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I am beyond puzzled with identifying the values of a wire wound, axial, through hole resistor that I'm replacing on a MRC Super Brain 989 relic that I burnt up after 50+ hours of charge/discharge cycles of (20) 6-cell NiMH battery sticks that make up the IMA battery in my Honda Civic Hybrid; in efforts to rebalance the pack.

The failed resistor, or actually a series of (4) identical resistors are responsible for the 10A discharge rate the 989 is capable of. I was pushing the discharge circuit beyond limits with dozens of discharges on these sticks at a 10A discharge rate at a 0.9mV/cell peak cut-off, resulting in a 6180mAh discharge capacity per stick.

The charger pauses the discharge cycle when the internal temp reaches 185ºF and resumes discharge when temp drops to 175ºF. This pause/resume would happen several times during a discharge.

All that being said....The resistors in need of replacing measure 17mm in can length and 6mm in diameter, and all 4 resistors read out on a MM with a resistance value of 0.5-0.7 Ohms.

*****THE 5-BAND COLOR SEQUENCE******

{ |BROWN| |BLACK| |SILVER| |RED| |BLACK| }

The best I can come up with is: (0.1 Ohm with 2% Tolerance) by ignoring the ending black band and treating this as a 4-Band Resistor.

The goal is to replace the resistors with a better grade, add more fans, and extend heat sink to get the charger in a workable condition to finish the project at hand.

Thanks!!

Resistor in questiong8.jpg

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    \$\begingroup\$ Post a picture of the resistor \$\endgroup\$ – BeB00 Jun 28 '18 at 22:37
  • \$\begingroup\$ Why wear them out even further?! use pulse charge over Cv with an inductor from float charge CV or get a 100W Panel mount 0.6 Ohm resistor \$\endgroup\$ – Sunnyskyguy EE75 Jun 28 '18 at 22:44
  • \$\begingroup\$ there is a discrepancy between your color list and the picture \$\endgroup\$ – jsotola Jun 29 '18 at 1:54
  • \$\begingroup\$ "...all 4 resistors read out on a MM with a resistance value of 0.5-0.7 Ohms" - are you saying that each resistor measures 0.5-.07 Ohms? What reading do you get with a dead short? \$\endgroup\$ – Bruce Abbott Jun 29 '18 at 2:27
  • \$\begingroup\$ If the center band is intended to be white, you would have 29 Ohms +\- 1%. It doesn’t look white to me, but maybe they thought off-white would show better? \$\endgroup\$ – Blair Fonville Jun 29 '18 at 3:05
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Looks like a 0.1\$\Omega\$ 2% resistor, so 4 in parallel would be 0.025 ohms.

At 2.5A the power dissipation would be 0.75W, which is plausible for the appearance, but you might want to compare the exact size against similar construction resistors.

That's probably too low for your meter to measure reliably, but you can get closer by subtracting the reading you get when you short the probes from that of the resistor.

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  • \$\begingroup\$ I'm thinking 0.1 Ohms, not 0.2. OP says that first band is brown and the picture agrees with him. Brown, Black, Silver \$\endgroup\$ – Dwayne Reid Jun 29 '18 at 4:13
  • \$\begingroup\$ @DwayneReid I think you're right, they look pretty close on this screen, but the left one is clearly brown. Changed. \$\endgroup\$ – Spehro Pefhany Jun 29 '18 at 4:22
  • \$\begingroup\$ I wonder why there’s an extra band. \$\endgroup\$ – Blair Fonville Jun 29 '18 at 4:37
  • \$\begingroup\$ @BlairFonville I've seen (Asian, mostly) resistors with an extra black band over the end cap to indicate which is the right-hand side. \$\endgroup\$ – Spehro Pefhany Jun 29 '18 at 5:20
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    \$\begingroup\$ @Blair: Resistor values always start with a non-zero digit so, at least, you won't see black on both ends. \$\endgroup\$ – Transistor Jun 29 '18 at 6:22

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