3AA DD vs 3AA BB700?

[Owen]

I don't know how much current 3AA in direct drive puts out, and wondered if I had anything to gain by installing a BB.
If it matters, the light is a 3AA Luxeon Task Light with a R2L HD/Fraen optic and the resistor removed from the board.
The BB would be installed in the space occupied by the stock switch and board (I use a Kroll tailcap switch on this light).
Thanks /ubbthreads/images/graemlins/smile.gif

 

[Rothrandir]

well i think you mean db right?

the main advantage here is to keep the output more level...

not sure what the internal resistance of the aa's will limit the led current to, but it can't be too much higher than 700. at least not for long.

 

[EvilLithiumMan]

Can you measure the current draw of the light in DD mode? To do this, you would set your meter to measure amps. Then remove the kroll switch. Now place one lead on the cell's negative terminal and the other on the inside wall of the light. (You would be effectively placing the leads on the same points that the kroll switch would use). Be sure to take your meter out of 'current' measuremnt mode when done.

Without knowing what the present current draw is, it becomes a matter of conjecture as to whether the BB700 will provide any meaningful increase in brightness.

 

[Owen]

I mean BadBoy for boost, since in DD, I'm getting good runtimes (left it on for 3+ hours with no noticeable drop in brightness), so I figured that unless I'm pushing the limits of the LED, maybe I could get more brightness out of it, and am willing to sacrifice runtime, though I do need at least 2 hrs out of this light, since it is getting used at work when I need good brightness, and a longer run than my L4 will provide.
How's that for a run-on sentence? /ubbthreads/images/graemlins/tongue.gif

 

[Owen]

Sorry, EvilLithiumMan, I did not see your post.
I am not up on electronics stuff, and didn't realize I could check current like that. I tried measuring across the LED, and was not getting a reading.
Thanks.

 

[Rothrandir]

badboys require the input voltage to be under the led vf.
unless your led vf is above 4.5volts, then it's going to kill the badboy.

 

[Owen]

This thing is only getting .49A with brand new batteries.
I can't really tell much difference between that, and the old batteries that were reading .36A, which kind of surprised me.
I wonder how much difference a BB700 would make?

 

[Rothrandir]

bb700 would make a big difference.
you might not get any light at all.

you need a downboy700.
the difference should be quite noticable.

 

[Owen]

I see what you're saying about the Vf, now. BB can't handle the input voltage from 3AA. My bad.
How is a DB going to give me more current, though?
I thought it was a stepdown.

 

[Owen]

I just went and reread the info on the DB. You are right, this looks like just what I need!
Wish I'd read this stuff more carefully awhile back.

 

[jtice]

What batts are you using? (chem?)

I forget what Vf L bin is...
I think thats too low,
If you had something with alittle higher Vf, 3AA would work, if you used Alkalines.

A BB can take about .5V over Vf, but thats IT.

 

[Rothrandir]

the name db700 implies 700ma.

it steps the voltage down, and regulates the current.
in the case of a downboy700 it will step the voltage down to the point where it delivers 700ma to the led.

 

[EvilLithiumMan]

I've run both a MM+WO (800ma) and a BB750 with 3 fresh charged NiMH cells without any problem. The maximum allowable voltage for these modules is Vf + .4 volt. You have relatively high binned device, voltagewise, so I wouldn't expect any problem.

But I do have to admit that you would be running near the edge of what is safe for these devices. The minimum input voltage for DB700 is 'approximately' 3 volts, so Rothrandir's suggestion would certainly be a safer way to go.

Whoops - I just read more of the DB description. "Will operate in DD mode when Vin is less than Vout (Vf)." Which means if your Vf is 3.75v, the DB won't be giving you anything over what you have now. I'm flip-flopping and changing my vote back to the Badboy. /ubbthreads/images/graemlins/icon15.gif

 

[Owen]

Vf of the LED is rated 3.75-3.99, and I'm getting 4.7V from 3 Rayovac Max Plus AAs so the DB does appear to be my only option.
Sorry for my confusion over the function of the boards. I read up on these things some time ago, and was going from memory.
Thanks for your help, guys /ubbthreads/images/graemlins/smile.gif

 

[EvilLithiumMan]

(Read the edit on my previous reply)

That 4.7 volts is rapidly going to drop below 4 volts when a 1 amp load is placed on them. And given the converter's efficiency, that is how much load the cells will see.

 

[jtice]

Yea, under load, they wont be near 4.7V.

Hmmm, your Vf is fairly high,,,, yep, go for the BB, I think it can take it.

Its REAL close, but the DB isnt gonna do much for you, not gonna be in regulation long at all.

 

[Owen]

I think/hope the BB will work ok.
Roth said "badboys require the input voltage to be under the led vf".
Measured under load, I'm reading 3.65V at the LED. That's with the brand new batteries, so it's only going to get lower. I suppose that's what would be coming into the board if I install it, too.
The Vf is supposed to be 3.75-3.99.
Hmmm. That would be more, then /ubbthreads/images/graemlins/cool.gif
Sounds good, anyway...
I'm going to try it.

 

[jtice]

Yep, sounds good, should work just fine.

You might want to test the diff. types of batts you plan to use, make sure none get alot higher V for some reason, but they shouldnt.

 

[Rothrandir]

if you're measuring at the led, you're getting the resistor figured in right?

maybe simply dropping the resistor would work for you?
i've made dd 3aa mods in the past, and they're very bright!

 

[Owen]

I took the resistor out. This one is already DD.
I also just ordered the last BB700 on the Shoppe.
Maybe I won't kill it /ubbthreads/images/graemlins/thinking.gif