Believe nothing, no matter where you read it, or who said it – no matter if I have said it! – except it agree with your own reason and your own common sense.” – Siddhartha Gautama, a.k.a. the Buddha

A little about Murph 

Yeah, last weekend Murphy was ensconced quite tightly in the comfy chair of my life.  I truly hate it when he visits, but I’ll be danged if I know anyone that has never had a visit from that rude character.

Anywhoos, the gremlin he brought with him ate the charge controller to my batteries.  It took a couple of days to isolate the issue, mostly due to a certain amount of ignorance in the true functionality of said controller.  I knew I was losing juice, and wasn’t gaining any even with 5 straight cloudless days.  (Zero wind for matter of interest but not consequence )

My ignorance was in the layout of the controller.  It is (was)a positive common with negative being the switched side.  That completely threw me for a loop.  My testing was showing good voltage every where, except when I was checking across the ground. (Should’ve been my first clue but I am quite stubborn)  There I was seeing -22vdc.  What?  Ground to ground from battery to input ground of the controller, showing a potential.  

Well, I went ahead and did all the usual checks, disconnected and isolated each battery for testing; all checked good, disconnected panels and checked no load output; all good.  Checked to see if I had any leakage in my blocking diodes; all good (I use them whether I need them or not, especially with the wind genny.) So, last check, since everything is disconnected, open the back of the controller and look for something obvious.  

First thing obvious was a distinct ‘burnt’ smell.  I couldn’t find what had fried, but something had.  Likely one of the several MOSFET’s on the board.  This was when I found I had positive commons.  All of a sudden, all of my probing and measurements made perfect sense. (I did say I was stubborn, didn’t i?)  

Well, to shorten this up a hair, I went ahead and spent FRN’s on a larger unit (60a vs 30a) and an MPPT unit where the other one was a PWM unit. 

It arrived today and I will be installing it tonight upon getting home.  I have been skirting with disaster the last couple of days by allowing the batteries to free charge with no controller.  I have been monitoring them closely and leaving a lite load on during the day while I can’t be there.  So far so good, but damned if that doesn’t make as nervous as a cat near a waterhose.  Tonight I get ease that nervousness.  (And before I do, I fully intend on mapping current flow on the new unit so that diagnosis in the future won’t bite me)

I want to think Murph is huddled in the doghouse now.


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