Have Light. Will Bike.

The bike@cartky.org mailing list has been lighting up (har har) talking about lightsets for the coming winter commute months. Got a great system? Join the list and tell us about it.

There is a huge variety of opinion on light power sources, with the generator hub contingent being perhaps the most vocal and persuasive group. However, there are also proponents of high-performance Li-Ion batteries and also dirt-simple AA rechargables.

More photos below the fold.


Li-Ion light in action - Photo Credit


AA / AAA battery charger, backbone of Dave's Lightset - Photo Credit

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Cross-posted: NiMH Chargers

Winter's coming, and that means night riding. Bike head lights and tail lights have made huge strides in the last few years, but nobody ever talks about powering them. This post is about recharging those lights using high quality rechargeable batteries you can buy at any Walgreens or Kroger, with special attention to the chargers for commuting.

But first back up and review the four methods of power, and briefly why I currently tend towards NiMH rechargable batteries versus the other technologies.

  1. Bike dynamos: These power the lights from the forward motion of the bicycle. They have various pros and cons, which I should not really get into here, except to say that they are the most sustainable solution if you can deal with the significant retrofit and monetary hurdles to installing them. In a perfect world, all transportation bicycles would have them built in.
  2. Proprietary battery packs: These are typically used to power very high-power headlights - 300+ lumens. They are usually Lithium Ion (Li-ion) or some such advanced/expensive cell. They are light weight,and typically come with their own rechargers. For this reason, they are favored by people in bicycle sports, and to some extent by commuters. You can't beat their photons-per-pound performance! However, they have a downside - if the battery wears out (and anyone with a cell phone or laptop knows this happens), then the owner is at the mercy of ONE COMPANY to support their product. This can become impossible if the company has gone belly up or no longer makes that model - many working multo-hundred-dollar lights go to the junk heap for this problem every year.
  3. Disposable batteries in lights. This has become a trend with watch batteries in tiny lights, which are fine for occasional riders who might get stranded in the dark, and as back ups, but they're not really serious for people planning to spend 5+ hours a week pedalling in darkness. AAA and AAs in headlights gets pricey real quick, and trying to squeeze the last bit of value out of a tail light that's 90% gone strikes me as penny wise and pound foolish. Avoid 'em.
  4. Rechargable batteries in lights designed for Alkalines. Nickel Metal Hidride (NiMH) has improved every year, and is now a very good technology. NiMHs are very affordable: $2.50 per cell at Walgreens,and each cell is good for hundreds of uses - about 1 cent per charge! Wow. That's what the rest of this post is about.

AA and AAA NiMH Batteries

NiMHs have a higher energy density - especially in high-drain headlights. For example, my light manufacturer estimates 20 minutes out of Alkalines in my high-power headlight, or 2 hours with NiMHs.

One bummer: NiMH AA and AAAs produce a hair less voltage than check-out-counter alkalines, and work in the same lights, though slightly dimmer. However, since LED lights are doubling in brightness about every 2 years, this lessened intensity is just a drop in the bucket, not worth worrying about.

Using NiMHs also has a subtle advantage over the Li-Ion battery packs: you have vendor independence and modularity. First, if your battery wears out, you can replace it easily (I retire worn-out headlight batteries out to lower drain devices, like flashlights). Secondly, if you're going for a Really Long Ride, you don't have to mail away for a second battery pack, you just go get the retired batteries out of the flashlights. Thirdly, the charger is also independent, and can be replaced. Heck, if life finds you low on juice, its often possible to borrow a charger at a friend's place.

The charger deserves special attention. Its the only way to judge to the health of your batteries. A really good charger can tell you a lot more than just "this battery is charged now". It can tell you how big a chunk of energy each battery can hold. Its good to group batteries from the same blister pack together, because they wear better, but sometimes one gets out of sync, and you can nurse it back to health with a good charger.

So what're the pitfalls in NiMH battery chargers?

$10 chargers that you buy in Walgreens will be trickle chargers. These have their place, but its not commuting. They can take up to a day to charge AAs. You need something that works while you're sleeping - less than 8 hours is a requirement. They are gentle on the batts though,and you can't really hurt a battery with these guys, which is nice. They're cheap, I'd get one.

$25 chargers tend to be fast chargers. They put a dangerous amount of juice into the batteries, relying either on a voltage spike or the cell temperature to figure out when to stop. Sometimes they miss this cut off, and electrocute the battery, which will hurt it I'm told. Bummer. They don't have any feedback other than one light per cell,that says either "charging" or "charged". Feh.

Chargers You Can Trust

The above chargers are what most people these days have. However, most people don't depend on their batteries day in and day out to keep them from becoming roadkill. We do. For that reason, investment in high end chargers is warranted. These chargers can tell you more about your batteries than a single light. These two models lead the pack:

  • Maha MH-C9000 "Wizard One": $60. (tested by me for last ~3 years - works!)
  • La Crosse BC-9009: $40 (plus includes $20 of free batteries.)

There's a great compartive review of the two of them here.

The bottom line is you'll want the LaCrosse and maybe a $10 trickle charger for back up. Its as cheap as vastly inferior fast chargers you can buy at Walgreens.

You'll want to read the instruction manual: if you treat it like a toaster, it'll toast your batteries. You need to treat it like a microwave oven, and build some common-sense when it comes to charging. If you can't deal with this, just buy a cruddy $25 fast charger, and prepare to fry. In exchange for reading the manual, you'll be able to see how much juice each battery has absorbed, and charge batteries both quickly, reliably, and fairly gently.

There are really three aspects to a well-lit bike: the headlight set,the taillight set, and the charger. Don't skimp on the charger just because its not attached to your frame. Without power, lights are just dead weight. With power they keep you visible. Hooray for NiMH rechargers!