Finding an appropriate driver

[davidt]

I have decided to build a p7 maglite and I am debating with myself to building either a 2D format or a 4C format. The 4C is easy for me to build. I would perfer a 2D because of the size and I already have a spare 2D laying around. But I am having difficult finding a driver for a 2D format.

I am planning to use 2 D sized nimh soldered to make a battery pack. But I can't find an appropriate driver that would drive a P7 with regulation from a 2D sized pack. The only one I have found that might work is this driver:

http://www.dealextreme.com/details.dx/sku.4735

Could I wire a couple of these drivers together to get higher current output? Someone made a comment on the review page that the mentioned driver won't work with higher powered LEDs.

Is there a better solution to my driver problem?

Thanks in advance.

 

[datiLED]

If you are set on the 2-D Mag, how about using four 1/2 D Cell 1.2 V NiMH rechargeable batteries, and a regulator to limit the current to 2.8A? (See the P7 Mag build tutorial for information on making a multi-level, or high power board.) You would probably have to shorten the spring, but it should fit.

I am toying with the same idea, because IMO, a 3-D, or 4-D Mag is just too big for most applications. They do make great clubs, though. Speaking of clubs, I saw some 6-C and 5-C Mags at the Ace hardware store recently. They are huge! I can't imagine trying to use a 6-D light.

 

[shakeylegs]

davidt,
the driver you reference probably doesn't put out enough amps. One user reports 500ma with 2 nimhs. With two of these boards wired in parallel and two nimhs he measured 1.2 amps. Still pitifully inadequate to take advantage of the P7. Electrolumens is using 3 C nimhs in a 2D m@g host for direct drive of a P7, but I think he milled out the tailcap. See if you can fit 3C nimhs into your host by modifying or eliminating the tailcap spring. That will give you 3.6 volts and should light up a P7. If you want a driver, follow Stefan's thread to build your own multimode driver - http://www.candlepowerforums.com/vb/showthread.php?t=195358. Or, you can get this direct drive board that uses PWM for multiple modes - http://www.kaidomain.com/WEBUI/ProductDetail.aspx?TranID=5025

 

[davidt]

Thank for the replies guys. I should also mention I don't want multimodes. I just want simple single mode with regulation. I thought about using 3 nimh but I had some concerns about just 3 batteries.

Most drivers on dealextreme and kaidomain need at least 3.6 volts to work properly but a nimh battery can fully discharge below 1.2 volts. My question is if the all three batteries discharge to 1.2 volts with all three batteries having a combined voltage or just 3.6, would that mean the driver quits working? If the batteries aren't fully discharged below 1.2 volt each won't that mean the full capacity of the batteries are not being utilized? I wanted to go with 4 batteries so that each battery may be completly discharged to about 1 volt each and the driver would still be working in regulation. If 3 batteries are being used and each are discharged below 1.2 volt than the driver would quit working?

I would like to not use undersized batteries such as 3C in a 2D mag because I see wasted space as wasting possible battery capacity. If my understanding of drivers and nimh batteries is incorrect than I would go with a 3C maglite and 3 C nihm instead of a 4c

 

[davidt]

Oops double post!

 

[monkeyboy]

Thank for the replies guys. I should also mention I don't want multimodes. I just want simple single mode with regulation. I thought about using 3 nimh but I had some concerns about just 3 batteries.

Most drivers on dealextreme and kaidomain need at least 3.6 volts to work properly but a nimh battery can fully discharge below 1.2 volts. My question is if the all three batteries discharge to 1.2 volts with all three batteries having a combined voltage or just 3.6, would that mean the driver quits working? If the batteries aren't fully discharged below 1.2 volt each won't that mean the full capacity of the batteries are not being utilized?

When Vin<Vf, the driver just goes into direct drive. You probably won't even notice until the batteries start to run out. This makes it very efficient and will utilise the full capacity of the batteries. 3 cells (or 1 li-ion) is the most efficient way to use the 7135 driver. 4 cells can also be used with the 7135 but this is less efficient.

 

[davidt]

When Vin<Vf, the driver just goes into direct drive. You probably won't even notice until the batteries start to run out. This makes it very efficient and will utilise the full capacity of the batteries. 3 cells (or 1 li-ion) is the most efficient way to use the 7135 driver. 4 cells can also be used with the 7135 but this is less efficient.

Thanks for clearing up my question. I have also been wondering about another issue. If the driver goes into direct drive when all 3 nimh have a combined voltage less than 3.6 volts what happens to the led, does it just slowly start to dim? Because the Vf of a p7 is 3.6 volts(I think), the led would still run if the battery voltage is below the led Vf?

For me the size of a 3C maglite is much more appealing than a 2D maglite.

 

[StefanFS]

Since you have one perfectly good 2D Mag I suggest you get one D-size LiION cell and one spacer (can be made from a piece of wood and some 2 mm copper wire, or can be bought from flashlightking.com) and one simple AMC7135 2.8A driver from KaiDomain. I also had a 2D Mag that I used with both one D LiION and three NiMH. The C NiMH does fit in the tailcap and a cutdown spring is necessary, you also need to deanodize the inside of the tailcap. Some lye (sodium hydroxide/caustic soda) will do that for you, put a few specks of drain cleaner and water in your tailcap wait a while, then rinse and sand the surface. Three C NiMH will give you good runtime and the led will dim considerably when vin goes below vf Make sure you get C***I bin SSC P7, the I means a vf of max 3.5V.

 

[LukeA]

Thanks for clearing up my question. I have also been wondering about another issue. If the driver goes into direct drive when all 3 nimh have a combined voltage less than 3.6 volts what happens to the led, does it just slowly start to dim? Because the Vf of a p7 is 3.6 volts(I think), the led would still run if the battery voltage is below the led Vf?

For me the size of a 3C maglite is much more appealing than a 2D maglite.

The LED Vf isn't always the same. As the voltage of the source drops, the current that the LED draws from the battery also drops.

 

[monkeyboy]

Thanks for clearing up my question. I have also been wondering about another issue. If the driver goes into direct drive when all 3 nimh have a combined voltage less than 3.6 volts what happens to the led, does it just slowly start to dim? Because the Vf of a p7 is 3.6 volts(I think), the led would still run if the battery voltage is below the led Vf?

For me the size of a 3C maglite is much more appealing than a 2D maglite.

3.6V is just the typical Vf, there is some variation. The quoted Vf of the LED is just the forward voltage of the LED at whatever current they choose to bin the LED's at. I believe the P7 is binned at 2800mA.

These are the common p7 voltage bins:

K 3.75 ~ 4.00V

J 3.50 ~ 3.75V

I 3.25 ~ 3.50V

Since the 8x7135 driver drives at 2800mA, It regulates the voltage so that Vin = Vf. The moment it falls out of regulation, the battery is supplying exactly Vf to the LED, it then follows the standard NiMh discharge curve (direct drive). This means that there is no discontinuity, i.e. no sudden jump in brightness. The NiMh discharge curve drops off fairly rapidly, so it won't dim too slowly.

The 3C mag with AMC 8x7135 is the best choice IMO.