Transformer issues

[tstage]

Anyone ever have a transformer go bad on them?  I have a 3-month old Miniatronics 1.5VDC "wall-wart" transformer (that I use to run the exterior lighting on my layout) that is acting strange.  The lights initially power up full but immediately reduce to about 1/2 power.  Over a matter of a several minutes the lights get dimmer and dimmer till they are barely glowing.  The outside of the transformer feels fairly warm to the touch but not hot.  It just started tonight so I really haven't had a chance to test it out fully.  Does this sound like a no-brainer problem with the transformer itself?  Thanks.

Tom

[Anonymous]

Anyone ever have a transformer go bad on them?  I have a 3-month old Miniatronics 1.5VDC "wall-wart" transformer (that I use to run the exterior lighting on my layout) that is acting strange.  The lights initially power up full but immediately reduce to about 1/2 power.  Over a matter of a several minutes the lights get dimmer and dimmer till they are barely glowing.  The outside of the transformer feels fairly warm to the touch but not hot.  It just started tonight so I really haven't had a chance to test it out fully.  Does this sound like a no-brainer problem with the transformer itself?  Thanks.

Tom

Since your wall wart puts out DC (instead of AC); it is more than a transformer.  It will have a few other components (capacitor, diodes, resistors, etc.); any of which could go bad.  Without knowing your load (in amps) and if the load actually changed (increased) due to some layout malfunction; it is not possible to really tell where the problem lies.  I would bet on a bad wall wart though.

 

[rrinker]

 That's a regulated power supply, so it could be overloaded, in which case the regulator is shutting down to protect itself, or the regulator is bad. Lucky it didn't fail in an unregulated mode, it could push double the voltage or more to the lights and blow them all out. I'm leaning towards overload, that woukld explain it starting up ok then cutting off.

                             --Randy

[betamax]

Since it's a DC output, there is probably something wrong in the DC section. Any way you look at it, it's junk.

Are you sure it is a 1.5V unit? That sounds pretty low to me. If that is the case, it is probably being overloaded. Probably too much current draw. The primary resistance would be very high at that ratio to limit the seconday current. The turns ratio would be like 100:1.

Transformers don't fail (as a rule) unless you abuse them. I scrapped a lot of current transformers the other day, one of them was purchased in 1927 and used up to the early part of this century.

[jeffrey-wimberly]

Tom, that definately sounds like an overload condition. I used to get that also, when I used small transformers to power lighting. I overcame the problem by pulling the power supply of an old AT type computer and wiring the lights to it.

[jbinkley60]

Tom, what is its current rating and how many lights do you have attached to it ?  It does sound like an over current condition.  If it has over current protection, it may not be toast.  You might try hooking just a few lights to it to see if will output the proper voltage and light the lamps to the proper brightness.  I think I recall you using 60ma lamps.  If so, just remember that 16 bulbs equals 1A.  Also the other thing is that with 1.5V you have to be extra careful about voltage drops.  Far more so than 12V or higher.  Its the same reason that neighborhood electrical distribution legs run at 14,000 volts and higher and not 220V.

 

 

[tstage]

Thanks everyone.  I really appreciate each one of your comments and inquiries.

To answer your questions:

• Michael - Yes, it is a 1.5VDC regulated transformer or power supply.

• Alan & Jeff - I'm using 1.5V-30mA bulbs and only have 12 bulbs hooked up to it so far.  That means that the bulbs are pulling slightly less than 1/4 of the maximum load on the transformer.
  
• Jeff - You were asking about voltage drop.  My longest runs are <4', and those runs I solder 22ga wire to the 30ga light wire.  The 30ga wire that's attached to the bulbs is 8" long.

Just to update everyone.  After I read everyone's comments, I went back downstairs to count the number of lights I had drawing off the transformer.  As I stated above, the count came to a total of 12 - well within the limits.  Just for fun, I plugged the transformer back into the electrical strip and - low and behold - the bulbs light up at full power now, with no overheating or dimming.

I'll double-check it again and leave them on for a little while to see if the problem reoccurs.  I did nothing at all to them between now and the time I posted the original thread.

I'll keep you posted.  Thanks again for the feedback.

Tom

[Anonymous]

Thanks everyone.  I really appreciate each one of your comments and inquiries.

To answer your questions:

Just to update everyone.  After I read everyone's comments, I went back downstairs to count the number of lights I had drawing off the transformer.  As I stated above, the count came to a total of 12 - well within the limits.  Just for fun, I plugged the transformer back into the electrical strip and - low and behold - the bulbs light up at full power now, with no overheating or dimming.

I'll double-check it again and leave them on for a little while to see if the problem reoccurs.  I did nothing at all to them between now and the time I posted the original thread.

I'll keep you posted.  Thanks again for the feedback.

Tom

IF everything continues to work; you have one or two possibilities for the problem (three, if something is really defective). 

1) You could have a high resistance connection where the power supply plugs in to the outlet (corrosion or poor joint - possibly to the actual outlet connections from the feed wire).

2) Some intermittent high resistance short in your lamp wires or supply wires to the lamps.  Something on the load side trying to draw way too much current from the supply.

You might have "corrected" either of these problems by jiggling things while you were checking everything out.  I sure would try my best to cause the problem to show up; so that it can be fixed once and for all (I am sure that your homeowners fire protection clause will rest easier if you can find out what caused your original problem).

 

[jeffrey-wimberly]

That's for sure! I would love to get affordable home insurance. They won't insure a 56 year old trailer.

[jbinkley60]

Tom, I was able to see from the label that it is a 1.5A supply, so yes, you are well within the limits. The voltage drop sounds fine too.  My only point was that a .1V drop at 1.5V is a 6% drop whereas at 12V it is less than 1%.  With the low amount of current and short distances you should be fine.

 

[jim22]

Where did you buy those 1.5v 30ma lamps?  I've been trying to locate some.  Do you have a supplier and part number for them?

Thanks,
Jim

[tstage]

Jim,

I got them from Miniatronics.  The model # is 18-C03-10.  They are 1.5V-30mA, 1.2mm OD, 1000 hr. bulbs.  I picked mine up at Hobby Town for around $10.

Tom

[tstage]

IF everything continues to work; you have one or two possibilities for the problem (three, if something is really defective). 

1) You could have a high resistance connection where the power supply plugs in to the outlet (corrosion or poor joint - possibly to the actual outlet connections from the feed wire).

2) Some intermittent high resistance short in your lamp wires or supply wires to the lamps.  Something on the load side trying to draw way too much current from the supply.

You might have "corrected" either of these problems by jiggling things while you were checking everything out.  I sure would try my best to cause the problem to show up; so that it can be fixed once and for all (I am sure that your homeowners fire protection clause will rest easier if you can find out what caused your original problem).

Alan,

I had a couple of exposed (uninsulated) soldered wire joints underneath the table that I'm wondering whether or not they were touching one another somehow.  That might cause an electrical "ruckus" to the transformer, wouldn't it?

Tom

[Soo Line fan]

Alan,

I had a couple of exposed (uninsulated) soldered wire joints underneath the table that I'm wondering whether or not they were touching one another somehow.  That might cause an electrical "ruckus" to the transformer, wouldn't it?

Tom

Absolutely.

One problem with these wall transformers is that they lack a circuit protection indicator. They are a good source for inexpensive power.

Jim

[rrinker]

 The regulated kind are a little better - if they use one of the common voltage regulator chips to obtain the regulation. Those chips tend to shut themselves off if overloaded as a defensive measure. No short indicator, but at least they tend to not be permanantly damaged. However, the typical unregulated wall-warts usually have a fusible link inside to protect them. One short on the output and that's it, there's no way to fix it.

                                                --Randy

[Tilden]

Jim,

  Minitronics also makes a 1.7 mm 1.5 volt 30 ma lamp with a 5000 hr rating they come 10 in a pack.  LHS has/had them (bought them all).  They were more expensive though about $12.  I don't have the part number on me at the moment but it's close to the 1.2mm number.

[jbinkley60]

I use Miniatronics 14v bulbs with a 16,000hr life rating.  I am hoping to never have to change them.

 

[jeffrey-wimberly]

I'll probably get tarred and feathered for this, but I use an old AT computer power supply to run my lights. The lights are 2.5 volt clear christmas lights. I use two lights wired in series per structure. All the structures are connected in a parallel circuit to the 5 volt side of the power supply. The 12 volt side is used to power specialty lighting fixtures like lamp posts and the such.