Convoy 8A driver and 100% mode does not work with SBT90.2. Why?

As in Title. Only the 100% mode in each group does not work. Instead, I have a low PWM mode (30-50%) and the driver additionally buzzes. I checked on two drivers and several new, charged batteries (mainly 40T and P42A). Thick spring on the tail, all contacts are solid.
What could be wrong?

Which host? I ask because I had a similar problem, but it may not be related to what you are seeing.


It could be because it has so low VF at 8A. Under the calculated range for feedback loop I think. Probably the same reason, why Simon had to stop offering them for quad 519A’s, until his driver engineer calculated new values.

Edit… to remove stupid question

Maybe others that are more well versed will chime in. I have had similar problems with other lights, but my S21B has always worked properly.
In other cases, I always have checked the retaining rings on both the driver and switch. I have had Convoys that had loose retaining rings in either or both locations.
I have lightly sanded with 1000 grit sand paper the end of the tube on the tail cap end. Scotch Brite would also work. Just lightly, enough to clean it, but not remove much if any material.
Clean the tail cap retaining ring to remove lube or oxidation.
Clean the retaining ring and center post with a pencil eraser, then alcohol. Get rid of lube or any oxidation.
Make sure the bezel is tight. Make sure the switch resistance is not high.
Pull the reflector and make sure nothing obvious is wrong. Soldering, pinched wires, etc.
Bypass the tail cap spring.

Of course, test after each thing you do. It is called linear troubleshooting.

The highest level not working can be caused by the driver not being able to get enough current. Or, of course, the driver being screwed up.

Lastly, contact Simon. Tell him the problem what you have done to troubleshoot. He will work with you to get it resolved.

I did some digging

Thanks, but I already did all the basics.

This may actually be it. I guess I’ll try the classic FET+1

Did you contact Simon? Probably not many know more about his lights than him…

Yes, He send me new driver, which also has this problem.

Simon pulled the 8A driver for at least a couple of months because he knew about the calibration flaw. The latest version was supposed to have been fixed.
If your light has the old one, maybe replacing it with the new version might fix it. I just got an S21D with the new version of the 8A driver and it works fine.
Incidentally, the problem linked above seems to have been the result of a bad switch, if you read closely. It also affected a quad 219 setup, not the SBT…

BTW, do you have a link to your light. I did some searching and could not find an S21B with the SBT 90.2 emitter in it for sale anywhere. I am sort of interested in trying something with that emitter. Though I wonder if the S21B host (heat) and single 21700 (current) would really do it justice?

Check this out.
@djozz found the Vf for the SBT 90.2 at 8A is 3.1 volts. It is not really that low. Again the linked problem may not apply to your situation at all.

Did you actually go through all of the steps I listed above? It is more than the basics. What is the resistance of your switch?

Just trying to be helpful…