question

Andrew avatar image
Andrew asked

3 panels 385w 7 x 375w (5x2 series)?

I have 3 panels from previous my house @ 385w and purchased 7 x 380w which was the nearest I could get. they are similar volts and amps and wiring 2 x5 strings in series. All 10 are in the same direction all south facing next to one another, shade free 15deg. 10m from nearest panel to easy solar gx 2, 48v 3kwa, 35, 250/70.

Wiring 6mm using y combiners and each string has 1 inline fuse @ 15a and a 1000v reverse current prevention diode then combined lines to a surge protector, then 32a 1000v disc

I have 3 panels from previous my house @ 385w and purchased 7 x 380w which was the nearest I could get. they are similar volts and amps and wiring 2 x5 strings in series. All 10 are in the same direction all south facing next to one another, shade free 15deg. 10m from nearest panel to easy solar gx2, 48v 3kwa, 35, 250/70.

Wiring 6mm using y combiners and each string has 1 inline fuse @ 15a and a 1000v reverse current prevention diode then combined lines to a surge protector, then 32a 1000v disconnector to inverter to 125a on live to pylontech 3000 and a 5000 correct wires for the batteries. Then to AC consumer box.

Q Grounding: should I wire earth to house DC earthing or separate to a earthing an rod?

Q Is there an issue with the 5w difference of the 3 panels, obviously I lose 15w but if anyone thinks it should be parallel?

Q Batteries: I was told to fuse the common and live with a 125a fuse on both but others say to wire just live. Is there a logic to wiring both poles?

Q Should I wire as series 5 x 2?

Any other advice greatly appreciated.



wiring
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4 Answers
Mike Dorsett avatar image
Mike Dorsett answered ·

1) Grounding - The panel frames and racking system should be grounded to a separate earth rod - lightning protection.

DC Ground - this will be done through the inverter frame ground, and should be bonded to the house ground.

2) strings of panels can be connected in parallel with no problems provided the open circuit voltage difference is <5%, and they all have the same orientation. Best to distribute the older panels through 3 different series strings to minimise the difference.

wiring panels - the more panels you wire in series, the higher the string Voc is, and the lower your cable losses are. As long as you don't exceed the max voltage of the MPPT, then 5 series, 2 parallel is the best way to do this. As long as the Voc of each panel is <50V at your lowest temperature, 5 series is fine.

3) Floating (un grounded) batteries are normally fused in both poles. Victron systems are negative ground , so fusing just the positive is OK. If you do want to fuse the negative, use a larger fuse, so the positive blows first.

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Andrew avatar image
Andrew answered ·

thankyou Mike,I am a complete novice but read for the past 6 months and seeked advice before doing this and with victron calc it stated I would need another mppt which is 700ukp and as they are getting same angle, no shading etc I opted for 2 lots of 5 in series with para wired.

I am assuming a small loss of power fusing both poles of the battery leads? Is there a good rationale if I have surge protected strings and taken other DC fuse breakers etc and wiring precautions

reason being, I have a spare 125a fuse just wondering the odds of why the common would be worth fusing. OK with Easysolar i have the disadvantage of one inbuilt mppt so i am taking as many precautions as possible but I take it this is more about the batteries overloading, and am in England so temp didnt seem a major consideration, moreover, i read some dont even bother fusing the pylontechs but would you err on caution and just add the fuse, = no big deal for me to do it?

thanks Andrew

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philippem avatar image
philippem answered ·

Hi, you never ground enough, I just recommend to put all the different grounds together (house, garage....) I would recommend to use 2 MPPT and to cable in serie. Victron products are getting very hot in full load so I think it is better to keep 50% marging in order to protect your installation. Fire in solar installations is a big issue so better you reduce the amps to the minimum. Best regards

1 comment
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nickdb avatar image nickdb ♦ commented ·
Complete nonsense. Living in a very warm region, the mppt's perform just fine - they are reliable and safe. Please stop spreading such misleading and incorrect advice.
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philippem avatar image
philippem answered ·

Mister I know everything, my last order was 2 x MPPT 250/60, 2 batterie sense, 2 x 700, 2x inverter 3000/48, within 2 months Victron replaced under warranty 1 x inverter, 1 x MPPT, 1 x battery sense.

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