Seoul P7 Failure? Light is HOT!

[user1016]

Tonight, I switched on my Maglite 3D with Seoul P7 Mod.

This mod has been faithful to me since 2009 with no major issues, although prior to this one, I had a P7 failure because I was very new to lights then and placed my batteries directly in the maglite fresh from the charger for immediate use, leaving no time for the voltage to stabilize. I remember that when it eventually blew the LED, the LED turned a bluish hue and the maglite switch area grew very very hot, literally too hot to hold.

So tonight, I was laying in bed relaxing for a bit, I put a blue filter over the maglite 3d to provide some cheap blue ambient lighting for the room. About 2 hours later, I reached over to switch it off and noticed that the entire maglite was red hot. I immediately whipped the batteries out, and the maglite was put off to the side to cool off. It wasn't producing the same blue hue as my last failed LED mod, and I always let my nimh rechargables stabilize for about 30 mins to 2 hours after coming out of the charger. This one had been sitting all day before it was used so the voltage should've dropped.

[EDIT Just checked voltage of the batteries, they're scoring 1.27v each, if I'm not mistaken, they should be around 1.2 or lower, strange. They're Jaycar nimH 9000mah rechargable D cells if that is of any use to anyone who can help me figure out what's going on)

My question is, what's the next step? I don't want to put them back in and have it blow up, what should I do to test whether or not the mod is faulty (or perhaps the batteries?).

Also, while I'm at it, what's the best plan to have for a battery explosion? I keep an Australian standard B:E Powder based fire extinguisher (Flammable, combustible and Electric fire) handy at all times in case of fire.

 

[user1016]

Just bumping as this was accidentally in the wrong category initially and has been relocated to homemade kits. If anyone has some further advice for me on what to do to avoid any explosions etc, it would be greatly appreciated.

 

[Chodes]

Very difficult to remote diagnose.
I have had direct drive P7 using 3 x Powerizer brand 10Ah D cells.
Very similar light, however with these lights, very small differences in resistances and LED Vf results in big differences to current (and therefore heat)

I also have had several shorter Mag Ds with P7s.
Any P7 Mag running at near spec, ie 2.8Amps will get very hot. I'd estimate after 15 mins or so it would be close to max.

I'd say obvious steps:
1st - ignore open cct NiMh volt reading. Almost totally irrelevant.
2nd - take a tailcap reading of current. That will be extremely relevant.

I notice Vinh mentioned possible short. Tailcap current reading should reveal that.
P7 LED base is +ve. Possibility if using non anodized heatsink that loss of insulation has occurred there too.

I would test now, with the cells having been run for 2 hours. They should be at least 50% depleted.
If, for example. you measured 4Amps, I'd be surprised P7 is surviving that. Good chance an Amp or so is being consumed by a partial short / HR joint.
Short at P7 legs, HR at Mag switch most likely.
There is a chance your P7 LED Vf has lowered with time / use. Maybe you are lucky and it is surviving 4Amps...

Tailcap measurement required!

 

[Chodes]

Still speculating...
Here are some resistor tailcap mod/springs I did for direct drive P7s.
They reduce current to LED to around 2 AMPs or so (probably 2.5 with 3 big D cells) on fresh cells.
If your problem is simply reduce Vf of LED, these would provide a simple solution.
The resistor/spring bits just pop out like a Mag spring, can be removed at anytime.

 

[Chodes]

HR example. Working light got dimmer but still consumed batteries at around normal rate.
The power was being consumed by this high resistance joint in a battery holder.
HR joint between the 2 arrowed parts. Pulled battery holder apart it was open cct.

Before repair - I soldered a piece of braid at the joint between brass tab and the post

Install cells and joint went reliably HR. So when I measured the pack, around 14.65V for 4 x 18650s open circuit seemed fine (into the tiny load presented by multimeter)
The far greater load of the (in this case) bulb resulted in big volt drop across the HR joint.
While you don't have battery holder, you have numerous areas that could have similar HR problem.

 

[user1016]

Took a look at it today.

Got tailcap measurement; recording at 0.5 amps approx (changes from 0.46 to 0.57 but seemed to stabilize around 0.5). Am wondering if the aluminium reflector is making contact with the soldering around the LED perhaps (and if so, could this be the cause of the entire body heating up).

When my last switch malfunctioned due to overcharged batteries, only the switch area grew red hot, not the batteries and tailcap, so it sounds like a possible short to me.

Also assuming it may be a short, if I turn it on, how long would it take to heat up? Should it be quick or would I have to leave it on for a while to test it?

 

[Chodes]

0.5 Amps is way too low. 3 x D NiMh direct drive P7 expect over 3 Amps fresh cells.
Even 3 x AA Eneloops expect close to 3 Amps intially, 2.5 after 10-20 mins ballpark.
At 0.5A P7 only puts out about 100 lumens so masssively reduced output should be obvious.

Bouncing around a bit topic wise- if heat localised to switch that is obvious sign of short, or High resistance joint.
A complete short, D NiMh would put out as much as their internal resistance would let them - 10-20Amps.
They would get very hot. If the short was in the switch I'd say expect switch to melt in a few minutes but I'd expect the D cells to destroy themselves before that.

Assuming your cells are healthy and 0.5 Amps is true reading, I'd say you have something acting as a big resistor in your light.
That could be a high resistance joint or a partial short.

P7 LED is huge and legs protrude on the sides - obvious place to check. Simple in a Mag, just loosen head or remove bezel/reflector.

 

[user1016]

0.5 Amps is way too low. 3 x D NiMh direct drive P7 expect over 3 Amps fresh cells.
Even 3 x AA Eneloops expect close to 3 Amps intially, 2.5 after 10-20 mins ballpark.
At 0.5A P7 only puts out about 100 lumens so masssively reduced output should be obvious.

Bouncing around a bit topic wise- if heat localised to switch that is obvious sign of short, or High resistance joint.
A complete short, D NiMh would put out as much as their internal resistance would let them - 10-20Amps.
They would get very hot. If the short was in the switch I'd say expect switch to melt in a few minutes but I'd expect the D cells to destroy themselves before that.

Assuming your cells are healthy and 0.5 Amps is true reading, I'd say you have something acting as a big resistor in your light.
That could be a high resistance joint or a partial short.

P7 LED is huge and legs protrude on the sides - obvious place to check. Simple in a Mag, just loosen head or remove bezel/reflector.

I had a feeling it might be the P7 LED legs, thanks for the advice. Loosened the head to the point at which the reflector is a good half inch away from the LED, will leave it on for about 15 minutes and see what happens.