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Dasa

multimeter not working on mr16 why?

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it works fine on batteries and everything else but as soon as i try using it to test a mr16 driver\transformer it just reads 0.00v it doesnt even twig

the only thing i can think of is that there is something about the current that it doesnt like

 

im looking at running 9 5w led from one transformer and since the max wire length is specked at 2m on the 12v side and it will be a little over that i wanted to see what the drop of was with heavier wire

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Does the MR16 driver have a load on it when you measure? Many of those transformers will have open circuit protection. (It's necessary to protect the driver in the event of open circuit if it's a constant current driver)

 

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yep i had two led downlights running and the multimeter was making contact with bare copper wire

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Next question: Is it a dimming driver?

 

Do you have an analogue meter?

 

Is it an autorange meter?

 

If it's dimming, it may be using PWM. This can do funny things to DMMs. If autorange meter try setting it to a normal manual range and try. But I think you'll get better results with an analogue meter.

 

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tried a old ironcore transformer and a newer osram redback transformer with no dimmer attached but they probably both support it

major tech mt22 is the multimeter its auto range is also manualy adjustable from 00.1mv to 000v i have had it set at 00.0v which works fine with a 12v battery that i grabbed to make sure the meter was still working

i also have a old $20 dig multimeter here but it has no leads at the moment might be worth sticking some wire into it and seeing if i can get a reading

dont have a analogue meter but maybe i can rip a analouge amp meter out of a dead 12v battery charger

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Not amp meter. Amp meter would be short circuit.

 

But yeah. I haven't really had a meter behave like that before except for when I said it was on auto-range. It'd start to range and because of the constant pulsing, it'd never range. Setting to manual range fixed it for me.

 

Curious.

 

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ahwell thanks for your input

tried the cheap multimeter without auto range but it didnt do any better

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At this stage, I'd scratch my head and ask to borrow my friends CRO.

 

If nothing else, it'd be informative.

 

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DING! Brain just kicked in.

 

You were measuring across the terminals of the MR16 driver. Yes?

 

Have you measured the impedance of that yet? It's entirely possible that it's got a funny impedance which is giving you a funny result. (ie. IF you have a 1MOhm impedance on your meter, and you measure a 1Mohm load, it'll give you a value of half of what is actually being pumped out)

 

Try measuring the voltage across a single LED.

 

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yes im measuring from the two output terminals on the mr16 driver

how would i go about measuring the impedance?

 

tried with a single led or a halogen globe without seeing anything different

 

 

 

edit

ok it was a two part problem one part user error...

 

one i was mostly using the newer transformer which the multimeter didnt like

 

two when i did try the old ironcore transformer i had it set to dc not ac

 

now over a heavy 2.2m wire with a 50w halogen power is dropping from 11.8 to 11.6v from one end to the other but with a 5w led it stays at 13.3v both ends

Edited by Dasa

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