P7 with alkaline batteries?

[sactime]

What will happen if I use 3 - D Cell Alkaline batteries with a 3D P7 mag? With the hi-current discharge, what might happen to the batteries? Explode, leak....?

Thanks

 

[LukeA]

They will leak if they get too low, but by that point the output probably won't be worth keeping the cells in the light.

 

[sactime]

Will they work just as well at powering the P7 as NiMH's? Obviously they wont have the battery life of a NiMH, but will they do the job to test the P7?

 

[ANDREAS FERRARI]

Past the point of optimal voltage range, you are simply shorting the P7's life span.

 

[sactime]

http://www.candlepowerforums.com/vb/showthread.php?t=195358

Even if I follow that guide, but use alkaline batteries? 3.6V~4.5V input voltage, technically it should work right?

 

[StefanFS]

http://www.candlepowerforums.com/vb/showthread.php?t=195358

Even if I follow that guide, but use alkaline batteries? 3.6V~4.5V input voltage, technically it should work right?

I recommend using 3 or four NiMH cells or one big LION cell in that guide. Alkaline will work for a short time at a reduced output level before it sags. It might work better if you underdrive the P7 at maybe around 2A or even less. Alkaline just cannot drive an SSC P7 at ~3A, that's my experience. I'll do a simple test when I get home in a 3D P7 Mag @ 3A I have, output with three D-cell alkaline and output from three D-NiMH. Lux, throw and spill.

 

[sactime]

with 3 - NiMH's it would be 3.6v, and the minimum input voltage is 3.6, so I would think it would fall out of regulation fast (once it goes below 3.6v).

Also, what driver are you using to drive the p7 at 3.0A?

Thanks

 

[StefanFS]

with 3 - NiMH's it would be 3.6v, and the minimum input voltage is 3.6, so I would think it would fall out of regulation fast (once it goes below 3.6v).

Also, what driver are you using to drive the p7 at 3.0A?

Thanks

I have been trying to convey my thoughts of that particular design in that thread for a long time now. When three fully charged D NiMH are used the voltage is ~4.2V. The P7 emitters I use with that build are C/D***I bin with a forward voltage of 3.25-3.50V. The driver sandwich based on AMC 7135 chips output 3.6-3.7V, made from one multimode 1A AMC7135 driver and two 1A AMC7135 drivers.. That's perfect with three D-NiMH, four C-NiMH or one D-LiION. Depending on cell/s used runtimes are long and regulated. With NiMH much depend on cell quality.

 

[TexLite]

with 3 - NiMH's it would be 3.6v, and the minimum input voltage is 3.6, so I would think it would fall out of regulation fast (once it goes below 3.6v).

Thanks

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.

I have been trying to convey my thoughts of that particular design in that thread for a long time now. When three fully charged D NiMH are used the voltage is ~4.2V. The P7 emitters I use with that build are C/D***I bin with a forward voltage of 3.25-3.50V. The driver sandwich based on AMC 7135 chips output 3.6-3.7V, made from one multimode 1A AMC7135 driver and two 1400 mA AMC7135 drivers.. That's perfect with three D-NiMH, four C-NiMH or one D-LiION. Depending on cell/s used runtimes are long and regulated. With NiMH much depend on cell quality.

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

 

[StefanFS]

A simple output test with my 3 D SSC P7 Mag with 3A AMC7135 based driver.

With three high quality NiMH D cells:
Throw @ 1m: 24 700 lux.
Spill @ 1m: 255 lux.


With three high quality alkaline D:
Throw @ 1m: 17 100 lux.
Spill @ 1m: 170 lux.

Alkaline cells will dip in output very quickly after a while.

 

[LukeA]

Past the point of optimal voltage range, you are simply shorting the P7's life span.

Nah, the alkies will sag under the load low enough that the LED won't see as much current as it would on NiMH.