Fuse Resistor Color Code
Adabella Frierdich
In the context of the repair of European audio and video gear, made by companies like Grundig or Philips, I come across "safety" resistors every once in a while, i.e. flameproof or fusible resistors. They are often marked in the schematic like this:
Note: This is just a temporary fix. The replacement part I used to bridge the defective resistor will likely fail prematurely. On the other hand, using a large 1...4 Watt resistor will last forever, but it will fail to protect the unit and I might create a fire hazard. This is just a temporary fix to check if the rest of this particular CD player still works (it does).
I would like to replace the resistors with the closest possible match. However, the service manuals often don't say what exact manufacturer or type they used, and I had no success finding data sheets by some of the companies that come to mind (Vishay, Beyschlag, BC components, ...)
White or black rings on more modern and often larger fusible resistors are common in today's switching power supplies etc., but any sources with data for safety resistors with yellow, orange or violet rings would be greatly appreciated.
Blue body, yellow fifth band: Firstohm FGE. Link to distributor for the catalog, because the individual data sheet from the manufacturer is only available upon request.The data sheet does not state the marking code, so we have to rely on the picture for the type/series on their website.
Pink body, black fifth band: Firstohm SCP. Link to distributor for the catalog, because the individual data sheet from the manufacturer is only available upon request.The data sheet does not state the marking code, so we have to rely on the picture for the type/series on their website.
Note (1): Firstohm uses a blue fifth band to mark high voltage resistors. For small types like 0207 especially, high voltage resistors will have high resistance values (above 100 kOhm, mostly above 1 MOhm) while fusible resistors will have low values (below 1 kOhm, mostly below 100 Ohm).
Note (2): The data sheets are not easily available for download from their website, there are no specifications for the marking codes, but hey - if you enjoy fancy artwork instead, they certainly have some on-topic stuff in their catalog, boom!
Note: KOA also has surge-rated resistors, they have a blue/grey body with a fifth band in black, green or white. Another example why one must check the footnotes and think about the application when replacing a special-purpose resistor. My favorite chemistry teacher once taught me that "one can do anything if one knows what they're doing". In the context of repair work: Fix anything, but know what you're doing. (And you won't cause someone's house to burn down.)
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A Fusible Resistor known by the names current-limiting resistors, fuse resistor, meltdown resistor is a type of resistor that has a low power rating and is designed to melt when a certain amount of current flows through it, thus breaking an electrical circuit. It is the only type of resistor designed to quickly burn up (and isolate itself) when overloaded with the current. Fusible resistors are used as safety devices to prevent electrical fires and other damage caused by excessive current being applied at once. They can be found in household appliances like washing machines and microwaves, as well as electronic devices like stereos. To learn more about fusible resistors and how they work, check out our below article.
Fusible Resistors are power resistors that are designed to fail in a controlled manner. These resistors start as high-power resistors, then have their lead ends welded together and placed in a ceramic enclosure. If the resistor has too much current applied to it, it will short out and the resulting heat will cause the fusible resistor to melt, encapsulating the melted material.
Because of their design, they can only be used once, but they can be used in applications where they may need to be replaced because they are intended to fail. The fusible resistor symbol is shown below. This is the combination of a resistor and a fuse.
The resistor consists of a non-inductive ceramic core with a winding of high resistance wire. The core is coated with a special glaze and the entire assembly is enclosed in a tough non-hygroscopic resin or epoxy case.
Fusible resistors are constructed such that their resistance increases as the temperature rises. This characteristic allows the resistor to function as both a current limiting device and as an over-current fuse, protecting circuits from transient over-current surges and fault conditions.
The Power supply or charger circuit using a fusible resistor is shown below. The main function of a fusible resistor is to restrict the inrush current flow. So this resistor is used as the overcurrent component within the charger or power supply circuit that can have 10ohms of resistance. This circuit is used to protect over current & restrict inrush current.
In contrast, a fuse and an NTC thermistor can also be used to attain inrush current limitation & equivalent over current protection. But by using Fusible resistors, we can save space instead of using separate thermistors & fuses. But, the heat produced through a fusible resistor could need spacing in between components. When this resistor is rated up to 10 then other parts need 0.5-inch spacing. Similarly, if this resistor is rated above 10 W then 1-inch space is necessary.
When power supplies, as well as chargers, need to be in small, then compact packages & the necessary spacing in the region of the fusible resistors could leave the designer of a circuit with insufficient space for the whole design.
Find the appropriate power rating for your resistor, based on whether it will be in series or parallel with your circuit. This can be done by multiplying voltage by current and then dividing by 2 (for series) or 1 (for parallel).
Presently, the Queen Mao resistor color-coding system is used for automatization. In a four-color band resistor, the first three color bands are used to decide the resistance. The fourth color band will represent the tolerance value.
In this color-coding system, the type of resistor can be determined based on the color band. In a resistor, if an additional 5th band color is black, then it is a wire wound resistor, if the fifth band color is white then it is a fusible resistor and If a resistor has one black band within the center, then it is known as a zero-ohm resistor.
The fuse splits the electrical circuit if an error within a device causes too much current to supply then this guards the wiring & the device if something goes wrong. The fuse includes a wire piece that easily melts.Fusible resistors combine the benefits of overcurrent protection & inrush current protection in one component. However, fusible resistors respond differently to overcurrents and have other impacts on charger and power supply efficiency than fuses.Difference between a Fusible Resistor and a ResistorThe difference between a fusible resistor and a resistor includes the following.
Thus, this article covers an overview of a fusible resistor which is a special kind of resistor used to protect any circuit. This resistor is very helpful for extremely sensitive circuits which are used for lower power applications where the requirements of surge handling & overload are not too severe. Here is a question for you, what is a wire-wound resistor?
OK, so I've had my first face plant. I'm OK, just a sore lip and nose. The KS 16 however is not so OK. The trip total was about 35 km. It happened in a pretty steep paved uphill at medium speed (maybe 20 degrees @ 10-15 km/h), not trying to accelerate, just keep the speed.
My 2 hypotheses was that either the KS 16 forced a shutdown because of low battery (it was in the end of a trip with 4 dots left of the 9 about 2 km before this happened) or a blown fuse. It did not respond when I tried to turn it on, but the battery charger would apparently charge the batteries and it eventually showed green. After searching this forum I found others had similar symptoms when the main board fuse was blown, so I opened it up and checked the fuse. It was blown. I changed it, and it will no turn on.
I decided to take a picture of the main board to see if I could find any other signs, and as the attached picture clearly shows, there is a resistor that has had an overload of current. So what is this? What will happen if it fails? Have anybody had this happen before? (for orientation: the fuse is above the upper right corner in the picture, so this resistor sits at the same edge of the main board as the fuse)
Interesting, never noticed that the KS16 has a through-hole power resistor in the board. What's it for, I cannot tell, but judging from the size (which is a bit hard as I can't really tell the scale, just trying to compare my 0.5-3W through-hole power resistors to an XT60 seen in the picture), it's likely something like 2W or 3W. Looks like ordinary metal film.
If you have a (proper ) soldering iron and a solder sucker and/or some desoldering wick (or one of those fancy stations that actually can suck tin out through the tip ), replacing that shouldn't be too hard, but be careful not to overheat any nearby components. Of course you need to know the value (maybe someone can measure it with the wheel off / batteries disconnected just in case, or read out the color rings to know the value). Using larger wattage resistor than the original shouldn't hurt, so going with a 3W one might be a good move, but if it's 2W, the 3W ones are slightly larger. As the legs can be bent, that shouldn't still pose a problem on getting it there.
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