Thanks dthrckt. Depending on optics, Id like to run 3 or 4 emitters at 3A each or 6 at 1.5A each. Can you recommend some good efficient optics for a flood beam?
The driver you linked looks great, but: Working voltage: 6-12V. I need to stay at 4.2V
I think so, but going from 4.6A to 9A might be a stretch. I need others to take a look and comment.
If it were my light. I would stick a small Aluminium heatsink to the back of that mosfet driver.
Then I would place one of these http://www.fasttech.com/products/0/10002999/1224400-10-ohm-potentiometer-trimpots-5-pack in parallel across any one of those sense resistors.
Then ‘Very’ carefully dial in the amps you want while simultaneously watching your amp meter.
Have you measured tailcap current on lower voltage? If it is higher than its regulated and if it is you could do a resistor mod. Worst thing could happen is to burn the useless stock driver.
Are all the LEDs parallel? Are the resistors in parallel?
Spasmod & Werner, great ideas! I’ll have to rig an axillary battery pack with lower voltage and take some readings. All emitters are wired in parallel.
I'm in the process of doing the same (or some kind) of mod to this light as well. I currently have it dissembled and posted a possible mod here (post #32) using Techjunkie's multi-AMC7132 circuit. He responded it could feasibly work provided I reconfigure the circuit with a bypass since 12A would likely fry the stock switch. He also suggested to use IMR cells for this application due to the high current necessary, but was really not keen on having parallel batteries due to the potential of uncontrolled cross charging. A better config would be to use 6 separate boards, but that would require some pretty skilled soldering and cramming them into the driver cavity.
I am open to any ideas here...
Thanks Hill, I had already linked your comment in my original post above. I know there is a lot there to read, but Im trying to avoid a master/slave setup if possible. If you can get it to work, have you considered how much heat 52W will generate within your host? (especially with the constant current IMR will deliver till the cells drops off). IMO, its probably going to be way to much heat to deal with for anything over a 10 minute run. Im considering 3 x 3.04A 7135 drivers, one per emitter for a total of 38W. Remove the memory from the drivers and run it in 3 mode without memory. 1.3A per cell should give descent run time without IMR.
Ive had far better luck while using 4 x 18650 matched cells in parallel rather then using them in serial (especially while driven hard). In parallel, if initial cell voltages are close to equal at the time of discharge, they will all discharge at the same voltage… they dont have a choice. Ive had some startling and often not repeatable results while measuring serial cell voltages after discharge… even while using brand new expensive tested and matched cells.
Are you going to change your optics or run stock?
The driver in mine is the same except R4, R5, R6, R7 and Q1 were all resistors marked 0
duh, what was I thinking, same problem w/ dry driver - there’s really no way to change battery config to serial.
unfortunately, I know very little about optics. I have done quite a bit of searching for small reflectors though, and CNQ has the best selection of reflectors near the size of what you require. kaidomain and dealextreme also have some.
spasmod’s suggestion sounds like a great way to start, and if it gets fried, you could pursue the amc mod.
Hi,
It’s a long shot but maybe RIC can help you , I bought an APEX 5t6 from him to make my project (APEX 5t6 bike light) and it was under driven 5.5A H and he send me a new replacement driver 8.5 A.
The driver alone is not listed in his site but maybe you can arrange with him the price and send you one - still you will have under driven t6 with 1.6 - 1.7 A but the amount of light will be good enough like an APEX
Jim
jlogres, thanks for the tip. An 8.5A driver split 3 ways would deliver around 2.8A per emitter (or 1.42A if driving 6 emitters) . Can you please measure yours and tell me the diameter?
And then the pot would burn up… they are only rated for a few milliamps of current, not the manyamps that can flow through a sense resistor.
I remember reading somewhere that the sense resistors only saw a few milliamps, I'm guessing that is incorrect?
yeah, i remember someone saying that too
No! Sense resistors see the full battery (or LED) current.
The sense resistor is direct in series with the led, so it sees all current. Of course it’s splited to all parallel resistors. That’s the way this works, the mcu measures the voltage drop and if there is a lower voltage because of a more empty battery than the mcu regulate the duty cycle up so that the current stays constant over the whole voltage range.
These pots are 0.25W max. So if these resistors are parallel we have
1÷(1÷0.082+1÷0.082+1÷0.082+1÷0.082)=0.0205 ohm
If we want double the current we have to parallel another 0.02 ohm resistor, that’s a too low value for the pot either.
P=R*I^2……so Pmax @3.5A. But real current 4.5A…Preal=0.41
Not too bad for such a little pot, worth a try perhaps to see what we can get from this driver and that is what spasmod said. I would try this too.
But first he has to find out if it is a regulated driver….
If it was in series or replacing the sense resistors I would agree but since it’s in parallel and the original sense resistors are still in place then the ‘amps’ are still flowing through the original sense resistors.
No! If you reduced the current sense resistance by half with the pot, half the current would be going through the pot.
Also, the power rating of the pot only tells half the story. There is a maximum (often unspecified) current that they can handle due to the wiper contact.
Actually, yes you’re right. For this application (9 amps) the variable pot wouldn’t handle the power.
AFAIK the sense resistors usually see between 30-90 mV. So 0.09 x 9 is 810mW… and even with half the current as you said, that’s still 405mW so too much for these 250mW variables.
Mind you it’s been 25 years or so since I studied electronics at college so I have an excuse 
FlashPilot: Is there any chance you can take a voltage reading at the sense resistors ?
It’s 49mm , it must be close to yours the two flashlights must have the same battery body only bigger head (yours)