12V lighting track ghost voltage?

[tortuga]

Greetings all I was sent to troubleshoot some 12V lighting track, it was installed about 7-8 months ago and has been burning thru lamps.
Its your typical low voltage halogen, two exposed aluminum bars are the voltage rails.
The track is working, and has no dimmer. The owner has the correct lamps 20W MR-16 but they are burning out in a month or two. Recently they also tried LED's
They observed the LED's to flicker and burn out one by one in a few days.
I have troubleshooted this kinda things before and its usually a dimmer issue, so I was thrown off by the no dimmer.
Then I took all the lamps out but one 20W halogen when I went to measure voltage between the two rails I only get 1-2 volts.
I would expect 12.
From each rail I get 10V to the metal case of the power supply.
If I put all the lamps in or take them all out still the same reading.
I checked my meter to make sure it was working, scratched the aluminum still 1-2 volts.
Then I used a different meter, still same reading.
Checked at the MR-16 socket still no voltage, but the 20W halogens were on and full brightness.
What am I missing here? how can the lamps be working with no apparent L-L voltage?

 

[synchro]

Can you measure the voltage across the contacts inside one of the lamp sockets? Perhaps you aren't getting a good connection to the rails for some reason.

 

[Electromatic]

I think there is something about the way a lot of electronic transformers for lighting operate that is incompatible with how most multimeters take readings. I can't remember the technical explanation but have often not been able to rely on my meter for troubleshooting low voltage lights.

 

[tortuga]

Can you measure the voltage across the contacts inside one of the lamp sockets? Perhaps you aren't getting a good connection to the rails for some reason.

I tired that also still very little voltage, like 1-2 volts

 

[Electromatic]

The video in this link isn't great but it does confirm some of what I said above.

https://www.electronicink.com/why-multimeter-wont-read-electronic-transformers/

 

[synchro]

Just speculating, but maybe the electronic transformer output waveform is switching at a higher frequency than your meter can handle accurately. Or maybe it's a DC voltage, but I'm not sure why that would be necessary for the application. You might set the meter to measure DC and then see what difference it makes.

 

[tortuga]

The video in this link isn't great but it does confirm some of what I said above.

https://www.electronicink.com/why-multimeter-wont-read-electronic-transformers/

Thats it thanks, I did not realize its a square wave so a regular meter cant pick it up, I'll have to remember to bring my old Simpson when I go back.

Or maybe it's a DC voltage

I did try my meter on DC also still nothing, and with the 20 watt halogen bulb on.
Guess that part of the mystery is solved.
Still need to figure out why its going thru bulbs so quickly.
Thanks all

 

[Seven-Delta-FortyOne]

Someone here with far more knowledge than myself could probably confirm or deny or further explain this, but it’s my understanding that peak voltage lasts longer on a square wave than a sine wave.

RMS voltage on a sine wave wave is .707 of peak. Whereas RMS on square wave is 1.

If I remember correctly, total power output is higher on square wave for the same voltage.

Also, square wave can mess with any solid state drivers or other components.

 

[Electromatic]

If the lamps are the two tiny pin base type, a lot of the time the spring clip contacts in the socket often get loose making poor contact with the lamp and causing failure. That would explain the flickering as well. I've ordered replacement sockets before, but the mounting can get tricky. It's usually better to replace the whole head and look for something with a different socket base.

 

[Dennis Alwon]

I had taken a 12v electronic transformer that I could not get any reading on it. I started a thread a long time ago about it.

12V Transformers

I have had a bunch of low voltage 120v- 12V ac transformers that I cannot measure the voltage. In fact, one specifically states not to measure the secondary side of the transformer but I cannot remember if that was a driver or a trany. I have used 4 different brand meters with the same result...

forums.mikeholt.com

 

[synchro]

... it’s my understanding that peak voltage lasts longer on a square wave than a sine wave.

Yes, the voltage stays at a constant value for nearly an entire half cycle, and so that value would be the essentially the same as the peak value.

RMS voltage on a sine wave wave is .707 of peak. Whereas RMS on square wave is 1.

Yes, the RMS of a practical "square wave" would get closer and closer to 1X of its peak value as the transitions between levels get shorter and shorter. In most cases assuming a 1X factor is close enough.

If I remember correctly, total power output is higher on square wave for the same voltage.

Yes. For the same peak value of the voltage, the power with a square wave would be 2X that with a sine wave. That's because the mean square (the "MS" in RMS) of a sine wave is 1/2 of its peak value. And so the RMS (Root Mean Square) of a sine wave is √ (1/2) = 0.707 of the peak value.

 

[tortuga]

I had taken a 12v electronic transformer that I could not get any reading on it. I started a thread a long time ago about it.

12V Transformers

I have had a bunch of low voltage 120v- 12V ac transformers that I cannot measure the voltage. In fact, one specifically states not to measure the secondary side of the transformer but I cannot remember if that was a driver or a trany. I have used 4 different brand meters with the same result...

forums.mikeholt.com

Interesting, yeah you had the same type of power supply units.
You should have mailed one to gar for analysis.
I am glad I still have a Simpson 260, however I don't keep it on my work van.
So are all these 'electronic low voltage' power supplies for 12V track a square wave?
Is there some advantage to them for dimming or lamp life or something?

 

[synchro]

So are all these 'electronic low voltage' power supplies for 12V track a square wave?
Is there some advantage to them for dimming or lamp life or something?

I suspect it's because high efficiency power electronics always involves switching circuity, and outputting just a raw square wave would be the cheapest thing to do. You could make a sine wave using a PWM driver followed by some filtering, but that would be considerably more expensive. And for lighting such as halogens it provides no significant advantages. The duty cycle of a square wave (and therefore the delivered power) can also be varied to implement dimming with negligible extra cost because it can be done within a digital controller that's likely there for other purposes.

 

[hillbilly1]

I think there is something about the way a lot of electronic transformers for lighting operate that is incompatible with how most multimeters take readings. I can't remember the technical explanation but have often not been able to rely on my meter for troubleshooting low voltage lights.

I had that issue the other day, lamp was burning, but track shown no voltage. I know electronic transformers will show no output with no load, but this was strange. Hooked my circuit tracer to it, it lit up and worked, double-checked my meter on an outlet, worked fine.

 

[gar]

220415-2125 EDT

I am going to make some broad statements on the problem.

First, ignore LEDs and just consider tungsten filament halogen bulbs. A tungsten filament has a positive resistance temperature coefficient. This means that as you raise the temperature of the filament the resistance increases. From memory I think that a 100 W bulb is about 10 to 12 ohms resistance when the filament is at room temperature. At 120 V it is about 0.8 A or R = 144 ohms. This remains very close to a constant value when excited with 60 Hz or higher, or DC.

If you power the bulb from a sine wave of sufficient frequency, 60 Hz is adequate, then brightness will be near some design level. Create another bulb of equal wattage, but designed for 12 V, then current goes to 8 A. Make a further change to 1.2 V and now current is 80 A.

Change the waveform from a sine wave to some other shape, then for the same brightness the RMS current will have to be the same as for what the bulb was designed to work at.

An electrodynamic meter within some frequency limitations will read RMS current to a load. An electronic meter may do a comparable job, depends upon design. A Simpson 260/270 is basically a DC instrument. So it should provide good information on DC. For AC it uses a rectifier and is calibrated in RMS for a sine wave. In AC it is really measuring an average value, and on different waveforms its reading will differ from that of a true RMS meter.

Possibly a little more after some responses.

.

 

[tortuga]

220415-2125 EDT

I am going to make some broad statements on the problem.

Gar the problem I was sent to solve is the brand new track system is burning thru lamps
both MR-16 20Watt 12 volt halogen that the manufacturer 'supports' and the Feit MR-16 LED the homeowner bought from home depot.

First, ignore LEDs

Ok done

and just consider tungsten filament halogen bulbs. A tungsten filament has a positive resistance temperature coefficient. This means that as you raise the temperature of the filament the resistance increases. From memory I think that a 100 W bulb is about 10 to 12 ohms resistance when the filament is at room temperature. At 120 V it is about 0.8 A or R = 144 ohms. This remains very close to a constant value when excited with 60 Hz or higher, or DC.

If you power the bulb from a sine wave of sufficient frequency, 60 Hz is adequate, then brightness will be near some design level.

OK got it

Create another bulb of equal wattage, but designed for 12 V, then current goes to 8 A. Make a further change to 1.2 V and now current is 80 A.

Change the waveform from a sine wave to some other shape, then for the same brightness the RMS current will have to be the same as for what the bulb was designed to work at.

Interesting

An electrodynamic meter within some frequency limitations will read RMS current to a load. An electronic meter may do a comparable job, depends upon design. A Simpson 260/270 is basically a DC instrument. So it should provide good information on DC. For AC it uses a rectifier and is calibrated in RMS for a sine wave. In AC it is really measuring an average value, and on different waveforms its reading will differ from that of a true RMS meter.

Possibly a little more after some responses.

.

Like I said I do have a Simpson 260, I do have access to a few scopes also.
I am planning on borrowing a scope and one of these electronic low voltage (ELV) lighting supplies this weekend and running some tests with a 20W 12V MR16 lamp.
I am not really good with the scope other than pushing buttons like 'auto range'
EDIT: the scope I grabbed is a Rigol DS1054Z
Cheers
Tortuga

 

[LarryFine]

Can you hide a low-value, high-wattage resistor somewhere, and wire it in series with the load?

 

[synchro]

There are apps for smartphones that purportedly can measure the color temperature of a light source that's illuminating a white surface such as a piece of paper. Perhaps you could use this to measure the color temperature of an MR-16 bulb powered by a known 12V AC or DC source, and then compare it to the color temperature when powered by the electronic transformer. A higher color temperature would correspond to a higher bulb filament temperature that could shorten its life.

At the app at the link below is the first one I found, and it's for Android phones (cost is 99 cents). But I believe there are ones for iPhones as well.
There seems to be some controversy about how good the accuracy of the app is when used on various phones. But for the purpose mentioned above the absolute accuracy doesn't matter, because it's just a comparison to see whether there's any significant difference.

https://play.google.com/store/apps/details?id=cassiopeia.camera&hl=en_US&gl=US

 

[gar]

220416-0832 EDT

When I look up an MR 16 incandescent bulb they appear to be 120 V and rated 50 W. Then at

L515 MR16 11° 20W Halogen Lamp

www.intl-lighttech.com

I find a rating of 12 V, 1.67 A and 20 W. So this is probably your bulb rating,

I would take one of your bulbs, apply 6 V DC, and see how bright it is. If it is a12 V bulb, then it won't glow real bright and be sort of orange.
If that seems to be the result, then increase the voltage to 12 V ( your car battery with engine off for maybe 8 hours ). Now you should have high brightness.

A Simpson 260 in AC mode has good bandwidth capability. Like out to around more than 500 kHz, and it gradually drops after that. To strip any DC component you use the OUTPUT terminal on a Simpson 260. Whereas my Fluke 27 goes to about 400 to 500 kHz, then just drops. What other meters do I don't know.

Try to get your meter across the two bus bars that connect to the two bulb pins.

Your scope can be of great assistance in providing a means to see the frequency of the AC excitation to the bulbs. I very much doubt the bulbs are fed DC.

If an AC square wave is feeding the bulbs, then its peak should be near 12 V for 12 V bulbs. That would be 24 V peak to peak, or if a sine wave 12 V RMS.

.

 

[hbiss]

I went to measure voltage between the two rails I only get 1-2 volts.

Sure sounds like it's DC. Did you at least switch your meter to DC and see what it says?

-Hal