SE MPPT60 getting F70 DC Over-voltage shutdown (DC output) fault

johnhall6095

I have two MPPT60-150 and one MPPT100-600 charge controllers.  The two MPPT60's have started getting these "F70 DC Over-voltage shutdown" faults during the most intense sun of day.  I understand how an over-voltage can happen on the DC input side, due to having too many panels connected in series.  But I don't understand how this can happen on the output side.  Doesn't the MPPT charge controller manage the output voltage/current to stay within the specified ranges?





As you can see, the DC Output Voltage is not unusually high and none of the other numbers are exceeding (or even close to exceeding) the specs of the controller.  I've tried researching the MPPT60 F70 fault code but only see information related to the XW6048, nothing on the MPPT60.  Does anyone know what could be the cause of such an error?  Here is the fault info I am receiving:



Thanks,
John

mike95490

Bad connections !

I had a issue like this years ago, with a failing wire in a bus bar behind a dead front.     I checked battery terminals with an IR thermometer for a week trying to pin it down,   as the wire made poor contact, it briefly surged voltage and set the error.  Pain to diagnose, as you have open the Midnight ePanel, and pull the deadfront, it's impossible to not kiss the battery breaker and trip everything off line.  Same with putting it back together.

see  https://forum.solar-electric.com/discussion/comment/350689#Comment_350689
orig post :   Melty Crispy Wires: https://www.facebook.com/media/set/?set=a.654873231252800&type=1&l=f5bcf8e0a7 

Dave Angelini

Firmware up to date?

Dave Angelini

Are the faults escalating and shutting down ?   Did you see voltage above what you expected? I doubt that as inverter would have shut down on HBCO.

The other thing, xw6048 has unspecified behavior with gateway per SE Solar.

 I tested alot of 6048 for offgrid and the old grey box worked fine with Gateway.  Definitely did not look at what a grid tie would do with Gateway.

johnhall6095

Thanks Mike and Dave.  Mike, I will check all my DC wiring, including inside the CC, to make sure there are no loose connections.  Dave, yes all my firmware is up to date.  The faults show up briefly on the Gateway device status screen, then the MPPT60's reset, and then go back to working normally after a few seconds.  Also, the faults are not showing up in the device fault logs, which I find odd.  Here's a short video to show what I'm seeing on the device status screen:

https://youtu.be/xR6EiKja4HA

Looking at the video, I can now see the DC Output Voltage jump to > 65 volts right before the fault/reset.

John

Solar Guppy

Since both charge controllers are seeing the battery voltage rise to 65V, it isn't the chargers. Even if there was a firmware bug, the rate of the increase from ~54V to 65V means that the charge controllers are disconnected from the battery banks and doing what they are designed to do, shutdown on overvoltage.

Best guess is you have a bad connection ( or breaker ) in the common path from BOTH charge controllers and the battery bank. It is likely a connection / breaker lug not properly torqued.

vtmaps

The charts in the OP show that both controllers are hooked up to the same solar panel array (Solar Array 1). Is that the case, or am I misunderstanding what I see in the charts?   --vtMaps

johnhall6095

Each controller is connected to a separate solar array.  I was not able to figure out how to create, and then associate, more than one solar array identifier.  Does this have an impact on the behavior of the MPPT60 or MPPT100? Or, is it just an informational note?

BB.

Probably just an informational note... Using one electrically connected array to two (or more) MPPT controllers can cause issues.

Each MPPT controller assumes it is 100% in control of "its" array. The controller will vary the current drawn from the array and monitor the array voltage... trying to solve the Pmax=Vmp*Imp and find the "peak power condition" (typically finding Vmp and varying current to keep Vmp near measured value).

The newer charge controllers do something "different" than what I said above--But I believe they still require dedicated array per controller (the Schneider controllers measure array current in the negative leg to the controller... Many other MPPT controllers can have a common array negative because they only measure current in the positive connection).

-Bill

Vic

Am sure that this has nothing at all to do with the OP's observations,   but:

These MPPT60-150s have a low-side shunt,  in the PV negative.  The output current appears to be calculated from this PV current measuremant.

It is very important to have the PV negative cable from each PV array connected only to the PV neg of each of these CCs,  and not to the common negative buss  --  separate PV arrays,  each array negative cable connected only to its CC PV neg terminal.

Am not certain how the 100A CC measures current.

FWIW,  etc,   Vic

johnhall6095

Yep, each PV negative cable is only connected to the MPPT handling just that array. 

Vic

johnhall6095 said:

Yep, each PV negative cable is only connected to the MPPT handling just that array. 

Good.   AND,  each negative cable from each,  separate PV array only is connected to the PV negative terminal of its respective CC,  RIght??

johnhall6095

Yes.

BB.

The Negative PV Input... The battery connects to the Negative Battery terminal.

The controller measures array current between Vp- and Vb-... (as I recall from years ago discussion).

For example, the (older and current?) FM XX controllers from Outback, the Vp- and Vb- are the same electrical connection and you may mix and match without effect.

-Bill

Solar Guppy

It does matter, you can not parallel pv inputs on the XW-MPPT60.  The charger has high precision  current and voltage measures ( 12 bit ADC ) on both the array and battery side, using shunts on the negative connections. The tracking expects it is the only source load on the array.

johnhall6095

I think I found the culprit... a 125 amp thermal breaker (from original install) between the CC output positive combiner block and the inverter positive battery terminal.  My system does not have a distribution box (2008 installer decision) so the CC's positive and battery's positive are both connected to the inverter positive terminal.  I watched closely and the fault was happening whenever the total CC output current went above 125 amps.  Good to know the breaker was actually working!

Now I need to decide on what size breaker to use as a replacement. The 2 x MPPT60 (3500 watts each) + 1 x MPPT100 (6000 watts) are capable of pushing 13kW total so:  13000 watts / 52 volts = 250 amps max.  The CC positive combiner block is rated at 250 amps max, but I will need to upgrade the 4 AWG wire to something like a 1/0 wire for the short run (10") between the combiner block and the inverter positive terminal.  So, a 250 amp breaker then?

Vic

Perhaps something like this?
Schneider 865-DCBRK-250 250 Amp DC Breaker | Northern Arizona Wind & Sun (solar-electric.com)

Using a Thermal breaker,  at that location,   is a bit astonishing,  to me   ...

Good that you found the culpret.   Vic

johnhall6095

Yep, that's the ticket!  Thanks!

BB.

And for "battery charging" -- I suggest that branch circuits (wiring/breakers) be sized 1.25x higher than expected constant current (battery charging can be "hours on bulk/full charging current". In North America, generally breakers will trip at 100%+ rated current and will not trip at 80%- current... Running hours of rated current at 80-100% current can cause unwanted trips.

And breakers can fail after years of use... Have had to replace a few over the years.

-Bill

Solar Guppy

You should have separate breakers for each charge controller, not a single one with all three tied together before the breaker. If there is a fault in one of the charge controller in your current configuration, your looking at a fire as the likely outcome as the internals of the XW-MPPT was not designed to handle more than the rated current.

johnhall6095

OK, I will do that as well.  Thanks.

Dave Angelini

You might want to hire an electrician to look this over. If you have house insurance for fire,  this system may be a reason to decline a claim!

 It does not sound like this system was inspected!  Very few building departments would allow an installation without a power distribution panel for grid tie. A PDP is a basic safety building block for SE Solar.