Need help replacing fusible resistor

[spaceludwig]

I've blown the resistor below in my PSU:

I have been unable to find any fusible resistors online rated in mA, they only sell them rated in watts.

If 23 Volts is going across it at a maximum of 500mA, does that mean I need a 11.5 watt resistor? That sounds huge. Or does anyone know where I can get a replacement rated in mA? Please advise, and thank you in advance!

Cheers.

 

[PRR]

It clearly says 3.9K ohms.

At 23V that is 1/8 Watt.

Seems odd for a fusable resistor.

How did you blow it?

 

[spaceludwig]

Agreed, there is a k there but the other two i measured in the PSU are 3.9 ohms. It's also 3.9 ohms in the schematics.

I believe it happend when i wired the +/- rails backwards trying to measure the current draw from the channels on my console.

Since it is under 4 ohms do I need a 10 watt resistor? If i can't find a replacement can i use a resistor in series with a fuse?

 

[JohnRoberts]

Perhaps the k in that case stands for 5%

500mA across 3900 ohms is some 1950V  and 975 W

Look for a flame proof 3.9 ohm 2-5W

The worst case is you use one too small is it flames out..

But I don't think 3.9K will light that sucker up...

JR

 

[gemini86]

note that it says 3.9(ohm)K, rather than kohm...


maybe just replace it with this?

http://www.mouser.com/ProductDetail/Littelfuse/0230500HXP/?qs=sGAEpiMZZMseCiJT91fwIvaLpwLql8p3NrIG28wYTfo%3d

 

[spaceludwig]

I like the fuses since it allows the board to retain some level of protection.

 

[gemini86]

What I linked to is a fuse...

 

[PRR]

> it says 3.9(ohm)K, rather than kohm...

You are correct. Sorry.

> i wired the +/- rails backwards

I've done that and sometimes the gear lived.... however in some cases not.

You probably need a few ohms for other reasons. Then, as you say, small/fast 500mA fuse, as Rodney said, in series for accidents.

 

[spaceludwig]

What I linked to is a fuse...

Yes, I was replying to your suggestion. I apologize if that wasn't clear.

 

[gemini86]

no, my apologies. I thought you were saying you liked the fusible resistors because of the protection...

Either way, PRR is probably right about the series R needing to be there as well...

Also I believe fusible resistors add more resistance once they warm up? (more current=more resistance) What would be the function of this?

 

[spaceludwig]

I've done that and sometimes the gear lived.... however in some cases not.

You probably need a few ohms for other reasons. Then, as you say, small/fast 500mA fuse, as Rodney said, in series for accidents.

Fortunatetly, there are 4 other DOA's in the console that are dormant since I don't plan on using the monitor section.