Step Down Transformer working but over heating feed back wanted

sam_sam_sam

Could any one answer this question for me

It take about 15 minutes for this Transformer to get so hot that you can hold on to it any more

The resistance test from winding to core is open
The resistance test from primary winding to secondary winding is open

This is with a 1.25 amp load on the Transformer load keep working even when the Transformer keeps getting hotter and hotter

Here are the speck to this Transformer

120 volts primary
19 volt secondary
2.2 amps

13.4 ohms primary winding
1 ohms secondary winding

Can any one tell me what could be wrong with this Transformer

This Transformer was powering my gate which was hit by lighting
which took out the following

Position Controller >>>> took a hit would NOT send commands to H25 Motor Controller >>> New Board
Basic Stamp Board >>>> took a hit >>> New Board Kit
Basic Stamp Chip >>>>> took a hit >>> New
Power transformer >>>> took a hit >>>> Replaced LED and by passed Fuse transformer over heats BIG TIME :skull: :skull::skull: >>>>>> BAD
H25 Motor Controller >>>> ????? more testing need to be done Replaced with new one
Memory Chip OK >>>> ???? Did not try to program with this chip yet


These speck are the same for the new Transformer the same part #
Which dose not over heat

Same 1.25 amp load over night Transformer is just warm

bill190

Measure the resistance of the primary winding and then the resistance of the secondary winding. See if you get what the specs say...

13.4 ohms primary winding
1 ohms secondary winding
(Per what you wrote above...)

The wires in a transformer are wrapped round and round. And the wire has an insulation on it. Perhaps that insulation has broken down somewhere within one winding or another? (In which case the resistance would be lower than spec.)

Also might want to measure the voltage output on the secondary and see what you are getting...

Basically if it is getting that hot, I would toss it, but might be interesting to find out what the problem is...

Franklin

If the windings have come loose or were damaged they could be setting up eddy currents in the core and heating it. Google induction heating for more info.

David B

So if it has a shorted turn, then it should get hot even with no external load.

You've said it gets hot with a 1.25 amp load.

Have you, or can you, run it for about 15 minutes with no load, and see if it gets hot?

sam_sam_sam

I will try this and see if it get as hot with no load on it

These reading are the same for both Transformer check with a meter
13.4 ohms primary winding
1 ohms secondary winding


Here are the speck that where on the case of both Transformer


120 volts primary
19 volt secondary
2.2 amps


The wires in a transformer are wrapped round and round. And the wire has an insulation on it. Perhaps that insulation has broken down somewhere within one winding or another?

The new one and the old one that over heats has the same resistance of the secondary winding
(In which case the resistance would be lower than spec.)

Bobb Fwed

I have looked for transformers recently, and found that more than a few manufactures state in their datasheets to expect the transformer to get hot. Some stated that an increase in temperature of 45C (113F) is normal. That's getting close to 200F!

I made a circuit with a transformer a while back, and it always got hot. The transformer was rated for 1.5A and I was only pulling 1A. They got burning hot. I added a fan over them in the enclosure, and it helped a bit. I am hoping it more so helps the longevity.

erco

Clearly something got fried inside. It's easier, faster & safer to replace a known overheating transformer than try to fix it.

The Shack has a candidate for $10.49 if you can live with 25V, 2A: http://www.radioshack.com/product/index.jsp?productId=2102703

sam_sam_sam

I bought a new transformer for it I had to buy a transformer that was for the charging board which I keep from the old gate opener board

I put the new transformer at the gate and it works good now

I just was want to understand how a transformer that seem to have the same resistance reading one would run hot and other would just warm

Most of the time a transformer would either have a open winding on the primary winding or secondary winding but not like this one where it get hotter as it running

sam_sam_sam

Thanks to all that replied to this post

LoopyByteloose

You say 13.4 ohms on the 120 volt primary.

120/13.4 = 8.95 amps

8.95 amps x 120 volts = 1074 watts of input

2.25 amps x 19 volts = 42 watts of output.

Hmmm. That 1000 plus watts has to go somewhere. It is difficult to believe that the new replacement has a 13.4 ohm primary too, but you might get the same reading because the meter voltage isn't high enough to work through the damaged insulation. Face it, lightning is extreme HV and tends to carbonize insulation. I suspect that if you did a 'post-mortem' and took the damaged transformer apart, you would see insulation damage.

sam_sam_sam

Some time when I have nothing beter to do I will take this Transformer apart and see what happen to it

btw most of the time if the max output on the secondary is 2.2 amps the
primary should be 1.1 amps or so at least that is what I seen in the past

Alan Bradford

The measurements you are making are DC and the transformer is AC.
When the magnetic field builds up the reactance is higher reducing the AC current.

You may have damaged insulation in the windings that will not show up on a DC ohm meter.
When the voltage goes to 120, the internal windings may be shorting out to each other and/or to the core.

Measure the input current on both transformers, with the 1.5 amp output.
Im sure you will see the old transformer draws much more input current than the new one.

It was a good idea to replace it.

LoopyByteloose

Forgive the shameless oversimplification. Resistance on a coil in an AC circuit means next to nothing in terms of what is really going.

But it does help to show that math is always involved and you MUST do calculations to determine failures - Ohm's Law AND the Power Equation are useful info about failure. And since Watts in excess converts to destructive heat, knowing the expected power consumption in comparison to the reality is very usefu.

The actual circuit in use has a combination of Resistance and Impedance. And ohm-meter might show a short in some cases or a complete open circuit, but the numbers are incomplete (no figure for impedance).

Properly measuring a faulty device would best be done with an AC amp-meter inserted into an actual 120VAC circuit (if and when it is safe to do so). A comparison of the new and the old would be obvious

Then the amps x volts would reflect real power consumption (but that heat is already telling you that it is way over the top).

Heat is always a useful indicator and when I build a new board, I power it up and immediately touch all the components to see if something is getting hot. Sure, I sometimes get burned fingers, but I do prevent a lot of damage due to solder bridges and other errors.

sam_sam_sam

Up Date

Ran this transformer until the next day with no load the transformer ran very very almost to the point of being to HOT to hold on to it dose not heat up real fast with no load

So I do not know but will not use for any thing where it has to be power hours and hours

David B

Sometimes parts break. If I were you I'd throw it away. Or take it apart. I wouldn't suggest using a lightning-damaged transformer for anything; it's a fire hazard waiting to happen.