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want to run 2 strings on one MPPT
#1
I have a string of 10 panels in NE direction connected to my MPPT that charges my 48V battery. (running a PIP5048GK MPPT/INVERTER all in one)

I would like to have another string of 10 in NW direction. I cant parallel them obviously as they are in different directions.

My questions, is there such a thing as automatic dc transfer switch that i can buy (best option) or if not build that will allow me to switch from one string to the other at the point where it feed to the MPPT. If it can switch automatically based on current i.e. the string at has the max current or even based on timer i.e. i can program it based on the time of the day i need to switch the string.

If there is an alternate option please let me know. If this has been asked before i apologize.

Thanks
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#2
Actually, you can parallel them.
You may want to add an inline diode into each string, to prevent current from the sunny string reversing into the other in the shade. There are neat units integrated into MC4 connectors. You might get away without one if both sides get enough ambient light.
And of course, the combined cable must be thick enough to carry double the current.

But depending on the intelligence of the MPPT, and the exact position of the sun / clouds, you may not get as much power as when having 2 separate MPPTs. It's possible that some times one string won't contribute at all.
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#3
Thanks ajw22, how would the circuit be? a diode or a mc4 connected at each end of string and join them before connectiong to mppt? sorry i am a noob
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#4
If you have 10 panels in series, that's some serious voltage that could easily kill you.  If you're even slightly unsure about it, don't do it.
It should not need saying, but if you're not a professional, do it after dark and wear insulation gloves, just in case.


Something like this would be convenient to use:
http://s.click.aliexpress.com/e/lyAU2FpW

Inside is basically a diode like this that allows current to flow only in one direction.  In this use, it's often referred to as a blocking diode.  The silver marking on the one end shows the direction of flow.
http://s.click.aliexpress.com/e/tiGW5nWu


This would be one possible circuit.  You can place the diodes just as well on the negative side, or even between the panels.
Again, you may not need it.  But it's not wrong to use it.
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#5
Its better to parallel them since that will gove more overall BUT best is of course to just buy another MPPT charger like an PCM60x and you get even more energy.
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#6
you just need a parallel combiner box - I have 3 parallel strings of 4 panels - I use a midnite solar combiner on the roof then run a single bit of 2 core down to the MPPT controller.

All modern panels have reverse protection diodes built in.
Current system: 9.6kWh wet Nicad batteries, 16S1P Calb LiFePo4 210aH, Batrium WM4, Outback vfx3048 inverter, mx60 mppt controller, flexware 500 mounting hardware, 2.4kW solar array, 6kW lister diesel genset. MY'13 Vauxhall Ampera
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#7
(09-06-2019, 11:49 AM)HughF Wrote: All modern panels have reverse protection diodes built in.

No, they do not.  This is a common misunderstanding.  Virtually all large panels made in the last ~10 years or so have several bypass diodes, which are not the same as reverse protection diodes.  It may be the same device, but is wired in differently to serve a very different function.  Bypass diodes are there to split a panel into typically 3 sections, and allow each to be bypassed individually.
Without these diodes, a single leaf covering just one cell would kill the output of the whole string to virtually zero.
With these diodes, that same leaf would disable the output of just 1/3 of a panel, and the rest of the string will keep producing.

Some smaller panels designed to directly attach to batteries may have reverse protection diodes built in.


Found some SMA documentation on using multiple strings:
https://www.sma-italia.com/fileadmin/con...083010.pdf
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#8
thanks ajw22 for the circuit diagram. the connection seems simple enough.

the mc4 connectors with inbuilt diodes have negligible cost compared to new mppt. efficiency is not an issue as i have more than enough panels then required for my battery.

thanks all for your inputs
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#9
You can buy MC4 diodes for a few $ off eBay or Ali like these (I use them on 3 separate parallel arrays)

https://www.alibaba.com/product-detail/W...05992.html
Do some research on sellers...
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......
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#10
Make sure the diodes are 1000V devices. Some are just eg. 45V and will get fried in your use case.
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