DIY dynamo to battery-backed USB charger - electronics Q

[jameso]

A Q that will help me piece together a DIY USB system..

I can charge a battery pack from the hub output passing through a rectifier. Apparently the battery pack has a max charge rate of 500mah from the hub but apparently a 'booster cap' could raise that - I guess that's a capacitor of sorts? What spec would I need? Happy to solder it up w/o one but a faster charge would be useful.

And does anyone know roughly what charge a 7.2V battery pack (6xAA Ni-Mh rechargeables with 2500-2800mah capacity, outputting through a 5V/600mah regulator) would put into a Garmin 800? Interested in the workings too, I really should know how to figure that out.

More to follow, if I get this working I'll post it up with credit to the originator of the wiring diagram.

[johnnystorm]

Garmin 800 has a 1Ah battery so you'll have 6 charges or so from your AA pack. 600mAh is the similar to a boggo USB charger for speed of charging.

[jameso]

Thanks. More than I thought .. just trying to estimate how the timing of charging the pack would work compared to Garmin battery life, seems promising. Batteries are actually 2400mah so maybe a bit less that 6, but enough. How do you work that out?
I think the whole system will end up running at around 500ma so will get it wired up as is.

[johnnystorm]

Duh. 2400mAh batteries (allowing for inefficiencies) should do your edge twice so err 12 times then?

[jameso]

Ok, so 2.4Ah battery = 1Ah Garmin charged just over 2x. And I have 6 of them. Could take a bit of pedaling to charge that AA pack but won't need much of the actual capacity that can be stored.

Simple .. I knew it would look like a daft Q once I understood it : )

[jameso]

Seems I'll get 2.4x Garmin charge max after all. 12x did seem a bit too good from one charge.. 6 x 1.2v cells in series give the 7.2V (ie a bit over 5V which I need, 5 cells should do it) needed for USB output, but only the same Ah as 1 cell. Parallel battery wiring would give 6 x 2.4Ah, but the same V ie only 1 x 1.2V.
http://batteryuniversity.com/learn/arti ... igurations