Hey guys. I have been a lurker on here for the last two years or so since I caught my disease. I finally just became a member and I would like to ask you gents a noob question. I stacked 5 380ma 7135 chips on a qlite 7135 *8 driver on a XinTD C8 v4. When I measure tail cap amp readings I get roughly 4.75A. But when measured at the emitter I’m only in the low 2200mA range. Why might this be? I used a Samsung 25r for tailcap reading and a bench power supply for tail and emitter readings. Any thoughts, ideas, suggestions or criticism would be appreciated
How thick are your wires from the driver to the emitter
Teeny weeny thin or 22ga wires?
One of the crappy choke points between the driver and the emitter is those stupid hair thick wires
They are the stock wires that came on the driver. To be honest I am trying to “copy” the super XinTD. I did notice that light does have larger wire gauge from the driver to the emitter. I can change the wires out and recheck I was being impatient and just trying to get the light up and running. What is the difference between tail and emitter amps exactly? I’m assuming it depends on the type of driver used? Ive seen threads on people taking tailcap readings and estimating the emitter current.
Tail cap current is how much current the driver is pulling from the cells (input), emitter current is how much current the driver is actually sending to the emitter (output)
I understand that I was just wondering if the amount of tail vs emitter varies depending on the type of driver used ( buck, boost, ect). I’ve seen some times the amount in should match the amount supplied and some the amount at the tail is roughly half of the amount to the emitter.
Anything electronics (especially regulators) current IN isn’t always what goes OUT…the chips that regulate the voltage down end up burning off some of the voltage/current as heat, depending on how much regulation and differential between supply voltage to the driver and then regulated out will determine the losses and the heat produced
That is for buck circuits…they pull in the voltage, then thru conversion (similar to a switching power supply) convert the power to much lower output…due to ohms law volts and amps in converted down decreases the volts but ups the current
Kind of like what a transformer does to AC voltage…the DC-DC buck converter works by first pulsing the DC (making a psuedo AC voltage[pulsating DC], runs thru coils and other electronic coverters and steps it down, cutting voltage and upping current)
In this case (AMC7135) current is the same in the whole circuit, no matter where you measure it, as these linear regulators can only “burn” voltage (current cannot be “burned”!). Different currents on input/output are only possible with switching regulators, they always have an inductor.
I’m sure, you limit the current in the different measurements by adding some kind of higher resistance in your test set-up. (e.g. long/thin leads). Therefore the voltage drops at this bottleneck to some point under the needed LED Vf for maximum current.
Did you solder copper braid or wire in the tailcap spring? That can easily be a bottleneck.
Yes I did do the copper braid on the tailcap spring. I’ll change the driver wires today to 22ga and check again. The leads coming from my power supply are 10 ga and the leads on my Fluke meter are the stock fluke leads prob around 14ga if I had to take a guess.
It shouldn’t be 4.75A at tail and only 2.2 at emitter. The losses are huge. Any decent 7135s will not be this lossy. My guess it that you have induced a short path on the driver that’s soaking up half the current when running, this can easily be a bad 7135 as well.
Did you stack by bending the 7135 leg?
I did not bend the legs on the chips. I followed one of the tutorials on here and it stated that bending the legs could possibly cause a break inside the chip (a great tutorial I might add). I put 20 ga wires on from the driver to the emitter (becuase I could not find 22ga locally) and I got 4.85A to the emitter. That is alot better than the 2200mA I was seeing before and alot closer to the 4940mA I estimated. Thanks for all the help guys.