Welcome, Guest. Please login or register.

August 12, 2020, 11:49:40 AM

Login with username, password and session length

Recent Posts

 

Author Topic: How to measure a transformer?  (Read 6252 times)

syndromet

  • Elite
  • ****
  • Posts: 197
  • Chip Points: 38
    • View Profile
How to measure a transformer?
« on: June 29, 2006, 12:06:25 PM »
Hi.
I have a broken Pioneer amp, and I'we ordered my first amp kit from Joe. I was hoping to use some of the parts of the Pioneer in my kit, mainly the transformer. My question is; how do I measure the secondary voltages on a transformer? And how much power does a stereo LM1875-amp need?

Nice place, by the way.  :tu:

syndromet

  • Elite
  • ****
  • Posts: 197
  • Chip Points: 38
    • View Profile
Re: How to measure a transformer?
« Reply #1 on: July 09, 2006, 05:56:58 AM »
I guess I was a little short on my last post, since I'm qiute shure some of you know this.
Here are some pictures of the transformer. Can anyone help me find wich side is the primary?
Pic1
Pic2
Pic3
Pic4

One side is marked with a red dot... Does that mean anything?

joecool85

  • SSGuitar Admin
  • Legendary
  • ******
  • Posts: 3310
  • Chip Points: 991
  • SSG Creator
    • View Profile
    • thatraymond.com
Re: How to measure a transformer?
« Reply #2 on: July 09, 2006, 07:46:29 AM »
I would assume that the red dot side is primary...but its not a good idea to assume when you are dealing with more than 9volts lol.  RDV, chris?
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

teemuk

  • SSGuitar Global Mod
  • Legendary
  • ****
  • Posts: 1074
  • Chip Points: 282
    • View Profile
Re: How to measure a transformer?
« Reply #3 on: July 09, 2006, 11:52:02 AM »
It's never good to assume anything when dealing with mains voltages. Plug it into a low voltage AC source and do some tests.

RDV

  • RIP - 2/5/10
  • Elite
  • ****
  • Posts: 291
  • Chip Points: 419
    • View Profile
    • Fatboy Effects
Re: How to measure a transformer?
« Reply #4 on: July 09, 2006, 12:53:20 PM »
The red dot may just be polarity marking also.

Here's one way to do it if you have a decent DMM. Set the DMM to measure resistance and on the lowest range available cause you'll be measuring fractions of an ohm.

You should see:

3.3 ohms +/-  between the primary wires.

.8 ohms +/-  between the secondary pairs.


I've tested a few this way and it seems to work pretty consistantly.

HTH

RDV

syndromet

  • Elite
  • ****
  • Posts: 197
  • Chip Points: 38
    • View Profile
Re: How to measure a transformer?
« Reply #5 on: July 09, 2006, 01:37:43 PM »
Thanx, RDV!
Here is the meaurements:
Side 1
Pin1 and 2 - 8,7 ohm
pin1 and 3 - 1.2 ohm
pin2 and 3 - 9.5 ohm

side 2
pin1 and 2 - 0.9 ohm
pin1 and 3 - 1.5 ohm
pin2 and 3 - 1 ohm


Does this tell you anything? The primary should see 230V, by the way.

RDV

  • RIP - 2/5/10
  • Elite
  • ****
  • Posts: 291
  • Chip Points: 419
    • View Profile
    • Fatboy Effects
Re: How to measure a transformer?
« Reply #6 on: July 09, 2006, 03:51:19 PM »
Side 1
Pin1 and 2 - 8,7 ohm = primary =Pin 1 = hot?
pin1 and 3 - 1.2 ohm = Pin 2 = common?
pin2 and 3 - 9.5 ohm = primary = Pin 3 =  hot?

side 2
pin1 and 2 - 0.9 ohm = secondary =Pin 1 = hot?
pin1 and 3 - 1.5 ohm = secondary = Pin 2 = common?
pin2 and 3 - 1 ohm    = secondary = Pin 3 = hot?

My guess would be side 1 being primary, with side 2 being CT secondary. When testing this, you really need to be careful

When taking apart the Pioneer amp it would have been useful to have noted where the mains voltage entered the transformer.

Is the side with the dot side 1?

I'd buy a transformer myself.

RDV
« Last Edit: July 10, 2006, 02:13:17 PM by RDV »

teemuk

  • SSGuitar Global Mod
  • Legendary
  • ****
  • Posts: 1074
  • Chip Points: 282
    • View Profile
Re: How to measure a transformer?
« Reply #7 on: July 10, 2006, 01:56:56 PM »
Pin1 and 3 = Secondary ??! Secondary with such a small resistance to primary side - sounds very unreal. More likely the additional pin in the (assumed) primary is a tap for another voltage. i.e. 220 or 240 V. Makes more sense if you think: pins 3-2 = whole winding (9,5 ohms) = smaller turns ratio, pins 1-2 = little less winding (8,7 ohms) = higher turns ratio. After all 9.5 ohms is pretty close to 8.7 + 1.2 ohms.

Edit: So whatever you do, do not connect only pins 1 and 3 as primary (1,2 ohms): This would probably result into a very high voltage at secondary.

Those resistances seem pretty odd since they should be related to each other. Perhaps you did something that interfered with the probes. I know that sometimes measuring taps like that is pretty difficult. If the secondary is center tapped (I guess it is) resistance between pin 1 and 3 should be pin 1 and 2 + pin 2 and 3. Assuming that pin 2 is the CT. The resistances are pretty similar though.
« Last Edit: July 10, 2006, 02:06:10 PM by teemuk »

RDV

  • RIP - 2/5/10
  • Elite
  • ****
  • Posts: 291
  • Chip Points: 419
    • View Profile
    • Fatboy Effects
Re: How to measure a transformer?
« Reply #8 on: July 10, 2006, 02:14:33 PM »
I'd buy a transformer myself.

RDV

syndromet

  • Elite
  • ****
  • Posts: 197
  • Chip Points: 38
    • View Profile
Re: How to measure a transformer?
« Reply #9 on: July 10, 2006, 05:45:24 PM »
Guess I'll buy a transformer! It seems Pioneer uses this transformer for a AC out,  to supply other stereo components with power.
Now I just have to find the right transformer at the right price. I don't really understand why everything has to be so expensive here in Norway. 50$ +shipping for a regular 24V 200vAC torodial. Guess it is worth it anyhow.

Thanx for the help, guys!

joecool85

  • SSGuitar Admin
  • Legendary
  • ******
  • Posts: 3310
  • Chip Points: 991
  • SSG Creator
    • View Profile
    • thatraymond.com
Re: How to measure a transformer?
« Reply #10 on: July 10, 2006, 07:24:49 PM »
Tranformers are always AC out.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com