I have a 63mA resistor in one of my boards. The resistor is rated at 4 ohms and 250 v.

The problem is that I started getting a lower output voltage on a the full assembled product. I narrowed it down the the resistor and I measured it at 16.8 ohms... How can a resistor that was once 4 ohms end up having 16.8 ohms??

 

There is no such thing as a 63mA resistor. Resistances are measured in ohms, not amps nor milliamps.

Three things can happen to a faulty resistor, the resistance can increase, decrease or remain the same.
Take your pick.

 

Are you measuring it in circuit? if so, take one lead out.

 

It got damaged?

It had the wrong resistor installed in the first place?

You are measuring it incorrectly?

 

Are you measuring it in circuit? if so, take one lead out.

Measuring a resistor in-circuit will give a reading at its nominal value or lower, not higher.
Exceptions can occur if there is residual charge on the board.

 

There is no such thing as a 63mA resistor. Resistances are measured in ohms, not amps or milliamps.

Three things can happen to a faulty resistor, the resistance can increase, decrease or remain the same.
Take your pick.

That was what I zoomed in on, too. But then he said that it was supposed to be 4 Ω, so I'm provisionally assuming that it is supposed to have 63 mA flowing in it under the conditions he is interested in. Now, as for that 250 V, that would equate to 62.5 A flowing through it. So I can't help but wonder if the TS meant 63 A instead of 63 mA. If so, that 250 V rating probably just says that it can't tolerate anything above 250 V across it and not that it CAN tolerate anything below it. The power rating probably reduces the actual voltage limit considerable (since 250 V across a 4 Ω resistor would have it dissipating more than 15 kW of power).

 

Are you measuring it in circuit? if so, take one lead out.

That wouldn't explain it in this case since the 4 Ω resistor would put an upper limit on the measured resistance in circuit (unless the circuit is powered, in which case all bets are off).

 

Sorry guys,

Maybe I stated it wrong. Let's make its simpler disregard the application. This is rated for 4 ohms. It measured 4 ohms, it now has 16.8 ohms....

 

It also is red.... I pulled a picture off goggle I am home already so do not have the actual one to take a picture of.

 

If it was measured properly both times, then it has been damaged.

What is the DigiKey part # for this resistor?

 

H

 

You mean a 63mH inductor. Measuring the resistance of the inductor has no bearing on the value of the inductance.

Edit: Now it is a 63mA fuse. So what should the resistance be?

 

I have a 63mA resistor in one of my boards. The resistor is rated at 4 ohms and 250 v.

The problem is that I started getting a lower output voltage on a the full assembled product. I narrowed it down the the resistor and I measured it at 16.8 ohms... How can a resistor that was once 4 ohms end up having 16.8 ohms??

That's 4K ohms, 4,000. to give 63 mA at 250 V.

 

You mean a 63mH inductor. Measuring the resistance of the inductor has no bearing on the value of the inductance.

Edit: Now it is a 63mA fuse. So what should the resistance be?

4 ohms.

 

That's 4K ohms, 4,000. to give 63 mA at 250 V.

It's not at 250. I just listed the specs from digi key. I just wanted to know if anybody knew how it could once have 4 ohms of resistance cold and it now at cold state is 16 ohms.

 

So the part number is Schurter 0034.6002

http://www.digikey.com/product-detail/en/schurter-inc/0034.6002/486-2001-ND/640372

max current = 63mA
max voltage = 750mV

R = 750mV/63mA = 12Ω

16.8Ω seems a reasonable reading to me.

 

You mean a 63mH inductor. Measuring the resistance of the inductor has no bearing on the value of the inductance.

Edit: Now it is a 63mA fuse. So what should the resistance be?

How good a meter do you have? You may not be able to tell a good fuse from your leads touched together. A few ohms maybe. They don't go "just a little bad".

 

It's not at 250. I just listed the specs from digi key. I just wanted to know if anybody knew how it could once have 4 ohms of resistance cold and it now at cold state is 16 ohms.

How about just listing the part number from DigiKey?

 

You mean a 63mH inductor. Measuring the resistance of the inductor has no bearing on the value of the inductance.

Edit: Now it is a 63mA fuse. So what should the resistance be?

That was a rhetorical question. I did not expect you to give me an exact answer.
Where in the spec sheet do you read 4Ω?

 

WK4225BK-ND

The spec sheet will say 3.8 ohms