C8 mod with fet and abnormal low readings

I have some unclear problem. New Convoy C8 host + FET+1 ( from BG ) + KD HI V3 on 20mm DTP copper MCPCB.
All connected and put into work, but only 2.8A with 30Q :FACEPALM: , bupass spring on tail and driver and get only increase to 3.2A :FACEPALM:

Assume that driver is bad, change it for new one ( I have 2 of them ), same problem… Don’t know what the hell is happening here, is there some secret with this Convoy C8 host that something must me done that all work as it should be ?

To mention couple a months ago I put 2x of this drivers in two Brinyte b158, without bupass springs and I measure about 3.8A which is ok for me. But now I don’t know what the hell is not ok here. Even if the led with star is bad that is not matter since driver need to deliver current for how much capable he is…

Any suggestions.

Is it your meter? Meters with little thin leads generally read very low. Most of us build our own very short, very thick leads for measuring current. Or even better use a clamp meter.

Dmm is not the problem since I measure on b158 3.8A, on some Skilhunt over 4A etc. Another parameter that I know that something is not ok, compare stock Convoy C8 with this moded and no differences.

Should be 4+ amps with both springs bypassed. I have pretty much the same light, XP-L HI, BLF A6 Fet and springs bypassed & I get 4.6A after several seconds and 4.9A initially.
Any chance you have the tube installed backward? The Silver threaded end goes into the head, anodized threads go to tailcap.
For the light, you swapped drivers and the only common is the emitter and the board its mounted to.
You could measure the voltage at the emitter.

Also you really should make some 6in 12AWG leads for the DMM. What is the model and max amperage of your DMM?
I ask because it could be limited by its internal build quality.
My Uni-T UT61E is rated 10A max and it has measured over 15A in triples and quad builds on a FET and single 30Q using custom made leads.

This question comes up quite often. In fact I asked the very same question on my first mod. Someone mentioned the resistance in my measuring method. I did not pay attention as I was proud of my newly perchased quality dmm.

It was brought up a couple times more and I kind of did my own little test on the side. I didn’t see a difference. I finally decided to really give it a try. I took one foot each of red and black 8awg battery cables and soldered them to a post that slid into the dmm slots. Then took my measurement. 4.2amps instead of 2.7! I was shocked! The cable size alone did not acount for the whole amp and 1/2. There were other resistances that were in the connectors and connections. Anyway, even under 5amps small resistances add up fast.

OP, this may not apply to you but I still write it to help the person that comes to the thread with the same problem that may be a result of the measuring meathod and not the hardware. :slight_smile:

Maybe solder blop both spring??

As lightrider mentioned it is also the quality connectors you use with your larger gauge wires. I have 4mm gold plated brass high current connectors left over from RC car builds. That is what I have used and 12 AWG fine stranded silicone wires at 6in.

As I already told my Mastech DMM is not the problem he will measure without problems higher currents on other lights…

The problem is specifically with this lamp. Tube is not installed backward. There is no problems in measuring method problem is in light, brinyte b158 stock and brinyte b158 fet ( without spring bupass ), I clearly see the difference when I put lamps to work on 200m distance, also first is reading about 3A second about 3.8A, but this convoy c8 no difference in work between stock and one with fet, a fet version behaved like it is stock…

That the thing is worse when I bupass the springs I get very little increase in amps. If there are some high resistance where it should be, what to check ?

I had to put solder blobs on the driver at the back side on the negative terminal because my C8 didn’t made contact at all with the driver. Try to put some solder on the driver to see if that will improve things.

I also notice that in that part can be insufficient contact, like a ring does not touch the whole surface good.

I measure on lvl 7 ( turbo ) a voltage on led and it is 3.71V.

It could be that your particular XPL has a bit higher forward voltage, resulting in less current. From djozz test of XPL HI the current at 3.71V is around 5.25A.

You say there is no problem with your current measuring system, but I still think your DMM probably has a high resistance which would cause your measurement to read low. Changing the leads can only do so much; the internal resistance of the ammeter can still be high. The current with a fully charged 30Q and XPL is usually close to 5A.

Put the XPL hi in the light with the “working” driver. Then measure. If your amps still measure low then you have a hi vf led and resistance in you dmm. Measuring different leds and reading higher amps does not necessarily mean your setup has low resistance. Maybe your other measurements are low as well without realizing?

Sorry, whether you are right or wrong, I know how you feel. We will keep helping either way. :slight_smile:

Try Sony vtc5a…

As I say I try with two fet drivers and both of them behave the same.
Host is new and there is no driver inside it, all parts I buy separately.

Possible, but all other light that are stock measure about 3A how it should be, higher current lights measure higher, maybe it measure 4A and it is 4.5A but this is not important in this case, since this mod convoy can’t go higher than 3.2A with spring bupass and brinyte with same fet driver and led on 16mm go to 3.8A with no spring bupass ( with bupass spring is will probably hit about 4.5 A ), that is the point, if the DMM is not ok, he will not be ok for all of the lights, not only for this one that I have problem with it ?

So something is not right and first thing that I will try is BobbyMK suggestion, so if it does not help then I guess something with this led is not ok, or there is some resistance on some other part of the lamp.

It’s hard to tell, but maybe this is the problem :

I just did some measuring in my C8 with mtn electronics fet+1 and it was reading only 2.5A on turbo. Aster messing around I found that unscrewing and retightening the bezel just enough to recenter the reflector made the reading go up to 3A, which was closer to what I expected with the battery I was using.

You could try this, it might be the reflector sitting weird because the MCPCB is thicker than what the reflector+gasket were made for

Lookng closer to my C8 A6 BLF I had also soldered the outer rings to get the driver to tighten up.

I have had the same problem with the Mtn E. Fet+1 1.6mm thick drivers many times in various hosts. Not so much with the thick A6 boards. Convoy M2 and S3 use an inadequate retaining ring. I have had several problems with those hosts retaining drivers.

your DMM adds most likely too much resistance

for accureate reading you need a shunt ot clamp meter

as a shunt you can use some 20cm AWG20 wire or similar, you know the resistance of it and simply measure the voltage drop

20cm of awg20 should have 6.88mOhms
for 5A you should have 34.4mV

then I=U/R

this makes no sense, no matter how the reflector sits the LED current cant be changed,
it just proves that you may have less resistance added to the circuit in the 2. measurement

So you have measured the same led and driver in a different host and got different results? What does it measure without any host at all? Can you measure this way, it is a bit tricky if you are not set up to do it…

I get about 4.21 amps with xpl-hi v3 3c and 4.19 v 30 q.