Common two pin pigtails - the voltage drop truth

[AussiePhil]

I'm sure that nearly all of us have some 2 pin pigtails that are used to run power injection, well this may make you rethink how and when you use them.

Personally I am going to move away from them for anything above about 2A or a bit. or for power injection runs to remote convertors that take 24v -> 5v

The ones I have are based on 2 x 0.5mm wires, are the Ray Wu variant but the vendor doesn't matter. If you have some based on 0.75mm wire then the numbers would be better and if anyone in AU has those and want's to send over a male/female pair I could test then in the same setup.

Test Parameters:
one by female
one by male
wires stripped at each end and directly connected to the respective binding posts.
total length under test @250mm - 10 inches ..... this does not include any wiring you would use that would also have voltage drop.
Bench supply, stable to 12A
E-Load capable of 60A/400w
Voltages tested 5v and 12v

Here is the picture of the test setup - the pigtails are out of different orders but use the same wire size.


Hardly a test but I kicked this off at 3A and got sidetracked for about 15 minutes, the connectors got warm and the entire voltage drop was around 600mA so 3 watts of heat


Next was 5A, a not unexpected number in some cases with a string potentially drawing 4.5A in theory.
About not it's really looking crappy, we have nearly a full volt and a start voltage well under ideal for a 5v string.
This is effectively not usable and doesn't even allow for any drop leading up to this point.


So is 12v better in relation to voltage drop ...... nope not really, sorry to the 12v fans. We are firmly in ohms law here. The resistance of the wires and connectors is fixed as is the current.
The voltage drop is still one volt.
This may well seem better and 12v pixels have greater headroom and may cope with this fine but you don't reduce the voltage drop being experienced.



It does look a lot better at two amps and really these pigtails are at best 3A in real use.


So what happens at 10A, I have been guilty of trying to run some higher currents at times and certainly i've had short circuits.
As expected the voltage drop goes up, nearly 14W is being dumped as heat.


Conclusion: by the time you had some actual cable to each end to get to a power supply and the prop if you have more than a couple amps your already well behind. Even in the 12v ecosystem you need to be aware and take account of voltage drops.

Cheers
Phil

 

[AAH]

I was a little shocked by these numbers and as I use and sell actual Ray Wu ones I did some testing as well. I was essentially using the same setup as you have. The pigtails are 20cm black, 2 core 0.75mm2 pigtails that I suspect are actually closer to 0.5mm2 but I haven't a micrometer handy to measure the wires. With a 5A load I got a drop of 0.16V and a 15A load I got 0.482V. The 2 pigtails that I had have a total overall length of 42cm. The appearance of the Ray Wu pigtails varies somewhat from the ones that you've tested Phil. The white pigtail that you've got has a number more ribs on it. Either the wire is even thinner than the 0.5mm2 0.75mm2 that I have here or there is fairly resistive joints either where the wire joins the connector and/or where the the male and female halves meet.


Any chance of a connector dissection? I might do the same and have a look at the pigtails internal joins of a Ray Wu one. Sometime over the weekend I'll grab a micrometer and measure the 0.75mm2 cable and see what it actually measures as.

 

[AussiePhil]

Thanks Alan for testing the newer ones that say 0.75mm, all the 2 pin ones i have are either not labeled or have 0.5mm on them.

I was a little shocked by these numbers and as I use and sell actual Ray Wu ones I did some testing as well. I was essentially using the same setup as you have. The pigtails are 20cm black, 2 core 0.75mm2 pigtails that I suspect are actually closer to 0.5mm2 but I haven't a micrometer handy to measure the wires.

It's why i captured the setup and measurements as photo's.

I'll bet based on all the recent measurements of pixel wire, pigtails 2/3 pin etc that the wire is 0.1mm

With a 5A load I got a drop of 0.16V and a 15A load I got 0.482V. The 2 pigtails that I had have a total overall length of 42cm. The appearance of the Ray Wu pigtails varies somewhat from the ones that you've tested Phil.

Mine were definitely Ray Wu ones, though getting on now but they were just grabbed from the unused stash so the ones tested had never been in the weather or been used.
just maybe yours are real 0.75mm and that is good, i did say originally that 0.75mm ones should be different

even 37 x 0.10 is no where close to that area rating

The white pigtail that you've got has a number more ribs on it. Either the wire is even thinner than the 0.5mm2 0.75mm2 that I have here or there is fairly resistive joints either where the wire joins the connector and/or where the the male and female halves meet.

I took the time to measure then count the wires used in three different 2 pin connectors.
All wires were 0.10mm though if they are US gauge based they would be 0.102mm, not sure the 2 thou counts.
What was interesting was one pair had 25 strands, one had 28 strands and one had 37 strands
A genuine 24x0.20 is shown as the grey wire in some of the photo's below.

View attachment 19242
Any chance of a connector dissection? I might do the same and have a look at the pigtails internal joins of a Ray Wu one. Sometime over the weekend I'll grab a micrometer and measure the 0.75mm2 cable and see what it actually measures as.

I don't think so based on the one i sacrificed for knowledge. What is evident is the crimp doesn't appear to be effective yet there was no measured resistance of any significance.

Measure a strand of wire then count the strands, it's the only close to accurate way.
The look similar till you measure the strands



One of the counts that resulted in 28 strands


There were no broken or cut strands on the others
Here is the cutaway, pins look clean and not corroded


Close up of the crimp joint, suggest the crimps are meant for larger cable.


Cheers
Phil
PS, always good to be sanity checked

 

[David_AVD]

0.75mm CSA with 37 strands would need 0.16mm diameter strands.

 

[AussiePhil]

Strands to square millimeters
fairly certain the calculations are correct as the 0.20 ones come out about right

Nominal Strand Dia	0.1mm	0.2mm
Strands	sq mms	sq mms
16​	0.126	0.503
17​	0.134	0.534
18​	0.141	0.565
19​	0.149	0.597
20​	0.157	0.628
21​	0.165	0.660
22​	0.173	0.691
23​	0.181	0.723
24​	0.188	0.754
25​	0.196	0.785
26​	0.204	0.817
27​	0.212	0.848
28​	0.220	0.880
29​	0.228	0.911
30​	0.236	0.942
31​	0.243	0.974
32​	0.251	1.005
33​	0.259	1.037
34​	0.267	1.068
35​	0.275	1.100
36​	0.283	1.131
37​	0.291	1.162
38​	0.298	1.194
39​	0.306	1.225

 

[David_AVD]

I just used my calculator: https://www.da-share.com/calculators/wire-cross-section-area/

 

[Katekate]

now test xconnect

 

[AussiePhil]

that has to be a really poor connection or crimp - I use the kind that DA has shown and I dont have any severe voltage drop like this ( etops version ) happy to chop one up if you want some comparison photos

Even if it is a poor crimp inside the molded plug or socket, there is nothing the average user could do about that and the findings stand.

Poor connection: well the photo's should tell the story.... the only possible poor connection would be between the male and female .... same outcome.

Sorry this is just a case of poor cross sectional wires and real life ohms law.

I did say my observations and measurements are related only to what i tested.

btw i grabbed a few of these and got a loop resistance for a pair around .25 ohm on average and this validates the measurements.

The best thing it to count the strands and measure the individual strands.

How have you confirmed you don't have the same voltage drop?

Cheers
Phil