Ebike lighting - Hook up to battery or get a dynamo hub?

[Ty]

HI all,

I have two bikes with Dynamo hubs with lights front and rear, all purchased from Peter. One is for my now sadly neglected rando bike - a Salsa Casseroll. The other bike is my Brompton folder, primarily for commuting and short, quick trips to the store.

But I also have an Xtracycle conversion with  mid-drive Stokemonkey. My batter is a 36V 15Ah LiPo, I currently have battery lights front and rear on it, but I've grown so used to never needing batteries with my other bikes, I am thinking about either getting ebike specific lights front and rear and hooking them up to my large battery. But I don't like the idea of reducing my range by using my bike's power to also power my lights. So I am also toying with the idea of having a dynamo  wheel built for my Xtracycle and powering the lights that way. The other advantage is if I ever run out of juice, I will still have lights and can still get where I need to go. The main downside I can see is it will be much more expensive initially to get a new wheel built.

There are pros and cons both ways obviously. Which is why I am here. Please let me know your thoughts on this matter.

Thanks in advance,

Ty

[Toshi Takeuchi]

My first reaction would be to go for a cheaper setup with the E-bike, since considerations such as efficiency/drag and weight are not major factors with E-power more than overcoming these small inefficiencies.  I think the Sanyo/Panasonic hub is cheap and good enough--I think you can find them for $60 or so.  You don't need an SON...

Toshi

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[Ty]

Agree. I have a SON on Rando bike for obvious reasons, but my Brompton has a Sanyo that works just fine. Thanks!

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[Kevin]

What you haven't factored in is that the drag from a dyno will also reduce your range, except when coasting downhill, which at best can only be half the distance for round trips, but since you go slower uphill than down, your battery is mostly going to be powering the light via battery->controller->motor->drive train->dyno most of the time.

Each of those four steps is less than 100% efficient, and they all multiply.   Any decent DC-DC buck regulator is going to be as or very nearly as efficient as the motor controller alone, so you will end up using far less battery to run the lighting by "running it off the battery."   My EE's WAG would be that the net (battery to light) efficiency with the dyno would be around 65-75% vs 85-95% for a buck regulator.

In addition, a buck regulator weighs less than 10% what a dyno hub does, and perhaps 1/3 of a bottle dyno, so your battery gets a tiny little bit more drain from toting the extra weight around.

Wiring in a buck regulator is a half-hour task.   Lacing and truing a dyno hub is considerably more than that.  I think my buck regulator cost less than $20...possibly less than $10.   What does a dyno hub cost?

That said, either way the drain of the lighting is miniscule when compared to the motor.   If you have a small motor, say 300W, then a bright 3W light will cost you 1% range, which you'd be hard pressed to notice between two identical trips, as your riding habits, how you catch a traffic light, etc. will make more difference than that.   If you have a bigger motor, then the light will matter proportionally even less.

The only advantage I can see for the dyno is that you will have lighting if you run your battery flat and have to leg it home at night.  Factor this against having lights at full brightness when stopped or at minimal speed. (stand light output is usually pretty weak)  Note that you are most likely to be slow/stopped at an intersection, which is where most "didn't see you" accidents happen.

BTW, I had a similar situation with my Yuba-Mundo.   Under pedal power, I ran the lighting via a Nordlicht bottle dyno.   I kept this setup when I electrified it with a Stoke-Monkey.    Eventually I replaced the bottle dyno with a buck regulator, and have never had so much as a moment's nostalgia for the dyno.

[Ty]

Kevin,

Thanks for laying that all out. Your pros and cons analysis is exactly what I was looking  for, thanks!  The crux and a big part of my dilemma was in fact the drag from the dynamo wheel vs. running off the battery. I just didn't express it well in my post. Most of my trips these days are 10 miles or less have only a few hills so I can easily get 40-50 miles out of a charge (I also have stokemonkey so I use as little or as much power as I want depending on how fast I want to get there.) 

So I think I will nix the dynamo idea and just use my 36V 15Ah battery to power the lights. I'll have to look into a Buck Regulator as well. That sounds like a great idea!

Any suggestions on where to get the lighting and/buck regulator? Peter White has been my source for dynamo lights for my Brompton and my Salsa Casseroll rando bike.

MUCH appreciated!

Ty

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