Problem transformer and Christmas lights

[DrClaude]

I have a very nice Christmas electric candlestick that is I can no longer get to work properly. Originally, it came with incandescent light bulbs running in 6 V DC. Some of the lights have burned out, so I looked for replacements and can now only find LED lights. The ones I got are labelled as AC/DC 10-55 V, so I bought a new transformer capable of 12 V DC, but I can't get the bulbs to light. I have even tried with a single bulb (out of 7 total), and it lights for a fraction of a second when I flip the switch, but that's it.

Any advice on what is going wrong? Do I need to find another transformer? By the way, I have tired both polarities, but that's not the problem.

 

[Asymptotic]

I have a very nice Christmas electric candlestick that is I can no longer get to work properly. Originally, it came with incandescent light bulbs running in 6 V DC. Some of the lights have burned out, so I looked for replacements and can now only find LED lights. The ones I got are labelled as AC/DC 10-55 V, so I bought a new transformer capable of 12 V DC, but I can't get the bulbs to light. I have even tried with a single bulb (out of 7 total), and it lights for a fraction of a second when I flip the switch, but that's it.

Any advice on what is going wrong? Do I need to find another transformer? By the way, I have tired both polarities, but that's not the problem.
View attachment 216990 View attachment 216991

Image courtesy Bulbtown. Did the originals look more like #46, or #605? The only thought coming to mind for why an 10-55 VDC/AC LED replacement won't work when fed from a 12 VDC, 27W supply is load current is below the minimum for this particular switching supply. Do you have a junk box of resistors at hand, or another way to put more load on the supply?

 

[DrClaude]

Did the originals look more like #46, or #605?

Neither. I have attached a picture of the bulbs. The left one is the old incandescent.

The only thought coming to mind for why an 10-55 VDC/AC LED replacement won't work when fed from a 12 VDC, 27W supply is load current is below the minimum for this particular switching supply. Do you have a junk box of resistors at hand, or another way to put more load on the supply?

I've never been much of an electronics enthusiast I'll try an see if I can find a resistor somewhere. What resistance do you suggest?

 

[Asymptotic]

I'll try an see if I can find a resistor somewhere. What resistance do you suggest?

Supply has 27 watt output rating so if we suppose 10% loading is required to keep the switcher running that's about 3 watts. Voltage is set to 12 volts. P=E²/R, so R=E²/P, or about 48 ohms, so a 47 ohm resistor rated 5W ought to do for the test.

Are there any identifying markings on the original bulb base?

 

[Asymptotic]

Do you have any other power supplies available? Lower current-rated "Wall Wart"s tend to be "linears" that use a transformer, diode bridge, and smoothing capacitor to produce DC as opposed to the pictured switching supply, and don't have the potential of having minimum required load issues.

 

[Asymptotic]

Don't know if this plays a role, but after zooming into your lamp photo to see if any text was visible noticed the original incandescent has one more thread than the LED replacement. Could it be that the bulb is "bottoming out" before making good contact with the center conductor in the lamp base?

 

[jim hardy]

Supply has 27 watt output rating so if we suppose 10% loading is required to keep the switcher running that's about 3 watts. Voltage is set to 12 volts. P=E²/R, so R=E²/P, or about 48 ohms, so a 47 ohm resistor rated 5W ought to do for the test.

Are there any identifying markings on the original bulb base?

Is the Wison switcher the supply that worked with incandescents ?
Good thought, minimum loading... Try a single incandescent , then two, then three , looking for a minimum that makes it happy ?

 

[Dadface]

Rather than buying and messing around with bits and bobs to get the old lights working would it not be cheaper to buy a new light system using LEDs .They are much more energy efficient than the old filament bulbs.

 

[DrClaude]

Do you have any other power supplies available? Lower current-rated "Wall Wart"s tend to be "linears" that use a transformer, diode bridge, and smoothing capacitor to produce DC as opposed to the pictured switching supply, and don't have the potential of having minimum required load issues.

I'll look again at what I have, but on first look I only found 6V transformers.

Don't know if this plays a role, but after zooming into your lamp photo to see if any text was visible noticed the original incandescent has one more thread than the LED replacement. Could it be that the bulb is "bottoming out" before making good contact with the center conductor in the lamp base?

I don't think so. There is a brief flash, so I assumed that the connection is made. Also, it might just be a trick of the photograph. I'll check this evening.

Is the Wison switcher the supply that worked with incandescents ?

No. It is one I bought separately.

Good thought, minimum loading... Try a single incandescent , then two, then three , looking for a minimum that makes it happy ?

Since the incandescent bulbs are rated 6 V, won't I just burn them if I try them at the 12 V needed by the LEDs?

Rather than buying and messing around with bits and bobs to get the old lights working would it not be cheaper to buy a new light system using LEDs .They are much more energy efficient than the old filament bulbs.

That why a started by saying the the candlestick was "very nice" . I can't find a modern equivalent, so I just want it to be able to work with the new bulbs and trying to figure out what transformer will do.

 

[Asymptotic]

I don't think so. There is a brief flash, so I assumed that the connection is made. Also, it might just be a trick of the photograph. I'll check this evening.

You are probably right, but I have a battery-powered LED lantern that becomes increasingly more finicky about (I assume) contact quality the more the batteries become drained. Physically shift the lantern around a bit, and light output abruptly changes from "not a bright as with new batteries, but completely acceptable" to "nothing". There appears to be adequate spring force on the batteries, cleaning contact surfaces yields only marginal to no improvement, but installing fresh batteries eliminates the symptom.

A "can't hurt; might help" maintenance and troubleshooting step is use a pencil eraser to clean the candlestick socket contact, swab it with a Q-tip dampened with alcohol to remove any eraser residue, and see if it helps.

 

[jim hardy]

There is a brief flash, so I assumed that the connection is made.

gosh that sounds like a capacitor charging...

Since the incandescent bulbs are rated 6 V, won't I just burn them if I try them at the 12 V needed by the LEDs?

Yes. But the Winson (or is it Vanson?) has a 6 volt setting...

jim hardy said: ↑
Is the Wison switcher the supply that worked with incandescents ?
No. It is one I bought separately

Hmm . Do you have a similar picture of the original? Or its datasheet ?

 

[Guineafowl]

Are the 7 bulbs just in parallel?

If so, isn’t the switching supply energising, lighting the LED, which then appears as a short, and cutting out?

Surely you need some current limiting.

 

[jim hardy]

I assumed this is the LED lamp information sheet

AC/DC 10-55 V 50 hz seems almost contradictory.

I'd try a 12 VAC wall-wart, maybe a 24 .. They're all labelled somewhere on their case as to output and thrift shops are full of them .

https://www.jameco.com/webapp/wcs/s... AC-to-AC / Wall Transformers&category=452030

 

[Asymptotic]

Are the 7 bulbs just in parallel?

If so, isn’t the switching supply energising, lighting the LED, which then appears as a short, and cutting out?

Surely you need some current limiting.

Thanks for bringing up the number of lamps, because it wasn't clear to me whether they are indeed in parallel, or in a series string. In this case, I'd just as soon learn they are in parallel and pose a larger load to the supply.

Supply is 27 watts max., switchable from 3V to 12V at 2.25 amps. It isn't clear to me how Vinson is specifying this. They have a website, but it appears to be down right now. Found a "manual" at clas ohlson, but it doesn't add to what we know from the sticker. 27 watt/12V = 2.25 amp. Current would be 9 amps at 3 volts (27W/3V), so does the 2.25A current rating mean it can deliver only 6.75 watts when set to 3 volt?

Bulb rating is 0.3W at 10-55 volts AC/DC.
At 12 volts, 0.3W is 25 milliamps.
Seven lamps in parallel is still only 175 milliamps, or 7.8% (0.175A/2.25A) of rated power supply current so we're far from overloading it.

 

[Guineafowl]

Thanks for bringing up the number of lamps, because it wasn't clear to me whether they are indeed in parallel, or in a series string. In this case, I'd just as soon learn they are in parallel and pose a larger load to the supply.

Supply is 27 watts max., switchable from 3V to 12V at 2.25 amps. It isn't clear to me how Vinson is specifying this. They have a website, but it appears to be down right now. Found a "manual" at clas ohlson, but it doesn't add to what we know from the sticker. 27 watt/12V = 2.25 amp. Current would be 9 amps at 3 volts (27W/3V), so does the 2.25A current rating mean it can deliver only 6.75 watts when set to 3 volt?

Bulb rating is 0.3W at 10-55 volts AC/DC.
At 12 volts, 0.3W is 25 milliamps.
Seven lamps in parallel is still only 175 milliamps, or 7.8% (0.175A/2.25A) of rated power supply current so we're far from overloading it.

At 25 mA each, the LEDs won’t overload the supply, but what is there to limit the current?

And if it’s a series string, 12V will be nowhere near enough.

Reverse engineer the device, please, OP!

 

[Asymptotic]

I assumed this is the LED lamp information sheet
View attachment 217022

AC/DC 10-55 V 50 hz seems almost contradictory.

I'd try a 12 VAC wall-wart, maybe a 24 .. They're all labelled somewhere on their case as to output and thrift shops are full of them .

https://www.jameco.com/webapp/wcs/stores/servlet/StoreCatalogDrillDownView?langId=-1&storeId=10001&catalogId=10001&categoryName=cat_4520&subCategoryName=Power Supplies & Wall Adapters / AC-to-AC / Wall Transformers&category=452030

Jim, I've seen LED bulbs intended for industrial pilot lamps similarly rated for AC/DC voltage, but the 50 Hz rating throws me (what, 60 Hz AC doesn't work?).

Been trying to find the LED replacement working back from the 0.3W, 10-55V spec, but I'm going to give it a rest before the babbling commences. :)

Everything so far is not quite right, such as 0.1W at 10-55V - a representative page of a UK supplier featuring flame tip lamps.

 

[DrClaude]

It is 7 bulbs in parallel.

The markings on the original bulbs were 6 V, 0.13 A.

I don't think I have the original transformer, but I don't see why it would be useful. The candlestick is basically just a fancy light bulb holder that connects to the new power supply I got.

Rummaging through old electrical stuff, I was able to find another transformer at 7.5 V, 0.4 A. Tried it just to see what happens, and again the bulbs only light up for a fraction of a second. I'll continue looking for a better transformer.

 

[Guineafowl]

It is 7 bulbs in parallel.

The markings on the original bulbs were 6 V, 0.13 A.

I don't think I have the original transformer, but I don't see why it would be useful. The candlestick is basically just a fancy light bulb holder that connects to the new power supply I got.

Rummaging through old electrical stuff, I was able to find another transformer at 7.5 V, 0.4 A. Tried it just to see what happens, and again the bulbs only light up for a fraction of a second. I'll continue looking for a better transformer.

Was the 7.5V supply a switch mode or linear?

 

[the_emi_guy]

LEDs that are intended to be chained in series may require constant current source vs. contant voltage source. The 10-55V range may be what the supply is expected cough up as we add LEDs while operating at its fixed current.

 

[Asymptotic]

If I had these bulbs, a piece of wire, and a couple of fresh 9V batteries at hand what I'd do is ...

• hold the bulb threaded shell against one battery post, and use the wire to connect the other battery post to the bulb's center connector. If it didn't light I'd swap connection polarity and try again. If it still didn't light then (provided the bulb is OK) a 9V battery won't cut it. Open circuit voltage for a new alkaline 9V battery ranges from 9.4 to 9.5V, and I wouldn't be surprised to learn the bulb does something (perhaps blinks on then off, or glows dimly) connected to a single battery.
• Connect two 9V batteries in series by plugging in the (+) post of battery 'A' to the (-) post of battery 'B', and repeat the previous test. 18V should be well enough to turn on the bulb.

Doing this wouldn't answer why they don't work when connected to this 12V power supply, but at least would answer whether the bulb lights when connected to a DC source somewhat above the 10V minimum specification and what (if anything) happens when connected to a source just shy of it.

 

[jim hardy]

Tried it just to see what happens, and again the bulbs only light up for a fraction of a second.

Sure sounds like they want AC.

 

[DrClaude]

Thank you all for the advice you have given up to now. I'll perform a few experiments tonight and will come back with the results.

 

[the_emi_guy]

If you happen to have an electric train under your Christmas tree, those transformers typically put out AC right in the range that you need.