I just got my reload 2 v2.1. Soldered it up, hooked up my power supply and there seems to be a dead short at the + & - pins as my power supply voltage drops to .03V for constant current of 500mA. No matter what I do to the pot, there is always a .1ohm resistance between + & -. I have checked for solder bridges, obvious shorts and even mounted the heatsink at a slight elevation to prevent a short of the 3 pins under it. I can't see anything wrong.

No smoke, just a dead short. What do I check or do next?

Hi Jeremy,

Sorry you're having trouble.

Is your power supply capable of more than 500mA?

My power supply is capable of up to 5A which I did turn it up to 4A to see if there was a change. No go. It just pegs at whatever current I set it to no matter what I do with the current setting knob.

Okay. Just to exhaust the stupid questions, are you certain it's not hooked up backwards?

.03v is a surprisingly low voltage drop; it ought to be higher than that just for the FET and shunt resistance. What sort of voltage drop do you see across it at 1A?

Did you buy your unit from Crowd Supply?

Unless the silkscreen is backwards, then it is not hooked up backwards. That was the very first thing I checked.

I think I typed a typo before with the 0.03V. It should be ~0.3V. When I set the power supply to 1A, the voltage was 0.35V.

Yes, I bought my unit from Crowd Supply.

Hm, very odd. I'm all out of easy explanations, I'm afraid!

Can you get in touch with Crowd Supply and ask for a replacement unit? CC nick@arachnidlabs.com and I'll make sure the shipping cost is covered too.

-Nick

Will do. I have an oscilloscope, do you have any points/voltages I could look for?

Sure! Check the voltage between the gate of the FET and ground for starters, and the voltage across just the FET and just the shunt resistor.

It works now!

As I was going through with my multimeter (oscilloscope seemed like overkill because the incoming voltage was being squelched so much) I took off the binding posts and found the issue. The washer on the red positive binding post scratched the soldermask just enough to make connection to the ground plane on the board.

So suggestion for all, don't use the metal washer on the positive binding post, only the nuts.

Nick,
Thanks for the help! You had quick responses and good customer support! For V2.2, I suggest either putting a copper resist on the board around the positive terminal or just making the pads larger to accommodate the washer size.