6 x XR-E w/bFlex Battery Question

[tyebud]

So I've been toying with the idea of putting together a bike light with two of the triple Cree XR-Es from Cutter Electronics. I'm set on using the bFlex as my driver. I'm mesmerized by the features and size. That said I'm limited to 1A of current, which probably isn't a bad thing. Anyways, I'd like to know what you guys would use for lithium ion battery packs? I've heard from this forum that running six cells in series is a bad idea for various reasons, so that may knock my second option out, but maybe there are other options? Maybe neither of these options are best suited for my needs? Let me know!

The two options I've come up with that would work with the bFlex are as follows:

1.) 2 series of 3 XR-Es with a max draw of 500mA @ 11.1V

2.) 1 series of 6 XR-Es with a max draw of 1A @ 22.2V


If I've overlooked something, lemme know.

As always, thanks!

 

[ktronik]

my 2 cents for what its worth, but there are plenty of people on this forum that know more than me...


if you run lithium cells in series you should have a BMS (battery management system) & charge via the parallel plug fitted to good lipo/ion packs... better than charging in series...

for 3 LEDs & to get the best use of the pack you need 14.4v.

Don't think you can run 6 in series but you can run in 2 parallel sets of 3 LED in series...(500ma per LED)

or you could use the same 14.4v battery & run a maxflex (boost driver)

same interface, but you could then run up to 1200ma to each LED!.. thats what I run & get about 1600lm...

hope this helps...

Ktronik

 

[znomit]

The two options I've come up with that would work with the bFlex are as follows:

1.) 2 series of 3 XR-Es with a max draw of 500mA @ 11.1V

2.) 1 series of 6 XR-Es with a max draw of 1A @ 22.2V

1) is almost 1000lm, 2) is over 1500, what do you need?

I'd do this:
3) get a maxflex and a battery from 14.4 to 20v. Run 6 leds in series. You can configure it to run at 500mA like option 1 or 1A like option 2. Choose battery V and mAhr to meet you runtime needs.


edit; must learn to type faster than Ktronik

 

[steve6690]

I have to agree...the MaxFlex is a better solution for you. I used a MaxFlex and 6 x Q5 XRE's in my dive light and it was fine with 4 x Li-ion's in series. You could run it at 700ma depending on your heatsinking. Another more expensive option could be 2 x bFlex in master/slave mode using the same 4 x Li-ion battery pack.

 

[tyebud]

Thanks for your responses.

Looking at the maxflex, I think that is a great alternative. For some reason I was under the impression the maxflex was controlled by a pot. I must have been thinking of the fatman.

So my next question is, how will picking a 14.4V battery configuration compare to a 20V configuration both with run time and charging time?

Initially I'm going to be running the lights of just the battery pack, but eventually, once I can afford it, I'll use a dynamo/tunecharger combo to charge the batteries. Should I be taking that in to consideration when designing my pack?

*EDIT* I've found some Tenergy Lo-Ion 18650 batteries with a capacity of 2.6Ah @ 3.7V. Has anyone had any experience with these?

 

[steve6690]

While testing my dive light (6 x Q5's and a maxFlex) I hooked up 4 x Trustfire 2500mah 18650's in series. Running the Led's at 700ma I started doing a runtime test. After 2 hours I got bored and switched it off. I reckon on around 2.5 hours. You could go for a higher battery voltage but 5 x Li-ion would give 21V straight off the charger. I think you'd need to measure the total forward voltage of your led string to make sure it is higher than the input voltage to the driver although I think the sag under load will make it ok. There are people on here that can advise you better than I can about that. As regards the Tenergy batteries, I found some tagged ones on Ebay and am tempted to buy them and make my own pack but I can't find a source of balancing/protection pcb's that I don't get stiffed on the postage charges to UK. I'm tempted to just buy a pack for $90 from this chap :

http://stores.ebay.co.uk/CampSolution

but I'd really like to build my own if I can

 

[tyebud]

While testing my dive light (6 x Q5's and a maxFlex) I hooked up 4 x Trustfire 2500mah 18650's in series. Running the Led's at 700ma I started doing a runtime test. After 2 hours I got bored and switched it off. I reckon on around 2.5 hours. You could go for a higher battery voltage but 5 x Li-ion would give 21V straight off the charger. I think you'd need to measure the total forward voltage of your led string to make sure it is higher than the input voltage to the driver although I think the sag under load will make it ok. There are people on here that can advise you better than I can about that. As regards the Tenergy batteries, I found some tagged ones on Ebay and am tempted to buy them and make my own pack but I can't find a source of balancing/protection pcb's that I don't get stiffed on the postage charges to UK. I'm tempted to just buy a pack for $90 from this chap :

http://stores.ebay.co.uk/CampSolution

but I'd really like to build my own if I can

Awesome, so a 4S4P battery pack should work fine then.

So is there a protection circuit out there that would accommodate a 4S4P 14.8V 10.4Ah pack?

 

[steve6690]

It'd work great but I think it would require more than 1 pcb.

 

[VanIsleDSM]

What's the issue with running more than 6 Li-Ion in series? I can see for charging.. but for discharge, I don't think there's an issue is there?

I saw some electric sports car on TV using tons of 18650 cells.. and it wan running 100's of volts, so he had to have many in series I'd imagine.. unless they were in parallel groups with DC converters.

..I was planning to use 12 in series for a project.. but not a battery pack.. they wouldn't be charged that way.

 

[steve6690]

What's the issue with running more than 6 Li-Ion in series? I can see for charging.. but for discharge, I don't think there's an issue is there?

I saw some electric sports car on TV using tons of 18650 cells.. and it wan running 100's of volts, so he had to have many in series I'd imagine.. unless they were in parallel groups with DC converters.

..I was planning to use 12 in series for a project.. but not a battery pack.. they wouldn't be charged that way.

I can't see a problem with that. If I could find cheap 18650 4s holders I would use those for my project and not bother with a pack at all.