Blown fuses

thermax292

My system was working OK but yesterday it blew the fuses on both Xantrex XW mppt-150 controllers. The company I bought it from updated the firmware Thursday and they went out Saturday. The error code says a severe leakage has happen between the PV array and earth ground has occurred. Is it possible something isn't set right that caused this? Thanks

Joe_B

Re: Blown fuses

If the fuses are actually blown, firmware could not have caused it. Basically you had a ground fault, current flowing on the PV frame ground.

BB.

Re: Blown fuses

You have a short circuit (somewhere) between the PV+ and/or Battery+ and earth ground.

It is either something accidental (wire cut by metal, earth grounded metal fell across battery + terminal, etc.) or a load was accidentally connected from Battery+ to green wire/sheet metal ground (such as a 12 volt car radio from Batt+ to chassis ground).

What you can do is connect a 12 volt (or whatever your bank voltage is) filament light bulb from Battery- to earth/chassis ground. And then start disconnecting wiring/loads until the lamp goes out.

If you do not have one yet, you might want to look for a DC Current Clamp Meter so you can trace DC current flow (this Sears unit works and is very inexpensive).

-Bill

thermax292

Re: Blown fuses

I went up to the combiner box. I have 9 switches, each one connects 3 224W panels.The earth ground coming from the PV panels is connected to a bar. Next to the earth ground on the same buss in the green wire that goes into the inverter. I took the one from the PV side and pulled it out of the buss bar. I set my meter to DCv to see if I'd get a voltage reading across the wires. I figured if there was leaking voltage coming from the panels it would flow through my meter to the earth ground going to the inverter.There was no voltage at all. Would it be safe to assume the problem isn't on the roof with the PV panels?

BB.

Re: Blown fuses

The problem with pure DC circuits is that there is no "galvanic isolation" between sections of the power bus... I.e., a short between any + lead (pv, load, battery buses, etc.) will look about exactly the same when blowing the Ground Fault Detection Fuses. Not like AC where the input or output side of a transformer can be shorted to ground, and the other side is "unaffected".

When debugging with a volt meter for DC shorts--it is actually quite difficult. My suggested steps:

• 12 volt lamp (or even one of those 12 volt test lamps you can get from a auto parts store) between battery- and earth ground at/near one of charge controllers. If you do not use a lamp (or some other "safe" resistor other other load), a digital volt meter may not load the circuit enough to give you useful readings.
• When you have a way of monitoring the voltage between Batt- and Earth Ground, hopefully the light is on or the meter is reading 5-12 volts or so, then start turning off fused/breakers/switches in your DC power system one at a time until the light/voltage reading drops to near zero. At that point you have isolated the "faulty circuit" and can search further for the exact problem (turn switch on and monitor lamp while disconnecting loads, etc.).

If you have a MSW inverter (most brands/models of MSW inverters are not electrically isolated between DC input and AC output), a short on the AC output to earth ground can also pop the Ground Fault Detection Fuse.

-Bill

thermax292

Re: Blown fuses

My unit is a Xantrex 6048 with two XW-MPPT-150 controllers 8 batteries in series giving me 48V. I have a 12 v circuit tester for checking trailer plugs but 48 volts will probably ruin it. I've got the company that installed it coming out tomorrow, I'll let you know what he finds out. Thanks for all your help.

BB.

Re: Blown fuses

You can probably use a 40-100 watt 120 VAC light bulb for the load/indicator---Or make one out of 4x 12 volt bulbs in series.

I would presume that the XW inverter has DC isolation (TSW inverter) so an AC short should not be part of the problem.

-Bill

thermax292

update

The company that installed the units came out yesterday. They spent the best part of the day trying to find the ground fault. The finally decided it was the # 1 charge controller. They shut it off and it stopped blowing fuses and ordered a warranty replacement. I have two controllers one handles 15 224 watt panels and the other one handles 12 panels. They pulled both 600v 1A fuses and and shut the 15 panel controller off. They said it would run on the 12 panel until a new controller comes in. We had a sunny day today and only collected 4.5 kw's. it should have collected at least 12. I have a combiner box in the attic and I've noticed that they were very careful to make the wires at the combiner to match which group they mated with. + #1 black with - #1 white and +#2 white with -2 black .However the negative wires ( the white ones) numbered 1 and 2 are crossed at the controller. Grid #1's neg wire is going into controller #2 and Grid #2 is going to controller #1's controller. They both leave the controller and go to the same buss bar so I don't know if the cross over is a problem or not or if they are common to each other any way. I'll let you know how this progress. Thanks

BB.

Re: Blown fuses

Finding DC Ground Faults is a pain in the behind. They really need to use some sort of load (like a 40 watt 120 VAC filament lamp) between -DC and Earth Ground.

If you do not have a stable "load" while chasing grounding/fault current problems, using a plain Digital Volt Meter can really cause confusion. There is usually enough capacitance in a larger DC power system that you cannot see the difference between a "floating" voltage (very low leakage current that charged a capacitor) and a true hard short somewhere (amp/multi-amp current flow).

The DVM's have virtually no load on the system and will not significantly discharge any stray capacitance in the DC circuit.

I am not sure how there is a bad Charge Controller--unless there is a loose part/wire/screw/sheet metal scrap that is causing the ground.

Regarding the return leads... The Arrays must have their +/- wiring paired to the correct (same) charge controller. If the + of array 1 goes to A charger controller and the - of array 1 goes to B charger--it will really confuse them (MPPT program/circuitry). And probably cause also sorts of DC ground current issues... I don't think it would cause a Ground Fault Detection Fuse to pop.

If you have a 4 string array with 1/2/3/4 and mix the connection order of +1/+2 with -2/-1 -- but both 1/2 going to controller A -- there should not be any issue. Other than somebody who does neat wiring probably will make fewer mistakes down the road.

-Bill

thermax292

Re: Blown fuses

Thanks for getting back to me on this issue. I'm going to send your advise to the solar company to add to their knowledge base. I did notice that the tech had removed both fuses in the controllers. I don't know how he did that with out shutting the units completely down. The unit they left on is only doing about 20% for some reason, maybe because the return wires are backwards at the controllers. Any way I'll keep you updated as things change.

BB.

Re: Blown fuses

If you wish, here is a fairly short tech document (PDF) for the Xantrex XW charge controller and Ground Fault configuration information.

It can be configured to operate with out GF detection... But the 20% output sure sounds like some major issues going on (don't know if if ground fault related or not).

-Bill

thermax292

Re: Blown fuses

Thanks Bill, I've sent the info to the installers. They are still going to replace the controller because the back lite on the LCD doesn't work either, maybe that will take care of both issues. T

thermax292

Update

When the installers replaced the controller that fixed it. They said there was a short inside the controller. Thanks

silvertop

Re: Blown fuses

I also run two XW 150 MPPT controllers. I don' think this has any bearing on your problem, but I called Xantrex about the ground fault 1A fuses. When I installed both of mine, I was quite confused with the manual because I believed it stated to remove one of the fuses only leaving one for both controllers . At first Xantrex support told me to leave both in then he went back and rechecked and he told me removing one and leaving only one for both controllers was correct.

Each of these contollers have their own seperate array, connected together only with ground and CAT5 communication cable.