Tortoise switch machine power supply problems

[dadret]

I have about 16 Tortoise switch machines on my layout hooked up to one 12V, 500ma, power supply using cross wired DPDT switches (Option 1 on the tortoise manual).  Most of the time they all work fine but for some reason completely unknown to me every few months I burn up the power supply - the power supply is completely dead and usually (at least on two of them) there is a noticable bulge in the side of the adapter.  All I do to fix it is put in a new power supply but I'd like to know why this is happening.  Any ideas?  I've checked the wiring for shorts, bare wires, crossed wires, etc and can't find anything.  I think (but am not completely sure) that this generally happens after I have added some new switch machines or done some work on the machines (and yes I work on them with the electricity on).

[Texas Zepher]

I have about 16 Tortoise switch machines on my layout hooked up to one 12V, 500ma, power supply ....every few months I burn up the power supply

If each one of those is pulling 25 ma. then the constant drain on the system is 400 ma.  That is a bit tight for my reconing.

 Any ideas?  ....I work on them with the electricity on).

Don't do that.

I would get a heavier power supply or get a second one and split the tortoise between them.  I would not work on them powered.

[dstarr]

   Hard to say.  Your total tortoise load is somewhere between 320 and 400 mA which is less than the 500 mA rating of the power supply.  You might try looking for a beefier power supply, just on general principles.  Or it could just be bad luck.  If it's going to fail, electronic stuff tend to fail when young as defective parts let go under load.  After running for a couple months, it will most likely run for years and years.  How long had your power packs been in service before they croaked?  couple a weeks? couple a months? couple a years. 

   Could be a lightning hit.  I lost the 12V 500 mA power supply for my router in an electrical storm.  

   The bulge in the case suggests a part, perhaps an electrolytic capacitor, blew up but the bang was contained by the casework and potting compound.   Manufacture of electrolytics is not well under stood, the industry has suffered from batches of bad electrolytics for years.  The first one I heard of was the GE CL65's on the antiballistic missle program back in the early 1970's.  Last one was a bunch of tantalum jobs going bad at Teradyne in 2003.  Were both failed units from the same maker?  If so, the maker could have had the bad luck to put a batch of bad capacitors into his entire production run before noticing the problem.  

    You might check the voltage out of the wall socket.  Should be between 115 and 125 VAC. Every so often bad things happen to house wiring and voltage goes way out of limits.   

[BigG]

  Hi. Something else to think about...  Where is the supply mounted? It is common for them to be a bit warm, but if the heat cannot be radiated away, it'll cause failure like you are having. Since you are running close to the supply's limit, I'd be going after a beefier supply (I consider 80% of the rated output to be tops for continuous use), or as suggested, split the load between 2 separate supplies. Do not connect supplies in parallel in an attempt to raise the available current! That is an invite for a fire.

    Have fun,   George

[jrbernier]

  A Tortoise normally draws about 17-18 ma when 'stalled'.  I would think your 500 ma 'wall wart' should handle it.  I have 11 Tortoises powered by a 850 ma unit and have had no problem(powered on for over a year).  Our club has a panel with about 16 Tortoises powered by a single Miniatronics WT16(800 ma/16VAC) wall wart power supply.  I suspect your power unit just is not capable of sustained power delivery.

  BTW, I am using the common ground AC wiring method in the Tortoise instructions using a pair of diodes - Works very well!

Jim

[dadret]

Thanks for the advise - I'm going to change to a 1000ma adapter and start turing off the power when the layout is not in use - the price of power supplies is going up too.

[BCSJ]

I'm a bit suspicious about the ventilation around the power supply. If you're close to rated power then you can be suffering from heat build up. If there is no air cirulation around the power supply then you are likely drastically shortening its life.

If, after it's been running for a few hours you can reach in and put your hand on the power supply and keep it there then you likely have enough ventilation. HOWEVER do NO just stick your hand on the power supply - hover it around slowly getting closer giving your hand time to tell you there is something very hot nearby. You could save yourself a nasty burn.

Finally,

1) are you sure there is nothing else attached to the power supply?

2) are you sure that there isn't some magic combination of electrical switches or contacts that shorts the supplies's output? Do you have track power wired to the contacts on the Tortoises? If so are there any shorts between the Tortoise motor power pins and other pins shorting your power supplies to the track?

3) Have you triple checked your wiring for shorts to *anything* else?

Good luck to you,

Charlie Comstock 

[steamnut]

All evidence is that your supply cannot handle the actual sustained current. If you are using a "wall wart" their ratings are often suspect, especially for sustained use. I am sure that if you go to a boxed 1 amp (1000 ma) supply you will never experience this problem again.

[BlueHillsCPR]

All evidence is that your supply cannot handle the actual sustained current. If you are using a "wall wart" their ratings are often suspect, especially for sustained use. I am sure that if you go to a boxed 1 amp (1000 ma) supply you will never experience this problem again.

That is my feeling too.  Also I believe you get what you pay for when buying power supplies.  Cheap is usually cheap for a reason.  If the wall warts are a problem maybe a converted computer power supply is a better way to go?