I need "D" cell NiMH that can handle 3.5 to 4amp draw?

[bigchelis]

I am planning a 3 D Maglight set-up that I will be using D rechargeable cells that can handle and give good results when pressed to 3.5-4amp draw.

I will be using a 3D Maglight with a P60 drop-in. Here is Norm's review on how to do it.
http://www.candlepowerforums.com/vb/showthread.php?t=193173


The P60 drop-in will serve double duty. For EDC it will be in a Surefire 6P bored for IMR 18650 cell. For camping trips I want the Maglight hosts.


Now about the P60 drop-in:
I spoke to Gene today of Malkoff Devices and he said he is making me a direct drive MC-E P60. Due to the Lower forward voltage when the MC-E on DD was fed 4.2v it net 3.5amp draw. Gene said it should be around 1000 lumens; at least initially. When it settled down (10 min) he said it got down to 2.8amp draw. So, 3 fully charged NiMH D size cells will be around 4.5v and slightly over 3.5amp draw untill it settles down.

Please advise on the cell options that can handle this high amp draw? I heard the Alkaline D are not ideal for high amp applications.

 

[rmteo]

4 Amps should not be a problem for any D size NiMH - that is only 0.4C for a 10,000mAH cell.

 

[bigchelis]

4 Amps should not be a problem for any D size NiMH - that is only 0.4C for a 10,000mAH cell.

Good to know. Thank you.

 

[Mr Happy]

Also a fully charged NiMH cell will fall to about 1.3 V almost as soon as you start using it. So you can expect 3 NiMH cells to be giving you 3.9 V initially, falling to 3.6 V for most of the run time, and 3.3 V near the end.

 

[bigchelis]

Also a fully charged NiMH cell will fall to about 1.3 V almost as soon as you start using it. So you can expect 3 NiMH cells to be giving you 3.9 V initially, falling to 3.6 V for most of the run time, and 3.3 V near the end.

So,
At 3.9V the MC-E would still make 700 plus lumens but not get as hot as measured by Gene at 4.2v.

I wonder if I can run 4D NiMH Cells. It would be under 5v fully charged and when it dropped off I assume it would drop to 4.5-4.2 rather quick.

Is the 4D set-up adviseable on Direct drive MC-E?

 

[Mr Happy]

Check your arithmetic:

4 x 1.3 = 5.2 V
4 x 1.2 = 4.8 V
4 x 1.1 = 4.4 V

 

[tommylight]

Direct drive with 4 Ni-MH is a no go and goes from blueish white to brown and to black very quickly . I have 12000 mAh cells that are capable of releasing huge amounts of energy, so the current draw is not a problem in your setup .

 

[Mr Happy]

Further to the :sick2: :mecry:story, it is like this.

Incandescent bulbs have self-regulation of current, so you can direct drive them from a supply of some suitable voltage and if the voltage is not too much they will operate happily.

LED emitters do not have self-regulation of current, so to drive one of those you must have some form of external current regulation. If you do not, then :sick2: :mecry: is the likely result.

In some cases you can use the internal resistance of the battery to provide the required current regulation, and this is called direct drive. But you must have a suitable match between the battery and the LED emitter to make this work. You can't just use any battery.

NiMH rechargeable batteries tend to have a very low internal resistance, and this also can vary with the age and condition of the battery, so the internal resistance is not very predictable. The internal resistance is also much lower with large batteries like D cells than with small batteries like AA cells. The end result is that if you provide even slightly too much voltage to an LED with a battery having low internal resistance you are going to experience :sick2: :mecry: and then you are going to feel .

Your best option is to use a regulated emitter like a normal Malkoff and then you can safely use different batteries and have no worries.

 

[bigchelis]

Further to the :sick2: :mecry:story, it is like this.

Incandescent bulbs have self-regulation of current, so you can direct drive them from a supply of some suitable voltage and if the voltage is not too much they will operate happily.

LED emitters do not have self-regulation of current, so to drive one of those you must have some form of external current regulation. If you do not, then :sick2: :mecry: is the likely result.

In some cases you can use the internal resistance of the battery to provide the required current regulation, and this is called direct drive. But you must have a suitable match between the battery and the LED emitter to make this work. You can't just use any battery.

NiMH rechargeable batteries tend to have a very low internal resistance, and this also can vary with the age and condition of the battery, so the internal resistance is not very predictable. The internal resistance is also much lower with large batteries like D cells than with small batteries like AA cells. The end result is that if you provide even slightly too much voltage to an LED with a battery having low internal resistance you are going to experience :sick2: :mecry: and then you are going to feel .

Your best option is to use a regulated emitter like a normal Malkoff and then you can safely use different batteries and have no worries.

Thank you for the very descriptive pros and cons.
I used the Malkoff P7 P60 in DD with a AW IMR 18650, but now he is building me the same thing but with an MC-E direct drive. The MC-E direct drive makes 3.5amp draw at 4.2v as opposed to the P7 2.8amp draw.

Gene just got back to me and said the Maglight hosts is not good for a P60 due to no tie between to the body for heat sinking. Per his advise I will go with the 3 "C" cell FM body for a hosts.

Thank you,
bigchelis