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Re: Testing small Transformer questions

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On 2023-02-22, StevWolf wrote:
> [on 2023-02-22, I wrote]
>> [...]
>> Quick sanity check for yourself -- grab something you know the 
>> resistance of (or can check easily), such as a 100 ohm resistor. You'll 
>> probably see it displayed in the range of " .105" to " .095" (under the 
>> assumption of a standard 5% tolerance resistor). 
>> 
>> My meter here does have some error between resistance and continuity, 
>> generally with continuity mode showing an ohm or two less than 
>> resistance mode; at least across the 10 resistors I tested with just 
>> now. 
>> 
>> HTH :) 
>> 
>
> Well thanks for your comments. You have encouraged me to dig into my
> meter a bit.
>  Here are some results of my meter using some resistors I have.
>
> 100R set to 200  is 107 Ohms - Ok I guess

107 ohms is within 10% tolerance; so it's fine assuming it's got a
silver (or no) tolerance band. What did this show in continuity mode?

The range doesn't "really" come into play here (it just means you can
accurately measure from 0 Ohms to 199 Ohms; usually to the nearest
tenth)

> 1 R set to Continuity says .974 Ohms - Yes seems OK.

What did this resistor show in Resistance mode?  I mean if your display
works the same as mine, it's showing just shy of 1k ohms.

> .39 R set to Continuity says .002  - thats close
> .39 set to 200 says  3.6 (which seems odd to me

With the assumption your display operates the same as mine, 2 ohms is
nowhere near 0.39 Ohms. Likewise if it really is showing milliohms; 2
milliohms is nowhere near 390 milliohms.

3.6 ohms reading on a 3.9 ohm resistor is within 10% tolerance.  Color
marking would be Orange, White, Gold; with a Silver (or no) tolerance
band.

(0.39 ohms would be Orange|White|Silver).

>
> Importantly The manual for the for the meter seems to say that it will
> show continuity for anything less than 50ohms.

Means it'll beep if the circuit total resistance is 50 Ohm or less -- so
a 100 Ohm resistor will never beep, but a 47 Ohm resistor most likely
will (noting, of course that 10% tolerance can get you as high as 51
Ohms).

> Also while the meter has no information about the following, in the
> manual, when I set it to Continuity there is a little 2 under the
> decimal point, in the same way that it shows up when set to 200 for
> example with the respective 200 under the decimal. I asume that means
> 2  Ohms, 

What's the meter make/model?

>
> Sooo Im still trying to figure out if this transformer primary is bad?

You get continuity, chances are "no", unless it's supposed to have more
resistance than it does.  But we'd need a datasheet or technical manual
to know for sure (I mean I have a couple of old rail locomotive
maintenance manuals that're like "if you need to rewrap the solenoid,
use 28AWG magnet wire until you get 75 ohms in the coil")

> Maybe transformers which are basically two sets of winding in simple
> transformers dont have much resistance. 

Depends on the wire gauge.  For example, 30 AWG magnet wire is something
like 100 Ohms / 1000 feet.  


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Thread

Testing small Transformer questions StevWolf <colinmarr0@gmail.com> - 2023-02-22 05:52 -0800
  Re: Testing small Transformer questions Dan Purgert <dan@djph.net> - 2023-02-22 15:32 +0000
    Re: Testing small Transformer questions StevWolf <colinmarr0@gmail.com> - 2023-02-22 09:42 -0800
      Re: Testing small Transformer questions Dan Purgert <dan@djph.net> - 2023-02-23 11:43 +0000
        Re: Testing small Transformer questions StevWolf <colinmarr0@gmail.com> - 2023-02-23 10:00 -0800
          Re: Testing small Transformer questions Dan Purgert <dan@djph.net> - 2023-02-23 23:24 +0000
            Re: Testing small Transformer questions StevWolf <colinmarr0@gmail.com> - 2023-02-24 18:11 -0800
              Re: Testing small Transformer questions Dan Purgert <dan@djph.net> - 2023-02-25 14:00 +0000
              Re: Testing small Transformer questions Lamont Cranston <amdx62@gmail.com> - 2023-04-29 18:00 -0700

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