<div dir="ltr">Hi all,<div><br></div><div>Following James' suggestion, I put my fluke 186 multimeter in current mode on the USB cable between the power source and the WD hard disk. I was able to capture a 1A current spike, and a ~ 3 second current transient of about 800mA during spin up. The idling current for the hard disk, while spinning, was 230mA.</div>
<div><br></div><div>The XO4, (sku306) did not reliably spin up the HD. In particular this failure was almost 100% when the 430mA load of the ethernet dongle, and MR3020 wifi access point was hanging on the other USB port.</div>
<div><br></div><div>I put the hard drive and wifi accessories on a powered "Plugable" model USB2HUB AG7, which has an adapter rated for 3A, and experienced no failures, during many startups.</div><div><br></div>
<div>I am concluding that an external hard disk requires a powered USB hub.</div><div><br></div><div>Other interesting measurements: </div><div><ul><li>The MR3020 wifi unit had maximum current spikes of 530mA with average current of 175mA. <br>
</li><li>The USB ethernet dongle had 230mA spikes with an average of 177mA and a minimum of 172mA<br></li></ul></div><div><br></div><div>George</div></div>