Run time of 3D P7 Maglite on alkaline?

I searched around a lot and could only find run times of P7 mag's on lithium batteries. Does anyone know roughly what the run time is on a 3D direct drive P7 maglite with alkaline batteries? Thanks!

https://www.candlepowerforums.com/threads/64660

15 minutes near full power maybe 1.5 hour by getting dimmer and dimmer continue hours on moon mod.

Thank you! Do you know how many amps a P7 draws? I have a C bin and a D bin, not sure if that matters...

orangeturtle said:

Thank you! Do you know how many amps a P7 draws? I have a C bin and a D bin, not sure if that matters...

Click to expand...

Depends what you're powering it with. Off a good regulated 4.5V power supply, I guess it'd draw >20A for a few milliseconds, then -- off a 3V or so supply, maybe a couple 100 mA. The rated maximum is 2.8A, which will happen around 3.5V. You can find typical I-V curves in the datasheet.

The C/D bin is a luminous flux bin, and tells how bright the LED is at a specific current; nothing to do with input power -- the Vf bin is what tells you what voltage, at a given current, and therefore what current from a decently steady voltage source (at least unless/until the LED heats up and goes into thermal runaway...). But on alkalines, none of that matters, because they can't really deliver 3A at any voltage for very long. Initial current could be as high as 3A, though I'd be surprised if it was over, but it'll quickly sag to a current level at which the batteries can maintain their voltage, and gradually roll off as the batteries die.

If you must have a DD KOH P7, I'd strongly recommend 4D instead of 3D -- you'll get a little more overdrive at the beginning, but if you just put fresh batteries in, the light's probably cool enough, and a Mag has enough mass, that you'll be fine for the first ~10 minutes. After that, it'll be underdriven anyway, but with 4 cells instead of 3, there'll be usable light for much longer -- brighter than a comparable single-die for at least 4 hours, IIRC.

And then, when you get bored with that light (and long for flat regulation), you can drop in an 8xAMC7135 LDO driver, and simultaneously stop the overdrive on startup and gain the ability to run regulated for ~3 hours on D NiMH.

OTOH, some are quite happy with their P7s DD on 3xNiMH D, so if the size is important, a 3D will work out too when you move up to rechargeables. It's just gonna do really really bad on KOH meanwhile.

For any high-powered LED, I would use a regulated driver setup. Direct drive would just be pathetic with any alkaline battery, so NiMH is a must if you direct drive.

I believe Benson & TheInvader are correct (imHo - I'm no expert on this). I've played around with a few alkaline C builds (2xC, 3xC, 4xC & also 4xD - the two threads in my sig). Alkalines just can't deliver the currents that would run the P7 to any satisfaction - NiMH are far better for currents over 1 amp. Trying to run an alkaline over 1 amp greatly decreases the possible watt-hours that the alkaline cell can deliver overall, and the P7 would like ~2.8 amps at 3x1.2 volts IIRC. The P7 direct-drive w/ 3xNiMH would be a very decent solution, far better than any alkaline configuration.

I am very new to this, but I find it very interesting. Thanks for the input- I'll have to start reading around more. I like the idea of getting batteries at the local grocery store for a very bright light, but i don't like the idea of not using the led to it's full potential. I'll have to look into some drivers and NiMh's, now that I have a taste of what good is, excellent sounds delicious

Another way to look at it:
(My recollection from running the calculations a while ago)

Trying to get 3 amps (IIRC) from 3 cells in series like you're talking about, 3x AA (NiMH) can deliver more total energy (in Watt-hours) than (the much larger) 3x D (Alkaline) cells can. That comparison never ceases to amaze me, alkalines are so incredibly inefficient at the high drain rates we want here.

Anyway, if I recall correctly - I might be off by a little, I haven't done the calculations in a while.

Hi,

You guys seem to be pretty well versed in this flashoholic world that I have fallen off into so maybe you can answer a simple question for me or point me in the right direction. I think I'm suffering from IO(information overload.) I have an old 2C with a 4-cell Mag LED bulb that is powered by 6 AAA alkalines. They are all around 1.2-1.3 volts and it seems to be as bright as my new A1 EOS which is rated at 190lm. My question is, can I put 6 fully charged NiMH AAAs' in it or do you think it will blow my bulb? Or is this a dangerous situation? Thanks in advance!

What would the runtime be if the 3D with Alkaline's where regulated with a 7135? Would it be drastically increased?

Unless the driver is set for very low output, the runtime will likely decrease, maybe even drastically.

gswitter said:

Unless the driver is set for very low output, the runtime will likely decrease, maybe even drastically.

Click to expand...

I have a 7135 driver running on 3 D cells in a Maglite powerwing a P7 @ 2.8 amps.

Driver, or not to driver?

Unless the driver behaves gracefully (reduces the output current or goes into direct drive) when the battery voltage sags, I wouldn't bother with a 2.8A driver and alkalines.

gswitter said:

Unless the driver behaves gracefully (reduces the output current or goes into direct drive) when the battery voltage sags, I wouldn't bother with a 2.8A driver and alkalines.

Click to expand...

Thanks, your a lot of help. By the way, I personally preffer Li-ion or nimh, but it was for my dad.
For my next build, I want to do the same, but with a 6D mag. If I'm using a P7, then I would have to use a driver. What driver can take in 10v and output 2.8 amps?

hipFlex from TaskLED, maybe. But, again, 2.8A @ 3.5V may not be realistic for even 6x alkaline D's.

If you have to use alkalines, I'd either go with a lower output driver/setting, stick to 3x D cells direct drive, or ditch the P7 for an XP-G or the like with lower forward voltage and current demands.

It all depends on what you want to do. Personally I have built a lot of Alkaline powered 3Ds for friends. It's still very bright, and they seem to last long enough, still MILES better than a standard 3D Mag. I do put in some AMC7135 drivers, as more of a safety measure for fresh batteries not blowing the LED, but they are also there if they want to go D Ni-MH down the road.

I know they wouldn't be to flashaholic standards, but for most of these people, they are more than happy with what I gave them, as it was a big improvement over what they had.

If nothing else, running the D Alkalines, you can buy the batteries basically anywhere, and they last a long time, just not at full brightness, but it's still bright enough.

Sure it's nice to run Ni-MH Ds which I have in one build, but most people wouldn't want to pay the $50 for the batteries, and then another $90 for a charger that would charge them at a decent speed.

There's no need and no wisdom in trying to run a P7 off of alkalines. I'm completely on board with the importance of avoiding rechargeable batteries for non-flashaholics. Most folks aren't willing to make a sizable investment in batteries and a charger. The solution is to use a lower power emitter such as P4, XR-E, XP-E or XP-G. These put out light that is impressive to anyone other than the jaded lumen freaks who hang out here. :naughty: The guy who now owns this one never before saw such a bright flashlight and will be quite happy putting in a new coppertop every so often:

https://www.candlepowerforums.com/threads/265528