On Wed,6/8/2016 8:42 PM, Jack Brindle wrote:
Thee is an issue with the cheaper solar controllers - they tend to place the switching transistor in the ground leg, making connections difficult. For example the Sunforce controller that Jim mentions uses an N-channel FET as its pass transistor, in the ground lead. If you then connect the radio or other load to the battery while it is being charged, you can end up with a floating ground. One local solar expert discovered that his setup of this kind caused massive current flow on the shield connection of a USB cable - it was essentially carrying all the ground current!
Thanks for the alert, Jack. However -- the controller I referenced is a low power product, specifically designed for a single panel charging a battery. Such panels are rarely connected to a ground except via the return side of the pair feeding the battery through the charge regulator.
Also, if a USB cable is the only connection between equipment in a system, that system lacks proper bonding.
Abuse of the return conductor is not limited to devices like these. The very popular Watts Up inline volt-ammeter meters in the return lead, which can lead to very wrong answers when used to measure current within a station, for exactly the reasons Jack notes -- DC return current divides between the intentional path (the return wire) and all of the other return connections between equipment in a station, and bonding conductors.
The Hamsource EZmeter ($80) and the West Mountain Radio PWRcheck ($180), both sold by DX Engineering, measure current in the positive conductor. I found the EZmeter at Pacificon last fall and quickly added it to my collection of test gear.
73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
