Edge 705 and dynamo question

[Mike Conway]

I lost my trusty Etrex 30 the other day going down a bumpy descent - the device came off the mount and went flying into a section of forested undergrowth. Despite searching for over an hour, I wasn't able to find it.

A friend has lent me his Edge 705 for a 400km audax I'm doing this weekend. Of course the device's battery won't last the distance, so I've rigged my dynamo / Luxos U combo to run off external power during the day with the plan being to unplug at night and use the dynamo for my front light. I've done a couple of rides testing this and it works fine as I want it to work - the device runs off external power and doesn't eat into it's battery.

There is a snag, however. At one point I simulated stopping at a control and taking the Garmin with me. This meant unplugging the Garmin form the external power and re-plugging it back in once I was back from lunch or whatever. Upon unplugging a message came up on the screen saying something like 'External power lost - OK'. I pressed 'OK' and left the device on - of course it started to use it's own power at that point. The problem occurred when I plugged it back into USB power from the dynamo - it went into mass storage mode.

Now I was able to over come this by leaving it plugged in and simply turning the device on again, however all the data from my ride was wiped off the data screen display and stored in the device's history. The issue I have is that I could not tell how far I had ridden, and if you know audaxing, you will know that the only way to accurately determine where controls are is by distance from the start...

Does anyone know of a way to stop the device from clearing the current ride data once it's un-plugged and then re-plugged into external power?

[alotronic]

I have used 705 with a shimano dynamo hub and not had that problem. It's not the hub of course! I rode that combo around on a tour for 7 days and while I often got the external power lost thing happening I didn't loose data ever. Have you checked in basecamp/training centre that the data is really lost? Yes, you will almost certainly lose your measured distance though as the device will reset ever now and then when you are running it on external (randomly it seems). In the end I bought a ten quid cache battery and used that for 300/400 instead which works very well though you do have to run a cord somehow from GPS to battery of course - I used mini topbar bag for that. However with a 600 coming up I think I will charge the cache battery from dynamo and plug the gps into that... hopefully that will work!

[zigzag]

from what i know there are two types of usb cable for garmin - the ones that are good for power and data transfer and the other type that only supports power (no data). you would need the latter cable. otherwise garmin thinks that it has been connected to a pc and turns into an external drive.

[Kim]

Sounds like you need a cable (or thing with an appropriately wired socket) that shorts the two data wires (normally green and white) together to tell the Garmin that it's plugged into a dumb power source rather than a USB host.

Yes, this is bad design.

*wanders off to check that the lanyard is still firmly attached to her eTrex*

[Mike Conway]

Cool, thanks - the ride's over now, but the problem didn't occur again even though it's a cable that can supply both power and data.

Will keep this in mind if ever I get another Garmin. Cheers