Measuring current from a controller
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Offline srtate1

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Measuring current from a controller
« on: October 05, 2018, 06:22:38 AM »
We are part of a three house light show on a cul de sac that has been building for several years.  So we have lots of props and lots of controllers.  We have been running by the seat of the pants as far as determining how many lights we can safely run from a single controller output.  But this year, as we add more props, I want to take the guesswork out of this part of the setup.  From picking up bits and pieces from various threads here, this is what it looks like I should be doing - just want to see if I have it right.  If I run all of the lights on the output cable of a single output on white, I would measure the amps at the cable and be looking to stay safely under about 5 amps.  To check the load on the power supplies, I would run all of the lights on white, measure at the DC output wires and try to keep the total load at less than 80% of the PS rating.  If there are two sets of DC outputs on a PS, I assume I could measure the current on each pair and add the numbers.  Does this sound right?  Thanks for the input!
Steve
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Offline pixelpuppy

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Re: Measuring current from a controller
« Reply #1 on: October 05, 2018, 12:36:22 PM »
Yep, sounds right.

And you probably know this, but just for the sake of others who may read this...  Most home/hobby-grade multi-meters are only rated up to 10A-max which is not enough for the 30A-60A supplies most of us use.  Its fine for measuring 5A pixel strings, but can be tricky when measuring a loaded 350w power supply.  An alternative is to use something like a Kill-A-Watt on the input side of the power supply and convert the amperage appropriately for the power conversion  (120v->12V with ~80% efficiency)
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Offline srtate1

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Re: Measuring current from a controller
« Reply #2 on: October 05, 2018, 08:04:11 PM »
Thanks for the reply.  I think I may have received a faulty meter from Amazon. It’s a relatively inexpensive clamp type amp meter/multimeter.  It is autoranging with 40 amp and 400 amp selections.  When I set it to the 40 amp range , it reads 0.03 amps before approaching a power cord and the same after I clamp it on.  I tried it on my refrigerator cord and soldering iron cord.  There certainly should be more than .03 amps when those are running.  I have it in AC mode and the digital display does change in the range of .07 to .03A.  I think the thing is faulty and plan on sending it back to Amazon.  Grrrr. :(
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Offline Ebuechner

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Re: Measuring current from a controller
« Reply #3 on: October 05, 2018, 08:30:14 PM »
It sounds to me like you don't know how to use an amp meter.
Read the instructions.
That type meter it's only going to get a reading if you clamp over one of the two power wires or use an adapter.
You can't just clamp it over an AC cord and get a reading.
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Offline srtate1

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Re: Measuring current from a controller
« Reply #4 on: October 06, 2018, 06:31:04 AM »
You are correct.  I’ve never used one.  I did read the instructions, but it never mentioned that you couldn’t read over a pair of wires. That’s why I posted, hoping someone would see if I was doing something wrong.  So, if that’s the case, how do you measure the current coming from a single output on a controller? There is nowhere along that string where the wires are separated. Is there a different instrument for such a measurement? Thanks!
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Offline Ebuechner

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Re: Measuring current from a controller
« Reply #5 on: October 06, 2018, 06:42:19 AM »
Like mentioned before a kill-A-Watt meter.
You were right, it should be reading 0 before it's clamped on something.
https://youtu.be/tpTjEighSak
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Offline srtate1

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Re: Measuring current from a controller
« Reply #6 on: October 06, 2018, 07:10:05 AM »
Outstanding!  Thanks for straightening that out for me.  I can get a delivery today for a Kill-a-watt meter from Amazon.  I’m no stranger to electrical work.  I rebuild top of the line vintage audio equipment as a hobby, and I have done Home wiring repairs and expansion.  I’ve just never had a need to measure current flow in any of my adventures.  I’m looking forward to getting the kill-a-watt meter and trying it out.  I assume I can use my clamp type meter on the DC wires coming out of my power supplies to test that current. I also ordered the line splitter shown in the video to be able to measure power cords with my clamp meter. Thanks again for the info and the video link. Very helpful!
Steve
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Offline lrhorer

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Re: Measuring current from a controller
« Reply #7 on: October 06, 2018, 09:41:56 AM »
Quote from: srtate1 on October 06, 2018, 06:31:04 AM
There is nowhere along that string where the wires are separated. Is there a different instrument for such a measurement? Thanks!

No.  It's not physically possible.  What you need to do is separate the wire pair.  A relatively easy way to do it is to make a break-out adapter.  Just wire a female connector to a male connector of whatever type you are using with a pair of separate wires and insert it inline.

Note many clamp meters cannot read DC current.  Reading AC current is easy, because a simple coil wrapped around a conductor creates effectively a transformer whose output voltage is directly proportional to the input current.  Measuring DC current is much more complex.  It requires a magnetic field measuring device like a Hall Effect sensor.
« Last Edit: October 06, 2018, 09:51:47 AM by lrhorer »
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Offline srtate1

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Re: Measuring current from a controller
« Reply #8 on: October 06, 2018, 02:35:15 PM »
Thanks for the info.  The manual says it measures AC or DC current.  There is a selector button to set between AC and DC when in amp mode.  However, I haven’t tried that yet, so can’t say for sure it will work.   I have ordered a line splitter as shown in the video linked by Ebeuchner from Amazon, along with the kill-a-watt meter.  I’m assuming I can measure the AC current through the PS with either method.
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Offline allknowing2012

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Re: Measuring current from a controller
« Reply #9 on: October 06, 2018, 04:43:30 PM »
Take some props off .. measure .. switch props .. measure again .. add them up?
No expert but I asked this recently .. so be sure the amps are less than the rating on the multimeter (mine is max 20A for at most 5 mins or something like that). Unplug power.
Disconnect + from a single port on controller. Make that run thru your meter -- in one probe out the other. Plug it in. Get the amps. Turn off, switch props and measure again.


Would this work?
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Offline lrhorer

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Re: Measuring current from a controller
« Reply #10 on: October 08, 2018, 10:08:08 AM »
Yeah, sure.  The only caveat would be if for some reason due to the topology the voltages on the strings drop when another string is added.  This would skew the data.  As long as the props are in parallel, not series, and the current is not over the regulation limit of the supply, and the various currents are within the ampacity limits of the respective power leads, everything should be highly linear.  Note that if it isn't, the system is far too close to its current limits or even over them.
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Offline lrhorer

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Re: Measuring current from a controller
« Reply #11 on: October 08, 2018, 10:14:28 AM »
Quote from: srtate1 on October 06, 2018, 02:35:15 PM
Thanks for the info.  The manual says it measures AC or DC current.  There is a selector button to set between AC and DC when in amp mode.  However, I haven’t tried that yet, so can’t say for sure it will work.
Yes, if the meter says it will measure DC, then it should measure DC current.  Otherwise it is a lousy meter.

Quote from: srtate1 on October 06, 2018, 02:35:15 PM
I have ordered a line splitter as shown in the video linked by Ebeuchner from Amazon, along with the kill-a-watt meter.  I’m assuming I can measure the AC current through the PS with either method.
You mean either your clamp-on meter or the Kill-a-watt?  Yes, surely.  Note the Kill-a-watt will give you a lot more information in addition to just the current.
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Offline lrhorer

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Re: Measuring current from a controller
« Reply #12 on: October 08, 2018, 10:20:30 AM »
Quote from: pixelpuppy on October 05, 2018, 12:36:22 PM
Most home/hobby-grade multi-meters are only rated up to 10A-max which is not enough for the 30A-60A supplies most of us use.  Its fine for measuring 5A pixel strings, but can be tricky when measuring a loaded 350w power supply.  An alternative is to use something like a Kill-A-Watt on the input side of the power supply and convert the amperage appropriately for the power conversion  (120v->12V with ~80% efficiency)


Another alternative is to purchase an external shunt, like one of these: https://www.newark.com/ohmite/shd1-100c075de/high-current-shunt-75mv-100a/dp/72T0825

This one produces 75mV @ 100A, so it would produce 7.5mV @ 10A, 22.5mV @ 30A, etc.
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Offline Ebuechner

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Re: Measuring current from a controller
« Reply #13 on: October 08, 2018, 11:32:15 AM »
MICTUNING DC 6.5-100V 0-100A LCD Digital Display Ammeter Voltmeter Multimeter Volt Watt Power Energy Meter Blue with 100A/75mV Shunt https://www.amazon.com/dp/B01JOUZELG/ref=cm_sw_r_cp_apa_1q5UBb1SP3R0X
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Offline srtate1

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Re: Measuring current from a controller
« Reply #14 on: October 11, 2018, 07:04:23 AM »
Thanks for all of the good info.  I did receive my kill-a-watt meter and the line splitter that I can use with the clamp meter.  The numbers on both systems agree very well.   :)
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