C***I P7 fueled by 3 x D Alkalines?

[M@elstrom]

Hello fellow lumen addicts!

I'd like to build a direct drive C bin P7 (correction I NEED to build it), I'm aware that I'll require a lower Vf unit (thus the I prefix) but what I'd really like to know is whilst I'm waiting to receive my NiMh D cells (and associated charger)...

* Could I get away with running it off D cell Alkalines (large stash purchased @ below cost)?
* Would their V output drop sufficiently as to not damage the emitter?

OR

* Should I just bite the bullet & build a light incorporating a regulated driver to enable a better variety of battery options? :thinking:



I was leaning towards direct drive because I was implementing the 'KISS' methodology...



Oops... sorry Mods I think I may have placed this in the wrong forum

 

[Greg G]

The alks will sag low enough under a load to prevent damage to the emitter.

 

[LEDninja]

Lots of people who bought Elektrolumens' 3 cell direct drive SSC-P7 M@gmods have run them using alkalines while waiting for NiMH to arrive.

 

[M@elstrom]

This is great news, I purchased those D's in bulk back when I didn't know much about custom flashlights, I thought a Terralux TLE-6EXB was the bee's knees ROTFLMAO


Thanks guys

 

[Greg G]

You can even DD a single die P4 on 3 alk D's. The voltage on the alks sag that much under a load.

 

[TexLite]

Hi sactime,yes,thats mostly correct.Unless you have an emitter with low Vf and minimize resistance in the host,then the "regulated" runtime will be very short.

I wouldn't waste my time or money on alkalines in this setup.At 3A you'll get about 10 minutes before the voltage falls below 1v.

An Eneloop has more capacity at that current.

Check out the graphs below for from Silverfox's battery shootout threads.

The cells won't hold that 4.2V under load.At 3A they'll drop to ~1.25V by 1/4th the useful runtime.Thats 3.75V at the batteries,you'll lose at least ~.3V-.4V due to dropout voltage on the driver and various resistance in the host such as spring and switch.

You end up with about 3.45V at the output.Enough perhaps to keep output up with a low Vf emitter,but nothing higher.If resistance isn't minimized or you use an emitter with a higher Vf then the problem is compounded.

My own experience as well as many others who have posted is that many times(not always) a fourth NiMH cell is needed to maintain rated output for the duration of the runtime.This is highly dependant on the Vf of the emitter as well as the factors listed above.

The upside is that after the driver falls out of full output it will go into direct drive,which with a good cell/cells will still maintain a steady output.Guess the driver used below by long time modder Lambda...

There is no driver,its direct drive.The steady output is because of the flat discharge characteristics of the NiMH.

-Michael

From Here:P7 with alkalines

Alakalines will fall flat on their face within a few minutes.

-Michael

 

[LEDninja]

Alakalines will fall flat on their face within a few minutes.

Alakalines will fall but not flat on their face within a few minutes. Remember the P7 does not do a constant 3A draw like silverfox's test equipment. As soon as the voltage drops so does the current. It won't be as bright but runtime will increase. Remember a P7 at 1A is still brighter than a P4 or XRE at 1A. So a P7 will start out at 3A at 3.6V dropping to 1A at 3.2A at which point a switch to a power P4/XRE/rebel torch is in order. My guess is ~1 hour of better than a single die LED performance (based loosely on Silverfox getting 180 minutes at 1A).

I managed to avoid the problem of running alkalines when my Accupower Cs won't fit my RayOvac LS3 charger. Button too short. While waiting for magnets I ran my Elektrolumens 3C P7 on 3AA NiMH in AA to C adapters. Only 2.5A now but still brighter than my MTE P7 at 2.1A (the bigger reflector helps). Then I remembered I have 2 RayOvac 2900 mAH NiMH in my 2C M@gLED. I went down to WalMart and got 4 more. Now I have 3 in my 3C P7 and 3 on the shelf giving me ~2 hours before I have to get the Accupowers.