Fried Wall-Warts - Are they toast?

Model Railroader Electronics and DCC
1

I now have two wall-wart power supplies that have died. I probably overloaded the first one by gradually adding more and more light bulbs to the circuit until it died. The second went because I mis-wired a light and caused a dead short.

Is there any hope for these things? Somewhere on the forum I read that they use a one-time wire fuse for protection, but once it’s gone, it’s gone. Is there any way to open these things up and replace the wire with a circuit breaker or a replaceable fuse?

I’m planning to put an automotive fuse in-line before I burn out another supply, but I’d rather not just toss these supplies if there’s a chance I can repair them with a bit of effort.

2

Get your hammer! ;o)

They are probably not worth the time it would take to hack the case apart,IMO.

3

Toss them.

Get a multimeter off of ebay for $10.00 including shipping, Buy It Now. I have three of them. Learn how to use the meter. There are plenty of links on how to use a multimeter by searching Google. Look at the specs on the wall wart and calculate on what you can power.

Next time ask here first.

Rich

4

I get my meters from Harbor Freight, $2.99 and no shipping [:D]

But yeah, it’s toast. You don’t even have to overload them, a slight short while hookign somethign up usually takes out the fusible link. Best thing is to get a circuit breaker rated at slightly under the wal-wart’s specs and use that, that way you won;t have to keep buying fuses when somethign shorts out.

–Randy

5

Right now Harbor Freight has them for $9.99. They just re-did their website. They are on sale every so often. I am on their email list for sales. I have their brick and motor store about ten miles from me. I have yet to check it out. Retired industrial machine mechanic so hard to justify new tools.

Rich

6

I wouldn;t use most of the Harbor Freight stuff as serious heavy duty tools. Their stuff is great for occasional use, but you do tend to get what you pay for. Now, as a source of something like cheap foam paintbrushes that you are just going to throw out, sure. Check out the actual store - I haven’t seen a sale flyer for some time that had the multimeters for $2.99 but they did have them in my local store at that price. Again, at $2.99 it’s not the greatest meter but it is more than sufficient for typical model railroad use. I have like 3 of them, on I keep in my car, one in my DCC toolbox, and one in my desk. If I need some seriously accurate measurements I have a Fluke benchtop meter, but I would have never paid for it - nothing I do ever needs more precision than the cheapy can give me. I was given the Fluke for free and it is pretty cool but definitely not required. Using the ultra low ohm,s range on a 20 foot spool of wire is kind of neat.and it seems to be able to get a more accurate reading on the DCC waveform than a cheapy meter but it’s still not accurate because it’s designed for standard sine wave AC.

–Randy

7

You seriously need to be careful where you buy those “wall wart” power supply’s A buddy of mine is a battalion commander in the FDNY and he was here over the holidays visiting he asked me what i was using them for as he saw a couple of them sitting on some bench work. He told me they are probably one of the biggest single causes of fires in the home. I was dumbfounded (which really isn’t all that hard to do) But as he pointed out a lot of them do tend to get pretty hot. He told me that what happens on some of the cheaper “import” crap and lets let it go at that. So for peace of mind sake I would stay as far away from Harbor Freight and maybe check out a Radio Shack store not necessarily to buy one but t get some what of an education on them. Is the difference in price really worth the risk?

8

All of the power to my trains goes through a couple of switched outlet strips, so everything gets shut off when I’m done in the train room. It’s not only a safety thing. Even when they aren’t drawing power to light bulbs, etc., wall-warts are still running and using energy. Yes, that includes your cell-phone charger. So, it’s always best to unplug them.

9

I was suggesting Harbor Freight as a place to get a multimeter, not wall-warts. Not even sure if they have them, other than in tools that might come with one.

And yes, the simplest precaution against fires is to NEVER leave anything running when you’re not there. There seems to be a ‘thing’ with DCC users about leaving the system powered up but in a ‘sleep’ mode between uses - NO WAY. Turn it all off, and if you can’t have the room wired so that there is a single wall switch controlling everything, then pull the plug. It very hard (but alas not impossible) for lightning to damage things that are completely unplugged (thinking DCC here so no tv cable or phone line). It’s also pretty much certain that a completely disconnected electrical device cannot start a fire. There are many potential hazards in the train room, from the electrical and electronic equipment to soldering irons, lights in enclosed spaces, and power tools. Be smart - disconnect it ALL when you aren’t around. Why chance it?

–Randy

10

I once tried repairing the fusible link in a wall wart for a cordless tool; it wasn’t worth the time I spent trying to open the glued-together case.

The best advice, which has already been pointed out, is to properly fuse and not overload the wall wart in the first place.

I’m also in complete agreement with Randy’s advice about powering EVERYTHING down in the train room when you’re not there. Mine is hard-wired so that a single wall switch by the door will kill everything, but the same thing can usually be accomplished by using a switched power strip, or better yet, a switched surge protector.

11

Mr. B.

I have done the Wall wart power supply burn-out dance several times now. Some stuff that I learned over the last four years (and three burnt out wall warts later)

  1. Don’t cheap out. The cost of several $10.00 wall warts that die will equal the cost of a regulated, high quality supply. Some cheapies just quit after a time or fry if over loaded. I am very frugal (cheap), it took me awhile to figure this one out.

  2. Cheap wall warts are unregulated. What this means is the voltage drops as the supply reaches rated amp capacity. New 12 VDC supplies usually start at around 14 VDC unloaded and eventually fall to 12 VDC as you add load to the circuit. This will usually happen gradually over time as you add more stuff to your power supply circuit. Does this matter?? Sure it does. If you set up your lighting resistors to look good at the voltage supplied when the supply is unloaded then they will dim as the voltage drops. Stall motors set with resistors when the supply load is light get balky as the voltage drops (don’t ask how I know this). Regulated supplies keep a steady voltage regardless of the load. I have now come to see the value in this. I had to cough up the bucks for regulated supplies.

  3. I didn’t realize how large the load on my RR had become. It is easy to overload the circuit as you add stuff. Some units will still work but will eventually burn out. Measure the amperage draw and then get the right size supply. Sounds like you have already been here. I had to buy larger amp capacity units.

Rob Paisley has a few links to digikey regulated power supplies here:

http://home.cogeco.ca/~rpaisley4/PSupply.html

scroll to mid

12

The real issue is users not realizing the current limitations of cheap wall warts. I have used them for some years but never use them at over 50 percent of their current capacity. I sometimes use a LM317 regulator, couple resistors, couple electrolytic capacitors for stable supply and then do not go over 50 percent of the wall wart capability.

Our club has used an old MRC throttle that has DC voltage for accessories since the 1980s. It is used for PFM and Tortoise machines and I tap off the 14 volts DC with LM317, TO-92, 200 ma or LM317 TO-220 case regulators for 5 volt logic circuits.

A couple wall warts are used to power Digital Panel Meters that monitor the DCC amp meter for remote viewing. The DPM’s do not have isolated ground and require their own isolated DC supply which are only are few milliamp’s each. Cheap enough.

Rich

13

Good example, I just scrounged a fairly heavy wall-wart from work, rated 12V at 1.5 amps. I cut the plug off that was on it, some proprietary thing for the device it was menat for, had like 10 pins in a min-DIN style connector. Behind all that - TWO wires! lol. I plugged it in and hooked up my meter - with no load it was 16.0 volts. It’s heavy enough to be a regular transformer and rectifier, not a switching supply, but I’ll lay more than even odds that any filtering was done inside the device to which it was connected.

–Randy

14

Well, I thank all of you for your advice and your sympathy. Before I started this grand adventure, I’d already ordered another supply, this time from All Electronics. So, I had a backup to put in once I figured out what was wrong.

As I suspected, I had a dead short. In all my crawling around over the last few months to add new wiring for Phase 2 of the layout, I knocked some wires loose, and put them back together, well, together. Not good, but fortunately easy to find and correct, the right way this time, with solder and electrical tape rather than crudely twisting them together and saying, “I’ll solder that next time I’ve got the iron out.”

The new supply is 4 Amps at 12VDC. I wanted slightly smaller fuses, but all Radio $hack had was 4 amps, so I got those. Once I’d wired in the fuse holder, I slowly brought up the load, which is separated into a half-dozen different sub-buses, each with its own toggle. As it turns out, I am drawing just under 3 amps, so the next supply I buy will be 5 amps to give me a bit mroe headroom.

So, the short took out a 4.5 amp supply, but what happened to the previous one? I took a look at it. This noble wart was rated at 1500 ma, so it ran for months at close to twice its rating. No wonder it finally gave up.

I now have this circuit fused, and I know about how much each of the sub-buses on the circuit draws. I’ve also learned that, unlike old train transformers, there are no circuit breakers in wall warts, and dead is dead forever.

15

My mantra is, “Distributed power supplies.” Every operating locomotive has its very own power pack (rated at something well in excess of the anticipated power draw - I don’t try to power catenary motors with two open frame juice hogs from a Life-Like toy train pack.) Each operating zone has its own dedicated switch machine and cosmetic lighting sources (plural intentional.) Even if my total structural lighting load begins to approach that of my room lighting I won’t be pushing any individuual supply to anywhere near its maximum.

I think highly of 3 amp filament transformers for accessory power (and as a basis for D-I-Y propulsion power packs.) Granted they have to be wired (properly) to 120VAC house power - mine reside in insulated housings and connect to the 120 through properly polarized plugs. Since they are center-tapped, each one has, effectively, 6 amps of 6.3VAC available for signal, structure and panel lamps if used for that purpose. Just bought three from AllElectronics, for the same price as wall warts with less than half their capacity.

As for wall warts and toy power packs, I have a choice collection that may get pressed into service if I need some low power supplies for animation or similar purposes.

Speaking of 120VAC, ALL of my layout electricals run off a single 20 amp ‘super extension cord’ plugged into the ceiling receptacle meant for the garage door opener that vanished with a previous owner. The master switch is mounted in the layout fascia directly opposite the room lighting switch. When I leave the layout space both switches are OFF - as is everything electrical in the room.

Chuck (Modeling Central Japan in September, 1964 - with adequate, safe electrical power)

16

I think your theory is good and quite frankly handle my own 120VAC power the same way. It is however a code violation to plug and RPT (power strip) or a second extension cord into an extension cord. Like I said, I do it too but since doing so violates International Fire Code. An insurance company may use it to beat a claim.

http://www.uiweb.uidaho.edu/safety/Electrical/0712-region2.pdf

UL RPT

17

To clarify, ‘super extension cord:’

One plug, into existing house power receptacle (dedicated 15A circuit, with a standard breaker in the main breaker box,) on the plug end of what used to be a 20A 100 foot outdoor exten