Resistor to trick 12v transformer

In summary, a new user is asking for help with a 12V transformer not lighting their LED lights. They have tried adding an incandescent bulb, which works, but they are looking for a different solution. Other users suggest checking the specs of the LED lights and the transformer, as well as trying different wiring configurations. It is suggested that the transformer may be a switching mode power supply and needs sufficient load resistance to operate. The conversation also involves discussions about load balancing and polarity.
  • #1
Joel2010
14
0
Hi guys, new here. I was wondering if anyone knew of a way to trick a 12 volt transformer into seeing more load. I have these lights http://www.lowes.com/pd_172832-24969-800CBL5N_0_?productId=1207073&Ntt=tiella&Ntk=i_products&pl=1&currentURL=/pl__0__s?newSearch=true$Ntt=tiella$y=0$x=0" and it won't light them. If I put back in 1 of the 20 watters it works.
So what I need to know is, would something like this work? https://www.amazon.com/dp/B0002KR4HU/?tag=pfamazon01-20
Any help would be greatly appreciated.
 
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  • #2
If you check out motorcycle accessory catalogs on-line you will see lots of gadgets to add load to lighting circuits so incandescent bulbs can be replaced with L.E.D. arrays. Perhaps one of those would fit your application.
 
  • #3
Any idea how many ohms and amps I'd be looking for?
 
  • #4
Joel2010 said:
Hi guys, new here. I was wondering if anyone knew of a way to trick a 12 volt transformer into seeing more load. I have these lights http://www.lowes.com/pd_172832-24969-800CBL5N_0_?productId=1207073&Ntt=tiella&Ntk=i_products&pl=1&currentURL=/pl__0__s?newSearch=true$Ntt=tiella$y=0$x=0" and it won't light them. If I put back in 1 of the 20 watters it works.
So what I need to know is, would something like this work? https://www.amazon.com/dp/B0002KR4HU/?tag=pfamazon01-20
Any help would be greatly appreciated.

I don't understand what you are asking. Are the LED light modules rated for 12Vrms (AC), or do they expect 12Vdc? You don't "load" the output of a transformer to get the LEDs to turn on...
 
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  • #5
It doesn't say if they're ac or dc.
What I'm saying is they leds work as long as there is one incandescent bulb (4leds, 1 incandescent) in the line but don't if I take it off so it seems the transformer wants to see a little more load. ?
 
  • #6
Joel2010 said:
It doesn't say if they're ac or dc.
What I'm saying is they leds work as long as there is one incandescent bulb (4leds, 1 incandescent) in the line but don't if I take it off so it seems the transformer wants to see a little more load. ?

No, that doesn't seem to be what is going on. What is the AC voltage with nothing connected (transformer open circuit voltage)? What is it with just the LED load? And with the added incandescent?

What is the part number of the LED light module? You should be able to find specs on it somewhere.
 
  • #7
Ok, with nothing it was .1 volt ac, with just leds .2 vac, add one incandescent 6.7 vac.

The only info I have on the leds are in that ebay link. There were no specs with them. Hong Kong!
 
  • #8
The need to do load-balancing in vehicles is generally related to the function of relays and flashers in lighting circuits, IIR. If you were going to replace a simple switched lamp with LEDs (brake light, tail light, etc) there would be no modification required.
 
  • #9
Joel2010 said:
Ok, with nothing it was .1 volt ac, with just leds .2 vac, add one incandescent 6.7 vac.

The only info I have on the leds are in that ebay link. There were no specs with them. Hong Kong!

No, not right. The unloaded output from the "12V" transformer should be over 12Vrms. When fully loaded, it should come down to about 12Vrms.

Try checking the voltages on the DC scale. Maybe the transformer has an output rectifier and filter?
 
  • #10
I opened it, it says 12vac 105 watts. Readings are the same. Doesn't make much sense.
 
  • #11
Joel2010 said:
I opened it, it says 12vac 105 watts. Readings are the same. Doesn't make much sense.

Could you maybe shoot a couple pictures and post them? Also, were you able to track down the datasheet for the LED light assemblies?
 
  • #12
If I short it real quick, the leds light up. Is there a safe way to short it all the time with a resistor or capacitor or something?
 
  • #13
Joel2010 said:
If I short it real quick, the leds light up. Is there a safe way to short it all the time with a resistor or capacitor or something?

No, something is not getting hooked up correctly.
 
  • #14
OK, a suggestion... incandescent bulbs don't care about polarity, but LEDs sure do. If the circuit is set up to reverse-bias the LEDs, they won't illuminate. I don't know why replacing one of the incandescents in the circuit will allow LEDs to illuminate, but just a thought.
 
  • #15
berkeman said:
No, something is not getting hooked up correctly.

Here's the whole thing then a closeup of the transformer. I can't find any other info on the leds. There's no numbers on them at all.
 

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  • #16
turbo-1 said:
OK, a suggestion... incandescent bulbs don't care about polarity, but LEDs sure do. If the circuit is set up to reverse-bias the LEDs, they won't illuminate. I don't know why replacing one of the incandescents in the circuit will allow LEDs to illuminate, but just a thought.

I don't get it either but the leds work perfectly as long as there is an incandescent in there.
 
  • #17
It says electronic transformer on the label you posted.

This means it is probably a switching mode power supply, not a conventional transformer. These do need sufficient load resistance to operate.

Are your lamps in series or parallel?
 
  • #18
Studiot said:
It says electronic transformer on the label you posted.

This means it is probably a switching mode power supply, not a conventional transformer. These do need sufficient load resistance to operate.
Good catch!
 
  • #19
Studiot said:
It says electronic transformer on the label you posted.

This means it is probably a switching mode power supply, not a conventional transformer. These do need sufficient load resistance to operate.

Are your lamps in series or parallel?

Parallel so my total for the leds is only 6 watts. They are 1.2 each. The extra 20 watts gets it all going. That's why I'm trying to add a load.
 
  • #20
Guess I could hide an incandescent in the wall lol. Not
 
  • #21
Joel2010 said:
Here's the whole thing then a closeup of the transformer. I can't find any other info on the leds. There's no numbers on them at all.

That looks to be a ballast, not a simple step-down transformer. Where it says "Output Frequency > 20kHz" is a clue.

It may be that your DMM can't measure that high of an AC waveform, and the extra loading just pulls the output frequency down closer to where it can start to see something.

Is it a dimmable ballast? Is there a dimming control somewhere? I tried to get the datasheet for the transformer, but am running out of time right now. If you power that light string with a standard 12Vrms step-down transformer, it should work fine.
 
  • #22
berkeman said:
That looks to be a ballast, not a simple step-down transformer. Where it says "Output Frequency > 20kHz" is a clue.

It may be that your DMM can't measure that high of an AC waveform, and the extra loading just pulls the output frequency down closer to where it can start to see something.

Is it a dimmable ballast? Is there a dimming control somewhere? I tried to get the datasheet for the transformer, but am running out of time right now. If you power that light string with a standard 12Vrms step-down transformer, it should work fine.
It does say it is dimmable and I am using a dimmer which everything works fine with so long as that one incandescent is in there. Would that transformer still allow for the dimmer? Just reply when you get time, no hurry. I appreciate everyone's input.
 
  • #23
That looks to be a ballast, not a simple step-down transformer. Where it says "Output Frequency > 20kHz" is a clue.

Can't see this as ballast.

It says 120v in 12 volts out and the wattage indicates a pretty inefficient conversion.

An incandescent will eventually burn out. You would be better off hiding two parallel 15 watt 15 ohm resistors. Perhaps you could simply attach them in the fitting. They are readily available.
 
  • #24
Joel2010 said:
It does say it is dimmable and I am using a dimmer which everything works fine with so long as that one incandescent is in there. Would that transformer still allow for the dimmer? Just reply when you get time, no hurry. I appreciate everyone's input.

Do you have access to an oscilloscope? On second thought, you'd need to use an isolation transformer before the 120Vrms 60Hz input side, to let you ground part of the output for watching the lighting waveform...
 
  • #25
Studiot said:
Can't see this as ballast.

Not a high-voltage ballast, true. I sure wish I could find the datasheet. There are multiple MDL corporations, and I've only gotten an address for this lighting MDL Corporation, but no website yet. Lots of people sell their stuff, but no datasheets so far on those websites...
 
  • #26
Studiot said:
Can't see this as ballast.

It says 120v in 12 volts out and the wattage indicates a pretty inefficient conversion.

An incandescent will eventually burn out. You would be better off hiding two parallel 15 watt 15 ohm resistors. Perhaps you could simply attach them in the fitting. They are readily available.

Ah, thank you! This is the info I'm looking for. If you think this will work I will definitely try it. Can I ask why 2-15's and not something closer to 105 watts?
 
  • #27
berkeman said:
Do you have access to an oscilloscope? On second thought, you'd need to use an isolation transformer before the 120Vrms 60Hz input side, to let you ground part of the output for watching the lighting waveform...
No I don't, I think you'd be way over my head there anyways. :)
 
  • #28
You said that it works with 20 watt load. You don't want to draw and waste more than necessary.

20 watts at 12 volts works out at 7.2 ohms.

Two 15 ohm resistors in parallel yield 7.5 - close enough. I said 15 watt not 10 watt because they will run cooler and more reliably. Using two resistors also increases reliability.

These are also common or garden standard sizes, readily and cheaply available.

These are only 5W (I am watching these for a different purpose) but something like these would do.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=300314832011&ssPageName=STRK:MEWAX:IT
 
  • #29
Studiot said:
You said that it works with 20 watt load. You don't want to draw and waste more than necessary.

20 watts at 12 volts works out at 7.2 ohms.

Two 15 ohm resistors in parallel yield 7.5 - close enough. I said 15 watt not 10 watt because they will run cooler and more reliably. Using two resistors also increases reliability.

I see. Awesome. I will head to Radio Shack this weekend and grab some and report back. Thanks you guys.
 
  • #30
Joel2010 said:
I see. Awesome. I will head to Radio Shack this weekend and grab some and report back. Thanks you guys.
I wonder whether the load problem was more from the dimmer? Same solution antway. :)
 
  • #31
Hi
I have an excellent test-equipment design I want to share with you because it will enable you to track down your fault.
It needs parts : 2 of 12v filament lamps; a mounting arrangement for the lamps, and a probe. Oh, and red and blue paint.

Connect the 2 lamps in series, and connect the series circuit to the battery which is supplying the circuit under test. Connect the probe to the joining between the 2 lamps.
The 2 lamps glow weakly as soon as they are connected. If the probe is touched to a part of the circuit at positive voltage, one of the lamps will glow. Paint this one red. Paint the other lamp blue.
Keep this test equipment forever! You will soon find faults like the one described in this thread using your 2-lamp tester!
 

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  • #32
Could it be that the leds are self-biasing themselves off in some way as charge is only flowing one way through the circuit? Foggy thinking on my part, here, but I seem to remember something of the sort happening in another context.
You could try connecting one of the led units the other way round which would stop this happening as current could then flow in both directions through the transformer.
If it works then I was right - otherwise I wasn't!
 
  • #33
Besides the fact that it is an "electronic transformer" (i.e. ballast), it also states:
Soft Start
Overload
Short Circuit Protection
Auto Reset
For 12V Halogen Lights Use Only

Correctly-biased LED's probably look like a short circuit to this device, therefore causing it to shut itself down.
 

1. What is a resistor?

A resistor is an electronic component that limits the flow of electric current in a circuit. It is typically made of a material with high resistance, such as carbon or metal, and is used to control the amount of voltage and current in a circuit.

2. How does a resistor trick a 12v transformer?

A resistor can be used to lower the voltage output of a 12v transformer by creating a voltage drop. This is achieved by placing the resistor in series with the transformer, which reduces the amount of current flowing through the circuit and therefore lowers the voltage output.

3. What is the purpose of using a resistor to trick a 12v transformer?

The purpose of using a resistor to trick a 12v transformer is to control the voltage output to a desired level. This can be useful in situations where the 12v transformer is producing too much voltage, which can damage or overload electronic components in a circuit.

4. How do I choose the right resistor for my 12v transformer?

The value of the resistor needed to trick a 12v transformer depends on the desired voltage output and the current flowing through the circuit. It is important to calculate the appropriate resistance value using Ohm's law (R=V/I) and choose a resistor with a wattage rating that can handle the current flowing through it.

5. Are there any risks involved in using a resistor to trick a 12v transformer?

There are some risks involved in using a resistor to trick a 12v transformer, such as the resistor becoming too hot and potentially burning out if it is not rated for the appropriate wattage. It is important to carefully choose the right resistor and monitor its temperature to avoid any potential hazards.

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