I thought that DD would get to hot, just call me chicken, after I have got something rammed in behind the driver, hopefully a bit of thick walled copper pipe, the wall will come tumbling down and turn into a bridge 
Cheers David
It's not going to do 5-6 amps no matter how many 7135s you throw at it, at least not with a single LED and cells in parallel.
Are you sure? Iāve gotten some really dangerous drive currents on DD with standard ICR cells, up to 7+ amps and a rather unhappy blueish XML as a result. Was in a p60 with just a contact board as a driver. Would the resistance of a 7135 driver board drop the maximum current that much?
Donāt see why you couldnāt get equally high draw if not higher using 2p cells and a single XML but then Iāve never pushed a 7135 driver much above 4.5A in a single cell situation.
Was this a XM-L or a XM-L2 their vf are slightly different? The op is using a XM-L2.
It was an XM-L, didnāt realise this made such a big difference. So XM-L2s are actually much safer to run DD since they wonāt exceed 5A on a single cell?
I am going by this graph, posted elseware on blf,
5A = 3.7v
Would sag drop 2P*3000mah fresh batteries below 3.7v ?
Going to have to go DD and find out, I donāt need extra heatsinking for a quick test.
Cheers David
Check out the 3ADischarge curve of the batteries you are using to see how far they drop.
It depends a lot which cells you useā¦.
lygte-info.dk/review/batteries2012/Common18650comparator.php
I second that, the battery type can make all the difference in the world. It greatly depends on the voltage sag of the battery used under a particular load, but your are correct in using the graphs to estimate current. Most graphs are created with very little resistance in the test. A flashlight has a lot of different places resistance can influence the numbers.
Thanks for the link, looks like I can get about 12~15 minutes at 3A, so 15min at 2.5A, I realise that these figures are for a starting charge of 4.3v and mine will be 4.2v
With my Samsungs there was no data for 3000mah so I used the 2800mah.
Again I should get 15min at 2.5A.
I think I need a hobby charger and some 3400mah batteries.
Looks like the minister of finances is going to be yelling at having a talk to me about my spending habits, ah well xmass is comming 
Will go DD tonight, after my daughter is asleep, she is special needs, so no using hot or sharp things while she is around 
Cheers David
OK, its now DD and only pulling 2.96A
Tried with one battery, got 2.56A :~ so its not shortage of current to the driver.
While I was measuring the current at the switch I got a 3.6~3.8A reading, then I started to act like a woodpecker, switching between the modes just stopping at full long enough to get a reading, the mystery turbo was very intermittent, not predictable and I cannot get it at all using the switch.
This turbo mode was mentioned a few times in the ZY T08 review thread Review: Small Sun ZY-T08 2 x 18650 (Parallel)
So it looks like the driver is not in DD even with the resistors shorted out, no use to me so when I put in my next order there will be a 8*7135 (380) driver that I will stack until the amps stop going up >)
That will give me some time to get some copper inside the pill.
Cheers David
'Direct drive' is when you bypass all the driver circuitry altogether and replace it with a piece of wire. Were you thinking that adding resistors would make it act like DD on high?
And with the 7135 thing, what I'm saying is that if your cells and your LED connected together with no driver at all only does 4.5 amps, stacking 16 7135s for a on-paper 5.6A is useless, it still won't ever do more than the 4.5A it did before the driver was added. They're not amplifiers, they are just current limiters that can be switched on and off.
The definition of direct drive is a bit loose:
- Is it direct drive if there is a switch.
- Is it direct drive if the switch is replaced by a mosfet.
- Is it direct drive if I switches the mosfet on/off at a fast speed (I could also do that with a manual switch, but it would not be as fast).
- Is it direct drive if the resistance from the battery to the led is 0.1ohm, due to thin wires, thin spring, switch, etc.?
- Is it direct drive if the resistance is due to a resistor?
The resistors are fully shorted out now, and I am getting no more current that when I added resistors.
I fully realize that I can only get whatever the batteries can deliver, but as one can deliver 2.65A why canāt two deliver 5A ??
Tomorrow Later today, after some sleep I will bypass the driver and go direct and see what that gives me, I should be right for heat if its only for 10~15 seconds to get a reading.
Night all,
Cheers David
Probably because you have resistance in wires, switches, circuit traces, DMM, etc.
Yes. Sharing the load between batteries will only increase the output if voltage sag under load was the main limiting factor.
If the battery was already delivering a healthy voltage, for example 4v (optimistic I think under ~3A load) but loosing say half a volt due to resistance losses on the way to the LED then youād be down to an led voltage of just 3.5v. This according to the graph posted for XM-L2s would give a current of around 3.5A. In a likely scenario where the batteries may sag more or the resistance losses are higher then you could quickly drop down even further to something like what you are seeing.
Also donāt count out the factor that thin or excessively long DMM leads can limit the total current reading that you are able to measure. I know on my cheap DMM with stock leads I simply canāt read any more than around 2.7A even though itās rated up to 10A. Thicker leads or a better suited current meter will help get more accurate results.
Cheers
Because it just don't work like that.
In a thread a while back there was an issue with XPG2s pulling less current after de-doming, and I ran a direct drive test to see if my numbers were what the others were seeing. One cell, direct drive, nothing but wires and an ammeter between the battery and LED, a Panasonic NCR 2900 would do 2.53A into the XPG2. Surely two cells in parallel would fry it, right?
Well no. Two cells in parallel did 3.07A. Three cells in parallel = 3.28A. FOUR CELLS(??!) = 3.42A. Each one added gave less increase the more cells there were. That's just how these things work. More voltage means more current will flow, but more current means more load which means more voltage sag, and more sag means LESS current. I imagine I could have connected thirty cells in parallel and the current still wouldn't have gone past 5 amps.
You have a two cell light, convert it to series and use a buck driver and you will not have to worry about any of this stuff.
Agreed, That is the best way if the application will allow it. Most buck drivers have a current sense resistor which can be modded to give even higher currents. Efficient buck circuits can give you almost a flat lumens output curve through out the entire run time(constant current).
Did you bypass the battery springs? What kind of DMM are you use, and what kind of leads?
Just a note. The zy-t08 has a good switch, its resistance is lower than 5milliohm (<0.005ohm). Usually a DMM self resistance (with leads) is between 0.05-1ohm. You can imagine how big will be the current difference through the DMM and through the switch. My DMM has 0.03ohm with thick and short leads, this is not even good enough for accurate measurement, at least at this light. The measured current will be lower in any case, than the real current when the light works with its own switch.
I have an Solarforce M8, with QLite driver, stacked chips totalling 16, pushing an XM-L2 at 4.90A using a rested Samsung 20R cell. Iāve seen it hit 5.34A with a fresh charge.
Thank you all for helping me to understand a bit more of this dark art 
The springs are braided and the wire changed to 22g.
My DMM has heavy duty speaker wire leads only 8ā long, and measures 6.5A on my Kung.
Those figures are close to what I got so,
As I am going to buy a new driver anyway going to 2S will only be a different driver and a bit of dremel work J)
Cheers David