Solar panel and cable length.

Submitted: Saturday, May 14, 2016 at 11:05
ThreadID: 132408 Views:3412 Replies:7 FollowUps:16
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Just wondering how much voltage I would lose if extended my solar panel cable .Currently its 3m from regulater to panel.I want to add 2m more to it .Cheers
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Reply By: LIFE MEMBER-snailbait - Saturday, May 14, 2016 at 11:09

Saturday, May 14, 2016 at 11:09
use the largest dia cable you can afford
Terry
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Reply By: Member - RUK42 (QLD) - Saturday, May 14, 2016 at 11:48

Saturday, May 14, 2016 at 11:48
Opinion please here from the experts. If the solar panel is putting out 20V and the regulator knocks it back to 12V then the main consideration here is the distance from the regulator to the battery. So, yes, use the biggest cable you can but as long as the regulator remains close to the battery it is not as much of a problem as the situation where the regulator is on the panel, meaning there will then be a drop between the regulator and the battery.
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Kevin
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Follow Up By: LAZYLUX16 - Saturday, May 14, 2016 at 12:09

Saturday, May 14, 2016 at 12:09
Thanks RUK42 my regulater is seperate from solar panel and thinking even making it shorter than 950mm from battery thats why need to extend the solar panel cable and to get panel out of shade when camping cheers
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Reply By: Frank P (NSW) - Saturday, May 14, 2016 at 12:34

Saturday, May 14, 2016 at 12:34
Lux,
You said somewhere above that your reg is close to the battery - good!!

Assuming you have the same size cable all the way from reg to panels, and if your panels put out 10 amps, then if you use

3mm twin core the voltage drop will be 3.07V. Power loss 30 watts
4mm twin core the voltage drop will be 1.87V Power loss 19 watts
5mm twin core the voltage drop will be 1.2V Power loss 12 watts
6mm twin core the voltage drop will be 0.76V Power loss 7.6 watts

Your panels may not output 10 amps. Say it's 7 amps. The voltage drop and power loss will be 7/10, = 0.7 of the above figures. If they put out 15 amps (!) then it would be 15/10 = 1.5 times the above. And so on.

If you double the cable length you will double the voltage drop and power loss. If you halve the length you will halve them.

As someone said, the bigger the cable the better, but there are practical limits so use the above to work out your choice.

Cheers
FrankP

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Follow Up By: Gronk - Saturday, May 14, 2016 at 14:10

Saturday, May 14, 2016 at 14:10
If the panel puts out approx 20V and the reg only needs approx 14V, then you can afford a bit of voltage drop.
But 6mm twin is a good size that will have minimal drop.

I have a 10M lead ( 6mm2 twin ) and a 15M lead ( 10mm2 twin ), but even with 6mm2, I would have no hesitation going to 30M long for a lead.

All assuming the reg is at the battery end, which yours is !
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Follow Up By: Peter_n_Margaret - Saturday, May 14, 2016 at 14:38

Saturday, May 14, 2016 at 14:38
The effect of the voltage drop from 20V will also be somewhat dependent on whether the regulator is MPPT (and can utilise the 20V), or PWM which will simply cut it back to the required charge voltage.

Cheers,
Peter
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Follow Up By: Allan B (Member, SunCoast) - Saturday, May 14, 2016 at 15:57

Saturday, May 14, 2016 at 15:57
But Gronk, a 6v drop from 20v may be acceptable if a PWM regulator (See Peter's FollowUp above) but what about when, due to solar conditions, the panel is only able to output 14v? Under those conditions you can afford no volt drop.
Cheers
Allan

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Follow Up By: Zippo - Saturday, May 14, 2016 at 15:58

Saturday, May 14, 2016 at 15:58
What Peter said.
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Follow Up By: Gronk - Sunday, May 15, 2016 at 10:59

Sunday, May 15, 2016 at 10:59
Allan, if you get 6V drop you have seriously undersized cables.

At 30m long, I get less than 0.5V drop, so if someone has the ability to work out they are getting 6V drop, they would have the smarts to rectify the problem as well.
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Follow Up By: Allan B (Member, SunCoast) - Sunday, May 15, 2016 at 11:29

Sunday, May 15, 2016 at 11:29
Gronk, you said...."If the panel puts out approx 20V and the reg only needs approx 14V, then you can afford a bit of voltage drop."
My point was that you imply that because there is a 6v 'surplus' it is OK to permit a "bit of voltage drop". If the application is using an MPPT regulator, every available volt is usable therefore why waste it with undersized cables?
Even with a PWM regulator, using undersized cable limits the available energy delivered to the regulator under conditions of less than ideal solar absorption.
Clearly you have adequate cables so why advocate accepting volt drop of the order you suggested?
Cheers
Allan

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Follow Up By: Gronk - Sunday, May 15, 2016 at 12:11

Sunday, May 15, 2016 at 12:11
Sorry I didn't get my lawyer to proof read my reply ??

I didn't think someone would dissect it and come to conclusions that I wasn't thinking of ??

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Reply By: Nomadic Navara - Saturday, May 14, 2016 at 16:47

Saturday, May 14, 2016 at 16:47
Forget the 20 V referred to above. The only time you will see 20 V across the panel is when it is lightly loaded. When you drawing more current the voltage drops quite a bit. See the following diagram. There are 36 cells in the "12 V" panels so multiply the voltage readings across the bottom of the curve by 26.

The open circuit voltage of a panel is in the region of 21 - 22 V. The maximum power is generated when the panel is working at 17 V or so. If you load the panel a bit more you will draw slightly more current but the voltage (and thus the generated power) drop significantly. To find the actual values of your panel you need to look at the specifications for your panel. The voltages vary between manufacturers.

LAZYLUX16, you did not give me much to go on. We really need to know the Vmp (maximum power point voltage) and the maximum power of your array. However it is safe to use 17 V as your Vmp. Another assumption I will make is your regulator has a 1 V drop across it and your absorption voltage is set at 14.3. V. This will mean that you should design your system with a maximum of 1.7 V drop between the panel and the regulator. Work on the conservative side as the Vmp drops a little as the panel heats up on a hot day.

I would not recommend you make up an extension lead for your system. Replace the whole cable between the panel and the regulator with heavier cable for better results. When you are looking at cable remember that 6 mm auto cable is not contain 6 square mm of coper, it's only 4.8 mm2 or less. Read about that here. There is also instructions on that page for determining the minimum size cable you need.
PeterD
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Follow Up By: LAZYLUX16 - Saturday, May 14, 2016 at 17:42

Saturday, May 14, 2016 at 17:42
Thanks NN unfortunately the panel came with no technical details.Its soft folding panel.I just was bored and made a bid on ebay and won it.It came with a instruction leaflet thats all. How do I measure what size cable it came with..cheers
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Follow Up By: Nomadic Navara - Sunday, May 15, 2016 at 00:17

Sunday, May 15, 2016 at 00:17
To find out the size you will have to cut a section of your cable and strip the insulation of it. You then compare it with some wire in an auto electricians shop or Jaycar. An auto electrician may be able to take a look at it and take a guess.
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Reply By: HKB Electronics - Saturday, May 14, 2016 at 16:58

Saturday, May 14, 2016 at 16:58
Give it a try you have nothing to loose, if it works fine, if adding a few metres tips the bucket then your set was most likely very marginal to start with and maybe an additional panel would be a good idea.

I have several different cables in my setup and use whatever is needed at the time, you may loose a few watts but for convenience that may no be of a concern to you, like if your camped under shade and need to run a long length of cable to the panel, you'll put up with the loses for the convenience factor.

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Follow Up By: LAZYLUX16 - Saturday, May 14, 2016 at 18:01

Saturday, May 14, 2016 at 18:01
Hi HKB I only have 100watt Mono crystalline soft folding panel about 3m of cable.I have 3rd battery 95ah. I will use that battery to charge notebook, 4 camera batteries and 3 phones.I have aux battery for 39l fridge Allrounder 105ah 760cca under bonnet connected to Redarc Isolater.And start battery is 810cca. So I hope it covers all basis.I need about 3m extension .I thought also like you, having different lengths. cheers
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Reply By: Member - Phil G (SA) - Saturday, May 14, 2016 at 18:26

Saturday, May 14, 2016 at 18:26
Your original cable is likely to be around 3 or 4mm twin. I'd follow Peter's response above and simply make up a new lead of the required total length. If you use 6mm tinned twin sheathed marine cable, you'll have everything covered.
AnswerID: 600052

Follow Up By: LAZYLUX16 - Sunday, May 15, 2016 at 10:28

Sunday, May 15, 2016 at 10:28
Yes at a guess Phil G be around the 3 to 4mm .Problem is can not access cable where it joins the solat panel as sewn into it.It has those MC4 connections .About 300mm length to panel and other end 3m to regulator ..cheers
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Follow Up By: Member - Phil G (SA) - Sunday, May 15, 2016 at 12:32

Sunday, May 15, 2016 at 12:32
Yes, I'd usually cut the wire about 20cm from the panel and soldered the new wire from there. Another option is to fit an anderson plug at that point and use a long anderson lead to hook it up.
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Follow Up By: LAZYLUX16 - Sunday, May 15, 2016 at 21:39

Sunday, May 15, 2016 at 21:39
Thanks Phil G can I use thicker gauge cable or havd to stick to the original size cheers
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FollowupID: 869426

Follow Up By: Member - Phil G (SA) - Sunday, May 15, 2016 at 22:54

Sunday, May 15, 2016 at 22:54
Thicker cable - my suggestion is 6mm tinned twin sheathed marine cable.
Can buy it off the roll at Whitworths or BCF:
https://www.whitworths.com.au/main_itemdetail.asp?cat=123&item=197570&intAbsolutePage=
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Follow Up By: LAZYLUX16 - Monday, May 16, 2016 at 11:13

Monday, May 16, 2016 at 11:13
Thanks Phil G owe you a few beers answering many of my questions..So be ok to connect thd 6mm to the 4mm cable .As can not acces the connection inside panel only the 30cm bit sticking out cheers .
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FollowupID: 869451

Reply By: Member - Cuppa - Saturday, May 14, 2016 at 23:45

Saturday, May 14, 2016 at 23:45
This is my ‘go to’ resource for sizing solar cables.
http://hobohome.com/news/?p=581
See 'My Profile' (below) for link to our Aussie travel blog, now in it's 4th year

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