"Rainproofing a bicycle bottle dynamo
A few months ago I kissed goodbye to my battery powered LED bicycle lights and embraced the world of dynamo driven lights.
Apart from having a power cable fall out once or twice from the front headlight (which has since been remedied with a pair of pliers), the only other challenge has been getting the system to work reliably in the rain.
After a few weeks of tinkering around with my bottle dynamo and on and off rain here in Melbourne, I thought I’d post my thoughts.
The biggest problem with riding in the rain with a bottle dynamo attached to your bike is maintaining friction between the dynamo roller and your bicycle tire. What works well in the dry can easily become a slipslide of ‘oh crap where did my lights go?’ in the rain.
My dynamo is a Busch and Mueller Dymotec 6 which comes with two rubber roller heads. Back when I was using a Gatorskin 700×28 on my rear the rubber roller heads were friction proof.
Whether it was raining, hailing or even cycling through swimming pool sized puddles the rubber rollers never stopped running along the tire.
These days I’m using Continental Travel Contact 700×37 tires and despite having a specific track along the sidewall of the tire for dynamos, they simply don’t perform in the wet. Infact I’m convinced this raised track is what’s causing the roller to slip in the rain.
It’s the same concept that explains why road tires are more grippy in the wet then their knobbly mountain bike counterparts.
With the Travel Contact tires you have a raised edge which prevents full contact of the roller along the tire sidewall. The Gatorskins on the other hand have no such track so the roller is able to make uninterrupted total contact with the tire sidewall.
So inefficient is the sidewall track on the Travel Contact tires that it doesn’t even need to be raining for you to lose lighting. If the roads are even slightly wet, after around ten minutes or so of cycling the tire is wet enough that constant friction is lost.
Not keen to go back to my recently retired Gatorskins (although I would in a flash if Continental ever put out a larger size then 700×28), I decided to stick with the Contact Travel tires and see if I could modify the roller in some way to work in the rain.
Luckily for me Busch and Mueller make a weatherproof roller for the Dymotec 6 specifically for riding in the rain. The downside?
Coming in at $15, the weatherproof roller is the most overpriced bicycle part I’ve ever bought.
The roller is essentially a stainless steel brush in the shape of a circle. Instead of the much more forgiving rubber wheel, the weather resistant wheel uses the harsh friction created by the ends of the steel bristles to maintain contact.
The end result is a dynamo with less drag and noise then the rubber wheel that works brilliantly in all weather conditions. Hell this setup works so well I reckon I could take the Long Haul Trucker underwater and still have lights.
Unfortunately though the weatherproof roller will decimate your sidewall.
When I left the bicycle store the guy told me not to use the weatherproof roller all the time, just in the wet. Figuring I only use the roller once or twice a week for a 10km commute and that replacing the rollers was quick but kinda annoying I’d just leave it on.
Surely 20km a week of dynamo damage wouldn’t be that noticeable would it? I mean I’d be using the roller rubber all through winter (4-5 nights a week) with no noticeable damage.
Oh my god was I wrong.
After just 2 weeks of using the weatherproof roller my sidewall looked battered. In the close up below you can clearly see the damage done by the weatherproof roller compared to the other side of the tire (note the near complete wear of the sidewall tread!).
Prior to using the weatherproof roller there was no noticeable wear on the sidewall tread.
Apart from the drastic increase in tread wear there’s also that worrying slice which runs the length of the sidewall. Oh and keep in mind this is with a sidewall tread, I’d hate to see what this roller does to normal sidewall tires!
I imagine a tire sidewall completely collapsing on you as you ride along isn’t a pleasant experience.
I have read some other stuff on the internet such as modifying a coke bottle cap into a roller that seems to work ok in the west but realistically that doesn’t seem to be a long term solution.
I’m convinced it’s the sidewall tread on the Contact Travel tires that’s causing the slipping in the wet with the rubber wheel so for now I’m just going to put up with it. I’ve found that if you ride slowly (15km/h or so) the rubber roller manages to maintain contact when it’s raining.
Winter is almost over here so I haven’t had to use the dynamo at all over the last week or so and on top of that Melbourne doesn’t tend to get much rain anyway. At this stage apart from trying a touring tire with a smoother treadless sidewall I’m happy with a dynamo that is functional most of the time.
Of course if I still can’t get the rubber wheel to work on a smooth sidewall (this should be do-able considering it worked brilliantly on the Gatorskins), there’s always the dynamo hub option but I kind of like the neatness of a bottle dynamo so I’d like to get the system working reliably in the wet first.
Something about having a removable dynamo that can be turned on and off appeals to me more then a non-removable hub dynamo. On the other hand safety is kinda important, no point dying trying to save money.
September 21st, 2009 at 10:05 pm Kevin(Quote)
Lots of useful info in the dynamo posts. Do you have any knowledge of regulators and/or inverters suitable for charging batteries from a bicycle generator? I’m looking for a system to charge a 7V bottle battery for my headlights, as well as charging a 9.5V netbook computer (if I can’t charge the netbook computer, I would like the dynamo to power a NiMH AA/AAA battery charger and mobile phone charger, both of which could otherwise be charged from the computer USB port). Presently, all these devices are charged using a couple of 240VAC power packs – I can’t use that while riding!
September 21st, 2009 at 10:32 pm ozsoapbox(Quote)
Hey Kevin, there’s a few manufacturers around that produce DC bottle dynamos but they are specific units and having not used them can’t comment on the efficiency/drag component of them.
Alternatively Busch and Muller recently released a doohickey called the e-werk that connects to a hub dynamo and can be used for charging.
Not sure how long it would take to charge a laptop on though!
Have you had a look at solar chargers too? I know that Deal Extreme stock a few and this is probably what i’ll wind up using at some point if I don’t use my dynamo power.
September 21st, 2009 at 11:42 pm Roly(Quote)
I’ve used both bottle and Dynohub lighting systems and the bottle dynamo (strictly alternator) is one of the least efficient devices invented by man.
Apart from the lousy drive system you are concentrating on, they are made with a crap magnetic circuit (for weight) and wound with a high inductance so they are self-regulating and don’t blow your bulbs at high speed.
I’ve seen lots of designs that try and correct these defects but none that look convincing. Dynohubs are a multi-pole alternators with a much better magnetic circuit and much higher efficiency, but at the expense of the non-standard hub/spoke complexity.
One style I have no experience of but look more hopeful are the knurled roller type mounted under the saddle and running on the tyre tread.
Whatever, part of the answer has to be rechargable batteries that keep your lights going when you stop, combined with some form of rectifier/charge regulator. I’ve only ever seen homebrew setups so I don’t think there is anything like this commercially available, and would be likely to be way overpriced anyway. Combined with LED’s rather than bulbs this should produce an effective, efficient, and reliable bike lighting system. HTH.
September 21st, 2009 at 11:52 pm ozsoapbox(Quote)
My Dymotec 6 dishes out full power at about 3km/h or so and doesn’t seem to have too much drag. At speed I don’t even notice it.
I believe these units run at about 40% efficiency which admittedly doesn’t sound great but is a hell of a lot better then the cheap Chinese bottle dynamos.
So far I’m pretty happy with mine.
As for keeping your lights on, dynamo lights with capacitors inbuilt are readily available. Typically my rear light stays on for 4-5 mins and the front 7-8. This is ample time at a red traffic light before you get going again.
September 22nd, 2009 at 4:02 am Roly(Quote)
The reason they are made the way they are is so that they come up to voltage at low speed, but use magnetic and electrical *inefficiency* to limit voltage as the speed increases. This is quite aside from the pathetic efficiency coupling to the wheel.
“40%”? At 5kmh I would assume. As speed goes up the electrical efficiency will drop to a very low figure, more like 4% than 40% in my experience. Don’t know about yours but mine used to get hellish hot; a seriously bad sign. Grinding the side tread off your tyre would have taken some energy too.
You’re right about the price of that wire wheel. $2 shops sell sets of three just like that in bronze, and at 66c each who cares if you have to replace one every 6-12 months?
I assume from the stay-alight times you mention that you are already using LED lights which are a huge advantage, but it also highlights just how poor the mechanical coupling to the tyre actually is.
The mechanical efficiency of the sidewall coupling is generally so poor (as you are observing in wet conditions) that improving the electrical efficiency doesn’t help a lot, and is in large measure why the Dynohub is much more *mechanically* efficient – no friction loss or slip.
I rode most of my life but I’m a bit past it these days, however if I was looking to trick out my bike with a lighting system now I think I start by selecting a stepper motor recovered from a printer or old floppy drive. Apart from being a vastly superior alternator this Dynohub/bottle hybrid would also allow a much larger diameter runner with a bigger footprint on the tyre.
I went for a bit of a snoop and came up with these two link-rich sites that should keep you occupied for a while. One of the designs even claims to be able to recharge your phone as well.
http://www.nscl.msu.edu/~daniel/regulator.html
http://yojimg.net/bike/equipment/lights/led_lights.php
November 17th, 2009 at 12:01 am Peter(Quote)
In the Netherlands you can buy what is called a ‘dynamo hat’ (dynamohoedje). It’s essentially a grippy rubber cap you slip over the original to improve friction: http://www.aaltenkruitbosch.nl/ProductDetails.aspx?ProductCode=S020647&SubPage=True
December 18th, 2009 at 5:19 am Jack(Quote)
Greetings from the US!
I enjoyed reading your posts on the Dymotec as I am considering one for my LHT with Travel Contacts as well. I will be using the Dymo with an Ixon IQ (with R&C), so I will have battery backup to get me through rain. But I would still like to be able to generate in the rain if/when needed and am wondering if you found a reasonable solution. Or, are you considering reverting to some other tires?
Also, is there any chance the positioning or anything else could’ve been tweaked to minimize the damage of the wire roller? The photos clearly show a huge problem. But its hard to imagine the wire rollers are a viable product if they cause that much damage to a tire in only 40 km. It seems like a problem B&M wouldn’t have.
Based on your two articles, I am convinced that the Dymotec 6 is the right generator for my situation. Thanks so much for taking the time to post this great info.
Jack
Durham, NC, USA
December 18th, 2009 at 6:30 pm ozsoapbox(Quote)
No worries mate, I’m using the dymotec 6 here in Taiwan with no problems (although I’m not looking forward to the rain seasons!).
When i was using the 700X28 gatorskins I had no problems in the wet with the rubber roller, it worked like a dream. The only difference I can see with the Contacts is the size and use of a tread.
As of yet I haven’t found a solution in the rain when using the Contacts (other then riding really really slowly). I don’t plan on using the wire roller again so I am going to try Schwalbe’s Marathon Plus tires (in a 700×32) and see if they hold dynamo grip in the wet.
If not, and if the rain season here is really bad (i’m led to believe it is) then I might have to look at investing in a hub dynamo solution.
With the wire roller I didn’t try adjusting it after fitting it as it’s roughly the same size as the rubber roller. I suppose you could try backing it off as far as possible so it *just* touches enough to spin, that should minimise the damage I guess.
I was told not to use it in the dry at all and removing the roller, whilst a simple task requires the carrying around of a screw driver to pry open the golden lockring.
If it rains a lot where you are it might be a viable solution but back in Australia we didn’t get nearly enough rain to justify swapping the roller over so I didn’t bother.
May 2nd, 2011 at 3:15 am Peter B(Quote)
I am using the sram ilight ,with homemade led with reflector,it is so good i can use it offroad on my hybrid bike . It is the lowest cost/most effecient /lowest drag – i cannot feel it even up the steepest of hills .
Unfortunately not in oz but the internet is a wonderful thing . I think i paid about $60 dollars au ,postage is the killer . i leave mine on all the time – i have had people say it is too bright!
I am using cree mce (4in 1) led ,led’s back to back to take advantage of the generator’s AC output .only disadvantage is that it has to be built into a wheel but then you will never have to worry about it again .
May 3rd, 2011 at 3:24 pm ozsoapbox(Quote)
Yeah the hub dynamos are obviously going to have less drag then the bottle dynamos, but I’ve come to love my trusty Dymotec – it’s never failed me and I like the fact that I can just turn it off.
The drag isn’t that bad once you get used to it. It’s not like the bike comes to a rolling stop if you stop pedalling or anything. Still, I suppose when it does fail I’ll look into hub dynamos for general research but if I can pick up another cheap Dymotec that I can just bolt in I’d probably wind up going with that.
February 22nd, 2012 at 5:08 am Bob Fairlane(Quote)
Why not make a “pie plate” of some type of grippy rubber surface (an old cutting board, or maybe an old mudflap) for the left side of the wheel, and have a bottle dyno run on that instead of the tire?
February 22nd, 2012 at 9:50 am ozsoapbox(Quote)
What would you attach the pie plate too?
I don’t think it’d be good for the spokes to have the dynamo pressure on them and that only leaves the rim (can’t because of the brake surface) or tire (same wet problems).