I have a shimano xt 1.5w dynamo on my do-it-all bike which has been grand for running lights over the winter.

I’m going away cycle touring in a couple of weeks and it would be nice if the output was sufficient to charge /keep topped up the garmin 810.

Trouble is with the 1.5w, I dont know if I will get suffienct charge at 16-24km/k sorta touring speeds. The person on the chat box at rose bikes seems to think so.

A simple way to test the output would be to test the amps of the ac output when cycling along, but cheap multimeters don’t tend to have this functionality.

i would prefer not to spend £70 on something whihc doesnt’t work.

From first principles, I know that 1.5w @ 6V ac should equate to 0.303A @ 5v dc, but unsure if this would charge the device, nor doo I know what speed the dynamo delivers this output.

Firstly has anyone used this hub to power a garmin, and secondly any suggestions how one could go about measuring the delivered output accross a speed range?

Quick google suggests the 810 battery is 1000mah – that means it would take one hour to discharge at a constant rate of 1000ma. Before even bothering to get the calculator out, that would suggest that you could fully charge the flat battery over 3-6 hours. Looking at it another way, if you start the ride with a full battery it’s very likely to be charging faster than it is discharging, id say you’re good to go.

https://www.cycle2charge.de/index.php/en/ produces a USB output of 5v/0.5a at 12kmh, so if the 1.5w dyno hub is half the power, presumably you’d need to be doing 24kmh (about 15mph) to produce 5v/0.5a?

I have no idea if what i’m saying is nonsense or not btw.

I’d be concerned about unregulated voltage spikes etc bricking my Garmin.

I’d assumed the OP was considering some kind of charging gadget like the cycle2charge or Busch Muller luxos etc..?

Yes, you’ll want a convertor- I borrowed a dynamo/cycle to charge setup from a friend for a few days. It was an sp pd 8 so I think a higher output but would charge a garmin with loads to spare.

Some garmins get a bit unhappy about power dropping in and out. I ended up charging a usb battery pack during the day then using that to charge garmin/phone at night.

I’d use a cache battery inbetween the dynamo and garmin. All the stopping and starting will break it. Cache will give a constant supply.