cable length

[salmirabile]

Hey guys,

So i have a simple setup of 1x 100w panel with a max amp rating of 8a, mated to a 20a MPPT control which is then connected to a 12v battery. I only need to draw around 1.5a from the battery so usage is quite minimal. this is to run a small alarm system for my garage.
My current cable run is 5m from the panel to the controller and less than 1m from the controller to the battery. all using 6mm2 cable.

My problem at the moment is I hardly get any sun in the day due to the panel placement. (i live in a block of flats in London so not many options here!)

My question is the cable sizing for a certain run. the new placement will place the panels around 15m away from the controller. and from what I've gathered from various online calculators, I'll need at least 25mm2 cable for that run...HUGE! is that accurate?

If so, can I run the 25mm2 cable as close as possible to each end of the circuit (from panel to controller) but then terminate the cable with 6mm2 cable to both the controller and solar panel? the reason being the controller won't take 25mm2 cable and neither can you get MC4 connectors that can take 25mm2 cable.

thanks for any help.
Sal

 

[schmism]

Can you put the battery and SCC at the location with the panels? Keep all that end "short" and run your long wire for whatever 1.5a load is 15m away.

 

[salmirabile]

I wish I could but impossible due to location.

 

[Forbisher]

I wish I could but impossible due to location.

Your calculators are way off if you get 25mm cable.
18Vmp
5.5A
15 meters
Needs 10 AWG
I put in typical values for a 100w panel but you can change.
Click the link.

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

 

[chrisski]

If you feel you need a thicker wire, I have only found Ampnenol H4 connectors are capable of as thick as 8 AWG wire.

I have not found a weatherproof IP67/IP68 Quick Disconnect that takes 6 AWG, but I am thinking about Anderson SB connectors. Those are not as weatherproof as the MC4s or Amphenol H4s.

As an American, I think in AWG not mm2.

Also not sure your 100 watt panel puts out 8 amps. That would mean its pushing about 12.5 volts, and usually a 100 watt panel designed for a 12 volt system pushes about 18 volts and 6 amps and needs a SCC to step it down for battery charging. I would think it could have a market for direct battery charging.

 

[salmirabile]

Ok cool Cheers guys. I've been using slightly ambitious numbers for the panel. I'll install 8 gauge as I like some head room.

 

[Forbisher]

Ok cool Cheers guys. I've been using slightly ambitious numbers for the panel. I'll install 8 gauge as I like some head room.

If you have minimal draw then why use 8 AWG over 10 AWG?
Why would you care if you lose a few watts?
10 is 3% voltage drop and perfectly aceptable.
8 is 1.89% drop

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

 

[salmirabile]

It's not the drop I'm worried about. It's the heat. If the panel is gonna give me the 5a then I don't wanna risk using a small gauge wire

 

[Forbisher]

It's not the drop I'm worried about. It's the heat. If the panel is gonna give me the 5a then I don't wanna risk using a small gauge wire

10 AWG is not small guage for that 100w panel.
There will be Zero "heat" in that 10 AWG wire with 5A.
There is Zero risk at 3% voltage drop!
You could run 12 AWG with no problems.
Also 5.5A is 100w 100% production and you are never getting that much.

 

[salmirabile]

Ok fair enough. Thanks for all the quick input, much appreciated!

By the way, do I need to double to run as I'm only counting 1 way. I've read you need to count both ways, so panel to controller and back to panel again? Is that right?

 

[Forbisher]

Ok fair enough. Thanks for all the quick input, much appreciated!

By the way, do I need to double to run as I'm only counting 1 way. I've read you need to count both ways, so panel to controller and back to panel again? Is that right?

Look at the calculator I linked with your inputs to see that it uses one way distance to calculate round trip distance.

 

[Hedges]

One "12V" panel, with MPPT charge controller and 12V battery?
Good chance that Vmp of the panel isn't enough above the battery voltage for MPPT charge controller to work. PWM would work.

Do you need 1.5A x 24 hours = 36 amp-hours per day?
5A from a PV panel converted by MPPT to 7A at battery voltage, x 5 hours of my San Jose sunshine (but not likely for your London Fog) would be 35 amp-hours. Might work for me. Lead-acid batteries are 70% efficient more or less, so maybe only 25 amp hours available, still won't work.

I think you need additional PV panels, connected in series. What is maximum input voltage rating of MPPT charge controller? Need to stay below that considering Voc of panels x number of panels x adjustment for cold weather.

IR drop in the wire will become a smaller percentage when you feed it a higher voltage from PV series string.
Any IR drop is generally tolerable between PV and SCC, it is just lost watts (made up for with extra PV panels.)

 

[Forbisher]

One "12V" panel, with MPPT charge controller and 12V battery?
Good chance that Vmp of the panel isn't enough above the battery voltage for MPPT charge controller to work. PWM would work.

Do you need 1.5A x 24 hours = 36 amp-hours per day?
5A from a PV panel converted by MPPT to 7A at battery voltage, x 5 hours of my San Jose sunshine (but not likely for your London Fog) would be 35 amp-hours. Might work for me. Lead-acid batteries are 70% efficient more or less, so maybe only 25 amp hours available, still won't work.

I think you need additional PV panels, connected in series. What is maximum input voltage rating of MPPT charge controller? Need to stay below that considering Voc of panels x number of panels x adjustment for cold weather.

IR drop in the wire will become a smaller percentage when you feed it a higher voltage from PV series string.
Any IR drop is generally tolerable between PV and SCC, it is just lost watts (made up for with extra PV panels.)

His previous post suggests that he has a 12V LFP battery so why wouldn't an 18Vmp 100 watt panel work with a 20A MPPT SCC?

 

[Hedges]

His previous post suggests that he has a 12V LFP battery so why wouldn't an 18Vmp 100 watt panel work with a 20A MPPT SCC?

What's the voltage of a "12V" LFP? Maybe 14V, at some state of charge?

Vmp of panels varies, of course, by model and with temperature and amount of sun.

Big question is what MPPT range the SCC operates over. How much headroom above battery voltage does it require? I think I've seen 5V in some data sheets.

I think another guy here also having difficulty with no charging or little output got better results with two panels in series rather than parallel. (That might also have been due to excessive resistance from long wires.)

 

[Forbisher]

What's the voltage of a "12V" LFP? Maybe 14V, at some state of charge?

Vmp of panels varies, of course, by model and with temperature and amount of sun.

Big question is what MPPT range the SCC operates over. How much headroom above battery voltage does it require? I think I've seen 5V in some data sheets.

I think another guy here also having difficulty with no charging or little output got better results with two panels in series rather than parallel. (That might also have been due to excessive resistance from long wires.)

LFP 14.2 to 14.6V is fully charged which will settle to 13.6?
LFP is 12.8 nominal voltage.
12V lvd with 10V bms cut off.
Victron requires 5V headroom but Epever is less.

 

[Hedges]

Many Epever models. Here's one data sheet that says battery +2V

https://www.epsolarpv.com/upload/file/1909/EPEVER-Datasheet-XTRA.pdf

Requirement of battery +5V would cause him problems, especially if conditions cause lower voltage from PV panel.
I think series connection of panels will move it to the sweet spot of an MPPT SCC, and if I understood power consumption correctly he needs more panels anyway.

 

[salmirabile]

Hey guys. Thanks for all the input!
So, I only need 1.5a for 8hrs per day which is between 10pm-6am. This is so I can run my security camera and other little bits which add up to around 1.5a, sometimes less.

I have an Epever mppt controller.

I'm definitely thinking of putting another panel in but not sure if it's best to go parallel or series.

Another question is do I NEED to put both panels together or can I have both in different locations?

I'll send some pictures of my setup in a bit and then you'll see why Im having such placement problems of the panels.

 

[salmirabile]

So here's my panel location in pic 3.

I want to move it to the green box but my problem is that i can only put 1 panel as i don't have any structure to put another panel next to it. If i put the panel below it, it'll get blocked by a staircase. If i put another panel below where my current panel is now, it'll get blocked by the tree! Can i put another panel where the green box is and leave my current panel where it is?

The red box in that same picture is my ideal placement but as it's the main tower, i'm not "allowed" to put anything on that wall.

In the other picture where the red box highlights the building, that's just showing where the sun goes behind during winter, so that's another problem i have and can't avoid unfortunately. So, my best sun times in the winter are around 9am-10.30am and then 1pm-4pm.

The summer shouldn't be a problem as the sun will be much higher than that building so i should have much more sunlight to play with.

Any ideas would be great!

 

[chrisski]

I’ve used butt splice connectors to join 10 AWG wire to 6 AWG Wire. The 10 AWG wire simply has the stripped part of the wire folded back on itself So it fills up the 6 AWG Butt splice. That way, you can splice a short piece of 10 AWG wire on each end of the longer 6 AWG wire so that you can get a MC4 connector on the end.

How To: Joining Different Gauge Wires

I have 6 AWG welding wire coming out of my solar component compartment in my trailer, joining up to 10 AWG on an SAE quick connect. The purpose of this thread is to show how I connected wires of dissimilar gauge using a butt connector. I cut the wire for the quick connect about half way. The...

diysolarforum.com

Using a thicker wire and butt splice on your project will only cost you a few extra dollars, provided you have access to a good crimper. If you want to spend the extra money to get 2% less loss, I don’t see a problem. Buying that much thicker wire and a butt splice is not going to break you and make you miss paying rent.

I used this to build 40’ long 6 AWG cables To carry up to 30 amps at 18 volts.

 

[Hedges]

1.5A x 8 hours = 12 Ah
Assuming 70% efficiency from LA battery, 12 / 0.7 = 17 Ah
17 Ah x 12V = 205 Wh

If PV panel PTC is 85% of STC output (might do better in cold),
205 / 0.85 = 242 Wh

What does an insolation chart/website say for your location, for December/January?
0.8 hours effective sun? 2 hours?
Ought to tilt panels for shortest day of year.
I assumed South West (due to your 1:00 to 4:00 exposure) and 23 degrees from vertical.
That gave 1.08 hours. The fact you have only 3 hours actual un-shaded time would reduce further.

Solar Irradiance Calculator

www.solarelectricityhandbook.com

242/1.08 = 224W (STC) of panels needed.

Possibly 2, 100 W panels would work, but 3 would give some margin.
I would orient all at the window of time that has best exposure, maximize Wh put in battery to be used at night.
Different orientations is OK for panels in parallel. If in series, must be same orientation.

Epever works down to Vbat + 2V, so probably single panel can produce enough voltage.

One Epever model only allow 60V (46V?) max, while another allows 100V (92V?) max.
You'll have to specify exactly which model.

PV panels specs too, so we don't have to guess.

What I want to do is put 2 or 3 panels in series. That way the voltage will never drop too low, and voltage drop in wires is minimized.
That's same orientation for all in series. 2s1p or 3s1p all oriented the same. All about same current when in series.
If you add some on the wall with a different orientation, 1s2p or 2s2p.
You can also mix "12V" panels and "24V" panels. Two 12V panels in series 2s, paralleled with a 24V panel 1s.
All series connections about the same current, all parallel connections about he same total voltage.