I have a couple of old 8.4v light batteries which power a cree led bike light. I never use them much these days but I wanted to know if anybody had used a usb power source such as a dynamo or usb power bank to charge a 8.4v battery?

I have found this cable on eBay that should actually so this, but I'm guessing at that price it won't last long or be much good.

https://www.ebay.co.uk/itm/5V-to-8-4V-D ... .l4275.c10

Any better ways to do this?

Cheers

d

IME * its not that successful to try and increase the voltage , from a DC battery source, as it is pretty wasteful of energy and is very sub optimal


I was on a boat trying to get 12 volts to 18 volt for a computer charger and t could charge the battery if off but not run the computer [ though it claimed to have enough A to do this. ]
Its probably worth paying £3 to see if it does actually work but i would not expect it to be very efficient.

Yeah I've taken a punt on it as for £3 its not the ned of the world if it doesn't work. To be honest it would be a backup for the dynamo and battery exposure lights. My plan for the Sweden races is to try to get each loop finished using just the dynamo light with the Diablo used as a fill in if the going is too slow. Hopefully it won't be much riding in the dark and then there will be a few hours to recharge everything at the basecamp before more of the same. It's only if I can't get enough charging done the I might need the Cree lights and hopefully this thing will allow them to charge from the bike's usb port during the day.

Well it's turned up and actually seems to work. On a mains socket usb port, it's charging the battery with a draw of just over 1a, so not actually worst than a smart phone. I guess it will be fine from a power bank and should be ok from a hub dynamo during the day. For £3 not too bad really to turn spare power into a backup light source.

sppose your issue now is whether you trust it as your only light source.

Not bad for the price i assume technology has moved on then given it works so well

I have B&M dynamo lights or Exposure dynamo lights on my bikes, which are used with a Helmet mounted Diablo. This wire is just incase I take along the old cree lights as a backup for the Diablo. So you could say it's to back up a backup. Realistically I might well start taking a cree along to use as a camp light with the knowledge I can top it up during the daytime now.

that is a lot of redundancy - what you doing/where you going?

Dynamo with light and an exposure joystick to get out of a mess/ as emergency back up light - you would get the best part of 5 hours at decent lighting levels[4-600 lumens]- is my solution. I tend to not do massive long multi day/week rides in winter though,

I

Cabin Fever in Sweden next month. I'll have limited mains in-between laps so I'd rather have more than I need than not enough.

I've always found the tiny Petzl backup headlamps to be more than enough light in camp — 20g and comes in its own pouch; comfortable to wear, and the two CR2032 batteries give several evenings of light.

And only 20g, or did I mention that?

Tiny, too.

Personally I wouldn't bother trying to charge anything while riding on that sort of event. Just take what you need and leave the rest at home. Don't think you need floodlights — you don't.