UltraFire 501B P7 - Problems.


I wasnt sure where to post this but im having a really anoying problem with my flashlight.

it was marketed as "UltraFire WF-501B SSC-P7-CSXO" what ever all that means.

Anyway here is a video I made of the problem and was wondering if anyone could help me out.

I have tried multiple batteries and tightened up everything I could and it just cuts out all the time.


The led is over heating I think. Is these any thermal paste under the led star and the pill?

Are the batteries charged to 4.20v?

The batteries are fully charged at roughly 4.19-4.20.

I didnt even know that LED's required TIM like CPU's. How would I go about checking if it has any?

Possibly low resistance tripping the protection circuit if your cells are protected? What type/brand of cells are you using? You say you've tried multiple cells... Different brand/type? Protected/Unprotected? Did the flashlight previously work and then stop working or is it new doing this?

Remove the head and remove the drop-in. Unthread the brass pill from the reflector (carefully! Don't accidentally stick your finger into the reflector like I did) then look at the LED on the pill. It should have some sort of an insulator like a paper or plastic disc around the emitter to keep the wires connected to the base from shorting on the reflector. Remove that disc, and check to see if the emitter has thermal compound underneath. It should be pretty obvious. Usually, it's a white caulk-like compound to hold the star in place while providing the thermal path to the pill.

<edit> Make sure you replace the insulating disc when you re-assemble. If you don't, it could short through the reflector frying your driver. Again, first-hand knowledge speaking here... Foot in Mouth

This is actually the second flashlight I have been sent as a replacement. The first was cutting out all the time.

This one has done it since I got it and now dealextreme is saying they need me to send it back but the postage just isn't worth it so was hoping I could just somehow fix it.

The time it takes for it to cut out changes a lot. When i first got it, it would work fine until I turned it off then it wouldn't turn on for a while. It got progressively worse and now it wont stay on for any decent amount of time.

Ok done. I does have TIM underneath the LED. just like the stuff Intel ships on there stock coolers, a thermal pad.

Does the P7 have a built-in overheat protection? If not, the light shouldn't cut out like that.

Was it like that from the beginning? Maybe you exceeded the manufacture rated runtime of 90 min? (Sorry, couldn't resist. DX specs are so funny :bigsmile: )

Does the light come back on if you just leave it for a while after it cut out? Then it may be some component/connection loosing contact when the heat is bulding up inside the pill. In that case you will have to disassemble the pill to inspect/check the connections. Or did you already do that?

edit: Partially obsolete post. I really need to train typing.

Getting a little overwhelmed with replies + technical names i have never heard before. Let me try and answer some stuff.

This torch has had this sort of problem since I got it.

The first reply about TIM, not sure if i did everything you asked, once I get the reflector off i can see some thermal pad under the LED thing.

Even when turned on from cold it cuts out after X amount of time.

Once the flashlight cuts out I can just turn it off then back on and it works again for X amount of time.

I put my bet on: It is overdriven (direct drive) hard and the PCB overcurrent triggers. The current climbs for 6sec before reaching it's treshold.

Have you tried with a batery around 3,8V? That would rule out the battery PCB entirely as you will not see currents above 2A for sure.

If you have a multimeter set it to 10A or 20A mode and connect the probes accordingly and see if the current climb's to 4A or similar befor cutting off.

I would exclude overheating (althrough it is tempting since the tint is very blueish and just look like the led was abused heavily) and suspect perhaps the driver that shuts down itself after being fed agressively at 4,2V. Never experienced it in budget segment as budget drivers are pretty simple circuits anyway.

So a 3,8V battery and/or a DMM woudl probably end the mistery behind.

And it doesn't come back on again if you just wait?

Does the light behave the same when you override the tailcap and use a piece of wire/paperclip instead?

Can you do a tailcap reading with a DMM and check if the current drops to zero when the light cuts out? If not you have a short which can be dangerous with Li-Ions.

Took a battery out of another flashlight that was at 4.02v and it has been on for roughly 3 minutes now, the head is getting hot which is what I would expect and its not cutting out.

That's the ticket. A DMM will confirm it is cut by the battery protection PCB. Get yourself 2 decent drivers and it will work like a charm. Get the KD 2,8A as thsoe are generally most cherished in the budget segment by many myself included.

Ok I don't really know what you just said to me, you seem to be way above my level of flashlight knowledge.

Do you have a multimeter available so you can check the current draw? You will need a meter with a 10Amp mode (or higher) to test that; remove the tailcap, and connect one multimeter lead to the base of the exposed cell and the other multimeter lead to the exposed aluminum threads that the tailcap would normally engage with. You shouldn't see a current of more than ~3A...

Looks like Budgeteer got it right while I was still in the process of localizing the problem... :tired:

Tried this, does 1.4a sound right? I had to play about with my DMM until I got a number that looked correct.

Hmm, is this with the partly discharged cell or with the fully charged?

Fully charged. I went through all the modes and the bright one pulls roughly 1.4a.

Then it is not the PCB tripping. Strange.

EDIT: which brings me back to the second question in post #10. Did you try that?