Does Outback CC shut off at 145v to protect itself?

Re: Does Outback CC shut off at 145v to protect itself?

The problem with CC input voltage is if for some reason the array has been disconnected and then you go to reconnect it on a clear cool day, the Voc could be too high and zap the controller before it even starts operating. The good news (as I understand it) is that the Midnite 150V input spec is figured on top of the battery bank voltage as it is relative to B+. So with a 48Vnom battery, the array can go nearly to 200V. Correct me if I'm wrong...

Re: Does Outback CC shut off at 145v to protect itself?

As we are speaking of MPPT CCs, the loading on the PVs is produced by the Buck Converter running. When there is too little PV input power to make sense to run the Converter the CC shuts if off, as it requires roughly 5 - 10 watts just to make the Converter run.

In very low light, the CC rests or sleeps with the converter off. Early in the morning, before sunrise (usually) the ambient temperature is at its lowest, and the CC is still sleeping -- no load on the PVs, so the PV string voltage is at Voc for the temperature of the PVs. Under these conditions, there is on sun striking the PVs, so there is not enough power to run the MPPT Converter.

If the Voc is too high, 145 + volts, the CC will try to protect itself, by continuing to sleep/rest. This means that there is no load on the PVs, and with the high input voltage, the CC will continue to produce NO power until the PV temperatures decline to a value below the high voltage shutoff point. This could take some time. So high string voltages, with cold temperatures can mean that the system will avoid producing power, while the CC WAITS for the temps to decline -- this is power wasted, compared to a system that uses a lower, more reasonable string voltage.

With strings of six 17.X-ish Vmp PVs, the STC (25 degree C PV Cell temps), the string Vmp would be about 106 V, and the string Voc would exceed 125 V. At colder temperatures, this Voc will rise.

Again, usually, the highest Voc will be before sunrise, on cold mornings (this means that there will be NO sun striking the PV cells at all). Your CC will show the Highest Voc to date in the Logs, somewhere.

FWIW, we run strings of three real 24 V PVs -- 35.4 Vmp + 106 Vmp string voltage. The highest recorded Voc is now 141 V on one system, in our moderate climate, over a ten year operating history.
These high string voltages redice CC efficiency a bit, and make the CC run hot. Even in the Summer, in Float with light loads, the Vin to the CC can approach 120 V, this results in considerable CC heating, even at low output currents.

Strings of five (as have been proposed in the past, IIRC) would be considerably better, except that your total number of PVs is not evenly divisible by five, with no remainder .. and so on. FWIW, YMMV, Vic

Re: Does Outback CC shut off at 145v to protect itself?

Hi Dan,

Well, you probably know that Kyocera did make some PVs eight or ten years ago, that had a number of Field Failures, which they were very good about replacing under Warranty.

Low output was the symptom.

A quick search did find this ... :
http://forum.solar-electric.com/showthread.php?5258-Defective-Kyocera-solar-panel

A Clamp DC Ammeter should be a big help. Radio Shack used to sell one, that is similar to the Sears one, and those both work well and are $50 - 60.

It can be difficult to measure the voltage of individual PVs in a string, in an operating system, but that info would be important. Parallel strings affect the string voltages of other strings.

Good Luck, Vic

Re: Does Outback CC shut off at 145v to protect itself?

Hi Dan,

BTW, fine on your maximum high Voc to date, hope that you will be OK, until you install the final configuration.

You either have some severe connection issues, or, the individual PVs SEEM to contribute in a very unequal fashion to the power of each string.

You may want to test each string individually, with the breakers for all other strings off. At least, this would let you test each string separately.

If you could possibly buy or borrow a Clamp DC Ammeter, this should be a big help in diagnosing the issues.

If you look at the link that other Thread, BB Bill suggested a good way to test each PV module, using a standard DMM ... just be careful to move the test leads as required for your meter. Good Luck, Vic

Re: Does Outback CC shut off at 145v to protect itself?

And, Dan, one further thing;

It is also important to open the breaker that feeds the PVs into the CC BEFORE you try measuring Isc with the DMM. If you do not disconnect the PV input, the MX-60 could be damaged.

So, open the MX-60's input breaker and measure the Isc at the input terminal of the that input breaker, or perhaps measure it closer to the PVs.

FWIW, Good Luck, VIc