2D's, Q5, 800ma to 1.5 amps or so CC

[VegasF6]

Is there a driver to do this? I haven't had any luck finding exactly what I want. The closest I have found is maybe the GD1000. Perhaps I can't draw this sort of amperage safely from 2D alkalines?

Frankly, this is mostly all over my head, but from what I understand I need a boost driver to bring voltage to 3.7 volts or so, and cc of at least 800ma's?
Thanks!

 

[Mr Happy]

To find out whether something might be possible, you have to balance volts x amps on each side of the equation, and then allow for efficiency.

So suppose you drive your Q5 at 800 mA, then its Vf might be 3.7 V (just suppose, I don't know the actual number).

This means 3.7 V x 0.8 A = 2.96 W (call it 3 W).

Now your 2D's have an average voltage of 2.4 V (say). That means the current they have to supply will be at minimum 3 W / 2.4 V = 1.25 A.

However, now we have to consider conversion efficiency. A good working estimate for this is 80%. So our actual current from the 2D cells becomes 1.25 A / 80% = 1.6 A.

Whether this can be supplied depends on the cell chemistry. When using NiMH rechargeable cells, a current of 1.6 A would be no problem. When using alkaline cells, it would be possible, but it would reduce the life of the batteries. Alkaline cells are designed for long run times at low current, and are not efficient at high current draws.

So a boost circuit to do what you want is technically possible, but as people are lamenting in another thread, there doesn't seem to be such a beast on the market at the moment.

(Edit: a possible reason for this is that most commercial circuits are designed with alkaline cells in mind, since 99.999% of all known consumers use alkaline batteries. With alkalines the current draw is limited, so nobody sees a market for designs that have a high current draw.)

 

[VegasF6]

Thank you Mr. Happy. I have a vague (read very vague) knowledge of Ohm's law. But I really don't fully understand what the batteries are capable of.

So, a couple of questions. Would I be better off attempting to do this with 2AA Eneloops in D cell adapters? The eneloops are capable of around 2000 mah's apiece, while one chart I found claimed as much as 16,500 mAh from a D alkaline. (exagerated?) But again, that is where the chemistry come's in and throws me for a loop.

Or, I would certainly be willing to buy nimh D cells if there are any that are actually capable.

I could also use a 2d to 6AA adapter for this project, but that would increase the price quite a bit in both cells, and the adapter. Not really what I am looking for.

So, say for instance I wanted a driver capable of doing what the Taskforce 2C cree is doing. Any idea what sort of amperage/voltage output the Taskforce is putting out? Is there an availble driver solution that could provide similar results?

 

[Greg G]

In a 2D light you can forget about alks for a Q5 at 1 amp. 2 MiMH and a Shark driver, maybe, but would still be pushing it. The Shark driver would need a really good heatsink for drawing that much out of those batts.

The cheapest and best way to get what you want is to get a 2D-6AA battery holder from FiveMega, some Eneloops, and an SOB1000 driver from the Sandwich Shoppe.

If you have a 3D light, alks are usable with a Shark and a Q5.

 

[Mr Happy]

Thank you Mr. Happy. I have a vague (read very vague) knowledge of Ohm's law. But I really don't fully understand what the batteries are capable of.
...

I suppose I'm not quite sure what it is you are trying to do. Do you have an existing 2D light that you want to modify?

Because quite seriously, the best way to get what you want would be to look around for an off-the-shelf light that has the brightness, the size and the run time you need and buy that. It will all be robust, designed and ready to go, and will come with a warranty.

If you are looking to save money, it could be a false economy. You could buy a Cree Q5, a driver board and modify a flashlight to take them, but one mistake and your money is wasted.

 

[VegasF6]

Ok, I checked the voltage going into the luxeon star on my donor light and it is only putting out 2.89 volts (under load of course).

I have to assume that is pretty low, even for an old luxeon, no? So is there any LED optimized for that low a voltage?

Otherwise, I will def have to replace the driver, and I guess go with your suggestion of 2D-6AA adapter. Was trying to do this on the cheap, but hey, I guess there is cheap, and there is good. Not both

 

[lctorana]

How hard is the LED in the TaskForce 2C driven?

 

[VegasF6]

How hard is the LED in the TaskForce 2C driven?

I dunno if you were asking me or not, I really don't know as I don't have it. I just figured if I can get this 2d light to output at least as much as the taskforce, I would be happy.

 

[Mr Happy]

What I think you need, going back to the top of the thread, is something like a cookbook that lists combinations of batteries, drivers and emitters that work together. Then you would go through the list and pick the one that was closest. I don't know if such a cookbook exists, but this thread comes close.

Regarding what you were specifically looking for, this other thread suggests such a driver doesn't exist.

By the way, I think 3AA-to-D adapters are only a couple of bucks from Kaidomain. They are not as substantial as the FiveMega ones, but they work OK for moderate loads.

 

[VegasF6]

I suppose I'm not quite sure what it is you are trying to do. Do you have an existing 2D light that you want to modify?

Because quite seriously, the best way to get what you want would be to look around for an off-the-shelf light that has the brightness, the size and the run time you need and buy that. It will all be robust, designed and ready to go, and will come with a warranty.

If you are looking to save money, it could be a false economy. You could buy a Cree Q5, a driver board and modify a flashlight to take them, but one mistake and your money is wasted.

Yes, I posted about this light in another area but with not quite the same question. I hope that wasn't breaking any forum rules, I just decided I wasn't in the right sub-forum. Here is my original post:
http://www.candlepowerforums.com/vb/showthread.php?t=189808
So, I am into the light for 17$, the Q5 should be around 10$, I figure 18 + shipping for the battery holder (which I can use in the future for my ROP build if it is high enough current that is) (looking at the one from the sandwich shoppe) and 20$ for the SOB1000.

So, if I do it right, it should be relatively cheap actually. Plus of course there is saying "I built this." Of course, I really want to learn from this project as well, but I guess I am more picking other people's brains then figuring it out myself. The most recent thread you posted, the cookbook so to speak looks great. I had actually come across it earlier, but that was when I was looking to use 2 cells. Now I realize that won't work, the information will really come in handy.

I sure appreciate your time and trouble. The longest hold up now will be getting the Q5 star, if I get it from Hong Kong. I have a few other lights I want to order from DX anyhow, notably the wf600 xenon, so I will just tack it on that order. Hopefully you will be seeing my first flashlight mod here soon!

 

[mdocod]

Mr Happy really nailed it on the head, great explanation. I'll try to elaborate some to help out:

Anything over an amp is going to kill an alkaline cell and really make it not worth running. For a 2D alkaline setup, go with a long running low current driver, something that pushes the LED at ~350mA or less (which will be around 0.5A at the cells). This will keep the strain on the cells within reason and give you your money's worth on the cells. For NIMH, a D size cell can handle nearly any current you can imagine within the realm of flashlight modifications. If you are willing to run NIMH D size cells, (the "true" D cells, like the 10,000mAH or better), then 10+ amps isn't a problem. 2D size NIMH cells could comfortably drive as many as 8 emitters at 3W each.

As I understand the TaskForce pulls about 1.2A from the cells, which works reasonably well, but still pushes the alkaline cells far below their label capacity, I run mine on NIMH.

If you can find a driver that pushes the current you want, NIMH D cells are the way to go.

As an alternative, a 6AA series pack, and a buck style driver would also work.

 

[Tidra]

Alkaline cells are 100% NO GO, my Duracell D drops in seconds from 3V below 2V when I try to power SSC P4 @ 700mA,....

LP
Iztok

 

[MorePower]

Alkaline cells are 100% NO GO, my Duracell D drops in seconds from 3V below 2V when I try to power SSC P4 @ 700mA,....

LP
Iztok

What driver are you using? I got over 5 hours to 50% output with an SSC P4 driven at 650mA by a Fatman driver. It sounds like a driver efficiency issue or a wiring problem.

Under a 1 ohm continuous discharge, an alkaline D cell shouldn't drop below 1.0V until around 5 hours. That means that until 5 hours, more than 1 amp is being drawn from the cell (V=IR, R=1 ohm, so V=I). In your setup, for 2 cells to drop below 2.0V "in seconds", you'd have to be drawing well in excess of 2 amps, probably close to 4 or 5 amps if not more.

 

[Tidra]

http://www.kaidomain.com/WEBUI/ProductDetail.aspx?TranID=3151

on the power-supply it works O.K., but on D Alkaline cells NO WAY...

will measure input current today and report...

 

[MorePower]

http://www.kaidomain.com/WEBUI/ProductDetail.aspx?TranID=3151

on the power-supply it works O.K., but on D Alkaline cells NO WAY...

will measure input current today and report...

I've got a few of those drivers, too, from DX rather than Kai, but of the 2 I've tried so far, one doesn't work at all and one only works in strobe. I haven't had a chance to try bypassing the mode chip on that one yet.

I think the variability between samples of that driver may cause some problems. The thread in the "Dealer's Corner" shows good efficiency as measured by some people and rather poor efficiency in other setups.

All I know is that a 2 alkaline D cells can stay above 2.0V for a good long time when discharged at 1+ amps.