voltage of dimmer output not reading same on two different DVM\'s...

[major]

I am using a 12 V 20 amp lamp dimmer to control some LED lighting.
While my two DVM\'s show nearly equal input voltage to the dimmer, they
both read separate voltages on the output side. One is reading 9 V and
the other 4 V. I am trying to determine wattage output at various
dimmer settings. Why the different in voltage readings on two different
DVM\'s and how to remedy?

 

[Phil Allison]

major wrote:

================

I am using a 12 V 20 amp lamp dimmer to control some LED lighting.
While my two DVM\'s show nearly equal input voltage to the dimmer, they
both read separate voltages on the output side. One is reading 9 V and
the other 4 V. I am trying to determine wattage output at various
dimmer settings. Why the different in voltage readings on two different
DVM\'s and how to remedy?

** Both are correct, but only one of them is \"true RMS \" ?

OR the controller use high frequency PWM and one meter cannot read it.

Next time, leave out all the facts just to make it harder.


..... Phil

 

[major]

On 11/5/20 1:10 AM, Phil Allison wrote:

major wrote:

================
I am using a 12 V 20 amp lamp dimmer to control some LED lighting.
While my two DVM\'s show nearly equal input voltage to the dimmer, they
both read separate voltages on the output side. One is reading 9 V and
the other 4 V. I am trying to determine wattage output at various
dimmer settings. Why the different in voltage readings on two different
DVM\'s and how to remedy?


** Both are correct, but only one of them is \"true RMS \" ?

OR the controller use high frequency PWM and one meter cannot read it.

Next time, leave out all the facts just to make it harder.


.... Phil

Sorry, the meters are a GE2524 Digital Multimeter that reads the 9V and
the other meter is a Etek 10709 that reads 4 V. The dimmer is one from
Amazon (sorry, 30 amps not 20 as I said originally):

https://www.amazon.com/Lighting-Controller-Solution-Eliminate-Connecting/dp/B076MVT1CR

Not sure about dimmer frequency, but I can hear a faint whine as it runs.

 

[Trevor Wilson]

On 5/11/2020 2:00 pm, major wrote:

I am using a 12 V 20 amp lamp dimmer to control some LED lighting. While
my two DVM\'s show nearly equal input voltage to the dimmer, they both
read separate voltages on the output side.  One is reading 9 V and the
other 4 V.  I am trying to determine wattage output at various dimmer
settings.  Why the different in voltage readings on two different DVM\'s
and how to remedy?

**Measure the output of the dimmer with a CRO and it may make a lot more
sense.

--
Trevor Wilson
www.rageaudio.com.au

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[Phil Allison]

major wrote:

===============

Sorry, the meters are a GE2524 Digital Multimeter that reads the 9V and
the other meter is a Etek 10709 that reads 4 V.

Not sure about dimmer frequency, but I can hear a faint whine as it runs.

** What range are you using ???

AC volts or DC volts?

PWM voltage waves can be read as an average value on any DC meter - but true power will require something much fancier.

Why not just measure the DC battery current and multiply by the voltage?

Then subtract a watt or so for losses in the controller.


..... Phil

 

[major]

On 11/5/20 6:48 AM, Phil Allison wrote:

major wrote:

===============


Sorry, the meters are a GE2524 Digital Multimeter that reads the 9V and
the other meter is a Etek 10709 that reads 4 V.

Not sure about dimmer frequency, but I can hear a faint whine as it runs.


** What range are you using ???

AC volts or DC volts?

DC on both meters on lowest range, 20 V.

PWM voltage waves can be read as an average value on any DC meter - but true power will require something much fancier.

Why not just measure the DC battery current and multiply by the voltage?

If you mean input from the battery into the dimmer, yes, tried that.
Both meters show the same 12 VDC @ 7 A when the dimmer is set at
maximum. Will have to check and see what happens as dimmer is adjusted.

Then subtract a watt or so for losses in the controller.

Would I only lose a watt or two through the dimmer? If so, I guess I
could take all my readings from the input side and go with those.

.... Phil

 

[major]

On 11/5/20 3:48 AM, Trevor Wilson wrote:

On 5/11/2020 2:00 pm, major wrote:
I am using a 12 V 20 amp lamp dimmer to control some LED lighting.
While my two DVM\'s show nearly equal input voltage to the dimmer, they
both read separate voltages on the output side.  One is reading 9 V
and the other 4 V.  I am trying to determine wattage output at various
dimmer settings.  Why the different in voltage readings on two
different DVM\'s and how to remedy?

**Measure the output of the dimmer with a CRO and it may make a lot more
sense.

You talking a scope here or something else? If a scope,
unfortunately, I don\'t own one.

 

[Jon Elson]

major wrote:

I am using a 12 V 20 amp lamp dimmer to control some LED lighting.
While my two DVM\'s show nearly equal input voltage to the dimmer, they
both read separate voltages on the output side. One is reading 9 V and
the other 4 V. I am trying to determine wattage output at various
dimmer settings. Why the different in voltage readings on two different
DVM\'s and how to remedy?

These dimmers MUST be pulse width modulated, othwerwise the heat production
would be huge. You can\'t expect a DVM to give accurate reading of a
pulsating source. Possibly some true-RMS meters may do a decent job of
averaging the result, but I would not trust such a reading without verifying
it with another instrument, like an oscilliscope.

Jon

 

[major]

On 11/5/20 10:05 AM, major wrote:

On 11/5/20 6:48 AM, Phil Allison wrote:
major wrote:

==============

Sorry, the meters are a GE2524 Digital Multimeter that reads the 9V and
the other meter is a Etek 10709 that reads 4 V.

Not sure about dimmer frequency, but I can hear a faint whine as it
runs.


** What range are you using ???

  AC volts or DC volts?

DC on both meters on lowest range, 20 V.


PWM voltage waves can be read as an average value on any DC meter -
but true power will require something much fancier.

Why not just measure the DC battery current and multiply by the voltage?


If you mean input from the battery into the dimmer, yes, tried that.
Both meters show the same 12 VDC @ 7 A when the dimmer is set at
maximum.  Will have to check and see what happens as dimmer is adjusted.


Then subtract a watt or so for losses in the controller.

Would I only lose a watt or two through the dimmer?  If so, I guess I
could take all my readings from the input side and go with those.



....  Phil

Ok, just as a follow up, I did keep both meters on the input side of the
dimmer. Voltage remained constant and nearly the same on both meters,
11.97 and 12.01 VDC, respectively, with dimmer off. At dimmer maximum
setting, voltage remained nearly constant (drop of -0.3 V) but current
changed from nearly nothing to the 7 A maximum with dimmer at max
setting. I swapped out the meters to read current just to be sure and
each showed the 7 A maximum. Then, I just adjusted the dimmer to
different positions, made some tick marks with current values indicated.
I think I\'ll just go with this. As you mentioned, losses through the
dimmer are probably slight and not an issue, at least in this
application. Thanks for your suggestions.

 

[Trevor Wilson]

On 6/11/2020 2:06 am, major wrote:

On 11/5/20 3:48 AM, Trevor Wilson wrote:
On 5/11/2020 2:00 pm, major wrote:
I am using a 12 V 20 amp lamp dimmer to control some LED lighting.
While my two DVM\'s show nearly equal input voltage to the dimmer,
they both read separate voltages on the output side.  One is reading
9 V and the other 4 V.  I am trying to determine wattage output at
various dimmer settings.  Why the different in voltage readings on
two different DVM\'s and how to remedy?

**Measure the output of the dimmer with a CRO and it may make a lot
more sense.

 You talking  a scope here or something else? If a scope,
unfortunately, I don\'t own one.

**Well don\'t waste your time until you acquire one. In this application,
most meters are almost useless.

--
Trevor Wilson
www.rageaudio.com.au

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[Phil Allison]

Trevor Wilson wrote:

=================>

**Measure the output of the dimmer with a CRO and it may make a lot
more sense.

 You talking  a scope here or something else? If a scope,
unfortunately, I don\'t own one.


**Well don\'t waste your time until you acquire one. In this application,
most meters are almost useless.

** So you are unaware even the simplest DC meter can read the power drain from a battery ?

I average x V ?


..... Phil

 

[Phil Allison]

Jon Elson wrote:

================

These dimmers MUST be pulse width modulated, othwerwise the heat
production would be huge.
You can\'t expect a DVM to give accurate reading of a
pulsating source.

** Still can certainly show the average DC voltage.

The usual input RC network doe the job nicely.

Possibly some true-RMS meters may do a decent job of
averaging the result,

** Only if the have response down to DC and up to the high harmonics of the PWM.

..... Phil

 

[Trevor Wilson]

On 6/11/2020 8:02 am, Phil Allison wrote:

Trevor Wilson wrote:

==================


**Measure the output of the dimmer with a CRO and it may make a lot
more sense.

 You talking  a scope here or something else? If a scope,
unfortunately, I don\'t own one.


**Well don\'t waste your time until you acquire one. In this application,
most meters are almost useless.


** So you are unaware even the simplest DC meter can read the power drain from a battery ?

I average x V ?

**Or you could do that.


--
Trevor Wilson
www.rageaudio.com.au

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[Phil Allison]

Trevor Wilson wrote:

===================

** So you are unaware even the simplest DC meter can read
the power drain from a battery ?

I average x V ?

**Or you could do that.


** ;-))

...... Phil

 

[brucek]

major <maj7789@aolspam.net> Wrote in message:r
> I am using a 12 V 20 amp lamp dimmer to control some LED lighting. While my two DVM\'s show nearly equal input voltage to the dimmer, they both read separate voltages on the output side. One is reading 9 V and the other 4 V. I am trying to determine wattage output at various dimmer settings. Why the different in voltage readings on two different DVM\'s and how to remedy?

i\'d guess because they are non-sinusoidal outputs and one of the meters is not true rms
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[Andy Burns]

brucek wrote:

> i\'d guess because they are non-sinusoidal outputs and one of the meters is not true rms

I\'d say neither of them are true RMS.

 

[whit3rd]

On Sunday, November 8, 2020 at 12:46:33 AM UTC-8, Andy Burns wrote:

brucek wrote:

i\'d guess because they are non-sinusoidal outputs and one of the meters is not true rms
I\'d say neither of them are true RMS.

Good point--measuring DC current average is the appropriate setting, and there\'s
no DC-scale on any of my meters that does RMS measure.

Voltage, averaged or RMS averaged, is going to deliver at-or-near nonsense numbers
for the purposes of evaluating an LED illuminator.

 

[jurb...@gmail.com]

>DC on both meters on lowest range, 20 V.

AHA, the keystone part of the puzzle. This blows Phil\'s statement out the water which is rare, there is no TRMS in DC.

Now you are down to the meters being plain old wrong, after all one just be, right ?

First of all realize that 100% LED compatible dimmers, which could be used on multiple lights must be the raw PWM. ON OFF ON OFF. If you smooth it off the a DC voltage, LEDS in parallel might fire at slightly different voltages and screw ya all up. So PWM is fine with LEDs as long as you never exceed the Imax (current rating) As such your meters on DC are actually measuring AC in the wrong mode.

It will help to know how the digital voltmeter works. Now when a voltage is applied to a DVM it is of course divided by the range control and whatever.. After that it goes to a comparator. The other input to the comparator is a sawtooth wave, generated quite accurately. When your input voltage and the voltage from the sawtooth cross, the comparator changes states and puts out an output. The exact time that happens is used to stop or read a counter to know just how much the internal voltage has risen.

It is easy to see that each DVM can have its own timing, or speed. higher speeds read faster and they are more expensive if they are accurate.

Now if you want a DC measurement, which could be useful, then you must feed the meter DC, not AC. As you can see frigs it all up. So, an extremely simple way would be to get like a 5K resistor and like a maybe what guys, 68uF ? Take the resistor from the output, connect it and the probe there, and the cap and the other end of the cap to ground. yyou just made an R/C filter.. This should make the meters read the same.

That is because they are measuring DC on the DC range.

I can\'t remember when the last time it was I had to make an R/C filter like that but I know I did a couple of times.

 

[Phil Allison]

jurb...@gmail.com wrote:
====================

AHA, the keystone part of the puzzle. This blows Phil\'s statement out the water which is rare, there is no TRMS in DC.

** FYI:

\" true RMS \" = DC equivalent value for the *heating* effect on a resistance.

Repeating waveforms may have a DC offset = average DC value.

The \"true RMS\" value of such wave is:

sqrt ( DC ^2 + ACrms ^2 )



...... Phil

 

[Phil Allison]

jurb...@gmail.com wrote:
====================

AHA, the keystone part of the puzzle. This blows Phil\'s statement out the water which is rare, there is no TRMS in DC.

** FYI:

\" true RMS \" = DC equivalent value for the *heating* effect on a resistance.

Repeating waveforms may have a DC offset = average DC value.

The \"true RMS\" value of such wave is:

sqrt ( DC ^2 + ACrms ^2 )



...... Phil