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simple? circuit measuring current...Mystery

ampedtech

Member
I got these LED arrays off Amazon.
I wanted to measure the current draw.

Connected the FLUKE 87V leads to COM and mA uA in series with the battery (12V 8Ah ) and the lamp as shown.
An unexpected event occurred.

What I did expect is a steady current flow.


The first instant the meter reads 5mA+
In about 1/2 sec The current dropped to 1+mA
The current kept dropping, but not in a linear fashion.
From 0.04mA to 0.03mA took 10 sec
From .0.02mA to 0.01mA took 30 sec
Eventually the ammeter reads 0.00
At no time does the array dim.
Not sure if this relevant but, these LED "bulbs" have no polarity requirements. This tells me that there is some circuitry aboard the "bulb". This perceived circuitry is why I put a ? next to the word "simple"

There is conflict in the Amazon post in the "Technical Details" it states 30w.
In the posters blurb they indicate 1.5w

There is a link to these LED arrays:
 

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danadak

Well-Known Member
Most Helpful Member
Blow a fuse inside meter ? Shorted array.....

Put a 120 ohm R in series with battery and meter and see if you get a sensible
reading, eg. 100 mA.

Regards, Dana.
 
Last edited:

augustinetez

Active Member
I see bridge rectifiers have become "constant current ic's" according to the advertising blurb :banghead:

I would suggest you might have a problem with your meter if the LEDs are working normally.

Not sure why you wanted to measure the current, but the specs do say 100mA current draw per panel.
 

picbits

Well-Known Member
20 x 1.5W lamps...

I agree with Pommie; some Fluke meters default to AC current and you have to switch to DC with a button.
Exactly this - my work Fluke 179 defaults to AC current and needs the yellow button pressing before I get to DC. It catches me out almost every time despite me using it every day for the last seven years ....
 

Reloadron

Well-Known Member
Most Helpful Member
My Fluke 87 defaults to DC and for AC requires a button press.

I would try as sugested here:
Blow a fuse inside meter ? Shorted array.....

Put a 120 ohm R in series with battery and meter and see if you get a sensible
reading, eg. 100 mA.

Regards, Dana.
Place a known load out there and see what you get.

Ron
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Are you sure, it looks like my 179 where AC is the default ? View attachment 137936

Never owned a Fluke, never used a Fluke, but is it possible that models intended for electricians default to AC (as that's mostly what they use), and models intended for Electronics use default to DC (as that's mostly what is used).

It would make obvious sense, and make them more user friendly.
 

picbits

Well-Known Member
We've got around 10 Fluke meters in our department, the only fault we've ever had with them have been worn out leads and one meter developed a loose socket which was easily repaired. Considering the abuse they get on a daily basis, we've never replaced one in the nearly 8 years I've been there although we've got through a lot of protection fuses from technicians thinking you measure current by putting the leads in parallel with the device ......

Having used lots of Fluke stuff over the years now, I do seriously rate them despite their price.
 

Reloadron

Well-Known Member
Most Helpful Member
Are you sure, it looks like my 179 where AC is the default ? View attachment 137936
Yep, about as sure as I can be. On an interesting note I noticed the symbols for mA A in the image are yellow as is the button below the display. Mine are Blue. Ahh, I got it. Meter I looked at was my older Fluke 87 no suffix. My Fluke 87 III is the same. However, here is the twist, my newer Fluke 87 V is exactly like your image and guess what it comes up AC for default.

Fluke.png


Over all the years I never noticed this difference, go figure? I do have one old 87 III that just flashes the display when turned on. Tried a few tricks / fixes I saw online but no joy.

Ron
 

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