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Home > Maintenance & Modifications > Solar controller MPPT series or parallel
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Lightwater



Member Since: 21 Aug 2014
Location: Sydney NB
Posts: 2230

Australia 2013 Freelander 2 2.0T SE Auto Fuji White
Solar controller MPPT series or parallel

I have 6 x 20 watt solar panels so I can fit them into the car or on the roof behind the second spare wheel to shield them from insects. I wired the panels up as recommended by the manufacture's controller instructions 2 x 3 sets in series rather than 6 panels in parallel. So 3 x 36 volts instead of 6 x 18 volts.

I have never been happy with the output at about up to 3.8 amps maximum, but it has always been enough.

With my 6 panel setup I could easily wire a pair in series & a pair in parallel & plug & play alternating between the 2 configurations to test volts & amps.

So the 3 x 26 AH auxiliary batteries were drained to 12.6 volts & now with 6 panels in parallel I am getting around 7.5 to 7.8 amps in Sydney on a sunny day. Before it was 3.8 amps maximum. Doubling the voltage was simply a loss of half the amps.

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Clamp meter really handy for testing current.
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At 5:50pm with a weakish sun I was still getting 6 to 7 amps.
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At 6:30pm in part shadow still getting 2 amps
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So I will see how this goes but it looks a lot better wiring in parallel.

One other note is that the cable is all really heavy. Mostly 6AWG, I added in another 4 metres of 8AWG extension. Then added in a 2 metre 12AWG extension cable & amps dropped from 7.4 to 6.9. So do not not skimp on wire thickness if you are after every last bit of solar energy. Procrastination, mankind's greatest labour saving device!

Acoustic insulation ARB TPMS 1.2kW air compressor Air tank Additional 50L fuel Carpet in doors 2x 1kg ABE Waeco 28L modified fridge Battery 3x 26ah Solar 120w Victron MPPT 100/20 Awning 6x 255/60R18 Petrol 10.48L/100 inc 500kg payload

Post #363543 12th Jan 2019 10:13 am
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Benzol



Member Since: 12 Jun 2017
Location: Perth
Posts: 20

Australia 

Hi Lightwater.
Having them in parallel is the only way. Using the series / Parallel configuration puts too much voltage onto the MPPT solar regulator and to keep a sensible voltage the regulator has to dump the excess. Loss of efficiency and current as you noticed. Probably cause some heat issue in the regulator as well.
Resistance of a conductor is measured by (R x L)/A where R is the resistivity of the material, L is the length of the conductor and A is the area of the conductor. Keep it short and fat (like me).

Post #363557 12th Jan 2019 4:03 pm
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Lightwater



Member Since: 21 Aug 2014
Location: Sydney NB
Posts: 2230

Australia 2013 Freelander 2 2.0T SE Auto Fuji White

Thank you.

When I originally set it up I followed what the manual said. So went for option 2: 'Recommended number of cells for highest controller efficiency'

12V battery and mono-or polycristalline connected to a 75V controller
• Minimum number of cells in series: 36 (12V panel).
• Recommended number of cells for highest controller efficiency: 72 (2x 12V panel in series or 1 x 24V panel).
• Maximum: 108 cells (3x 12V panel in series).

The manual could not have made it more clear which is the best option! I'm at a loss what the Victron manual is trying to achieve by recommending 72 cells in series when one clearly gets half the amps. Because I have wired in a volt & amp meter I can continuously see the energy input.

In the late afternoon I get about the same amps whether it's 36 or 72 cells. There is a point during the stronger sunlight the amps are much better with 36 cells by twice the panels in parallel. So 72 cells is NOT the best setup as Victon are suggesting.

All the wiring is 6AWG (13.3 mm2), the short lenghts on the back of the panels & in the controller are 12AWG.

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 Procrastination, mankind's greatest labour saving device!

Acoustic insulation ARB TPMS 1.2kW air compressor Air tank Additional 50L fuel Carpet in doors 2x 1kg ABE Waeco 28L modified fridge Battery 3x 26ah Solar 120w Victron MPPT 100/20 Awning 6x 255/60R18 Petrol 10.48L/100 inc 500kg payload

Post #363569 12th Jan 2019 5:43 pm
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Lightwater



Member Since: 21 Aug 2014
Location: Sydney NB
Posts: 2230

Australia 2013 Freelander 2 2.0T SE Auto Fuji White

A total stuff-up on my part. I forgot that I installed the amp meter upstream of the controller, a senior moment! The smart controller is a bit smarter than I am! So I was showing amps in & not out. So after rewiring in parallel & testing volts & amps, I have rewired back to series. Series setup is squeezing a bit more out of the panels but it's not much. The biggest difference is late in the day where you get a little bit more scrounging around for the last little bit of power.

The main benefit will be half the amps through longer extension cables to get the solar panels into the sun. I really needed another extension cable even though I have 3 cables totaling 10 metres (4m 6AWG, 4m 8AWG & 2m AWG). One cable I pinch from my compressors as I will not running the compressors & using solar panels.

I have not used the load terminals on the controller but I did partly in this test. But need to fiddle around a bit more with this in the settings so it always supplies power to the fridge even if the batteries are a bit low.

Screenshot 1: Parallel with the 16.20 volts input.
Screenshot 2: In series 32.53 volts & upper view of screen with graph.
Screenshot 3: Battery 11.96 volts so up to 9.8 amps (did get 123 watts & 10 amps)
Screenshot 4: 8 watts & 0.6 amps charging.
Screenshot 5: Graph of each day's harvesting.

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Really needed more extension cables in both these situations.
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Now if I could only squeeze one more battery in somewhere!

A few more photos from Kosciuszko National Park.

Serious harvesting of solar!
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Cave!
 Procrastination, mankind's greatest labour saving device!

Acoustic insulation ARB TPMS 1.2kW air compressor Air tank Additional 50L fuel Carpet in doors 2x 1kg ABE Waeco 28L modified fridge Battery 3x 26ah Solar 120w Victron MPPT 100/20 Awning 6x 255/60R18 Petrol 10.48L/100 inc 500kg payload

Post #363749 15th Jan 2019 1:44 am
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