# Thread: multi tap transformer

1. what is the resistance supposed to be on a 208/240 pri 24v sec 40 va transformer, i know when its bad, ive replace many in my time in the field, but was wondering!
like what scale do i check it on? high res or low res? this one that i have right now is bad, no 24v on sec, and i have 240v pri, when i checked the resistance earlier on 400k ohm i got nothing but on 200k ohms i got a reading.I know this is a stupid question but never hurts to learn more

2. Professional Member
Join Date
Nov 2001
Posts
1,874
Post Likes
Ohm out a good and you'll have your answere.

That will be different from a 120 to 24,
the number of windings will be different.

3. Why would anybody care what the resistance is?

Voltage in + no voltage out = bad transformer.

Keep it simple.

Be sure you find the short before you leave it.

4. Professional Member
Join Date
Nov 2001
Posts
1,874
Post Likes
Originally posted by Wild Leg

Be sure you find the short before you leave it.

They don't always have shorts,
Some just break down and burn up.

5. I don't know i guess i was bored!

6. Professional Member
Join Date
Nov 2001
Posts
1,874
Post Likes
Stay in the field long enough you'll find plenty to rattle the brain

7. Odds are you are looking at the secondary with your ohm meter for the failure. Better odds suggest that you look at the high voltage side since it is likely the turns that are open.

8. Regular Guest
Join Date
Sep 2006
Posts
91
Post Likes
If V=IR
Your V is 26v You I for a 40Va is 40Va / 26V ~ 1.5a

Then 26v / 1.5a ~ 17 ohms?

Now I gotta go check...

9. Regular Guest
Join Date
Sep 2006
Posts
91
Post Likes
Originally posted by stafford
If V=IR
Your V is 26v You I for a 40Va is 40Va / 26V ~ 1.5a

Then 26v / 1.5a ~ 17 ohms?

Now I gotta go check...

I measured 1.1 on the secondary, 56 on the 230v primary

Always knew that Ohm guy was full of crap.
Man I need a service call

10. Only reason to know is if wires are un-indentifiable....

11. Regular Guest
Join Date
Jun 2006
Posts
451
Post Likes
Odds are, the leads on your meter are intermittant or you have some other measurement issue or operator error.

Stafford:

Learn the diffeence between impedance and resistance.

[Edited by keepitsimplestupid on 11-02-2006 at 08:23 PM]

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•

## Related Forums

The place where Electrical professionals meet.