Adapting battery packs from Cree T6 light to USB charger

[freeflow]

I have two of the cheap Chinese Cree T6 bike lights which have worked well. Now the lighter nights are here I was wandering if I could get a cable adapter theat would allow me to use the battery packs to power my phone whilst riding. Can anyone help.

[edocaster]

Short answer: yes - http://www.action-led-lights.com/produc ... sb-adapter

Here's someone's DIY attempt too: http://forums.mtbr.com/lights-diy-do-yo ... 65259.html

One of the respondents on the second link hypothesised that the DIY version didn't make full use of the battery, as he used a DC regulator designed for 12V. He could certainly pick a regulator which didn't need much of a voltage margin (i.e. a 'low dropout' regulator), in which case he could get usable USB power from the battery from fully charged (8.4V) right down to low voltage cut-off (these batteries shut down around the 6V mark). I can't vouch for it, but the parts would probably total £8 (note:iamnotanengineer).

[DoctorRad]

This would appear to be a pretty handy regulator board for such a purpose, but I've not tried it myself.

http://www.hobbytronics.co.uk/s7v7f5-5v-regulator

One caveat is that it could drive many rechargeable batteries into an over-discharge state unless they are well protected against such an event.

EDIT: Also this from eBay: http://www.ebay.co.uk/itm/281216550302

[niggle]

This idea seems to have potential for me: I also have two of the 4x18650 Li ion battery packs for Magicshine lights and have been wondering how I can use my smart phone for navigation without running out of battery power. I did look at the USB power packs such as http://www.amazon.co.uk/PowerGen-12000m ... power+pack but the amount of Ahs is less than you can store in 4x18650 I believe as well as costing more? I will have to buy something ready made like the Magicshine unit as electrickery is well beyond me.

[freeflow]

I'm not an electronic hobbyist so I've just bought one of these which looks as though it will fit in the battery bag.

http://www.amazon.co.uk/gp/product/B00G ... UTF8&psc=1

[mig]

off topic i know but if anyone has a use for two sets of such lights, batteries, chargers etc (that no longer charge for some reason) as spares then they're free to a good home.

[edocaster]

This would appear to be a pretty handy regulator board for such a purpose, but I've not tried it myself.

http://www.hobbytronics.co.uk/s7v7f5-5v-regulator

One caveat is that it could drive many rechargeable batteries into an over-discharge state unless they are well protected against such an event.

EDIT: Also this from eBay: http://www.ebay.co.uk/itm/281216550302

I'd seen that second unit elsewhere (http://www.thorncycles.co.uk/forums/ind ... g61219#new). Tempted to just buy a couple to play with.

The difference between that and a low dropout linear regulator is the switching regulator wastes less energy as heat. But if it stops regulating at around 7V or even higher, that may be too high (i.e. not making full use of the battery capacity). The risk of damaging the batteries through deep discharge is low, as Magicshine-type batteries (should) always have a low voltage protection circuit. If anything, mine are too sensitive, with the battery cutting out in cold weather too soon (they have to be reset by the charger after that).

NIggle: Unfortunately, the mAh of the 4x18650 batteries is effectively 4000mAh, as they tend to be 2000mAh cells in 2-serial, 2-parallel. A dedicated USB pack (if the stats don't lie - depends on whether they are counting all cells at 3.7V or output at 5V) should still beat it. Plus, you can't charge the 4x18650 via USB without buying yet another device.

[niggle]

NIggle: Unfortunately, the mAh of the 4x18650 batteries is effectively 4000mAh, as they tend to be 2000mAh cells in 2-serial, 2-parallel. A dedicated USB pack (if the stats don't lie - depends on whether they are counting all cells at 3.7V or output at 5V) should still beat it. Plus, you can't charge the 4x18650 via USB without buying yet another device.

Understood, though I have no particular need to charge via a USB. I might go back to the Plan A 12000mAh pack as I often use the bike light as a torch when camping- it was very useful recently attached to a propped up bike when pitching the tent in the dark.

PS why does everyone use, e.g., 4000mAh instead of 4Ah? In my profession as a nurse I previously came across drug doses written as, e.g., 1000mg instead of 1g and was challenged when I used the latter and told it would cause confusion, and with the non trained nursing staff in the residential settings I was working in at the time I could see that, but with the tech minded people in electronics it seems odd.

[DoctorRad]

Something like this might be more versatile (and suitable for driving with a dynamo with suitable rectification and over-voltage protection) but you'll have to roll your own USB socket output:

http://www.ebay.co.uk/itm/310908010643

(Edited to link to similar product without extortionate postage prices)

[edocaster]

PS why does everyone use, e.g., 4000mAh instead of 4Ah? In my profession as a nurse I previously came across drug doses written as, e.g., 1000mg instead of 1g and was challenged when I used the latter and told it would cause confusion, and with the non trained nursing staff in the residential settings I was working in at the time I could see that, but with the tech minded people in electronics it seems odd.

The true techies say even odder things, like '5V5' instead of 5.5V...

[edocaster]

Something like this might be more versatile (and suitable for driving with a dynamo with suitable rectification and over-voltage protection) but you'll have to roll your own USB socket output:

http://www.ebay.co.uk/itm/310908010643

(Edited to link to similar product without extortionate postage prices)

Great link. Useful device, but I'm not certain buck and boost are necessary for a dynamo - lack of volts doesn't seem to be the problem. For over-voltage protection at the input, do you have any ideas?

Is the output voltage selected by the little brass screw on the blue block? Is there any way to calibrate it other than monitoring the output with a multimeter?

[DoctorRad]

I've yet to implement the idea, but see this and subsequent posts for information on why you need overvoltage protection and how to implement it:

https://yacf.co.uk/forum/index.php?topi ... #msg952080

The thyristor / zener solution is probably the best, but needs either a second rectifier (as per the one already in the Reecharge) or a following diode as per this circuit:

http://en.wikibooks.org/wiki/Practical_ ... ar_circuit

The page above explains how the protection circuit operates. In the regulator protection application, you don't need the fuse or the capacitors, but you will need a rectifier and smoothing capacitor. See here for similar circuits to drive LEDs:

http://pilom.com/BicycleElectronics/DynamoCircuits.htm

At some point, I plan to pull all this together and do a DIY guide.

[edocaster]

I've yet to implement the idea, but see this and subsequent posts for information on why you need overvoltage protection and how to implement it:

https://yacf.co.uk/forum/index.php?topi ... #msg952080

The thyristor / zener solution is probably the best, but needs either a second rectifier (as per the one already in the Reecharge) or a following diode as per this circuit:

http://en.wikibooks.org/wiki/Practical_ ... ar_circuit

The page above explains how the protection circuit operates. In the regulator protection application, you don't need the fuse or the capacitors, but you will need a rectifier and smoothing capacitor. See here for similar circuits to drive LEDs:

http://pilom.com/BicycleElectronics/DynamoCircuits.htm

At some point, I plan to pull all this together and do a DIY guide.

The implementation in the first link looks like it would work well to protect the regulator (I know very little about SCR/thristors), without burning off too much power in a zener diode. But the note about using the charger parallel to lights which will also switch off is worrying. So, for example, with lights off the input voltage could trigger the crowbar to the charger, which would then drag voltage down to a couple of diodes-worth, and would only reset on stopping the bike. If you're unaware this has happened and try to switch the lights on while moving (e.g. for an upcoming tunnel)... you'd get a nasty surprise. One way to prevent this would be to put a large enough zener diode before the SCR (large enough to keep the crowbarred voltage above what your lights need), but that is back to using big zeners again.

Is there an overvoltage protection which will leave the regulator input at open circuit, rather than close to short circuit?

[DoctorRad]

There's an alternative, more complex protection circuit here which uses a MOSFET to break the ground connection to the smoothing capacitor before the regulator so as not to allow the voltage across the former to rise above a certain value:

http://pages.citebite.com/w3j1c7b1x9ctx

Lots of analysis and alternative approaches on that website.

It may be possible to hybridise these two circuits and use a thyristor and a MOSFET in a simpler circuit which will allow a lamp in parallel, I'll have a think.

However, I think it's the case that if the LED light is PERMANENTLY in parallel with the regulator, you don't need overvoltage protection for the latter. This is because the LEDs will act as a shunt regulator, preventing excess voltage from appearing across the regulator input. However, as it's a parallel circuit, the current from the dynamo will be split between the LEDs and the regulator, so charging ability will obviously be diminished.

[edocaster]

Well, that is pretty complicated - i.e. I don't think I understand it.

Regarding a permanently attached light, it would have to be permanently 'on' to shunt enough. Or it would have to be a permanent part of the regulator to fire up if voltage is allowed to climb due to the regulator having no load - i.e. lots of LEDs and possibly a zener in series to stack enough voltage drops. It would be a waste of space and would also need heatsinking.

How do the commercial lights with USB (Axa Nano/Luxx, B&M Luxos) do it? They clearly allow charging with lights off (in fact, some don't allow charging with lights on), and must expect users to occasionally forget to connect a load.