Today I opened an old adapter to salvage the transformer and found this component which I also desoldered.

What is this component and what is it used for?

Component Component on PCB

It seems to have a resistance of 10 Ohms as shown and it's labeled as R1, but the joule is confusing me, so I don't think it's a regular resistor. I haven't been able to find anything online.


3 Answers 3


It's a 10 ohm resistor hence the label on the PCB called "R1".

The "J" stands for 5%.

what is it used for?

It's a power resistor and may be used for many things so I would urge you to read Wikipedia's page on resistors and hopefully it might enlighten you given that you have the device in your hand whilst all I have is a picture of it.

  • 2
    \$\begingroup\$ And since it reads "KOA" and "W1" the manufacturer might be KOA Speer and product series might be BWR1. \$\endgroup\$
    – Justme
    Jul 22, 2020 at 14:21

10 ohm +/-5% wirewound resistor (probably inductive, perhaps fusible but it's hard to tell). Called a "cement" resistor. Made by KOA (Nagano, Japan-based company). If it's 13mm long, then 1W rating. J is the JIS or EIAJ standard code for +/-5% tolerance.

Here is a datasheet.


That's a 10Ohm fusible cement resistor with a 5% tolerance --->(J).

  • 2
    \$\begingroup\$ The datasheet doesn't say anything about "fusible". What does "fusible cement" mean? \$\endgroup\$
    – Transistor
    Jul 22, 2020 at 16:20
  • 3
    \$\begingroup\$ It means that the cement based body of the resistor can act as a good fusing agent against high inrush current (last feature point in the datasheet) \$\endgroup\$
    – Saad Hasan
    Jul 22, 2020 at 20:06

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