I'm reverse engineering a circuit board for a 180V dc motor driver and one of the components which is presumably a power resistor (white rectangular with two leads) is marked "N5W0Ω03J" is there a standard or at least best guess for interpreting the value for this component? Google is no help in this circumstance due to the Ω character and any attempt to find a resistor code key just comes back with the color codes.

  • 1
    \$\begingroup\$ It's not google or the 'Ω' symbol that is the problem, but what is there available for it to find online. Googling 'N5W0Ω03J' brings up this question as the only hit. \$\endgroup\$ – Neil_UK May 4 '18 at 6:06
  • \$\begingroup\$ Notice you'll have to get the heat out of that resistor. If no moving air flow, nor vertical-style convection, then the PCB traces and planes are the mechanism. Thus you need to reverse engineer the Heat Extraction paths as well. \$\endgroup\$ – analogsystemsrf Sep 1 '18 at 4:33

I would not bet the bank on this, but that code looks a lot like 5 watts, 0.03 ohms, which would be a good in-rush current limiter for a motor. A sign (sometimes the letter 'R') is placed between the ohms value to indicate it is 1 ohm or less, or a fractional value. The 'sign' is a virtual decimal point.

A white rectangle means it is wire-wound ceramic, which are very durable resistors and are designed to run too 'hot' to touch as a normal operating condition.

If the resistor gets too hot for long periods the code marked on it will burn away. A huge overload can make them crack open.

30 milliohms is difficult to measure without an expensive DVM. An option is a 1.00 amp constant current source, which would give you a 30 millivolt drop across the resistor. Little difference, as it is probably only 10% tolerance.

NOTE: Based on the chart I found it is a 5% tolerance resistor. About as good as it gets for off-the-shelf wire-wound.

I found this Resistor Tolerance Chart on the web.

(Reference IEC60062):

$$ \begin{array}{ccccccc} Colour& Value 1& Value 2& Value 3& Multiplier& Tolerance& Letter Code\\ Silver &&&&x 0.01& 10\% & K\\ Gold& &&&x 0.1 &5\% &J\\ Black& 0& 0& 0& x1\\ Brown& 1& 1& 1& x10 &1\% &F\\ Red &2 &2 &2 &x 100 &2\% &G\\ Orange& 3 &3 &3 &x 1K&\\ Yellow& 4& 4& 4& x 10K\\ Green& 5& 5& 5& x 100K &0.5\% &D\\ Blue& 6& 6 &6 &x 1M &0.25\%& C\\ Violet& 7 &7& 7 &x 10M &0.1\%& B\\ Grey& 8 &8 &8 &x 100M &0.05\% &A\\ White &9 &9 &9 &x 1G\\ Blank&&&&& 20\%& M \end{array} $$

  • \$\begingroup\$ 0.03 ohms is probably a current measuring shunt rather than an inrush current limiter but otherwise I think this is spot on. \$\endgroup\$ – Brian Drummond May 4 '18 at 8:29
  • \$\begingroup\$ Do you know what the J stands for? \$\endgroup\$ – Sanchises May 4 '18 at 9:30
  • \$\begingroup\$ Either 5% or 10% tolerance. Not so important with resistors that are wire wound. \$\endgroup\$ – Sparky256 May 4 '18 at 9:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.