The twelve hour battery life of the Garmin Edge 205/305 is a shortcoming that needs addressing if you do daylong rides such as Audaxes and the like. There are a few options out there similar to the emergency mobile phone chargers such as Cellboost and PowerMonkey etc and the Homebrew route that I tried.
Part of the problem when your Edge gets down to one blob of battery life is recharging it on the move. On the Audaxes time was a bit tight in the control points and the Edge doesn’t recharge in 5 minutes. You dread seeing a low battery warning after 100 of 125 miles I can tell you.
My Edge is mounted on the stem but there is also a clearance problem with USB connector. Its a tight fit and any pressure on the cable means the Edge won’t take a charge. This tight fit rules out the use once Emergency Mobile phone packs like CellBoost (£5 at Tesco,s). Riding colleague and Garmin route planning mentor Ray has a pack from Akhter that works that cost him about £20 I’ve been told, it gets put in a pouch that gets looped onto the handlebar. His setup works but I still like the Heath Robinson efforts that abound.
There are two methods of regulating the voltage to your Edge charger first is the step down method. You start with a higher voltage and drop it down to 5v through a regulator . The excess voltage generates heat and is not efficient. It’s easy to do though and the parts are cheap. Cheap enough for the Cellboost pack to be thrown away.
The other method is DC-DC conversion. This is what I think is in the more expensive chargers like Ray,s. This is the blood out of a stone method and is more efficient than the step down method. Without going in to too much detail it allows you to extract all the energy out of a set of cells to top up your Edge. You can quite literally charge your Edge from a single AA cell.
The Energiser Energi to Go charger looks like it might work Ok . I might end up getting one instead of faffing around but where would be the fun in that.
To be continued. The solution is out there.
Mustn’t forget to mention Andy Walshes charger from Poundland. Cost need you ask £1. Battery under the seat, with a switch. He completed a 12 hour Race with it.
MK 2 battery pack is coming up with a 5 volt regulator in it. Been to Maplins for the bits.
Fabricated the Regulator side of the charger into a PP3 cell top. Then potted it in Araldite. The regulator is a 78s05 5volt regulator that I’v had since the days when I used to do computer repairs. I bought a 6 x AA cell battery pack from Maplins whech should supply 7.2 v if fitted with Nicads or Ni-Mh batteries. All thats required now is to fit the mini USB plug to cable and test it.
A 7805 voltage regulator needs around 6 volts before the regulation starts to suffer and is good for 1 amp of current on a heatsink. One final word of warning Nicads and Ni-Mh batteries generate large currents when shorted due to having next to no internal resistance. Take care to insulate any exposed metal or you could end up with more than a melted jersey like I did. If you’ve poor soldering skills don’t attempt to solder a mini USB connector.
The Edge is quite a hungry beastie drawing 380 mA from the PSU falling back to 190 mA after an hour. The regulator draws 4 mA without the Edge connected so it would eventually flatten the batteries if left connected.
Like I have mentioned before the Edge USB port is a very tight squeeze when the Edge is mounted on the stem. The Madone is fitted with an oversize stem and the Maplin USB connector just comes in to cantact with it. It is going to need a bit of adjustment to make it foolproof.
Next project is likely to be a LED headlight unit. The price of the LEDs must be at a level where it is cheap enough to play around with them.
Next test: Field trials.
The field trials in the Discovering Shropshire Audax went fairly well but they weren’t the full onbike trial. The Edge was down to two blobs by the final control and a 15 minute or so charge put another blob back on the battery charge indicator. The exposed part of the 7805 regulator is hot to the touch but these are robust devices incorporating various methods of protection. I also used the pack to charge up the mobile phone on the way home as it is also fitted with a mini USB connector.
Cost without rechargeable batteries is around £2.50. The regulator was in the junk box.
Maplin Part Number
L53AZ USB 2.0 Mini Plug 5p £1.79
HQ01B 6AA Battery Box 74p
UJ54J L78S05CV 2A reg 77p
Or if you’ve no soldering skills don’t posses a soldering ironyou could try one of these for £1.99
Edge 705 update. Not going to be available until 1st Quarter 2008 !!!!!!