Failure Mode of Charge Controllers (Xantrex MPPT60-150)
I have an inherited Xantrex grid-tied, battery backed system in a house I purchased. I've been debugging it over the last week and have got most things figured out.
In the process of debugging, I discovered that I had a failed Xantrex MPPT60-150 charge controller. The system has two strings of panels on the roof, each going to a separate MPPT60 and then both of those going to a common battery bank. One charge controller consistently generated power and the other one consistently did not. The readings I saw on the charge controllers: working one with nominal voltages of 75-95V and amperage commensurate with the amount of sun; non-working one with nominal voltages of 75-95 but amperages next to zero (it would read about 3W). I made the assumption that there was something going on up on the roof with the panel wiring as that is the most exposed component in the system.
But to be sure, I thought I'd switch the positions of the charge controllers relative to the strings of panels. Did that this morning before the sun came up. So now I had the charge controller that was working on the string that wasn't putting out any power previously. Lo and behold, when I fired things back up and the sun came out, the previously powerless string was now putting out nominal power. And the string that was putting out power previously was now not putting out any power. So the fault is clearly with the charge controller.
I can't say for sure, but I am assuming that it has never worked from the time I purchased the house. I would assume that it worked at some point in it's 10 year life with the previous owner, but again, impossible to say. I never checked the system in detail except to see that the blinky lights were blinking. My experience with the system on my primary house with a similar Outback system has been "set-it-and-forget-it". So I got lazy on checking this before plunking down the cash.
At this point, I know I have to get a new charge controller, but I'm curious, what is the typical failure mode of a charge controller like this one? An overcurrent problem? A temperature problem? Old age?