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Fists of Ham
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90 Posts
Discussion Starter · #1 ·
Okay - bear with me, I'm pretty rusty with electrical stuff. After posting on this thread it struck me that I really aught to sort out that triple Cree Q5 i'd been meaning to put together.

Now, I've got a MaxFlex3 in the post from george at taskled, which is a boost driver yes? So it will drive 3 x Q5's with any battery of less than (3 x 3.7v) 11.1v.

My initial intention was to re-use my 6v 4600mAh bottle battery from my old electron lights. Another option would be to use a NiMh battery donated by a mate - prior use in a RC car, think it's a 7.2V 3300mAh. Would prefer the bottle battery, primarily for ease of mounting on the bike.

So - if i remember my (long time ago) physics lessons - the power consumption of the leds (at max drive) would be 1.2a x 3.7v x 3 (max current x led drive voltage x no of leds) = 13.32W. According the the blurb, the MaxFlex is >85% efficient so worst case would be 13.32 / 0.15 driver overhead - say another 2w. So I reckon that the lamp will consume around 15.5w of power from the battery. This should give me a current draw of around 15.5w / 6v = 2.58amps - around 1hour 45mins from the 6v battery or 15.5w/7.2v = 2.15amps - just over 1 and a half hours from the 7.2v.

I know that these figures are highly speculative, and there are a number of variables not considered such as:

The batteries are not new, and are likely to be a bit down on capacity

I'm not likely to actually run the MaxFlex at 1200ma - percieved wisdom being that 700ma is probably enough, the higher figures resulting in more heat than light.

My question is - what have I missed, and what silly mistakes have I made? :confused: I'm sure that someone can save me from doing something silly along the line :)
 

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Mmm... Tasty
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684 Posts
I think you've got it. Your math checks out, and you have a lot of the reality checks in there (like the wisdom of not driving at max, etc.).

LEDs have a wide range of forward voltages, so you'll have to test the ones you get with an voltmeter to really know what the draw will be. Also, your batteries could easily be down by 20-30% capacity if they are more than a couple years old and used moderately.

The only thing i didn't see you mention is that when running at low currents (the light set to a "low" light level), the forward voltage drops as well, so you could easily be in the 9V forward voltage range, but your batteries are below that, although a fully charged 7.2V battery will get close (in the mid 8V range, i believe). Should still work, though.

good luck, sounds like you have it figured out!
 

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Fists of Ham
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90 Posts
Discussion Starter · #4 · (Edited)
Thanks for the replies - Sounds promising.

So - part 2 of the silly questions session. Just had a quick look at the MaxFlex3's manual - apparently, it has a facility for giving an indication of how the battery rundown is proceeding.

I've just checked my 6v bottle battery and fresh from the charger it's actually putting out 7.5v. After running a couple of DIY Dinotte lights in front of the desk fan for 45 minutes it's down to 6v.

It seems that the MaxFlex is configured out of the box for a 2xLi-Ion battery (7.4v nominal or nearer 8.5v off the charger). So - MaxFlex experts, what would be sensible figures for VCut, VLow and VMed - or am I just going to have to run the battery with a couple of lights and log the Voltage every 5 minutes or so to graph up a battery curve? :yawn:

And Part 3 of silly questions - am I overthinking all of this ;)
 

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Fists of Ham
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90 Posts
Discussion Starter · #5 ·
Couldn't resist having a bit of a bash - just to check out the rest of my build, you understand ;) So i've pieced together the easy end of the wiring loom, mounted and sorted the optics, emitters and heat-soak, and just for the purposes of testing, dropped in a cheap 5w driver that I sourced on fleabay. All the stuff has been mounted into a nice MR16 sized clone of a Lumicycles can, again from Fleabay, and i've made up a crufty battery pack from 2x6AA battery holders wired in series and a bunch of AA NiMh cells. It's just done half a hour on the bench in front of my desk fan and it's warm to the touch but not hot - sans fan it reached quite hot very quickly, so it seems my heat-soak is working, and passing the therms onto the casing. All in all, i'm a happy bunny! :D :cornut: :cornut: :D,

Whats that? Pictures? okay, here goes..







First impressions - looks like a pretty tight beam with a reasonable amount of spill around the edges. I don't think that the crufty battery is up to the rigours of tonights group ride, to be honest, so unless one of the lads has a spare 14.4v I can scrounge up, it looks like it's more of a statement of intent rather than an actual build - but it certainly seems to prove the idea works reasonably well.
 

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Fists of Ham
Joined
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90 Posts
Discussion Starter · #6 ·
And an admission...

In the process of sorting the above light, I managed to mung up one of my Q5 stars - knocked the little bubble clean off. :madmax: :madman: :madman: :madmax:

I was amazed to find that it hadn't broken any of the connections and the dies still lit when i tested it via the Multimeter. Anyone know of a way to re-attach it or have I stuffed it forever? :cryin:

Curse these fists of Ham and fingers of Butter !
 
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