at doing what you want. I'd also agree that "100 amps" is also way beyond what any bike electrical is going to provide (and probably a few cars too) – Christopher Hunter Jul 5 at 19:27
  • Yep. Thanks Chris. Looks like I'll have to get fit on the exercise bike! Which, in this energy conscious time, has be say, I reckon ALL fitness exercise bikes should be sold retail with alternators for 12 or 24VDC household systems on them! Healthy energy! – Max Jusro Cook Jul 7 at 11:44
  • @MaxJusroCook Joking aside, please note that fitness exercise bike won't produce more than about 200 watts due to human limitations, so unless you can hire a competitive cyclist, you won't power all that you need. Seriously, please get a generator designed for converting gasoline into 120 or 230 volts AC, as some people have already suggested. – juhist Jul 7 at 11:48
  • (Swearword!) Well? thanks again juhist, for that advice. And to think, I had 3 petrol genies in varying states of repair, but gave them away, (was conned into it tho!) 'Mates'! Sheesh! – Max Jusro Cook Jul 8 at 5:21

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