acidfast7

I think that breakage of the dynamo to light isn't a problem. Most decent bikes run them in the fork.

I think that breakage of a wire going into/out of a battery is a serious problem.

I think that double conversion of energy is negligible when compared to shorting/breaking a wire to/from a battery.

noglider 

Thank you for clarifying. Those points make sense.

acidfast7

Sorry man, buys day. Students are back this week

noglider 

@PatrickGSR94, let us know what you end up doing and how it works.

wphamilton

It makes sense, that just because it's an e-bike doesn't mean you don't want the dynamo sometimes. It is going to be less efficient for the light though and probably not as bright.

Regarding a wire shorting, I think I'd want an inline fuse on any hot wire from the battery.

PatrickGSR94

@alan s Because my post isn't about e-bikes, it's about dynamo hubs. The fact that I was thinking about adding one to my e-bike makes zero difference to the questions I was asking. Maybe try reading elsewhere instead of making smartass comments that don't relate to the topic at hand.

alan s 

There is also the Electronics, Lighting and Gadgets subforum.

acidfast7

Don't worry, he's always been a pain in the ass.

PatrickGSR94

I didn't think about that one actually, as I rarely peruse that forum. I posted here because the majority of people using dynohubs are most likely commuters and/or transportational cyclists.

alan s 

Maybe try Touring as well.

alan s 

I think he called me a smart ass, which is quite different.

acidfast7

No comment is required.

rhm

Oops, I posted this in the wrong thread, sorry!

Viich

So, to summarize:

@PatrickGSR94 - You mentioned wanting to build a wheel with a dynohub, possibly to get more range. I tried to say that it wouldn't give you any noticeable more range, if any. Because of how you asked the question, I think you already have lights powered by your traction battery (the one that powers the motor).

@AciDfast - as far as 'well designed' ebikes, a circuit for lighting should have a fuse, preferably a ptc inside the battery housing, with a port to plug in a harness for the light. Removing an existing light is more likely to cause problems than continuing to use it, I don't think hacking into a well-integrated system to power a light was ever a topic in this thread.

@alan_s - I don't think a discussion of lighting is off-topic in commuting - I know I'm biking to work in the dark already, and have considered a dynohub, but the payoff isn't there with the cheap USB lights being so effective. I bought a spare that can switch between red and white.

alan s 

Never said it is off topic. Just made suggestions as to other places where one can get input that the OP may not be aware of, particularly with a motor vehicle that has unique attributes (i.e., a huge battery and motor and related electronics) that are beyond most bikes commuters' experience.

downtube42

It's a low-cost hub, a low-cost rim, and low-cost spokes and nipples. A machine-built wheel, shipped at low cost. I've run a similar arrangement on my commuter for a decade, with no issues. I suspect your e-bike is heavier than my bike, probably ridden faster, maybe for more miles (my commute has typically been < 4 miles round-trip). Whether a low-cost wheel is appropriate for your application is ultimately your decision.

The question of efficiency re: electricity converted to forward motion converted to electricity is legit, but the variables make it too complex to answer. On a straight pedal bike, it takes more energy out of the legs to move from point A to point B with the dynohub. Pretty simple. On a power-assist bike, I suppose it takes a percentage of energy out of the legs and a percentage out of the battery - the ratio depending on how the e-bike is configured and ridden. It may or may not make sense to run a dynohub, depending.

I run dynohubs on all three of my bikes. FWIW, in your shoes, I'd probably run lights off the bike battery or run battery lights.

PatrickGSR94

Nope, never said anything like that. I first asked about a dynohub with the possibility of buying a hub and re-lacing my current front wheel because I want to learn wheel building. Someone else mentioned e-bike lights that run off the e-bike battery, but I said I'm already at the edge of available range on a single charge and didn't want to add any power draw that might reduce that range. I'm using a USB rechargeable light currently. A dynohub would serve as a way to have lights powered all the time without having to charge them, but also not affect the range that I currently have on the e-bike.

My e-bike's current 26" disc wheelset did in fact cost me less than $100 total (both wheels) from Niagara Cycles. I think it uses straight-gauge spokes, and low-end SRAM hubs. But they work just fine. The wheels have a total of over 2,600 miles on them, used on this bike both before and after the e-bike conversion, and I've only broken a single spoke from several months ago.

Darth Lefty 

This is where people are shaking heads at you. A dynohub makes 1.8W or 3W, and since it's not perfect, it takes about 2x that to run it. That power comes either out of your legs or your motor, and it's going to reduce your speed and range. Taking power out of the battery though the speed control and motor and drivetrain and tire to put it on the ground and taking back up again with the generator and rectifier is going to be less efficient than merely taking a wire off the battery.

noglider 

Right. The energy cost to running dynamo lights is low, but it's not free.

acidfast7

We have different descriptions of so.

Inexpensive, yes.

Functional, yes.

Effective, marginally.

Classtime 

Wow. The price of a decent dynohub has come down. Until this year, I put on my bottle generator in the fall and took it off in the spring. Then this Summer, I got a 30 lumen USB light for my son's nighttime rides and use it myself for my dark thirty commute. I have to agree with most folks who pedal to work and also suggest that you should just plug in a brighter light or see what the other folks on the motorbike sub forum are using.
P.s. I try to sit on my hands but motor bikes considered as bicycles is just so other-worldly that I get perturbed.

PatrickGSR94

well that's been discussed ad-nauseum so you can "get perturbed" elsewhere thankyouverymuch.

Sure wish I had dyno lights this morning! I forgot to plug in my lights after Tuesday's commute, and as a result my front light was pretty dim, and one of my rear lights was nearly dead when I started, and all the way dead at the half-way mark. Luckily my other light was still working, and it was steadily getting brighter outside. But with dyno lights I wouldn't even have to think about it. Wheels rolling? Lights are on.

alan s 

Battery lights vs dynohubs has been discussed ad naseum, but that didn't stop you from bringing it up. If you are the type who isn't attentive to charging, and doesn't need much light, then a dynohub could work. Like anything, it's good to have a backup in case the primary light fails, in which case you should probably carry a battery light anyway and keep it charged. I'd assume someone could advise you on adding a charging port to your electric motor battery as a further backup, but again, perhaps in another subforum.

PatrickGSR94

I actually do have a USB output on my e-bike head unit, but didn't have a cable with me. I need to try it to see if it will charge a light while it's also in operation.

And once again, if you would read the OP you would see my original question wasn't about battery vs. dyno lights. Someone else brought that up. I've never paid much attention to dyno lights until recently, but it seems like there are some pretty dang bright and well focused models available these days, that would rival some of the better USB headlights.

noglider 

OK now you're making a point I didn't think of, which is that dynamo powered lights probably use less electrical energy than the bright battery powered lights. German law -- a dumb law if you ask me -- forbids them from using more than about 3W. Their genius is in their optics which maximize that low power into lots of useful light.

Still, you're proposing to draw ~6W from your bike's drive battery while saying that you're nearing that battery's limit.