i attached the RL2 20w to a 12v battery and immediately blew RO50 off the board. I think this is a 1% 50mohm resistor. All wiring is correct polarity but suppose I could have reversed when I plugged power into RL.
Any idea how this happened?
Am i likely to have damaged anything else?
How can I repair it?
If it caused the shunt resistor to blow, it was definitely hooked up in reverse!
This is a known issue, unfortunately. Replacing that resistor - it is indeed an 0.05 ohm resistor - is necessary, but not sufficient; other parts may have been damaged. Does the device power on fine?
device still working as determined by attatching to variable power supply.
I suspect (novice speaking here) that the polarity was correct but that the pot was wound out to max and the inrush current was too great? What is the power rating of this smd resistor? Your version one unit used a 3w through hole component. I see a few current sense R050 smd chips on Elements4U but only up to 2w. Can you do me a favour and identify suitable item? Not sure of temp coeff requirements? Maybe you could post me a couple if I cover costs?
It definitely shouldn't be possible to burn it out if it's connected the right way around. If you're able to reproduce that(!) I'd be very interested to see the conditions that cause it.
Any 2512 0.05 ohm resistor should do the job just fine. They're 2 watts, but 6 amps ^ 2 * 0.05 ohms = 1.8 watts, so that's fine.
Thanks, i found some but with postage that was half the cost of the dummy load. If you believe the failure was due to reverse connecting to the 12v battery could you please clarify the limitations of the statement "Virtually indestructable. As long as you don’t exceed 40V, there’s not much you can do to damage this. ESD, overcurrent, overtemperature and reverse polarity are all protected against".
The body diode in the FET passes reverse polarity; it won't damage the device directly, but enough of it - such as from a very low impedance source like a lead acid battery - will cause the shunt resistor to overheat as you've observed.
Let me know what your original order number was, and I'll send you out a replacement unit.
Thanks for the clarification and fix. Cheers.