Quad-P7 .... Ampere?

I just finished my quad P7 light last night. I have the DSVOJ (Vf=3.5-3.75) coupled with (2) D-size li-ion from Kaidomain. The LEDs are wired in a series/parallel configuration. All direct drive with batteries in series.

My question is, does anyone know what my light is suppose to read at the tailcap? I got a reading of ~4.5A (Tailcap) and ~4.7A when the LEDs are wired directly to the batteries. That means each LEDs are getting a supposed 2.25A instead of closer to 2.8A. Does this sound right to anyone? BTW, the measured voltage across the two battery is 8.10v.




Edit: typo...it's 8.10v, not 4.10v

You will get much more current flow if you remove your amperemeter because of the shunt.

So your measurement is incorrect.

A amperemeter has ususally 0.1-0.2ohm of resistance.

At 4.5A it causes a voltage drop of 0.45 to 0.9V. So if you remove the amperemeter the LEDs will get 0.45 to 0.9V more voltage.

That means each LED 0.225V to 0.45V more. So you can add about 0.5A to 0.8A more each LED ( maybe more). Furthermore the LED will heat up and the current will increase as well.
If you have a good heatsink then that should not be a problem.

However there is resistance in the protectioncircuit and in the light which can damp down the currentrising a little bit

Thank you for your post. Is there any way real way to measure the current? Or do I just have to trust the nature of physics? From just looking at the beamshot to the wall, the output looks about the same regardless if I have the DMM on or not. Would regulated lights be affected in the same way? My single P7 mag reads ~2.8A at the tailcap using the same method. Thanks again!

You measure the voltage at the LED.

Then connect the led to a powersupply and measure the current. Set the voltage at the LED with the value you have measured before.

Regulated lights are not effected they will go up with the voltage automatically when there is a voltage drop caused by resistance. Thats why they are regulated :thumbsup:

Be careful with the quad P7 mod.

ElektroLumens Wall-of-Fire is a 205 F flashlight
https://www.candlepowerforums.com/threads/207960
Be careful you do not cook the Lithium batteries to the point where they go .

Heh. Thanks for the link.

Fortunately, I plan to NEVER turn on this light for more than 1 minute. I think the longest I have ever left this on was 15 seconds. It's purely for show anyhow. My single P7 throws farther than this light.

I guess you could say it's like having 16 P4 Seoul LEDs since each p7 has 4 dice on each p7. And they are tightly pack to.

LEDninja said:

Be careful you do not cook the Lithium batteries to the point where they go .

Click to expand...

I'm thinking of finding an alternative way to power the 4 P7s instead of using Li-ion. I'm just worried someone might grab my light for fun and decide to go on a lighting rampage with it. I just can't figure out what battery setup (preferrably NiMH) that will get me the right voltage without having to bore out the body.

A 6x AA NiMH pack will give you 7.2V, but I don't know how well they will handle a 4.5A+ current draw.

How about getting a 12x 2/3A 1500mAh Elite custom pack from LuxLuthor ?
It should just fit in a 2D Mag. (EDIT: Needs a tri-bore)
With the P7's rewired in series, current draw is back to a more manageable 2.8A and the Elite's are a high current cell.

KD has some cheap lifepo4 cells
http://www.kaidomain.com/ProductDetails.aspx?ProductId=5141

they won't explode and can handle more current

I do not think the LifePo4 can provide enough voltage for DD.

Elektrolumens measured 127°F after 10-15 minutes. So I think it is usable if the runtimes are reasonable.
If you or anyone is actually holding the torch, it will be too hot to hold long before 205°F. In the case I linked to the torch was left lying around unattended.

Just found this discharge chart for the Elite 1700 AA's.
Looks like they can easily handle the current.

the current will not be much more than the ROP high which can be run many types of NIMH cells 6X series. Get to it!

What kind of switch is used? If it's the stock switch the resistance is pretty bad and will get worse at higher currents as it heats up. Assuming a mag is used.

tebore said:

What kind of switch is used? If it's the stock switch the resistance is pretty bad and will get worse at higher currents as it heats up. Assuming a mag is used.

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Yes. the stock switch was used. When I measured the current with and without the switch, the difference in reading was ~0.1A total. I may be switching it out for something better, but the output is insane enough for me to delay the mod

GSteg said:

Yes. the stock switch was used. When I measured the current with and without the switch, the difference in reading was ~0.1A total. I may be switching it out for something better, but the output is insane enough for me to delay the mod

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In your system of about 17watts of power ~0.1A is a lot of loss. That's 100mah or more. As the contacts hear up that loss is only going to increase.

You might want to work on fixing up the switch to minimize loss. That's one of the problems i had to overcome when dealing with ~100 hotwires.

Hi, what kind of head or housing are you using???

tebore said:

In your system of about 17watts of power ~0.1A is a lot of loss. That's 100mah or more. As the contacts hear up that loss is only going to increase.

You might want to work on fixing up the switch to minimize loss. That's one of the problems i had to overcome when dealing with ~100 hotwires.

Click to expand...

How did you get 17w? I was hoping i'd get more than that. Theoretically, each LED should be getting ~10w. Maybe I'm missing something

Changchung said:

Hi, what kind of head or housing are you using???

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I'm using the stock head. Each reflectors are 20mm in diameter. I took out the stock thin metal strips inside the switch and replaced it with thicker metal. Only the metal ring inside the switch is stock. I'm enjoying my light as of now. Took it to the beach last night and I was able to light up a good amount of land

GSteg said:

How did you get 17w? I was hoping i'd get more than that. Theoretically, each LED should be getting ~10w. Maybe I'm missing something

Click to expand...

Oops I missed a whole string of LED. I only calc'd for 2 in series but still that's quite a bit of loss.

~36-37watts. 8.1 x 0.1 = 0.81 watt. 0.81/36 that's 2% loss in nothing but the body. As everything heats up it'll be more.