Quantifying the difference a USB cable can make

[Etheav8r]

OK so it appears that different USB cables make a difference to the voltage supplied to the PAW and it’s subsequent reliability, but just how much?  I decided to do a test;

My power supply is a 4s 4500mAh LiPo into a DC 12v 24v 40v to 5v USB Step-Down Power Supply Module, one of these http://www.ebay.co.uk/itm/111473997718 (falcoguy also has one of these).  The output of the PSU is 5.2v (which under the PAW Load drops to 5.14v).  I have 2 cables, the white high quality 97cm cable for a Samsung phone, and the black 50cm JuicEbitz cable recommended by Lee.

Powering up the PAW and have it fully running I took voltage readings from the Pi header.  The under load 5v output was a steady 4.37v!!!  A significant drop.  I then swapped over the USB connection to use the JuicEbitz cable….. and the under load running voltage was a steady 4.99v, almost perfect, and a 0.62v improvement with the only variable being the USB cable itself!

I repeated this test with all 3 PAW units I have and got exactly the same results.

'nuff said!

[Admin]

Great analysis, I made a similar thread somewhere else on the forum, I was amazed the difference made by a good quality USB cable

[Richard]

Jerramy has a lot of experience in USB power, He could be the person to produce a 12V PSB to be added into the PAW box to eliminate the USB cables. OK the PAW box is not big enough to add this directly to the case. I'm thinking if this could be added we can start to look at a more suitable case for our PAW, I have found something off the shelf but it may still be too small to add another 12v PSB inside. I'm trying to finish the prototype so I can post pictures but I'm awaiting Jeremy's regulator to complete the box.

[Richard W]

Not as dramatic as Etheav8r's results, but I have a 100 cm white cable which came with my Motorola phone, and the recommended JuiceBits 50 cm cable.  The drop on the white cable is 100mV more than the JuiceBits.

Given that I am only getting 4.84V with the JB cable and my cigarette lighter USB adaptor, that 100mV is critical.  I would like a link to a better cigarette lighter style adaptor, if someone knows of one.  It's effectively a hire aircraft, so I can't go for permanent installation.

[stephenmelody]

I'm using this:

http://www.amazon.co.uk/gp/product/B00WWPGB2C

Gives me more stable power than my 22000mah power pack.

[Richard W]

I'm using this:

http://www.amazon.co.uk/gp/product/B00WWPGB2C

Gives me more stable power than my 22000mah power pack.

Thanks, do you know what voltage you get at the PA, with either the supplied or 'approved' cables?  I am looking to improve on 4.8V

[bnmont]

Anker 1m long cable gives me 4.93V at the pi, jucebitz .5m cable gives me 4.94V.
 Powered by the standard apple phone charger.
http://www.amazon.co.uk/gp/product/B00NAN3O20?ref_=pe_1909131_77697001_tnp_email_TE_AMZLdp_1      for the Anker cable.

[ianfallon]

Anker 1m long cable gives me 4.93V at the pi, jucebitz .5m cable gives me 4.94V.
 Powered by the standard apple phone charger.
http://www.amazon.co.uk/gp/product/B00NAN3O20?ref_=pe_1909131_77697001_tnp_email_TE_AMZLdp_1      for the Anker cable.

If this has proven to be a good solution do add it to the known good hardware thread 

[bnmont]

I'm going down the airfield shortly, will see what voltages I get when using my cheapo 12v to 5v supply!
Just thought I would run the test whilst waitying for correct wifi dongle to arrive.
These voltages were recorded with no real current draw I guess as no dongles attached.

[bnmont]

OK so went to the airfield this afternoon, before going for a  flight I checked voltage on the pins of the Pi with engine off.
Engine off battery voltage was 12.3V. With the .5m juicebitz cable was 4.87V at the Pi with the Anker 1m cable was 4.86V, so I'm reckoning with engine running the voltage across the battery will be up a little and a smaller voltage increase at the Pi.
Hopefully will work OK.

This is what I'm using  note this is not an approved item in any way! just seems to do the job.
http://www.ebay.co.uk/itm/DC-9V-12V-18V-20V-to-5V-30W-4-USB-Step-Down-USB-Step-down-Power-Supply-Module-/400755801997?hash=item5d4ee83f8d