> On Dec 19, 2015, at 2:18 PM, Robert Jarratt <robert.jarr...@ntlworld.com>
> wrote:
>
>> From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Dave
>> Wade
>>
>> Seeing as it already seems to have over current sensing, I guess it has some
>> small resistors in there so perhaps it is possible to measure the current. I
>> notices one looks like this:-
>>
>> http://uk.farnell.com/welwyn/oar1-r020fi/resistor-1-0r020/dp/1200359
>>
>
>
> Ah! So that is what those things are! I definitely think this one is
> detecting something wrong and shutting down the 12V side.
Something to watch out for with high current sense resistors: they often have
four connections rather than two. This is a "Kelvin connection": two
connections are for the current to be sensed, and the other two pick up the
resulting voltage difference. The idea is that you get the voltage drop across
the resistor itself, as opposed to the voltage drop across the resistor PLUS
the solder joints. That makes a difference if you have a sense resistor of
just a few milliohms.
If you have a high current supply but it doesn't use Kelvin connected current
sense, you're vulnerable to false shutdown if the solder joints are less than
perfect. If so, switching to the Kelvin hookup, if you can see how, is a good
answer; failing that, make sure the joints are in excellent condition.
paul
